Performance Prediction and Uses of PV Band Drains under the Embankments on Soft Marine Clays of Bangkok

The use of prefabricated vertical (PV) drains for the improvement of soft clays is a widely adopted technique today. Vertical drains arc used to accelerate the consolidation under preloading by taking the advantage of higher rate of horizontal flow of water through the soil. The present paper is aimed at the prediction of the performances shown by the ‘Alidrain’, used in the soft marine clays of Bangkok, in the field under embankment loading and in the laboratory in a in-house designed large scale consolidometer, by using a Finite Element model of the transient, axi-symmetric flow problem considering equal strain. This model also considers the disturbances caused by the driven mandrels to the surrounding subsoil (smear effect) and the effect of the sizes of mandrel used for installation. The data collected from field and laboratory has been compared with the results from this model. The model demonstrated good prediction of both the field and laboratory performances with proper choice of the Cfield/Clab ratio, the smear zone diameter (ds), the kh/kh\u27 ratio for the smear zone and the other input soil parameters found from different laboratory experiments. For the prediction of consolidation settlement in the field, a proposed value of kh/kh\u27 ratio around 10 with the combination of ds=2dm has been found to give the best results