Study Of Jointed Rock Mass In Tunnel By Blasting Technology

Tunnels and underground engineering plays an important role in the national economic construction. Nowadays, because of the strong adaptability for geological conditions, low-cost excavation, drilling and blasting method is still the main means of tunnel driving construction. The success or failure and good or bad of blasting excavation, not only affects the stability of surrounding rock, tunnel driving speed, but also has a close relation with the engineering quality and cost. Natural rocks contain a large number of faults, joints, fracture and other defects which effect the result of blasting .At the same time it will lead to the phenomenon of owe or ultra digging and collapse that frequent occurred, the impact of construction quality and safety, impact on the stability of surrounding rock. The study of jointed and fractured rock masses Tunnel blasting technology, has the theoretical guidance and practice significances to improve the blasting effect. The research results of this paper can guide tunnel construction blasting, blasting optimization design, effectively reducing the occurrence of owe or ultra digging and unnecessary expenditures of the economy, there will be a relatively good market prospects and social benefits.This passage is based on the most universal theory of Smooth Blasting in the tunnel driving to calculate blasting parameters(interval of holes,minimum resist line,coefficient of decoupling charge,blast hole number,hole depth) by the theory of smooth blasting. Otherwise explosive and charge structure,stemming quality,decouple coefficient,hole distance and minimum resist line and other blasting parameters on the effect of blasting results are discussed. Then the concept of joint fissures and structural plane is introduced, of which the basic characteristics is described to summarize that controlling role of joint fissures and structural plane on blasting effect.In this paper according to Surrounding Rock Mass Classification Data which is collected in the tunneling construction at left line of Gaoling tunnel, the distribution of every section joint and spatial composing relations in tunnels, in-situ blasting parameters and so on, the correlation between 5 joints fissures structural plane and blasting effect in the tunnel is summarized. They are:1. When line connecting points closed-type joints and around blast hole, there is the phenomenon of zigzag owe or ultra digging in the intersection of joint and contour.According to the basic principle of smooth blasting, joints prevent stress wave superposition. Joints change the action direction of blasting gas under quasi-static pressure. So that the initial radial crack of blasting produced in the direction of the Vertical joint, not the line connecting blast hole.2. When closed-type joints appeared in contour around and parallel to line connecting blast hole, there are obvious owe or ultra digging in the scope of joints . Thus there is the phenomenon of zigzag owe or ultra digging in the intersection of joint and contour. From coefficient of hole-spacing, it is found that when the joints appeared, line of least resistance become smaller that is reducing the thickness of smooth blasting layer. As borehole spacing is unchanged, coefficient of hole-spacing m is increased. When m>1, owe digging will appear between two holes. The greater m value is, the more serious degree of owe digging.3. When the line connecting filling-type joints and peripheral hole intersect, the intersection of hole at the joint interface with the contour line will produce super-dug.The existence of filling-type joints, leading to the lower strength of the rock mass around the contour line, due to the differences in rock strength, resulting in high-speed outward invasion of the explosive gas along the structural surface , and ultimately the intersecting rocks rupture under the explosive gas with high- temperature and high-pressure.4. When the filling-type joints are exposed in the vicinity of contour lines and parallel with the peripheral hole connecting line, there will be obvious less-dug phenomenon at the explosive scope of the joints and super-dug phenomenon in the intersection of joints and contour lines.Causes of this situation are nearly the same as the closed-type joints .It is also mainly affected by coefficient of hole-spacing Secondly, filling-type joints as a result of the internal medium is relatively weak, caused a large number of stress wave energy loss, which eventually led to a lot of owe digging in the scope of joints.5. When the filling-type joints exposed close to contour, that is the filling-type joints develop on design contour and beyond contour, there will be obvious super-dug phenomenon at the joints exposure site.The reason for the situation is the same as that joints effect blasting result when the line connecting filling-type joints and peripheral hole intersect. Mainly the existence of joints leads to extremely crushing rocks in contour. Due to the differences in rock strength, the tunnel face rock is caused to over cut in the area.After analyzing the reasons for these five joints having ultra digging, the blasting parameters are adjusted(Including adjustments to charge weight at peripheral hole , adjusting the distance between peripheral holes, etc.),and then burst in the field test .Ultimately the result of blasting effect of tunnel face is satisfying.