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TABLE OF CONTENTS

AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852

TRANSACTIONS

Paper No. 1193

THE WATER-WORKS AND SEWERAGE OF
MONTERREY, N. L., MEXICO. [1]

By George Robert Graham Conway, M. Am. Soc. C. E.

With Discussion by Messrs. James D. Schuyler, David T. Pitkethly, George S. Binckley, Vicente Saucedo, George T. Hammond, Rudolf Meyer, and George Robert Graham Conway.

Introductory.

[1] Presented at the meeting of February 1st, 1911.

Monterrey, the Capital of the State of Nuevo León, Mexico, is built on the site of the old village of Santa Lucía de León, which was established in 1583 by the Governor of the Kingdom of León, Don Luis Carabajal. Four years later Carabajal was imprisoned by the Inquisition, and the village of Santa Lucía was abandoned by its few inhabitants.

In 1596, Captain Diego Montemayor, a resident of Saltillo, in the adjoining State, wishing to render a service to his king, Philip II of Spain, assembled his friends, and on September 20th of that year, proceeded to establish a town on the site of the old village on the northern side of the principal spring at the place. The town was named "Nuestra Señora de Monterrey" (Our Lady of Monterrey), after the Count of Monterrey (Ojos de Santa Lucía y Valle de Extremadura), the ruling Governor of New Spain, as Mexico was then called.

Monterrey is approximately in the center of the State of Nuevo León, 1° 12´ west of Mexico City, and in latitude 26° 40´ N. It is a distributing railway center on the main line of the National Railroad, 270 km. from the Rio Grande at Laredo, 1,022 km. from Mexico, and 520 km. from Tampico by the Mexican Central Railway. It is the center of many large industries, and is the second largest manufacturing city in the Republic.

The Concession.

The works described in this paper were carried out under a guaranteed concession granted by His Excellency, General Bernardo Reyes, Governor of the State of Nuevo León, to Messrs. James D. Stocker and William Walker, of Scranton, Pa. The concession is dated October 19th, 1904, and is for 99 years from that date; the works for a complete water and drainage system were to be finished in 3 years from the time of their commencement. Before the works were designed and begun, the concession was acquired by Mr. William Mackenzie, of the firm of Mackenzie, Mann and Company, Limited, of Toronto, Ont., Canada, who, on May 4th, 1906, organized the Monterrey Water-Works and Sewerage Company, Limited (Compañía de Servicio de Agua y Drenaje de Monterrey, S. A.), under the laws of the Dominion of Canada, of which company he is President. Mr. Mackenzie is also President of the Monterrey Railway, Light, and Power Company, Limited, which was constructing the street railways of Monterrey concurrently with the water-works. Under the provisions of the concession, the Government appointed a Financial Interventor, who had authority to examine and check the company's expenditures, and also a Technical Inspector to examine and report on the construction. The duties of these officials also apply to the operation of the system when the construction is finished. The Government has the right, after the system has been operated 40 years, to purchase the entire property, subject to 6 months' notice, for a sum equal to 16²⁄₃ times the average annual net proceeds during the 3 preceding years. This right may be exercised at the end of 40 years, or at the end of any 10-year period thereafter, up to 99 years from the commencement of operations.

Geology and Topography.

Monterrey lies in a plain at the foot of the Eastern Sierra Madre Mountains which constitute the eastern margin of the Mexican Cordilleran

Plateau, and is surrounded by the magnificent mountains of that group, among the most notable of which are the beautiful Mitra and Silla Mountains. In the neighborhood of Monterrey these mountains attain heights of from 2,000 to 2,400 m., and are noted for their broken and jagged sky-lines. The leading geological characteristics of the district are the uplifted limestones of the older cretaceous age which form the main mass of the mountains.

Primarily, the mountains are compressional folds which, in the Sierra Madre, near Monterrey, are close and vertically compressed.[2] The drainage areas of the Santa Catarina River, which flows through Monterrey, and of the Estanzuela and Silla Rivers, its tributaries, are of limestone and shale; originally the shales were above the limestone, but the convulsion which formed the Sierra Madre as an anticlinal fold, left the originally horizontal strata standing nearly upright, and subsequent erosion in the upper part of the anticline has exposed nearly vertical strata in many places. The limestone being hard and resisting erosion, there is generally, along the line of contact, an abrupt drop vertically on the face of the limestone to the shale below. In many places this abrupt drop is broken by a limestone talus, but the line of contact can generally be traced. Mining operations in these mountains have revealed the presence of large caves at a considerable elevation, many of which contain large reservoirs of water, delivered to them through numerous faults. The river valleys are formed of masses of limestone conglomerate and coarse gravels, re-cemented in many cases by the lime deposits of the flowing waters. One of the chief characteristics of the subsoil of Monterrey itself is a local rock called "sillar," which is a superficial deposit of carbonate of lime from the evaporated waters. In some places the "sillar" is largely mixed with a conglomerate called "tepetate," or "impure sillar."

[2] Transactions, Am. Inst. Min. Engrs., Vol. XXXII (1902), pp. 163-178.

Plate II.—General Plan Of The Water Supply And Drainage Works For Monterrey, N. L., Mexico.
[Larger.]

Topographically, the region around Monterrey is distinguished by the drainage area of the River Santa Catarina, which rises in the Sierra Madre near the Laguna de Sanchez, at an elevation of 1,850 m., as shown on [Plate II]. From this Laguna it follows a tortuous course between precipitous mountains through the Boca of Santa Catarina to Monterrey, for a distance of 90 km., eventually finding

its way to the San Juan River, a tributary of the Rio Grande. Throughout its course it disappears, flows underground, and again appears; and, except in flood time, it has a subsurface flow for a distance of 16 km. above the city. In the Cañon of Santa Catarina it appears at the surface, having a normal flow of about 1,415 liters (50 cu. ft.) per sec., and its waters at that point are divided into two parts and carried into irrigation canals. The drainage area of the river above Monterrey is 1,410 sq. km., and its bed at Monterrey is between 518 and 545 m. above sea level.

Southward from Monterrey the country rises along the valley of the Silla for a distance of 19 km., where the Silla is separated from the San Juan by a low divide, the former flowing northward to Monterrey and the latter southeastward toward Allende. The Silla Valley is bounded on the east and west by the steep ranges of the Silla and Sierra Madre Mountains. The floor of this valley is gently rolling, but is cut by many arroyos which carry little or no water during the greater part of the year. The chief feeder of the Silla River is the Estanzuela, a stream which derives its waters from several springs coming to the surface near the line of contact between the limestone and the shale, at elevations of about 800 and 900 m.[3] above datum. The water-shed of this stream is rich with abundant vegetation due to the precipitation being greater than on the Santa Catarina water-shed. To the south of the divide the country is well wooded, and El Porvenir, 35 km. from Monterrey, is the garden spot of the State of Nuevo León. Here the rainfall is much greater than at any other point near Monterrey, and there are many streams which are used for irrigation purposes. Monterrey is built on a plain, chiefly on the north side of the Santa Catarina River. This plain has a general fall toward the northeast, and beyond the city it slopes gently northward for several miles toward the Topo Grande River, and then southeastward to join the great coastal plain of the Gulf of Mexico. The general elevation of the city lies between the 519- and 550-m. contours. The Plaza Zaragoza, in the center of the city, is 533.90 m. above sea level; the elevation of the highest part of the city, at the western boundary, is 550.05 m., and of the lowest part, at the northeastern boundary, 518.0 m. above sea level.

[3] Throughout this paper datum refers to the height in meters above the mean sea level of the Gulf of Mexico at the Port of Tampico.

Plate III, Fig. 1.—General View of Line, Estanzuela Aqueduct.

Population, Area, and Mortality.

The population of Monterrey has increased as follows:

The greatest progress, it will be noted, was between 1891-1901, with an increase of more than 22,000 in 10 years. In designing the new works, provision has been made for the future requirements of a city of 200,000 persons.

The actual area within the city limits proper is 960.5 hectares (2,374 acres), forming the area to be provided with water and drainage, but the municipal district extends to many surrounding suburbs, and covers an area of 33,758 hectares (83,426 acres).

TABLE 1.—Population And Death Rate Of Monterrey, N. L.,
Mexico, From 1901 To 1909, Inclusive.

[4] Excluding deaths due to drowning in the great flood of August 27th and 28th.

Table 1 gives particulars of the death rate for 1901 to 1909, inclusive, and data relative to the mortality due to typhoid fever. The high death rate is caused by the excessive infantile mortality, which is so prevalent throughout the whole of Mexico. The climatic condition of Monterrey, with its exceptionally healthy subsoil, ought to make it one of the healthiest of cities, if proper care were taken to enforce sanitary laws. The data regarding typhoid mortality are probably

understated, as they were compiled by the writer, in the absence of any official publications, from the actual death certificates, but no special care is taken by the authorities to insure accuracy in such certificates. Attention is called to the typhoid rate in May, June, July, and August, 1909; this high rate coincides with a scarcity of rainfall and the greatest period of drought experienced in 30 years, and immediately precedes the great flood of August 27th. It was probably due to the lowering of the ground-water throughout the city and the consequent contamination of the private wells, which were largely in use during that time. Throughout the city the wells are sunk to a depth of about 12 or 15 m., in order to reach the subterranean waters, and the cesspools are often in dangerous proximity to them and at a much higher level. The nature of the subsoil, which is often much fissured and open in the conglomerate and sillar strata, would make the passage of contamination an easy matter, and this alone would account for a high mortality due to water-borne diseases.

