Design considerations for one-strut failure according to TR26 - a practical approach for practising engineers

摘要

Technical Reference 26: 2010 (TR26: 2010) requires the design of an earth retaining and stabilising system (ERSS) to be structurally safe, robust and has sufficient redundancy to avoid catastrophic collapse of the ERSS system resulting from an isolated case of overloading or failure of any particular member which may lead to the failure of adjacent members thus leading to progressive failure. One such redundancy check is the condition, where failure of a single strut, anchor or tie-rod occurs or more commonly known as one-strut failure (OSF) stated in Clause 3.7.4 of TR26: 2010 at each stage of the construction works. Analysis for OSF is actually a three-dimensional (3D) problem and carrying out such 3D analyses covering all the cases of wall stiffness, properties of the soil layers, friction between retaining wall panels in the case of diaphragm wall, soil arching effect due to the deflection of the retaining wall, etc. is very time consuming. In the conventional approach for OSF using two-dimensional (2D) plane strain analysis, the whole layer of failing strut is removed and thus provides paths to distribute the forces in the vertical direction only. This usually leads to more conservative design with heavier struts sections. In this paper, a procedure to rationally idealise OSF from a 3D analysis to a 2D plane strain analysis is presented. This simplified approach will be more practical for practising engineers to arrive at a more efficient design without the need for rigorous 3D analysis. The results of this simplified approach are compared with the conventional approach and results incorporating appropriate strut stiffness from 3D analysis. The comparison showed that the approach is reasonable.