Development and application of a model test system for rockfall disaster study on tunnel heading slope

Abstract

To study the motion law of rockfall which collapses from the tunnel heading slope and the dynamic response of the open-cut tunnel to the impact, a large-scale three-dimensional model test system is developed by taking the heading slope above a tunnel exit of the under-constructed Chengdu–Lanzhou Railway as the study object. The system consists of high-strength model test bench, three-dimensional release device of falling blocks, a high-speed video camera and fiber Bragg grating-monitoring device, etc. Test bench whose largest exterior dimension is 3.4 m × 2 m × 2.5 m (length × width × height) is made of high-strength steel framework and tempered glass as body material to realize the visibility of the test process. The block-releasing device is mainly composed of a releasing box, three groups of slide rails, hydraulic cylinder and gas cylinder, by which can satisfy the requirements of the initial slip angles of rockfall in various test conditions. The high-speed video camera is adopted to capture the trajectory of the rockfall and video-processing software is used to calculate the motion parameters. Fiber Bragg grating-monitoring device is adopted to collect the information about force and deformation of the open-cut tunnel under the impact of rockfall and to study the dynamic response of the structure. Similar materials of slopes, falling blocks and open-cut tunnel are developed based on the existing geo-mechanical materials. Construction of the models and the arrangement of fiber Bragg grating-monitoring devices are explained systematically in the paper. The results of rockfall impact tests show that the mass, release height and impact angle of rock blocks have significant effects on the velocity restitution coefficient of blocks after impacting on the open-cut tunnel structure. The normal restitution coefficient of the block’s velocity is basically between 0.3 and 0.45. The model test system is reliable and can be applied in subsequent model test researches of rockfall disasters.