Study On The Factors Of Foundation Static Load Test

In geotechnical engineering practice, the method of determining bearing capacity of foundation is a very important in foundation design, it’s also a divergent problem in soil mechanics. The shallow plate loading test is the situ test method to determinate the bearing capacity and deformation characteristics of foundation, which has the outstanding advantages of intuition, accuracy, reliance, therefore it has been widely used in the foundation investigation. But in the practice, there are so many factors that shallow tablet static load test can’t accurately reflect the bearing capacity of foundation.In this paper, the elastic theory method and finite difference method was, respectively, used to qualitatively and quantitatively analyze the effects of side effect of counterforce device, relative displacement of point, additional stress and the size effect of the bearing plate on the test process and the result in the shallow tablet static load test.On the basis of elastic theory analysis, no matter accumulation load method or ground anchor method is used in static load test, when the distance of ground anchor or heap load platform, bearing plate and reference points less than a certain value, and the foundation soil as a medium can pass three interactions, it will have a larger difference between the field test result and the actual real situation. The vertical additional stress caused by the heap load will produce a preloading pressure before loading on the foundation soil, which is equivalent to the additional load applied to the bearing plate in the loading process. The level additional stress caused by heap load applies the relatively confining pressure on the soil under the bearing plate, which improve the bearing capacity of the foundation.On the basis of theoretical studies, the finite difference software FLAC3D is used to carry out numerical simulation analysis on the plate loading test, and the results showed that, the displacement of datum point and the additional stress caused by preloading would make the characteristic value of foundation bearing capacity, which was obtained from the load-displacement curve, become overestimated. So the bearing capacity of foundation got from piling-up weights method of shallow plate load test is actually large than its real value.The size effect of the bearing plate exists in the static load test of natural foundation and composite foundation. In the static load test of foundation, the displacement of bearing plate increases with the increasing in the size of the bearing plate; relative displacement ratio curve influenced by the soil cohesive force shows a different variation, and compared with sand layer with cohesion of zero and cohesive soil layer and clay layer with larger cohesion, relative displacement ratio variation is opposite, with the increasing in size of the bearing plate, and the cohesive soil layer with smaller cohesion is in the transition region. In static load test of composite foundation, with the increasing in the size of the bearing plate, the displacement of bearing plate augments, and the relative displacement ratio has a declined trend on the whole.