The stress-strain behavior of soils is highly non-linear and stiffness of soils depends on the current state of stress, stress history, stress path and small strains level. However, such non-linear stress-strain behaviors of saprolitie soils are not well defined and seldom applied in geotechnical practice in Hong Kong. In order to improve our understanding and assist our design analysis in the future, it is necessary to conduct research on stress-strain behaviors of residual soils in Hong Kong....[ Read more ]

The stress-strain behavior of soils is highly non-linear and stiffness of soils depends on the current state of stress, stress history, stress path and small strains level. However, such non-linear stress-strain behaviors of saprolitie soils are not well defined and seldom applied in geotechnical practice in Hong Kong. In order to improve our understanding and assist our design analysis in the future, it is necessary to conduct research on stress-strain behaviors of residual soils in Hong Kong.

This research project consists of two parts: the first one is to examine the small strain behaviour of decomposed granite by the use of some local strain measuring devices - Hall Effect Small Strain Gauges on the intact and remolded samples in triaxial test. The second part is to monitor and study the performance of a deep excavation retained by a diaphragm wall in decomposed granite. Two constitutive models, the Mohr-Coulomb and the non-linear Brick model, were adopted for a back-analysis of the deep excavation using the laboratory test results. Numerical results are evaluated through comparisons with field measurements.

It is found that the stress-strain characteristics and the stiffness-strain relationships of decomposed granite are highly non-linear. Shear stiffness decreases as shear strain increases. Using the Mohr-Coulomb model with conventional stiffness assumption (E'=l000 kPa) significantly underpredicted wall deflections. However, the predicted wall deflections by using the non-linear brick model are generally consistent with monitoring data. Predicted shear stains around the site at the end of the main excavation were small and generally less than 0.5%.