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<br />8 <br /> <br />LAWN LAKE DAM AND CASCADE LAKE DAM FAILURES, COLORADO <br /> <br /> <br />FIGURE 5.-The cross section of Lawn Lake dam following failure. Arrow indicates dark organic layer 4 to 5 ft below <br />top of dam. <br /> <br />TABLE I.-Geotechnical characteristics of the Lawn Lake dam eanhfiU <br />[From the Office of the State Engineer, 1983J <br /> <br />Triaxial shear tests (remolded; <br /> <br />M,""'" <br />property <br /> <br />Sample <br />2L <br /> <br />Ground <br />mwolno <br /> <br />Sample <br />5L <br /> <br />Sample <br />6L <br /> <br />Wet density. in pounds per cubic foot ------ <br />Dry density, in pounds per cubic foot ------ <br />Moisture, in percent --------------------- <br />Saturation, in percent -------------------- <br />Void ratio ------------------------------ <br />Cohesion (effective stress), in pounds <br />per square inch ------------------------ <br />F:ictfon, ~gl~ (effective stress), in degrees -- <br />LIqUId limit. m percent ------------------- <br />Plastic limit. in percent ------------------ <br />Plastic index, in percent ------------------ <br /> <br />102.1 <br />87.1 <br />17.15 <br />52.3 <br />.84 <br /> <br />1.4 <br />18.4 <br />40 <br />34 <br />6 <br /> <br />115.4 <br />88.9 <br />29.8 <br />96.1 <br />.79 <br /> <br />o <br />39.2 <br />56 <br />43 <br />13 <br /> <br />99.5 <br />89.2 <br />11.6 <br />38.2 <br />.78 <br /> <br />135.0 <br /> <br />o <br />32.1 <br />no value <br />nonplastic <br />nonplastic <br /> <br />100 <br />45 <br /> <br />required the prerequisite conditions of a closed or nearly <br />closed outlet gate and a near-full reservoir, to supply <br />the head necessary for accelerated leakage and subse- <br />quent progressive piping through the years. Just prior <br /> <br />to failure, the outlet gate was nearly closed and the <br />reservoir was full. <br />The void created along the outlet pipe would have <br />become enlarged by the internal erosion of embankment <br />