Fracture Network Of Rock Mass Research Articles

Fracture evolution and failure characteristics of sandstone under freeze-thaw cycling by computed tomography

Long-term freeze-thaw (F-T) action causes the expansion of the fracture network in rock mass with ice-filled joints, triggering more serious engineering geological disasters. This study explores F-T damage effects and loading failure in double-fractured white sandstones with different saturation types (saturated and ice-filled). Saturated intact, saturated fractured, and ice-filled fractured sandstones were subjected to F-T cycle tests and uniaxial compression tests. Three-dimensional images of the specimens under various F-T cycles and stress states were obtained using computed tomography. The evolution in fracture morphology was evaluated visually, with pore network model parameters used for quantitative characterisation. Sandstone fractures evolved according to four main processes: frost-heave cracking, progressive expansion of damage, rock bridge penetration under load, and shear failure. The proportion of connected pores was used to estimate the influences of F-T cycling on pore-structure connectivity and fracture expansion in different specimen layers. During F-T cycling, pore characteristics vary according to size: micropores (equivalent radius < 100 μm) account for >60% of pores and increase in number more than pores of other sizes. Mesopores (100–500 μm) gradually decrease in number but their volume fraction remains >70%. Macropores (500–1000 μm) have the greatest increase in volume fraction. Early F-T cycling induces the connection of pore throats, while later cycling accelerates their expansion. Hydrostatic pressure increases are the leading cause of damage in ice-filled fractured sandstone, which exhibits greater variations in porosity, heterogeneity coefficient, and pore-throat parameters under F-T cycling than saturated fractured sandstone. The results provide insight into fracture evolution and failure characteristics in fractured rock masses with different saturation types (saturated and ice-filled) in cold regions.

Stress–strain relationship in elastic stage of fractured rock mass

Discontinuity is the main factor affecting the stress–strain relationship of rock mass. Based on the statistical parameters of the fracture network of rock mass and combining them with the strain energy theory from continuum and fracture mechanics, the elastic stress–strain relationship of fractured rock mass is proposed and its elastic modulus is derived. The stress–strain relationship can truly reflect the weakening and anisotropy of the mechanical properties of rock mass. On this basis, experimental and calculated stress–strain curves are compared, both of which exhibited the same slope. Additionally, monitoring data from a tunnel excavation is compared with the numerical simulation results, indicating that the displacement of both is basically consistent. Then, we compare three constitutive models with the statistical mechanics of rock mass (SMRM) model to highlight the advantages of the latter in terms of reliability and adaptability. Finally, based on the results of a bearing plate test of a rock mass at Jindong Bridge, the anisotropy of the elastic modulus and its influencing factors are studied. The results show that the weakening and anisotropy of the elastic modulus of the rock mass are notable, and the modulus changes according to the inter-angle between the stress axis and the normal of the discontinuity, reaching the minimum at an angle of 57.5°. The modulus is positively related to the friction angle and the cohesion of the plane and is inversely correlated to the average radius and density of the discontinuities. When the average radius of the discontinuities exceeds 3 m, the weakening of the elastic modulus of the rock mass tends to be stable. The stress environment also has an effect on the elastic modulus, which rapidly increases with the normal stress at the planes.

Analysis of Coupled Three-Dimensional Seepage and Temperature Fields in Fracture Network of Rock Mass

The coupling effect of seepage and temperature fields in fractured rock mass is a hot topic in the area of water conservancy, nuclear waste disposal and geothermal resources development. A coupling mathematical model of the seepage, flow temperature and rock mass temperature fields in the fracture network of rock mass is established based on the seepage and temperature interaction. A calculation program is developed and applied to calculate the seepage and temperature fields of the dam foundation of a water conservancy project. The interaction mechanism of the seepage, flow temperature and rock mass temperature fields is analyzed in this paper. Results show that the seepage field largely influences the temperature field, which can provide several suggestions for the deep underground disposal of nuclear waste, geothermal resources development and fractured rock mass in dam foundations. Considering the coupling effect of the seepage, flow temperature and rock mass temperature fields by the fracture network method is necessary.

Variational Inequality Formulation Method for Unconfined Seepage in 3D Fracture Network

A variational inequality formulation method to define the free surface of fracture network was given, related formulas were deduced and the Finite Element Method was used to solve the equations. By computing, the following conclusions were gotten, that is the variational inequality formulation method to solve unconfined seepage in 3 dimensional fracture network of rock mass is possible, and had a better numerical stability and much less mesh-depenciency.

Unsteady Seepage Through Random Fracture Network in Rock Mass

It is of great importance to study the unsteady fluid flow in the fracture network in rock mass and to simulate the seepage field in the fractured rock mass. The random distribution of the fracture network in rock mass is simulated by the Monte-Carlo method. The numerical program is developed based on the mathematical model of unsteady seepage in the fracture network. A case study is carried out by means of the program. It can be concluded that (1) the hysteresis of the hydraulic head distribution in the unsteady seepage field occurs in the case when the boundary condition is varying; (2) the hysteresis of the hydraulic head distribution in the unsteady seepage field is more obvious on the condition of the randomly variable apertures than the uniform apertures; (3) the seepage discharge is centralized in the larger-aperture channel; and (4) the hydraulic head distribution in the unsteady seepage field can be effected greatly by the variable apertures when the boundary hydraulic head conditions of the upstream and the downstream are varying greatly.

Numerical Study of Water Flow Induced by High-Pressure Air Intrusion into Fracture Network of Rock Mass

A numerical simulation was carried out to study the high-pressure air intrusion into fractured rock mass and the flow of fissure water induced by the intrusion: The fracture network model consists of many interstices of different widths and various directions.The results show that the air replaces the fissure water much fast-er in larger interstices than in smaller ones. Thus, larger interstic-es serve as the path of the air flow, while smaller ones function to store the water. This flow characteristics of the air and the fissure water is important to control the leakage of compressed air by water injection in fractured rock mass whose density of interstices is too small to regard rock mass as porous medium.