Movement trigger limits when applying the Observational Method to embedded retaining wall construction on highway schemes

This report provides advice on suitable movement trigger limits to allow the Observational Method to be implemented for the design and construction of highway retaining structures. A contingency action plan defining trigger limits for horizontal wall movements for low, moderate and high stiffness supported retaining structures is presented. These limits are derived from the results of a TRL study of wall movements where retained cuttings and cut-and-cover tunnels were being constructed for highway schemes (Carder, 1995). The contingency action plan will enable the use of the Observational Method to be evaluated and, where appropriate, incorporated into the design and construction methodology. This report should, therefore, be of direct interest to all engineers involved in the planning, design and construction of highway schemes. (A)