Protection of neighbour buildings due to construction of shield tunnel in mixed ground with sand over weathered granite

Abstract

In south China, many geological formations are composed of weathered rock covered by a thin layer of Quaternary soft deposits, e.g., clayey soil or sandy soil. When the tunnel was constructed in these kinds of compound strata, geohazards such as sinkhole and large settlement are ready to happen. This paper presents a field case of shield tunnelling, which was conducted at the interface of mixed ground between completely weathered granite covered by residual sandy soil at Humen, Guangdong, China. To prevent damage to existing buildings, optimisation of tunnel construction parameters was adopted. During construction, lateral displacements of the subsoil around the tunnel, and horizontal and vertical displacement hazards of seven buildings were monitored. The monitoring results show that maximum settlements and lateral displacements of the buildings were 18.9 and 8.8 mm, respectively, which are all within the allowable value for buildings. The construction parameters such as total thrust, chamber container pressure, grouting pressure and grouting volume are presented and inducing hazards limits to buildings are discussed. The results show that the optimised tunnel construction parameters are sufficient in reducing the hazards of both existing buildings and surrounding soil during tunnel excavation.