DEVELOPMENT OF A LABORATORY COMPACTION-DEGRADATION TEST FOR SHALES

Hard but nondurable shales must frequently be incorporated in embankments in the Midwest. It is essential that these shales be thoroughly degraded and compacted into thin, dense lifts. Yet there is no simple, widely accepted laboratory test for predicting the difficulties of mechanical degradation. The development of a laboratory compaction-degradation test that will make it possible to compare the behavior of shales in the laboratory with their behavior during the construction process is described. After testing three very different Indiana shales over a range of gradation and compaction variables, it was concluded that two types of compaction tests are suitable for this purpose: impact and static. Degradation was evaluated by sieving both before and after compaction and was expressed as the reduction in mean aggregate size caused by compaction ( the index of crushing). The static compaction test allows the ready evaluation of compactive work (rather than nominal compactive energy), and the impct test has the advantages of familiarity and acceptance by lmost all testing laboratories. It is likely that the impact test will be more widely accepted for the stated purpose. The development of the laboratory test is an important first step, but correlation of the laboratory values with breakdown under field rolling is necessary beofore the total engineering objective is achieved.