Analysis Of Ground Settlement Caused By Shield Tunneling

The subway tunnel shield construction inevitably produce strata displacement.If the ground displacement is large enough,it will affect the normal use of underground pipeline and the building.At home and abroad study of subway shield tunnel exxcavation produced the surface subsidence is not suitable for Nanning area.It needs to make a detailed analysis in this area.(1)Longitudinal settlement curve is greatly influenced by the construction parameters of settlement changes,at the same time,related to the properties of soil.(2)In construction parameters and construction of shield tunneling under normal circumstances,the single shield tunnel excavation in all kinds of soil lateral end surface settlement curve and peck formula describes fall curve is similar.Round gravel layer and silty and fine sand layer in the shield tunnel construction of ground surface settlement is larger;Clay and silty sandstone layer,breccia layer of shield tunnel construction in the surface suubsidence is smaller.In the former of shield excavation shoouuld bbe paid attention to control all kinds of construction parameters,guarantee the surface settlement within the security control valluces(3)The region in the round gravel layer and siltstone,single shield tunnel excavation horizontal width of the surface settlement curve and maxximum ground settlement value is as follows:In the round gravel layer,a=-7.97,b=0.21,c=0.0026,k=0.67,d=-2.93.In powder sandstone layer,a=-14.05,b=0.3,c=0.0019,k=0.49,d=-4.72.Type combining Peck formula settling tank curve can be obtained.(4)Parallel double shield tunnel exxcavation is completed,after the lateral stability of surface subsidence,in general,when H>d,settling tank curve is "unimodal type";When H<d,settling tank curve "bimodal type".(5)Parallel double shield tunnel excavation around the region,the final horizontal ground surface settlement curve similar to the superposition principle.The correesponding computation formula is as follows:In the round gravel layer,a=-7.97,b=0.21,c=0.0026,k=0.67,d=-2.93.In powder sandstone layer,a=-14.05,b=0.3,c=0.0019,k=0.49,d=-4.72.(6)Overlapping double shield tunnel construction produce horizontal curve of surface subsidence trough,arranged in "V" shape curve.The 4 line overlap tunnel is in the shape of "bow".