| The geological conditions are fairly complicated in China. Tunneling engineering plays a significant role in highway, railway, and other transportation line projects. In addition, drilling and blasting method is the main method for the construction of tunnels in China. This method accounts for over 95 percent of tunnel engineering in China. However, during the process of using the drilling and blasting method, the over-under-excavated phenomenon and collapse accidents usually happen. The over-under- excavated phenomenon can have a negative influence on the quality and safety of the construction of tunnels. Currently the study of the over-under- excavated phenomenon caused by natural factors is more widely studied than the study of over-under-excavated phenomenon that is caused by human factors; the study of slope and open-pit jointed rock mass blasting technology is concerned more than the study of tunnel jointed rock blasting technology. To conclude, the study about the phenomenon of over-under- excavated of the jointed rock mass tunnel caused by natural factor is even less concerned. This paper is based on the scientific and technological project of the transportation department in Jilin Province"The Study of Jointed Rock Mass Tunnel Blasting Technology", the Gaoling Tunnel on Tuhui high way is used as an example to investigate the effect of jointed and fractured rock mass to the shape blasting of the tunnel.The factors that caused the phenomenon of over-under-excavated are listed below: first, it not fully concerns about the effect of geologic situation; second, it uses the improper blasting parameters. Natural rock mass is not homogeneous mass, plenty of faults, jointed rock mass, fractures and other disadvantages which can lead the deterioration of the rock mechanic parameters so that the rock mass have the non-continuous property and obvious anisotropy. The fracture and the other weak structures have two different effects on the blasting result. On the one hand, joint fissure has an impact on the rock mass mechanical property; the existence of the weak surface makes the propagation of the stress wave more complicated and it becomes a barrier to the stress wave which decreases the effect of blasting energy. Also, it leads the leakage of detonation gas and the pressure that influence the blasting effect. On the other hand, joint fissure influences the rock mass destruction form; the existence of the weak surface breaks the integrity of the rock mass which leads the formation of the original fracture inside the rock mass. And it changes the stress state of the rock unit structure. Meanwhile, it leads the change of the rock mass destruction form and influences the blasting effect.The paper talks about the influence that cost from joint fissure to the mechanical properties and the destruction form of the rock mass from the following three aspects separately:(1)Commences from blasting mechanism: Analyzing the reflection and the transmission phenomenon of blasting stress wave and studying the joint fissure strength's barrier effect to the blasting stress wave. According to the smooth surface blasting mechanism, stress analyzing and the damage criterion, to study the effect that the joint fissure shape may have to the blast-forming result.(2)Commences from the on site data: By statistical sorting of the joint fussier distribution and the peripheral blasting effect of five surrounding rock tunnel faces in level 2 and five surrounding rock tunnel faces in level 3, to analyze the effect of existence of the joint fissure to the blast-forming result.(3)Commences from the numerical simulation values: By supposing the rock mass situation and according to the blasting characteristics of the rock mass, the rock mass model, damage criterion, dynamite model and the state equation are assured. By using ANSYS/LS-DYNA finite elements program to simulate the breaking process of different occurrence joint rock mass under the effect of blasting load. Researching the effect that the joint rock may have on the tunnel blasting forming result. And barrier effects of different strengths of joint and different width of joint is towards the blasting stress wave were simulating-analyzed.The influence of joint fracture to the mechanical property of the rock mass mainly incarnate at:Because of the various structural plane existed in the rock mass the propagation of blasting stress wave is more complex. Through analyzing the reflection and transmission phenomenon of the blasting stress wave on the joint interface, it establishes the mathematical expression about the stress of both sides of the rock mass of the joint under the blasting stress wave. The results showed that: the stress in both sides of the joint rock is affected by the attenuation of blasting stress wave and the reflection and transmission of the blasting stress wave on the joint interface. The propagation of the blasting stress wave is main effected by the blasting source, the distance between the joint and the blasting source, the relationship of wave impedance matching of rock and filling material in joint as well as the width of joint. Among them the relationship of wave impedance matching of rock and filling material in joint plays a main role. The stress which is close the blasting source is the sum of the incident stress, the reflection stress and the transmission stress of