Theoretical And Experimental Research On The Negative Skin Friction Of Plastic Sleeve Pile

Negative skin friction is one of the common problems in civil engineering design and construction. Setting a prefabricated plastic sleeve on the surface of piles is a method of decreasing the negative skin friction of piles. This dissertation has mainly studied the properties of negative friction on these piles covered by prefabricated plastic sleeve. The study was conducted in three methods: laboratory tests, theoretical analysis, finite element analysis, and research efforts and achievements are as follows:(1) With improved direct shear apparatus, direct shear tests on shear properties of interface of plastic materials and sand were carried out. Considering the change law when categories of plastic and the particle size of sand vary, shear tests on sand-four categories of plastic materials(PVC、ABS、PC and PP) and sand-concrete were conducted. The results show that shear strength of these four categories of plastic materials-sand contact interface was significantly less than that of concrete-sand, the shear strengths of PP-sand contact interface is the lowest. That’s to say, the bigger the particle size of sand is, the higher the shear strength is.(2) Based on the effective stress method, the formula used to calculate the neutral point of piles with plastic sleeve was derived in this paper. The change law of the neutral point of piles under the vertical load were carried out. Without taking pile top load into consideration, the neutral point of normal pile is located at a distance of 0.707 times of pile length from the top, while neutral point location of pile with plastic sleeve is at the place of 1(1?K)?0 ?K ?1? times from pile top.(3) In addition, upon load transfer analysis method, this dissertation constructed a mechanical model which puts both vertical load on pile top and surface load into consideration, and derived two formulas that respectively describe two kinds of relationship: negative skin friction of pile with plastic sleeve-displacement relationship and the nonlinear pile-soil load transfer relationship.(4) In this dissertation, the large commercial finite element analysis software was applied to building a two-dimensional numerical model to simulate the properties of negative friction of piles with plastic sleeve and normal piles. Under the respective function of surface load and vertical load on pile top, the laws of negative skin friction’s distribution, pile-soil relative displacement, and the location of neutral point changing with pile settlement were analyzed. What’s more, a comparison was made between the analyzed results to pile with plastic sleeve and normal pile, and it presented that piles with plastic sleeve are more effective on optimizing negative skin friction.