| With the steady advancement of new industrialization and the proposal of the “double carbon” goal,the demand for green and clean energy such as hydropower has increased rapidly in my country.However,more than 60% of my country’s hydropower resources are mostly concentrated in the mountains and valleys in southwestern regions such as Yunnan,Sichuan,and Tibet.So we often face the problem of the excavation of high dam foundations,during the construction of hydropower stations.The excavation of high dam foundations generally adopts the step-by-step bench blasting from high to low.The part of the transition from the steep slope to the horizontal dam foundation has a small slope,which is called the dam foundation gentle slope in engineering.In order to ensure the contour forming effect and reduce the disturbance of blasting excavation,the excavation of dam foundation gentle slope often use the pre-splitting blasting.According to the different arrangement of production blastholes and buffering blastholes,it can be divided into two excavation methods: blast-holes along the slope(BHAS,the production blastholes and buffering blastholes are laid along the slope)and blast-holes reverse the slope(BHRS,the production blastholes and buffering blastholes are laid reverse the slope).Due to the gentle slope,the drilling operation is limited,which will easily lead to the reduction of drilling accuracy and efficiency.So the blasting technique with shock-reflection device(BTSRD)is proposed to be applied to the dam foundation gentle slope.However,the existing dam foundation construction has not comprehensively considered the blasting effect,dynamic disturbance and construction speed under different excavation methods in the dam foundation gentle slope.Therefore,it is necessary to carry out comparative research on the different excavation methods of dam foundation gentle slope,so as to provide reference for onsite construction.The main work and research results are as follows:(1)Relevant onsite experiments were carried out.And the effect of blasting excavation,drilling efficiency,and the effect of disturbance control under two ways of blasthole arrangements(BHAS,BHRS)were compared in onsite experiments.The results show that the contour forming effects of the two methods are basically the same.Although the loose coefficient of muckpile in BHRS is relatively high,the muckpile is located on the gentle slope,which has little effect on the efficiency of shovel loading and transportation.Compared with BHAS,the BHRS has lots of advantages,such as its drilling perforations is less difficult,the hole position is easy to control,the drilling efficiency is high.Meanwhile,the BHRS is beneficial to reduce the disturbance to the reserved rock mass,which can reduce the damage depth by 11.6%～13.9% and the vibration velocity by 6.4%～53.7%.(2)The blast-induced damage evolution characteristics and vibration distribution law were analyzed under the above two ways of blasthole arrangements,by using the 3D dynamic finite element numerical simulation software(LS-DYNA).Moreover,the inherent mechanical mechanism under different ways of blasthole arrangements was revealed.The results show that the disturbance of the reserved rock mass is different,the internal reason lies in the change of the intersection angle between the blast-hole and the reserved rock mass surface.As the intersection angle increases,the projected area of the main work direction of the explosive explosion(the radial direction of the blast hole)to the retained rock mass decreases gradually,which will reduce the transmission of blast energy to the reserved rock mass,thereby reduce the disturbance in the reserved rock mass.Compared with the traditional BHAS,the BHRS increases the angle between the production blastholes or buffering blastholes and the contour surface.(3)Relevant onsite experiments were designed to verify the mechanism of blasting technique with shock-reflection device,and numerical simulation was used to compare the damage control and contour forming effects of BHRS and BTSRD under the same parameters.The results show that using BTSRD can effectively control the damage of reserved rock mass and increase the horizontal breaking of rock mass,through the reflection of shock-reflection structure and the buffering effect of flexible cushions.Compared with the conventional charge structure,the use of BTSRD can reduce the damage depth of the reserved rock mass by about19.2%,and increase the damage radius of the hole bottom by about 21.9%.In addition,compared with BHRS,under the same blasting parameters,the use of BTSRD on the dam foundation gentle slope can achieve the damage control of reserved rock mass.Meanwhile,the particle peak vibration velocity is reduced by about 13.7% and the damage depth is reduced by about 6.5%,while the forming effect of overall profile surface is slightly worse.(4)This paper compares and analyzes the damage distribution under different blasting parameters of BTSRD through numerical simulation.It is recommended to choose the blasting parameters with uncoupling coefficient of 1.28(blasting hole diameter of 90 mm,charge diameter of 70 mm),blasting hole distance of 1.5 m,and adopt the top and bottom mixed detonation of adjacent holes.The field application results show that the blasting damage and the effect of vibration control and the forming effect of profile surface of BTSRD with the optimized blasting parameters are basically the same as BHRS,while the efficiency of blasting excavation has increased significantly. |
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