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900 apart were drilled around the periphery. The first set of holes was drilled so that one hole was at the invert; the alternate holes along the centerline were rotated 450 from the first set. Standard grouting procedure was used.
33. Borrow Area Operation. - (a) General. --Preconstruction investigations near the job site disclosed ample deposits of suitable materials for dam construction. Borrow areas 1, 2, and 7 were designated as containing suitable materials, when properly processed, for the construction of zone 1. Borrow area 3 was the only designated source of material for zones 2 and 3. Borrow areas 4, 5, and 6 (fig. 4) were the sources of suitable rock for the rock blanket and riprap.
(b) Area 1.--This deposit, located upstream from the dam near station 160+00, consisted of salt and fine sand. From 6 inches to a foot of the blown sand was stripped from the surface with tractor-drawn scrapers and was used to form dikes around the area. At the low point of the area before the dike was constructed, two 30-inch pipes were laid to provide a means of drawing down the water. To increase the water content of the material before placement, water from Spring Creek was diverted into the dike-enclosed area and allowed to completely cover the area for 2 weeks. The water was then drained off and the material was ready for excavation and transporting to the site.
Considerable difficulty was encountered in obtaining material of uniform or proper moisture content. Some portions contained approximately the optimum moisture content while other portions were excessively wet. The water table was so high that the depth to which the material could be excavated was not sufficient in many places to permit a satisfactory mixture of the material to be obtained. It was found that when the excavation depth was less than 2 feet above the water table, the equipment would bog down. A satisfactory mixture of material was obtained when the cut was made from the bottom to the top of the working face. The flooding method was not used in the east half of the borrow area because of the difficulty experienced in keeping the moisture content uniform. An additional 340,000 cubic yards of suitable material was obtained from a large pocket just east of the designated area. Accord ing to the soils laboratory tests, this material was almost identical with that in borrow area 1.
(c) Area 7. --When borrow area 1 was depleted, several hundred thousand cubic yards were still needed. Investigation revealed that an area about one-half mile below the dam contained suitable material for zone 1. The materials and conditions in borrow area 7 were similar to those in area 1. The same operational methods were followed, except that the sprinkler system was used exclusively for moistening the material.
(d) Area 2. --This area was located above the west abutment of the dam. The surface, consisting of silt to fine sand, was covered with a relatively heavy growth of sagebrush and wild grass. The stripping was accomplished on a 1,000-foot front running east and west, progressing southward. The underlying sand was suitable for zone i material. To moisten the area, water lines with sprinkler heads (fig. 18) were laid on contours from the east to the west side of the block. For more economical use of water, furrows were plowed 5 feet a part on contours. When a selected area was properly moistened (fig. 19), the sprinklers were moved to an adjacent area. The depth of excavation ranged from 4 to 20 feet with an average of 14 feet.
Prior to excavation of material, the contractor constructed a 40-foot-wide haul road and surfaced it with material from borrow area 3.
(e) Area 3. --This area was located on the sand and gravel terrace north of Lind Coulee and adjacent to the valley of Crab Creek. The material in this pit was designated for use as zone 2 and zone 3 material in the dam. It was found that if one part of topsoil was mixed with four parts of the underlying sand and gravel, the mixture when properly processed was satisfactory zone 2 material (fig. 20). The tops oil averaged about 2 feet in depth, so that when a 10-foot cut was made with a shovel the correct mixture was obtained. The material underlying the topsoil, being of sand and gravel, was ideal for the zone 3 material. The underlying material in the west side of the area, after the excavation of two 10-foot lifts, was found to contain too much sand in proportion to gravel and was not suitable for zone 3. In the east side of the pit the material was consistently suitable throughout the excavation operation.
Figure 18. --Sprinkler system for adding moisture to zone 1 material, On the sloping portion of the area, furrows were plowed on contours between pipe lines for more economical use of the water.
Figure 19. --Moisture penetration on the face of a 12-foot cut in borrow area 2 after sprinklers had operated 72 hours. A cut from the bottom to top of the face resulted in a dry and moist earth mixture of near optimum moisture content.
Figure 20. --View of borrow area 3 showing depth of cut and general type of material. The material shown here was considered excellent. : In other parts of the area the material contained much less gravel, but it was still usable.