Rainfall and Temperature.

The precipitation records of Monterrey and its neighborhood are very meager, and cannot be relied on for a longer period than from 1894 to 1909, inclusive. The records are available from 1886, but in the early years there are many apparent discrepancies, and they are probably inaccurate. The average rainfall for the 15 years (1894-1908) is 21.94 in.; the driest years for this period are as follows: 1894, 14.14 in.; 1902, 15.29 in.; 1907, 15.23 in.; 1908, 15.11 in. Assuming the early records to be correct, the average rainfall for the period, 1886-1908, would be 19.86 in.

At Saltillo, which is 50 miles due southwest, at an elevation of about 1,520 m. above sea level, the average rainfall for the 23 years, 1884-1908, inclusive, is given as 21 in. The maximum year was 1889, with 33¹⁄₂ in., and the minimum 1903, with 7¹⁄₂ in.

At Carmen, in the State of Tamaulipas, 144 km. southwest of Monterrey, at an elevation of about 310 m. above sea level, the average fall for 12 years is 24.70 in., the maximum year being 1897, with a fall of 34.09 in., and the minimum year, 1905, with 13.41 in.

Fig. 1.—Annual Rainfall In Monterrey
Covering The Period From 1894 To 1909.

Fig. 1 shows the annual variation of rainfall at Monterrey for 1894-1909. Fig. 2 shows the monthly variation during the same period, and gives the minimum, average, and maximum for each month.

From these diagrams it will be seen that the months of least rainfall are December, January, February, and March, with averages of 0.66, 0.59, 0.79, and 0.93 in., respectively. The months of greatest rainfall are August, with an average of 4.39 in., and September with 4.87 in. The maximum in any month prior to 1909 was 16.75 in., during September, 1904.

Rainfall in 1909.—The rainfall in 1909 was unprecedented, causing the disastrous flood in the Santa Catarina River, which will be referred to when describing the works. Fig. 3 shows the monthly rainfall for 1906 to 1909, inclusive, and has been plotted to show the variation of rainfall prior to the great precipitation of August, 1909. In that month there were two heavy falls, one beginning at midnight on August 9th, and during the following 42 hours a fall of 13.28 in. was recorded by the gauge at the Water-Works Company's general offices, 10.20 in. of which fell, during the first 24 hours. From 6 P. M. to 11 P. M., on August 10th, 5.019 in. were recorded, or an average of 1 in. per hour.

Fig. 2.—Monthly Rainfall in Monterrey Covering The Period From 1894 To 1909 Inclusive.

Fig. 3.—Monthly Variation Of Rainfall At Monterrey 1906-1907-1908-1909.

After 13 dry days, another rainstorm began, at 4 P. M., on August

25th, and continued more or less intermittently until August 29th. During this 98-hour period there was an additional fall of 21.61 in., 11.27 in. falling in 24 hours.

The total precipitation during the month amounted to 36.00 in. The highest previous record for the month of August was in 1895, with a fall of 6.61 in. Fig. 4 gives the details of the two heavy precipitations in August. As no automatic recording gauge was available,

the maximum intensity could only be computed approximately, owing to the intermittent character of the readings taken from the ordinary rain gauge on the roof of the Water-Works Company's office in the city. From the readings thus obtained, it was shown that the maximum intensity occurred early on the morning of the 28th, and was nearly 2 in. per hour. Above Monterrey, in the Santa Catarina water-shed, it is believed that the precipitation was considerably greater, but no gauges were accessible during the month.

Fig. 4.—Curve Of Rainfall At Monterrey During August 10th & 11th And From August 25th To 29th - 1909.
[Larger.]

The total rainfall for 1909 amounted to 47.46 in., of which 75% fell in August. This is 50% greater than the previous highest annual record (31.65 in. in 1900) for Monterrey.

Temperature.—Fig. 6 gives a record of the temperature at Monterrey from 1901 to 1909, inclusive. These records were taken at an altitude of 520 m. It will be noted that the lowest recorded temperatures are in January and February. The lowest during these years was 24° Fahr., in January, 1905. The monthly maxima vary between 80 and 110° Fahr. The mean annual temperature is 72.65° Fahr. (The mean annual barometer is 28.2 in.)

Fig. 6.—Diagram Of Temperature Variation At Monterrey, 1901-09.

Available Sources of Supply.

The question of the best sources from which Monterrey should be supplied with potable water was one that had been long under discussion, and was the subject of many investigations prior to the granting of the present concession. Several of the original schemes called for an impounding reservoir in the Cañon of Santa Catarina and it was on the assumption that a dam would be built that a clause was inserted in the concession for the purpose of making its construction obligatory. The general character of the physical and geological conditions surrounding Monterrey has already been referred to. A thorough study of these conditions proved that no suitable site for impounding the Santa Catarina River could be found, apart from the fact that periodically this river is subject to enormous floods which tear through the steep cañon with tremendous velocity.

At the site originally proposed for the dam, a considerable underflow was found, and later investigations, carried out under the present concession, proved that, although borings were carried to a depth of 54 m., bed-rock could not be found, the strata being composed of gravels, conglomerate and sand. Assuming that such a dam could

have been built, the quality of the water draining from a comparatively barren water-shed, on which many thousands of goats are pastured, would have made its filtration an absolute necessity before it could be delivered to the consumers.

The various available sources from which water could be delivered to the city by gravity were investigated by Mr. F. S. Hyde, in the autumn of 1905, and also by J. D. Schuyler, M. Am. Soc. C. E., who was afterward retained as Consulting Engineer for the Company. The various investigations made from time to time showed that the question of a satisfactory supply was one of extreme difficulty, requiring prolonged observation and study, more particularly into the character of the underground sources of supply.

One of the chief characteristics of many of the streams in the State of Nuevo León, is their disappearance and reappearance at different points along their routes, and the Santa Catarina River, under normal conditions, as already remarked, is a very notable example of a river which is very dry at the surface for many kilometers of its length. In the writer's opinion, the waters of this and similar rivers in the State pass through many open caverns underground, so that experience gained in the investigation of underflow waters in other places would be insufficient to determine the quantity passing at any point along the river if ascertained by merely computing it from the velocity of the underflow and the area of the water-bearing gravels. The rainfall on the water-shed of the Santa Catarina River is probably 25% greater than at Monterrey, and all ordinary rains sink rapidly into the limestone soils and quickly disappear. In another water-shed of a very similar character, namely, that of the Rio Blanco, in the southern part of the State, the underflow waters appear at the surface at a place called Mezquital, where a metamorphosed sandstone barrier prevents them from disappearing underground. At this point the normal quantity of water is about 5,660 liters (200 cu. ft.) per sec., but it gradually disappears, and a few kilometers below it has sunk to an insignificant stream, finally disappearing altogether for about 20 km. In the neighborhood of Monterrey similar conditions exist with regard to the surface-water supplies, and investigations, therefore, were directed toward obtaining unpolluted supplies from springs and underground sources.

Santa Catarina Sources.—The chief points from which it was

thought desirable to obtain underflow supplies were (1) at the barrier of San Geronimo, and (2) at the Cañon of Santa Catarina, both shown on [Plate II].

Conditions at San Geronimo, which is only 6¹⁄₂ km. west of Monterrey, were investigated by the State Government in 1892, to determine the depth of bed-rock, the rock on either side of the valley being shale, with its original bedding planes standing almost vertical. To determine this depth, borings were made by driving 2-in. tubes until it was assumed that bed-rock had been reached, a method which, in strata containing so many boulders, was obviously unreliable. These borings indicated that bed-rock was from 12 to 15 m. below the surface. If these had proved to be correct, there is no doubt that a development of the underground water at this point, by constructing a submerged dam combined with an infiltration gallery, would have yielded a large supply.

In March, 1906, the Company commenced operations at San Geronimo by sinking a well a few meters north of the then dry bed of the river. Water was found in considerable quantities a few meters below the surface, practically at the level of the river, that is, 570 m. above datum. This supply was used for provisional purposes, and will be referred to later in describing the San Geronimo gravity supply works.

Between August, 1906, and January, 1907, 4-in. bore-holes were sunk in the river bed and on the high ground to the north with a "Keystone" driller outfit. These borings showed bed-rock immediately under the river bed, at a depth of from 15 to 45 m., but dipping gradually as the borings were carried northward.