the blasting stress wave. The stress which is far from the blasting source is the sum of the transmission stress of the blasting stress wave. When the physical and mechanical properties of filling material of the joint and the rock are similar, the blasting stress wave can smoothly through the joint. Not consider its role in stress wave barrier, only consider the normal attenuation of stress. When the physical and mechanical properties of filling material of the joint and the rock are different, joint has a significant influence barrier action on the stress wave.Using the ANSYS/LS-DYNA simulation calculation program, the rock material and joint material is assumed to be ideal elastic-plastic body. Blasting load uses of the JWL equation of state which is consider the detonation gas. Use equivalent stress of the unit to show the barrier action on the blasting stress wave of the joint. It uses the combination of different intensity and different width of the joint. It selects for three different strength of joint-joint 1, joint 2 and joint 3, in each group of strength of joint it selects three different widths of joint-5cm, 10cm and 15cm. It sets up nine models to study. Simulation results are show by stress ratio of both sides of the joint under the blasting stress wave. The theoretical method and the numerical simulation show the same law: the weaker strength of the joint, the wider of the joint, the closer of the joint to the blasting source, the barrier action on the blasting stress wave of the joint is stronger. The theoretical method is well in accordance with numerical simulation in the stress ratio of both sides of the joint under the blasting stress wave.The influence of joint fracture to the destructive form of the rock mass mainly incarnate at:The investigation shows that since the blasting wave are limited by the joint interface, it makes a shallow and a wide blasting funnel in the rock planes which are vertical to the tunnel axis. Thus it is easy to get a deep and narrow blasting funnel in the rock planes which are parallel to the tunnel axis. On this basis, this paper proposes that the effect of the joint aptitude to the tunnel blasting effect is mainly influenced by the smoothness of its tunnel face. And the effect of the joint inclination to the tunnel blasting effect is mainly influenced by the smoothness of the contour line around it. Thus this paper predigests the investigation to the plane problem.According to the smooth surface blasting mechanism,based on analysis of the unit body stress it investigates the influence that was made by joint structure surface to the smooth surface's blasting destruction. The investigation shows that: when the angle between the structure plane and the direction of the blast hole line satisfy special conditions, the rock mass would form a smooth blasting fracture towards the direction of the blast hole line. This is also the blasting contour of the designed smooth surface. When the angle between the structure surface and the blast hole line doesn't satisfy this condition, the rock mass would fracture towards the direction of the joint. The structure surface after the damage doesn't take the tensile stress which influenced the stress situation of the acting surface that is vertical to it. So it forms the"z-shape"fracture surface.To form a smooth surface blasting contour, the condition is that the angle between the structure surface and the blast hole line has to be larger than a certain value. This value depends on the joint surface's shear strength and its poisson ratio. The angle is usually about 70 degrees. The stronger the shear strength of the joint surface and the smaller the poisson ratio, the influential area is smaller, which means the stronger of joint surface has a lesser influence. When the joint becomes almost vertical to the blast hole line, the strength of the structure surface has no effect on the smooth surface blasting.Combined with specific engineering, in the Gaoling Tunnel, When the angle between the closing joint structure surface and the blast hole line in the level 2 surrounding rock is during 68 to 90 degrees, and in the level 3 surrounding rock when the angle between the closing joint structure surface and the blast hole is during 69 to 90 degrees; the structure surface has no effect on the smooth surface blasting. When the angle between the closing joint structure surface and the blast hole line in the level 2 surrounding rock is less than 68 degrees, and in the level 3 surrounding rock when the angle is less than 69 degrees; a"z-shape"fracture surface would appear after explosion. The larger the distance between the blast hole or the structure surfaces, the larger the convexity and the concavity of the fracture surfaces will be. When the angle is less than 45 degrees, the convexity and concavity will raise up with the angle's degree. When the angle is 45 degrees the convexity and concavity is the largest. When the angle is larger than 45 degrees the convexity and concavity decrease with the angle's degree. When the angle between the closing joint structure surface and the blast hole line is certain, the convexity and concavity will be smaller by decreasing the distance between the blast hole. The distribution statistic and the blasting effects of the test objects showed consistency in the calculated results.On the basis of engineering project, it