Study On Anti-sliding Mechanism Of Micro-pile Structure

Micro-pile is a type of small diameter bored pile constructed by strong reinforcement and pressure grouting, of which the diameter is between 70 and 300mm,slenderness ratio is larger than 30. In recent years, as a new type of slope supporting structure, micro-pile has a more and more wide application in slope reinforcing engineering. Furthermore, good engineering and economic effects have been produced by using micro-pile structures. However, little theoretical studies have been done on the anti-sliding mechanism of micro-pile under lateral loads. In view of the research situation at home and abroad, it is an urgent task to start researches on design theory of micro-pile.In this paper, based on all kinds of micro-pile structure applied in domestic projects, micro-pile structures can be classified into four types: independently distributed micro-piles, plane frame micro-pile structure, space frame micro-pile structure and micro-pile composite structure. The main contents of this thesis focus on studies of design and calculation theories of micro-pile structures. First of all, anti-sliding mechanism of independently distributed micro-pile system and plane frame micro-pile structure for reinforcing bedrock slope is studied. Then the design theory and anti-sliding mechanism of micro-pile composite structure are analyzed. Finally, a project case is designed on the basis of theories discussed in this paper. By deep studies in this thesis, following conclusions are drawn:(1) Beginning with analyzing the calculation methods of shear ability,two methods are presented,by one of which only steel shear ability is taken into account and by the other of which the interaction of pile and joint surface is taken into account.Mechanical model is built to analyze the shear ability by taking into account interaction of pile and joint surface. Method is introduced to determine the potential sliding range of bedrock slope and calculate landslide thrust. slope stability coefficient after reinforced by micro-piles is analyzed and design flow chart of independently distributed micro-piles system is provided. (2) Calculation model is established to study the anti-sliding mechanism of plane frame micro-pile structures, the result of which shows that the plane frame micro-pile structure can increase the anti-sliding force of partial unstable rock-mass, but the total ani-sliding force won't increase.(3) Displacement analysis model is built to analyze the displacement of pile top for independently distributed micro-pile system and plane frame micro-pile structure respectively. It can be deduced that plane frame micro-pile structure is better for decreasing slope displacement, controlling generation and development of fracture in rock-mass between two piles, and has more positive effect on slope stability.(4) Focusing on micro-pile composite structure commonly used in practice and taking 3×3 pile group as an example, calculation models are built to analyze the internal force and stability of two kinds of structure: micro-pile group without bolt and micro-pile group with bolt. In addition, pile-soil interaction model is established on the basis of Winkler elastic foundation theory.(5) Combined with the typical slope in a highway, micro-pile composite structure is designed on the basis of theoretical analysis. And the internal force deduced by the calculation theories given in this paper is compared with the monitoring results of the small scale model test.