Research On Stress Distribution Of Columnar Jointed Basalt Anchored By Pressure Diffusion Anchor Cable

Pressure diffusion anchor cable can disperse the anchoring force to rock of different depth. So the concentrated force is divided into several small force that on several short anchored segments. Then each anchored segment will have the same properties with pressure-type cable and the strength of the whole rock-soil mass will be made full use of. It is an important technical measure in geotechnical engineering. Previous study results show that researches of the pressure diffusion anchor cable focus on two aspects. One is the stress distribution of grouting body, and the other is the stress distribution of the contact surface between grouting body and surrounding rock. But there are few researches on the stress distribution of different parts of the surrounding rock.This paper is based on the reinforcing project of left-bank underground powerhouse of Baihetan Hydropower Station. By making theoretical summary as basis, engineering application as dependence, physical simulation as main method and numerical simulation as secondary method, the stress distribution of columnar jointed basalt that anchored by pressure diffusion anchor cable is studied. Conclusions are conducted in the end, which may be a reference for engineering practice.On the basis of a large number of references, research methods of pressure diffusion anchor cable are classified into three types: theoretical analysis method, experimental analysis method(including field test and indoor model experimentation) and numerical simulation method. According to the actual engineering and the aim of this study, indoor model experimentation is chosen as the major method and numerical simulation as secondary method in this paper. Starting from the geological condition investigations of left-bank underground powerhouse of Baihetan Hydropower Station, especially engineering-geological characteristics of the columnar jointed basalt, field test of pressure diffusion anchor cable is carried on. The results show that both of the tensioning measures(cyclic loading by grouping-and-grading and integral loading by grading) are workable.The first step is to develop similar material. The ratio of similitude is determined according to similarity theory. By using cement, water, quartz sand, barite powder and iron powder as raw material, orthogonal tests are conducted to develop similar material of basalt. Effects of different proportions are analyzed from unit weight, compressive strength, elasticity modulus and Poisson's ratio. Finally the expected material ratio for this physical simulation test is found out.Before the model is built, resistance strain gauges are pasted on each block to monitor the strain. The wire is used to simulate cable, circular iron plate is used to simulate loading plate, and increasing the number of standard weights to simulate loading surcharge. According to the actual engineering, two methods that are cyclic loading by grouping-and-grading and integral loading by grading are applied to the test. Data acquisition machine records the strain of each block in different stages. The strain distribution and variation rules are analyzed according to the experiment results. And some valuable conclusions are obtained that can provide reference for the optimization design of pressure diffusion anchor cable.In the end, FLAC 3D is applied to study the single anchor cable, including axial stress distributions in anchorage zones, axial stress distributions in grouting, shear stress distributions between grouting and surrounding rock and stress distributions on free face. Then Phase 2 is applied to study the reinforcement effect according to displacement, maximum principal stress and minimum principal stress of typical section of the underground powerhouse.