| Cut blasting plays an important role in tunneling blast,in which the most widely used was wedge-shaped cut.But at present in engineering blasting,for how to determine the wedge cut parameters and under what circumstances should increase the cut hole is mostly based on experience and engineering analogy,which has great randomness and is not conducive to the improvement of blasting efficiency in tunneling,and may even lead to failure.This thesis is based on the project of "Research on Controlled Blasting Technology of Horizontal Layer III Surrounding Rock Tunnel",aiming at the present situation of the poor effect of existing tunnel blasting in Banjie Tunnel of Chengdu-Kunming Railway,from the following five aspects of the research carried out on the quasi-parallel cutting method,hope to find the right blasting parameters for the quasi-parallel cutting,so as to improving the blasting effect of tunnel excavation.(1)Based on the theory of explosive stress wave,considering the columnar explosive properties and stress wave superposition effect,to study the distribution of stress field between two wedge-shaped holes,derivation results of analytical solution of stress sistribution on the free surface,and find the stress of the middle point of the two wedge-shaped holes is the smallest.(2)Based on the hypothesis of rock breaking mechanism of wedge-shaped cut and the broken?cravked areas formula in rock,considering the failure modes of different surfaces fully,systematically and sort out the theoretical formula of blasting parameters,and gives the range of the length of the drug should to be added:0.75H/sin?<le<0.75H/sin?+6(2?4)× 0.3 x 1/3,increase the center hole;0.75/H/sing?+(2?4)×1/3<le<H/sin?+Hi/sin?i,increase the shallow depth of the wedge-shaped hole;le>0.75(H/sin? +Hi/sin?i),the center hole and the shallow depth of the wedge hole are increased.(3)On the basis of satisfying the explosion similarity rate,carrying out several sets of concrete blasting model tests,the depth of cavity and the blasting degree after blasting were statistically analyzed,it was found that the blasting effect of center hole blasting was better;at the same time,using multi-channel dynamic test equipment record the explosive stress of the explosive in the model,obtained the relationship between the peak value of explosion stress and the propagation distance,it is similar to the theoretical analysis.(4)In order to verify the rationality of the theoretical results,a numerical calculation model is established to compare the maximum effective stress value in the cavity with the effective tensile stress on the free surface.The results show that the stress of the middle point on the two wedge-shaped holes is the smallest,The central hole blasting in the trough area can obviously improve the dynamic stress intensity of the bottom of the trough,which shows the rationality of the theoretical analysis.(5)The quasi-parallel cutting parameter design and field industrial test were carried out according to the theoretical calculation formula of the cut parameters obtained above and the actual situation of the blasting site,and a good blasting effect was achieved. |
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