Study On Anti-blasting Numerical Simulation Of Urban Shallow Tunnel Lining Structure

Subway tunnel lining structure mainly builds up with reinforced concrete. Experimental and theoretic studies have made clear that increasing the thickness of lining layer is not an effective method to enhance the defensive performance, but the adoption of a new complex lining structure can enhance the anti-blasting capability remarkably. Complex lining structure mentioned here is a structure which is mainly made up of reinforced concrete with foam energy-absorption layers embedded in it.The study method of this paper is a numerical simulation on complex lining structure in sand soil using LS-DYNA by selecting reasonable model and material parameter, compounding stress wave theory. This paper studies the law of transmission and attenuation of stress waves in the compound lining structure, dynamic responses and failure patterns of normal lining structure and compound lining structure, and the influence of interlayer material and thickness and location of foam concrete in complex lining structure on anti-blasting capability of structure.The studies indicate that for the existence of foam-concrete layer, the propagating state of stress waves altered. The foam material plays an important role to the reflection and attenuation of shock waves. The foam material has great capability in deformation and energy absorbability and the foam concrete will absorb a part of energy in its deformation process. The total energy of the complex lining structure decreased, and the drop is about 97.3%.The dynamic response between normal lining structure and complex lining structure is quite different under the penetrate blasting. The fracture pattern of normal lining structure represents a punching failure on the whole as a result of material response. For the complex lining structure, the failure pattern of outer arch represents a punching failure generally. The failure pattern of inner arch represents a flexural failure as a result of coupling action between material and structure. Calculation results indicate that the enhancement of the anti-blasting capability of complex lining structure with foam interlayer is the best of the three adopted complex lining structures with air, sand soil and foam interlayer, and the optimal density of interlayer material is approximate to be 31.8% of that of reinforce concrete. The optimal thickness of foam concrete in complex lining structure is approximate to be 22.2%-33.3% of whole arch thickness. The optimal location of the foam concrete is obtained, and the thickness ratio of outer reinforce concrete to inner is about 1:2.