136. Safety. - (a) Government forces. --The safety program for Government forces was executed by the supervisors and foremen. Safety conferences among wage-hour group foremen were sponsored by the project safety engineer. The safety division also conducted first aid classes. The contractor's blasting accidents prompted the safety division to conduct a course in the safe handling of explosives for Bureau employees who might be engaged in blasting or rock excavation inspection work.

At Dry Falls Dam a first aid man and ambulance driver was appointed to assist the injured. Employees who drove Government vehicles attended the driver's clinic and submitted to the mental reaction tests recommended by the Federal Interdepartmental Safety Council.

Inoculations against Rocky Mountain Spotted Fever were administered to employees, and to their families, if requested. Snakebite kits were carried in vehicles and kept available at the Government camp.

Supervisors were conscious of the hazardous nature of the work, and insisted upon adherence to safety rules. Cooperation by employees was exemplary.

(b) Contractor's forces. --Soon after construction was started a Government safety inspector was designated. He made thorough weekly inspections of all of the contractor's activities.

Unsafe practices were called to the attention of the foreman in charge. If corrective action was not prompt, the problem was referred to the superintendent. A representative of the Safety Division of the Washington State Department of Labor and Industries visited the job at regular intervals. In most cases, the contractor complied with recommendations of safety inspectors.

Signs or barricades warned workers and visitors. Ambulance service was provided at all times and a qualified first aid man was in every crew. Equipment operators were given qualification tests before being assigned to the job. Safety regulations pertaining to earthwork were rigidly enforced by the superintendent. Maintenance of haul roads was generally satisfactory; dust was controlled by use of sprinkler trucks, and holes, mud, and snow were controlled by frequent blading.

Lights for embankment construction were provided by portable generators equipped with short distribution lines and movable towers. Handrailings were provided where high work was in progress. Good housekeeping was difficult to enforce around the headworks. Workmen were reluctant to wear hard hats, safety belts, and goggles.

The contractor encountered a greater than normal number of accidents during the early phases of the job, largely centered around the drilling and blasting operations. In addition to numerous minor injuries to jackhammer operators, three blasting fatalities were incurred. Through a concerted effort by the Government and the contractor safety measures were constantly improved.

An unusual hazard was presented in the operation of springing the boreholes to make way for the final blasting charge. The springing charge formed gas pockets in the severely jointed,wet rock, and in the interflow zones with the result that the usual stemming material would not be cleared from the hole. While clearing the stemming material from the hole, the highly compressed gasses violently raised the drill and steel, injuring the driller and nearby workers. Several stemming materials

were tried with pumice proving to be the most effective, as 94 of 100 experimental holes were blown clear with an air pipe. In addition, 24-inch handles were added to each side of the jackhammer to allow two operators to operate the drill from a safer distance.

Great care was exercised in excavating the partially blasted rock. Unexploded powder and caps were removed from the surface prior to moving in the shovel. The shovel operator was protected by a heavy screen placed around the cab, while the oiler and truck drivers withdrew to a protected spot during the loading period. The foreman removed unexploded powder and caps as they were uncovered.

The following is a tabulation of the accident record of the contractors forces on this job.

137. Government Camp. - The camp housing the supervisory, engineering, and inspection personnel was located one-quarter mile northeast of Coulee City. It consisted of 36 houses, 3 dormitories, a washroom, a concrete and soils laboratory, a maintenance shop, and a community hall. The buildings were quonset huts, measuring 20 by 48 feet inside. The dormitories contained 8 single rooms. The houses were divided into a living room, kitchen, utility room, bathroom, and 2 bedrooms. Cooking and heating were by electricity. The Government cleared and graded the site in May 1946 and built the electric distribution system connecting to the nearby Washington Water Power Company substation. The contractor excavated water and sewer line trenches and constructed a septic tank under extra work order No. 1. A spring one-half mile north of camp supplied water for both the Government and contractor's camps. The water was stored in a 100,000-gallon tank on a hill 500 feet east of the Government camp. Coulee City school facilities were used by children of Government and contractor's employees.

