A Numerical Investigation for Rock Fall Impact Behavior of Pithead of Tunnel with Falling Weight Impact Loading

In order to establish a rational impact resistant design procedure for Arch type rock-shelter based on not only allowable stress design but also on ultimate state design and/or performance based design method, impact resistant capacity and/or maximum input impact energy for the RC structures must be clearly estimated. At present, the RC structures have been designed statically based on allowable stress design method. Here, maximum input impact energy for reaching ultimate state was numerically estimated by means of three-dimensional elasto-plastic finite element method for existing real arch-type RC rock-shelters with sand-cushion and EPS layer under falling heavy- weight impact loading. In this numerical analysis, solid elements were employed for concrete, falling heavy-weight and sand-cushion, and beam elements for rebar. Drucker-Prager and rebar yield criteria were used as material constitutive law for concrete and rebar, respectively. Cracks were estimated by allowing tensile stress cut-off at reaching at the tensile strength. In this paper, weight impact force, total axial force at the side-walls, displacement wave at the loading point, and crack patterns of the shelter at the time occurring of the maximum displacement are output. The results obtained from this study are as follows; 1). About twice the bending moment are generated at the edge as compare to the centre of falling weight in the direction of road axis. 2) It was observed that maximum response generation time of the bending moment and shear force is different. 3) When three layer buffer structure is set up in the tunnel pithead part, the sectional force can be decreased to about 1/2 to 1/5 in the mid-span compared with the case for sand cushion. Keywords: Pithead of tunnel; Three-layered absorbing system; Transmitted impact force; elasto-plastic response