Small-scale Collapses Research Articles

1-G experimental study of the collapse effects on buried steel gas pipelines

Collapse disasters are commonly occurring geological disasters around buried gas pipelines and severely threaten the safety of pipeline operations. In this study, to investigate the soil deformation characteristics and mechanical response law of the pipeline under collapse, an experimental box (6 m × 1 m × 1.2 m) was built, and 1-G collapse experiments with different pipe diameters and burial depths were performed. The soil deformation laws, change in earth pressure around the pipeline, and mechanical response of the pipeline during the expansion of the collapse range were obtained by comparing and analysing the experimental results. Pipeline collapse disasters can be divided into two stages: before and after large-scale collapse disasters. The burial depth has an influence on pipeline collapse disasters mainly in a small-scale collapse range. As the collapse range increases, the influence of the burial depth on the strain distribution of the pipeline gradually decreases. However, an increase in pipe diameter can lead to a significant increase in the large-scale collapse range. Large-diameter pipelines bear greater strain than small-diameter pipelines after a large-scale collapse. This study provides data support for further research and serves as a valuable reference for pipeline safety evaluation in collapse disasters.

Retraction Note: Characteristics of rainfall pattern change in mountainous area based on dynamic adaptive and sustainable development of agricultural tourism

The research content of optimal control is to find out the admissible control rules according to the dynamic characteristics of the control system under specific constraints. According to the control object to be executed, the corresponding performance index is optimized. This kind of problem generally exists in the field of technology and practical engineering. In order to solve the optimal control problem, it is necessary to establish a mathematical model describing the motion process of the control object, specify the initial state and target set, give the allowable control range of the control variables, and define the performance index, so as to evaluate the quality of the motion process. According to the analysis of the splash rule of single raindrop on loess, the experiment of increasing rainfall was carried out, and the splash holes were produced around the slope in the first 10 min. With the increase of water, the slope erosion trough is formed due to continuous rainfall, which gradually expands to both sides and develops to the deep, resulting in small-scale collapse on both sides of the trough. With the acceleration of urbanization, ecoagricultural tourism is becoming more and more popular among tourists. Ecoagricultural tourism alleviates the environmental damage caused by over exploitation of tourism resources, makes the new agricultural mode and new business form obtain greater economic benefits, and also makes tourism find a new development path in China. This paper first expounds the background of the development of ecoagricultural tourism and the significance of the topic selection. On the basis of studying a large number of domestic and foreign literature on the development mode and approach of ecoagricultural tourism, it explains the related concepts and theoretical basis of ecoagricultural tourism.

Comprehensive evaluation on the stability of deposit slope from reservoir bank

In the construction of hydropower station in high mountains and canyons of southwest China, it is common to encounter deposit slopes of scattered collapse and debris flow. The deposit is formed by multi-phase and multi-genesis. Their material composition is dominated by crushed and lumpy rock and soil, and their structure is relatively dense. In natural conditions, the failure mode is mostly small-scale collapse, which has little influence on the project. With the construction of hydropower station, some deposits will be partially or completely submerged after reservoir impoundment. In reservoir impoundment condition, the stability of the deposit body decreases, and the local instability of the deposit body may cause the overall instability of the bank slope, resulting in surges and thereby endangering the safety of the dam and residents nearby.In this paper, a typical reservoir bank of a hydropower station in western China is taken as an example. The seepage characteristics and stability of the deposit body are calculated by using Geostudio series software. On this basis, the three-dimensional numerical simulation of the deformation of the deposit body is carried out by using FLAC-3D software. Through the comparison and analysis of the calculation results, the stability, deformation development trend and failure mode of the deposit body are summarized. It can provide reference for the comprehensive determination, monitoring arrangement and treatment of the similar deposit body.

