Pozzolanic consolidation of stabilized soft clays

Abstract

The presence of soft clays underlying foundations has been responsible for failures in several geotechnical and geo-environmental projects. The three aspects of this study dealing with the stabilization of a soft clay through the addition of cement and lime include: (a) determination of the optimum proportions of both cement and lime needed to obtain a stabilized soil, (b) the phenomenon of pozzolanic consolidation which occurs in the cement–lime stabilized soft clay, and (c) using knowledge of the pre-consolidation stress and compression index of the stabilized soft clay as a practical criterion for determination of the optimum additive percentage in soft clays stabilization. The experimental research program designed to investigate the behavior of the soft clay before and after stabilization involved a series of tests that included sedimentation testing, cation exchange capacity measurement, X-ray diffractometry, unconfined compression and consolidation tests. The results indicate that pozzolanic reaction creates a form of pre-consolidation in the cement–lime stabilized soft clay. The reduction in soil settlement is attributed to the pozzolanic reaction in soil-additive interaction resulting in an increase in pre-consolidation stress of stabilized soil. The test results show that pozzolanic consolidation causes an increase in initial pre-consolidation stress of 70kN/m2 for a soft clay soil to 375kN/m2 for the stabilized soil with 6% lime, and to 385kN/m2 for stabilized soil with 6% cement. The series of XRD experiments conducted are used to study the micro-structural aspects of the stabilized soil. The results show that pozzolanic consolidation not only improves strength behavior of clay soils in general, but also reduces the potential for large settlements of the stabilized soft clays — indicating that there is considerable merit in using the consolidation behavior of the stabilized soft clays as a means for determining the required percentages of additives for cement–lime stabilization of soft clays and soft soils in general.