ASCE 1193: The Water-Works And Sewerage Of Monterrey, N. L., Mexico Part 3

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.

_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 cla.s.sifications:

(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 cla.s.sification 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 cla.s.sification, 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 finis.h.i.+ng 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 quant.i.ties of excavation were:

TRENCH: No. 1 11,115 cu. m.

No. 2 18,096 " "

No. 3 6,650 " "

-------------- Total 35,861 cu. m.

ROADWAYS: No. 1 4,165 cu. m.

No. 2 1,999 " "

No. 3 30 " "

------------- Total 6,194 cu. m.

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:

1 Foreman at 8 pesos (proportion). 2.00 pesos.

1 Pipe layer at 3 pesos. 3.00 "

1 Pipe layer's a.s.sistant at 2 pesos. 2.00 "

1 Cement mixer at 2 pesos. 2.00 "

2 Outside plasterers at 2.50 pesos. 5.00 "

2 Inside plasterers at 2.25 pesos. 4.50 "

1 Water boy at 0.50 peso. 0.50 "

----------- Total. 20.00 pesos.

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 12-1/2 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.

[Ill.u.s.tration: PLATE IV, FIG. 1.--TYPICAL REINFORCED CONCRETE GIRDER BRIDGE, ESTANZUELA AQUEDUCT.]

[Ill.u.s.tration: PLATE IV, FIG. 2.--ELLIPTICAL ARCH BRIDGE CARRYING ESTANZUELA AQUEDUCT.]

_Bridges._--The line as laid out pa.s.sed 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 28-1/2 mm. (1-1/8 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 s.p.a.ced 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 1:2-1/2:3-1/2 mixture, the crushed stone used having all pa.s.sed a mesh of 19 mm. (3/4 in.). The piers were of 1:3-1/2:5-1/2 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 furnis.h.i.+ng 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 4-1/2% of the whole length of aqueduct.

_Concrete Ap.r.o.ns._--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 ap.r.o.n 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.

[Ill.u.s.tration: 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 1-1/2 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.

[Ill.u.s.tration: PLATE V, FIG. 2.--PLACING CONCRETE PIPES IN FORMS FOR BRIDGE CROSSING AT NORTH END OF TUNNEL, ESTANZUELA AQUEDUCT.]