Simulation and evaluation of improvement effects by vertical drains/vacuum consolidation on peat ground under embankment loading based on a macro-element method with water absorption and discharge functions

Abstract

The authors previously extended the macro-element method proposed by Sekiguchi to include water absorption and discharge functions and incorporated this into a soil–water coupled finite deformation analysis code capable of accounting for inertial forces. The primary objective of this study is to validate the ability of the proposed method to simulate actual ground behavior by comparing the simulation results with the actual measurements of the embankment loading of a soft peat ground improved with vertical drains and vacuum consolidation. It was found that the proposed method is capable of comprehensively and closely simulating not only the magnitude of settlement, but also various ground behaviors, including the deformation of the surrounding ground and pore water pressure distributions. Furthermore, additional simulations were performed to elucidate the effect of a continuous middle sand layer found to exist and to span the entire improved area at an actual embankment site.The next objective of this study is to investigate the impact of ground improvement, using vertical drains and vacuum consolidation with embankment loading on a soft ground, placing a particular focus on the effect of drain spacing. In this case, an ultra-soft ground with alternating peat and clay layers was modeled to represent a typical ground to which vacuum consolidation would be applied. Based on a series of simulations, it was found that, although the use of vacuum consolidation in combination with vertical drains is effective in cases where it is necessary to limit the deformation of the surrounding ground, the same reduction in residual settlement can be achieved using vertical drains alone, provided that the drains are deployed at a sufficient frequency.