Out-of-plane behavior of confined masonry walls with aspect ratios greater than one

An experimental study on the out-of-plane behavior of confined masonry walls is presented. Four confined walls with aspect ratios greater than one were tested in the laboratory. Walls were subjected to combined axial and out-of-plane uniform loads. The variables studied were the aspect ratio and the axial compressive stress of walls. It was observed that the out-of-plane strength of walls increased as the aspect ratio or the axial compressive stress increased. Failure of walls was associated with crushing of masonry. Analytical out-of-plane strength of walls was determined using the yielding line, failure line, modified yielding line, compressive strut and bidirectional strut methods. It was concluded that the experimental out-of-plane strength of walls was best predicted with the bidirectional strut method.

Deviatoric Stress Evolution Laws and Control in Surrounding Rock of Soft Coal and Soft Roof Roadway under Intense Mining Conditions

Aiming at the problem of large deformation and instability failure and its control of soft coal and soft roof roadway under intense mining, laboratory experiments, theoretical calculations, Flac3D numerical simulation, borehole peeping, and pressure observation were used to study the deflection characteristics of the deviatoric stress of the gas tailgate and the distribution and failure characteristics of the plastic zone in the mining face considering the strain softening characteristics of the roof and coal of roadway, and then the truss anchor cable-control technology is proposed. The results show the following: (1) The intense mining influence on the working face will deflect the peak deviatoric stress zone (PDSZ) of the surrounding rock of the gas tailgate. The influence distance of PDSZ is about 20 m in advance and 60 m in lag; the PDSZ at the gob side of the roadway is located in the range of 3–5.5 m from the surface of the coal pillar, while the coal wall side is mainly located in the range of 3–4.5 m at the shoulder corner and bottom corner of the solid coal. (2) The intense mining in the working face caused the nonuniform expansion of the surrounding rock plastic area of the gas tailgate. The two shoulder angles of the roadway and the bottom of the coal pillar have the largest damage range, and the maximum damage location is the side angle of the coal pillar (5 m). Angle and bottom angle of coal pillar are the key points of support control. (3) The plastic failure line of the surrounding rock of the gas tailgate is always between the inner and outer contours of the PDSZ, and the rock mass in the PDSZ is in a stable and unstable transition state, so the range of anchor cable support should be cross plastic failure line. (4) The theoretical calculations and numerical simulation results agree well with the drilling peep results. Based on the deflection law of the PDSZ and the expansion characteristics of the plastic zone, a truss anchor cable supporting system with integrated locking and large-scale support function is proposed to jointly control the roof and the two sides, which effectively solves the problem of weak surrounding rock roadway under severe mining deformation control problems realizing safety and efficient production in coal mines under intense mining.

CRUSHING CHARACTERISTICS OF SOIL PARTICLE ON THE EFFECT OF STRESS PATH

In previous studies, we have conducted tests under various conditions of stress for the particle crushing. Anyway, it is necessary to perform the crushing test that assumed stress conditions in ground under controlled each principal stresses individually, to find the mechanical characteristics of the soil with particle crushing. Therefore, the purpose of this study is to confirm the effect for particle crushing under various stress paths in the combination of principal stresses. We planned four combinations of principal stresses when operate the mean stress p and deviatoric stress q up to the Shear Failure Line (SFL) on the 𝜋-plane. First, we set tri-axial extension test as Lode angle 𝛳=60° and tri-axial compression test as 𝛳=0°, and set two of the remainder as 𝛳=40°, 20°. The crushing tests are carried out using the high pressure true tri-axial compression apparatus under the planned stress paths. As a result, the progress of the particle crushing becomes active in order of 𝛳=40°, 20°, 60°, 0°, and found out that deviatoric stress q has essential effect on the particle crushing.

Shear test as calibration experiment for DEM simulations: a sensitivity study

Purpose The effect of micromechanical parameters on the macromechanical behaviour of granular materials is analysed by using discrete element based model of the standard shear test. Design/methodology/approach Discrete element method based standard shear test simulations. Findings The approximate mathematical functions related to the effects of DEM micromechanical parameters density, Young-modulus, Poisson number, frictional angle, bond normal cohesion, bond tangential cohesion, rolling friction and particle shape on the macromechanical parameters of shear failure line (internal friction and cohesion) are determined by modelling large number of standard shear tests. Originality/value By knowing these effects of micromechanical parameters to the macromechanical behaviour of the simulated particle assembly, the calibration of discrete element models can be significantly accelerated.

The Modified Maximum Shear Stress Failure Theory of Ductile Material

In this study, the maximum and smallest vertical principle stresses σ1 and σ3 as well as maximum shear stress τmax distributions, obtained from Mohr circle in each quadrant, are used to investigate the applicability of various ductile material failure theories. Based on the yield tensile stress σyt equals to yield compressive stress σyc (σyt=σyc=σy) and the known practical yield shear stress and yield stress ratio τy/σy=0.42~0.75 of ductile materials, we prove that the maximum vertical stress failure theory cannot be applied to the first quadrant (σ1>σ3≧0) as well as the third quadrant (σ3<σ1≦0) while τy/σy< 0.5, and it does also not applicable to the second or fourth quadrant (σ1>0 and σ3<0). In this study, the modified maximum shear stress failure line can be fit all ductile material depending on τy/σy=0.42~0.75 in all quadrants, thus the more reasonable results can be obtained.