Soil nailing support for tunnel stability

Due to the rapid growth in urban development in most major cities, and space limitations the demand for tunnels construction for various purposes (utilities, and transportation systems) is increasing. These tunnels are constructed at shallow depths mostly, for accessibility, serviceability and economy reasons. Since the ground at shallow depth consists of either soft soils or weak rocks, shallow tunnels are usually exposed to the occurrence of excessive settlement. In such areas, settlements induced by the tunneling excavation may cause serious damage even collapses to nearby structures. Accordingly, maintaining the tunnel stability has the highest priority since the instability issues may cause a loosening of the ground leading to a complete tunnel collapse.

Soil nailing supporting technology is applied widely in China, soil nailing and prestressed anchor cable combined is a new composite soil nailing structure for foundation pit supporting, and there are more advantages. According to a composite soil nailing supporting in foundation pit, horizontal displacement of pile body was measured by reasonable measuring point. Some conclusions were drawn by displacement curves: horizontal displacement was progressive and sensitive to upper several layers digging, and was affected greatly by upper two layers, anchor cables arranged in upper layers were advantageous to reducing deformation of foundation pit slope, horizontal displacement of supporting structure was affected obviously by structure dimension. According to field test of soil nails and prestressed anchor cables, the conclusions were drawn that horizontal displacement was affected by them.