Study On Permeability Mechanism Of Fiber Reinforced Concrete Tunnel Lining Based On Fracture Mechanics

Concrete has the characteristics of high compressive strength,easy forming and easy construction,it is widely used in tunnel engineering.Tunnel lining structure is an important barrier to protect the tunnel safety,it is necessary for it to meet the strength,stiffness and stability requirements.However,from the analysis of long-term use,the cracks in concrete reduce the impermeability and thus the durability of concrete.Currently,the application of fiber reinforced concrete at home and abroad to improve the impermeability of the method is more common.This paper mainly studies the fracture properties and impermeability of concrete with different fiber content and fiber types.Through the fracture mechanics test,the fracture process of fiber concrete was observed,and the influence of fiber content and type on fracture parameters was analyzed.Then,the impermeability test of fiber reinforced concrete was conducted.According to the test results,the change of impermeability properties of concrete with fiber content and type was analyzed.Finally,the results of fracture test and impermeability test were used to analyze the relationship between permeability coefficient and fracture parameters.The test results show that compared with polypropylene fiber,steel fiber can improve the compressive strength and split tensile strength of concrete;Compared with ordinary concrete,the elastic modulus of concrete decreases slightly after adding fiber;With the increase of the content of polypropylene fiber and steel fiber,the values of the cohesive tenacity K^c and G^c of concrete gradually increase,and the values of the cohesive toughness values K^c and G^c can be used as the evaluation criteria for the crack propagation capacity of cracked concrete;Polypropylene fiber has a lower degree of impermeability to concrete,and steel fiber can improve the impermeability of concrete to a great extent.The degree of impermeability of hybrid fiber to concrete depends on the content of polypropylene fiber and steel fiber;In the experiments in this paper,for the steel fiber with the same volume fraction,the more polypropylene fiber,the smaller the concrete permeability coefficient and the better the impermeability.Based on the fracture toughness Kⁱⁿⁱ,it can be used as a criterion to evaluate the crack propagation capacity of uncracked fiber concrete.Combined with the results of the permeability of uncracked fiber concrete,it is found that the fiber crack resistance is significant,and there is a certain correlation between the permeability coefficient and the fracture parameters.And the permeability coefficient,the fracture parameters Kⁱnini and fiber content were used as model parameters for regression analysis to obtain the permeability coefficient formulas of polypropylene fiber reinforced concrete and steel fiber reinforced concrete,which can be used for practical reference of the project.