Mechanical coupling mechanism of multi-level face guard units in large-mining-height hydraulic supports: Theoretical modeling and design optimization

Abstract

This study proposes a hierarchical mechanical analysis framework for three-level face guard units in large-mining-height hydraulic supports. Through theoretical modeling based on plane bar system theory, we establish a multi-body dynamics model considering the nonlinear coupling between discontinuous contact states and coal wall unevenness. Introducing compound variation coefficients ( $k_{\mathrm{f}}$ , $k_{\mathrm{s}}$ , $k_{\mathrm{t}}$ ) and single-factor influence coefficients ( $a_i^{\mathrm{spo}}$ , $b_i^{\mathrm{spr}}$ ), the work quantitatively reveals the position-pressure coupling mechanism across hierarchical units. Experimental validation demonstrates 18.7% higher prediction accuracy compared with conventional integral rigid body models, particularly in second-level stress distribution (RMSE reduced from 4.32 to 3.51 MPa). Field data from Ningdong Mine confirm that the proposed overhanging design (>40 mm) reduces stress concentration by 32% at the upper plate edge. The stepwise cylinder diameter configuration (Level 1:200 mm > Level 2:180 mm > Level 3:160 mm) effectively prevents sequential failure risks under extreme loads. This research provides a theoretical foundation for optimizing multi-level face guard systems in 8 m+ ultra-high mining faces, addressing critical challenges in coal wall spalling control.