Deterioration Mechanism And Performance Of Deep Mine Shotcrete Security Analysis

In our country,the coal mining is gradually transferred to the deep.In addition to the deep outer load,there are also high ground temperature,rising humidity and various environment such as salt water erosion.In the deep roadway bolting and shotcrete support process,the concrete spray layer is influenced by the high temperature and erosive environmental factors,resulting in the decline of the durability of the spray layer and the effect of the support and sealing effect of the spray layer.In view of this problem,this paper studies the law of shotcrete deterioration under the deep environment through theoretical research,experimental measurement and simulation analysis,and puts forward the design scheme for improving the durability of concrete spray layer under deep well environment.Select the typical environmental factors of deep mine,and design the experiment of carbonization of shotcrete.The results show that the water cement ratio is the main material factor affecting the carbonization of concrete,and temperature is the main environmental factor to promote the carbonization of shotcrete.The 28d compressive strength of concrete after carbonization is about 1.1～1.2 times of that of the non carbonized specimen,but the carbonization of the spray layer reduces the basicity of the spray layer,which is not conducive to the protective effect of concrete on the bolt(net),so the carbonization process is controlled by the way of introducing water reducing agent.The result shows that the water reducer can improve the carbonization depth of the concrete spray layer.The microscopic measurement results show that the proportion of macro concrete in concrete decreases obviously and the density of specimens is increased.The results show that the quality of shotcrete increases first and then decreases with the increase of age of erosion,and the mass loss rate tends to be stable between 28d and 42d.The damage degree of shotcrete shows that the damage degree is not obvious at the early age,and tends to be stable at the age of 42d,and the damage degree increases irreversible after 56d.By adding steel fiber to study the erosion characteristics of concrete sulfate layer,the results show that steel fiber has a significant improvement on concrete damage.The reasonable interval of the thickness of the concrete spray layer under the bolting and shotcrete support is calculated,and 3 different shotcreting values are selected to simulate the bearing characteristics of the concrete shotcrete layer under the high ground stress environment of the deep well.The results show that the plastic zone range is reduced,the pressure of the spray layer and the displacement of the vault also decrease when the depth of the first injection is 70mm.Considering the characteristics of the protective layer of the shotcrete,it is more reasonable to choose the 70mm spray thickness.With the optimized mixture ratio and the obtained spray thickness to guide the field application,the sample of shotcrete was sampled in the field.Under the experimental conditions,the 28d compressive strength of the specimen and the displacement of the vault and two groups of displacement were measured.The results showed that the 28d compressive strength of the specimens accorded with the requirements,and the convergence of the vault and the convergent amount of the vault conforms to the requirements.The results show that the optimized spray layer has better strength development and supporting characteristics,and can meet the support requirements of the tunnel.