Modified method for predicting lateral displacement of PVD-improved ground under combined vacuum and surcharge loading

A modified method is proposed to predict the lateral displacement (δ) of prefabricated vertical drains (PVDs) improved ground under combined vacuum and surcharge loads, which is derived based on a few modified triaxial tests and a series of finite element analyses of PVD unit cells. It is observed that reducing the surcharge load (ps) and loading rate (LR) and increasing the vacuum pressure (pv), pre-vacuum consolidation period (tv), and initial undrained shear strength (su0) could be effective in controlling the outward δ. Variations of the effective stress ratio (Ke) that controlling the δ with ps, pv, LR, tv, and su0 are then presented. A synthetic relationship between the normalized horizontal strain (εh) by a reference one-dimensional vertical strain (εv1) and the normalized Ke by the at-rest earth pressure coefficient (K0) is proposed for cases with and without tv. Further, a modified index parameter (β1) is introduced for quantitatively considering the effect of ps, pv, LR, tv, su0, and consolidation properties of the soil, a relationship between Ke and β1 is then established for evaluating the value of Ke. Combinations of the εh/εv1–Ke/K0 and Ke–β1 relationships enable modified predictions of the δ from basic preloading conditions and soil parameters.