Bearing capacity and settlement behaviour of foundations in unsaturated soils

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Classical soil mechanics valid for saturated soils are conventionally used for foundation designs even for unsaturated soils of semi-arid and arid regions. This may be attributed to the lack of simple tools available for the measurement of in situ soil suction and a simple framework that is consistent with the conventional geotechnical engineering practice protocols. Three different research activities will be undertaken by the applicant to focus on these issues: (i) Simple techniques for measurement of suction: In situ suction values (i.e., less than 500 kPa, which is of significant practical interest) in fine-grained unsaturated soils are proposed to be estimated using a simple tool, pocket penetrometer. This technique is based on the assumption that there is a strong relationship between the penetrometer resistance and the suction value of fine-grained soils. (ii) Interpretation of the bearing capacity and settlement behaviour of foundations in unsaturated soils: The applicant proposed simple techniques for predicting the bearing capacity of both the coarse- and fine-grained soils based on model footings studies using the saturated soil properties and the soil-water characteristic curve. More studies will be performed to understand the influence of depth, inclination, shape, size and scaling factors to propose general bearing capacity equation for unsaturated soils. The applicant proposed a technique for estimating settlement behaviour in unsaturated coarse-grained soils extending the elasticity approach. Similar approach will be undertaken to estimate the settlement behaviour using compressibility behaviour as a tool for unsaturated fine-grained soils. (iii) Simple techniques for the estimation of the heave and swelling pressure of expansive soils: Presently used techniques are cumbersome and time consuming to estimate the swelling pressure and 1-D heave of expansive soils, which are typical examples of unsaturated soils. The applicant proposes to develop a simple technique to predict both the swelling pressure and heave of natural expansive soils using only the information of plasticity index and the variation in natural water content with respect to depth in the active zone.