ANALYSIS OF AN EARTH-REINFORCING SYSTEM FOR DEEP EXCAVATION

A limit-analysis procedure for a reinforced lateral earth support system is described. The system is composed of a wire-mesh-reinforced shotcrete panel facing, an array of reinforced anchors grouted into the soil mass, and rows of reinforcing bars that form horizontal wales at each anchor level. Excavation starts from the ground level and, after each layer, reinforcement is applied immediately on the exposed surface and into the native soil. This system thus forms a temporary earth support that has the advantages of requiring no pile driving, not loosening or sloughing the soil, and providing an obstruction-free site for foundation work. It has been successfully used for large areas of excavation to depths of up to 18 m in various ground conditions. However, in the past, no rational and proven analytical design procedure was available, a problem that resulted in coonsiderable reservation toward the use of the system among engineers and contractors. The two-dimensional plane-strain limit- analysis formulation includes consideration of design parameters such as soils type, depth of excavation, length of the reinforcing members, inclination, and spacing. The analysis procedure can be used to evaluate the overall stability of the system and to determine the proper size, spacings, and length of the reinforcement for a given site condition. (Author)