Ground Improvement for Open Foundation on Soft Clays Using Stone Columns and PVD Drains for Retaining Walls and Approaches of a Cable Stayed ROB

Abstract

This paper presents the case study for ground improvement of approaches of a four-lane cable stayed road over bridge. The approach ramps comprised of two side retaining walls on open foundations and earthfill between the two walls. Due to presence of soft clay below the ramps, allowable bearing capacity was very low, and settlements were high to support the weight of ramps which had a maximum height of 12 m. Hence, it was essential to evaluate the ground conditions and take suitable measures to enhance the capacity of ground so that it can transfer the pressure due to self-weight and applied loading on the structure. Soil investigation report indicated that the topsoil was observed to be filled up to 2–3 m depth overburden underlain by clayey soil. The clayey soil was found to be of soft to medium consistency till a depth of around 15.0 m and below this 15 m depth, a layer of stiff to very stiff clayey soil was observed till the 30.0 m depth. Looking at the ground conditions, two ground improvement methods were considered suitable for the proposed bridge such as (a) ground improvement using stone columns beneath retaining walls and (b)ground improvement using PVDs for soil fills for embankments/approaches. The details of these ground improvement and the extent of ground improvement are discussed in this paper.KeywordsGround improvementStone columns and PVDs