| Blasting is a commonly used method for rock excavation,which will make the rock break and inevitably cause disturbance and damage in the reserved rock mass.Therefore,blasting-induced damage will affect the mechanical properties of rock mass and the slope stability.Evaluation of the damage effect caused by rock blasting is an important technological problem in the field of rock engineering.In this paper,the mechanism of blasting damage and the theory of damage evaluation was summarized.The spatial distribution of blasting damage zone in the rock masses was investigated via theoretical derivation and numerical simulation.The degradation of rock mass mechanical properties induced by blasting damage was studied based on Hoek Brown criterion.The influence of the blasting damage zone and its distribution on a rock slope stability were investigated.The main contents and some conclusions are summarized as follows:(1)The evaluation methods of blasting damage zone were summarized.The blasting damage evaluation methods mainly include acoustic method,ultrasonic CT method and theoretical formula method.In the aspect of exploring the blasting damage degree,evaluation methods mainly include the velocity test results based on engineering specification and damage cloud images obtained by numerical simulation.(2)According to the field test data of rock mass wave velocity before and after blasting,statistical analysis and data fitting were performed to obtain the variation regularity of rock mass wave velocity,the results meet the feature of piecewise linear function.Based on the disturbance factor DHB in Hoek Brown's strength criterion,the damage of rock blasting weakening effect was discussed.To investigate the rule of DHB change within the depth of blasting damage,a formula was derived by associating DHB with compressive wave velocity of rock mass and the result shows a exponential variation of DHB change,which might provide guidance for quantitative evaluation of blasting damage.(3)Numerical simulation method was performed to explore the single hole blasting process and the attenuation rule of the blast induced damage.Based on the relevant engineering blasting design data,the numerical model was established using five different sets of blasting parameters respectively,and the rationality of the numerical simulation method was verified by comparing with the theoretical formula analysis.Based on the calculation results of DJHC in JHC model,the spatial distribution of blasting damage degree with the bursting distance was analyzed;the above numerical results are compared with the exponential spatial variation of the disturbance factor.The results show that the degree of rock mass blasting can be quantitatively characterized by the DJHC from 0 to 1.With the increase of the detonation distance,the blasting damage degree parameters drop slowly initially,following by a steeper decrease process,and eventually returns to gentle decrease.The theory of DHB's exponential change law has a good rationality when the damage threshold is considered.(4)Based on the Hoek-Brown's strength criterion,the deterioration of the mechanical parameters of rock slope in the area of rock mass was calculated,while the effect of blasting damage area and the damage degree of distribution regularity on a rock slope stability was analyzed.The results show that the value of DHB affect the slope stability significantly;if the influence of blasting damage was not considered,the slope safety factor will be overestimated;if DHB was set as constant value,the stability safety factor is conservative;and the consideration of gradual weakening of DHB can better reflect the actual effect of blasting damage on slope stability.The system bolt can be used to control the blasting damage zone effectively,so as to ensure the slope stability after excavation.In addition,the influence of DHB's distribution pattern and range were also discussed in this paper. |
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