2004-02-27_REVISION - M1977424 - Laserfiche WebLink

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MATERIAL QPTA~IJM HALF OF ESTIMATED CLASSIFICATION MOISTURE OPTIMUM DRY DENSTI'Y CONTENT MOISTURE (LBS/CU FT) (PERCENT) CONTENT (PERCENT) GM 14.5 7.3 92.8 SM 14.5 7.3 92.8 ML 19.2 9.b 90.9 The data froth the Hunt reference did not include typical strength values for GM sods. Therefore, for the sake of conservatism, it was assumed that the soil plug material would be either SM or ML type sods. It is seen that the dry density estimated as shown in the above tabulation would match either the moderately dense to dense ML soils with internal friction angles ranging from 31 to 33 degrees, or the loose SM soils with an internal friction angle of 29 degrees. Based on these values, it was assumed that the internal friction angle at peak strength is 30 degrees. Again, for the sake of conservatism, it was assumed that the material would not exhibit ally cohesion The shear friction strengdt along the contact surface between the soil plug and the mine edit might be afightly less than the material°s peak strength if the surface exhibits a degree of smoothness. For such a case, it is reasonable to assume that the surface is not rough enough to develop full peak strength but >g sufficiently rough to develop the ultimate strength (the strength exhibited after high shear strains) which can be approximated by decreasing the peak strength friction Angie by 2 degrees, or, based on the assumptions used for this material, using a friction angle of 28 degrees. Four potential failure modes were considered for the soil phrg and are described below: a. Slope Stability -Based on information you provided, for practical purposes, the soil phrg can be considered as an earthfill dam with a vertical upstream face held with a steel bulkhead, a 40 foot wide crest and a downstream face with a 4 (horizontal) ro 1 (vertical) slope (see the attached caictdation sheet sketches). Typically, evaluation of the stability of an earthfill dam ittvoh~es detailed slope stability calculations which take into account the soil strength as well as pore pressures which would be expected to occur in the embankment as a result of seepage. However, due to the small size and side configuration of this plug, it did not appear that such a detailed evaluation could be justified at this time. The USBRr presents presumptive recommendations for maximum slope steepness for small earthfill dams with compacted embankments based on embatiltment soil type, embankment configuration and foundation type as follows (Note that these recommendations are for homogeneous storage dams on stable foundations subject to rapid drawdown):