Research On The Lining Mechanical Properties Of Strong Weathered Surrounding Rock Tunnel In Deep Seasonally Frozen Soil Region

In the high-latitude seasonal frozen area of northeast China,the lining of old tunnels in weathered surrounding rock often suffers from leakage,ice hanging,and cracking caused by freezing and melting,which seriously affect the safety of train operations.Therefore,it is particularly necessary to propose a targeted treatment pl an using the external and internal forces on the lining during the water-rich and frozen periods.Based on the Middle East Railway Xing'anling Tunnel Project,this paper uses indoor physical property tests,theoretical analysis and numerical modeling to ana lyze the mechanical performance of the lining in the water-rich and frozen periods.Besides,the current grouting prevention methods are used to study the effects of surrounding rock grouting on the mechanical performance of the lining,which can provide a reference for tunnel disaster prevention in seasonal frozen areas.The main research contents and important results of this paper are as follows:(1)The cohesion,internal strength angle and thermal conductivity of the samples collected from the Xing'anling Tunnel site were obtained through completed triaxial consolidation undrained tests and thermal conductivity tests with different dry densities and moisture contents considering freeze-thaw cycles.Then,a temperature field model was established using ABAQUS based on local meteorological data and laboratory test results.(2)A mechanical model of the weathering surrounding rock tunnel in season frozen area was established by making use of the numerical temperature field.Then the dynamic water pressure and frost heave force of the model in the water-rich and frozen periods were verified respectively according to the analytic solution of lining water pressure and the monitoring data of frost heave force.At the same time,the change law of the external force and the axial bending moment of the lining during water-rich and frozen periods are analyzed.The analysis results show that the axial force of the lining above inverted arch increases with the increase of buried depth,and at inverted arch decreases with the increase of buried depth during the water-rich period and the freezing period.The moment diagram of the lining in the water-rich period is "inverted peach-shaped ",and in the freezing period is "gourd-shaped".(3)Finally,considering the grouting prevention method and the influence of the horseshoe-shaped grouting ring on the fully weathered tunnel model in the seasonal frozen areas,the changes of mechanical parameters of the lining,of the surrounding rock of the tunnel,such as dynamic water pressure,frost heave force,axial force and bending moment under the condition of grouting ring and without the grouting ring during the water-rich period and the frozen period were compared,and the changes of the external and internal forces on the lining were analyzed after changing the permeability coefficient and thickness of the grouting ring.Based on those,a form of circular grouting ring was proposed and compared with the traditional grouting ring form,which verified the feasibility of the circular grouting ring.