Blasting Damag Study Of Surrounding Rock In Badaling Tunnel

The newly built Beij ing-Zhangzhou high-speed railway is a supporting infrastructure construction project for the 24th Beijing Winter Olympic Games.The newly built Badaling Tunnel has become a controlling project for its large buried depth,crossing railway lines and ancient buildings,and its surrounding rocks are mostly grade III and IV weak weathered granite.In the construction of tunnel by drilling and blasting method,the surrounding rock near the working face is inevitably affected by explosion,and the surrounding rock at a certain distance from the face will be damaged under the impact of frequent blasting stress waves,thus affecting the stability of the surrounding rock.In this paper,SHPB test system is used for rock specimen impact test and cyclic impact test.The correlation between impact times and damage and energy dissipation during impact are analyzed.The acoustic wave velocity of rock mass under the action of repeated blasting is tested in the borehole of the newly built badaling tunnel.The following conclusions are drawn:(1)The typical stress-strain curves of granite mainly include four stages:linear growth stage,primary fracture compaction stage,strengthening stage and unloading stage.Rock failure under dynamic uniaxial impact compression is tensile stress failure.The amplitude of the waveform curve decreases with the increase of the number of shocks,and the reflected wave undergoes the transformation from V-shape to W-shape,and from W-shape to V-shape.The peak strength decreases gradually with the increase of impact times,and the peak strength decreases greatly at the later stage of curve development.The elastic modulus of rock decreases gradually with the increase of impact times,but it decreases slightly in the initial stage,and more in the later stage.(2)The failure of rock under repeated impact is that a main crack is first cracked in the direction of specimen diameter,which causes the failure of the whole specimen with the increase of the number of shocks;when the specimen is damaged,it becomes small blocks and does not produce powder breakage.The number of shocks coincides with the cumulative damage.The parameter a affects the cumulative damage in the initial stage,the cumulative damage in the early and late stages is controlled by ?,the cumulative damage in the late stage is controlled by y,and the cumulative damage in the early and middle stages is controlled by ?.With the increase of the number of shocks,the incident energy and reflection energy decrease gradually,but the incident energy decreases slightly;the transmission energy and dissipation energy increase gradually,but the degree of dissipation energy increase is less than that of transmission energy.The number of shocks and cumulative damage are linearly and positively correlated with cumulative dissipated energy.(3)The distribution of sound velocity in the hole has the following rules:the velocity of sound wave tends to decrease along the hole depth,and the velocity at the bottom of the hole is higher than that at the mouth.Sound wave curve has obvious regional characteristics and can be divided into two or three regions.The area near the orifice is often fragmented and less affected by explosion shock.The effect of blasting on zone 2 or 3 is obvious,and the change of sound velocity is not obvious in the previous blasting.After the multiple blasting,the value of sound velocity decreases rapidly.Rocks in fissure zone are not sensitive to blasting,while plastic zone is sensitive to blasting.With the increase of blasting times,the cumulative damage increases,and the hole location has a great influence.The cumulative damage increases with the number of blasting,and the average damage value increases with the number of blasting.The influence range of blasting action is determined to be 50m.(4)According to the causes of damage in tunnel blasting,the causes of damage are attributed to secondary damage caused by blasting,excavation unloading and space effect,and it is pointed out that the damage caused by space effect does not play a dominant role.Based on H-B criterion,the parameters of rock mass at the location of blasting are determined,and the coefficients method and wave velocity method are used to calculate and compare.The coefficients method is recommended.(5)The radius of the converted circular tunnel is 9.78m based on the method of equivalent circle.According to the theory of loosening circle,the range of loosening zone and plastic zone of surrounding rock are 2.6m and 3.5m,respectively.Based on the attenuation law of acoustic wave,a unified cumulative damage prediction polynomial with the number of blasting times is fitted by regression in different surrounding rock areas,and the accuracy of the prediction is verified.