Study On Dynamic Response Characteristics Of Metro Shield Segment Under Explosion Load

In recent years,terrorist activities have become increasingly rampant,and subway tunnels,as an essential part of urban transportation,are often targeted for terrorist attacks.When explosives detonate inside a subway tunnel,the resulting shockwave can cause severe casualties.In addition,excessive explosive force can damage the subway tunnel’s structure,leading to the collapse of the surrounding soil and the instability of nearby building structures.Studying the dynamic response characteristics of subway tunnel shield segments under explosive loads is of both theoretical and practical significance for ensuring the structural safety of subway tunnels under explosive loads and the anti-explosion design of subway tunnels.Existing studies on the dynamic response of subway tunnel shield segments to explosions mainly use numerical simulation methods,with few involving experimental research on the dynamic response of shield segments under explosive loads.This paper focuses on single-ring subway tunnel shield segments and conducts non-contact and contact prototype experiments with explosives.Based on the collected data of shield segment strain,pressure,and acceleration during the experiments,the dynamic response characteristics of the shield segments to explosions are analyzed.The dynamic response of subway tunnel shield segments under explosive loads is simulated using ANSYS/LS-DYNA finite element software,and the numerical simulation results are compared with the field test results.The main conclusions are as follows:(1)In the non-contact explosion test,a 5kg emulsion explosive was placed at the center of the pipe ring,and the pipe segment did not suffer any damage.The pipe segment concrete was first subjected to compression and then tension,remaining in an elastic state.The overpressure on the pipe segment surface showed multi-stage peak values and an increasing trend in peak values.Near the ground,the pipe segment acceleration exhibited a secondary peak value,which was greater than the first peak value.(2)In the contact explosion test,when a 5kg explosive was placed close to the center of the standard block A2,the pipe segment structure was damaged,forming a rectangular explosion pit,with exposed rebar and angular cracks appearing at the top.Both the pipe segment concrete and rebar were first subjected to compression and then tension.In the circumferential direction,the tensile and compressive stresses in the concrete decreased with increasing distance from the explosive,while the tensile stress in the rebar increased with increasing distance from the explosive.In the axial direction,the tensile stresses in both the concrete and rebar increased with increasing distance from the explosive.In the radial direction,the concrete and rebar near the outer side of the pipe segment experienced greater tensile stress than compressive stress,while the concrete and rebar near the inner side of the pipe segment experienced greater compressive stress than tensile stress.At the same position,the outer concrete and rebar experienced greater tensile stress than the inner ones.Acceleration near the ground showed the appearance of a secondary wave peak.The surface overpressure of the pipe segment exhibited multi-stage peak values and an increasing trend in peak values.(3)In the contact explosion test,when a 5kg explosive was placed close to the edge of the standard block A2,the pipe segment structure was damaged,forming a rectangular explosion pit,with exposed rebar and angular cracks appearing at the top,and layer cracking at the edges.The pipe segment concrete was first subjected to compression and then tension.In the circumferential direction,the tensile stress in the concrete increased with increasing distance from the explosive.The other patterns were similar to those observed in the contact explosion test with a 5kg explosive placed close to the center of the standard block A2.Under the contact explosion,the pipe segment connection was the most severely damaged area apart from the area close to the explosive and should be the focus of attention in anti-explosion design.(4)The field explosion tests for the three cases were simulated using the ANSYS/LS-DYNA finite element software,selecting the JHC model to simulate the shield segment concrete,the MAT＿PLASTIC＿KINEMATIC model to simulate the rebar,and the D-P model to simulate the surrounding soil.The numerical simulation results for the damage patterns and various dynamic responses were compared with the field explosion test results to finally determine the parameters for each model used in the numerical simulation.The numerically simulated model and parameters validated by the field test results provide a basis for numerical simulation in the study of the dynamic response of a complete subway tunnel under explosive loads.