Mobilisable strength design for flexible embedded retaining walls

Abstract

Soil-structure interaction may have an important influence on the behaviour of embedded retaining walls, affecting both wall bending moments and ground movements. However, it can be difficult and time consuming to capture in design, especially in a way that gives a physical insight into the key behavioural mechanisms involved. A calculation procedure has been developed for retaining walls propped near the crest that takes into account both the non-linearity of the stress-strain behaviour of the soil and the flexibility of the wall. Results for different pore water pressure conditions, soil strengths and soil and wall stiffnesses are presented in the form of look-up charts, and are compared with those derived from factored limit equilibrium analyses. A dimensionless parameter is introduced to represent the relative soil-wall stiffness, and its importance is demonstrated. A critical flexibility ratio is identified at which the bending moments start to reduce below those given by a conventional limit equilibrium calculation. This ratio is linked to the wall deflection, and is used to distinguish a stiff from a flexible system in soils of different strengths and pore water pressure conditions. The approach is discussed in relation to previous studies.

A design method for flexible retaining walls in clay

“…The analysis procedure developed here builds on the work of Diakoumi and Powrie (2013) in assuming that the stress state of soil adjacent to a particular wall segment is a function of the strain mobilised at that point. The strain distribution can be calculated for any given wall shape by assuming a compatible deformation mechanism with the corresponding earth pressures being subsequently calculated through a simplified constitutive model.…”

“…The transformation of the wall deflection profile from a cosine to an exponential shape may provide some benefits, but the real deformed shape of the wall is still not well reproduced. Diakoumi and Powrie (2013) presented a technique for carrying out mobilisable strength design for flexible retaining walls, in which the soil strain was calculated based on the superposition of the mechanisms proposed by Bolton and Powrie (1988) for rotation of each of a series of wall segments. However, the superposition of the four mechanisms utilised and shown in Figure 2 would imply a discontinuous wall shape with the wall shearing instead of bending at each hinge (Haigh et al, 2013).…”

Mobilizable Strength Design for Multibench Retained Excavation

“…In 14- (18), there are 4 unknown parameters, which are 1 , 2 , 1 , and 2 . Meanwhile, there are 2 force equilibrium equations and 2 moment equilibrium equations for the 1RS and 2RS.…”

“…Bolton and Powrie [16] introduced the concept of "mobilizable soil strength (MSD)" to the design of cantilever retaining wall. Then, the MSD method was also applied to the prediction of the ground movements of braced excavations [17] and the design of the flexible walls propped at the crest [18]. Wang et al [19] modified the MSD method by considering the undrained anisotropic shear strength of 0 normally consolidated soft clay and bending strain energy of the retaining wall.…”

DISCUSSION: Mobilisable strength design for flexible embedded retaining walls

“…The discusser read with interest the paper by Diakoumi & Powrie (2013) proposing an interesting method for the analysis of propped flexible retaining walls based on the mobilisation of active and passive pressures on the wall due to movement of wall segments. An assumed deformation mechanism within the soil is used to estimate the strain associated with rotation of a particular wall segment.…”