Research On Tunnel Collapse Mechanism And Treatment Measures In Jiu Mian Expressway

Collapse in tunnel construction is one of the most common disasters.Due to the complexity and unpredictability of the geological conditions of tunnel engineering,large deformation,support damage and even collapse accidents are easy to occur in the construction of soft rock tunnel,such as SLATE and qiuchiao rock.Therefore,it is necessary to carry out targeted research on it,to summarize the mechanism of collapse and treatment measures,and to provide valuable experience for the subsequent construction of similar projects.Papers to Sichuan buffalo home nine continuous highway tunnel hole deformation of landslide and slope instability accident as an example,using the theory of geological survey,supplementary geological exploration,analysis and numerical simulation on the deformation of the tunnel and collapse mechanism is summarized,and the corresponding treatment measures were studied,and put forward the geological conditions in tunnel supporting parameters optimization of construction scheme.The main research results are as follows:(1)Based on the analysis of the engineering geological characteristics of the portal section of Shuiniujia tunnel and the process of large deformation of its initial support,it was concluded that the main factor of the collapse of the portal section of Shuiniujia tunnel was the poor engineering geological environment of the surrounding rock in the portal section of Shuiniujia tunnel,the surrounding rock was mainly soft rock,its rock quality was relatively soft,and the combination between rock layers was poor.After the tunnel was excavated in the air,it was affected by gravity and unloading deformation.The interlayer friction of the rock mass was not enough to support the gravity of the upper rock mass,resulting in soft rock deformation and large deformation of the tunnel vault(2)Through the supplementary survey of the engineering geological environment of Shuiniujia tunnel,it was found that the tunnel collapse was caused by many engineering geological factors.The engineering geological factors could be summed up into two reasons:(1)the surrounding rock of tunnel body was similar to that of portal section,the rock mass belonged to soft rock,the strength was very low,and the occurrence of rock stratum was steep.(2)There was gully landform on the surface above the left tunnel,and the survey data showed that there was a hidden fault under the gully,which was easy to sink and infiltrate,and the softening surrounding caused the poor mechanical properties of the rock stratum in the left tunnel.(3)Based on the analysis of the geophysical prospecting data of the tunnel surface slope,it was found that the tunnel surface slope was located in an obvious deep valley terrain,and there was a phenomenon of stress zoning in the distribution of the ground stress of this terrain,that was,there were stress change areas and original rock stress areas on the bank slope,and there were stress concentration areas at the valley bottom.The construction of the tunnel intensified the valley.The evolution process of stress field leaded to horizontal creep of weak rock mass,resulting in surface cracks,and then leading to the instability of the slope.(4)According to the mechanism and causes of the collapse in different parts of Shuiniujia tunnel,the corresponding treatment measures were put forward.The overall reinforcement plan of the tunnel was to change the road construction of the bridge outside the tunnel → reinforce the anti-slide pile on the front slope → change the arch construction of the temporary support section of the tunnel portal → construct the 17 m self-propelled pipe shed → dismantle the second lining trolley section by section → reinforce the end of the collapse by spraying concrete → use the geological radar to collapse in front Body tracing and detection → excavation construction.(5)In order to optimize the support system,the orthogonal test was carried out with the aid of the finite element software in this paper.A series of indexes such as displacement,plastic zone distribution and support structure stress of 16 groups of test groups were analyzed.After data processing and analysis,the optimization of the support system was completed.The optimal parameters of the support system were obtained as follows: the spacing of the steel arch was 0.5m,and the anchor bolt was locked the length of rod was 7m,and the length of system bolt was 7m.