| Shear strength is one of the most important properties for design of engineering structures built on or within mudrocks (claystones, mudstones, siltstones, shales, etc.), and also the most difficult to evaluate. This is because it is usually difficult to obtain undisturbed samples of mudrocks, due to their weak nature, as required for determination of shear strength parameters. This research investigated geological characteristics and engineering properties that can be used statistically to predict the shear strength parameters of a broad range of mudrocks. Forty-five samples of various types of mudrock were collected from highway cuts from eleven different states. Clay content, clay mineralogy, water content, Atterberg limits, specific gravity, dry density, void ratio, absorption, adsorption, slake durability, and shear strength parameters of cohesion (c) and friction angle (&phis;) were determined for each sample. Data were analyzed statistically, using bivariate and multivariate regression techniques, to determine the relationships between shear strength parameters, geologic characteristics, and engineering properties. Prediction equations were developed for all mudrocks using selected number of independent variables on the basis of bivariate plots. Results show that cohesion and friction angle of mudrocks can be meaningfully predicted from a few geologic or engineering properties. Cohesion is found to be controlled by percent expandable clays, absorption, adsorption, and slake durability index, whereas friction angle is controlled by percent expandable clays, absorption, adsorption, and plasticity index. The adjusted R2 values for cohesion and friction angle are 0.278 and 0.370, respectively. However, the role of lithologic characteristics and engineering properties involved in the prediction equations is clearly evident. |
