ASCE 1193: The Water-Works And Sewerage Of Monterrey, N. L., Mexico Part 8

+--------------+----------+----------------------------------------+ 76 CM. (30 IN.) +-------+------------+--------+----------+ Employees. Rate for Total Total cost No. of Cost per 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 20 0.498 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 12 12.00 ... ... Water boy 0.50 1 0.50 ... ... ... 22 36.50 ... ... +--------------+----------+-------+------------+--------+----------+ 61 CM. (24 IN.) +-------+------------+--------+----------+ Employees. Rate for Total Total cost No. of Cost per 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 5 15.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 25 0.410 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 10 10.00 ... ... Water boy 0.50 1 0.50 ... ... ... 21 37.50 ... ... +--------------+----------+-------+------------+--------+----------+ 50 CM. (20 IN.) +-------+------------+--------+----------+ Rate for Total Total cost No. of Cost per Employees. 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 35 0.287 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 12 12.00 ... ... Water boy 0.50 1 0.50 ... ... 22 36.50 ... ... +--------------+----------+-------+------------+--------+----------+ 45.7 CM. (18 IN.) +-------+------------+--------+----------+ Rate for Total Total cost No. of Cost per Employees. 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 40 0.221 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 8 8.00 ... ... Water boy 0.50 1 0.50 ... ... 18 32.50 ... ... +--------------+----------+-------+------------+--------+----------+ 38 CM. (15 IN.) +-------+------------+--------+----------+ Rate for Total Total cost No. of Cost per Employees. 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 45 0.196 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 8 8.00 ... ... Water boy 0.50 1 0.50 ... ... 18 32.50 ... ... +--------------+----------+-------+------------+-------------------+ 30.5 CM. (12 IN.) +-------+------------+--------+----------+ Rate for Total Total cost No. of Cost per Employees. 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 60 0.147 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 8 8.00 ... ... Water boy 0.50 1 0.50 ... ... 18 32.50 ... ... +--------------+----------+-------+------------+--------+----------+ 15 CM. (6 IN.) +-------+------------+--------+----------+ Employees. Rate for Total Total cost No. of Cost per 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 100 0.082 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 6 6.00 ... ... Water boy 0.50 1 0.50 ... ... 16 30.50 ... ... +--------------+----------+-------+------------+--------+----------+ 10 CM. (4 IN.) +-------+------------+--------+----------+ Employees. Rate for Total Total cost No. of Cost per 10-hour No. of labor. pipes linear day. men. Pesos. laid. meter. Pesos. Pesos. +--------------+----------+-------+------------+--------+----------+ Foreman 4.50 1 4.50 ... ... Caulkers 3.00 4 12.00 ... ... Lead pourers 2.00 2 4.00 ... ... Lead melter 1.50 1 1.50 150 0.0574 Pipe cutter 2.00 1 2.00 ... ... Peons 1.00 6 6.00 ... ... Water boy 0.50 1 0.50 ... ... 16 30.50 ... ... +--------------+----------+-------+------------+--------+----------+

TABLE 11.--CAST-IRON WATER PIPES.--COST OF MATERIALS AND LAYING AT MONTERREY.

MATERIALS PER STANDARD LENGTH OF PIPE .

Key: cm = centimeter in = inch mm = millimeter kg = kilogram m = linear meter +-----------+------+-------+--------+-------------+--------+--------+-------+ PIPE Weight Cost/ LEAD OAk.u.m CHARCOAL Total DIAMETER Thick- of piece +------+------+--------+--------+ Ma- +------+----+ ness Pipe fob Mon- Weight Cost Cost Cost terial terrey Cost cm in mm kg pesos kg pesos pesos pesos per m +------+----+------+-------+--------+------+------+--------+--------+-------+ 10 4 10.3 109 11.65 2.0 0.37 0.025 0.0525 3.30 15 6 11.1 163 15.74 3.7 0.67 0.0675 0.065 4.51 30.5 12 15.8 463 76.50 7.9 1.44 0.1225 0.1 21.35 38 15 17.4 680 79.36 10.6 1.94 0.175 0.12 22.30 45.7 18 19.0 871 90.28 13.4 2.42 0.2375 0.1375 25.42 61 24 22.2 1,261 117.60 18.8 3.42 0.335 0.175 33.20 76 30 25.4 1,946 199.05 24.5 4.42 0.44 0.2125 55.77 +------+----+------+-------+--------+------+------+--------+--------+-------+

LABOR.

