Numerical Simulation For Steel Fiber Reinforced Shotcrete And Its Application To Tunnel Lining

With the improvement of construction level,steel fiber reinforced shotcrete is widely used in the field of civil engineering construction.As a multi-phase composite material,steel fiber reinforced shotcrete has a relatively complicated internal structure in the space.It is difficult to describe the distribution of the steel fiber and the interaction between the steel fiber and the concrete matrix if only homogenization is used in the study.In this paper,a multi-scale research method is used.Firstly,a numerical simulation analysis is performed on the representative volume element of steel fiber reinforced shotcrete from a meso level to study the effects of steel fiber orientation,content,and aspect ratio on physical and mechanical properties of steel fiber reinforced shotcrete,calculate the macroscopic elastic modulus of the steel fiber reinforced shotcrete material based on the mechanical response of the representative volume element;then use the macroscopic elastic modulus to establish three numerical models of steel fiber reinforced shotcrete support schemes,and study each support scheme in tunnel excavation support suitability and technical requirements.Through the above research,the main results obtained in this paper are as follows:(1)The angle between the steel fiber and the spray direction in the plane of the vertical rock wall is deduced to satisfy the form of a sine function.Based on the distribution function,a three-dimensional numerical model of steel fiber is established.(2)(1)Effect of steel fiber distribution on the mechanical properties of concrete matrix.Steel fibers distributed along the direction of the external force can better exert resistance and help the concrete matrix share stress;when the angle of the steel fiber changes near the direction of the external force,the mechanical properties of the concrete matrix will be greatly affected;when the spray angle and the action direction of external load is vertical,the mechanical performance of steel fiber reinforced shotcrete is better than steel fiber pouring concrete.(2)Effect of steel fiber content on mechanical properties of concrete matrix.The maximum principal stress of the concrete matrix appears in the boundary area with less steel fiber content,and its value is about 2to 3 times of the maximum principal stress of the internal area.As the content of steel fiber increases,the average stress of the concrete matrix gradually decreases.(3)Under the action of high-pressure spraying,the steel fiber reinforced shotcrete has a higher bonding strength with the surrounding rock surface,so that it can better bear the surrounding rock pressure and control the surrounding rock deformation(3)Steel fiber mainly affects the mechanical behavior of concrete crack development stage and failure stage,but has little effect on the mechanical behavior of concrete elastic stage.The influence of steel fiber on the elastic modulus and compressive strength of concrete is small,and it can be considered that the same grade of steel fiber concrete and ordinary concrete are approximately equal in elastic modulus and compressive strength;the addition of steel fiber significantly improves the ductility of concrete and improves the residual strength and damage of concrete deformability.(4)Design three steel fiber reinforced shotcrete support schemes and conduct numerical simulation research.The suitability and technicality of each scheme are discussed from the perspective of tunnel deformation control;Study the effect of the thickness of the sprayed layer and the depth of the tunnel on the supporting technology of steel fiber reinforced shotcrete.For the excavation section with poor hydrogeological conditions,low surrounding rock grade,and deep tunnel burial depth,steel fiber reinforced shotcrete composite lining can be used for support.For good hydrogeological conditions,high surrounding rock grade,and shallow tunnel burial depth of the excavation section can be supported by single layer lining of steel fiber reinforced shotcrete and anchor rod;the supporting capacity of steel fiber reinforced shotcrete can be increased by increasing the thickness of the sprayed layer,but the thickness of the lining should not exceed 200 mm.