RETRACTED ARTICLE: Characteristics of rainfall pattern change in mountainous area based on dynamic adaptive and sustainable development of agricultural tourism

The research content of optimal control is to find out the admissible control rules according to the dynamic characteristics of the control system under specific constraints. According to the control object to be executed, the corresponding performance index is optimized. This kind of problem generally exists in the field of technology and practical engineering. In order to solve the optimal control problem, it is necessary to establish a mathematical model describing the motion process of the control object, specify the initial state and target set, give the allowable control range of the control variables, and define the performance index, so as to evaluate the quality of the motion process. According to the analysis of the splash rule of single raindrop on loess, the experiment of increasing rainfall was carried out, and the splash holes were produced around the slope in the first 10 min. With the increase of water, the slope erosion trough is formed due to continuous rainfall, which gradually expands to both sides and develops to the deep, resulting in small-scale collapse on both sides of the trough. With the acceleration of urbanization, ecoagricultural tourism is becoming more and more popular among tourists. Ecoagricultural tourism alleviates the environmental damage caused by over exploitation of tourism resources, makes the new agricultural mode and new business form obtain greater economic benefits, and also makes tourism find a new development path in China. This paper first expounds the background of the development of ecoagricultural tourism and the significance of the topic selection. On the basis of studying a large number of domestic and foreign literature on the development mode and approach of ecoagricultural tourism, it explains the related concepts and theoretical basis of ecoagricultural tourism.

Process of overburden failure in steeply inclined multi-seam mining: insights from physical modelling.

Ground surface damage caused by steeply inclined coal seam mining is widely distributed in China, but there is little research on the failure process and movement mechanism of strata induced by steeply inclined multi-seam mining. In this paper, a physical model test is carried out to study the failure process and movement mechanism of overburden in steeply inclined multi-seam stepwise mining. The results show that at the initial stage, the main failure of the rock mass is the small-scale collapse at the initial cut and the roof (stability stage of the rock mass). After the roof is exposed over a certain range, the rock mass in the downhill direction slips into the goaf and gradually destroys the interburdens of the goaf, similar to the displacement effect of dominoes (severe failure stage of the rock mass). When the structure of the goaf fails, the overburden subsides, causing extensive damage to the ground surface. The surface damage directly above the goaf is mainly caused by serious subsidence deformation, while the surface damage in the downhill direction is dominated by cracks.

Active hydrothermal fluids circulation triggering small-scale collapse events: the case of the 2001–2002 fissure in the Lakki Plain (Nisyros Island, Aegean Sea, Greece)

In 2001–2002, two ground collapses occurred in the island of Nisyros (Aegean Sea, Greece), which formed a 600 m long and up to 5 m wide fissure in the vegetated central part of the Lakki Plain caldera. The fissure was alternatively ascribed to tensional stress release and hydrothermal alteration. In this study, we present original data of diffuse CO2 soil fluxes, soil temperatures, mineralogical and chemical composition of the caldera-filling deposits exposed on the fissure walls, and chemical and isotopic composition of interstitial soil gases collected from: the bottom of the fissure, the adjacent vegetated areas, the hydrothermal craters, and selected sites outside the caldera. The occurrence of intense hydrothermal alteration was shown by both mineralogical and chemical analyses of the fissure walls material. Typical mineral assemblage and enrichments in incompatible elements related to advanced argillic alteration, characterizing steam-heated hydrothermal environments, were recognized. Although the low-permeable sediment cover in the Lakki Plain concealed the underneath hydrothermal gas flow, preventing anomalous soil temperatures and CO2 fluxes, the chemical and isotopic composition of the interstitial soil gases revealed an active hydrothermal fluids circulation below the collapsed area, likely controlled by buried structural lineaments. Hydrothermal alteration can then be invoked as the most likely trigger mechanism for the 2001–2002 collapse event.

Hierarchical Star Cluster Assembly in Globally Collapsing Molecular Clouds

We discuss the mechanism of cluster formation in a numerical simulation of a molecular cloud (MC) undergoing global hierarchical collapse (GHC). The global nature of the collapse implies that the SFR increases over time. The hierarchical nature of the collapse consists of small-scale collapses within larger-scale ones. The large-scale collapses culminate a few Myr later than the small-scale ones and consist of filamentary flows that accrete onto massive central clumps. The small-scale collapses form clumps that are embedded in the filaments and falling onto the large-scale collapse centers. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps. Thus, the filaments feed both gaseous and stellar material to the massive central clump. This leads to the presence of a few older stars in a region where new protostars are forming, and also to a self-similar structure, in which each unit is composed of smaller-scale sub-units that approach each other and may merge. Because the older stars formed in the filaments share the infall motion of the gas onto the central clump, they tend to have larger velocities and to be distributed over larger areas than the younger stars formed in the central clump. Finally, interpreting the IMF at face-value as a probability distribution implies that massive stars only form once the {\it local} SFR is large enough to sample the IMF up to high masses. In combination with the increase of the SFR, this implies that massive stars tend to appear late in the evolution of the MC, and only in the central massive clumps. We discuss the correspondence of these features with observed properties of young stellar clusters, finding very good qualitative agreement, thus providing support to the scenario of global, hierarchical collapse of MCs, while explaining the origin of the observed cluster structure.

