การวิเคราะห์พฤติกรรมระยะยาวของอุโมงค์รถไฟฟ้าใต้ดินกรุงเทพด้วยวิธีเชิงตัวเลข / ศรัณย์ บำรุงชาติ = Numerical analysis of long term behaviour of Bangkok MRT tunnels / Sarun Bamrungchat
The existing Bangkok MRT Blue Line has been operated almost 10 years. There were many challenging geotechnical works during construction especially controlling of ground movement induced by tunnelling and excavation. However, during MRT operation, groundwater pressures around the tunnel gradually change due to consolidation process or leaking from lining joints and cracks. This change of groundwater condition causes the long-term ground movement around the tunnel and thus results in the settlement of ground surface. This research aims to predict the long-term settlement of ground surface using PLAXIS finite element programme. Twin tunnels and stacked tunnels with different soil properties were selected as case studies. The hardening soil model (HSM) was used to model the soft and stiff Bangkok clays. The Biot’s theory of consolidation was adopted in the long-term analysis. The 2D finite element analyses of tunnelling were based on the contraction method, stress reduction method, and modified grout pressure method. In addition, the 3D finite element analyses employed the recorded pressures and the back-calculated values. The results indicate that settlement of ground surface increases gradually with the decrease of the groundwater in both of transverse and longitudinal section. According to 2D finite element method, modified grout pressure method is simulation of tunnelling indicate the most reliable settlement of ground surface, stress strain and force in lining. In the same way, defining face pressure and grout pressure with minimum values in 3D finite element method indicate good results that, both settlement and trough of ground surface are compariable to field measurement
