| In recent years,with the progress of science and technology and the development of economy in China,the national investment in infrastructure construction has been increasing year by year.The focus of the construction has also been gradually changed from the eastern coastal areas of China to the mountainous areas such as the central and western regions,and from the first and second tier cities to the third and fourth tier cities.Great achievements have been made over the years.The tunnel can greatly shorten the length and improve the operation efficiency.It is widely used in the construction of highways and high-speed railways in the central and western regions of China.The length of Bridges and tunnels can account for 40%～85% of the total length of the whole line.Meanwhile,China is a country with abundant karst geology,which accounts for more than 50% of the whole stratum area,so it is inevitable to encounter karst geology in the tunnel construction process.In the construction of tunnels in karst areas,blasting vibration may connect tunnels with karst caves,leading to geological disasters,such as water inrush,mud outburst and collapse.Secondly,the size and direction of the designed resistance line may be changed,which will affect the smooth blasting effect of the tunnel and cause blasting guns and flying stones.In addition,the existence of karst caves may reduce the explosion power and affect the lumpiness of rock after blasting,resulting in uneven rock lumpiness and increasing the difficulty of slag transportation.Finally,blasting excavation in karst areas may cause irreversible damage to surrounding rocks,affect the stability of surrounding rocks,reduce the service life of the tunnel in operation period,and leave serious safety risks.Therefore,through the optimization of smooth blasting parameters,it can effectively prevent the penetration of cracks between the tunnel and the karst cave,and reduce the possibility of water inrush and mud inrush in the cave.In addition,due to the improvement of blasting quality,can greatly reduce the over-undercut and collapse,while saving materials,reduce the project cost,can speed up the construction schedule,ensure the construction safety.In this paper,the influence of karst caves on the smooth blasting effect of tunnels is studied by means of theoretical analysis,numerical simulation and field monitoring.Firstly,the smooth blasting mechanism is analyzed,and then the influence of karst parameters on the single hole rock-breaking effect in homogeneous surrounding rock is simulated by numerical software.Then the influence of smooth blasting parameters on tunnel blasting is studied in the case of concealed karst caves around the tunnel.Finally,according to the above research results,the blasting parameters of the engineering are optimized.Through the research of this paper,the following research results have been obtained:(1)The rock breaking mechanism of tunnel smooth blasting and the design method of smooth blasting parameters are theoretically analyzed,and the discrimination basis of rock damage and the detection method of surrounding rock loose zone are summarized.(2)The numerical software,ANSYS/ls-dyna to simulate different spacing,different sizes,different shapes,different fillers and location of the cavity of the effects of the single broken rock discussed the existence of the karst caves will increase the damage radius of surrounding rock,compared with the homogeneous rock blasting damage radius,caves exist damage radius can increase 20%;The damage area of rock mass is negatively correlated with the damage degree of rock mass after blasting.(3)Establish the blasting model of surrounding hole with and without karst cave,and compare the influence law of karst cave on the damage and failure of surrounding rock under different working conditions.It is found that the existence of karst cave will increase the stress distribution of rock mass between karst cave and tunnel,so as to increase the damage range in this area.Due to the energy absorption and energy release of the cave,the stress of the rock mass unit behind the cave is obviously reduced compared with that without the cave.(4)Through the establishment of the numerical model of karst cave is located in the tunnel vault,peripheral hole spacing is analyzed,the density of resistance wire size,line of blasting parameters,such as the impact on the tunnel blasting,and through the monitoring of a particular unit,found within the rock mass stress distribution decreases with increasing peripheral hole spacing and resistance line,and with the line density increases,so the smooth blasting excavation in karst region,advice around the hole spacing of 40 cm,resistance line take 60 cm,line density of0.125 kg/m.(5)To evaluate the effect of smooth blasting,the total station and acoustic monitor are used to measure the amount of over-under-excavation and the surrounding rock loose ring,and the measured value of the loose ring is compared with the numerical simulation result and the static calculation result to verify the reliability of the research method. |
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