Boring operations were also carried on at Santa Catarina, during November and December, 1906, and in January, 1907, to determine the geological conditions, and the results are shown on [Fig. 7]. From the area of water-bearing gravels found, it was proposed to tap the underflow water at the 630-m. level by an infiltration gallery. This would have necessitated a gravitation tunnel 3,000 m. long, and an aqueduct of 14 km., which it was proposed to carry to one of two distributing reservoirs at Guadalupe, on the south side of the river, opposite Monterrey. In May, 1907, the writer, after making a study of all the available data which had been accumulated, had additional borings sunk farther across the valley to the north, and these revealed a considerable area of water-bearing gravels, and proved that, in former

geological times, the Santa Catarina flowed about 500 m. north of its present position, and to the back of Obispado Mountain, instead of through the city. This aspect of the subject was discussed with Mr. Schuyler, who agreed with the writer that, in the interest of economy, it was better to tap this supply by an infiltration gallery at the 560-m. level, and bring the water thus obtained to a reservoir to be placed at the western limits of the city, dividing the city, for distribution purposes, into two interchangeable systems, a high- and a low-pressure, the high-pressure system being supplied from Estanzuela, 18 km. south of the city. One advantage to be gained from this change was that the scheme was capable of considerable extension, and any future developments at Santa Catarina Cañon would form part of the works to be constructed for both high- and low-pressure districts.

Fig. 7.—Cross-section Of Santa Catarina River At Santa Catarina.

The future extension of the Santa Catarina sources, the writer believes, can be developed best by driving an infiltration gallery 10 m. below the surface of the Santa Catarina River, a little west of the village of the same name, and then conveying the water through a comparatively

short gravitation tunnel and pressure conduit to a main reservoir near San Geronimo having a top water level at an elevation of about 590 m. above datum.

Southern Sources of Supply.—The available sources of supply southward from Monterrey include a number of springs at various points in a distance of 40 km. Many of these springs are of uncertain quantity, and some are quite dry during periods of drought. The chief perennial springs near Monterrey are those which contribute to form the Estanzuela and Diente Rivers, both tributaries of the Silla, while farther south, at the Potrero Cerna, near El Porvenir, there are excellent springs, at a considerable elevation, with a minimum flow of from 170 to 200 liters (from 6 to 7 cu. ft.) per sec. The total quantity of water available from all these springs during the driest season would probably not be less than about 560 or 700 liters (from 20 to 25 cu. ft.) per sec.

The Estanzuela springs issue at the foot of the Sierra Madre Mountains, and have a normal flow of from 56 to 85 liters (2 to 3 cu. ft.) per sec. in an ordinary dry year; they probably derive their water, through the limestone formation, from the neighboring water-shed of Santa Catarina, as the catchment area of the stream is only 910 hectares, and the stream has never been known to fail, even in the driest periods of prolonged drought. The rainfall on the area is about 30 in. per annum, and the catchment area is well wooded and covered with abundant vegetation. The El Diente springs have an ordinary dry-weather flow of about 28¹⁄₂ liters (1 cu. ft.) per sec.; but part of the water is carried underground, and the real quantity is much greater and could be developed by a small submerged dam carried down to bed-rock.

The elevation and the extreme purity of the water of the Estanzuela River made its acquisition very desirable, and the Company, therefore, purchased the Federal water rights owned by various members of the Estanzuela community, amounting to 91 liters per sec., and has since acquired a Federal concession to all the flood-waters of that river. It was decided, therefore, to adopt the Estanzuela River as the first step toward developing the water to the south of Monterrey for a high-pressure supply, the advantage of the scheme being that from time to time extensions could be made to tap other sources by gravity, as the demands of the city required. The Estanzuela scheme, therefore,

is a preliminary step toward future extensions which will be necessary in this direction as the city grows. The springs near El Porvenir, and others which contribute to the San Juan River, can be tapped at a sufficiently high level to convey them by a gravity pressure line to the Estanzuela Aqueduct near Mederos.

The two sources definitely decided on in July, 1907, were those from Estanzuela and San Geronimo. The works were designed to supply 40,000,000 liters daily, which it was assumed would be sufficient for all future developments for a population of 200,000 at a per capita consumption of 200 liters per day. The present requirements of the city's population, assuming that all the water was supplied by the Company, would be, at that rate, which is a very liberal one, only 18,000,000 liters daily. This, it was thought, would be easily met by the San Geronimo source alone, as it was estimated that it would provide not less than 20,000,000 liters, if the infiltration gallery was driven far enough into the water-bearing gravels.

The question of a high-pressure water supply for domestic use in a city like Monterrey is not a serious one, as practically nine-tenths of the houses are of one story. The increase in the number of large commercial buildings, however, will make the demand greater in the future, and this point has been kept in mind in arranging the division of the distribution systems.

Materials for Concrete.

Cement.—In the early stages of construction the cement for the work was obtained from the Associated Portland Cement Manufacturers, Limited, of London, which supplied the "Pyramid" brand, from the Knight, Bevan, and Sturges Works, but later the supply was obtained from a new factory at Hidalgo, near Monterrey. The total quantity of Portland cement used was 42,500 bbl. of "Pyramid" and 32,500 bbl. of "Hidalgo." The English cement was tested for the Water-Works Company in London before shipment and again at Monterrey, to conform to the British Standard Specifications; the "Hidalgo" cement was required to pass the Standard Specifications advocated by the Special Committee of the American Society of Civil Engineers. The quality in each case was of the very highest, no difficulties being experienced at any time.

Sand and Rock.—One of the chief difficulties in connection with the construction work in its initial stages was in procuring satisfactory sand for the concrete. An investigation of the quality of all the available sands in the neighborhood of Monterrey resulted in the decision to use a manufactured sand obtained from the calcareous shales in the foot-hills opposite the city, on the south side, and near the site of one of the proposed reservoirs. A quarry was opened, and the raw material was delivered by a gravity plane to a crushing plant, 230 m. from the quarry and at a level about 50 m. lower.

The plant consisted of a No. 5 Austin gyratory rock-crusher, fitted with elevators and revolving screens of various dimensions, driven by a 150-h.p. Erie steam engine; two sets of Traylor's heavy-duty crushing rolls, one having 30 by 16-in. and the other 18 by 12-in. rolls; and a Niagara sand disintegrator. This plant, except during a short period when the requirements were beyond its capacity, was able to produce all the sand and rock required for construction purposes. More than 40,000 tons of rock were quarried, the greater part of which was converted into crushed stone and sand.

Table 2 gives the chemical analysis of the chief constituents of the various sands examined.

TABLE 2.—Analysis Of Sands In The Neighborhood Of Monterrey.

The chief sands used for ordinary building purposes in Monterrey are Nos. 10 and 11, which are procured from the bed of the Santa Catarina River. As these sands contain large proportions of lime carbonates, which make them very undesirable for important structures, their use was limited to relatively unimportant work. The best sands procurable were Nos. 5 and 9, but the long distance of the pits from Monterrey, and consequently the heavy freight rate, made their use prohibitive on economical grounds. The best of the available sands, although it was very fine, was No. 7, from Hornos, near Torreon, as it could be depended on for uniformity and could be obtained f. o. b. cars at Monterrey for 3.18[5] pesos per ton.

[5] All costs given in this paper are in Mexican pesos, one peso being equivalent to 50 cents in U. S. currency.

The bulk of the sand and crushed rock used was similar to Nos. 12 and 13, and reference to the cement sand tests in Table 3, will show that the manufactured sands gave very satisfactory results.

Table 3 gives the average tests made with the "Hidalgo" cement and various sands, alone and in combination, for the purpose of obtaining comparative results; the mixtures tested were composed of 3 parts of sand to 1 of cement.

TABLE 3.—Tests Of "Hidalgo" Cement With Various Sands.

The Hornos sand was used during a few weeks in the latter part of 1908, when the crusher was unable to produce all that was required. Its use was restricted to thick walls which were required to be water-tight, and it was always used in equal proportions with the crusher dust.

Estanzuela Supply.

Fig. 8.—Location Plan of Estanzuela Dam.
[Larger.]

Intake Works.—The intake (Fig. 8) is about 1 km. below the lowest spring and at a point where the maximum flow of the stream was observed. The works consist of a small monolithic concrete dam, placed obliquely across the stream at an angle selected for the purpose of obtaining a foundation running parallel to the direction of the strata, which at this point were lying almost vertically across the bed of the stream. Above these strata the stream bed was formed chiefly of large cemented limestone blocks and smaller conglomerate. No storage being possible in this valley, which has a very precipitous fall, the height of the dam was fixed merely to obtain a small settling basin for sand and débris brought down in time of flood. The dam foundation was excavated to bed-rock, from which the upper disintegrated portions were carefully removed; the rock was then stepped, and dovetailed recesses were left for properly bonding the concrete.

The dam is carried well into the banks. Its extreme length is 52 m., its maximum height 4.50 m., and its greatest thickness 2 m. The up-stream face has a batter of 1 in 12, and the down-stream face, 1 in 8. The top of the wall is 1 m. thick. For the discharge of flood-water there is a weir 10 m. long, and it was calculated that with a depth of 1 m. it would discharge about 400 times the ordinary flow, or about 23,000 liters per sec., but, in addition, the whole length of the dam (excluding that occupied by the gate-house) was arranged for the discharge of abnormal floods, one of which, on August 27th, reached the enormous quantity of 82,070 liters (2,900 cu. ft.) per sec., or 825 cu. ft. per sec. per sq. mile of drainage area, a remarkable run-off from so small an area as 910 hectares. The concrete forming the dam is a 1:3:5 mixture. The overflow sill is 692 m. above sea level. When the dam was completed it was filled to the overflow level, in order to test the water-tightness of the basin, which, when cleared, was found to be slightly fissured on the north side. The leakage was sufficient to cause a serious loss during periods of drought, and it was then decided to line the basin with concrete, so that the stream would enter it without being under a head greater than its own depth. The length of the basin, measured along the center line of the original stream surface, is 85 m., and its area is 1,100 sq. m. At its upper end it is merely a lined channel, 5 m. wide at the entrance. The floor of the basin has a fall of 4 m. The lining was formed in

two thicknesses totaling 30.5 cm. (12 in.) of 1:2¹⁄₂:3¹⁄₂ concrete, laid in panels approximately 3 m. square, the upper panels breaking joint with those immediately below; in this way a very satisfactory and water-tight lining was obtained. A parapet wall, 45.7 cm. high, surrounds the basin. For scouring out the basin a 30.5-cm. (12-in.) cast-iron pipe was taken through the dam at the lowest point, this pipe being provided with a gate-valve encased in concrete on the down-stream face.

