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<br />4) Saturation of the foundation and wall backfill material by water from the unlined <br />stream channel which flow behind aJld above the west wall <br />5) Overflow from the stream channel and road surface which is directed toward the <br />west wall <br /> <br />The chute needs an extension to accommodate the downstream slope of the embankment, <br />and the outlet channel needs riprap to protect the downstream end of the chute against <br />undercutting. <br /> <br />3.0 MAJOR FEATURE OF MODIFICA TroNS <br /> <br />3.1 GENERAL <br /> <br />Modification of the spillway structure so that it can be safely operated at its design <br />capacity necessitates that all of the structures deficiencies and perceived deficiencies be <br />addressed. Some features of the design modification are redundant. However, given thee <br />history of this structure and the many uncertainties about the site, excesses in the design <br />are appropriate. <br />Demolition <br /> <br />3.2 DEMOLITION <br /> <br />The severely damage concrete in the inlet stfUcture will be removed. This includes all the <br />concrete upstream of the chute for a distance of 80 feet, except for the east wall and crest, <br />which are crack free except for the spall along the toe of the wall. A 3-foot wide strip of <br />the floor slab along the toe of the east wall will not be removed. Foundation anchor will <br />be installed along this strip to insure the stability of the wall until the new floor slab is in <br />place. Similarly a 3-foot wide strip of the west wall adjacent to the chute headwall will <br />be retained to insure wall stability. The under drains will also be removed in the areas <br />where the floor and wall concrete are removed. Depending on the condition of the 6-inch <br />collector drain beneath the chute floor, it Jllay be necessary to excavate portion of the <br />floor slab to correct deficiencies. Backfill behind the inlet and chute calls will need to be <br />removed to facilitate construction of the structure. <br /> <br />3.3 UNDERDRAIN SYSTEM <br /> <br />A drainage system will be installed to insure that any foundation seepage or surface water <br />that may accumulate behind or beneath the structure will be conveyed away. An 8 inch <br />thick gravel layer will be placed over the foundation material and 6 inch diameter <br />collector drains at about 20 foot centers will be provided to convey seepage from beneath <br />the structure. The existing drains that are to be retained will be connected to the new <br />drainage system. Four inch thick insulation is provided over the gravel and drain system <br />to prevent freezing. The chute extension wiil have drains along the outside of the walls. <br /> <br />, <br />~ <br />