Volume 25, Issue 2 (June 2002)
Bidimensional Swell Effect on Accuracy of Footing Heave Prediction
The direct method (the Texas Highway Department Method TEX-124-E) and the Jennings and Knight “Double Oedometer Method” are widely used by practicing engineers for heave prediction of footings located on expansive soils. These methods are simple to use and yet simulate field conditions too. These two methods, however, are characterized by overpredicting the value of footing heave. The degree to which these methods overpredict heave is dependent on the soil conditions, as well as the applied footing pressure. The present work studied the influence of footing pressure on the precision of the two mentioned methods. It was found that the factor needed to adjust the predicted footing heave by these methods (“Heave Reduction Factor Rf”) decreases markedly with increasing footing pressure. The heave reduction factor Rf decreased from 0.92 and 0.88 to 0.62 and 0.53 for the direct method and the double oedometer method, respectively, as the footing pressure increased from 25 to 50 kPa. Soil strength depends upon the level of soil suction. Soil wetting contributes to reduction in soil suction, and consequently, to a loss in bearing capacity. Therefore, a test experiment with footing pressure of 100 kPa suffered bearing capacity failure after about one day since the beginning of the test experiment.