Study on the Creep Damage Characteristics of Shale under the Combined Action of Osmotic Pressure and Disturbance Load

In the in situ modified fluidized mining engineering, the surrounding rock of the shaft wall is prone to creep instability damage under the action of disturbance and seepage water pressure, which seriously affects the stability of the surrounding rock of the deep in situ modified fluidized mining. In order to study the nonlinear creep damage and fracture characteristics of deep rocks under the combined action of seepage water pressure and disturbance load, a self-developed rock perturbation creep test rig under the action of seepage water pressure was used, and shale was used as the rock sample. In the method of staged loading, the rock uniaxial compression perturbation creep test under static axial pressure, different perturbation frequencies, and different seepage water pressures was carried out, and the creep characteristics of shale under the combined action of perturbation and seepage were studied. The results show that with the increase of seepage water pressure, the creep failure time of the rock decreases, and the ultimate strain value increases; with the increase of the disturbance frequency, the creep failure mode of the rock gradually transitions from shear failure to tension failure. When water pressure and disturbance load exist at the same time, rock creep is more sensitive to seepage water pressure; based on experimental results, a shale perturbation creep damage model considering the influence of seepage water pressure and disturbance frequency is established, and the model is verified. The research results have important theoretical significance for guiding the wellbore stability control of in situ modified fluidized mining engineering.

Study on the influence of stress wave disturbance on ultra-low friction effect of broken blocks

With the increase of mine mining depth, deep rock mass tends to be broken into block medium. The roof-rock layer-floor can be regarded as block system fractured rock mass. Under the condition of high ground stress and mining disturbance, the ultra-low friction effect of block system fractured rock mass is easy to occur, and then induce rock burst and other disasters. Taking the block rock mass as the research object, the self-developed ultra-low friction test system is used to carry out the experimental research on the ultra-low friction effect of the broken block under the condition of stress wave disturbance. Taking the horizontal displacement of the working block as the characteristic parameter reflecting the ultra-low friction effect, by changing the stress wave disturbance frequency and amplitude, the characteristic law of the horizontal displacement, acceleration and energy of the working block during the occurrence of the ultra-low friction effect is analyzed. The research results show that the stress wave disturbance frequency is related to the generation of ultra-low friction of the broken block. The disturbance frequency of the stress wave is within 1 ~ 3Hz, and the maximum acceleration and horizontal displacement of different broken degree blocks increase significantly. This frequency range is prone to ultra-low friction effect. The greater the intensity of the stress wave disturbance, the higher the degree of block fragmentation, and the more likely to have ultra-low friction effects between the blocks. The greater the intensity of the horizontal impact load, the higher the degree of rock mass fragmentation, the easier it is for ultra-low friction effects to occur. Stress wave disturbance and horizontal impact are the main reasons for the sliding instability of broken blocks. When the dominant frequency of the kinetic energy of the broken block is within 20 Hz, the ultra-low friction effect is more likely to occur.

Strength Weakening Effect of High Prestatically Loaded Marble Subjected to Low-Frequency Dynamic Disturbance under Point Load

The deep high prestatically loaded rock is often subjected to low-frequency dynamic disturbance and exhibits unusual strength characteristics, and thus, it is important to investigate the strength characteristics under the coupling effect of prestatic load and low-frequency dynamic disturbance loading conditions. In this study, a series of point load tests were conducted on the high prestatically loaded marble subjected to low-frequency disturbance by the MTS system, focusing on exploring the role of prestatic load level and low-frequency disturbance frequency in the process of rock strength change. Based on the average static failure load (Fmax) of samples under the static point loading, the high prestatic load levels (Fp) were selected as 70%, 80%, and 90% of Fmax, the corresponding low-frequency dynamic disturbance was loaded by sinusoidal waves with amplitudes of 60%, 40%, and 20% of Fmax, and the low-frequency dynamic disturbance frequencies (f) are 1, 2, 5, and 10 Hz. The change curve of the point load strength with the prestatic load level or the disturbance frequency was analyzed, which indicates that the point load strength under the coupled high prestatic load and low-frequency dynamic disturbance load was significantly lower than that under the pure static loading, presenting a significant point load strength weakening effect. Only when Fp or f reaches a certain level, the point load strength decreases significantly as f or Fp increases. Moreover, the point load strength weakening rate was proposed to characterize the degree of strength weakening. The comprehensive analysis demonstrates that Fp has a greater effect on the point load strength weakening effect than f, which is mainly reflected in the point load strength weakening level dominated by the Fp, and the weakening degree is affected by f.

