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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />genous structure, the lowest tested value of 2.4 million psi was assumed for the <br />analyses of the existing structure to represent the instan~aneous modulus of <br />elasticity. This value, in turn, was reduced by about 60% to convert it to a <br />sustained modulus of elasticity as recommended by the USBR. The sustained modu- <br />lus takes long-term creep effects into account and should be used in the analy- <br />sis of the structure. Thus, a modulus of elasticity value of 1.5 million psi <br />was used in our ADSAS studies of the existing dam. <br />It was assumed that when repaired, the voids and cracks of the dam would <br />be filled with a high strength grout or shotcrete to make a more homogenous <br />structure. The Bureau recommends a modulus of 3.0 x 106 psi when no laboratory <br />tests are available to be used in the design of new dams. It was assumed in <br />this analysis that the composite system of shotcrete, bolts and grouting will <br />bring the overall modulus of the structure up to 2.5 x 106 psi. It should be <br />noted that the modulus in the existing dam varied greatly in both vertical and <br />horizontal directions. Therefore, these estimates of concrete modulus would be <br />representative averages. <br />As previously discussed, the modulus of deformation for the foundation <br />rock was estimated at 1.0 x 106 psi. In concrete dams there should be as near a <br />compatibility as possible between Youngs Modulus of Elasticity of concrete and <br />the deformation modulus of the rock mass in order to reduce stresses in the <br />concrete caused by concrete deflection. It is generally accepted that the ratio <br />of concrete modulus to rock deformation modulus should preferrably be less than <br />4.0. ((Rocha 1974) When this ratio is in the range of 4.0 to 10.0, an arch dam <br />can be built but expenses go up. In view of these guidelines, the ratio of <br />concrete modulus to rock modulus for the Bluebird Dam site is favorable. <br />Results <br />A total of 6 studies were run and output in the form of stress maps is <br />-21- <br />