Study On The Pile Raft Foundation Stress Characteristics Of Artificial Freezing In Cretaceous Stratum

This paper mainly adopts the method of theory analysis, filed measurement and numerical simulation. The load-bearing characteristics of shaft tower pile raft based and foundation in cretaceous formation are analyzed, and the ultimate bearing capacity of single pile and the mechanical law of pile raft based which considered the effect of freezing are investigated.Based on the theoretical analysis and numerical simulation, the paper adopts the thick plate theory to analyze the raft foundation of shaft tower. The results show that the top of the raft has the stress concentration phenomenon of the pile raft foundation, and all of the stress concentration phenomenons appear at the four horns points of the raft. Combined the frozen soft rock creep test data of the cretaceous, the viscoelastic-plastic model and derived the flexibility matrix of the frozen soft rock are obtained.Through numerical simulation and the measured data of foundation pile static loading test, the results show that the ultimate bearing capacity of single pile is13102kN with diameter800mm and length18m of pile in cretaceous. The ultimate side resistance and the ultimate tip resistance could reach650kPa and8000kPa of medium weathering sandstone of cretaceous in Inner Mongolia area, and the medium weathering sandstone can be used as a good natural pile foundation.Through the pile raft foundation in situ monitoring and numerical simulation, they show that the raft reinforced first bear tensile stress and then bear compressive stress, and the stress curve is "V". The pressure distribution of the pile top is not balanced, which is closely related to the inhomogeneity of the base settlement. The maximum load of the pile top is only one-third to the ultimate bearing capacity. With the depth increased of pile body the vertical reinforced stress reduced, and the pile side friction is closely related to the load, which is first increases and then flattens out, finally stability with the increase of the upper loads. The pile side friction has the inverse relationship with the depth, and the biggest pile side friction is between70kPa and80kPa.The structure stress and deformation of foundation from numerical simulation conforms to the results from field measurement when consider the foundation creep characteristics of pile-raft-freezing soft rock common function. It is give the reference.to the design and construction of pile raft foundation in cretaceous formation...