Cluster Assembly in Hierarchically Collapsing Clouds

AbstractWe discuss the mechanism of cluster formation in hierarchically collapsing molecular clouds. Recent evidence, both observational and numerical, suggests that molecular clouds (MCs) may be undergoing global, hierarchical gravitational collapse. The “hierarchical” regime consists of small-scale collapses within larger-scale ones. The latter implies that the star formation rate increases systematically during the early stages of evolution, and occurs via filamentary flows onto “hubs” of higher density, mass, and velocity dispersion, and culminates a few Myr after than the small-scale collapses have started to form stars. In turn, the small-scale collapses occur in clumps embedded in the filaments, and are themselves falling into the larger potential well of the still-ongoing large-scale collapse. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps towards the larger potential trough, so that the filaments feed both gaseous and stellar material to the hubs. This leads to the presence of older stars in a region where new protostars are still forming, to a scale-free or fractal structure of the clusters, in which each unit is composed of smaller-scale ones, and to the eventual merging of the subunits, explaining the observed structural features of open clusters.

Sea saltwater weakening of chalk and the impact on cliff instability

Chalk forms one of the major coastal cliff formations throughout Northwest Europe, with large population centres and critical infrastructure being exposed to and at risk from cliff collapses in this rock type. Traditionally, the two main factors leading to chalk cliff collapse have been considered to be: (i) waves attacking and eroding the base of the cliff and (ii) water weakening as the chalk becomes saturated. This work challenges the established view by identifying the role of salt from seawater in the degradation of porous rocks in coastal environments as a third and potentially the most important mechanism leading to chalk cliff collapse. Field and laboratory investigations have identified and quantified the role of sea saltwater weakening of chalk in coastal environments. A series of triaxial strength tests have identified that coastal chalks are up to 55% weaker than their inland equivalents. This weakening process is as a result of saltwater ingress into the chalk. SEM imaging has shown that seawater penetrates the porous chalk and the salt progressively concentrates, forming salt crystals which disrupt the pore structure and weakening the rock material which then leads to catastrophic cliff failure. Saltwater weakening of cliffs could be one of the main factors leading to large- and small-scale collapses observed along the chalk coast line, and is likely to be the primary reason for the increasing frequency of cliff failures along protected coastal sections as the sea salt progressively concentrates in the cliff reducing its mechanical strength. Rock strength is not usually considered to be temporally variable and is, therefore, rarely considered in relation to climate change. However, this is not true of soft rocks like chalk, which weaken and collapse in short time periods as they are exposed to external factors.

Geology of a submarine volcanic caldera in the Tonga Arc: Dive results

A submersible dive conducted on Volcano #1 located near 21° 09′S–175° 45′W on the Tonga Arc showed that the volcanic edifice with a caldera floor area of 30 km 2 located at and 450 m deep (b.s.l.=below sea level) was constructed recently during episodic volcanism. The sequential volcanic events are recorded along a faulted terrain formed in response to the collapse of the caldera wall. The post-caldera events are marked by occasional eruptions that have built scoriaceous cones associated with low-temperature hydrothermal venting and localized small-scale collapse features. The stratigraphy of the caldera wall indicates that the volcano was built by explosive volcanism alternating with quieter eruptive events. The repeated, violent explosive events formed ≤ 20 m thick sequences composed of alternating fine-grained ash beds and sand- to boulder-sized pyroclastic layers. During quieter volcanic events, dykes and massive flows intruded and/or accompanied the eruption of the volcaniclastic deposits throughout the sections of the wall explored. Massive columnar-jointed flows consist of viscous, silica-rich lavas forming tabular and giant radial-jointed (GRJ) flows formed in large (> 8 m in diameter) conduits and extruded onto the sea floor. In addition, massive lava flows forming sill-like complexes were observed underneath and near the giant radial-jointed columnar flows. Also, an intermittent quiet type of eruption produced vesicular lava flows, which are interbedded within the pyroclastic layered deposits. The massive and vesicular lavas consist of andesites and dacites with Ca-depleted (pigeonite) and Ca-enriched (salite) pyroxene, and intermediate (andesine-labradorite) to calcic (bytownite) plagioclase. They are depleted in total alkalis (Na 2O + K 2O < 3%), K 2O (< 1%), Zr/Y (< 1.8), Nb/Zr (< 0.01) and light Rare Earth Elements. We interpret that these andesite–dacite series were erupted after undergoing crystal-liquid fractionation in a magma chamber located underneath the caldera floor.

