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Optimization of the Excavation Sequence of Overlapped Tunnels
in Sandy Cobble Stratum
(Key Laboratory of Transportation Tunnel Engineering, Ministry of Education; School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031)
Abstract The construction of overlapped shield tunnels in sandy cobble stratum, such as in the case of the Chengdu metro line 2, are rare in China. Therefore a method combing numerical simulation and field measurement is adopted to study the movement characteristics of the twice-disturbed ground and the effects of the force applied on the structure under different exaction sequences. A FLAC3D numerical model is established to analyze the whole process of shield construction from parallel section to overlapped section; and to simulate the effects by shield overcut based on practical measurements. The results show that it is relatively reasonable for the overlapped tunnels to take the excavation sequence from lower tube to upper tube; ground loss induced by shield overcut results in an increase of ground surface settlement up to two times; large settlement occurs above the upper tube; and the lower tube heaves slightly due to a secondary disturbance by the shield construction. The numerical simulation agrees well with the practical measurements.
Abstract：
The construction of overlapped shield tunnels in sandy cobble stratum, such as in the case of the Chengdu metro line 2, are rare in China. Therefore a method combing numerical simulation and field measurement is adopted to study the movement characteristics of the twice-disturbed ground and the effects of the force applied on the structure under different exaction sequences. A FLAC3D numerical model is established to analyze the whole process of shield construction from parallel section to overlapped section; and to simulate the effects by shield overcut based on practical measurements. The results show that it is relatively reasonable for the overlapped tunnels to take the excavation sequence from lower tube to upper tube; ground loss induced by shield overcut results in an increase of ground surface settlement up to two times; large settlement occurs above the upper tube; and the lower tube heaves slightly due to a secondary disturbance by the shield construction. The numerical simulation agrees well with the practical measurements.
2013, Vol. 50 