Experimental Study On The Mechanism Of Closed-type Collapse In The Tunnel Of Near Horizontal Strata

The strata of the layered structure in China account for a large proportion,and the tunnel location will inevitably encounter horizontal stratigraphic strata.We can find that the tunnel collapse accident which is not uncommon in horizontal rock formation,often appeared closed-type collapse caused construction workers trapped.The particularity of this kind of collapse and the possibility of rescue means that the study was urgent.In this paper,carried out Experimental study on the mechanism of closed-type collapse in the tunnel of near horizontal strata by similar model test which based on the near-level rock formation in this paper.This paper makes an exploratory study on the mechanism of closed-type collapse experiment by means of similar model test and numerical simulation.The main contents of this paper are as follows:First,based on the literature review,the paper studied the influence factors of tunnel collapse,the present research situation of layered rock mass,the stability of tunnel surrounding rock and the tunnel collapse failure mode of layered rock.This paper has made an in-depth understanding of the present situation of tunnel collapse,identified the significance of the study of closed-type collapse,clarified the research ideas,and put forward the research content and research methods corresponding to this subject.Secondly,according to the research content and research ideas,this paper designs a test scheme which is suitable for this subject,and sets up a research method of the closed collapse experiment mechanism.Based on the theory of similarity simulation test,taking the IV grade surrounding rock as an example,the similar model test of three layers of 5cm,10cm and 15cm was carried out according to the working condition of layer thickness.The displacement and stress variation of supporting structure and surrounding rock are analyzed by experimentally determining the change of support and surrounding rock displacement stress state and failure development.Third,the finite element software ANSYS was used to simulate the displacement and stress of the support structure,the variation law of the stress distribution of the surrounding rock and the development of the plastic zone,and as a supplement to the similar model test.Finally,based on the analysis of the stress of the horizontal strata,combined with the "space effect" theory of the tunnel face,the mechanism of the closed-type collapse test of the tunnel under the near horizontal strata is studied by the similar model test and the comprehensive analysis of the finite element simulation analysis.