The Study On Mechanics Principle And Countermeasure Of Approaching Excavation In Underground Works

In recent years, with the development of the basic establishment, especially means of transportation (railway, highway, etc.), the engineering phenomena that new line (such as double-track railway, high speed railway, expressway, etc.) is built close to existing line (such as railway, highway, etc.) appears. The size is larger and lager, and the space between is closer and closer. That must be done the new structure is close to the existing structure, with complex mechanics behaviors and some bad influence to the existing structure. With the increase of construction size, these examples are increasing, such as newly-built tunnel close to the existing tunnel, two or more closely spaced tunnels built at the same time, large cross section cavern excavated partly and construction methods optimized. At the same time, this problem is faced more and more in plentiful construction of urban underground works liked Metro. This kind of problem is called approaching excavation of underground works.In course of the approaching excavation of underground works, the construction of new structure will change the mechanics case of existing structure and brings some bad influence, such as load bearing capacity of structure decreasing, structure breaking, or too much deformation of structure and construction gauge inroaded. At the same time, the mechanics mode of newly-built structure is not the same as that single cavern is excavated in the half-unbounded space. Its original stress field is disturbed by former time and time again, and once more by excavating of later. So the mechanics mode of the later is not symmetrical generally and infinite variability is put up. Resumptively, the construction of new structure will change the third stress field to the fifth stress field in surrounding rock, and bring the safety problem of existing structure and the complexity problem of newly-built structure. It is a ineluctable problem that we must face and treat. However, the mechanics mechanism is very complicatedbecause of the difference of the size of newly-built structure, position between newly-built structure and existing structure, stratum condition, healthiness degree of existing structure, construction methods of new structure, etc. So the urgent affairs is study of the complexity mechanics mechanism and corresponding countermeasure. Therefor, everyone of insight all over the world pays great attention to and study it.Overseas, the problem is studied relatively excessive and early. Some productions have been the guide of design and construction. In Japan, the problem of approaching excavation that newly-built structure is close to existing railway tunnel is studied and summarized by the numbers, and the guide was published. But it bases on experience and is not summarized to comprehensive problem of approaching excavation.Interiorly, with the increase of these examples in recent years, some study is developed and some successful experience is obtained. But most study is considered as it stands, systemic theory analysis is scare and specification has not been established in design and construction. The result is that conservative countermeasure which brings serious waste is adopted or hazardous and eyeless countermeasure which brings safety problem is adopted.A good many case of approaching excavation are studied in this article, such as the study of infection of be coal mining to the Huayingshan tunnel, technology study of strucked tunnels of Metro in Shenzhen, countermeasure study of tunnel approaching pile foundation of Metro in Guangzhou, excavation methods optimized of large cross section subaqueous tunnel approaching pile foundation of LRT in Chongqing, etc. On the basic of analysing and concluding relative study production all over the the world by the numbers, classification of approaching excavation, partition of approach zone, formula of partition of approaching zone, approach degree and countermeasure grade of generalized approaching excavation of underground works are put forward. General methods studying...