Displacement And Pore Pressure Due To Pile Driving In Soft Clay

Piles are now widely used in civil engineering, especially in soft clay foundation, because they have various advantages. However, for the displacement piles, when they are installed into the ground, the same volume of soil will be displaced, and the pore pressures will be developed around the piles. That will result in the influence on the surrounding soil and nearby structures. Many researchers studied the problem, but they did not get completely satisfied results up to now for the complication of the problem.On the basis of the work available, the author has further studied the problem of the soil squeezing effect with new approaches. The main work includes:Firstly, based on the results of on-the-spot survey and experiment, the author find that lateral pressure and pore pressure caused by installation of pile in soft foundation changes along with depth, so the question for discussion of the effect of soil squeezing during driving-pile should be regarded as a three-dimensional question but not a plane one. In addition, soft clay can be cemented naturally and behave special properties of mechanics, particularly the stress-strain relationship shows stain-softening after yielding, so the author makes the improvement by considering the influence of soil structural strength on analyzing the soil stress and pore water pressure by pile-driving in soft foundation.Secondly, based on the fundamental principles of soil plastic mechanics, the three-dimensional analytical solutions of the stress and the eventual expansion force in the expansion of cylindrical cavity are deduced taking the soil structural damage into account. The distributions of the stress and the lateral frictional force with the vertical coordinate are considered in the newly- developed model. So the shortcoming of the classical cylindrical cavity expansion theory can be overcome. And the mechanism of soil squeezing during driving- pile will be revealed more clearly.Thirdly, based on the solutions of the stress have been deduced previously, and adopting the Henkel's formula, the three-dimensional analytical solutions of the pore water pressure are gained. The relationships between pore water pressure and coefficient of soil structural strength damage and depth are also presented.Finally, for the study of effect of soil squeezing in pile group in soft soil foundation, the engineering practice of monitoring the process of pile-driving is presented. The influences of pile driving in clay are analyzed, with emphasis on the excess pore pressure and the lateral displacement, and a new method for calculation ofthe lateral displacement of soil in pile group during driving piles is given. The main measures against soil squeezing during pile driving are summarized. It is shown that the adoption of holes to relax stress is an effective one.