| Rockburst mainly occurs in the deep-lying region. It is because deep-lying region is easy to take on higher terrestrial stress under the action of self-weight stress and tectonic stress. However, during the construction of Kuocangshan tunnel, rockburst occurred in two relatively shallow areas (under 250 meters), and not in the most deeply position. This kind of phenomena has certain particularity to research.The theoretical investigation of rockburst is developed from the 1920s～1930s. During the research process, Many scholars have been analyzing the occurrence mechanism of rockburst from various angles. Moreover, the typical theory includes the strength theory, the energy theory, the rigidity theory, the defect theory, the energetic disturbances theory etc. The condition of the occurrence of rockburst is various. There is not a kind of theory to explain the occurrence mechanism of rockburst completely. Generally speaking, the occurrence of rockburst is caused by the synthetic action of intrinsic factor and extrinsic factor. In addition, the intrinsic factor includes the rockburst orientation of the rock. The extrinsic factor includes terrestrial stress, explosion disturbance influence etc. Among the numerous influence factors, the terrestrial stress is the most important.The project region of Kuocangshan tunnel is in the southeast of Zhejiang province. This area is controlled by Cathaysian and neocathaysian structure. The author evaluated the environment of the terrestrial stress about Kuocangshan tunnel through regional geological reconnaissance, focal mechanism solution and terrestrial stress test. As a result, the author got the following formulae:σH = 0.0373H + 4.4065,σh = 0.0288H + 2.4219,σv = 0.0258H (σH is the most horizon principal stress,σh is the least horizon principal stress,σh is the vertical stress, H is the depth of burial ). In the research of the terrestrial stress, the author can also calculated that the direction of the most horizon principal stress is N61°W. Based on the formulae, the terrestrial stress of Kuocangshan tunnel region is on the normal level.The rockburst mainly occurs at the enclosing rock which has the attribute of densify, integrity, stiffness, low in decay, low in dampnessand friability. It is because supra enclosing rock takes on the favourable performance of storing energy. Through the research of both domestic and international, we could understand that the occurrence of rockburst is closely related to the physical mechanic property of the rock. In this article, the author appraises the orientation of Kuocangshan enclosing rock applying Wet,σc, Kb and Ku. As a result, the enclosing rock of Kuocangshan takes on the strong orientation of rockburst.The rockburst that occurred in the relatively shallow areas is in the scope of feebleness to medium. From the numerous engineering geology characteristics about the rock burst region, the condition such as the rock to be stiff and integrated, the joint to be scarce, the tunnel to be dying is the same to the instance before. However, the condition that the rockburst area is near the valley and dislocation is particular. Therefore, we could infer that the source of the higher terrestrial stress is probably related from the effect of the valley and dislocation. This problem is worth to research.In this article, the author calculates the value of the initial terrestrial stress about Kuocangshan tunnel through founding 3D finite element mountain model ( the valley and the dislocation are contained ). At the same time, the author could plot the stress cloudscape and the stress choropleth of the mountain model. From the stress cloudscape we could descry that the stress of the rock mass near the valley and dislocation is concentrical transparently. From the principal stress choropleth, we could descry that the maxima of all theσ1,σ2 andσ3 appears at the position near the valley and the dislocation. More over, the rockburst area is exactly at this position. Consequently, the stress concentration caused by the valley and the lithological change caused by the dislocation are the source of the higher terrestrial stress. This conclusion could explain the phenomena that the rockburst occurred in two relatively shallow areas equitably as well.The stress differentiation caused by the tunnel excavation induced the value of the terrestrial stress to be higher from the original foundation, and such stress differentiation is favourable to the rockbust. In this article, the author calculates the value of the terrestrial stress about the tunnel enclosing rock through founding 3D finite element tunnel model. From the principal stress choropleth, we could descry that the maxima of bothσ1andσθappears at the ceiling dermal enclosing rock afterthe excavation of the tunnel. More over, the value of the stress is in the scope of feebleness to medium. This conclusion could explain the phenomena that the rockburst occurred in two relatively shallow areas equitably as well. Consequently, this conclusion is concurrent to the actual rockburst phenomena.During the process of the tunnel construction, the explosion could brought P wave, Equivoluminal wave, Bow wave and Rayleigh wave and these waves could disturb the enclosing rock sorely. The rockburst of Kuocangshan tunnel is the most fierce just after the explosion of the breast. This phenomena could explain that the explosion is the important inducement of the rockburst.The measure of rockburst managed mainly includes ameliorating the physical and mechanical character of the enclosing rock, ameliorating the stress state of the enclosing rock, diminishing the disturbance etc. As far as Kuocangshan tunnel is concerned, the measure such as improving the predictive ability of rockburst, short digging, weak exploding, spraying water to the surface of the enclosing rock, anchorage and gunite supporting etc. As a result, the effect of the measure is favourable.This article not only analyzs the occurrence mechanism of Kuocangshan rockburst but also gets an important inspire. Generally speaking, the inspire is that the rock mass near the valley and dislocation is easy to get higher terrestrial stress with the influence of the stress concentration. In the following forecast of the rockbust, people should bring the valley and dislocation to the prognostic range.
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