Key: cm = centimeter, in = inch, m = meter +-----------+------+------+------+------+-------+-------+---- Total DIAMETER Cubic Cost Back- cost, OF PIPE: Width Depth meters of filling exca- of per exca- and re- vation +------+----+trench linear vation moving back- Continues meter per surplus filling cm in m m lin. m Pesos etc. Pesos +------+----+------+------+------+------+-------+-------+---- 10 4 0.55 0.90 0.50 0.60 0.18 0.78 15 6 0.60 1.00 0.60 0.72 0.22 0.94 30.5 12 0.65 1.20 0.78 0.94 0.29 1.23 38 15 0.70 1.30 0.91 1.10 0.34 1.44 Below 45.7 18 0.80 1.40 1.12 1.34 0.41 1.75 61 24 1.00 1.50 1.50 1.80 0.55 2.35 76 30 1.10 1.60 1.76 2.11 0.65 2.76 +------+----+------+------+------+------+-------+-------+----

--+----------------+--------+--------+--------+ HAULING PER Cost Total Total of hauling excava- LINEAR METER laying and tion and per laying laying, +--------+-------+ linear per labor, Haul- Misc. meter linear complete ing Pesos meter Pesos Pesos Pesos Pesos --+--------+-------+--------+--------+--------+ 0.0275 0.005 0.06 0.0925 0.8725 0.45 0.005 0.825 0.1325 1.0725 0.18 0.0075 0.1475 0.335 1.565 0.2725 0.01 0.19 0.4775 1.9125 0.2725 0.01 0.245 0.5275 2.2775 0.825 0.08 0.41 1.315 3.665 0.83 0.10 0.53 1.46 4.22 --+--------+-------+--------+--------+--------+

NOTE.--The above costs of earthwork are based on the following rates and percentages over the whole city:

Earth, per cubic meter 0.35 pesos 50% Soft sillar 0.75 " 20% Hard sillar 1.50 " 20% Rock (chiefly conglomerate) 4.00 " 10%

SUMMARY OF TABLE 11.

+------------------------+-------------+------------+------------+ DIAMETER Total labor Materials. Total cost OF PIPE : cost. Pesos. per linear +--------------+---------+ In pesos. meter, in Centimeters. Inches. pesos. +--------------+---------+-------------+------------+------------+ 10 4 0.8725 3.30 4.1725 15 6 1.0725 4.51 5.5825 30.5 12 1.565 21.35 22.915 38 15 1.9125 22.30 24.2125 45.7 18 2.2775 25.42 27.6975 61 24 3.665 33.20 36.865 76 30 4.22 55.77 59.99 +--------------+---------+-------------+------------+------------+

The flood destroyed about 1,200 houses in the neighborhood of the river.

In a number of blocks the smaller mains were scoured away, but considerable salvage was done afterward, and, as it is the intention of the authorities not to permit rebuilding along the flood-path of the river, these mains do not require reconstruction.

MAIN SEWERAGE SYSTEM.

The Company's obligations, as far as drainage is concerned, were limited to the removal and disposal of sewage, no provision being required for storm-water, which is allowed to find its way to the natural watercourses. Apart from that fact, however, the best system for a city like Monterrey, where rainfall for many months at a time is very scarce, is the strictly "separate system." In the design advantage was taken of the natural topography of the drainage district, which is almost an ideal one for a gravitation system of sewers, the general fall in all directions being northeast; it was also in this direction that the best available land could be obtained for disposal purposes.

[Ill.u.s.tration: PLATE XX.--DIAGRAM OF THE MAIN SEWERS OF MONTERREY.]

Plate XX shows in skeleton form the general lay-out of the sewers. Two drainage districts are arranged, divided by Calle de Was.h.i.+ngton, which may be regarded as practically the center of the city, and each of these districts has an independent main collector connecting to the outfall sewer at the northeast extremity of the city.

The system has been designed so that extensions may be made and may cover any part within the city limits; the main collectors are large enough for the whole area when fully built up.

