ASCE 1193: The Water-Works And Sewerage Of Monterrey, N. L., Mexico Part 2

ESTANZUELA SUPPLY.

[Ill.u.s.tration: FIG. 8.--LOCATION PLAN OF ESTANZUELA DAM.]

_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 debris 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 quant.i.ty 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 1:2-1/2:3-1/2 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.

+===========================================================+==========+ Description. Length, in meters +-----------------------------------------------------------+----------+ Cast-iron pipes, 45.7 cm. (18 in.) in diameter, along the stream bed of the Estanzuela River 110 Concrete tubes, 55.9 cm. (22 in.) in diameter, to Mederos (including 281 m. of tunnel) 4,473.81 Cast-iron siphons, 45.7 cm. (18 in.) in diameter: Calabozos 239 m South Virgen 124 " North Virgen 177 " Mederos 426 " ----- 966 Concrete tubes, 63.5 cm. (25 in.) in diameter, Mederos to South Reservoir. 12,039.19 Cast-iron siphons, 50.8 cm. (20 in.) in diameter: Necaxa 315 m. San Augustin 796 " ----- 1,111 +-----------------------------------------------------------+----------+ Total 18,700 +===========================================================+==========+

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.

[Ill.u.s.tration: FIG. 9.--ESTANZUELA PIPE LINE STEEL FORMS FOR THE MANUFACTURE OF CONCRETE PIPE.]

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. (2-3/4 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 crus.h.i.+ng 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 1-1/4 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:

Crushed rock broken to pa.s.s through a 19-mm. screen 0.136 cu. m.

Manufactured sand (run of rolls) 0.119 " "

Portland cement 0.090 " "

------------ Total 0.345 cu. m.= (12.2 cu. ft.)

[Ill.u.s.tration: PLATE III, FIG. 2.--STEEL FORMS FOR MOULDING CONCRETE TUBES, ESTANZUELA AQUEDUCT.]

The above quant.i.ty 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, ill.u.s.trates 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 quant.i.ty 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 a.s.sisted 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 quant.i.ties and cost of the materials used in the manufacture of these pipes.

TABLE 5.--COST OF CONCRETE PIPE.

========================================+=============================== FOR 1,126 PIPES 63.5 CM.

IN DIAMETER.

Materials. +-------------+----------------- Quant.i.ties. Cost.

----------------------------------------+-------------+----------------- Portland cement, at 8.00 pesos per bbl., delivered at pipe-making yard. 401 bbl. 3,208.00 pesos.

Sand, at 2.65 pesos per cu. m. 85 cu. m. 225.25 "

Crushed rock, 19-mm. (3/4-in.), at 2.65 pesos per cu. m. 62 cu. m. 164.30 "

No. 6 galvanized-wire hoops. 4 rings to each pipe. 4,504 203.00 "

----------------------------------------+-------------+----------------- Totals. ... 3,800.55 pesos.

----------------------------------------+-------------+----------------- Cost per pipe. ... 3.37 pesos.

========================================+============================== FOR 1,095 PIPES 55.9 CM.

IN DIAMETER.

Materials. +-------------+---------------- Quant.i.ties. Cost.

----------------------------------------+-------------+---------------- Portland cement, at 8.00 pesos per bbl., delivered at pipe-making yard. 303 bbl. 2,424.00 pesos.

Sand, at 2.65 pesos per cu. m. 68 cu. m. 180.20 "

Crushed rock, 19-mm. (3/4-in.), at 2.65 pesos per cu. m. 50 cu. m. 132.15 "

No. 6 galvanized-wire hoops. 4 rings to each pipe. 4,380 183.00 "

----------------------------------------+-------------+---------------- Totals. ... 2,919.45 pesos.

----------------------------------------+-------------+---------------- Cost per pipe. ... 2.66 pesos.

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.

========================================+=============================== FOR 1,126 PIPES 63.5 CM.

IN DIAMETER.

Materials. +-------------+----------------- Quant.i.ties. Cost.

----------------------------------------+-------------+----------------- Portland cement, at 8.00 pesos per bbl., delivered at pipe-making yard. 401 bbl. 3,208.00 pesos.