The blasting load during tunnel construction generates significant dynamic disturbances to the surface slopes.The poor stability of the accumulated layer slopes makes it highly susceptible to forming landslides in the accumulated layer and causing tunnel collapses.Based on the Qiaoping Mountain Tunnel project on the Yu-Xiang Expressway,a numerical model of the soil-rock mixture granular flow accumulated layer slope was established by combining CT scanning technology and the clump command in PFC.Dynamic triaxial tests were conducted to calibrate the mechanical parameters of the accumulated layer model.The FLAC3D-PFC3D coupling analysis method was used to study the stability of slopes with different accumulated layer thicknesses under tunnel excavation blasting.The results show that under the action of explosive stress waves,as the thickness of the accumulated layer increases from 0.25 times to 1.0 times the tunnel span,the particle velocity in the accumulated layer decreases by about four times,and the range of particle loosening almost disappears.The particle settlement slowly decreases from 2 cm to 1 cm and then remains stable.The bond-to-tension force chain ratio between particles rapidly increases from 2.2 to 4.5.Subsequently,the tensile failure between particles is minimal,and particle sliding is less likely to occur,leading to improved stability of the accumulated layer.When the accumulated layer thickness exceeds 1.0 times the tunnel span,the area of the plastic zone produced by blasting is almost symmetrically distributed and approximates the cross-sectional area of the tunnel.The plastic zone is located within the bedrock range and is concentrated near the arch crown and arch base.Overall,when the accumulated layer thickness exceeds 1.0 times the tunnel span,the dynamic disturbance effect of tunnel excavation blasting on the slope is significantly reduced.These findings provide theoretical support for the design and construction of tunnel entrance sections.
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