Roof Collapse Research Articles

Support Technology of Long Bolt in Roadway under Crushing Condition

In order to solve the problem that the roadway roof is large and easy to collapse under crushing conditions. Test shows that: Under the crushing condition, a considerable part of roadway surrounding rock deformation is in a given deformation state. The control effect of support resistance on surrounding rock deformation is limited at the level of existing technology. In this kind of roadway support, the deformation method of anchor cable high rigidity support should be abandoned. It is changed to adopt the long bolt with high elongation to adapt to the deformation of surrounding rock, and continue to provide high support resistance to prevent loose rock caving caused by roof collapse. Based on this, the supporting technology of replacing anchor cable with docking bolt is put forward to increase the coordination between supporting member and roadway surrounding rock deformation. The industrial test results of Baode coal mine show that the technology can adapt to the deformation of surrounding rock and effectively prevent the tunnel roof from caving due to the break of anchor cable.

Study on Law of Overlying Strata Breakage and Migration in Downward Mining of Extremely Close Coal Seams by Physical Similarity Simulation

Extremely close coal seam groups are widely distributed in China, and the main mining method is downward mining. In the downward mining process of extremely close coal seam groups, the violent movement of overlying strata will cause the redistribution of surrounding rock stress. It not only produces stress concentration on the pillar but also causes the roof of the lower coal seam to be broken and difficulty in maintaining the mining roadway. In this study, the physical similitude modeling method and field observations were used to study the breakage and migration law of overlying strata in the downward mining of extremely close coal seams. Results show that in the process of mining upper coal seam, the first weighting step of the main roof is 37.5 m and the periodic weighting step is 12.5 m. The occurrence of strata separation is beneficial to the prediction of roof weighting. When the working face advances to 25 m, the rock stratum approximating a parallelogram of height 5 m does not collapse, and the working face is relatively dangerous. When mining the lower coal seam, the overall pressure of the working face is large, but the periodic weighting of the working face is not obvious. The first collapse step of the immediate roof is 15 m. When mining the upper and lower coal seams, the subsidence of the monitoring point increases significantly at 17.5 and 15 m, respectively. The roof collapse of the lower coal seam occurs 2.5 m ahead of that of the upper coal seam. The hydraulic value of the support, roof fall height, and sloughing depth in the entire working face reach the maximum at the coal pillar, and the extreme points at the coal pillar are relatively concentrated. This research provides some guidance for the safe and efficient mining of extremely close coal seams in the future.

The Roof Support Load Analysis for Pre-Driven Recovery Room Parameters Design

Submitted by generalized experience entry longwall into pre- driven recovery room (PDRR) in foreign and Russian mine.Submitted by research characteristic state parameters of the roof at failed entry. Give a classification of roof collapse at the entrance longwall into PDRR.On the example of longwall panel 5а-10-18 mine Raspadskaya reviewed formation process of stress-strain condition in area for PDRR. Has been modeled process of entry longwall into PDRR in the conditions of heavy roof. Determine the expected load on the anchor and standing support, installed in the PDRR. Assessed the load on the longwall shield. When calculating the loads was taken into account the following parameters: width pre-driven recovery room, number of standing support in the PDRR and especially its placement, the rate of entry longwall into PDRR.

Rapid urban flood damage assessment using high resolution remote sensing data and an object-based approach

Torrential rainfall can generate landslides, flash floods, and debris flows which might become disasters, causing loss of life and damage to property and infrastructure. To respond opportunely to hydrometeorological hazards, it is necessary to assess, rapidly and accurately, damage to the affected area. This is commonly done through time-consuming reconnaissance visits to obtain detailed field information. This paper proposes a methodology which uses: i) high resolution satellite and RGB images from unmanned aerial vehicles (UAV), ii) digital elevation models (DEM), and iii) object-based image analysis (OBIA) for rapid urban flood damage assessment and estimation of the number of houses washed away, or with a total or partial roof collapse, by comparing pre- and post-event data. The case study was Tropical Storm Earl in 2016 that affected the town of Chicahuaxtla, Puebla, Mexico, due to the overflow of the Zempoloantongo River that cuts through the town causing several loss of life and severe property damage. The results indicate that the three-pronged approach proposed herein is able to discriminate changes before and after the event and improve image classification of washed-away or destroyed houses. The overall accuracy of the proposed automatic classification obtained with UAV data had a value of 97.4%. Structural damage was not assessed in this study.

Common Design Problems and Optimization Measures for Flat Slab Floor Structures

Compared with the traditional beam-slab structure, the flat slab floor structure has the advantages of simple load transmission path, beautiful appearance and outstanding economic benefits. It is widely used in the roof design of residential underground garages. In recent years, there have been many roof collapse accidents of underground garage in China. This makes the safety of the beamless floor become a hot topic. As a common structural form, the flat slab floor structure has the advantages of cost saving and convenient construction, but the potential risk factors for continuous collapse are more complicated than the traditional structure. Therefore, the study of the mechanical behaviour of the flat slab floor structure is very important. The article points out some common problems in the design of flat slab floor, and proposes many optimization and improvement measures, such as considering unbalanced bending moments and construction conditions, improving design methods, adding structural measures, etc.

