Experimental Study On Bearing Properties Of Large-diameter Rock-Socketed Pile With Steel Casing In Deep-water Wharf

In recent years, with the Three Gorges Reservoir built up, the density of shipping increases and the enterprise of inland river navigation is steady development. So large-diameter rock-socketed pile with steel casing is widely applied to the pile foundation of inland river deep-water wharf. But at this moment the mechanical behavior of large diameter steel casing rock-socketed pile is relatively scarce. It combines with the "twelfth five-year plan" of the National Science&Technology Pillar Program of China about "the key technology research of maritime project construction of permanent backwater region of the Three Gorge"(2012BAB05B04), bases on indoor physical model test and numerical simulation test, considers different rock-socketed depth conditions and whether the steel casing is on pile, researches the action of mechanical characteristics of vertical and horizontal force on pile foundation. The main work and achievements of this paper include the following aspects:(1) The selections of text method、model scale and model material. According to actual sizes of large-diameter rock-socketed pile with steel casing and the indoor model condition, choosing model scale as20, and material strength as1, which is1/20of prototype piles, and choose material parameters of the prototype piles to do the model. Based on geological conditions in Chongqing port area, we use different mix proportion to simulate material of pile body and mudstone foundation. For confirming the mix proportion of concrete, we do some research about model test cube of standard size, also about strength and deformation parameters. According to the calibration test we make clear the relation between date collecting by sensor and the real one, and do some text about the data acquisition system of physical model test.(2) Physical model test of rock-socketed pile with steel casing in vertical load. In accordance with the similar theory of physical model test,6piles which have different socketed depths were tested vertical bearing properties. Some of them have steel casing and the others have no. In the test, it’s found that how the vertical displacement of the pile top change as the load and how the side resistance and the end resistance of the pile generate as the load vertical. It’s analyzed that whether setting steel casing and different socketed depths have influence on pile foundation’s vertical bearing rule. The pile with steel casing has deeper position when its side resistance reaches the peak than the normal pile. Beside that, rock-socketed pile with steel casing has bigger peak value.Compared with the common ock-socketed pile, the side resistance of pile foundation decreased. That is, tip resitance of ock-socketed pile with steel casing could play a role easier. The result of comparing two kinds of pile foundation under the same socket length is that setting up steel casing has an npparent influence on vertical bearing capacity; no matter rock-socketed pile with steel casing or common rock-socketed pile, the rock-socketed depth of pile body has significant mpact on bearing capacity. As the rock-socketed depth of pile body increased from3D to5D, the vertical untimate bearing capacity of rock-socketed pile with steel casing improved ibout40%. Meanwhile, with the increase of rock-socket length of pile body, the tip sistance’s proportion in the total bearing capacity is decreasing, while the colateral sistance’s is adding.(3) The model test of rock-socketed pile with steel casing’s horizontal properties. Model pile is the same as model test’s behavior of vertical bearing. With horizontal load on the pile:op, it monitors the change law of horizontal displacement when horizontal force changes and the distribution law of pile, based on this research we can analysis the horizontal compressive intensity rule when the pile has steel casing or not an different rock-socketed lengths. The flexural behavior of rock-socketed pile with steel casing is greatly improved when it is under horizontal load. It means that horizontal bearing capacity of rock-socketed pile with steel:asing is better than common pile. At the same time, the horizontal displacement of pile’s top and rock surface of pile’s is small. The maximum value of pile’s moment has a corresponding site which is lower than common rock-socketed pile’s. Under lateral load, the rock-socketed length is bigger, the horizontal displacement of pile’s top and rock surface of pile’s is smaller and the bearing capacity is better too.(4) Base on the test parameters of physical model with the finite element software well apply, we do numerical modeling about rock-socketed pile with steel casing using"Abaqus" the finite element software,using The contact element to simulate the steel-concrete and concrete-rock interface mechanical properties. We find that the numerical simulation fits the laboratory test results well and able reflect the working properties of rock-socketed pile and rock-socketed pile with steel casing. It’s a effective methods of analysis when refer to the research of load-bearing characteristics of rock-socketed pile with steel casing.