Intermittent disturbance mechanical behavior and fractional deterioration mechanical model of rock under complex true triaxial stress paths

Mechanical excavation,blasting,adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass,leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters.Therefore,a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed.True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro.The effects of intermediate principal stress and amplitude on the strength characteristics,deformation characteristics,failure characteristics,and precursors of monzogabbro are analyzed,intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism.Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance.Based on the experimental result,the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed.A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established,and the model predicted results align well with the experimental results.The sensitivity of stress states and model parameters is further explored,and the intermittent disturbance behaviors at different f are predicted.This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.

Synergistic effects of tropical cyclones on forest ecosystems:a global synthesis

Tropical cyclones are large-scale strong wind disturbance events that occur frequently in tropical and subtropical coastal regions and often bring catastrophic physical destruction to ecosystems and economic disruption to societies along their paths. Major tropical cyclones can infrequently move into the midaltitudes and inland areas. Ecologically, tropical cyclones have profound impacts on diversity, structure, succession and function of forest ecosystems. The ecological effects are both dramatic and subtle. The dramatic effects can be visible, noticeable and to some extent predictable over the short-term and relatively well documented in the literature. However, the subtle effects are often invisible, complex and at smaller scale relatively unpredictable in the long-term. Many factors, meteorologic, topographic and biologic, simultaneously interact to influence the complexity of patterns of damage and dynamics of recovery. I present a global synthesis on the effects of tropical cyclones on forest ecosystems and the complexity of forest responses, with particular attention on the response to large hurricanes in the neotropics and the temperate North America, and strong typhoons on the subtropical and temperate forests in the East and Southeast Asia. Four major aspects provide on organizational framework for this synthesis：（1） consistent damage patterns,（2） factors that influence response patterns and predict damage risks,（3） complexity of forest responses and recovery, and（4） the long-term effects. This review reveals highly variable and complex effects of tropical cyclones on forest ecosystems. A deep understanding of the synergistic effects of tropical cyclones is essential for effective forest management and biodiversity conservation.

Impacts of fire severity and cattle grazing on early plant dynamics in old-growth Araucaria-Nothofagus forests

Background: Fire has historically shaped the dynamics of Araucaria araucana-Nothofagus pumilio forests in the Andean region of South America. Nevertheless, human disturbances and stronger drought events have resulted in increased occurrence and severity of wildfires. Regardless of their conservation relevance, the initial response to fire of Araucaria-Nothofagus forests has not been well documented. Through this research we tested the hypothesis that plant composition of Araucaria-Nothofagus forest after fire will initially differ in its recovery depending on fire severity, but over time, plant similarity will increase among areas with different levels of fire severity. The study was carried out in old-growth Araucaria-Nothofagus forests in south-central Chile(38°S) that were burned in 2015. We studied vegetation response to three levels of fire severity(low(LS), moderate(MS) and high(HS) severity), also including an adjacent unburned forest(UN), which were assessed one, two and three years after fire. We also evaluated the impact of cattle on plant recovery after fire. We measured species richness, abundance, plant diversity and origin of all vascular plant species.Results: Species richness and plant abundance responded differently to fire severity. Time-since-fire had a significant effect on plant richness and abundance. Plant composition within LS areas was similar to UN areas, but MS and HS areas were significantly less diverse compared to UN and LS. In absence of other major disturbances, similarity in plant composition tended to increase over time across the different levels of fire severity, becoming more similar to UN. We also found a synergetic effect of cattle and fire on species richness. This interaction promotes the establishment of nonnative species and limits the recovery of native species following fire.Conclusions: Fire severity had a significant impact on the plant community of old-growth Araucaria-Nothofagus forests,especially in areas of high fire severity, where the native tree N. pumilio was completely absent. Nevertheless,plant communities can recover gradually, depending on fire severity, time-since-fire, and the absence of cattle grazing. Management actions should include the exclusion of cattle within fire-affected areas and afforestation with N. pumilio in areas high fire severity due to its unsuccessful recruitment after fire.

Consolidation solution for composite foundation considering a time-and depth-dependent stress increment along with three distribution patterns of soil permeability

In actual engineering practice,the stress increment within a composite foundation caused by external loads may vary simultaneously with depth and time.In addition,column installation always leads to a decay of soil permeability towards the column.However,almost none of the consolidation theories for composite foundation comprehensively consider these factors until now.For this reason,a stress increment due to external loads changing simultaneously with time and depth was incorporated into the analysis,and three possible variation patterns of soil's horizontal permeability coefficient were considered to account for the detrimental influence of column installation.These three patterns included a constant distribution pattern(Pattern I),a linear distribution pattern(Pattern II),and a parabolic distribution pattern(Pattern III).Solutions were obtained for the average excess pore water pressures and the average degree of consolidation respectively.Then several special cases were discussed in detail based on the general solution obtained.Finally,comparisons were made,and the results show that the present solution is the most general rigorous solution in the literature,and it can be broken down into a number of previous solutions.The consolidation rate is accelerated with the increase in the value of the top to the bottom stress ratio.The consolidation rate calculated by the solution for Pattern I is less than that for Pattern II,which in turn is less than that for Pattern III.