| In the process of tunnel blasting excavation,the impact load caused by explosion will cause the damage of surrounding rock and affect the stability of the initial support structure.Under the action of cyclic blasting load,the damage of surrounding rock will continue to increase,which leads to the continuous expansion,extension and even instability of the cracks in the surrounding rock.At the same time,with the stability of surrounding rock gradually worse,the stress of surrounding rock carried by the initial support structure is increasing,which affects the stability of the support structure.This paper relies on the National Natural Science Foundation Project "Study on the mechanism of damage evolution of tunnel surrounding rock under cyclic blasting load".Based on the theoretical analysis,the force model of surrounding rock and initial support structure under cyclic blasting load is established by using the finite element software MIDAS GTS NX,and the numerical simulation research under different working conditions is carried out.The main research contents and achievements are as follows:(1)Based on the theoretical analysis of the influence of blasting vibration wave on surrounding rock and initial support structure,this paper puts forward the influence of blasting vibration on surrounding rock and initial support structure from the displacement of surrounding rock particles,and on the basis of one blasting,puts forward the formula of particle displacement accumulation after cyclic blasting load in two cases with or without initial support structure.And the displacement accumulation formula of concrete spray layer.(2)The maximum displacement and maximum vibration velocity accumulation values of the measuring points at 1-1 sections of ?,? and ? were studied and analyzed respectively after 5 cyclic blasting under 2 m excavation ruler conditions.From the maximum displacement analysis of the measuring point: on the basis of the first blasting,after 4 cyclic blasting,the maximum displacement cumulative value of the measuring points in the 1-1 section of ?,? and ? levels is about 4mm,9.5mm and around 18.5mm respectively,and the lower the selfstabilizing properties of the surrounding rock can be seen,the greater the influence of the cyclic blasting load.From the maximum vibration velocity analysis of the measuring point: the vibration velocity value of each measuring point in the 1-1 section of ? class surrounding rock is less than the particle vibration velocity(0.14m/s)of the old crack expansion of the surrounding rock after 5 cyclic blasting,and the vibration velocity value of each measuring point in the 1-1 section of ?-class surrounding rock is close to;The vibration velocity value of each measuring point in the 1-1 section of ? class surrounding rock exceeds the vibration velocity of the particle with the expansion of the old crack of surrounding rock after the second cyclic blasting.The influence of each cyclic blasting on the 1-1 section is analyzed from the stress of surrounding rock.In this paper,the initial support structure and the time of applying support in the blasting excavation process of ?,? and ?-class surrounding rock are put forward.(3)Comparing the maximum displacement and maximum vibration velocity accumulation values of each measuring point in the ~5-5 section of the 1-1 section,it is found that the displacement and vibration velocity accumulation value of each measuring point is the largest in the 5 sections of ?,? and ?-class surrounding rock,which indicates that the surrounding rock damage is the most serious 3-3 in 3-3 section.Compare Arch Bottom,vault The maximum displacement and maximum vibration velocity accumulation values of the left arch waist and the right arch waist are found,and the cumulative value at the bottom of the arch is the largest.Therefore,in the initial support process should pay attention to increase the 3-3 section and arch bottom arch foot support strength.(4)The cumulative value of maximum displacement and maximum vibration velocity of ?,? and ?-class surrounding rock after 5 cyclic blasting under the condition of excavation of 2 m ruler the accumulated values of each section,such as ? and ? level surrounding rock,can be appropriately increased by blasting excavation ruler,? class surrounding rock should reduce excavation ruler.The excavation ruler of ? and ?-class surrounding rock were changed to 3 meters,the ? of the surrounding rock was changed to 1 meters,and the section with the greatest influence of cyclic blasting load was selected to compare the displacement accumulation values of each measuring point under different excavation ruler conditions,and the excavation ? of the surrounding rock of ?,? and ruler stage was obtained.(5)Based on the study of the influence of cyclic blasting load on the surrounding rock of tunnel without initial support structure,it can be seen that the selection of 2 meters or 3 meters of excavation ruler in ? class surrounding rock is suitable,the ? level surrounding rock should choose 2 meters excavation ruler,? grade surrounding rock should choose 1 meters excavation ruler.?,? class surrounding rock in 2 meters excavation ruler under the working conditions of the application of anchor spray support structure,? level surrounding rock in 1 meters excavation ruler under the conditions of the application of anchor spray support structure and the addition of reinforced mesh,study 5 cycles after different spraying thickness of the measurement point displacement accumulation value and no support structure,and select the appropriate spray thickness.The influence of cyclic blasting load on the initial support structure is analyzed by the change of displacement value of each measuring point of 1-1 section and the displacement cloud map and mises stress cloud map after cyclic blasting of concrete spray layer. |
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