Numerical simulation based on two-directional freeze and thaw algorithm for thermal diffusion model

Freeze-thaw processes significantly modulate hydraulic and thermal char- acteristics of soil. The changes in the frost and thaw fronts （FTFs） affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil com- prising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil tempera- ture at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation, showing potential applications of the method in land-surface process modeling.

Disturbance response instability theory of rock bursts in coal mines and its application

Aiming at the rock burst prevention in coal mines,this study argue that a rock burst is the instability of the coal mass deformation system with the infinite deformation response subjected to a small disturbance,and the concepts of control,disturbance and response variables of the coal mass deformation system are proposed.The analytical solution of rock bursts of circular roadways is derived,using a mechanical model of the coal mass deformation system of circular roadways,and the stress and energy conditions of the disturbance response instability of a rock burst are also presented.Based on the disturbance response instability theory,this study identifies the factors controlling the occurrence of rock bursts,involving the coal uniaxial compressive strength,coal bursting liability and roadway support stress.The relationship between the critical stress and the critical resistance zone of surrounding rock in roadways,the coal uniaxial compressive strength,roadway support stress,roadway geometric parameters and coal burst liability is revealed,and the critical stress index evaluation method of rock burst risk is proposed.Considering the disturbance and response variables of rockburst occurrence,a monitoring system of rock burst based on stress and energy monitoring is established.Considering managing the disturbance and control variables,regional and local prevention measures of rock burst are proposed from four aspects:destressing in coal mass,avoiding the mutual disturbance between multi-group mining or excavation,reducing the dynamic load disturbance and weakening of the physical properties of the coal mass.Based on the enhancement principle of the roadway support stress on the critical load of rockburst occurrence and the energy absorption effect of the support,an energy absorption and anti-bursting support technology for roadways are proposed.The disturbance response instability theory of rock bursts has formed a technical system from the aspects of mechanism,prediction and prevention to guide the engineering practice for rock burst mitigation.

Study of a damage constitutive model for water-bearing coal measures sedimentary rock with nonlinear deformation during compaction stage

The problem of repeated immersion-induced fatigue damage in engineering coal measures sedimentary rock,including coal-rock pillars,reservoir bank slopes,and water-rich tunnels at the boundary of coal mine underground reservoirs,has profound implications for their stability,safety,and operation,and can even lead to geological disasters.To address this issue,this paper aims to construct a constitutive model that accurately captures the comprehensive process of deformation and failure in water-bearing coal measures sedimentary rock.It explores the deformation characteristics of these formations and provides a theoretical foundation for numerical simulations of geological disasters induced by water-rock interaction.This study integrates the deformation mechanisms of void and matrix deformation in coal seam sedimentary rocks,while considering the influence of immersion cycles.Subsequently,it formulates a segmented constitutive model to depict the entire process of deformation and failure in cyclically immersed water-bearing coal measures sedimentary rock under uniaxial compression.The proposed model's accuracy and rationality are validated through comparisons with experimental research findings and existing theoretical curves from similar models.The results demonstrate the model's effectiveness in describing the deformation behavior of non-dense water-bearing coal measures sedimentary rock under uniaxial compression or low confining pressure before reaching peak stress,although further refinements may be necessary to precisely capture post-peak deformation characteristics.Model parameters,including the deformation caused by voids(γ0)between voids,increase exponentially with immersion times,while the elastic modulus(Ev)of voids and the parameter(F0)related to the average strength of microelements decrease exponentially.The homogeneity degree(m)exhibits no discernible pattern.These research outcomes provide valuable insights for the stability control of engineering coal measures sedimentary rock under water-rock interaction and the mitigation of related geological disasters.

Influence of cyclic dynamic disturbance on damage evolution and zoning effect of coal-rock under local static load constraint

In order to obtain the characteristics of the effects of cyclic impact loading on the damage of coal-rock in the presence of a local static load constraint,the evolution of the damage factor and the fracture rate during the process and incremental cyclic impact on raw coal and briquettes has been studied.Experimental results show that the presence of local static load restraint improves the impact resistance of the coal-rock,and the damage factor of the coal-rock shows obvious zoning characteristics.When the coal-rock is in an elastic state,the partition with a larger static load restraint area has stronger impact resistance,when the coal-rock is in a plastic state,the partition with a larger static load restraint area has a weaker impact resistance.Increasing impulsive cyclic impacts have a higher damage efficiency to coal-rock than constant impulsive cyclic impacts.The difference in rock breaking efficiency between the two cyclic impact methods is mainly reflected in the partition with the largest constrained area.The crack propagation on the coal-rock surface is more consistent with the partition characteristics of the damage factor.When the static load constrained zone is in an elastic state,the static load has an inhibitory effect on the crack growth.When the static load confinement zone is in a plastic state,the cracks mainly propagate in the static load confinement zone,and the constrained zone mainly consists of tensile cracks that grow in the vertical direction,while the cracks in the non-constrained zone mainly grow in an oblique direction.Finally,fracture mechanics was applied to analyze the failure type of the sample.