Study On Compacting Effects Of Displacement Pile

Displacement pile is widely used in both saturated and un-saturated soils. However, the compacting effects caused by it may have severe influence on surrounding environment which would result to the cracking of neighborhood buildings, the upheaving of roads, the rupture of underground canals and so forth. It is always a difficult problem which puzzles engineers and researchers. So the study on the compacting effects of displacement pile and the measurements which can decrease it will be very meaningful to practice. This paper, firstly, analyzing and summarizing the work has been done by far on this point, and then, on the basis of that, further works which rank as follows have been done.Firstly, on the basis of the theory of spherical cavity expansion and large-strain presupposition, combining with the Modified Cambridge Model and the theory of Water Power Cracking and following the Least Consumption Principle to go from the viewpoint of energy, the analytical expressions of the stress, displacement, excess pore water pressure are deduced after the expansion of sphere cavity in the whole field of soil around the pile, which comprises the elastic zone, plastic zone and failure zone. Moreover, the effect of soil's overconsolidation ratio on the result is analyzed.Secondly, comparing the Terzagi's consolidation theory with the Biot's consolidation theory, on the basis of elastic deformation presupposition and the forgoing result, combing with the Biot's consolidation theory, the changing of the stress, displacement, excess pore water pressure in the ideal elastic-plastic soil around the pile in the course of consolidation are analyzed.Thirdly, considering the transformation of soil's volume, the analytical expression of the stress's and displacement's distributing in unsaturated soil after the expansion ofsemi-sphere cavity are deduced on the basis of the cavity expansion theory combining with the Modified Cambridge Model;and the effect of soil's overconsolidation ratio on the result is analyzed.Fourthly, on the basis of forgoing analysis, suppose in the course of expansion of semi-sphere cavity in the unsaturated soil, the expansion velocity of the elastic-plastic boundary comprises two part, and through introduce the concept of plastic wave, the velocity of displacement of the elastic-plastic boundary is induced in the paper, as well as the ratio of displacement's velocity of any point in plastic zone to that of elastic-plastic boundary. Moreover, on the presupposition of small strain and even speed of expansion, the analytical expressions of the radius of plastic zone, failure zone and the stress, displacement of any point in the soil around the pile are deduced after the sphere expansion.Fifthly, some construction measurements that are used to decrease the compacting effect are introduced, and the validity of a measurement namely prebored hole has been analyzed on the basis of forgoing theories.Finally, the shortages of the induced theories in the paper are pointed out, and some advices for the farther research are suggested.