Page images
PDF
EPUB

60. Tamped-Earth Fill (Special Compaction). - The extremely irregular foundation and abutments resulting from the blocky characteristics of the exposed andesite rock surfaces required a great amount of special compaction or tamped-earth fill. Areas along abutments were tamped with small pneumatic hand tampers and one large trailermounted pneumatic tamper to a thickness of 2 feet measured in a horizontal direction from the contacted surface. On the foundation it was necessary to use the same procedure in filling small depressions to obtain a cushion and a reasonably level floor before employing sheepsfoot rollers. Material used was from the same source as the remainder of zone 1. After dumping, the material was shoveled into place by hand and larger rocks removed so that mechanical tampers could obtain the desired results. A total of 1, 643 cubic yards of material was placed in the dam and dike in this manner.

61. Rock and Cobble Fill (Zone 3). - A major portion of this material was originally intended to be obtained from designated slide rock borrow areas adjacent to the dam site. Preliminary estimates of yardages contained in these areas were higher than actually existed, and the supply was augmented by rock spalls and smaller weathered, but sound, rock fragments from the riprap quarry. The remainder of the material was oversize cobbles recovered from the separation plant. The quantity of this material was reduced approximately 7 percent when the maximum size of rock allowable in zone 1 was changed from 3 to 5 inches.

Material was placed in approximately 3-foot lifts with no special compactive effort, the larger rock being bulldozed to the outer slope. Because of the high moisture content of material in zone 1 borrow areas, it was necessary to stockpile some cobble screenings and reprocess them after drying in order to remove objectional amounts of sand and clayey material before placing.

62. Riprap on Upstream Slope. - Riprap material was quarried from designated areas as previously described (sec. 56). The rock was quarried within the gradation requirements and was hauled in end-dump trucks and dumped and bulldozed into place. Some barring and hand placing was necessary to fill voids and maintain a reasonably regular slope. Riprap placement was maintained as close as possible to the average fill elevation during construction.

63. Special Zones at the Top of the Dam. - Slopes on zone 1 material were altered to provide for a 12-foot horizontal width of material where it was discontinued at elevation 10,044. Zone 3 material on the upstream slope of the dam was discontinued at elevation 10,038, 10 feet below the crest elevation. Downstream zone 3, zone 2, and riprap materials were continued to elevation 10,047 plus camber, or 1 foot below the crest. A maximum camber of 1.5 feet was placed in the main dam section; and 0. 7 foot was placed in the dike section. The remainder of the fill consisted of 12 inches of selected gravelly material. The upstream slope of the dike section was varied at the left abutment to provide for an access road to the dam. (See order for changes No. 5 in section 28.)

D. Foundation Drilling and Grouting

64. General. - Drilling and grouting operations were initiated on the dam and dike foundation August 27, 1949, and all foundation drilling and grouting were completed November 8, 1950, work being discontinued during the winter months. Filling of voids behind the tunnel lining, which was performed by grouting methods at the contractor's expense, was initiated November 25, 1949, and completed May 25, 1950. Pressure grouting of the tunnel was not initiated until May 23, 1950, since all void filling back of the concrete lining was required to be substantially complete prior to pressure grouting operations. Pressure grouting of the tunnel was completed June 30, 1950.

65. Drilling Grout Holes, - (a) Foundation. --Foundation drilling throughout the the grout cap was performed on 10-foot centers and generally to stage depths of 35 and 60 feet in alternate holes, and to stage depths of 55 and 110 feet in alternate holes.

[graphic]

Figure 26. --Large pneumatic tamping machine being used to compact zone 1 material on

60. Tamped-Earth Fill (Special Compaction). - The extremely irregular foundation and abutments resulting from the blocky characteristics of the exposed andesite rock surfaces required a great amount of special compaction or tamped-earth fill. Areas along abutments were tamped with small pneumatic hand tampers and one large trailermounted pneumatic tamper to a thickness of 2 feet measured in a horizontal direction from the contacted surface. On the foundation it was necessary to use the same procedure in filling small depressions to obtain a cushion and a reasonably level floor before employing sheepsfoot rollers. Material used was from the same source as the remainder of zone 1. After dumping, the material was shoveled into place by hand and larger rocks removed so that mechanical tampers could obtain the desired results. A total of 1, 643 cubic yards of material was placed in the dam and dike in this manner.

61. Rock and Cobble Fill (Zone 3). - A major portion of this material was originally intended to be obtained from designated slide rock borrow areas adjacent to the dam site. Preliminary estimates of yardages contained in these areas were higher than actually existed, and the supply was augmented by rock spalls and smaller weathered, but sound, rock fragments from the riprap quarry. The remainder of the material was oversize cobbles recovered from the separation plant. The quantity of this material was reduced approximately 7 percent when the maximum size of rock allowable in zone 1 was changed from 3 to 5 inches.

Material was placed in approximately 3-foot lifts with no special compactive effort, the larger rock being bulldozed to the outer slope. Because of the high moisture content of material in zone 1 borrow areas, it was necessary to stockpile some cobble screenings and reprocess them after drying in order to remove objectional amounts of sand and clayey material before placing.

62. Riprap on Upstream Slope. - Riprap material was quarried from designated areas as previously described (sec. 56). The rock was quarried within the gradation requirements and was hauled in end-dump trucks and dumped and bulldozed into place. Some barring and hand placing was necessary to fill voids and maintain a reasonably regular slope. Riprap placement was maintained as close as possible to the average fill elevation during construction.

