Study On Freeze-Thaw Damage Mechanism Of Surrounding Rock In Houwaizi Tunnel In Seasonally Frozen Area

With the in-depth implementation of the “Belt and Road” strategy in China,a large number of infrastructures are gradually developed.More and more tunnels must be built under extreme natural conditions such as high altitude and severe cold.Among them,the seasonally frozen areas that occupy nearly half of China ’s land area Most tunnels.Due to the obvious periodic changes of the ambient temperature in the seasonally frozen area,and the tunnel excavation will bring the ambient temperature into a certain depth of the tunnel,resulting in the freezing and thawing cycle of the surrounding rock and lining of the tunnel in the axial and radial areas of the seasonally frozen area.Disasters such as frost heave damage of tunnel surrounding rocks and the instability of supporting structure in the seasonally frozen area have seriously affected the stability,applicability and durability of the tunnel lining structure and seriously affected the driving safety of the tunnel.Careless handling will cause great economic losses and even threaten life safety.At the same time,the freeze-thaw damage problem in the tunnel engineering in the seasonal frozen area is a comprehensive problem,which needs to comprehensively consider the stress and strain,water migration and heat conduction during the freezing and thawing of the rock and soil body.The situation is not precise.Therefore,studying the destruction mechanism of tunnel surrounding rocks in seasonally frozen areas is of great significance to the rational design,maintenance and economy of tunnels.This article relies on the Houweizi tunnel project in the seasonally frozen area,using laboratory tests,theoretical calculations and numerical simulation methods to study the freezing and thawing damage mechanism of the tunnel surrounding rock.The main contents include:(1)Through the rock physical and mechanical tests on the limestone freeze-thaw cycle,the freeze-thaw degradation law of the limestone in the study area is obtained,and the freeze-thaw damage model of the tunnel limestone in the seasonal freezing area is established;(2)Using scanning electron microscopy images to obtain the microscopic pore fractal characteristics of rock,the microscopic pore characteristics and permeability of limestone after freeze-thaw cycles were studied,and the microscopic freeze-thaw damage mechanism of limestone in Houweizi tunnel was analyzed to obtain the freeze-thaw cycle The influence and variation characteristics of the test on the microscopic pores of the rock,and the mechanism of the effect of freeze-thaw on rock damage was obtained from a microscopic perspective;(3)According to the calculation of the frost heaving force of the surrounding rock of the Houweizi tunnel,the stress-strain frost heave law of the surrounding rock lining area,frozen area and unfrozen area of the tunnel is obtained.Through the numerical simulation of the three-field coupling of the hydrothermal force of the tunnel surrounding rock The influence law of freezing and thawing on surrounding rock damage.The research of this thesis has great research significance for the construction of tunnel engineering in the seasonally frozen area and the smooth development and safety evaluation of the traffic road network in China.