The gate-house was built in connection with the dam at the north end of the overflow weir, its inner dimensions being 4.34 by 2.80 m. The substructure, to the level of the dam, is of concrete founded on the solid rock, and the superstructure is of brick rendered with cement plaster. The roof is of framed timber with red French tiles.

The intake pipe is of cast iron. 40.6 cm. (16 in.) in internal diameter, fitted outside with a movable copper screen which is further protected by a wrought-iron hinged screen to prevent damage from stones, floating timber, etc., during times of flood. Inside the gate-house the outlet pipe is provided with a 40.6-cm. (16-in.) sluice-valve, operated from the floor level by a vertical head-stock with worm-gearing. The gate-house has a scour-out pipe (also operated by a head-stock) and duplicate copper screens fitted to iron frames. From this house the water is conveyed to the upper portion of the conduit, which is a 45.7-cm. (18-in.) cast-iron pipe.

Of the total area of land, 885 hectares (2,187 acres), owned by the company, 392 hectares (970 acres) have been fenced in, to prevent any contamination of the springs. This fence is formed of five lines of barbed wire protected with stout hog netting at the bottom, in order to prevent more particularly the entrance of goats, many thousands of which pasture in the adjoining mountains.

On the high ground immediately below the intake, a 3-roomed stone house has been constructed for the inspector in charge of the intake works, who also keeps in daily touch with the general office and records the condition of the stream, particulars of rainfall, etc.

Aqueduct.—The total length of the aqueduct, from the intake dam to the South Reservoir, is 18,700 m., made up as shown in Table 4.

TABLE 4.—Estanzuela Aqueduct.

The gradient of the concrete pipes is 0.43% from Estanzuela to Mederos, and 0.53% from Mederos to the South Reservoir. The calculated discharging capacity of the conduit when running full is 364

liters (13 cu. ft.) per sec. for the upper, and 465 liters (16.4 cu. ft.) per sec. for the lower section. For these pipes, the coefficient, n, in Kutter's formula, was taken at 0.013. At present the line has been limited by overflows to discharge three-quarters full.

The increase in the size of the pipes from Mederos is for the purpose of receiving the waters of the Mederos River and other springs in the San Pablo and Aqua Verde catchment areas, as shown on [Plate II].

The invert of the concrete conduit where it leaves the Estanzuela River is 684.25 m. above datum, and at the valve-house of the South Reservoir it is 589.00 m.

The concrete pipes were manufactured and laid under contract with Mr. Arthur S. Bent, of Los Angeles, Cal., the Company providing all materials, labor, etc. The contractor was paid 10 cents per lin. ft. of pipe manufactured and 10 cents per lin. ft. laid. He was also responsible for the satisfactory completion of the work.

Fig. 9.—Estanzuela Pipe Line Steel Forms For The Manufacture Of Concrete Pipe.
[Larger.]

Fig. 9 shows the details of the joint recommended by Mr. Schuyler and adopted for these pipes. The 63.5-cm. (25-in.) pipes were 61 cm. long and 76 mm. (3 in.) thick. The 55.9-cm. (22-in.) pipes were of the same length, but 70 mm. (2³⁄₄ in.) thick. For the purpose of strengthening these pipes while hauling them over very rough roads they were reinforced with four rings of No. 6 galvanized-iron wire.

Manufacture of Pipes.—The pipes were manufactured under the Supervision of Mr. H. Stanley Bent, at a pipe yard established below

the crushing plant, from which the crushed rock and sand were delivered by gravity in bogies run on narrow-gauge rails. The area of the pipe yard was approximately 1¹⁄₄ hectares, and it was laid out with parallel lines of 76-mm. (3-in.) galvanized-iron piping with hose couplings for sprinkling purposes. After trials with aggregates of various sizes, the concrete for the pipes was proportioned by volume as follows:

Plate III, Fig. 2.—Steel Forms for Moulding Concrete Tubes, Estanzuela Aqueduct.

The above quantity manufactured two 63.5-cm. pipes; a 55.9-cm. pipe required 0.1415 cu. m. (5 cu. ft.) of the material, in the same proportions. Fig. 9 shows the forms for these pipes, and Fig. 2, Plate III, illustrates the process of moulding. The forms consist of cast-iron bottom rings, to the proper section of the joint, and inner and outer steel forms of 3-mm. plate, provided with inner and outer locking arrangements. The concrete was poured through a cast-iron hopper which fitted to the top of the outer form.

The concrete, which was mixed very dry, in a ¹⁄₂-cu. yd. batch, "Smith" mixer, was thoroughly tamped with a 22-lb. tamper, and worked until it was of a stiff jelly-like consistency, the wire rings being added as the concrete was placed. The best results were obtained with the minimum quantity of water. The upper joint was moulded with a heavy cast-iron ring. The jacket and core forms were loosened immediately, and placed over other rings, a sufficient number of bottom rings being used for a day's work. For the pipes required for curves, special forms were used to give the necessary bevel to the joint. After 24 hours the finished pipes were lifted from the bottom ring with a special lifter, and ranged in position for coating internally with a Portland cement grout to which a little freshly slaked lime was added. The pipes were all numbered, and were kept moist for 10 days by constant sprinkling. They were not hauled to the work until 28 days after they were moulded, although this rule was sometimes broken, to the detriment of the pipes. More than 32,000 pipes were

manufactured, but some were used for purposes other than the Estanzuela Aqueduct.

Cost of Pipes.—The contractor brought with him experienced concrete pipe makers from California, and these were afterward assisted by Mexican labor. In a day two tampers could manufacture from 45 to 50 pipes of the larger (63.5-cm,), and from 55 to 60 of the smaller (55.9-cm.) size.

The cost varied from 2.75 to 3.25 pesos per pipe for the smaller, and from 3.50 to 4.00 pesos for the larger size.

The approximate cost of manufacturing is as follows: Taking, as a fair example, one week's work during March, 1908, the wages paid to the 74 men comprising the total pay-roll (though part of this labor was intermittent) amounted to 981 pesos. This includes a general foreman at 10 pesos per day, four American tampers at 7.50 pesos, and Mexican labor varying from 4 to 1 peso, and all labor necessary to handle and finish the pipes, including coating the interiors. During this week there were made 1,126 of the 63.5-cm. and 1,095 of the 55.9-cm. size. The pay-roll includes 520 pesos for the larger pipes (46 cents each) and 461 pesos for the smaller pipe (42 cents each). Table 5 shows the quantities and cost of the materials used in the manufacture of these pipes.

TABLE 5.—Cost of Concrete Pipe.

From Table 5 it is seen that the cost of the 63.5-cm. pipes was 3.37 pesos for material plus 0.46 peso for labor = 3.83 pesos per pipe, or 6.26 pesos per lin. m. (1.91 pesos per lin. ft.).

The cost of the 55.9-cm. pipes amounted to 2.66 pesos for material plus 0.42 peso for labor = 3.08 pesos per pipe, or 5.05 pesos per lin. m. (1.54 pesos per lin. ft.).

The cost of cement included hauling from the bodega to the yard, a distance of about 5 km. At a later date, after the Company had commenced using the "Hidalgo" cement, some additional 55.9-cm. pipes were manufactured, so as to have them on hand as a reserve in case of emergency. In this work only Mexican labor was used, as the previous gang had been dispersed, but the tampers had previous experience. Taking the cost of 418 pipes made during one period of 9 days, the detailed cost was as given in Table 6.

TABLE 6.—Cost of 55.9-Cm. Concrete Pipes.

Excavation for Pipe Line and Siphons.—The excavation for the pipe line and for bridge works, etc., was let by contract to Messrs. Scott and Lee, of Monterrey, under three classifications:

(1) "All material which in the judgment of the Engineer can be economically loosened with picks and handled with shovels."

(2) "Indurated earth or gravel, shale or rock which can be loosened without blasting, and 'sillar', locally so-called, whether pure or mixed with other substances, and whether it requires blasting or not."

(3) "All rock not included in the above which requires drilling or blasting."

Locally, this classification is well understood, particularly No. 2, as it covers the sillar soils which are common in the neighborhood of

Monterrey. The contract prices were: No. 1, 50 cents; No. 2, 1.50 pesos; and No. 3, 2.50 pesos per cu. m. These prices were over and above the clearing and grubbing of the line, which was paid for at the rate of 100 pesos per hectare.

