========================================+===============================
| FOR 1,126 PIPES 63.5 CM.
| IN DIAMETER.
Materials. +-------------+-----------------
| Quantities. | 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. +-------------+----------------
| Quantities. | 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 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:
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 assistant 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.
[Illustration: PLATE IV, FIG. 1.--TYPICAL REINFORCED CONCRETE GIRDER
BRIDGE, ESTANZUELA AQUEDUCT.]
[Illustration: 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 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 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
1:2-1/2:3-1/2 mixture, the crushed stone used having all passed 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
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 4-1/2% 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.
[Illustration: 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.
[Illustration: 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 (CaCO_{3}) 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.