Effects of cyclic freeze-thaw treatments on the fracture characteristics of sandstone under different fracture modes: Laboratory testing

Effects of the lining structure on mechanical and fracturing behaviors of four-arc shaped tunnels in a jointed rock mass under uniaxial compression

Water-bearing joints within rock engineering in cold areas are often subjected to frost heaving force in cold season due to water–ice phase transition. To evaluate the damage and stability of rock mass in cold regions, a 3D model that considers moisture migration loss during freezing and thawing was established to study the characteristics of frost heaving force within joints. Then, the numerical simulation of cyclic freeze-thawing of water-bearing joints was carried out through equivalent expansion coefficient and particle flow calculation methods. The distribution of frost heaving force in and around the joints was obtained. According to the results of the numerical tests and theoretical calculations, the frost heaving force in joints is basically stable, the tensile stress concentration area appears at the joint tip, and the frost heaving force decreases gradually away from the jointed rock mass area. The frost heaving force decreases considerably with increasing cycle number and moisture migration loss but it increases with increasing mechanical strength and joint geometric size of rock and ice. The comparison between the numerical solution of the equivalent expansion coefficient method and the theoretical solution shows that the force size and distribution law of frost heaving for the two methods are consistent.

Analytical and numerical analysis for frost heaving stress distribution within rock joints under freezing and thawing cycles

In this paper, the propagation mechanism of an oblique straight crack has been studied theoretically, which reveals its mechanical characteristics under in-plane biaxial compression. Firstly, the stress components away from the boundary are derived based on the superposition principle. The normal stress components are strengthened and shear stress component is restrained compared to the uniaxial condition. Then the relationship between stresses and stress intensity factors is analyzed, and the effect of stresses on the strength of cracked rocks is discussed. The analysis of wing crack growth shows that the reliable experimental results are very demanding for sample preparation. Based on Mohr-Coulomb criterion and Mohr’s stress circles, the failure mechanism of cracked rocks is analyzed, and the physical meaning of some formulas is vividly displayed. Moreover, we study the relationship between friction angle θ0 and angle β, which determines the minimum compressive strength of cracked rocks. There are evidences that the increase of crack opening width leads to β0 (a value of β) away from the theoretical value determined by sliding crack model, so that the role of stress σx can no longer be ignored. Theoretically speaking, for an initially closed crack, we find that, for the first time, both wing crack growth and shear compression failure are more likely to occur when the angle β between 22.5 and 45 degrees combining the statistical results of Barton and Choubey (Rock Mech Rock Eng 10:1–54, 1977). As for an initially open crack, the characteristics of stress intensity factors and circumferential stresses are also discussed, especially when σ1 equals σ3. Finally, we study the effect of osmotic pressure on stresses and stress intensity factors, the weakening of the properties of crack surfaces by water is also considered, and the mechanical behavior of a rock sample with an oblique straight crack changes dramatically.

The propagation mechanism of an oblique straight crack in a rock sample and the effect of osmotic pressure under in-plane biaxial compression

Nonlinear shear constitutive model for peak shear-type joints based on improved Harris damage function

An elasto-visco-plastic model based on stress functions for deformation and damage of water-saturated rocks during the freeze-thaw process

The invention discloses a construction method of a rock structural plane damage statistical constitutive model considering a size effect, which comprises the following steps of: firstly, simplifying astructural plane into an equivalent thin layer, and determining damage variables according to the number of damaged mesoscopic microelements and the total number of the mesoscopic microelements in the thin layer; secondly, obtaining a damage probability density function of the mesoscopic unit body; then, determining a reasonable damage initial stage, simulating the structural plane load condition, and obtaining a statistical damage constitutive model of the structural plane under the shearing effect; secondly, according to stress balance in the shearing process, determining the relation amongnominal shearing stress, effective shearing stress borne by the undamaged infinitesimal body and shearing stress borne by the damaged infinitesimal body, and obtaining a damage evolution model and astructural surface shearing deformation damage constitutive model of the structural surface in the shearing deformation process; determining parameters m and u0 of the structural plane shear deformation damage constitutive model, and establishing a structural plane shear constitutive model considering the size effect based on the nonlinear relationship between the parameters and the size; finallyverifying the correctness.

Ping Zou

Papers

An elasto-visco-plastic model based on stress functions for deformation and damage of water-saturated rocks during the freeze-thaw process

Construction method of rock structural plane damage statistical constitutive model considering size effect