Passive soil pressure on sloping ground and design of retaining structures for slope stabilisation

Soil-retaining structures, such as anchored, gravity and diaphragm walls can be used effectively to stabilise unstable, shallow slopes. The present work focuses on assessing the passive soil pressure that can be mobilised by passive and active retaining structures used for slope stabilisation purposes; passive structures are taken to be those left free to move and find their own equilibrium against the soil pressure, and active structures those equipped with pre-stressed ground anchors that lead to an upward movement against the unstable sloping soil. The numerical analyses performed with the Abaqus finite-element code and the comparison drawn with available theoretical solutions show that, in the case of passive retaining structures, the maximum horizontal soil pressure that can be exerted by the unstable soil layer on the retaining structure is independent of soil-wall friction and coincides with Rankine's passive value. However, in the case of active retaining structures, the passive soil pressure may be much greater than Rankine's value and should be evaluated as suggested by Eurocode 7 (geotechnical design). Such a high soil pressure is only meaningful for the purpose of sizing the retaining structure, however, because (just uphill from the stress region perturbed by the soil-wall friction and ground anchor) the stress state at rupture coincides with Rankine's theory in the case of active retaining structures too. Thus, even in the case of anchored retaining structures, the maximum soil pressure that can be exploited for slope stabilisation coincides with Rankine's value. These conclusions have important consequences for the dimensioning of soil-retaining structures for slope stabilisation purposes. A practical application for slope stabilisation is discussed in the final part of the paper.