The ghost of disturbance past: long-term effects of pulse disturbances on community biomass and composition

Current global change is associated with an increase in disturbance frequency and intensity, with the potential to trigger population collapses and to cause permanent transitions to new ecosystem states. However, our understanding of ecosystem responses to disturbances is still incomplete. Specifically, there is a mismatch between the diversity of disturbance regimes experienced by ecosystems and the one-dimensional description of disturbances used in most studies on ecological stability. To fill this gap, we conducted a full factorial experiment on microbial communities, where we varied the frequency and intensity of disturbances affecting species mortality, resulting in 20 different disturbance regimes. We explored the direct and long-term effects of these disturbance regimes on community biomass. While most communities were able to recover biomass and composition states similar to undisturbed controls after a halt of the disturbances, we identified some disturbance thresholds that had long-lasting legacies on communities. Using a model based on logistic growth, we identified qualitatively the sets of disturbance frequency and intensity that had equivalent long-term negative impacts on experimental communities. Our results show that an increase in disturbance intensity is a bigger threat for biodiversity and biomass recovery than the occurrence of more frequent but less intense disturbances.

Disturbance-induced changes in size-structure promote coral biodiversity

Reef-building coral assemblages are typically species-rich, yet the processes maintaining coral biodiversity remain poorly understood. Disturbance has long been believed to promote coral species coexistence by reducing the strength of competition. However, such disturbance-induced effects have since been shown to be insufficient on their own to prevent competitive exclusion. Nevertheless, Modern Coexistence Theory has revealed other mechanisms by which disturbance and, more generally, environmental variation can favour coexistence. Here, we formulate, calibrate, and analyze a size-structured, stochastic coral competition model using field data from two common colony morphologies. These two coral morphologies, tabular and digitate, differ in their size-dependent vulnerability to dislodgement caused by wave action. We confirm that fluctuations in wave action can promote coral species coexistence. However, using a recently proposed partitioning framework, we show that, contrast to previous expectations, temporal variability in strength of competition did not promote coexistence. Instead, coexistence was enabled by differential fluctuations in size-dependent mortality among competitors. Frequent and intense disturbances resulted in monocultures of digitate corals, which are more robust to wave action than tabular corals. In contrast, infrequent or weak disturbances resulted in monocultures of tabular corals. Coexistence was only possible under intermediate levels of disturbance frequency and intensity. Given the sensitivity of coexistence to disturbance frequency and intensity, anthropogenic changes in disturbance regimes are likely to affect biodiversity in coral assemblages in ways that are not predictable from single population models.

Mapping the forest disturbance regimes of Europe

Forest disturbances shape ecosystem composition and structure, and changes in disturbance regimes can have strong consequences for forest ecosystem services. Yet we currently lack consistent quantitative data on Europe’s forest disturbance regimes and their changes over time. Here we used satellite data to map three decades (1986-2016) of forest disturbances across continental Europe, covering 35 countries and a forest area of 210 million ha at a spatial grain of 30 m, and analyzed the patterns and trends in disturbance size, frequency and severity. Between 1986 and 2016, 17% of Europe’s forest area was disturbed by anthropogenic and/or natural causes. The 25 million individual disturbance patches had a mean patch size of 1.09 ha (range between 1st and 99th percentile 0.18 – 10.10 ha). On average 0.52 (0.02 – 3.01) disturbances occurred per km2 every year, removing 77% (22 – 100%) of the canopy. While trends in disturbance size were highly variable, disturbance frequency increased and disturbance severity decreased since 1986. Changes in disturbance rates observed for Europe’s forests are thus primarily driven by changes in disturbance frequency (i.e., more disturbances), and only to a lesser extent by increasing disturbance size. We here present the first continental-scale characterization of Europe’s forest disturbance regimes and their changes over time, providing spatially explicit information that is critical for understanding the ongoing changes in forest ecosystems across Europe.