The route of the pipe line being along broken country, at some points difficult of access, service roadways, about 3 m. wide, for hauling material were constructed, and, for about 7 km., a roadway was made along the line of the trench.

The prices for the roadway, under the above classification, were: For No. 1, 35 cents; No. 2, 1.50 pesos; and No. 3, 2.50 pesos per cu. m.

The trenches were excavated 5 cm. below the required finishing depth, to allow for grading the pipes in selected material, and were taken out to an average width of 40 cm. greater than the outside diameter of the pipe, to allow for their proper jointing, and also to give sufficient room to roll the pipes in the trenches.

The final quantities of excavation were:

The route of the pipe line was laid out so as to obtain an average fill of not more than 1 m. over the tops of the pipes, but in some cases the cuts, for short lengths, were 3 m. deep. The excavation for this work began in June, 1907.

Hauling Pipes.—The pipes were hauled to the site of the work with ox-carts and mule teams. The cost of hauling varied from 25 cents per pipe at the lower end, to 1 peso per pipe at the upper and, comparatively speaking, inaccessible portion of the line. The weight of each 55.9-cm. pipe was about 182 kg.; that of each 63.5-cm. pipe was about 216 kg.

The breakages in all the pipes cast at the pipe yard amounted to about 1%, due chiefly to unloading them carelessly near the pipe line.

Pipe Laying.—The pipe-laying gang was composed of 7 Mexicans under the direction of an American foreman, who was in charge of several gangs. One gang could lay daily from 60 to 73 m. (from 100 to 120 pipes). The following was the ordinary pay-roll for one gang:

This brings the average cost of laying the pipes to 32.8 cents per lin. m.

The pipes were jointed with 1:2 cement mortar, the outer joint being rounded over both pipes for a width of 12¹⁄₂ cm. (5 in.) and a height of about 19 mm. (³⁄₄ in.). In making these joints the pipe layers wore rubber gloves. The joints were kept moist, and the trench was back-filled with fine, screened material to a depth of 10 cm. above the top of the pipe. Inside, the joints were carefully caulked with cement and rendered smooth, the plasterers working continuously along with the pipe layers, doing from 20 to 35 m. at a time. Water had to be conveyed to the trenches by barrels on burros, and during the dry season it was sometimes carried 5 or 6 km.

Plate IV, Fig. 1.—Typical Reinforced Concrete Girder Bridge, Estanzuela Aqueduct.

Plate IV, Fig. 2.—Elliptical Arch Bridge Carrying Estanzuela Aqueduct.

Bridges.—The line as laid out passed over many gulches and dry arroyos, and these were crossed with reinforced concrete bridges of varying spans and heights, two being shown on Plate IV.

These bridges were formed of continuous horizontal girders, 1.10 m. deep and 1 m. wide, with a cantilever overhang at the abutments, varying in length from 1 to 2 m., so as to avoid settlement between the pipes and the bridges. The bottom reinforcement consisted of from 2 to 6 twisted bars of mild steel, varying in different spans from 12.7 to 19 mm. (¹⁄₂ to ³⁄₄ in.) in diameter. The turned up bars were 28¹⁄₂ mm. (1¹⁄₈ in.) in diameter; they were placed on either side, carried over the upper part of the beams, and continued along the end for the

overhanging part of the girder. These bars, when not obtainable of the full length, were spliced with a lap of 1.2 m. with No. 6 galvanized-steel wire. The vertical stirrups were 4.7 by 25.4 mm. (³⁄₁₆ by 1 in.), of mild steel; they were equally spaced 30.5 cm. (12 in.) apart, and carried all around the girders, lapping at the center about 15 cm. (6 in.), all the steel being carefully wired together before placing the concrete.

The general type of the piers and abutments is shown by Fig. 1, Plate IV, and varies in height with practically every bridge, the foundations in every case resting on hard rock. The concrete for the girders was a 1:2¹⁄₂:3¹⁄₂ mixture, the crushed stone used having all passed a mesh of 19 mm. (³⁄₄ in.). The piers were of 1:3¹⁄₂:5¹⁄₂ concrete, and heavy "displacers" were embedded within them.

The concrete was placed after the pipes had been laid through the form by the pipe contractor, the joints being kept clear of the bottom to the required distance by small moulded concrete blocks. The tops of the girders were moulded to a slightly segmental form. The bridges were all kept watered for about 15 days, and the forms were not struck for 28 days after placing. At Station 13.4 the pipes were carried over a picturesque arroyo on an elliptical arched bridge (Fig. 2, Plate IV) of 11 m. clear span.

The abutments of all bridges were protected by rubble walls in cement mortar carried up 60 cm. above the tops of the girders.

The contract price for the concrete work of these bridges, the Company furnishing the steel and cement, was 14 pesos per cu. m., and for placing reinforcing steel 35 pesos per metric ton (2,204 lb.).

There are 49 single-span bridges, the larger spans being 9.10 m.; 8 two-span, and 11 three-span bridges, their total length, including the overhang, amounting to 870.50 m., or 4¹⁄₂% of the whole length of aqueduct.

Concrete Aprons.—At 76 points there were small depressions which did not necessitate the construction of bridges, and at these places the pipes were encased in blocks of concrete carried up the hillside in the form of an apron having small abutment walls from 1 to 2 m. apart. This also served to protect the pipes from scouring action during rainstorms. At the upper end of the line, near the intake, the pipe had to be protected by concrete continuously for a distance of about 300 m., in order to prevent damage from falling rocks.

Plate V, Fig. 1.—Ventilating Column and Entrance Manhole, Estanzuela Aqueduct.

Ventilators and Manholes.—Along the route of the concrete pipe there are 27 ventilators, one of which, together with an entrance manhole, is shown by Fig. 1, Plate V. They consisted of simple concrete columns, 3.35 m. high, above the ground line, the interior of the shafts being formed of fire-clay pipes, 15 cm. (6 in.) in diameter. At each ventilator the pipe was cut and a block of concrete, the width of the trench, filled in as a foundation. Entrance manholes were also placed at 49 points, at 27 of which they immediately adjoined the ventilating columns.

Estanzuela Tunnel.—At 1,560 m. from the intake at Estanzuela, the conduit is laid through a tunnel 281 m. long. The tunnel was driven through hard calcareous strata from the open cuttings at each end. The inner dimensions were trimmed to approximately 2 m. high and 1¹⁄₂ m. wide. At the ends of the tunnel the rock was moderately easy to take out, but the inner section was very hard and difficult to blast. Ordinary hand drilling was adopted, and the actual cost of driving varied from 28 pesos per lin. m. at the ends to 50 pesos in the center.

The pipes were laid through the tunnel in the ordinary way, and back-filled from the center, so as to give a cover of about 45 cm. above to protect them from falling pieces of shale.

Plate V, Fig. 2.—Placing Concrete Pipes in Forms for Bridge Crossing at North End of Tunnel, Estanzuela Aqueduct.

Siphons.—It has already been mentioned that there are 6 cast-iron pipe siphons. The head on these varies between 10 and 38 m. All are provided with special inlets and outlets, forming combined overflow and ventilating chambers, and have wooden hand-sluices to divert the water when necessary. The bottoms of all siphons are provided with 20-cm. cast-iron scour-out pipes, fitted with valves, and carried down to a lower point to obtain a free outlet. The valve-boxes are protected by being placed in heavy concrete chambers carried up above the level of ordinary floods.

The siphons are formed of cast-iron socket pipes, 3.65 m. (12 ft.) long, caulked in the ordinary way with lead joints. The thickness of the 45.7-cm. (18-in.) pipes is 19 mm.; that of the 50.8-cm. pipes is 21 mm. On the steep hillsides the pipes are anchored securely to the rock in concrete blocks reinforced with heavy iron chains. In some cases these siphons were difficult of access, but ox-teams hauled the pipes in a very efficient and satisfactory manner.

Overflow Chambers.—The ordinary overflows, of which there are 14, are similar in design to the siphon inlets.

Testing, etc.—When the line was completed it was tested for water-tightness, and the loss was found to be about 5%, part of which was probably due to absorption. At a later date it was found that the waters of the Estanzuela River, which contain 150 parts of calcium carbonate (CaCO₃) per million, deposited a very fine film of lime on the interior of the pipes, completely filling any pores there might have been. At the present time there is no measurable leakage, thus proving that the character of the work is very satisfactory.

The water was turned into the conduit on June 11th, 1908, and delivered to the city on the following day through a by-pass, before the reservoir was completed.

The pipe line is patrolled daily by an inspector with the authority of a gendarme, so as to prevent the unlawful abstraction of water, a very necessary precaution in so dry a country.

South Distributing Reservoir.

The distributing reservoir for the Estanzuela supply is at Guadalupe, on the foot-hills to the south of the Santa Catarina River, about 2 km. from the center of the city. The reservoir is a covered one, of reinforced concrete, and its capacity is 38,000,000 liters (10,000,000 U. S. gal.).

Plate VIII, Fig. 1.—General View of Excavation and Embankment for South Reservoir Before Lining.

