Suction Compression Index based on CLOD Test Results

Determination of the suction compression index, Ch, is necessary for predicting expansive soil heave based on soil suction. The CLOD Test is a convenient laboratory procedure for determining Ch, however it is not widely used. Rather, engineers often rely upon empirical correlations to find Ch. A laboratory investigation was conducted to verify previously established empirical relationships. The investigation involved CLOD tests on relatively undisturbed drive samples of clay and claystone bedrock from the Denver, Colorado area. Test results generally matched previous studies. Samples utilized in this investigation spanned a large range of suction and moisture characteristics. A new empirical relationship for determining Ch over a broader range of materials is presented. In an effort to expedite the CLOD test, studies were performed to ascertain the effect of various procedural simplifications on the test results. Information obtained by these studies is used to suggest a modified procedure for professional practitioners. Filter paper suction, one-dimensional swell, Atterberg Limits, and gradation tests were also performed on numerous select samples. Swell prediction based on soil suction and the CLOD test results compared well with direct laboratory swell measurements. The average Ch measured in the Denver area is shown to be a function of bedrock geology. A semi-empirical relationship is also presented between Atterberg limits, percent passing the No. 200 sieve and Ch.