Large simple shear testing of soft Bangkok clay stabilized with soil-cement-columns and its application

In practice, the slip circle analysis is still commonly used to determine internal stability of soil-cement-columns (SCCs) -stabilized ground subjected to lateral load. Conventionally, the weighted average shear strength of stabilized soil columns and soft soil is calculated, with a correction factor applied to reduce the strength of unstabilized soil. In this study, a new large simple shear apparatus has been developed and used to test soft Bangkok clay stabilized with SCCs of different patterns, namely, Square Group Columns (SGC), Longitudinal Tangent Wall (LTW), and Transverse Tangent Wall (TTW). From the experimental results, the LTW pattern yielded the highest strength gain from SCCs, while the TTW specimen had very minimal gain in strength, as compared to the original reconstituted sample. It was also observed that the SCCs had failed predominantly as a result of tilting and bending, and the columns would not have fully mobilized its shear strength as in unconfined compression. A modified weighted average shear strength equation was thus proposed whereby the reduction factor is applied to the SCC strength, and not to the strength of unstabilized soil. A slip circle analysis of an actual failure case was performed based on SCC shear strength estimated using the modified approach, which gave much more satisfactory results. The concept that the correction factor be applied to the stabilized soil is recommended for the slip circle analysis of the cases in which tilting and bending of SCCs would govern the failure. This would be cases of soft ground stabilized with SCCs with a relatively low improvement area ratio of 0.1-0.3.