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| Similar modelling study on the multi-peak attenuation effect of double tunnels in water-sealed storage cavern under variable amplitude impacts |
| HU Hongli1，CHANG Suling1，CONG Yu1，2，WANG Xiaoshan1，WANG Zaiquan1，ZHANG Jigang1，2，LI Renjie3，JIANG Hao3 |
(1. School of Civil Engineering，Qingdao University of Technology，Qingdao，Shandong 266520，China；2. Engineering Construction and Safety Collaborative Innovation Centre in the Blue Economic Zone，Qingdao，Shandong 266520，China；
3. Shandong Electric Power Engineering Consulting Institute Corp.，Ltd.，Jinan，Shandong 250013，China)
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Abstract In order to study the effect of variable amplitude impacts loading on straight-wall-top-arch double tunnels，similar model of large-size high-strength concrete tunnels were prepared，and a self-developed pendulum impacting system with biaxial stresses was used to carry out impact tests. A super-dynamic information acquisition system was used to record the impact wave and three-directional strain，and digital image correlation was used to characterize the surface strain and the displacement field，so that the mutation characteristics of double tunnels under pendulum impacts were investigated in multiple perspectives. The experiment revealed the following findings：(1) The frequency of the shock wave applied by the pendulum was 100～200 Hz，and there was peak incremental stage，oscillatory decay stage and stable stage in the wave curve，which is a variable amplitude shock wave with amplitude attenuation. The frequency decay amplitude increased from 9.30% to 43.88% under multiple impacts. (2) Five symmetrical cracks appeared in the spandrel and foot of the double tunnels with straight-wall-top-arch，and the wide and deep crack at the inter-cavern-arch-foot was in the form of upward concavity. The damage pattern was mainly affected by the first wave peak of impact force，and the width of the crack at the inter-cavern-arch-foot increased by nearly 6 times under multiple impacts. (3) The strain was mainly tensile strain，with the peak strain of axial direction about 10 400 μ? distributed at the inner arch foot，the peak strain of radial direction about 10 600 μ? distributed at the inter-cavern-arch-foot，and the peak strain of circumferential direction about 24 800 μ? distributed at the outer arch spandrel. The strain increased about 25 times and 5 times in the axial and radial direction under multiple impacts. (4) The vertical strain concentration zones appeared firstly in the inter-cavern-arch-foot within 350 μs. The inter-cavern-arch-foot crack developed from the two inner arch feet，and the strain was stable in the range of 0.002～0.005. The shear strain concentration zones appeared in the outer spandrel and inter-cavern-arch-foot，with the opposite strains occurring in the left and right. The vertical strain peak of the inter-cavern-arch-foot increased by 42.98%. Combined with the crack width and three-directional strain，it was considered that the inter-cavern-arch-foot was the weak part of the double tunnels under the variable amplitude impacts，and the monitoring and supporting should be strengthened in this position.
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