Pile Grouting Mechanism And Engineering Applications

Post-grouting is an effective construction technology to improve bearing capacity of cast-in-place piles. Based on the summarization and analysis for the application research status of the post-grouting technology, and the engineering test results in Changzhou-Shanghai segment and the Lancun station of Shanghai Metro, which is part of the high-speed railway in Beijing-Shanghai, the mechanism, the grouting material, the grouting pressure prediction, the construction technology and the improvement effect have been studied by synthesizing theory study, laboratory tests and the field tests. The research works and conclusions are mainly summarized as follows:(1) According to research on grouting material and formulating methods, and study on the physical and mechanical properties of soil pre-and-post grouting through in door experiments. Some important conclusions were obtained about formulating methods of grouting material and soil's physical and mechanical properties have been improved obviously.(2) Based on the theory of compression mechanism to analysis the cavity expansion, according to the unite failure criterion, the stress-strain-volume change relationships, energy conservation equations, the rules of large strain and non-associated flow under high stresses, the volume change of cavity expansion is balanced with the compression of soil and the energy given out from cavity expansion is absorbed by the volume change and shear strain caused in soil. The limit pressure of cavity expansion is given with the large strain, dilation and shear module. The developed theory is agreed with the results of field tests by comparing and analyzing.(3) By using the theory of cavity expansion, hydro-fracture and pore water pressure theory, on the assumption that the sum of initialization stress of soil and increment due to cavity expansion is equal to the pull strength of soil, the soil is fractured by grouting. If the major and minor principal stress of soil is conversion, the second fracture grouting takes place. Based on the theory above, the fracture grouting pressure formula in saturated soil was given. The results from the proposed formula is very close to those of the practical engineering, and the availability of this formula was validated.(4) The effection of various factors on the bearing capacity of cast-in-place piles improved by post-grouting technology had been analysed, and construction technology and construction control points about post-grouting were summarized.(5) The conclusions deduced from the theory study in this thesis was performed to design the grouting scheme of cust-in-place piles of practical engineering. The field tests data from bearing capacity of grouted pile and un-grouted pile showed that the bearing capacity of grouted pile was increase 40%.