Abstract:
Twin TBM tunnels were constructed to a length of 870m in one of the underground metro projects. They were passing through the complex geological conditions (soil, rock and mixed conditions). This paper compares the ground response and volume loss 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 are directly derived from the two parameters: the volume loss and trough width parameter. These 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 tunnelling to 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 directly obtained from Plaxis 2D.
Instrumentation arrays are 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 due to the excavation of twin tunnels are compared with the actual field instrumentation and monitoring data. From the field instrumentation data, the actual volume loss values are calculated. The compatibility of calculated ground settlement and volume loss by analytical and numerical methods over the field instrumentation data is discussed in this paper.
Keywords: ground settlement; volume loss; field instrumentation; twin tunnelling; monitoring;
Abstract: Theme 2