Study On Mechanical Model And Stability Evaluation Method Of Rock Between Small Spacing Tunnels

With the advancement of urbanization,the space above ground is becoming increasingly scarce.In order to meet the traffic demand more effectively,reduce the damage to the natural environment and accelerate the development of economic construction,the development of underground space has become the mainstream of construction.As a common form of underground space,small spacing tunnels have unique advantages such as "saving underground space resources,protecting environment,and convenient for route selection".As the carrier of force transmission between small spacing tunnels,the stability of rock between tunnels is an important component to ensure the stability of small spacing tunnels.At present,there are many problems in the study of rock inclusion in small spacing tunnels,such as " calculation method is complicated and practical application is difficult".Based on the threedimensional construction effects of parallel tunnels,overlapping tunnels and inclined parallel tunnels,the failure mechanism of middle rock mass under the corresponding tunnel distribution is determined by field measurement,theoretical analysis and numerical simulation methods,and the corresponding mechanical model and stability evaluation method of middle rock mass are established,which can provide guidance for engineering design and construction.The main achievements are as follows:(1)Based on the disadvantage of biaxial compression in the construction of parallel tunnels,taking the first principal stress of middle-distance tunnel as the mechanical index and the ultimate stress under biaxial compression as the stability evaluation index,the mechanical model of rock between parallel tunnels and its stability evaluation method are established.The critical value of internal friction angle-cohesion is obtained which satisfies the stability of rock between parallel tunnels during construction period.(2)Based on the overall and local stress characteristics of rock between overlapping tunnels during construction,two failure modes of rock between overlapping tunnels are proposed,which are global instability and local failure.According to the overall vertical balance of rock and the ultimate stress of local control section,the evaluation methods of overall and local stability of rock between overlapping tunnels are established.The critical value of internal friction angle-cohesion is obtained which satisfies the stability of rock between overlapping tunnels during construction period.(3)Based on the decomposition of self-weight stress field,the stability study of rock between inclined parallel tunnels is decomposed into two forms,i.e.bias horizontal parallel tunnels and bias overlapping tunnels.The mechanical model and stability evaluation method of rock between inclined parallel tunnels are established by synthesizing the stability evaluation methods of two decomposition forms.The critical value of internal friction anglecohesion is obtained which satisfies the stability of rock between inclined parallel tunnels during construction period.(4)The influence characteristics of distance,span,burial depth,lateral pressure coefficient,cyclic footage and inclination angle on the stability of rocks in between tunnels,overlapping tunnel and inclined parallel tunnel are determined.The above theoretical calculation methods have been verified by numerical simulation,which can provide theoretical guidance for practical engineering design and construction.