Analysis Of Excavation-Induced Additional Responses Of Adjacent On-service Pile Foundations

During the past few years, a large number of researches have been conducted to investigate soil excavation-induced environmental problems. However, in recent years, buiding collapse accidents induced by tunnelling or deep excavation happened again and again. Most often, the reason for these accidents is that some aspects about this problem are not well understood or considered by researchers and engineers, for example, pile-soil load transfer history, interface slip characteristics and coupling effect of longitudinal and lateral deformations of the pile shaft etc. And previous displacement control standards adopted by most unban underground structures lack of theoretical basis and pertinency. In order to overcome these deficiencies, systemic researches are carried out in this dissertation to establish more accurate and applicable methods for predicting soil excavation-induced responses of adjacent on-service pile foundations.Firstly, methods for predicting the free-field soil movement due to tunnelling and deep excavation are further improved. In consideration of the actual features of modern deep excavations, such as great excavation depth, strong support structure and strict control standard of soil displacement etc., a modified "m" method is presented to calculate the deflection of the enclosure structure. This modified "m" method can take into account the development processes of earth pressures within the active and passive regions with the deflection of the enclosure structure. Then by utilizing Sagaseta's solution, an analytical method is proposed to evaluate the diaplacement of the outside soil on the basis of the deflection curve of enclosure structure. Meanwhile, almost 200 analysis conditions are performed to investigate the three-dimentional (3D) deformation of the soil ahead of the tunnel face using the elastoplastic numerical simulation method. The results show that the horizontal intrusive displacement of the tunnel face basically follows Gaussian distribution. The relationship between the maximum dimentionless intrusive displacement of the tunnel face and the stability number is almost unique for different conditions, and it will not be influenced by the embedded depth of the tunnel, excavation diameter and undrained shear strength of the soil. Based on these conclusions, a normalized mode of intrusive displacement of the tunnel face is established and a semi-analytical method is proposed for estimating the equivalent gap parameter due to 3D deformation of the tunnel face. The results of verification examples domenstrate that the proposed methods for predicting the free-field movements induced by soil excavations are reliable.Secondly, analysis methods applicable to passive single piles and pile groups are focused on. According to the mechanical characteristics of passive single piles, an improved nonlinear two stage analysis method (TSAM) is proposed. This improved method can more factually take into account the nonlinear characteristics of the pile-soil interaction, load history of the pile-soil interface and deformation coupling effect of the pile shaft etc. And a MATLAB program is compiled to implement the proposed method. Through a series of parametric studies, it can be found that the influence of the prophase working load on vertical response of the pile shaft in the passive stage is significant. Also, for the passive piles, it is necessary to consider the deformation coupling effect, and the relative error between the results from the decoupled and coupled methods may be up to 25%. Then, in consideration of pile-pile interaction within pile groups, a solving approach is put forward for the shield effect of the pile groups by using the displacement transfer coefficients. Subsequently, the method for passive single piles is successfully extended to those for passive pile groups with and without rigid elevated caps. These methods are then employed to carry out some parametric studies. The calculated results indicate that the shield effect in the vertical direction is evident and must be considered. In contrast, the shield effect in the horizontal direction is not obvious, it can be neglected when the soil is not very soft, and accordingly, the bending moment of the pile shaft beyond the influence range of the pile cap can be calculated by treating it as a single pile.Thirdly, analysis methods for the cases that slip displacement is possible at pile-soil interface are discussed. On the basis of achievements of structure-soil interface tests, modified hyperbolic and damage model, which can rationally consider the cyclic shear behaviour of the interface, are proposed. Subsequently, a "double springs"-"elastic foundation beam" model is established. This model is applicable to any pile-soil interface model. According to this "double springs"-"elastic foundation beam" model, a calculation program which can factually deal with the potential slip effect of the pile-soil interface is developed. The results of case studies show that when the interface strength factor is less than 0.7, the interface slip effect should be considered regardless of whether there is working load on the pile head or not. Also, it is necessary to take into account the shear dilatancy effect of interface. If an elastic-perfect plastic is adopted to substitute the damage model, the relative deviation may exceed 25%.Finally, the elaborate simulation measures and implement methods for the interaction problem between the on-service pile foundations and soil excavations are concentrated on. Existing numerical simulation methods tend to neglect some details of pile-soil interface. Aiming at these deficiencies, an numerical implement method is developed, and the corresponding subprogram is compiled by using FISH language embedded in FLAC3D. This subprogram is applicable to all the interface models. Then, after comprehensively investigating the construction details of shield tunnels, an elaborate simulation method is proposed to simulate the advancing of shield machines. The results of case studies domenstrate that the proposed elaborate simulation method can well consider the depth effect of the confining stress along the pile shaft in sand and be applicable to different analysis conditions.