Slab-on-ground foundations constructed over expansive clay: parameters to predict volume change potential

A field and laboratory study sponsored by the National Science Foundation was begun in 1985 to evaluate the engineering behavior of expansive clay soUs. Over 60 months of field data consisting of surface elevation, soil suction, and soU temperature measurements along with climatic data have been collected for two research sites in Texas. These measurements were analyzed and conclusions were drawn about the long-temi distortion mode and the method of moisture movement underneath a covered surface. Laboratory testing was also peifomied to develop die parameters necessary to predict die volume change potential of the soU as influenced by the climate. All of the parameters that were used in die predictions were analyzed and evaluated. Tliese parameters include the Suction Compression Index, the characteristic curve, the diffusion coefficient, the equilibrium suction, die depth to equUibrium suction, die lateral restraint factor, the Thomdiwaite Moisture Index, the monthly suction change, and the dieoretical steady state wet and dry suction boundaiies. From the analyses of these parameters, current metliods for predicting potential volume change were evaluated in terms of both accuracy and die assumptions made in the formulation of the model. A new model based on diffusion theory is developed and evaluated for the prediction of the maximum amount of sweU that is likely to occur. Tliis model increases the accuracy of the predictions by 50 percent and reduces the number of assumptions made in the foniiulalion of the previous models. A new laboratory method for detemiuiing die Suction Compression Index and a new empirical equation for detemiining die diffusion coefficient are developed for die new maximmn swell prediction model.