138. Housing for Contractor's Forces, - Near Coulee City and the construction site the contractor provided four 1-story barrack type buildings for single men, and canvas-covered insulated frame buildings resembling quonset huts for married employees. The huts were provided with cold water and limited electrical installations. Also near the water-supply spring there were electric, water, and sewerage facilities for employees who had trailers. A large house near the spring was utilized as living quarters for two families. The remainder of the contractor's personnel secured their own quarters.

139. Construction Equipment. Types of equipment used by the contractor on excavation and embankment construction are given in the following tabulation:

140. Excavation for Approach Channel, Headworks Structure, and Main Canal. The contractor began common excavation operations for the approach channel, headworks structure, and the Main canal in August 1946. Overburden was generally shallow in depth and consisted of fine-grained silts and soils of volcanic origin which were considered unsatisfactory for use in the impervious zone of the dam. Common materials, north of Main canal station 9+00, were excavated by bulldozers and tractor-drawn 12cubic-yard scrapers. Disposal locations were the highway detour embankments, gatekeeper's residential area, and natural potholes. The relatively deep overburden between canal stations 9+00 and 24+00 was excavated by J. A. Terteling and Sons, Incorporated, a subcontractor. The work was performed by a 15-cubic-yard dieselpowered walking dragline which disposed of the soil by side-casting into the spoil banks located well beyond the top of the excavation slopes.

Work was started on rock excavation in the early fall of 1946 and continued with only minor interruption until July 1948. Work was resumed in May 1949 and completed in June 1949. Rock excavation for the headworks structure, including the transitions and the canal to station 7+50, was completed in 1947.

Each basalt flow encountered was treated as a separate blasting and excavation problem. Deep holes through interflow materials and deep charges produced large blocks that required extensive secondary blasting. Wagon drills were used for all comparatively deep drilling, while jackhammers were used to drill for the shallow trimming work, Blasting was accomplished by use of stick and bulk dynamite of 40- and 60- percent strength. Heavy blasting at infrequent intervals allowed the contractor to minimize moving delays The largest blast occurred on November 12, 1947, when 34, 000 pounds of powder were detonated between stations 11+50 and 14+50 of the approach channel.

Excavation was performed by 1-1/4-, 2-, and 2-1/2-cubic yard shovels working two shifts per day. The bulk of the rock was transported by 12-cubic-yard dump trucks Wherever possible the rock was hauled directly to zone 3 embankment About 20,000 cubic yards were deposited in, and later reloaded from, stockpiles located 500 feet north of dam stations 74+00 to 78+00. Surplus rock was deposited in shallow stockpiles located on both sides of the dam between stations 87+00 and 91+50.

Excavation overbreak between canal stations 3+00 and 9+00 was extensive, although the contractor appeared to exercise reasonable care during the blasting operations. Excavation for the canal beyond station 9+00 produced little overbreak, possibly

because of the closer spacing of joints in the basalt of this section. Overbreak in the approach channel was negligible, resulting in finished 1-1/2 to 1 slopes usually neat in appearance.

Final trimming was accomplished by light blasting, barring, and scaling. Shovels loaded dozed stockpiles from the canal floor to complete final cleanup operations.

141. Stripping Dam Foundation. - Excavation under the impervious zone of the dam was carried to bedrock. Minimum width of the cutoff trench was established at 30 feet. Only brush and other deleterious materials were stripped from the area to be covered by zones 2 and 3. Stripping depths were slight except in the cross channels; and in many locations where rock outcrops occurred, foundation cleanup was the only work required.

The necessary work was performed with bulldozers and tractors with 12-cubicyard scrapers. Stripped materials were wasted in potholes outside the toes of the dam.