What is the natural rhythm of temperate and boreal forest disturbances in the absence of human management?

<p>The vast majority of temperate and much of the boreal forest have been completely transformed by human activities, changing forest composition and disturbance regimes. Whilst our capability to observe this transformed state has improved dramatically in recent years, we have precious little information on the state of these forests in the absence of management. To what extent do our forests currently suffer from a surplus or a deficit of disturbance relative to their natural state? What are the implications of this for carbon turnover? Using a novel fusion of satellite observations of stand-replacing disturbances in 80 protected areas, statistical analysis and dynamic vegetation modelling, we generated wall-to-wall estimates of disturbance frequency across northern hemisphere temperate and boreal forests. Analysis of disturbance events in the protected areas revealed that the probability of disturbances from agents including fire, wind-throw and bark beetles was related to community mean functional traits and climate. We used the LPJ-GUESS dynamic vegetation model, which explicitly simulates plant functional types covering different successional stages, to simulate forest functional composition in the absence of human management. We interactively coupled this simulation to a new disturbance probability module to generate estimates of natural disturbance probability across all northern-hemisphere temperate and boreal forests. Disturbance frequency ranged from ca. one stand-replacing event per hundred years in parts of the boreal to less than one per thousand years in broadleaved temperate forests. In many regions the unmanaged disturbance frequencies differed dramatically from those observed in reality over the last two decades, with both disturbance surplus and deficits being recorded. In addition to providing the first quantitative continental-scale assessment of human impact on forest disturbance regimes, our results also provide a lightweight modelling approach for the inclusion of natural disturbances in large-scale vegetation models. They thus facilitate simulation of forest structure, a crucial driver of ecosystem function, from carbon uptake to biodiversity.</p>

Species traits, patch turnover and successional dynamics: when does intermediate disturbance favour metapopulation occupancy?

Background In fragmented landscapes, natural and anthropogenic disturbances coupled with successional processes result in the destruction and creation of habitat patches. Disturbances are expected to reduce metapopulation occupancy for species associated with stable habitats, but they may benefit species adapted to transitory habitats by maintaining a dynamic mosaic of successional stages. However, while early-successional species may be favoured by very frequent disturbances resetting successional dynamics, metapopulation occupancy may be highest at intermediate disturbance levels for species with mid-successional habitat preferences, though this may be conditional on species traits and patch network characteristics. Here we test this ‘intermediate disturbance hypothesis’ applied to metapopulations (MIDH), using stochastic patch occupancy simulation modelling to assess when does intermediate disturbance favour metapopulation occupancy. We focused on 54 virtual species varying in their habitat preferences, dispersal abilities and local extinction and colonization rates. Long-term metapopulation dynamics was estimated in landscapes with different habitat amounts and patch turnover rates (i.e. disturbance frequency). Results Equilibrium metapopulation occupancy by late-successional species strongly declined with increasing disturbance frequency, while occupancy by early-successional species increased with disturbance frequency at low disturbance levels and tended to level-off thereafter. Occupancy by mid-successional species tended to increase along with disturbance frequency at low disturbance levels and declining thereafter. Irrespective of habitat preferences, occupancy increased with the amount of habitat, and with species dispersal ability and colonisation efficiency. Conclusions Our study suggests that MIDH is verified only for species associated with mid-successional habitats. These species may be particularly sensitive to land use changes causing either increases or decreases in disturbance frequency. This may be the case, for instance, of species associated with traditional agricultural and pastoral mosaic landscapes, where many species disappear either through intensification or abandonment processes that change disturbance frequency.