The sewers are designed on a very liberal basis, namely, on the a.s.sumption that when flowing half full the quant.i.ty to be dealt with will be 380 liters per capita per day, with a maximum rate of flow of 200 per cent. It was a.s.sumed that each house would be occupied by 7 persons and have a frontage of 12-1/2 m. The minimum velocities in the sewers, when running full, vary between 0.91 and 1.5 m. per sec., with the exception of a few blocks.

The minimum size adopted was 24.3 cm. (8 in.) in internal diameter. The sewers of diameters between 24.3 and 50 cm., are 0.91 m. (36 in.) long, and are of salt-glazed vitrified clay, imported from San Antonio, Tex.

Table 12 gives the details of the length of the various sewers laid.

TABLE 12.--LENGTH OF SEWERS.

+----------+------------------------------------------+-----------+ DIAMETER: +-----+----+ Kind. Length, cm in. in meters. +-----+----+------------------------------------------+-----------+ 24.3 8 Fire-clay 38,332.85 25.4 10 " 16,400.69 30.5 12 " 7,953.15 38.1 15 " 4,850.56 45.7 18 " 2,023.40 50.8 20 " 1,450.53 55.9 22 Reinforced concrete tubes, 6.9 cm. thick 3,134.20 61.0 25 " " " 7.6 " " 357.40 68.6 27 Brick and concrete 484.05 76.2 30 " " " 662.69 Total 75,649.15 +-----+----+------------------------------------------+-----------+

The greater number of the manholes are of brickwork, 23 cm. thick, and have concrete inverts. They have a diameter of 1.2 m., which is reduced to 0.61 m. at the top, and each is provided with a heavy cast-iron frame and closed cover weighing about 190 kg. There are 521 manholes, and they are placed at every block and on long lines about 80 m. apart.

[Ill.u.s.tration: FIG. 16.--STANDARD 300-GAL. FLUSH TANKS.]

The sewers are flushed with 15-cm. (6-in.) automatic flus.h.i.+ng siphons of the Miller pattern with 20-cm. (8-in.) discharge pipes. There are 278 of these siphons, and they are placed in flush-tanks (Fig. 16) built of brickwork and plastered with 1:1 cement mortar. Their capacity varies from 800 to 1,200 liters, and they discharge from 22-1/2 to 28-1/2 liters per sec. They are timed to flush once in 24 hours.

The system is at present ventilated by 23-cm. (9-in.) steel ventilating columns (Fig. 16), with ornamental cast-iron bases. There are 220 of these columns. Most of them are 7.85 m. above the level of the edge of the sidewalk, and are connected to special 15-cm. branch pipes leading from the sewer on the outside of the flush-tanks. In the center of the city they are provided with extension lengths, giving a total height of 12 m.

Table 13 gives the particulars of the average distributed cost of laying the 75.6 km. of sewers.

TABLE 13.--AVERAGE COST, PER LINEAR METER, FOR 75.6 KM.

OF SEWERS, FOR MATERIALS AND LABOR COMPLETE.

+----------+-----------+--------+-----------------------------+--------+ INTERNAL Cost of EARTHWORK AND LABOR: Total DIAMETER mater- -------+------------+-------- cost of OF ials Cost of Cost of sewer SEWERS. includ- Average excavation, labor complete Kind of +------+----+ ing depth including in per Sewer. 10-cm. of back- laying linear (4-in.) sewer filling, (includ- meter. cm. in. branches removing ing every m. surplus, hauling, 4-1/2 m. etc. etc.). Pesos. Pesos. Pesos. +----------+------+----+--------+-------+------------+--------+--------+ Fire-clay 24.3 8 2.00 2.10 3.46 0.21 5.67 " 25.4 10 2.78 2.25 3.97 0.2625 7.0125 " 30.5 12 3.64 2.50 4.705 0.305 8.65 " 38.1 15 6.14 2.75 5.50 0.4375 12.0775 " 45.7 18 8.80 3.00 6.745 0.645 16.19 " 50.8 20 11.30 3.50 8.275 0.815 20.39 Concrete 55.9 22 5.93 3.50 9.19 1.325 16.445 " 61.0 25 7.30 3.75 11.245 1.685 20.23 One brick} thick on } 68.6 27 7.17 3.75 11.735 3.93 22.835 concrete } 76.2 30 7.925 4.00 14.53 4.515 26.97 founda- } tions } +----------+------+----+--------+-------+------------+--------+--------+

[Ill.u.s.tration: FIG. 17.--SKETCH SHOWING DISCONNECTING TRAP ON HOUSE DRAIN.]

