| In China,gypsum or anhydrite has been deposited in almost every period,In most cases,gypsum or anhydrite is easy to deposit together with other carbonate rocks,To form this kind of mixed salt rock containing gypsum or anhydrite.This kind of rock is called the gypsum rock in this paper,This kind of rock can be further divided into gypsum rock,hydrated anhydrite rock and anhydrite rock.Gypsum rock stratum has special engineering characteristics,Especially expansibility and corrosiveness.Engineering construction experience shows that gypsum bearing strata have special engineering properties,uneven composition,low strength,poor water stability,weak to moderate expansibility,corrosiveness and solubility,It has an important influence on the stability of the surrounding rock,the structural design and the selection of lining parameters.In some engineering cases,the corrosivity of corrosive rock and soil,the changes in the process of later environmental changes and their long-term effects have not been considered.It causes deformation and damage of tunnel structure,which is also increasing day by day.The strength of gypsum rock decreases after corrosion,on the other hand,it makes groundwater rich in sulfate ions,corroded tunnel concrete structure.Therefore,the experimental study on the corrosive gypsum rock of this tunnel is carried out.This paper focuses on the changes of hydrogeological characteristics,environmental water corrosion types and grades in the tunnel area.Then,the multi-level indoor corrosion immersion test under different factors is carried out by using the gypsum rock samples taken from the tunnel site.The attenuation process and degree of physical and mechanical strength of gypsum rock samples under indoor immersion conditions are studied by wave velocity test and hydrochemistry analysis of immersion solution.Based on the calculation of the corresponding rock mechanics parameters by the gypsum rock immersion corrosion test,using FLAC3 D numerical simulation software to study the influence of the change of surrounding rock strength on the change of stress and displacement of surrounding rock of tunnel.According to the above research ideas and methods,this paper summarizes the following research contents:1.General situation of special engineering geology in research and analysis area,It mainly includes regional geological structure,regional hydrogeological characteristics,types of corrosive rocks in tunnel area and changes of environmental water corrosion grade in different stages before and after tunnel excavation,etc.2.The corrosion immersion test of gypsum rock from the site of this tunnel was carried out,after soaking,the water chemical analysis of the soaking solution is made,and the effect of soaking erosion on the physical strength of gypsum rock is measured by the change of wave velocity of the sample.3.Based on the immersion corrosion test of gypsum rock,the mechanical parameters of the rock samples are converted,the FLAC3 D numerical simulation software is used to analyze the stress and displacement changes of the surrounding rock of the tunnel caused by the decrease of rock strength.4.Combined with the theoretical change law of stress and displacement of surrounding rock of tunnel and the actual formation lithology change and regional geostress characteristics of this Tunnel,And select the typical section of the tunnel to establish the model,analyze and study the change of the surrounding rock stress and displacement caused by multi line tunnel excavation and the influence of the reduction of the surrounding rock strength on the change of the surrounding rock stress and displacement. |
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