Prediction of Embankment Settlements by In-Situ Tests
The compressibility of soft Bangkok clay preloaded with an instrumented test embankment was studied using the results of a series of in-situ and laboratory tests. In the field, eight screw plate and eight pressuremeter tests were performed at four test levels in the subsoil. In the laboratory, twelve Rowe cell consolidation tests were carried out. The method of Asaoka (1978) was used in determining the coefficient of consolidation from the screw plate test. It was found that Cv values obtained from the Rowe cell consolidation tests were twelve times smaller compared to those derived from the screw plate tests. The soil parameters obtained from the two types of in-situ tests conducted in this study were then used to predict the settlement behavior of the two test embankments, one improved by prefabricated vertical drains (PVD), and the other, on unimproved ground. The difficulty associated with the proper choice of the drained modulus values are highlighted, and it was found that the predicted settlement magnitudes using elastic theory can vary considerably for the ratio of drained and undrained soil moduli, E'/Eu, ranging between 0.25 to 0.50. The undrained modulus from the screw plate test corresponding to the fitted data was found to be 1.38 times the undrained modulus from the pressuremeter test. General agreement with the observed settlement was found using the graphical procedure of Asaoka (1978) and adopting the coefficient of consolidation from the screw plate test.