Grouting-based treatment of tunnel settlement: Practice in Shanghai

Excessive tunnel settlement, especially differential settlement, will deteriorate the operational serviceability and safety of a metro system. This paper presents grouting-based treatment technology for tunnel settlement in the soft deposits of Shanghai, China. The aim of the grouting treatment is to control the development of the tunnel settlement. The mechanism of settlement control through grouting is presented. A dual-fluid system of cement and sodium silicate is adopted in the proposed grouting-based treatment technology. A new front-end device is designed specially to avoid blocking the grouting holes. The grouting parameters are determined based on field tests and engineering practices. Engineering cases of a double-O-tube (DOT) tunnel and twin tunnels are used to present the feasibility and efficiency of the grouting treatment. For the DOT tunnel, the grouting treatment was carried out in multiple stages; the tunnel settlement finally ceased, from an initial settlement rate of 0.4 mm/d, and the maximum horizontal differential settlement decreased from 20 mm to 10 mm. For the twin tunnels, the tunnel settlement recovered after grouting; the recovery of the maximum tunnel settlement was 8 and 11 mm for the upper- and lower-line tunnels, respectively, and the settlement finally ceased, from an initial rate of 0.027 mm/d. Moreover, in situ measurements of the surroundings indicate that the proposed grouting-based treatment technology creates minimal disturbance to the surrounding soil. This grouting-based treatment provides an effective way to control the settlements of tunnels in soft deposits.