Study On Mechanical Properties Of Surrounding Rock In Loess Tunnel Circle Partial Collapsible

In the past hundreds of years,with the development of China’s infrastructure,high-speed and special railway,highway,urban rail transit construction projects are increasing.Loess area also built a large number of railway,highway and other tunnel projects,has accumulated a wealth of engineering experience,but also faced with a series of urgent problems.Loess as a kind of very special soil,its collapsibility is a problem plaguing the construction of the project.And with the increase in the moisture content of loess,with a certain degree of suddenness.In the tunnel construction,the localized collapsing of the surrounding rock can cause the stress concentration of the lining structure in the collapsed part.And with the phenomenon of bias,resulting in lining cracking,peeling,falling,large deformation and other adverse effects.Therefore the paper takes the tunnel construction of Menghua Railway as the research object,and studies the above problems through field investigation,geotechnical test,model test and numerical simulation.The result are as follows:(1)Through the field investigation that bad terrain and geological conditions,such as:the development of gullies,rock and soil boundaries,etc.,under the action of groundwater and thawing water may lead to loess tunnel local collapse of ring surrounding rock.Resulting in reduced loess strength,lining structure to withstand increased load,causing large deformation of the tunnel,cracking and other phenomena;(2)Through the physical properties of the loess and the mechanical properties of the test,we can see that the new loess particles in the region than the major component of the powder particles,cohesion is low,under the action of water easily become flow plastic,the structure is damaged,resulting in reduced mechanical properties;(3)Through the methoud of numerical simulation,the variation law of stratigraphic settlement caused by the surrounding rock partial collapsible of loess tunnels is analyzed,and it is learned that the settlement of the overburden in the tunnel is proportional to the size and thickness of the collapsed area;(4)From the model test and the numerical results,it can be seen that the vault local area of loess moisture content increases the process of collapse,the greatest impact on the vault and arch shoulder;The right side of the shoulder collapse of the situation,the greatest impact on the right arch shoulder and right arch waist,but the rest of the location has also been a certain impact;Right arch waist collapsed in the case,the greatest impact on the right arch waist and right arch foot,right arch shoulder has also been a greater impact,the rest of the smaller impact(5)The model test and numerical analysis of the three kinds of working conditions of the vault,the collapse of the vaulted rock,the collapse of the arch shoulder rock and the arch waist rock,it can be seen that most influential factors of the collapsible collapse is the arch shoulder rock collapse.For the lining of the structure in the wet side of the arch shoulder and arch waist,vault and arch foot followed.