Study On The Effect On Shotcrete And Mid-rock Caused By Reconstruction And Expansion Blasting Of Heiyu Tunnel

Taking the blasting construction of the reconstruction and expansion of the Heiyu Tunnel as the engineering background,this paper takes the shotcrete and the medium rock as the research objects.Firstly,the basic mechanical parameters of C25 concrete and limestone are obtained by uniaxial compression test,and then a single impact and cyclic impact compression test is carried out on C25 concrete and limestone,and the dynamic mechanical characteristics under different strain rate conditions are obtained.According to the damage theory,the time dependent damage model is established and verified according to the measured data.The cumulative damage effect of C25 concrete and limestone under cyclic impact load is reversely deduced by the time dependent damage model.In this paper,the related relationship between blasting concrete and the cumulative damage,damage increment and equivalent distance,equivalent charge,vibration velocity and vibration energy of shotcrete and medium rock is studied,and the following conclusions are drawn:1.Study on static and dynamic mechanical characteristics of C25 concrete(1)The average uniaxial compressive strength of C25 concrete is 24.87MPa,the elastic modulus is 11.82GPa and the acoustic velocity is 3692m s-1.(2)The SHPB test on C25 concrete shows that there is a good power function correlation between the peak stress and the strain rate,and both the peak strain and the peak stress increase with the increase of the strain rate.(3)The cyclic impact compression test of C25 concrete is carried out,and it is found that the peak stress and elastic modulus decrease gradually with the increase of cyclic impact times,on the contrary,the peak strain increases.When the strain rate is similar,the cumulative damage of concrete has a good exponential correlation with the impact times.(4)According to the damage theory,a time dependent damage model is proposed,and the measured data are fitted.According to the proposed time dependent damage model,the theoretical cumulative damage of C25 concrete after multiple impact is deduced.It is found that the theoretical damage and the measured damage have a good correspondence,and it is pointed out that the test damage threshold of C25 concrete crack is within the range of 0.198?0.391,and the theoretical damage threshold is within the range of 0.314?0.351.The experimental damage threshold of C25 concrete damage threshold is greater than or equal to 0.554,and the theoretical damage threshold is within the range of 0.554?0.693.2.Study on static and dynamic mechanical properties of limestone(1)A number of single-axis tests were carried out on the limestone,and the average uniaxial compressive strength was 93.76MPa,the elastic modulus was 21.96GPa,and the acoustic velocity was 5122m·s-1.(2)A single impact compression test was conducted on limestone,and the peak strain and the peak stress increased with the increase of the strain rate,showing an exponential correlation.The,degree of fragmentation becomes more and more serious with the increase of strain rate.The incident energy,transmission energy,absorption energy and reflection energy are all positively correlated with the strain rate exponentially;on the contrary,the energy dissipation rate is negatively correlated with the strain rate exponentially.(3)The cyclic impact compression test with constant strain rate(similar strain rate)was carried out on the limestone,and it was found that the peak stress of the limestone decreased gradually with the increase of impact times,and on the contrary,the peak strain increased accordingly.The cumulative damage of limestone has an exponential relationship with impact times.With the increase of impact times,the incident energy did not change much,and the transmitted and reflected energy decreased gradually.On the contrary,the absorption energy and energy dissipation rate increased gradually.(4)The time dependent damage model was verified with the measured data.According to the proposed time dependent damage model,the theoretical cumulative damage of limestone after repeated impact is deduced.The theoretical damage and the measured damage have certain correspondence.At the same time,it is pointed out that the test damage threshold of limestone crack is within the range of 0.202?0.531,and the theoretical damage threshold is within the range of 0.486?0.673.The experimental damage threshold of limestone crushing is greater than 0.531,and the theoretical damage threshold is greater than 0.673.3.Study on cumulative damage of shotcrete caused by blasting(1)Compared with the traditional formula,the vibration velocity attenuation formula based on the equivalent charge and the equivalent distance has a better fitting correlation and smaller relative error,which is basically within the range of 20%.The wavelet packet theory was used to study the vibration energy of blasting at each measuring point,and it was found that the vibration energy was mainly within the range of 0?100Hz,about 98%,of which the energy was most concentrated in the range of 0?62.5Hz,accounting for more than 80%of the total energy.Both the vibration velocity and vibration energy attenuate rapidly in the range of 0-20m,and slowly in the range of 20?40,and the vibration energy attenuation coefficient is approximately twice of the vibration velocity attenuation coefficient.(2)The cumulative damage cycle times of shotcrete caused by blasting increase gradually,while the damage increment decreases gradually,and the damage is irreversible.After 4 cyclic blasting,the cumulative damage of 1th measuring point near the explosion source is the greatest,is 0.274,greater than the standard damage threshold of 0.19,but the shotcrete does not have instability damage.According to the 2nd chapter of the laboratory test,the damage threshold of concrete damage loss of bearing capacity is greater than 0.554,it is known that the 1th monitoring point and more distant concrete failure instability is less likely.(3)When the distance from the working face is about 20m,the cumulative damage is about 0.05,and the vibration velocity,vibration energy attenuation speed and damage increment have an inflection point,indicating that when the distance from the working face is less than 20m,the damage increment is larger and the damage caused is greater,and the vibration velocity and vibration energy attenuation are faster.Above 20m,the vibration velocity,vibration energy,damage increment and cumulative damage tend to be stable.(4)The equivalent charge and equivalent distance were used to fit the concrete damage increment and vibration velocity caused by each blasting.The correlation coefficient was greater than 0.9,and the two had a good power function correlation.4.Study on cumulative damage of medium rock caused by blasting(1)The energy of the blasting vibration signal of the middle rock pillar is mainly concentrated in the low frequency band(0-100Hz).The higher the blasting vibration energy,the faster the attenuation.With the increase of distance,high frequency energy is absorbed,and energy is concentrated in low frequency band.The energy attenuation coefficient is approximately twice that of the velocity attenuation coefficient.In the range of 0?20m from the working face,the vibration velocity and vibration energy attenuation are extremely fast,and in the range of 20?40m,the attenuation of both tends to be flat.(2)The cumulative damage of the middle sandwiched rock pillar at the monitoring point of this test caused by blasting is small,with the maximum cumulative damage of the monitoring section at the distance of 9m from the working face being 0.078,and the maximum increment of the first damage being 0.0384,indicating that the blasting has little impact on 9m and other medium rock.According to the attenuation trend of damage increment,vibration energy and vibration velocity with distance,the damage increment,energy and vibration velocity attenuation are extremely fast within the range of 0?20m from the working face,and tend to be flat within the range of 20?40m.(3)The equivalent charge and the equivalent distance were used to fit the damage increment and the vibration velocity caused by each blasting.It was found that they could use the same fitting function,with different fitting coefficients.The correlation coefficients were basically greater than 0.9,and the correlation was good.There is a good power function correlation between damage increment and vibration velocity.