(4) Saturated fill to elevation 5620.0;

Tailwater elevation 5601.6;

Earthquake.

For conditions (3) and (4), shear friction factor should be larger than 2.0.

137. Visitors' Center Foundation. The concrete foundation for the visitors' center building consists of grade beams on piers. The piers were designed for the dead loads, a live load of 30 pounds per square foot on the roof, and a 90-mile-per-hour windload on the bent, assuming the bent hinged at the roof and fixed at the pier. All piers are embedded 12 inches minimum into rock. Crushed rock covered with polyethylene was placed under the grade beams.

138. Utility Service Tunnel. The concrete utility service tunnel extends approximately 185 feet from the utility service adit in the dam to the mechanical equipment room in the visitors' center building. For the tunnel adjacent to the dam and under the roadway, the design was for a hydrostatic head of 10 feet of water and H 20 highway loading. From the roadway to the building the tunnel was designed for the depth of cover and a wheel load of 2, 000 pounds.

139. Visitors' Parking Area. The main parking area at the right abutment of the dam has a capacity for parking approximately 100 cars. Originally, the area that is now taken up by the visitors' center building and promenade was intended for parking. In the future, should demand for additional parking be required, the filled area upstream (approximately 400 by 100 feet), which was used for the tailtower runway during construction of the dam, can be utilized. It would entail removing a few sections of the concrete parapet to make a passageway, paving the portion desired, and providing guardrail or fence protective works.

A sidewalk and parapet totaling 4 feet in width traverses the boundary of the parking lot. The height of wall supporting the sidewalk and parapet varies from a minimum of 18 inches to a maximum height of about 10 feet. The parapet is similar to that used on the dam. Four 2- by 2-foot concrete pedestals spaced along the parapet serve as bases for lighting standards which illuminate the parking area. The parking area surfacing is made up of a 6-inch selected material subbase covered with a bituminous-surface-treated 4-inch crushed rock base. Details are shown on figure 172.