Estimation of in situ stresses using anisotropic elasticity and suction measurements

Sampling and specimen preparation produce changes in mean effective stresses and pore water pressures, even with ‘perfect sampling’. The paper takes an existing simplified three-parameter cross-anisotropic elastic model and uses it to model these changes. The required ratio of cross-anisotropic parameters J/3G* can be obtained from standard CIU triaxial tests. If measurements are also made of suctions in unloaded specimens in the laboratory, then a combination of J/3G*, the measured suction, and the effective overburden pressure permits an estimation of the horizontal effective pressure and the K 0 ‘at rest’ coefficient. This can be helpful in numerical modelling that needs to start from in situ conditions, and in planning pressure levels for reconsolidation of clay specimens in the laboratory. Tests were done on Belfast Upper Boulder Clay from a depth of 28 m. Values of horizontal in situ effective stress estimated from these measurements compare favorably with conventional estimates of the ‘at rest’ coefficient K 0 and the overconsolidation ratio. Estimates of horizontal stress in London Clay were made using published data and the results compared with actual measurements. Again reasonable agreement was obtained.