Figure 21. --View of east side of borrow area 3. The material was excavated in 12-foot lifts to a depth of 60 feet below original ground.
The deepest point of excavation was 60 feet below the original ground surface (fig. 21).
(f) Areas 4, 5, and 6. --When the specifications for the spillway were changed (sec. 205, it became necessary to located an additional suitable rock source for surfacing the dam. The resident engineer and contractor's representatives located three sites of suitable rock and designated them as borrow areas 4, 5, and 6 (fig. 4). Area 4 was located 500 feet downstream from station 5+00, area 5 was located about 300 feet downstream from axis station 97+00, and area 6 about 200 feet downstream from axis station 163+00. All areas contained an overburden of soil and loose rock of varying depth up to a maximum of 4 feet, which the contractor was required to strip prior to any drilling or blasting. Areas 5 and 6 had a working face about 20 feet deep and all holes were drilled at 20-foot centers to this depth. Enough holes were drilled to produce an adequate volume of rock and only two rows in from the face were blasted at one time. Then the loosened rock was loaded and placed on the dam and the blasting process repeated. A similar drilling pattern was adopted in area 4, but holes were drilled to 24 feet and, in addition, coyote holes were put in along the bottom of the face and loaded and blasted. The contractor later tried drilling 2-foot holes and then blasting. This method was not satisfactory as it was slower and resulted in the loss of steel when drilling the second lift. The rock broken by the first blast would wedge in the hole while drilling the second lift.
34. Placement of Material. - (a) Zone 3. --The contractor deviated from the normal procedure in constructing this zoned earth-fill dam because the cutoff trench excavation resulted in a considerable delay in grouting and embankment placement. Special permission was obtained to place zone 3 material prior to placing zones 1 and 2 materials. Zone 3 material was hauled from borrow area 3 in bottom-dump trucks and dumped into windrows spaced about 4 feet a part (fig. 22). Bulldozers were used to break the windrows down and spread the material in layers about 12 inches thick. The deposited material was incorporated into the fill by sluicing. By experimentation it was found that if a horizontal sprinkler pipe with numerous perforations so placed as to direct the flow downward was attached to the water wagon about 10 inches above ground, sufficient water could be applied by an average of four passes with the water wagon to properly sluice the gravel into place (fig. 23). When placing zone 3 material ahead of zones 1 and 2, the height to which it could be placed was limited. The outer slope of zone 3 material was made to conform to the required slope 4 to 1, 3 to 1, or 2 to 1 depending on the location. Because there was no material for the zone 3 material to lie against, the inside slope became a 1-1/2 to 1 reverse slope. As a result, the cross-sectional area of zone 3 material was trapezoidal.
Under normal placing conditions, placement of zone 3 material was permitted only when zone 1 and 2 material was higher than zone 3. This procedure prevented water which was used to sluice zone 3 material from draining into zones 1 and 2 and raising their water content above optimum.
(b) Zone 1.--Certain preliminary steps were carried out in the area on which zone 1 material was to be placed. When placement was on rock, the low spot in the area was dampened with water and the material deposited to a depth of approximately 10 inches with a moisture content at optimum or slightly more. The material was hand tamped. When material was placed upon earth, the surface was compacted by tamping rollers. After this preparatory treatment the surface was ready for fullscale placement operations.
The zone 1 material was hauled to the point of placement by bottom-dump trucks and discharged at wide-open position into windrows approximately 6 feet apart. The trucks moved at speeds of 20 miles per hour or less. A bulldozer was used to level the windrows to a layer about 10 inches thick. The newly placed 10-inch lift of material was compacted into a 6-inch layer by 12 passes of the sheepsfoot roller, as required by the specifications.
Near vertical walls or other places where a tamping roller could not be used, the contractor was required to compact the material by hand tamping. The commercial machine did not compact the material within specification limits unless operated over the area for so long a time that the cost of compaction was excessive. A more economical tamping machine (fig. 24) was made from a pneumatic jackhammer. This converted jackhammer, because of its greater weight, heavier pounding action, and
Figure 22. --Placing embankment, zones 3, 2, and 1 materials. The trucks on the extreme left are placing zone 3 materiál, the water wagon is sluicing it into place, the two tractors pulling rollers are compacting zone 2 material into place, and the trucks and bulldozers are placing zone i material.
Figure 23. --Sluicing zone 3 material in place into the embankment,