73. GENERAL. Approximately 900 cubic feet per second of water will be required for the future irrigation needs of the Hardin unit. This water will be diverted through the Grapevine Tunnel intake. Since a large part of the irrigable lands in the Hardin unit lies in an almost continuous strip extending along the west side (left abutment) of the river, the Grapevine Tunnel intake was located at the left side of the dam. The Grapevine Tunnel will convey the water to the Grapevine penstock. The first 300 feet of the Grapevine Tunnel was constructed under the initial contract, specifications No. DC-5525.

Details of the Grapevine Tunnel intake are shown on figure 98. One 9-foot 6-inch diameter steel-lined conduit with an elliptical dished bulkhead was provided through the left side of the dam and extended into the left abutment approximately 105 feet. The centerline of the intake is at elevation 3535.00, normal to a reference plane which slopes about 3° with the vertical. The intake to the conduit is a formed transition, approximately 11 feet long, changing gradually from a rectangular section to a circular section. Gate frames for a fixed-wheel gate at the intake were provided at the upstream face of the dam. Guides and seats for stoplogs were installed upstream from the fixed-wheel gate location. The fixed-wheel gate, hoist, and controls, the structural steel trashrack bars, and the stoplogs were not provided under the initial contract. When provided, the stoplogs will provide a means for installing the fixed-wheel gate, and inspecting the gate guides and the gate. The entrance to the Grapevine Tunnel intake is protected by a semicircular reinforced concrete trashrack structure which will be provided with structural steel trashrack bars when the tunnel is completed and the fixed-wheel gate installed. The trashrack structure was extended to approximate elevation 3595 which is 48 feet above the top of the inactive space. Access to the steel-lined conduit is provided by manholes from an adit in the dam.

74. TRASHRACK STRUCTURE AND GATE HOIST STRUCTURE. Details of the trashrack structure are shown on figure 99. At the upstream face of the dam semicircular reinforced concrete trashrack structure having six bays protects the Grapevine Tunnel intake. Between the face of the dam and the semicircular trashrack structure, massive gate guide supports encase the gate slot and provide blockouts for installation of the gate guides, track and frame, and stoplog guides. The gate guide supports were designed to withstand the differential head between the waterload in the reservoir at elevation 3640 and the unwatered interior when the stoplogs are in place. The

roof of the trashrack structure is approximately at elevation 3595. There is an opening in the roof enclosed by marginal beams and brackets to permit passage of the stoplogs, so the fixed-wheel gate, gate frame, and guides may be inspected and serviced. A removable structural steel slot closure is seated over the opening.

Details of the gate hoist structure are shown on figure 100. From the roof of the trashrack structure to the top of the dam, a box-type gate hoist structure encases the fixed-wheel gate guides on the upstream face of the dam and protects the gate stems from debris. At the top of this gate hoist structure the hydraulic hoist will be supported, and the controls and other equipment will be housed. The gate hoist house on the top of the dam is equipped with a removable roof and panel to facilitate servicing the gate and hoist.

The following loads and assumptions for designing the various sections of the trashrack structure were used:

(1) Roof slab, ribs, brackets, and columns.— The design loads and assumptions for these structure parts were similar to the criteria outlined for the outlet works trashrack structure in section 64.

(2) Marginal beam adjacent to gate opening.— This beam was designed to be simply supported and subjected to the following design loads:

A 20-foot differential waterload; Dead load of the beam; and

A horizontal load equal to a 20-foot differential waterload acting against the beam, with the beam considered simply supported at the ends.

(3) Roof marginal beam.-The design loads and assumptions for this beam are identical to the criteria outlined for the roof marginal beam of the outlet works trashrack structure (sec. 64).

(4) Gate guide supports.-The supports were designed assuming the stoplogs in place and the reservoir at elevation 3640. Sections were analyzed at various elevations, assuming a hydrostatic head equal to the difference between elevation 3640 and the elevation at the section being analyzed.

The width of the gate guide supports is ordinarily governed by shear stresses rather than stresses from the moment. Shear, tensile, and

Figure 98. Grapevine Tunnel intake