Study On Evaluation Of Bearing Capacity Of Large-Diameter Cast-in-Place Pile Foundations Embedded In Rock With Defective Piles

The pile foundations are an important part of high-piled wharf. The application of large-diameter cast-in-place pile embedded in rock is more and more widely in inland terminal depot. Research on bearing capacity of the pile foundations embedded in rock has been more deep-going and mature. There are two main factors affecting the bearing capacity of pile foundations: One is the strength of the foundation soil; and the other is the structural strength of the pile body. When researching the bearing capacity of pile foundations, people mainly consider the former factor and ignore the latter. Defective pile is very common in pile foundations construction of port engineering, including broken pile, stem enlargement pile, stem shrinkage pile, pile with mudcake and pile with bottom sediment, etc. The present study for the pile foundations embedded in rock with defect is mainly focused on the bearing characteristics with little efforts made on the qualitative and quantitative research of bearing capacity. Under this premise, the author aims at the two kinds of common pile defects of cast-in-place pile embedded in rock underwater concrete pouring process of port engineering. It analyzes and studies the variation, prediction and evaluation of bearing capacity of broken pile and stem shrinkage pile of rock socketed.The author establishes the finite element analysis model of the normal pile foundations embedded in rock by using the finite element analysis software ABAQUS. By modifying the model, it simulates the defects with the broken pile and stem shrinkage pile of the pile foundations embedded in rock. Through this analysis model, it calculates the ultimate bearing capacity of the pile foundations embedded in rock with different defect forms, different defect size and different defect depth. Comparing the calculation results with the bearing capacity of the normal pile foundations embedded in rock, it concludes the effect proportion of various factors on the bearing capacity of pile foundation. As a result, it can analyze and discuss the variation of the bearing capacity of the pile foundations embedded in rock with defects. The results show that for the corner pile and the center pile of the pile foundations embedded in rock with broken defect, the ultimate bearing capacity respectively accounts for 79% and 83% of that of the normal pile foundations embedded in rock. For the corner pile and the center pile of the pile foundations embedded in rock with stem shrinkage defect, the ultimate bearing capacity accounts for 97%-98% of that of the normal pile foundations embedded in rock. When the location of defects is in the upper half segment of pile segment embedded in rock(namely the upper segment of middle position of defect pile), the effect of changes in the defect position for the bearing capacity of the pile foundations embedded in rock is more obvious. On the contrary, it is not so obvious. In addition, the ultimate bearing capacity of the pile foundations embedded in rock is not always in proportion to depth. But it is a peak, due to the pile group effect and the existence of cushion cap of the pile foundations embedded in rock.Based on the grey system theory, combining with the results of finite element analysis, grey correlation analysis is made on the factors of defect depth and defect size that influence the bearing capacity of pile with defect. Furthermore it deduces the number representation of the magnitude of this relevance, namely the grey correlation degree, which lays the foundation for the establishment of bearing capacity prediction model of the pile foundations embedded in rock with defects based on the grey theory. The results show that by the grey model GM(1,1), the method of grey system theory can predict and evaluate the bearing capacity of the pile foundations embedded in rock with defects under the accurate conditions.