Study On Disturbance Range In Soft Rock With Drill Blasting Technology Tunnel

From the point of engineering view, the paper studies formation process, theory calculation and influence factor of fractured zones etc, which connect to soft rock characteristics. Sonic method and multi-displacement instrument method are widely used on many present in-situ test methods, because of its easiness and relatively reasonable result.Based on the soft rock characteristics, the cutting way and blasting way of peripheral hole is explained. Furthermore, the calculated method of smooth and pre-cracking blasting parameters is given which are used in soft rock with drill blasting technology tunnel.At the present studies of fractured zones of soft rock, the study on blasting vibration is not many. Thus it is necessary to do further research. On the background of entrance section of Heluoshan tunnel in Dali railway, calculate the blasting parameters. Considering the vibration effect of blasting excavation, the fractured zone is simulated by the model, which is built through the finite difference software—FLAC^3D . upper and lower benching method is used and the surrounding rock is IV class. The cross section is horsed shoe shaped. On the upper bench excavation, the length is about 6-8m in vertical direction which the fractured zones is affected by blasting vibration. After steady, the thickness is about 2.2m, however, on the excavation of lower bench, it increases to 8-10m. the fractured zones reduce when tunnel invert is made in the lower bench excavation. It is correspond between the tunnel excavation shape and fractured zones.Based on the model of blasting vibration, the seepage is considerly simultaneous. assuming the surrounding rock is fully saturated, further research is made. The result illustrate: after excavation, the pore pressure begin to reduce, and the ground water begin to permeate to the excavated surrounding rock at the same time which lead to the enlarging of fractured zones. The tunnel temporary invert is not made on the upper bench excavation, the thickness of fractured zones in bottom enlarged obviously, therefore, more attention should be paid to two sides arch springing. After the excavation of lower excavation, the tunnel invert is made in time. Compared with the result of model of which have not ground water, the thickness of fractured zones change little in the tunnel invert, but the crown is affected obviously. If can control the effect of ground water better in project, from the ultimate shape of fractured zones, it may be not enlarged much.Based on the fractured zones, the supporting countermeasure and technology of big fractured zones tunnel is further simply studied.