A Research On The Post-grouting Pile Field Test And The Slurry Diffusion Mechanism

Considering of construction technology, traditional bored pile may produce hole collapse, thick bottom sediment, mud pile skin, hole stress release and so on. Based on a great deal of practices, post-grouting technology of bored piles is an advanced construction technique developed to solve these defects. Therefore, the research on the diffusion theory of post-grouting bored piles has very important engineering significance and practical value.This thesis bases on the test of post-grouting bored pile static load in Henan Coal Chemical Group Science and Technology Research Center. The law of the diffusion of the slurry is explored by the analysis of this test. According to the basic principles of geotechnical plastic mechanics and elastic mechanics, the soil is assumed to be homogeneous isotropic elastic-perfectly plastic body. On the basis of the research on the law of the diffusion of the slurry in the post-grouting bored pile, the analytical solution of the cylindrical cavity expansion can be derived by the introduction of the concept of effective stress ratio and the Mohr-Coulomb yield criterion considering the compaction grouting pressure filtration, including the plastic zone size of the surrounding soil and limit grouting pressure after the cylindrical cavity expansion. And then the fracture grouting formula of the various types slurry is calculated and analyzed according to the tablet slit model. Finally, influence factors of the climb height in fracturing grouting are analyzed based on the axial annulus model.In this paper the main achievements are as follows:(1) The test results show that the post-grouting of cast-in-situ pile can be used to improve the bearing capacity of pile and decrease the pile top subsidence. The shaft resistance of post-grouting cast-in-place pile is about1.8～2.7times that of cast-in-place pile at the test site. Whether the nearby anchorage of the pile in the site has been grouted or not has little effect on the pile bearing capacity.(2) The theory equation of cavity expansion theory of compaction grouting was derived by introducing an effective ratio. In this theory equation, the pressure filtration can be taken into account. Furthermore, the plastic scope and ultimate grouting pressure were derived under a certain radius at various effective stress ratios. It shows that the more dilute slurry, that is to say the smaller the effective stress ratio is, the greater impaction various parameters have on the ratio between limit grouting pressure, plastic radius and limit radius.(3) Based on the assumption of narrow plate model, the formulas were deduced for calculating the penetration radius, gap height and grouting pressure difference in Newtonian fluid, Bingham fluid and power law fluid during fracturing grouting process. Taking power law fluid as an example, it shows that the ultimate grouting pressure gets smaller and the penetration radius increases with the increasing of water cement ratio of grout and gap width.(4) Based on the assumption of axial annulus model, this thesis takes power law fluid as an example to deduce the formulas for calculating the climb height during the post-grouting. It shows that the climb height increases with the increasing of water cement ratio of grout, grouting pressure and gap width.