Research On Calculation Method Of Earth Pressure On Row Pile Retaining Structure Of Round Deep Foundation Pit In Sand-Cobble Soils

In recent years, the engineering of round deep foundation pits gradually appeared in Chengdu. The stratums of that area are almost sand-cobble soils, and the structure type widely used in engineering is row pile retaining structure. But the traditional design methods of row pile retaining structure mostly cannot consider common deformation effect in space between retaining structure and soils, so that results have a big difference with actual. Therefore, the article base on the earth pressure on the rear of row pile retaining structure of round deep foundation pit which is in sand-cobble soils, and put forward the calculation method of earth pressure which consider the interaction between soils and retaining structure. The principal research results are as follows:1) Utilizing differential limit equilibrium method to analyze the sliding mass around round deep foundation pit, and deduce the approximate theoretical formula of earth pressure on the rear of piles which consider strength parameters on the interface between piles and soils. Approximate theoretical method obtain the earth pressure distribution on the rear of piles, and the results show that earth pressure is in non-linear distribution which increases or decreases sharply on the interface of different soils. Comparing with theoretical calculations and Rankine earth pressure results, it is apparently that their distribution are approximately similar to each other, and Rankine results exceed about ten percent in average.2) Applying the method of approximate theory to analyze the factors of earth pressure. The results show that the earth pressure on the rear of piles increase linearly with the depth of pit and the self-weight of soil, and decrease non-linearly with the angle of internal friction of soil, and also decrease linearly with the cohesive strength of soil. The earth pressure decrease linearly with the angle of external friction angle and cohesive strength on the interface between piles and soils too.3) The laboratory model tests are carried out to analyze the row pile retaining structure of round deep foundation pit in sand-cobble soils. The tests can get the distribution law of earth pressure on the rear of row piles by stick miniature pressure cell on model piles. Results show that earth pressure on piles increases non-linear with the depth of pit. Comparing with experimental results and theoretical calculations, it is apparently that their distributions are approximately similar to each other. The theoretical value exceed the test results about twenty four percent in average.4) Using the method of three-dimensional finite difference to analyze the excavation and support process of round deep foundation pit in sand-cobble soils, the earth pressure distribution on the rear of piles is obtained. The results show that the distribution of earth pressure on a pile is approximately triangular. Comparing with numerical results and theoretical calculations, it is apparently that their distributions are approximately similar to each other. The deviation is between twenty percent and thirty percent.5) The excavation and support process of different pit diameter are contrasted by numerical simulation to analyze the impact law of soil arching with earth pressure on the rear of piles. The results show that soil arching space of round deep foundation pit is mainly affected by the pit depth to radius ratio. When the pit depth is certain, arching space will be increasingly apparent with the decrease of radius. The resultant of earth pressure on the rear of pile has the feature of nonlinear reduce.The research of this article can provide guidance and reference for the design calculations of the earth pressure on the rear of row pile retaining structure of round deep foundation pit, and contribute to a comprehensive understanding of the characteristics of such deep foundation pit engineering.