| The displacement field and stress field of surrounding rock can be regenerated in the tunnel constructing.The influence of space effect brought to bear on the displacement field and stress field above is significant in tunnel construction,it is important to master the law of deformation and variation of stresses of surrounding rock under its influence,and providing theoretical basis for choosing reasonable construction scheme.So this paper will put the release of surrounding rock load throughout construction process and the construction space effect as the main research content.Firstly, this paper introduces the current situation of the research on the space effect of the tunnel at home and abroad,elaborating the understanding of the theory of space effect of the tunnel; In the next place,analyzing the mechanical mechanism of tunnel deformation under the space effect deeply;Finally, based on the theoretical analysis, selecting engineering examples,according to the mechanical properties of construction of the tunnel and the theory of space effect,adopting the mean of finite element analysis to simulate the process of tunnel construction,the following results were obtained.(1)Establishing two-dimensional elastic plastic model,conducting elastic and plastic analysis to the excavation and support of tunnel which belong to large span and deep buried,and using "virtual support force method" to achieve the release of the stress of surrounding rock in different degrees,evaluating the displacement of surrounding rock and the stress of lining structure under different rate of stress release of surrounding rock,grasping the changeable course of the deformation and stress of the deep buried tunnel with the process of the excavation.The analysis shows that the different release degree of the load has a great influence on the deformation of surrounding rock and the stress of lining structure.(2)On the purpose of studying the space effect of tunnel construction,establishing a three-dimensional finite element model,adopting the engineering method that is “segment excavating-reserved core soil”,displaying dynamiclly the process of tunnel construction.Setting a section as the target section,studying on the change rule of deformation and stress of the target in the process of construction,mastering the changeable space course of the deformation and stress of the deep buried tunnel with the process of the excavation.Research shows,in a certain space range,regardless of the excavation face through the target section or not,the forward propulsion process will bring some influence to the deformation and stress of the surrounding rock of the target section.For example,when the excavation face is not through the target section and there is still a large distance between the them,the deformation and the principal stress are changed of the surrounding rock of the target section.And this change even more obvious as the distance between the two becomecloser,when the distance between the two decreases to zero,the deformation and stress of the surrounding rock of the target section develops rapidly.(3)In order to maintain the stability of surrounding rock and ensure the safety of construction,most reasonable scheme must be chosen as the construction programme to the project.In this paper,establishing corresponding several conditions respectively upon three aspect that are excavating method, the length of the lower steps and the two times lining are exert to analyses,at the same time, it is still from the surrounding rock deformation, stress change and the two lining stress several angles to discuss the characteristics of surrounding rock under the influence of the three factors.Finally,synthesizing three factors above,then preferring construction program.In the selection of excavation method,using “segment excavating-reserved core soil”,“step by step excavation method” and “heading method”,three kinds of construction methods for numerical simulation.The results show that compared with the other two methods, “step by step excavation method” has great advantage in terms of restricting deformation of surrounding rock.In the selection of the lower step length,establishing the corresponding working conditions of different lower steps length such as 2 meters, 4 meters, 6 meters, 8 meters and 10 meters to calculate. The results show that when the step length is 10 meters,the tunnel can be fully played the space effect of surrounding rock,forming a closed support system in time under the situation that there is no large deformation.In the selection of two times of support,establishing the corresponding working conditions of different supporting opportunity that is the distance between two times of support and lower steps respectively is 0 meters,4 meters,8 meters,12 meters,16 meters,20 meters.The results show that the deformation of surrounding rock has not changed much when the distance between the two lining and the tunnel lower step is 20 meters,and the maximum principal stress of the two lining is smaller at the same time.Synthesizing the analyses above,selecting “step by step excavation method” as the excavation method,10 meters as the lower step length,the moment that the distance between the two lining and the tunnel lower step is 20 meters as the supporting opportunity of two lining. |
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