Excavation and Embankment.—The heavy slope of the ground at the selected site made the circular form the most desirable. On the low side the ground was excavated about 2 m. below the original ground line, while the excavation at the upper part of the slope was about 12 m. deep. The excavated material consisted chiefly of sillar and limestone conglomerate, which when broken up forms a calcareous clay of an excellent character for the formation of embankments, when proper care is taken. The dimensions fixed for the internal diameter of the finished concrete work of the reservoir were: 81 m. (265.68 ft.) at the top, and a depth of water of 9 m., with sides sloping 55 in 100.

Fig. 10.—South Reservoir Plan Of Excavation.
[Larger.]

Fig. 10 is a plan of the reservoir, with a cross-section of the excavation and embankment. On the lower side the original ground line was cut down in steps, and all loose earth, roots, etc., were carefully removed. The floor of the reservoir was chiefly sillar conglomerate, a hard material that required a considerable amount of blasting for its removal. The embankments were formed in 10-cm. layers

of sillar and conglomerate broken into small fragments and then rolled with 3-ton sectional rollers drawn by teams of 4 and 6 mules, which assisted in disintegrating the mass thoroughly, and produced by constant wetting a homogeneous and compact clay. The excavation and embankment were left so that 15 cm. of trimming could be done at a later date, immediately prior to the lining of the reservoir. The excavated material amounted to about 34,000 cu. m., and, of this quantity, 31,500 cu. m. were used to form the embankment; the

remainder was taken to a spoil bank immediately adjoining, the black earth stripping being separated and reserved for covering the reservoir, etc. The contract prices for the excavated material placed in the embankment were:

The prices (for the same classification) for material taken to the spoil bank, were 0.40, 0.80, and 1.40 pesos, respectively. Of the material taken out, 15% came under No. 1 classification, 80% under No. 2, and 5% under No. 3.

The excavation was begun at the end of May, 1907, and completed in January, 1908, by Scott and Lee, the contractors. The embankments were then allowed to stand until the beginning of July, 1908, to permit the whole to become thoroughly settled and consolidated prior to beginning the lining. In July the work of trimming the embankments and excavating for the foundations of the reservoir columns was commenced, under the Company's own administration, which completed the entire work.

Plate VI.—Details Of Beams And Columns For South Reservoir.
[Larger.]

Plate VIII, Fig. 1.—Details Of Forms For South Reservoir.
[Larger.]

Plate VIII, Fig. 2.—View of Western Half of South Reservoir, Showing Final Setting Up of Derrick on Central Columns.

Concrete Lining and Roof.—The general arrangement and details of the side-walls, columns, and roof are shown on Plates VI, VII, VIII and [IX]. The principal feature consists in dividing the reservoir into radial sections and supporting the roof on 135 primary and 670 secondary beams, from 135 columns, spaced as follows:

The inner bottom diameter of the reservoir is 70.32 m. (230.64 ft.); the upper inside diameter is 81 m. (265.68 ft.); the water depth at the overflow level is 9 m. (29¹⁄₂ ft).

The roof was designed to carry a dead load (the earth cover) of 150 lb. per sq. ft., and a live load of 100 lb. The maximum compressive fiber stress in the concrete was assumed at 550 lb. per sq. in. for the beams, and at 350 lb. for the columns, a low figure, because of their eccentric loading. The tensile strength of the steel was taken at 14,500 and 16,000 lb. per sq. in. The twisted steel used for the column reinforcement was made at the local steel plant, but for the beams, etc., a twisted lug bar, of higher quality and greater permissible tensile stress, was used. The total quantity of steel used was 178 tons. It was calculated that the load on the column foundations would not exceed 1¹⁄₄ tons per sq. ft. With the exception of the side-wall and floor, all the concrete was reinforced with steel, of the sizes and spacing shown on [Plate VI].

General Construction and Erection Scheme.—The question of ordinary forms, requiring very heavy timber work, was a serious one, as suitable lumber is very expensive in Mexico; and the necessity of finishing this reservoir before the end of the first term allowed under the concession, which expired on December 31st, 1908, led to the adoption of what the writer believes is an original scheme for so large a structure. This scheme was to cast the columns in short sections, mould the radial and secondary beams as separate members, and then place them in position with derricks. At the same time, in the case of the beams, it was important not to sacrifice either the benefit of that part of the slab which is ordinarily assumed to act as a part of the beam, or the additional strength due to continuity; and, in case of the columns, the strength due to the reinforcement extending from the foundation to the beams.

The T-beam section was secured by notching the tops of the moulded members, with notches 10 cm. deep, throughout the lengths of the beams, as shown on [Plate VI]. A computation of the maximum flange increment shows that these notches are sufficient to transfer the flange stresses to the stem, but, for additional security, flat steel bars were bent to a Z-shape and embedded in the top of the beam, about 60 cm. apart. Continuity in the beams was secured by carrying the steel to the tops of the beams over all supports, and, after erection, concreting them into the roof slab. The secondary beams, after casting, were dropped into recesses left in the radial beams for the purpose.

Concreting, Mixing, etc.—The radial beams and column sections were cast as nearly as possible under their ultimate positions; the secondary beams were cast outside and immediately adjoining the reservoir.

The rock and sand was brought from the Company's crushing plant, in 3-cu. yd., side-dump cars, running on a 30-in. track by gravity a distance of 1 km., the last 150 m. requiring hauling with 6 mules. The cars returned all the way to the crusher by gravity. These cars dumped the material into bins on the high ground above the reservoir; from there it was hoppered into cars which carried to the mixer all the material for one batch of concrete. Two No. 1 Smith mixers were used, and from 25 to 30 batches per hour could be handled in each machine.

The concrete was transported from the mixers to place in ¹⁄₂-cu. yd., 18-in. gauge, swivel, steel dump-cars pushed by two men. All the concrete used in the bottom of the reservoir, for the main beams, columns, and floor, amounting to about 2,460 cu. m., was dumped through a chute into smaller cars. The chute had so many baffle-plates and bolts that it resembled a gravity mixer, but, although it was 12 m. long, it effectively prevented the separation of the materials.

Concrete Placing and Moulding.—The square foundations for the columns were deposited in situ, a recess being left for the reception of the pedestals, which were moulded in place afterward. The capitals and pedestals were cast in one piece, and the columns in 1.21-m. (48-in.) sections, eight 5-cm. holes being left in them by using wrought-iron pipes, held in place by templates and removed when the castings were about 3 hours old. The columns were erected by threading them on the 15.8-mm. (⁵⁄₈-in.) reinforcing rods, which extended from the pedestals up through the capitals. The rods were in two lengths, arranged to lap alternately at one-fourth, the center, and three-fourths of the height of the columns. In erection, a light timber frame was used in conjunction with the derrick, and, as the columns were placed, the reinforcing steel was grouted solid with 1:2 cement mortar.

All the erection was done with a combined stiff-leg or guy derrick, having an 80-ft. boom and a 50-ft. mast, and fitted with a 30-h.p. Lambert hoisting engine. The derrick was erected seven times at the circumference, and its final position was on top of the center columns. The moving of the derrick a distance of about 45 m. and its subsequent

erection occupied usually about 48 hours. The erection work was carried on continuously, day and night, the placing of the whole of the radial and secondary beams and columns occupying 2¹⁄₂ months.

Forms.—As the erection scheme was designed to reduce the cost of forms, economical construction was of considerable importance. The wall was formed in 40 panels, about 6 m. wide and 11.27 m. high. The chief object in arranging them in this manner was to permit an expansion joint, 30 cm. wide, at each panel; this joint was not filled until after the completion of the roof, when the temperature inside the reservoir was uniform and not subjected to such great fluctuations as if exposed alternately to the hot sun and comparatively cool nights. The range of temperature during the construction period sometimes amounted to 80° Fahr. in 24 hours.

The expansion joints were left to the last, when a uniform temperature of about 70° inside permitted the filling of the joints, thus avoiding all trouble from expansion cracks.

The forms are shown in detail on [Plate VII]. They consisted of shutters stiffened with four trapezoidal trusses. The bottom posts of the trusses were fixed in holes formed in the foundation block; they were propped back from the embankment at the top, and secured to anchorages by iron rods.

Six sets of these forms were used to construct the whole wall. The concrete was placed in position through stove-pipe chutes, 20 cm. in diameter, in continuous layers, the workmen treading and spading it well as it was deposited. The forms were allowed to remain 4 or 5 days, and were then struck and removed to another section. The pedestals and capital forms were of lumber, and five of each were used to cast the total number required. In the column sections the outer steel forms used in the manufacture of the Estanzuela pipes were adapted for this purpose. The radial beam forms, shown on [Plate VII], were arranged with internal wedge-shaped blocks to mould accurately the recess for the secondary beams. The bottom forms were left attached to the beams for 28 days, but the sides and ends were removed after 24 hours. Eight forms were sufficient for the whole 135 beams.

For the secondary beams, 29 forms were used for the 670 beams, the bottom lumber also being left until they were mature for handling.

By referring to the cross-section of the secondary beam, it will

be noticed that it is jug-shaped, shelves being left on either side for the support of the roof forms, which were placed after the secondary beams had been properly grouted to the radial ones. The lagging was laid diagonally, so that the short diameter was slightly greater than the distance between the beams. This greatly facilitated the removal of the lagging, as it was merely necessary to strike the wedge-shaped fillets beneath, and turn them clockwise, after tearing out the end lagging.

