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<p>Negative Poisson’s ratio (NPR) bolts combine high strength, high ductility, and substantial energy-absorption capacity, making them promising for stabilizing jointed rock masses. However, the shear behavior and failure mechanism of the free segment of full-scale NPR bolts remain insufficiently understood. This study conducted full-scale double-shear tests on NPR bolts embedded in rock-like specimens with uniaxial compressive strengths of 20, 35, and 50&#xa0;MPa, representing soft, medium-hard, and hard rock, respectively, under three prestress levels. Conventional MSGLD-335 positive Poisson’s ratio (PR) bolts tested in 35&#xa0;MPa specimens served as controls. The results show that free-segment failure is governed by combined tensile and shear action, and the dominant failure mode changes from tension-dominated to shear-dominated as host-rock strength increases. A deformation model demonstrates that host-rock strength controls the extent of the shear-deformation and shear-reaction zones and the distribution of plastic deformation, thereby determining the failure mode. Under the same host-rock strength, the peak shear force, rupture displacement, and energy absorption capacity of NPR bolts were 1.37, 1.86, and 2.76 times those of PR bolts, respectively. A relative necking index was proposed to quantify deformation compatibility and material utilization; its lower mean value for NPR bolts indicates more uniform plastic mobilization. These findings clarify the free-segment shear mechanism of full-scale NPR bolts and provide a basis for the design of bolting systems in jointed rock masses.</p>

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Study on shear behavior of the free segment in jointed rock masses anchored by full-scale NPR bolts

  • 期刊论文

  • 发表日期：

    2026年8月1日

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  • Jun Yang,
  • Qingshuo Hao,
  • Wenhui Bian,
  • Chuanjiu Zhang,
  • Zhaoxi Zhai,
  • Kexue Wang

摘要

Negative Poisson’s ratio (NPR) bolts combine high strength, high ductility, and substantial energy-absorption capacity, making them promising for stabilizing jointed rock masses. However, the shear behavior and failure mechanism of the free segment of full-scale NPR bolts remain insufficiently understood. This study conducted full-scale double-shear tests on NPR bolts embedded in rock-like specimens with uniaxial compressive strengths of 20, 35, and 50 MPa, representing soft, medium-hard, and hard rock, respectively, under three prestress levels. Conventional MSGLD-335 positive Poisson’s ratio (PR) bolts tested in 35 MPa specimens served as controls. The results show that free-segment failure is governed by combined tensile and shear action, and the dominant failure mode changes from tension-dominated to shear-dominated as host-rock strength increases. A deformation model demonstrates that host-rock strength controls the extent of the shear-deformation and shear-reaction zones and the distribution of plastic deformation, thereby determining the failure mode. Under the same host-rock strength, the peak shear force, rupture displacement, and energy absorption capacity of NPR bolts were 1.37, 1.86, and 2.76 times those of PR bolts, respectively. A relative necking index was proposed to quantify deformation compatibility and material utilization; its lower mean value for NPR bolts indicates more uniform plastic mobilization. These findings clarify the free-segment shear mechanism of full-scale NPR bolts and provide a basis for the design of bolting systems in jointed rock masses.