Measurement and Numerical Analysis of Drilling Holes for Rotary Excavation Pile in Deep Sand Layer in Shanghai
Currently,the pressure balance method is mostly used in the calculation for hole-forming stability of cast-in-place piles.The slurry wall protection effect is equivalent to the slurry hydrostatic pressure to balance the external water and soil pressure.The slurry hydrostatic pressure is often simply considered as the multiplication of the slurry weight and depth.Relevant studies have shown that the slurry wall protection effect is related to the formation properties and mud quality.The mud quality in the sandy soil layer is mainly affected by the slurry viscosity.Therefore,the mud pressure balance method should adopt slurry viscosity as a calculation parameter.Taking the pile foundation project of a super-large railway hub in the Shanghai coastal area as a case for analysis,the site stratum is the distribution of overlying clay and the underlying sand layer.The thickness of the clay layer is 30m,and the thickness of the sand layer is 50m in the depth of pile forming.Surface orifice collapse and deep sand soil shrinkage occurred during the trial pore-forming process.Based on the measured results of deformation,a numerical calculation method for pore-forming stability considering both slurry density and viscosity was established.The necessity of considering viscosity parameters was verified by comparing the measured results.The influence of each slurry index on pore-forming stability was further studied.
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