Determination of Deformation Mechanism and Countermeasures in Silty Clay Tunnel: Fid-Bau Portal

Determination of Deformation Mechanism and Countermeasures in Silty Clay Tunnel

Wu, Kui / Shao, Zhushan / Qin, Su / Li, Boxiao

Deformation control and stability analysis are very important for tunnel construction. Large deformations of the constructed primary support accompanied by lining cracking and spalling occurred in the Dongxishan Tunnel located in Chaozhou City, northeastern Guangdong Province, China, posing a serious damage to the tunnel safety. In order to determine the causes of large deformations, comprehensive investigations have been performed by combining field monitoring, laboratory tests, and mechanism analyses. The results show that there have been three main factors resulting in the occurrence of large deformations in the Dongxishan Tunnel: the plastic flow of surrounding rock due to low strength of silty clay, obvious creep behavior, and water-weakening effect of silty clay. Besides, based on the preceding mechanism analyses of large deformations, many countermeasures were proposed during construction, including double row pipe pregrouting reinforcement, strengthening primary support, and timely closing of temporary support. These countermeasures can effectively deal with large deformation problems in the Dongxishan Tunnel from the in situ feedbacks. This paper can provide useful guidance for avoiding the similar anomalies in the following excavation and support of Dongxishan Tunnel.