Document Type


Publication Date

January 1978


The engineering properties of waste spoil from phosphate mines in Southeastern Idaho were determined through field and laboratory testing. Based on these properties, the slope stability and settlement characteristics of phosphate spoil dumps were determined. Hypothetical examples illustrate possible modes of foundation failures. Such failures might occur when weak foundation soils exist of when there is a lack of embankment-foundation preparation prior to the disposal of waste material. Adequate protection against slope failure occurring through the embankment material can be accomplished by grading embankment finish slopes to 2 ½ horizontal to 1 vertical or flatter and taking proper caution to prevent the build-up of a phreatic surface near the embankment surface. Post construction settlement in spoil dumps is caused principally by increases in the moisture content in layers of middle waste shales and soft cherts. A rational method for predicting magnitudes of post construction settlement in spoil dumps is also presented.