Laboratory Investigation on Performance of Soil–Cement Columns Under Axisymmetric Condition

Abstract

The inclusion of soil–cement columns in soft soil is a ground improvement technique that is used to reduce the settlement and improve the bearing capacity of the soft soil ground. In the present study, model tests have been carried out on soft soil improved with groups of end-bearing and floating columns under the axisymmetric condition to evaluate the relative improvement in the stiffness and failure stress of the soft ground due to the installation of soil–cement columns. The effect of various group foundation parameters, such as area ratio, length and diameter of columns and binder content are investigated. The failure mode of end-bearing and floating columns after exhumation are presented. For the same area ratio, of the improved soil–cement columns to the present soft clay deposit, the usage of the smaller sized soil–cement columns rather than large size soil–cement columns is found to be relatively more beneficial in case of both end-bearing and floating columns. The stiffness and failure stress of the composite ground increase with an increase in the length of the columns. However, the increase in strength is only marginal for the increase in column length beyond 10 times the column diameter. In the case of end-bearing columns, area ratio has a significant effect on failure pattern. At an area ratio of 25%, the column failed by outward displacement and bending. On the other hand, at an area ratio of 32%, the columns failed due to bending at approximately one-half to two-third of the column length from the base of the footing. In the case of floating column, the relative strength of columns to the soil $$( {c_{\text{uc}}}/{c_{\text{us}}})$$ appears to be the major governing factor. For the high value of $$( {c_{\text{uc}}}/{c_{\text{us}}})$$ used in the present study, punching failure was observed with slight outward displacement and some horizontal cracks for area ratios of 25% and 32%. For validation, the failure stresses of model ground were compared with the results obtained using numerical analysis. The results show a good agreement between the bearing capacity value obtained from the experiment and the numerical software.