Weathering, structure and in-situ stress in residual soils

No theory exists which relates the formation of a residual soil to the in situ stresses which develop in it. A theory is developed in this Paper which relates in situ stress in level ground to weathering modelled as a weakening process. The loss of stiffness during weakening is modelled by isotropic elastic theory with reducing elastic parameters, and loss of strength by a Coulomb failure criteria with reducing c' and φ'. A small amount of weakening causes in situ horizontal stress to approach a limiting value set by the value of Poisson's ratio assumed. Low horizontal stresses are thus predicted. The solution is extended to the infinite slope, in which even lower stresses are predicted. Internal shear failure, which may lead to densification of high porosity soils, is predicted due to loss of strength in the final stages of weathering. Porosity changes in weathered granite are found to be consistent with the predictions of the theory. Conditions in which the weathering theory would be inapplicable are discussed.

• Introduction

• Weathering as a Weakening Process—Level Ground

• The Effect of Ground Inclination—The Infinite Slope

• Loss of Strength Due to Weathering

• A Comparison with Observations in Weathered Granite

• Limitations to the Use of Weakening Theory

• Summary and Conclusions

• Acknowledgements

• References