penstocks prior to raising the fixed-wheel gates at the upstream face of the dam. Access is provided into the upper ends of the three penstocks located in blocks 13, 14, and 15 for inspection and maintenance. (d) Utility Gallery at Elevation 6015. --This gallery is located 32 feet below the crest of the dam and extends practically the full length of the dam. The left end terminates in the foundation gallery and the right end joins the foundation gallery, then continues to join the control cable tunnel that extends to the switchyard area beyond the right end of the dam. Control cables which extend from the powerplant to the switchyard, and water and sewer lines to the visitors' center in the right abutment parking area are installed in this gallery. Space is also provided for the installation of compressed air equipment used for the deicing of the river outlet and penstock trashracks and for the spillway intake gates. All of the above longitudinal galleries provide access into the interior of the dam and space for reading stations for observation of structural behavior instruments. The six transverse grouting adits on either abutment were laid out so that the pattern of consolidation grouting drilled from the adits would cover the foundation area in the most advantageous manner. This required adits at about 50-foot intervals in elevation located as near the excavated foundation rock as practicable. Two of the adits on either abutment were extended to the downstream face of the dam to provide improved access for foundation drilling and grouting and possible access to theodolite piers located on the abutment slopes downstream of the dam. In addition to the consolidation grouting, the adits provided access for drilling of additional high-pressure foundation grouting and drainage holes for both abutments. In addition to the above-described galleries and adits, an elevator shaft is located in block 15. This 11-foot 5-inch by 14-foot 6-inch shaft accommodates an elevator cage that operates between the top of the dam and the lower part of the foundation gallery, providing access to the entire gallery system for the dam. In addition to the cage, space is provided for control cables which terminate in the switchyard, and air, water, and sewer lines. There is also a visitors' adit and a control cable gallery extending from the elevator shaft to the powerplant building at the toe of the dam, and a pump sump and chamber for pumping drainage water from the lowest elevation of the foundation gallery. (e) Reinforcement for Galleries, Adits, and Shafts. --A pattern of reinforcement steel. was designed for all of the galleries, adits, and shafts in the dam. For all of the openings, with the exception of the utility gallery, the reinforcement was designed from dam stresses for either the dead load of the concrete in the dam or a combination of dead load and hydrostatic load, whichever governed. For the utility gallery, which is located near the crest of the dam, the amount of reinforcement required was first based on a differential temperature effect in the concrete of 13° F. acting through a 5-foot ring of concrete. This amount of reinforcement was revised by decreasing the computed transverse reinforcement by about 50 percent and arbitrarily increasing the longitudinal reinforcement. A substantial mat of reinforcement at the crest of the dam was assumed to be the most effective means of controlling cracking between the crest of the dam and the top of the gallery. The following assumptions were made in the design of the reinforcement for the gallery and shaft system: (1) For live load conditions, 75 percent of the compressive stress from arch or cantilever loading at any face of an opening may be used to reduce the tension at this face from either arch or cantilever loading. (2) For dam stresses that are direct tensions adjacent to openings, reinforcement should be provided in an amount to resist tensions to which an assumed inplace concrete would be subjected. (3) Minimum reinforcement requirements: a. Longitudinal galleries. --Top and bottom reinforcement 3/4-inch-diameter bars at 12-inch spacing. Side reinforcement 3/4-inch-diameter bars at double the spacing of top and bottom reinforcement. b. Transverse galleries. --Top, bottom, and side reinforcement 3/4-inchdiameter bars at 12-inch spacing. C. Stairwells. --Horizontal reinforcement 3/4-inch-diameter bars at 12-inch spacing. The reinforcement design for the various openings in the dam was based on all or part of the referenced technical memoranda.2/3/4/ 37. Roadway and Bridges. The top of the dam was designed to accommodate a 27-footwide roadway plus a 3-foot downstream sidewalk. The 27-foot roadway width was required due to the 24-foot gage of the tracks for the 70-ton-capacity gantry crane, which traverses most of the crest length and is stored at a crane siding recess at the right end of the dam. The required roadway and sidewalk width demanded substantial cantilevers at the crest of the dam, both upstream and downstream, since the theoretical thickness of the dam at the crest is only 20 feet. Temperature studies for the mass concrete at the crest of the dam indicated tendencies for severe cracking. In an effort to minimize the possibility of cracking, a substantial pattern of reinforcement steel was specified, located immediately below the roadway surface. To avoid interference with mass concrete placement for the top lift in the dam, the reinforcement was placed in two layers, each layer consisting of 1-3/8-inch-diameter bars at 12-inch centers traversely and 1-inch-diameter bars at 12-inch centers longitudinally. To avoid the possibility of arch stresses near the top of the dam being carried by the comparatively slender roadway cantilevers, these cantilevers were divided into segments by the construction of 1/2-inch expansion joints at the one-third points for the lengths between contraction joints. For the length of the dam traversed by the gantry crane, the cantilevers were designed for the wheel loadings of the 70-ton gantry crane (downstream loading 65, 250 pounds for each of two wheels at 2-foot 6-inch spacing; upstream loading 77,500 pounds per wheel for similar wheel spacing). The cantilever in block 12 was extended upstream an additional 5 feet to provide storage space for the hoist and stems when a penstock gate is removed for servicing. The platform was designed for the following loads in addition to the crane loads: In lieu of a hoist load a live load of 500 pounds per square foot was used. Beyond the travel of the crane the cantilevers were designed for the wheel loadings from a special 60-ton trailer hauling unit. The axle and wheel arrangement are so spaced for this trailer (16 wheels on 2 rear axles and 8 wheels on 2 front axles) that the individual wheel loads induce much less stress in the cantilevers than do the crane wheel loads. For roadway details see figures 29 and 30. To span the spillway intake structure with the roadway at the left end of the dam required a curved bridge of variable width. The bridge was designed as a concrete slab resting on steel stringers. An H20-S16-44 loading was used in accordance with "Standard Specifications for Highway Bridges, of the American Association of State Highway Officials, 1957 edition, and subsequent revisions. In addition, the steel stringers were designed for outrigger loads of 28, 000 pounds each at 14-foot centers for a 20-ton truckmounted crane, provided the outriggers were placed directly over a steel stringer. The slab was not designed for these outrigger loads. The roadway beyond the spillway intake bridge at the left end of the dam was originally designed to be founded on benched excavation into the steep hillside. When the roadway excavation was performed, considerable portions of the required bench foundation were 2/Interoffice Bureau of Reclamation Memorandum of January 15, 1959--"A Photoelastic Stress Analysis of Rectangular Openings in an Infinite Plate" (unpublished). 3/Interoffice Bureau of Reclamation Memorandum of July 29, 1954--"Stress Distribution along Vertical and Horizontal Centerlines of Various Shapes of Galleries" (unpublished). 4/Technical Memorandum No. 457, dated May 24, 1935--"Stresses and Reinforcement Steel around Circular Openings in Concrete Dams" (unpublished). |