Experimental study on instability of bases on natural and lime/cement-stabilized clayey soils

In many sub-tropical and tropical and regions of the world, marly soils (marls) and lime or cement stabilization of marl soils are used as a convenient and expedient means of developing foundation base courses and inexpensive wearing courses for transport purposes. The failure of many of these natural and stabilized marls to perform their function has been reported. Mechanical factors, commonly used to explain the causes of the foundation failures, are unsatisfactory and have not been accepted. This study uses physicochemical (reaction) factors to explain the general basic causes of the deterioration of support capability for these types of soils. The presence of palygorskite and sepiolite in marl soil provides it with some very unique features in its natural state, particularly when it is stabilized with lime or cement. The formation of an expansive mineral, ettringite, as a transformation product of palygorskite increases the swelling potential of the stabilized soil. A set of physico-chemical and mechanical experiments, which include slake durability, specific surface area measurement (SSA), California bearing ratio (CBR), atterberg limits testing, and Xray diffraction (XRD), were performed. In addition, the impact of curing on the stabilized soil behaviour was investigated. The results show that the immersion of the natural marl reduces the dry CBR value to at least one-fourth the dry value. Furthermore, the XRD results indicate that with increasing time and availability of dissolved aluminum and sulfate, ettringite forms in stabilized soil and then the rate of ettringite growth increases. Based on the findings of these experiments, the various interactions, reactions and factors contributing to the stability and instability of marl soils, and lime/cement stabilized marls are discussed. It is concluded that the general traditional soil stabilization evaluation methods are not capable of accounting for the failures that occur in stabilized marl. It is shown that soil mineralogy and pore fluid analysis, in conjunction with X-ray diffraction testing, can be combined to provide a set of practical ways to monitor the possibilities of these failures. (C) 2006 Elsevier B.V. All rights reserved.