The house connections are chiefly of 10-cm. (4-in.) pipes, laid on a minimum gradient of 2-1/2%, from oblique branches on the sewer to siphon intercepting traps near the house, as shown by Fig. 17. From this trap a 10-cm. fire-clay inspection pipe is carried up and capped at the sidewalk level with a cast-iron box having a locked cover. From this inspection pipe a branch is connected to a cast-iron fresh-air inlet, in most cases set in the wall of the house, the inlet being 30 cm. above the level of the pavement.

_Effect of the Flood on Sewers._--The flood of August 27th and 28th, 1909, partly destroyed one of the main collectors, which was laid along the banks of the river and encased in concrete. This has now been relaid farther north, and out of the way of any future floods. The total length of the new sewers replacing those damaged amounts to 1200 m., and they vary in internal diameter from 20 to 55.9 cm. (8 to 22 in.).

MAIN OUTFALL SEWER.

The direction of the main outfall sewer was determined after a thorough study of all the available land lying to the north and northeast of the city, as it was the intention of the Company to utilize for irrigation purposes the sewage and any surplus waters that might be developed. The best available site was found to be about 12 km. north of the city, a little northwest of the village of San Nicolas de los Garzas, as shown on Plate II. The long length of outfall required was justified by the cheap cost of the land and its excellent character for sewage irrigation. The sewer was designed for a capacity of 90,000,000 liters a day (36.76 cu.

ft. per sec.) in order to allow for conveying surplus waters as well as sewage.

[Ill.u.s.tration: PLATE XXII.--OUTFALL SEWER: PLAN OF GROUND SHOWING SEWER; ALSO DETAILS OF VARIOUS SECTIONS.]

The outfall intercepts the two main branches of the city sewers at Calle de Allende and Calle de Tapia, and its total length is approximately 11,900 m. The chief type adopted is shown on Plate XXII. It is formed with an invert of radial bricks laid in 1:2 cement mortar, on a foundation of 1:3:5 concrete approximately 7 cm. thick. As the ground was chiefly in hard sillar, only a little concrete was required to mould the bottom to the correct shape. The arch was formed of special radial bricks, 15 cm. (6 in.) deep, laid in cement mortar. These bricks were adopted in preference to concrete, owing to the heavy cost of sand and rock, due to the long haul, and for the purpose of obtaining rapid work. Plate XXI shows the sewer arch, and one of the ventilating columns and manholes. The bricks were obtained from the local brick plant, and form a very satisfactory material for sewers, being well burnt, thoroughly hard, and absorbing not more than 7-1/2% of their weight of water. The contract prices for the labor on the brickwork were 1.25 pesos per sq. m., and 1.38 pesos for the arch.

[Ill.u.s.tration: PLATE XXI, FIG. 1.--VIEW OF ARCH, OUTFALL SEWER.]

[Ill.u.s.tration: PLATE XXI, FIG. 2.--VENTILATING COLUMN AND MANHOLE, OUTFALL SEWER.]

The general route of the sewer is very direct, long straight lines of several kilometers being possible, and these were joined by curves of approximately 30 m. radius. The gradient of the sewer invert is 0.2% (1 in 500) which is approximately the general fall of the ground northward from Monterrey.

The total quant.i.ty of excavation was as follows:

No. 1, soft earth 8,960 cu. m.

No. 2, sillar 18,492 " "

No. 3, conglomerate rock 9,822 " "

------ Total 37,274 cu. m.

The contract prices for this excavation were: for No. 1, 32 cents; No. 2, 85 cents; and No. 3, 2.17 pesos per cu. m.

All the excavation was in perfectly dry ground. Where the sewer was partly out of the ground it had a foundation of concrete, 1.75 m. wide, from 15 to 23 cm. thick, below the bottom of the brickwork, and carried up to the springing of the arch, and a well-tamped embankment, with slopes of 1-1/2 to 1, to protect the sewer to a height of 30 cm. (12 in.) above the arch.