Building Embankments with Shales

Indiana Shales (which cover a wide behavior spectrum from hard and durable ones, to those which will rapidly weather into soil, are of relatively low plasticity and do not possess highly expansible characteristics) were studied with a view to assessing their suitability for use in highway embankments. Existing tests were modified and new tests were developed for the engineering classification of shales which ranked them in different embankment use categories. Fifteen sampling sites were selected and the quantity of material varied between 150 to 1,500 lb, depending upon its type and ease in sampling. Shales of three sites were used as embankment material in small dams and shales from four locations were used in highway embankments. The details are outlined of 4 groups of tests: degradation type tests, soil type standard identification tests, compaction and load deformation tests, and miscellaneous tests. It was determined that the shales could be suitably rated with only 4 tests, viz., a slaking test of one cycle in water; a slake durability test on soaked samples; and a modified soundness test. The results (tabulated) of slaking in one cycle of wetting (broken piece of shale was immersed at least 0.5 inch below water surface) revealed that only 2 of the 15 shales were significantly affected. A slake durability test was conducted which measured the weight loss in water which can be expressed as a durability number. The modified soundness test measured the degradation of shales when subjected to five cycles of alternate wetting and drying in a sodium sulfate solution. The performance of the shales is reviewed, and on the basis of 4 simple degradation type tests, the shales are classified into 4 groups. Based upon the experimental data, qualitative statements are made about the strength and durability of these shales in embankments.