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contact surfaces for this darn was assumed to be represented by an intemal friction <br />angle of 40 degrees and a cohesion of 2,6001bs/sq fk It was necessary to reduce <br />the contact surface area to account for a combination of void spaces and filling of a <br />portion of the contact area between concrete bags with the bags themselves. It was <br />previously estimated that ae much as 50 percent of the dam volume may consist of <br />voids. This analysis included a fwther assumption that 50 percent of the bag-to- <br />bag contact area is separated by the bag material. The attached calculation sheets <br />show safety factors against intetriak shear friction fat7ure. Internal shear friction <br />analysis was ottly performed far the maximttm reservoir wafer level. It is seen that, <br />the minimum shear friction safety factor at full reservair level is greater than 5 near <br />the base of the dam. These calculated safety factors are conservative because they <br />do not consider any shear fiiction contribution of the gunite coveting. <br />e. Upstream Tension Cracking - Tensile stresses can occur in the upstream <br />face of the dam due to a combination of flexure (bending) from the upstream <br />hydrostatic loads and internal seepage pressure. The seepage pressure on the <br />upstream face is equal to the hydrostatic reservoir pressure. These tensile stresses <br />are resisted by a combination of the weight of the dam and tensile sirengdi of the <br />concrete. As was described above for shear friction, the weak planes for tensile <br />cracking are along bonding surfaces where concrete sacks were stacked on top of <br />each other. The allowable tensile stress along these weaker planes would again be <br />expected to be similar to rift joints of a holler Compacted Concrete dam <br />constructed of conventional concrete but without joint bonding provisions. Typical <br />values of tenst7e strength for fatty bonded conventional concrete joints° range from <br />3 to 9 percent of the compressive atrengtlt. Tensile strength across unbonded joints <br />can be approximately half of that for bonded joints. The fully hydrated <br />compressive strength of the sack-crete was assumed to be 3,tlOQ psi. Thet~efore the <br />tensile strength of actual concrete-to-concrete contact surfaces for this dam was <br />conservatively assumed to be l.5 pt7cent of that amount, or 4S psi. As was <br />discussed alwve for shear friction, it was necessary to reduce the contact surface <br />area to account for a combination of void spaces and the separation effects of the <br />bags. The attached calculation sheets show safety factors against upstream tension <br />cracking. Upstream tension cracking analysis was only performed for the <br />maximum reservoir water level. It is seen drat, the minimum tension cracking <br />safety factor at full reservoir level is about 6 near the base of the dam. These <br />calculated safety factors are conservative because they do not consider any shear <br />friction contribution of the gunite covering. <br />f. Foundation Failure - No calculatiotrs were performed to estimated safety <br />factors against foundation failure for the concrete dam. However it seems very <br />unlikely that the rock floor of the mine adit would not have sufficient bearing <br />capacity to support thin relatively light structure. <br />