Study Of Ground Settlement And Volume Loss Associated With Tbm Tunnelling By Analytical And Numerical Methods

Twin tunnels were constructed to a length of 863m using TBM in one of the underground metro projects. The tunnels pass through complex geological conditions (soil, rock and mixed conditions). This paper presents the consideration of volume loss and the corresponding ground settlement associated with the excavation of twin TBM tunnels by analytical and numerical methods. Empirical methods were used to calculate the ground settlement induced by the excavation of twin tunnels. The ground settlement values were directly derived from the two parameters: the volume loss and trough width parameter. These parameters are calculated based on the geological conditions at the tunnel face and tunnel overburden. The finite element software, Plaxis 2D was used to model the soil parameters with appropriate geological conditions. Twin tunnel excavation is simulated in Plaxis 2D and the effect of tunnelling on the ground was simulated by percentage volume loss. The suitable line contraction value was applied to the tunnel linings to simulate the volume loss. The surface ground settlement was directly obtained from Plaxis 2D. Instrumentation arrays were proposed along the twin tunnel alignment, to provide the ground settlement monitoring data within the influence zone of tunnelling activities. The derived ground settlement values from analytical and numerical methods were compared with the actual field instrumentation and monitoring data. From the field instrumentation data, the actual volume loss values were calculated. The compatibility of ground settlement and volume loss calculated using analytical and numerical methods and those measured using field instrumentation data is discussed in this paper.