142. Cutoff Trench for Dam. The cutoff trench was excavated to bedrock for the entire length of the dam. The trench had a 30-foot-minimum bottom width and 1-1/2 to 1 side slopes except in the three deep channels. From station 26+00 to station 29+50 the upstream side was standard with a half bottom width of 15 feet and 1-1/2 to 1 backslope but on the downstream side the downstream boundary of the impervious zone was extended to bedrock with a backslope of 1-1/2 to 1 to original ground level. From station 33+50 to station 36+00 the upstream and downstream boundaries of the semipervious zone were extended to bedrock with backslopes of 1-1/2 to 1 to the original ground level. From station 70+50 to 78+00 a hypothetical 4 to 1 slope from elevation 1550 on the upstream slope of the dam was extended to the original ground level and the overburden excavated on a 1-1/2 to 1 back slope to bedrock. On the downstream side the overburden was excavated to bedrock on a 3/4 to 1 back slope from the downstream toe of the dam.

Between stations 26+00 and 29+50 the foundation was excavated deeper than that shown on the contract drawings (fig. 75). The Government paid for the unwatering on this work on a cost-plus basis. Foundations were unwatered by gasoline-powered pumps. Fire hoses and steel pipe conveyed the water to potholes outside of the toes of the dam.

trench near station 27+00.

14978-3, February 12, 1947

Approximate maximum depths of foundation excavation were: stations 26+00 to 29+50, 60 feet; 33+50 to 36+50, 42 feet; 70+50 to 78+00, 26 feet; 100+00 to 103+25, 23 feet.

The bulk of the excavation was performed by one 2-cubic-yard shovel and one 2-1/2-cubic-yard shovel with cleanup by 3/4-cubic-yard draglines. Transportation was furnished by 12-cubic-yard dump trucks and 12-cubic -yard powered trailers. Shallow excavation was performed by tractors and scrapers.

Rock excavated from the cutoff trench was placed in nearby zone 3 embankment. Finely shattered rock from the cutoff wall footing excavation was placed along the inner slopes of the zone 3 embankment. All common material from foundation excavation was wasted. These materials were dumped in potholes outside the toes of the dam.

The final estimate quantities for foundation excavation were 241, 772 cubic yards of common and 47, 050 cubic yards of rock.

143. Cutoff Wall.

A continuous plain concrete cutoff wall is located on the centerline of the cutoff trench 17.5 feet downstream from the axis of the dam (figs. 76 and 77). The wall footing extends into bedrock to a minimum depth of 3 feet and varies in width from 3 to 5 feet. The wall, which varies in height from 5 to 10 feet, is 12 inches wide at the top and batters 1/4 inch per foot on each face. Dowels were placed in the footing on 1 to 1 and steeper slopes.

The trench for the cutoff wall footing was excavated by hand using paving breakers, and by blasting and mucking out with small draglines and backhoes. Holes were loaded lightly and line drilling was employed wherever the rock was hard. The vertical side walls of the trench were trimmed with paving breakers. Final excavation was done by hand, and blowpipes were used to complete the cleanup prior to concrete placing. Grout pipe nipples were located on 10-foot centers and grouted into the foundation rock on the centerline of the footing trench. Two 2- by 4-inch screeds were fastened to the grout pipe at the footing grade to form the bottom 4 inches of the wall which was poured with the footing. This procedure provided an upset to which the contractor tied the forms for the wall. Footing forms were provided on steep slopes and in locations where small potholes intersected the trench.

Discharge from springs encountered in the footing trench was collected in French drains which were later grouted.

144. Grouting. The grouting plan was formulated to reduce seepage under the dam by consolidating the upper strata of foundation rock, and sealing the upper interflow zone that outcropped at several places along the foundation. To accomplish this, a 30foot-minimum-depth cutoff curtain along the centerline of the dam was grouted. The exploratory holes on the dam axis, 17.5 feet upstream from the centerline, were also grouted.

There were 33 holes drilled along the axis of Dry Falls Dam in connection with the preliminary investigation program. Of these, 25 were covered by the dam. To insure that the holes would not interconnect the various ground-water horizons, plugs were placed between each horizon prior to grouting the top part of the holes, including the first ground-water horizon. Of the 24 holes grouted, there were five which either refused water at the maximum allowable pressure, or accepted it slower than the specified minimum rate of injection for grout. These holes were declared tight and were not grouted. Ten holes accepted between 2 and 10 sacks each, four between 10 and 100 sacks each. The remaining five holes accepted more than 100 sacks, and were grouted as summarized in the following tabulation: