Studies Of Stress-strain And Instability Mechanism For Horizontal Directional Borehole

From the analysis of regulation of stress-strian of surrounding rock of deeply horizontal directional borehole, regarding the surrounding rock of borehole as perfect elastic surrounding rock, Burger linear viscoelastic surrounding rock and perfect elastoplastic surrounding rock to deduce its analytical solution of borehole's stress-strain. Analyse the regulation of borehole's stress-strain and displacement according to analytical solution, take the hackneyed physical mechanics parameter of soil to calculate and analyse the borehole's stress-strain and displacement; Systematically studied two great factors, i.e. geological factors and engineering factors about the stability of boreholehole, analyzed the stability condition of borehole and the instability mechanism of borehole, got the calculation formula of superior drilling liquid pressure, obtained some important ways and countermeasures to maintain stability of boreholehole; Vie the numerical simulation of the finite difference software (FLAC-2D), analyzed the radial displacement of borehole boundary, the surface settlement of borehole, the principla stress difference of surrounding rock of borehole, the biggest shear strain of surrounding rock of borehole, and the district of elastic-plastic distribute of surrounding rock of borehole for shallow borehole and deep borehole at water pressure and mud pressure, compared the results of the simulation solution and analytical solution, analyzed the influence of regulation of shear strenth index, ie. cohesion and angle of friction to stability of borehole.Through the research analysis, this paper mainly has following conclusion:(1) The main factors of stability for Horizontal directional borehole are the following: the pressure of ground floor, the property of surrounding rock of borehole, the dynamic load on the ground, the activity of groundwater, the diameter of borehole, the laying depth of borehole, the length of borehole, the activity of drilling tool, the erosion corrosion and vibration of borehole, the density of drilling liquid, the viscosity of drilling liquid, the water compatibility and filter loss performance of drilling liquid, and the time of drilling and so on. The form of deformation and instability of surrounding rock of borehole mainly has plasticity-extrusion, expansion-inside belly, and plastic flow-gush and so on different type.(2) Regardless of the surrounding rock of borehole as the perfect elastic surrounding rock, Burger linear viscoelastic surrounding rock or perfect elastoplastic surrounding rock, regardless of borehole in shallow state or deep state, the larger diameter of borehloe, the greater radial displacement of borehole and of reducing diameter, the larger pressure of drilling liquid, the smaller radial displacement of borehole and rate of reducing diameter; Horizontal directional borehole must take into account the property of the creep of surrounding rock, the longer time of nude borehole, the greater radial displacement of borehole and of reducing diameter; Rational configuration the density of drilling liquid, could make the radial displacement of borehole to reach the minimum, and the borehole will not appear the phenomenon of reducing diameter.(3) The nearer of distance between soil and hole wall, the greater of the principla stress difference and the biggest shear strain of surrounding rock of borehole. When the surrounding rock of borehole is perfect elastoplastic surrounding rock, the plastic radius of borehole of side greater than the vertical, the shear failure of borehole begin from the side.(4) Increases with the shear strenth index, ie. cohesion and angle of friction of surrounding rock, the radial displacement, the principla stress difference, the biggest shear strain of surrounding rock of borehole become smaller. And the same condition, the angle of friction of surrounding rock has greater effect than cohesion of surrounding rock.