Experimental Study And Theoretical Analysis Of Surrounding Rock Under Cyclic Blasting Load

With the great support of our country to the water conservancy and hydropower,the water conservancy and hydropower project in the southwest region is developing constantly.In the process of construction of hydropower station,many of them are under high ground stress,so it is more difficult to carry out excavation.In the process of blasting,the surrounding rock will continue to damage under the action of cyclic blasting load.And according to the level of the surrounding rock and the damage of tunnel surrounding rock to design the supporting structure,play a certain reference role.Based on the National Natural Science Fund Project "blasting load of tunnel surrounding rock damage evolution mechanism",to Jinping Hydropower Station Diversion Tunnel as the engineering background,model tests are carried out under the relevant conditions,to analyze the damage of surrounding rock in blasting loads.Through the design of the model box,research and development of similar materials,complete the relevant test.The main research contents are as follows:(1)The size of the model box is designed in order to meet the convenience of the experiment,as well as taking into account the spatial range of the model,the similarity ratio of this test is 10.The three dimensional model test system of the water diversion tunnel mainly includes reaction frame,hydraulic system,measurement system and data acquisition system.(2)By continuous research and try to select the quartz sand and iron powder as the aggregate of barite powder as modifier,the mixed solution of rosin and alcohol as cementing agent,the mixture of materials.It is used to study the similar material ofsurrounding rock damage under cyclic blasting load.(3)When the confining pressure is 0,with the increase of the number of cycles,the sound velocity in the medium decreases.In other words,after the role of the cycle of blasting,the integrity of the media is constantly deteriorating,the damage intensified.(4)Considering the influence of confining pressure,the comparison of 5MPa,20 MPa and no confining pressure.The damage degree of the medium is related to the initial level of the stress field,and the smaller the confining pressure is,the greater the damage degree is.At the same time,can be observed when the confining pressure is 0,the damage curve is steep,with the increase of confining pressure,the damage curve tends to be slow,that rock damage under the effect of confining pressure on smaller,namely the surrounding rock damage in confining pressure decreases with the increasing of blasting times.Millisecond blasting can improve the rock fragmentation,but the damage to the surrounding rock is not obvious.Damage in circulating blast loads each blasting rock is different,after five times third times blasting blasting,rock damage,second,four times the damage of surrounding rocks of the first and five minimum damage of surrounding rocks.(5)By fitting curve,sound change rate curve and the damage degree and the depth of excavation blasting and excavation depth curve overall trend is the same,the rate of change of velocity and damage degree increased with the increasing of the depth of excavation blasting.