establishes a simplified calculation model. Using the ANSYS/LS-DYNA numerical value simulating program, it considering the assumed condition, it simulates the effects that a single closing joint may have on the blasting-forming effect. By using the MISES yield criterion; the effective stress up to the limit of the yield criterion, the material starts to get into the plastic status, and the destruction appears. The angle between the joint and the blast hole line that are 30 degrees, 45 degrees, 60 degrees, 70 degrees, 80 degrees and 90 degrees are selected. The results show that when the angle is 30 degrees, 45 degrees and 60 degrees, the over-under-excavated phenomenon appears at the intersect position of the joint and the peripheral hole. When the angle is 70 degrees, 80 degrees and 90 degrees, the contour line is approximately equal to the designed contour line. The joint will then have no influence on the blasting effect. Here the numerical value is basically same as the conclusion in the fifth chapter.The data acquired on the job site showed that the when the filling joint extends over the designed contour line, the contour structure surface would explode with the blasting layer. This is what causes the over-excavated phenomenon. The wider the joint, the weaker the strength, and the longer the extension is, the over-excavated phenomenon is more serious. When the closing joint exists and makes the concentration coefficient is bigger than 0.8 to 1, the under-excavated would appear. The larger the concentration coefficient, the larger the amount of under-excavated phenomenon would occur.In conclusion, it uses the blasting mechanism, the data from the field, the numerical simulation to investigate the influence which results from the shape of the joint to the blasting-forming effect, and the barrier effect which results from the strength of the joint to the blasting stress. The results by the three methods match well. The paper offers a reference to the study of joint fractured tunnel blasting.Main creative spots of the paper:(1)Commences from the reflection and the transmission of the blasting stress wave in the joint to investigate the barrier effect of the joint strength to the blasting stress wave. The investigation about this aspect is fewer, this paper systematically considers the condition of the blasting source, the distance between the joint and the blasting source, the wave impedance matching coefficient between the filling material and rock. It establishes a mathematical expression about the stress ratio of both sides of the rock mass of the joint under the blasting stress wave to represent the barrier effect's strength. The simulation of the numerical value and the theoretical calculation matches well. Thus this offers some reference on the study of the damage mechanism of the filling joint under blasting stress wave.(2)It proposes that the main factor that influences the blasting tunnel effect on the joint tendency is the smoothness of its tunnel face. The main factor that influences the blasting tunnel effect of the joint dip angle is the smoothness of its surrounding contour. This paper is concerned only on the blasting effect of the joint dig angle. The spatial problem is simplified to plane problem.(3)Commences from the smooth surface damage mechanism. The investigation concluded that the influence was caused from the joint to the smooth surface blasting forming effect. When the angle between the structure surface and the blast hole locker line is above a certain numerical value, the rock mass would form a smooth blasting fracture surface towards the direction of the blast hole line which is the designed contour line of the smooth blasting surface. The critical value of the inclination depends on the shear strength and the poisson ratio. The angle is usually around 70 degrees. When the angle is below 70 degrees, it will form a"z-shape"fractured surface along the joint surface and the structure which is vertical to the joint surface. When the angle is 45 degrees, the"z-shape"fracture surface has the largest convexity and convexity. The convexity and concavity will be smaller by decreasing the distance between the blast hole. The result is verified by using three separate mechanisms i.e. theoretical calculation, the statistics of the field data, and the numerical value simulation. It provides a theoretical basis to the optimal operation of the blasting parameters. (4)The ANSYS/LS-DYNA method is more often used to predict the transmission of the blasting stress wave, the blasting fragmentation, and the blasted ore pile shape in the joint fractured rock mass. This paper made a preliminary exploration of the existence of the joint fracture and the tunnel blasting-forming effect. This paper also analyzes the over-under-excavated phenomenon that was caused by the joint. The conclusion was beneficial for it made a basis for a future quantitative study.(5)In regards to the influence that comes from the joint occurrence to the blasting-forming effect and the barrier effect of the blasting stress wave influenced by the strength of the joint. This paper investigates the blasting mechanism, the field data, and the numerical simulation. The conclusions verified each other and offered some reference for the study of joint fractured rock mass tunnel blasting.
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