ABSTRACT
To examine the disparity in deformation behavior and mechanical qualities between anchor cables with C-shaped tubes and regular anchor cables under shear conditions. The double-sided shear tests of free-section anchor cables and anchor cables with C-shaped tubes were conducted utilizing the indoor large-scale double-shear test equipment with varying pretension loads. The indoor double-shear tests indicate that the inclusion of the C-shaped tube alters the stress distribution of the anchor cables inside the anchor cables with C-shaped tubes and mitigates the impact of stress concentration. Moreover, it facilitates the transition of the anchor cable's failure mode from a mix of tensile and shear breaking to mainly tensile breakage. In addition, ABAQUS finite element analysis software was used to establish a double shear test model of the anchor cable with C-shaped tube to accurately simulate the interaction and stress distribution among the anchor cable, C-shaped tube, and concrete block in the double shear test. The findings of the simulation results reveal that the numerical model can adequately depict the evolution of the stress distribution in the prestressed anchored structure and the damage of the concrete block with increasing shear displacement. The relational equation for the yield state of the anchor cable with C-shaped tube under combined tensile and shear loads is found by integrating the experimental and simulation data, the static beam theory, and the concept of minimal potential energy.
ABSTRACT
To analyse the influence of normal stress (σn) and steel tube strength on an anchor cable with a C-shaped tube (ACC), we selected Q235 steel tubes and Q345 steel tubes as representative ACCs and carried out double shear tests of ACC-reinforced jointed rock masses. Based on the test results, the influence of the steel tube strength on the ACC axial force and shear force under different normal stresses, the characteristics of the shear force-shear displacement curve of the anchored flat structural plane (FSP) in the rock mass, and the ACC failure mode and contribution to the anchored concrete surface shear strength were studied. The test results show that under 2 ~ 10 MPa of σn, the failure angle varies between 28° and 40° due to the bending of the ACC near the structural plane and increases with increasing σn. Compared with Q235-ACC, Q345-ACC contributes more to the shear strength of the structural plane and can better exert its axial force when resisting the lateral shearing action of the structural plane. Additionally, we proved that σn is a main factor affecting the shear stiffness of the structural plane and that the Q345 C-shaped tube effectively improves the shear stiffness of an ACC-reinforced jointed rock mass and can more fully mobilize the anchor cable during shearing ductility in the tangential direction compared to the performance of the Q235 C-shaped tube. The research results can provide a reference for the further application of ACCs to roadways.
ABSTRACT
Preexisting cracks are of great significance for the stability of rocks, they can influence the growth and propagation pattern of cracks. For revealing the failure characteristics of rocks with prefabricated cracks, the mechanical behaviors of red sandstone with two close-collinear-equal length cracks were studied by acoustic emission (AE) monitoring experiment. The results indicated that the stress of red sandstone specimens showed an obvious stepwise growth phenomenon, and AE ring counts can better characterize the growth of microcracks of rocks. Moreover, AE events were mainly distributed near the prefabricated cracks of rocks. Then, a novel modified Kachanov method for analyzing collinear-close cracks was proposed. The influences of crack length and crack spacing on the interaction force of cracks were discussed. Then, it can be found that this modified method had a good applicability for two close-collinear-equal length cracks of rocks under compression.
ABSTRACT
A geological structural surface frequently appears in underground engineering and it significantly affects the stability of engineering structures. To elucidate the spatial-temporal failure characteristics of discontinuities between rocks, red sandstone with a firmly cemented discontinuity was investigated under uniaxial compression. The results revealed that adding a strong binder to rock discontinuities can improve the shear strength and stability of rock mass. The stress curve indicated that red sandstone specimens had elastic-brittle failure characteristics without obvious plastic deformation. The acoustic emission ring counts did not have large fluctuations, and its values were smaller (less than 2.5 × 104/s) at elastic deformation stage, which was termed as the "quiet period". The acoustic emission ring counts initially exhibited an obvious jump increase phenomenon at the forthcoming brittle failure stage before stress curve produced an obvious turning point, and then, it entered the "relatively quiet period". Based on the acoustic emission index (rise angle and average frequency), at the initial destruction stage of rocks, the types of internal fractures were simple and clearly (tensile cracks or shear cracks), and the fracture location was also relatively scattered inside specimens. Subsequently, the internal fracture developed into mixed tensile and shear cracks, and then, the fracture location exhibited a progressive evolution trend in the vertical space of specimens.