Model Test Study On Vertical Bearing Behavior Of Red Mudstone Pile Foundation

In recent decades, many tall buildings and super high-rise buildings have emerged, meanwhile, pile foundations are increasingly put into use with it. As a widespread soil, the red mudstone is threaded by the pile foundation projects in different degree with the increase of buildings'upper loads. At present, there are some deficiencies in the study of pile foundation's bearing behavior by considering the red mudstone as foundation, especially the study of pile foundation's vertical load bearing behavior when the defects of Bottom slime and shaft mud cake exist. From the wide view of the pile foundation codes, the defects are not taken into consideration when the ultimate bearing capacity of pile foundation is reduced, leading to a huge security risk in buildings. Based on the existing problem, combined with the similarity theory, laboratory model experiments and field tests were performed to analyze the vertical load bearing behavior of pile foundation, which aims at increasing the economy and the feasibility of pile foundation under the condition of safety. The paper is conducted mainly from the following:(1) A set of device which is suitable for the red mudstone pile foundation model test is designed and processed. In addition, through soil test, an approach to prepare sediment and mud cake in laboratory and simulate the thickness of them is put forward. Moreover, a way to prepare the improved soil of cement with different blend ratios is obtained, and through comparison and analysis, the blend ratio of 4%,6% and 10% with the improved soil of cement are adopted to simulate the whole-weathered, intense-weathered and moderate-weathered red mudstones.(2) On the basis of applying improved soil of cement to simulate the red mudstone foundation in different weathering degrees, methods such as the similarity calculation and model test are employed, thus, the ultimate bearing capacity of different weathered red mudstone pile foundation are acquired.(3) Through the model test for pile foundation contained sediment, the influence of sediment thickness on pile foundation's vertical bearing behavior is analyzed. And the result indicates that the ultimate bearing capacity of the pile foundation decreases with the increase of the sediment thickness, and the settlement of pile top increases with it, leading to the pricking destruction of pile body.(4) According to the model test, the effects of mud cake's thickness on pile foundation bearing behavior is researched. And the result shows that the thicker the mud cake is, the lower the ultimate bearing capacity is, while when the thickness of mud cake exceeds a certain value, the constraint in soil around the mud cake to the interface between the pile and the mud cake is not the leading role, and the interaction between the pile soil mainly depends on the strength of the mud cake itself.(5) Based on the above results, the factor'a'and the factor '?' to revise the ultimate bearing capacity by thickness of sediment and thickness of mud cake, respectively, are presented. Moreover, the bearing capacity calculation formula of the pile foundation in specification is revised, and the rationality of the revised formula for calculating the ultimate bearing capacity is verified by engineering examples, which makes the design of pile foundation more safe and reasonable.