Plate IX, Fig. 1.—View of Separately Moulded Secondary Beams in Yard Below South Reservoir.

Plate IX, Fig. 2.—Setting Primary Beams, South Reservoir.

The writer believes that the adoption of forms of this type, rather than the ordinary kind, led to a saving of lumber of about 400,000 ft. b. m. During the erection and placing of the concrete, all the joining surfaces were carefully picked and cleaned, particular care being taken at the junction of the secondary with the radial beams, and the upper surfaces of all beams before laying the roof slab.

After the greater part of the roof was completed, the floor was laid in those sections where it was protected from the sun's rays. The concrete was placed in two 15-cm. thicknesses, and the work was carried on night and day, without any joints. The laying of the floor occupied 8 days, or an average of nearly 100 cu. m. daily.

Plate X, Fig. 1.—View of Completed Section of South Reservoir. Expansion Joints in Side-Wall Not Yet Filled.

Proportions of Concrete.—All the concrete work was brought to a smooth face by careful spading, no plastering being used throughout the reservoir, except in the superstructures. The work was kept well watered in every case for about 15 days. The whole of the concrete work in connection with the reservoir was completed in 5¹⁄₂ months. The concrete for the columns and foundations was a 1:3:5 mixture, the aggregate consisting of equal parts of 19-mm. (³⁄₄-in.) and 38-mm. (1¹⁄₂-in.) crushed stone. The remainder of the concrete, except that for the roof, was a 1:2:4 mixture, the aggregate also consisting of equal parts of 19-and 38-mm. stone. With the exception of a short length of the side-walls, the sand used was that manufactured by the Company. When the crushing plant was unable to produce all the sand required, the Hornos sand (see Table 3) was used in the side-walls in equal proportions with the crusher sand.

Reservoir Outlet and Entrance Tower.—The outlet, 61 cm. (24 in.) in diameter, leads from a well in the center of the reservoir and passes under the floor and embankment to an outside valve-pit, 89 m. from the center. This pipe was laid in a trench in a solid cutting before the construction of the embankment, and was encased in 1:4:8 concrete.

Where it passes under the embankment a 1:2:4 concrete cut-off wall, 3.6 m. wide, 2.5 m. high, and 1 m. thick, was placed across it at right angles. The cast-iron pipe is curved upward in the central well, and has a bellmouth on which rests a movable circular copper screen.

Above the outlet well, and on the roof of the reservoir, there is a central tower, giving access to the interior by a steel stairway. This tower also serves as a main ventilating shaft, and in it are arranged the guide-screens and gearing for raising them for cleaning purposes. In addition to the ventilation provided in the tower, 20 circular openings, 30 cm. in diameter, are carried through the roof of the reservoir at the circumference and into the parapet walls.

Inlet Gate-House, etc.—The inlet gate-house is above the reservoir and about 54¹⁄₂ m. from its center. The conduit enters at 589.00 m. above datum, and the gate-house contains the valves for controlling the inlet pipe to the reservoir, the by-pass, overflow, scour-out pipe, and the copper screens. The inlet, which is 45.7 cm. (18 in.) in diameter, is of cast-iron flanged pipes, carried on iron hangers on the side-wall of the reservoir, and, at a point 90 cm. above the floor level, it is turned at right angles to the side-wall and carried on concrete piers to the center of the first row of columns. The end of the pipe is closed by a blank flange, and the water is deflected at right angles through two 30-cm. (12-in.) branches, for the purpose of setting up a slight circular motion as it enters the reservoir.

The valve-pit is clear of the embankment, and in it are brought together the main supply and by-pass pipes on which are placed two 61-cm. (24-in.) sluice-valves; and between them there is a 20-cm. (8-in.) scour-out pipe, for emptying the reservoir into an adjoining arroyo. The arrangement of the valves gives complete control over the contents of the reservoir.

Venturi Meter-House.—Fig. 11 shows the arrangement of the Venturi meter and its automatic register in a house over the main supply pipe. This house is designed to form a feature of the entrance gateway of the reservoir grounds, which cover an area of 12 hectares.

Fig. 11.—Venturi Meter-House.
[Larger.]

General.—The roof of the reservoir has been laid out as a garden, and the embankments are turfed. The intention is to develop the Company's land as a public park, as it commands fine views of the city and the surrounding mountains. An inspector's house has been built, and a private telephone line provides for communication with the Estanzuela intake and also with the general offices in the city.

Plate XVIII, Fig. 1.—View of South Reservoir, Looking Toward the City.

San Geronimo Gravity Supply.

Provisional Supply.—It has already been stated that the Company began operations at San Geronimo in March, 1906, by sinking a well on the north bank of the Santa Catarina River at San Geronimo. At this point, a little later, a small steam pumping plant, sufficient to handle about 8,000 liters per min., was installed. The lowest depth to which this well was ultimately sunk in water-bearing strata, was 7 m., the normal level of the water during 1906 and 1907 never falling lower than 569 m. above datum. Tests made from time to time during 1907-08, showed that this well was capable of supplying nearly 10,000,000 liters (264,000 gal.) of water daily.

The excellent supply yielded by this well made it desirable to adopt it immediately as a provisional measure, pending the completion of the larger works forming the western source of supply. To utilize the well to its fullest extent, a reinforced concrete reservoir, of 3,000,000 liters capacity, was constructed on the south bank of the river, the top water level being 585 m. above datum, that is, at the same elevation as the proposed reservoir for the Estanzuela supply. The reservoir is 53.80 m. long, 21 m. wide, and has a water depth of 3.25 m. at the overflow level. It is excavated on a steep hill slope, and has an earth embankment on the lower side. The lining is of concrete, 20 cm. thick, and the roof is of reinforced concrete composed of flat arches springing from beams carried on 46 by 35-cm. reinforced columns. There are 68 of these columns, and they are 3 m. apart longitudinally and 5 m. apart transversely. The roof was not constructed until October and November, 1907, and prior to that time the necessity of covering the reservoir was amply demonstrated by the growth, during hot weather, of considerable quantities of green algæ, which had to be skimmed from the surface of the reservoir every few days.

The delivery pipe from the pumping plant was originally of riveted steel and was asphalted. It was 30 cm. in diameter, 2 mm. in thickness, with slip joints, and where it crossed the river it was encased in concrete. This pipe was afterward replaced by a cast-iron pipe of the same diameter. The supply pipe to the city was also of sheet steel, 30 cm. in diameter. For a part of its length it was laid in the high ground of the south bank of the river, which it crossed near the western limits of the city, and was then connected to a 30-cm, cast-iron pipe in the

distribution system. The total length of the pipe from the reservoir to the city distribution system was 2,850 m.

This provisional pipe continued in service from October, 1906, until August 27th, 1909, when the river portion was completely swept away, together with the provisional pump-house at San Geronimo, during the great flood in the Santa Catarina River. Fortunately, the permanent supply works were completed at the time, so that the destruction of this pipe line, which had already served its original purpose, had no effect on the supply of water to the city.

Plate XI.—Section of Infiltration Gallery, San Geronimo Gravity Supply.
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Infiltration Gallery.—The chief feature of the San Geronimo gravity supply is the infiltration gallery. By referring to the profile on Plate XI it will be seen that at this place there is a considerable area of what is undoubtedly water-bearing gravel. The main conditions were revealed by the borings previously carried across the valley, but the profile has been corrected to show the actual conditions as established at a subsequent date by shafts. Practically, the water-bearing strata are not limited merely to the sand and coarse gravels, as the clay formation lying above and below them is full of small gravel deposits containing considerable volumes of water. The main direction of the underflow is toward the east, and the hydraulic gradient, which was established from wells sunk farther west, was found to be approximately 1%, or practically the same as the average surface of the bed of the river above the line of the infiltration gallery.

The general scheme for tapping this underflow was to drive a main gallery at the 560-m. level on a grade of 0.05%, which was sufficiently high to take the supply by gravity to the western reservoir, having a top water level at 558.75 m. above datum. This elevation is sufficient to give an excellent pressure over about 60% of the city, and a fair pressure to reach the upper stories of the highest houses, if required, over the whole supply district. From this gallery it was proposed to sink shafts at frequent intervals, for a total distance of 300 m., carrying them below the gallery level, to tap any water-bearing gravels there might be in the clay formation underlying the gravels and sands. From the main gallery it was proposed to construct branch galleries up stream on a flat gradient, so as to obtain the advantage of an increased head due to the steep hydraulic gradient of the underflow water.

Fig. 12.—Diagram Showing Variation In Water Plane 1905 To March 1910 At San Geronimo.
[Larger.]

In investigations of this kind, it is of first importance to have a continuous record of the level of the water plane, and Fig. 12 has been

plotted to show its variation at San Geronimo from the beginning of 1905 to March, 1910. From January, 1909, to March 31st, 1910, these levels are averages of daily readings taken in 9 shafts sunk along the proposed line of the infiltration gallery. In 1902 the water plane was standing at 570.18 m. above datum, but from that date until 1905 the writer has been unable to find any records. This diagram should be examined together with the rainfall diagram, Fig. 3, and it will be noticed that the fall in the water plane drops with the general scarcity of the rainfall during 1907-08, and until July, 1909. The year previous to July, 1909, is regarded, by many competent local observers to have been the longest period of extreme drought in 30 years in Nuevo León, and the evidence which the writer has been able to gather regarding stream flow in the neighborhood of Monterrey supports this view. The total rainfall at Monterrey for the year prior to July 1st, 1909, amounted to 9.98 in., or 4.16 in. less than the lowest record for any

calender year since 1894, or, in other words, about 45% of the average annual rainfall.

