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Deformation Processing Technology of Fine Silty Sand Layer Cofferdam Primary Support at Shangbai Tunnel

Shangbai tunnel on Datong-Xi'an Passenger Dedicated Railway Line traverses the loess and sand layer boundary strata.The layer is dry,dense,and cohesionless,so it's easy to be in flow state after excavation-disturbance.Consequently,it's prone to lead to large deformation,collapse and so on at primary support step.After analysis of special geology cofferdam,an arch changing technology based on horizontal jet grouting piles cross construction at forward direction and backward direction,is proposed.And this new technology is used on large deformation section(DK596+214~+199) of Shangbai tunnel.The technology solves successfully the problem of deformation treatment of the tunnel in this kind of geology.And it's a good reference to similar geological disaster treatment and construction.