The Research On Characteristics Of Tunnel Excavation Built In Accumulation Slope

With the further development of mountain transportation construction in Western China,the highway tunnels have to constructed in loose accumulation inevitably which is distribute in the surface of the mountain slope.Since the loose accumulation accompany with negative geotechnical characteristics like loose structure,strong sensitivity to disturbance and mountain bias,problems like sprayed layer cracking,secondary lining intrude limit and deformation of accumulation slope often appear in the tunnel excavation and tunnel operators process,thus the safety of tunnel construction and operations is threaded by problems above.Undoubtedly,a direct link between deformation of accumulation slope and negative loading on tunnel support structure is exist.Current study on response characteristics of accumulation slope deformation which caused by tunnel excavation is fewer.This paper relies on research project of Department of Transportation in Hunan Provincial focusing on “Research on supporting structure crack mechanism and control technology of tunnel considering the slope deformation of loose accumulation”,and selected a title " The research on characteristics of tunnel excavation in slope of accumulation" as the research object.Methods like case study analysis,theoretical analysis,field testing and numerical simulation is combined to probe the response characteristics and variation between slope deformation and tunnel excavation in the slope of loose accumulation,engineering safety evaluation of slope pre-reinforcement structure,control methods for tunnel deformation and several other issues.(1)The formation reasons and unstable causes of accumulation slope can be qualitative analyzed by formed tears,space form,spatial structure and spatial evolution process.The origin survey and engineering comparison methods defined that internal power source of geotechnical self-gravity and outer power source of rainwater infiltration lead to the formation of slope.In the long-term accumulation process,being pushed process of accumulation from trailing edge to leading edge and compressive consolidation from outside to the inside are throughout the entire process.The interface of rock and overlying accumulation is found during the excavation process,but the indications of sliding and cross-cutting sliding structure surface don’t exist.Sliding in study area was occurred in 1950,so the slope is in the process of steady state.Under the control of the remaining forces,the potential instability mode is interface mode with circular slip sliding mode and interface sliding under the control of the remaining forces,so slope stability is mainly controlled interface of rock and overlying accumulation,rock similar plane and potential shear fracture plane.(2)Tunnel-slope collaborative deformation need to hold the identification of potential damage accumulation slope type and structure of a possible landslide,thus relationship between accumulation slope deformation and tunnel construction process can be recognized accurately.On the basis of referring to the relevant norms and engineering cases,a displacement monitoring system consists of GPS wireless machine,surface fixed point and deep inclinometer hole is built to do uninterrupted monitoring on accumulation slope from shallow and deep displacement.Meanwhile,mechanical characteristics of tunnel support structure and prereinforced piles is got by reinforced stress meters.Methods above can effective tracking the slope deformation and force variation of supporting structure for the effectively.(3)The main factors of accumulation slope deformation is the disturbance in deep geotechnical structures which is leaded by tunnel excavating,and the deformation has cyclical changes with the constructed order of tunnel:Tunneling→Rock loosening(Landslides and roof collapse is appear)→Trailed traction slip of slope(Stress on lining structure is increases)→Tunnel cracking(Stress loaded on liner structure is release)→ Tunnel reinforcement →Continuing creep slip of slope(Lining stress agglomeration)→ tunnel cracking(Stress loaded on liner structure is release).Slope surface deformation is lags behind the tunnel excavation,and deep deformation of accumulation slope can be respond promptly by a more reasonable arrangement for deep inclinometer.Slope deformation of tunnel support structure will produce secondary disturbance and stability of surrounding rock needs longer time.Force variation of pre-tunnel reinforcement structure can be used to evaluate the evaluation of slope safety(4)Tunnel built in the slope of loose accumulation has a loose surrounding rock.When the tunnel in the shallow side is excavated firstly,undesirable phenomena such as out of blocks and collapse appear in the place of dome frequently,and junction of lining structure is bulge up by extrusion of surrounding rock,so the cracking and bulging of shotcrete is observed.Meanwhile,excavating the shallow tunnel leads to a large tensile failure area above the tunnel and slope,and these unstable area has a interconnected trend.When the tunnel in the deep side is excavated firstly can give full play to the self-stability of surrounding rock,and subdivision on excavation steps lead to a reasonable adjustment for stress of tunnel lining structure.