63. Special Zones at the Top of the Dam. - Slopes on zone 1 material were altered to provide for a 12-foot horizontal width of material where it was discontinued at elevation 10,044. Zone 3 material on the upstream slope of the dam was discontinued at elevation 10,038, 10 feet below the crest elevation. Downstream zone 3, zone 2, and riprap materials were continued to elevation 10,047 plus camber, or 1 foot below the crest. A maximum camber of 1.5 feet was placed in the main dam section; and 0. 7 foot was placed in the dike section. The remainder of the fill consisted of 12 inches of selected gravelly material. The upstream slope of the dike section was varied at the left abutment to provide for an access road to the dam. (See order for changes No. 5 in section 28.)

D. Foundation Drilling and Grouting

64. General. - Drilling and grouting operations were initiated on the dam and dike foundation August 27, 1949, and all foundation drilling and grouting were completed November 8, 1950, work being discontinued during the winter months. Filling of voids behind the tunnel lining, which was performed by grouting methods at the contractor's expense, was initiated November 25, 1949, and completed May 25, 1950. Pressure grouting of the tunnel was not initiated until May 23, 1950, since all void filling back of the concrete lining was required to be substantially complete prior to pressure grouting operations. Pressure grouting of the tunnel was completed June 30, 1950.

65. Drilling Grout Holes, - (a) Foundation. --Foundation drilling throughout the the grout cap was performed on 10-foot centers and generally to stage depths of 35 and 60 feet in alternate holes, and to stage depths of 55 and 110 feet in alternate holes.

[graphic][subsumed]

Figure 26. --Large pneumatic tamping machine being used to compact zone 1 material on

(b) Void Filling. - Since only a few grout nipples which were placed during concrete lining operations could be located, drilling was required at most points of grouting. Drilling was accomplished by use of rotary drills.

(c) Tunnel. --Patern drilling of the tunnel was accomplished in a manner similar to that shown on figure 7, to depths of 25 feet. No unusual formations or rock characteristics were encountered during the drilling of 3,057 feet of holes.

66. Foundation Grouting. - (a) Foundation. --The foundation of the dam and dike consists of a massive adesite flow, which has been eroded by stream action and glacial scouring. The andesite is severely fractured, and localized shear zones are present in the foundation and both abutments. The very small grout acceptance in the foundation indicated that the fracture planes and shear zones are well healed. No special problems were encountered in the grouting process and no special levels noted where grout acceptance was either generally high or low. The maximum quantity of grout taken by any hole was pumped into a 55-foot hole at station 8+00. A total of 94 sacks of cement was injected, 92 with a packer at 35 feet and 2 on the nipple.

In all stages a total of 9, 285 feet of grout holes was drilled, or an average of 5.8 feet of hole per foot of grout cap length. This includes 92 feet of drilling in the spillway crest wall, which is essentially a part of the grout cap. A total of 1,041 cubic feet of grout (sacks of cement) was used in grouting the foundation, or 0.11 sacks per foot of hole drilled.

(b) Tunnel. --Rock characteristics throughout the tunnel are essentially the same as reported in (a) above. No special problems arose during grouting of the pressure section of the tunnel and only two water flows of any consequence were found. They were located at stations 7+20 and 7+71, near the gate chamber. They were grouted and apparently sealed. Although the grout acceptance here was somewhat higher than in the foundation (0.43 sack per foot of hole drilled), this can be partially explained by additional localized shattering of the rock during excavation and the possibility that some voids around the lining were filled that were unavoidably missed in backfilling operations. Generally, the area was tight. The maximum amount of grout pumped in any hole was 166 sacks at station 3+90.

A total of 3,057 feet of holes was drilled, with a total grout acceptance of 1,316 cubic feet (sacks of cement).

67. Void Grouting in Tunnel. - Grouting of the voids between the concrete tunnel lining and natural rock, at points of excessive overbreak, was performed at low pressures averaging about 20 pounds per square inch and was necessarily completed prior to highpressure pattern grouting. A total of 1, 181 cubic feet of grout (sacks of cement) was pumped into holes throughout the arch section by means of grout nipples or packers.

E. Final Concrete Control Report

68. Aggregates. - The source of aggregates for all concrete was river-deposited material in gravel area No. 2 (fig. 19). The processing and stockpilling of concrete aggregate produced in 1949 was subcontracted by the prime contractor to R. B. Millay of Lakewood, Colo. Aggregate processing was started July 26, and was completed August 22, 1949. During this time, approximately 3, 300 cubic yards of finished aggregate was produced. Of this amount, 35 percent was sand and the remaining 65 percent was gravel of 3/4-inch and 1-1/2-inch maximum size on a 50-50 basis.

An additional quantity of concrete aggregate was also produced in June 1950. When it became evident that the quantity originally produced would be insufficient, the prime contractor modified the screening unit of the separation plant and produced approximately 500 cubic yards of sand, 300 cubic yards of 3/ 16- to 3/4-inch gravel, and 150 cubic yards of 3/4- to 1-1/2-inch gravel.

During production, aggregate was checked for conformance with specifications requirements concerning gradation and manner of stockpiling. Aggregate tests at the gravel plant were summarized for transmittal with the monthly concrete control reports.

« PreviousContinue »