Influence Of Softening Of Basement Surrounding Rock On Mechanical Properties Of Invert In Mudstone Tunnel Of High-peed Railway

With the deepening of the strategic policy of "Western Development",the construction of high-speed railway in western China will be vigorously developed.Mudstone is widely distributed in western China and even in the whole country.Many tunnels will be built on the mudstone stratum.As one of the common diseases of mudstone tunnel,the floor heave of inverted arch will seriously affect the construction,operation and safety of tunnel structure.The failure reason,process and mechanism of the inverted arch floor heave of mudstone tunnel are complicated.At the same time,the softening of mudstone caused by groundwater is the main reason for the failure of the inverted arch floor heave.In addition,the dynamic action of trains during the operation period makes the surrounding rock and the tunnel structure in an extremely complex stress state.Therefore,it is of great significance to study the mechanical properties of the invert of the mudstone tunnel of high-speed railway under the condition of base softening.In order to satisfy the safety and comfort of high-speed train running,the important scientific problems of mudstone softening and train vibration on the floor heave of tunnel invert are solved.Relying on the project of National Natural Science Foundation of China,this paper adopts the method of combining mathematical statistics and numerical simulation to study the mechanical characteristics of surrounding rock and tunnel under the condition of mudstone softening,and then analyzes the dynamic response law under the combined action of softening and train load,and carries out consolidation and reinforcement according to the most unfavorable condition of basement softening.The main conclusions and results are as follows:(1)The temperature field plate of ABAQUS software is used to simulate the softening effect of mudstone tunnel after construction.Two conditions of softening of base and softening of both base and side wall are set,which are found by changing the softening depth of base: With the increase of softening depth,the deformation of surrounding rock and backfill increases correspondingly;When the softening depth is greater than 3m,the deformation of arch floor uplift changes significantly.The softening of both the sidewalls and the base can inhibit the arch floor uplift to some extent,but the softening has little effect on the settlement of the vault.With the increase of softening depth,the deformation law of backfill layer under the two conditions is basically the same.(2)Under the softening of the base,the influence range of the surrounding rock stress is near the bottom of the arch,while the softening of the sidewalls and the base makes the influence range of the surrounding rock stress extend to the upper area of the tunnel;ter both the side wall and the base are softened,the stress curve of the backfill layer tends to be basically stable when the softening depth is greater than 3m;With the increase of softening depth,the stress of primary lining arch foot changes significantly,and the softening of sidewalls can weaken the stress of arch foot to some extent;om the perspective of structural damage,the tensile and compression damage of the structure is 0 in the Microsoft stage,and the damage of the arch foot of the primary lining begins to appear in the middle softening stage.With the increase of the softening depth and degree,the damage value and range have a tendency to expand.(3)Under the train vibration load,the uplift of the bottom of the arch decreases with the loading time,while the settlement of the arch is opposite;The time history curve of the surrounding rock stress of the vault and the bottom of the arch showed an opposite law,but both of them first changed rapidly with time,then fluctuated first and then gradually tended to be stable;With the increase of softening depth,the stress of backfill layer decreases rapidly at first and then gradually becomes stable.With the long-term effect of train vibration load and base softening,the concrete in the middle of backfill layer is easy to crack and damage.(4)Based on the analysis of the acceleration response of basement surrounding rock and tunnel structure,the softening of surrounding rock not only affects the vertical acceleration peak,but also affects the amplitude after the acceleration time history curve is stabilized;With the increase of the base depth,the peak acceleration of the surrounding rock and its stabilized amplitude decrease significantly,and the softening of the base is the main factor affecting the acceleration.(5)The calculation results of basement softening treatment show that the softening effect of surrounding rock is significant when using anchor bolt and changing invert thickness,while the effect of changing invert strength is not significant.