| The mountain tunnel portal section has this character, such as weak rock thickness, surrounding rock property worse than the body, and steep front slope, in this unfavorable geological conditions section, when an earthquake occurs, the portal section of tunnel will become the heavy disaster area of seismic damage. Therefore, tunnel portal section must be taken special earthquake resistance and shock absorption measures, but affect of soft rock length, rock property and gradient of front slope on the lining dynamic response depth and the dynamic disturbance zone of surrounding rock need further study.In response to these problems, relying on the National Natural Science Foundation of highly seismic area mountain tunnel design standards for anti-shock technology research system based on the basic theory, this paper has studied seismic dynamic response and parameter of rockbolt of the shallow tunnel portal section with using of three-dimensional numerical simulation techniques, main research contents are as follows:1) Analysis of relationship between the influence factors of seismic damage such as seismic parameters, tunnel buried depth, rock geological conditions, terrain conditions and lining conditions with the degree of damage to the tunnel entrance.2) This paper introduces the basic principles of FLAC3D dynamic calculation, and discuss some key issues of dynamic analysis, such as dynamic boundary conditions, damping matrix, element mesh size and the baseline correction of seismic waves.3) By using of three-dimensional numerical simulation techniques, study affect of soft rock length, rock property and gradient of front slope on the lining dynamic response depth and the dynamic disturbance zone of surrounding rock, using internal forces and relative displacements to evaluate the seismic dynamic response depth of the lining, taking on the first and third principal stress as the evaluation index of the rock dynamic response transverse influence scope.4) Based on the dynamic disturbance zone of surrounding rock, optimization of the length of rockbolt was carried out, and solved the matching relationship between the length of rockbolt and dynamic disturbance zone of surrounding rock, according to the research,6m is the best optimal anchor length, namely, if the rockbolt length is equal to the dynamic disturbance zone of surrounding rock, the earthquake resistance and shock absorption function of the rockbolt are excellent, but has no obvious increase when the length of the rockbolt exceed the radius of rock dynamic disturbance zone. Based on those results, optimization of the rockbolt interval and diameter was carried out, obtained the optimal spacing and diameter of the rockbolt. |
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