The lowest point to which the water plane dropped was during June and July, 1909, when the levels stood slightly above 565.00 m., or 5 m. above the level of the floor of the infiltration gallery. During this period pumping tests were made in the various wells, and from these it was quite clear that the infiltration gallery, if carried far enough to meet them all, would yield a supply of from 25,000,000 to 40,000,000 liters daily. During the great rainfall of August, 1909, the water levels rose very rapidly; the heavy precipitation between August 9th and 10th caused the level to rise to 568.00 m. in about 4 days, and 6 days after the great flood of August 27th, the water level, which had continued rising gradually, reached 571.40 m., and then fell gradually until at the end of March, 1910, it was practically the same as it had been from 1902 to 1905.

Plate XII.—San Geronimo Gravity Supply.
[Larger.]

It should be noticed that the readings were taken in the shafts on the high ground to the west of the present river bed, and were independent of any flow there might be in the river. During times of ordinary floods in the river, it was very noticeable that, notwithstanding the fact that the river water might be turbid to an extreme degree, the well even in immediate proximity to the river bed did not show the least sign of discoloration.

Design of Works.—Plate XII shows the general design of the gravity scheme, which consists of a main tunnel 550 m. long and a concrete aqueduct, 1.06 m. (42 in.) in internal diameter and 2,311 m. in length, discharging into a low-service distributing reservoir at the extreme western limits of the city. The tunnel and aqueduct were laid on a gradient of 0.05%, and the latter was designed to discharge 55,000,000 liters per day (22.8 cu. ft. per sec.) if flowing to its full capacity.

Gravitation Tunnel.—This tunnel, shown on Plate XII and Fig. 13, was completed prior to driving the infiltration gallery into the water-bearing gravel, so that the water encountered in the gallery could be easily drained off by gravity, thus avoiding a heavy outlay for pumping. The tunnel passes through various strata, the principal ones being calcareous shale, conglomerate, and gravels. The tunneling operations were carried on from 5 shafts, No. 1 being 23 m. deep, and the others varying from 20 to 10 m. The shafts in loose ground were

timbered in the usual way, having clear inside dimensions of 2 m. Shaft No. 1, which was entirely in shale, was taken out approximately to 3.35 m. in diameter, so as to permit it to be lined with concrete having a finished internal diameter of 2.43 m.

Fig. 13.— General Details San Geronimo Gravity Pipe Line.
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Fig. 13 shows the details of the tunnel, which was lined with concrete, the bottom and sides being approximately 23 cm. (9 in.) thick. The interior dimension is 0.91 m. at the invert level and 1.016 m. at a height of 1.22 m., the corners between the side-walls and the floor being slightly curved. The arch is formed of two rings of brickwork in cement mortar, this thickness being increased in some lengths to three rings. Where the rock was in good condition, and not likely to disintegrate easily, the arch, for a distance of 90 m., was left unlined. Of the total distance of 550 m., careful timbering was required for 300 m. In lining the timbered portion of the tunnel with concrete, all the timber was removed, except in loose ground, where the laggings were left in position.

While the tunnel was being driven, a start was made to drive the north end of the infiltration gallery, which was in rock for a distance of 44 m. Water appeared at about 35 m., and then the work was temporarily suspended until the gravitation tunnel was completed and a length of the aqueduct had been constructed far enough down stream on the north bank of the river to permit of draining direct to the river. This point was reached at 1,170 m. from Shaft No. 1, and there a temporary overflow chamber was constructed.

When the tunnel was completed, the two intermediate shafts were filled up, the remaining three being retained permanently. Shafts Nos. 2 and 3 were lined with concrete, 76 cm. (30 in.) in internal diameter, and 23 cm. thick. They were domed at the top to form circular openings to receive cast-iron covers. Progress on this tunnel was slow, taking from December, 1907, to November, 1908, to complete, owing chiefly to difficulties with an incompetent contractor. The contract was subsequently transferred to Mr. John Phillips, of Mexico City (who was also the contractor for the aqueduct), who completed it satisfactorily.

Continuation of the Infiltration Gallery.—When the aqueduct (to be referred to again) was completed as far as 1,170 m. from Shaft No. 1, the driving of the infiltration gallery, which was 2 m. high and 1¹⁄₂ m. wide, was continued until gravel was encountered in the roof, at 44 m.

from the shaft. At this point the rock dipped at an angle of 45°, and the gravels contained quantities of large boulders mixed with fine sand; immediately after encountering the gravel, a flow of about 90 liters per sec. was met, evidently coming through from a pot-hole in the shale. This quantity diminished in about 10 days to about one-fourth, but gradually increased again as the driving proceeded. The operations of driving the tunnel from 44 m. forward were begun in the dry season, in February, 1909, and the gravel was encountered for a distance of 24 m., or up to 68 m. from the shaft. The center of this gravel bed was about 30 m. south of the old river channel, which had been continuously dry at the surface for several years. Up to 68 m. the work was very difficult, owing to the upper part being of loose gravel and the lower in very contorted shale. The timbering of the tunnel in the full gravel section consisted of heavy square settings, 1 m. apart. At 68 m. the clay and gravel formation was met, and the rate of progress then was about 4 or 5 m. a week. A short branch gallery was also driven about 7 m. up stream near Shaft No. 2. The total distance the infiltration gallery was carried from Shaft No. 1, was 100 m., when the floods of August, 1909, caused its suspension.

During the progress of the gallery, attempts were made to sink a 3¹⁄₂ by 2-m. shaft at a point along the line of the infiltration gallery, about 130 m. from Shaft No. 1, but water in such abundance was encountered that it was practically impossible to sink it in the ordinary way more than about 6 m. deep, the quantity of water to be dealt with amounting to about 20,000,000 liters daily. Seven shafts were then sunk in the high ground to the north of the river, five of these being on the line of the gallery and two 30 m. westward. They were sunk during the dry season prior to July, 1909. These were ordinary timbered shafts, 2 m. square between the walings, and were carried to the depths shown on [Plate XI]. In Shafts Nos. 5, 6, and 7 the water was flowing with considerable velocity, while Shaft No. 9 seemed to have penetrated a different water plane and one which was probably independent of that showing in any of the other shafts, in which the water was practically at a uniform level. The evidence obtained showed that if the gallery could be carried to Shafts Nos. 6 or 7 a great abundance of water would be intercepted. Owing to the difficulties of sinking ordinary shafts in the wide river channel, circular shafts were put down. These were 1.37 m. in internal diameter and 23 cm.

thick, and were of concrete reinforced with No. 10 vertical rods, 19 mm. in diameter, tied together with No. 6 wire. These shafts were provided with steel cutting edges.

Shaft No. 2 was sunk to a depth of 1 m. below the infiltration gallery level, No. 3 within 2 m., and No. 4 within 4 m., before August, 1909. The shafts were sunk by digging them out and loading them at the top, the top of the shafts being kept generally 3 m. out of the ground. Shaft No. 3 encountered great volumes of water, and, in order to enable sinking operations to proceed, a pumping shaft, 2¹⁄₄ m. square, was sunk a little west of it to draw off the water. Notwithstanding the fact that the prolonged period of drought had lowered the general water plane in all the shafts to 565.00 m. above datum, the difficulties of handling the water even at that level were considerable. At the beginning of August the work was progressing very satisfactorily, but the extraordinary rainfall of that month caused the work to be shut down temporarily.

Effect of the Floods in the Santa Catarina River.—The area of the water-shed of the Santa Catarina River above Monterrey is about 1,410 sq. km. (544 sq. miles), and its area at San Geronimo, owing to its configuration, is practically the same. Its general character has already been referred to. On the night of August 10th and early on the morning of August 11th, a big flood came down the river, flowing at its maximum about 1,130 cu. m. (40,000 cu. ft.) per sec., due to the heavy rainfall [(Fig. 4)]. This flood carried away all the temporary staging around the shafts, seriously wrecking the temporary pumping station, as well as destroying the 30-cm. cast-iron pipe, notwithstanding the fact that it had been encased in a block of concrete 3 m. wide and 1¹⁄₂ m. thick right across the river; but no damage was done to the infiltration gallery or to the shafts in the river channel. The effect of the flood on this pipe is shown by Fig. 2, Plate XXXI.

Plate XXXI, Fig. 2.—Profile Sketch, Looking Up Stream On Line Of 24-inch Main Supply Pipe.
[Larger.]

Following this flood, which had caused the loss of 14 lives in the city, 3 miles below San Geronimo, there was practically no rain for 13 days. Then, on August 25th the second heavy precipitation began and continued until August 29th, the details being shown on [Fig. 4].

This precipitation, therefore, fell on a water-shed which was completely saturated, as it had already absorbed a large proportion of the 13.38 in. of rain which fell during August 10th and 11th; and at every point along the river, prior to August 25th, springs were issuing forth,