Measurement of ski snow-pressure profiles

Bulge-disc type pressure sensors of diameter 6 mm were fitted as near as possible to the running edge of a modern carved ski. The pressure signals were sampled at 30 Hz during long turns on snow, synchronously with signals from a geomagnetic compass and a pressure pad in the ski boot. The pressure from the snow was found to be highly variable with a mean value of about 50 kPa and dynamic pressure spikes up to 300 kPa. With the outside leg, the snow contact width in the rear part of the ski was found to be slightly wider, on average, than for the front part, as expected for a carving turn. Correlation within the pressure sensor data showed that the rapid pressure fluctuations were probably not due to bumps or features on the snow; instead they were probably caused by many small-scale collapses of the snow structure as the ski passed.

Investigation and Restoration Countermeasure Work for the Slope Disaster Induced by the 2005 West off Fukuoka Earthquake

The slope disaster and damage in Genkaijima, induced by the 2005 West Off Fukuoka Earthquake, have been investigated and studied by the investigating commission organized by the Japanese Geotechnical Society. The slope disasters in this island are classified into three areas: (1) damages of the housing site foundations and the retaining walls of steep slopes in the resident area, (2) landslides over the circumference road of the island, (3) small-scale collapses and cracks on the eastern slope from the Genkai elementary school to the Genkai junior high school. For each area, the results from on-site inspections, filed tests, indoor tests, measurements and analysis are reported together with the suggestion on restoration countermeasure work in this paper.

Coastal chalk cliff instability in NW France: role of lithology, fracture pattern and rainfall

Abstract Coastal retreat has been studied along 120km of French Channel chalk coast from Upper Normandy to Picardy. During the investigation period, 1998–2001, 55 significant collapses were recorded. Of these 5.5% were very large-scale, 34.5% large-scale, 34.5% medium-scale and 25.5% small-scale collapses. Observations indicate that the larger the collapse size the greater the coastal cliff retreat. Four types of cliff failure were observed: (1) vertical failures in homogeneous chalk units; (2) sliding failures where two superimposed chalk units were present; (3) wedge and plane failures mainly recognized in the UK in formations with stratabound fractures; (4) complex failures in cliffs with more than one style of fracturing. Rainfall in relation to the timing of cliff collapse indicates two periods that trigger a collapse. The first occurs about one month after heavy rainfall within poorly fractured chalk and the second occurs when a dry period is interrupted by sharp rainfall in cliffs with major karst features (pipes etc). Medium to small-scale cliff collapses were, in some cases, caused by marine erosion at the base of the cliff creating a notch. A key factor controlling the type of collapse is the lithostratigraphic unit, while the extent of the collapse scar may be controlled by fracture type.

Ground deformation monitoring at Mt Etna; evidence for dyke emplacement and slope instability

Ground deformation monitoring at Mount Etna has successfully enabled the sub-surface paths of two shallow feeder-dykes to be traced, and their dimensional parameters, depths and departures from the vertical, to be constrained. Determinations of horizontal movement have recorded the displacement, by 3.6 m (maximum), of a rim segment of the Valle del Bove flank caldera, due to dilation associated with dyke emplacement adjacent to the rim over the period 1981 to 1989. Small-scale collapse along this rim segment, associated with the opening of the 1989 fissure, points to increasing slope instability, and highlights the potential for major failure and debris avalanche generation.