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Stability analysis when tunnelling in soft soil condition in Hochiminh city

The rapid development in the economy and the urban population in cities in Vietnam in recent years leads to dramatic growth in traffic congestion, noise and air pollution, and environmental degradation. Urban underground infrastructure thus becomes an inevitable solution since the surface space becomes too expensive and restricted in spite of the high cost of tunnel construction. However, tunnelling in deltaic urban areas, in particular in the cases of Mekong Delta and Red River Delta areas, often faces to difficulties of soft soil conditions and the existence of important historical buildings on the surface. The first metro line constructed in Vietnam from Ben Thanh to Suoi Tien, which is located under crowded areas of Hochiminh city, was tunnelled in such conditions. This paper presents a back analysis for the stability of the tunnelling process in the project. The minimum support pressures is estimated by using the wedge model proposed by Jancsecz, S., & Steiner, W. (1994). Meanwhile, the maximum support pressure is estimated by the blow-out model proposed by Vu et al. (2016). Based on these results, the range of support pressures recommended for the Earth Pressure Balance Tunnel Boring Machine in the Hochiminh Metro Line No.1 project soft soil conditions is derived and compared to in situ support pressures obtained from the monitoring data in this tunnelling project. The study result shows a good agreement between the support pressures obtained from stability analysis models and the monitoring data from the construction site. Based on this back analysis, some recommendations are proposed with the purpose of successful construction in the next tunnelling projects in Hochiminh city.