Studies On Effects Of Super-deep Excavation On The Bearing Capacity And Settlement Behavior Of Compression Piles Beneath The Basement

The high-rise buildings and large underground structures promote the development of super-deep excavations. The intense stress relief and basal heave will influence the capacity and settlement behavior of the compression piles beneath excavations.Firstly, four centrifuge modeling tests are carried out. The effect of deep excavation on the capacity and settlement behavior of piles is investigated. Also, the responses of piles with different surface roughness are compared. The results show that the deep excavation could reduce the capacity and stiffness of smooth piles. However, for the rough piles the capacity and stiffness are increased due to excavation. Beside, for both cases the excavation could lead to the tension in piles. The finite element analysis is conducted on the smooth piles using the interface model without dilation and Mohr-Coulomb model in ABAQUS. It is found that the stress relief during excavations reduces the normal stress of piles. Hence, the capacity and stiffness decrease. The basal heave would not lead to a reduction of capacity, but it could reduce the stiffness of pile.Furthermore, the parametric study on smooth piles under the condition of deep excavation is conducted by changing the length of pile, the radius of excavation and the modulus of pile. It is shown that the reduction of smooth pile increase with the increasing of normalized excavation depth and radius. The heave-induced tension in pile increases at the first and then decreased. Moreover, as the the modulus ratio of pile to soil increases, the tension in pile increases and appears earlier during excavation.The Norsand model with considering dilation is modified to make the modulus as a function of confining pressure and void ratio. The Modified Mohr-Coulomb model with dilation is introduced to capture the dilation of the pile-soil interface. The Bolton's equation is adopted in the moidified interface model, which could consider the effect of confining pressure on the dilation and strength.On this basis, the centrifuge tests of rough pile are simulated. The mechanism of vertical load transfer of the rough pile is analyzed and the results of numerical simulation are compared with that of the centrifuge tests. It is found that the excavation enhance the dilation of the soil. This leads to an increase of normal stress and shear strength of the interface. Therefore, the capacity and stiffness of rough pile is increased.