Fractured rock masses are common in engineering projects, such as tunnels, slopes, and open-pit mines, where the presence of internal defect structures significantly influences the stability of the rock mass. Among these, internal joints, as typical nonpersistent structural planes, are prone to progressive propagation and eventual coalescence in engineering practice, often causing geological hazards. In slope engineering, jointed rock masses are especially prone to shear-sliding failure along joint planes. Thus, understanding the shear behavior of rock masses with internal joints is highly important. However, most previous studies have focused on persistent joints, with limited research on rough internal joints due to challenges in sample preparation. To address this gap, this study employed sand-powder 3D printing (3DP) technology to fabricate rock-like samples with different joint roughnesses. Direct shear tests were carried out to examine the effects of roughness on shear strength, stress–displacement evolution, and failure morphology. Comparative analysis was performed between internal and persistent joints, and a constitutive model was developed on the basis of Jennings’ criterion. This research extends the applicability of sand-powder 3DP and demonstrates its potential as a novel methodology for investigating rough-jointed rock masses. The main findings are as follows: (1) The normal stress (σn) significantly suppresses the dilatancy effect, resulting in reduced peak dilatancy displacement. The samples with high joint roughness coefficients (JRC) exhibited “secondary dilatancy” in the post-peak stage. (2) Under the lower σn state, failure is dominated by slip-climb mechanism with brittle fracture of rock bridges. In the higher σn state, failure shifts to shear-off and abrasive wear with more complex crack patterns. (3) The shear strength increases nonlinearly with increasing JRC, with a marked increase once the JRC exceeds 10. The strengthening effect of σn weakens with increasing JRC, and persistent joints are more sensitive to this effect. (4) The residual strength is mainly controlled by the σn state, showing a stepwise increase with increasing magnitude, whereas the influence of the JRC is relatively minor. Under a higher σn state, samples with internal joints exhibit higher residual strength than those with persistent joints do. (5) the proposed shear strength model, constructed on the basis of the joint area ratio and JRC, demonstrates high predictive accuracy, with an error of 3.3% for internal joints and 8.57% for persistent joints. This study provides theoretical insights into the shear failure mechanism of rough-jointed rock masses and offers methodological support for slope stability evaluation in engineering practice.

Shear Behavior and Constitutive Models of Rock-Like Samples with Different Joint Roughnesses: A Novel Methodology Based on 3D Printing

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发表日期：

2026年4月13日

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Lishuai Jiang,
Chaolei Wu,
Yang Zhao,
Shichuan Zhang,
Xuepeng Zhang,
Qi Wu

摘要

Fractured rock masses are common in engineering projects, such as tunnels, slopes, and open-pit mines, where the presence of internal defect structures significantly influences the stability of the rock mass. Among these, internal joints, as typical nonpersistent structural planes, are prone to progressive propagation and eventual coalescence in engineering practice, often causing geological hazards. In slope engineering, jointed rock masses are especially prone to shear-sliding failure along joint planes. Thus, understanding the shear behavior of rock masses with internal joints is highly important. However, most previous studies have focused on persistent joints, with limited research on rough internal joints due to challenges in sample preparation. To address this gap, this study employed sand-powder 3D printing (3DP) technology to fabricate rock-like samples with different joint roughnesses. Direct shear tests were carried out to examine the effects of roughness on shear strength, stress–displacement evolution, and failure morphology. Comparative analysis was performed between internal and persistent joints, and a constitutive model was developed on the basis of Jennings’ criterion. This research extends the applicability of sand-powder 3DP and demonstrates its potential as a novel methodology for investigating rough-jointed rock masses. The main findings are as follows: (1) The normal stress (σ_n) significantly suppresses the dilatancy effect, resulting in reduced peak dilatancy displacement. The samples with high joint roughness coefficients (JRC) exhibited “secondary dilatancy” in the post-peak stage. (2) Under the lower σ_n state, failure is dominated by slip-climb mechanism with brittle fracture of rock bridges. In the higher σ_n state, failure shifts to shear-off and abrasive wear with more complex crack patterns. (3) The shear strength increases nonlinearly with increasing JRC, with a marked increase once the JRC exceeds 10. The strengthening effect of σ_n weakens with increasing JRC, and persistent joints are more sensitive to this effect. (4) The residual strength is mainly controlled by the σ_n state, showing a stepwise increase with increasing magnitude, whereas the influence of the JRC is relatively minor. Under a higher σ_n state, samples with internal joints exhibit higher residual strength than those with persistent joints do. (5) the proposed shear strength model, constructed on the basis of the joint area ratio and JRC, demonstrates high predictive accuracy, with an error of 3.3% for internal joints and 8.57% for persistent joints. This study provides theoretical insights into the shear failure mechanism of rough-jointed rock masses and offers methodological support for slope stability evaluation in engineering practice.