Comparison Of Model Test And In-situ Test For Self-balanced Pile Load Test

The self-balanced method has been applied and developed widely at domestic and abroad as a new technology of Detecting Piles. Compared with traditional pile test method, this method is time and labor saving, small occupation area and not subject to test site constraints. The test method at home and abroad has been applied in these main researches:(1)The difference of pile side friction between self-balanced upper pile and traditional static pressure pile and uplift pile. (2)balance position determination and the continue using problem of test pile after self-balanced test. However, the property of rock and soil is complex. Theoretical and practical problems still exist in the self-balanced test.Research methods include theoretical analysis, numerical simulation and field test. A lot of valuable research results have been obtained. This paper adopts the granite residual soil as the experiment soil to conduct the comparative model test of ultimate bearing capacity and load transfer of self-balanced and traditional test pile. Piles strains of different embedded depth can be obtained by pasting resistance gauge at lateral pile groove. The transfer regularity of pile side friction and pile axial force of self-balanced and traditional test pile has been gained under the same boundary conditions. The model tests also reveal load transfer regularity and relationship of positive and negative friction of them. Besides, field test has been conducted combining substantial project. This article achieved the following main conclusions:(1)Due to the difference of loading methods, the load of upper support pile transfer from bottom to top. However, condition of uplift pile load is reversed. Moreover, the load transferring speed rate of upper support pile is smaller than the uplift pile.(2)The pile side friction of upper support pile and uplift pile is different with depth. Because of local force enhancement effect, the pile side friction of upper support pile beard major part of load. However, the pile side friction of uplift pile distributed evenly. so as the load increases, the effect of uplift pile lower soil layer has a better performance than upper support pile upper soil layer.(3)The correction coefficient of positive and negative friction ranges from 0.5 to 0.6 in completely decomposed granite.(4)Before the load reaches limit, the pile around loading position experience radial expansion because of loading pressure. Simultaneously, the soil displacement occurs and soil arching forms along with the pile position changing. Under the function of covering load, the soil arching effect leads to the increment of lateral pile radial stress, the pile side friction increase at the same time.(5) Using the relative coefficient of sand and gravels to conduct experimental designing is portable at completely decomposed granite soil and strong weathered layer.