Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Civil and Environmental Engineering

Committee Chair(s)

Loren R. Anderson


Loren R. Anderson


Roland W. Jeppson


Fred Kiefer


The engineering properties of waste spoil from phosphate mines in Southeastern Idaho were determined through field and laboratory testing. The testing included compaction tests, grain size analysis, powder x-ray defraction tests, permeability tests, compression tests, triaxial and direct shear strength tests, and nutrient analyses. Based on these tests, the slope stability and settlement characteristics of phosphate spoil dumps were investigated.

The study showed that the foundation is an important component of the stability of a spoil dump. Hypothetical examples were used to illustrate possible modes of foundation failures. Such failures might occur when weak foundation soils exist or when there is a lack of embankment-foundation preparation prior to the disposal of waste material. When considering failures through only the middle waste shale embankment material, the study showed that dumps constructed by end-dumping the spoil material over angle of repose embankments or by scraper filling the material in horizontal lifts will be adequately safe against slope failure if:

o Embankment slopes are graded to 21/2 horizontal to 1 vertical or flatter.

o Proper precautions are taken to prevent the build-up of a phreatic surface near the top of the embankment.

The study also showed that post construction settlement in spoil dumps can be attributed to:

o A slow continuing settlement which is linear with the log of time.

o Saturation collapse settlement which occurs with increases in the moisture contents.

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 rationale method for predicting magnitudes of post construction settlement in spoil dumps was also developed as part of this study.