A Coupled Thermal–Hydrological–Mechanical Damage Model and Its Numerical Simulations of Damage Evolution in APSE
This paper proposes a coupled thermal–hydrological–mechanical damage (THMD) model for the failure process of rock, in which coupling effects such as thermally induced rock deformation, water flow-induced thermal convection, and rock deformation-induced water flow are considered. The damage is considered to be the key factor that controls the THM coupling process and the heterogeneity of rock is characterized by the Weibull distribution. Next, numerical simulations on excavation-induced damage zones in Äspö pillar stability experiments (APSE) are carried out and the impact of in situ stress conditions on damage zone distribution is analysed. Then, further numerical simulations of damage evolution at the heating stage in APSE are carried out. The impacts of in situ stress state, swelling pressure and water pressure on damage evolution at the heating stage are simulated and analysed, respectively. The simulation results indicate that (1) the v-shaped notch at the sidewall of the pillar is predominantly controlled by the in situ stress trends and magnitude; (2) at the heating stage, the existence of confining pressure can suppress the occurrence of damage, including shear damage and tensile damage; and (3) the presence of water flow and water pressure can promote the occurrence of damage, especially shear damage.
Gas flow in hydraulic slotting-disturbed coal seam considering stress relief induced damage
Abstract Gas extraction in destressed coal seams is one of the effective measures to improve degasification efficiency and reduce gas disasters in deep coal seams. In order to reveal the influence of damage zone induced by stress relief on gas extraction of slotted boreholes, a multi-field model incorporating stress, damage, gas diffusion and gas flow in heterogeneous coal was established. By using this model, the stress relief induced coal damage around slotted boreholes was simulated with the example of Guhanshan Coal Mine. Besides, the effects of homogeneity coefficient, Langmuir volumetric strain constant and overburden stress on coal seam damage and gas extraction were analyzed. The following results were drawn: The rationality and engineering applicability of the model were verified by comparing the numerical simulated results with the field test data in Guhanshan Coal Mine. The stress relief induced coal damage zone around slotted boreholes rises gradually with the increase of the homogeneity coefficient and overburden stress, and the coal seam permeability rises gradually with the increase of Langmuir volumetric strain constant and the decrease of overburden stress. The reasonable borehole distance is determined to be 8 m which is obtained based on the variations of total gas production and gas pressure with different borehole distances. Therefore, reasonable borehole distances under varying conditions can be determined by integrating different geological conditions of coalmines with the proposed simulation method. The simulation results can provide theoretical guidance for the layout of stress relief boreholes and the improvement of gas extraction efficiency in the future.
Interaction of Diclofop-Methyl and MCPA on Wild Oats (Avena fatua)
Diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate} loses part of its activity on wild oats (Avena fatua L.) when it is applied in combination with ester or amine formulations of MCPA {[4-chloro-o-tolyl)oxy] acetic acid.} Uptake of diclofop-methyl is reduced in the presence of commercial formulations of MCPA, particularly amine formulations, which are only partly compatible with the diclofop-methyl formulation. With added MCPA, regardless of formulation, hydrolysis of diclofop-methyl to the acid diclofop is slowed down, both in intact wild oat plants and in a crude leaf extract. At the same time, conversion of any acid formed to inactive conjugates is accelerated in the presence of MCPA. It is concluded that the loss of activity of diclofop-methyl by MCPA can be accounted for by the effects of MCPA on uptake and metabolic conversion of diclofop-methyl.