Disaster-causing mechanism of roof “toppling–slumping” failure in a horizontal sublevel top-coal caving face

To reveal the disaster-causing mechanism of roof collapse in horizontal sublevel top-coal caving faces for steeply inclined thick seams, a mechanical model is proposed based on the engineering background of the Jiangcang #1 coal mine in China. It is indicated that there is a “toppling–slumping” roof failure mode in horizontal sublevel top-coal caving faces, and the impact load generated by roof topping and slumping is the main cause of disasters. The impact load increased with the increase in impact height and the decrease in top-coal fragmentation degree. The experimental results of granular top-coal impact experiments showed that the impact load decreases with the increase in top-coal laying thickness. The top-coal layer acts as a cushioning in the process of roof collapse, and the cushioning correction coefficient is between 0.40 and 0.65. The cushioning correction coefficient increases as the impact height, top-coal fragmentation degree and laying thickness increase. A method is proposed to calculate the impact load in this study, and it is validated by field measurements.

The method of prediction of roof collapse hidden trouble in the roadway of No.2 in Anjialing

The thickness and strength of strata composing roof stratum will change a lot because of the change of coal forming environments and long time geological evolution. Only knowing these changes exactly, we can get the right design and prevent roof collapse. We can get the thickness, relative position and location of cracks and roof separation of strata with the changing of length of roadway at any time, and design the roof of roadway dynamically according to the lithology and combination changes of roof. In accordance with these, we can ensure not only the economic, but also safety in production.

Eruptive chronology of the Acoculco caldera complex – A resurgent caldera in the eastern Trans-Mexican Volcanic Belt (México)

The Acoculco caldera complex (ACC) is located in the eastern part of the Trans-Mexican Volcanic Belt in the northern part of the State of Puebla. The complex sits at the intersection of two regional fault systems with NE-SW and NW-SE orientations. The ACC was built atop Cretaceous limestones, the Zacatán basaltic plateau of unknown age, early Miocene domes (~12.7–10.98 Ma), and Pliocene lava domes (~3.9–3 Ma). Detailed field mapping and stratigraphy studies complemented by 40Ar/39Ar and 14C dating allowed the division of the ACC volcanic succession into 30 volcanic units. Based on the new results and previous studies, the ACC eruptive chronology was grouped in four eruptive phases: syn-caldera, early post-caldera, late post-caldera, and extra-caldera. Inception of the ACC volcanism began around 2.7 Ma with the dispersion of an andesitic ignimbrite followed by the collapse of the magma chamber roof as attested by the presence of a lithic breccia in isolated parts of the caldera rim. The collapse produced a 18 × 16 km caldera depression which was partly filled by the ignimbrite (total volume of ~127 km3) followed by the establishment of an intracaldera lake of unknown total extension. Early post-caldera collapse activity (2.6–2.1 Ma) was restricted within the caldera producing 27 km3 of lava flows and domes dominantly of basaltic trachyandesite to basaltic composition. Late post-caldera collapse activity (2.0-<0.016 Ma) migrated dominantly to the caldera rim and periphery emplacing 90 km3 of magma as rhyolitic domes, lava flows, scoria cones, and two younger ignimbrites. The 1.2 Ma Encimadas ignimbrite (26 km3) was vented through the eastern margin of the caldera and dispersed to the northeast, and the 0.6–0.8 Ma Tecoloquillo ignimbrite and dome (11 km3) erupted from the southwestern margin of the caldera. The most recent eruption of this phase was vented close to the southeastern caldera rim producing the Cuatzitzingo (<16,710 ± 50 years BP) scoria cone. Extra-caldera activity (2.4–0.19 Ma) of the Apan–Tezontepec volcanic field produced scoria cones and lava flows of basaltic trachyandesite to basaltic andesite composition that are interbedded with the products of the caldera complex.Aeromagnetic data further constrains the edge of the caldera rim and is consistent with the presence of at least four intrusive bodies at depths of >1 km hosted in the Cretaceous limestones. These bodies might represent a series of horizontal mafic intrusions located at different depths that provide the energy that maintains the Acoculco geothermal system active.

Agricultural land degradation by piping erosion in Chaco Plain, Northwestern Argentina

Soil piping has been pointed out as an important water erosion agent in a wide range of climatic regions. It is responsible for high soil losses in loess derived soils. The goal of this study is to evaluate the factors that are acting in the generation of piping processes and explain the mechanism of pipe collapse initiation. The study was carried out in loess derived soils located in a rural area of the Chaco Plain, between Tucuman and Santiago del Estero provinces, in northwestern Argentina. Pipe collapse types were described and soil loss estimation was performed. Factors influencing the process were studied under six different categories, i.e. physico-chemical and soil mechanical, soil mineralogical, microstructural, biological, and land use properties. In the study area, pipes took place in agricultural fields, principally in pastures, with slope gradients between 1% and 3%. Soil pipe collapse occurred in the area as a consequence of sudden wetting of the collapsible soils during summer storms. Pipe collapse forms vertical pipes or macropores that provide pathways for runoff directly into the soil pipe network. In addition, tension cracks adjacent to pipe collapses can provide pathways for preferential flow from the surface to the soil pipe network. With successive water infiltration the size of the pipes tends to increase and evolves to advanced stages of the process by internal erosion and eventually more pipe collapse. Blind gully formation is the final step of the piping process after the pipes roof collapse.

Increased Flexibility in Lab-on-Chip Design with a Polymer Patchwork Approach.

Nanofluidic structures are often the key element of many lab-on-chips for biomedical and environmental applications. The demand for these devices to be able to perform increasingly complex tasks triggers a request for increasing the performance of the fabrication methods. Soft lithography and poly(dimethylsiloxane) (PDMS) have since long been the basic ingredients for producing low-cost, biocompatible and flexible devices, replicating nanostructured masters. However, when the desired functionalities require the fabrication of shallow channels, the “roof collapse” phenomenon, that can occur when sealing the replica, can impair the device functionalities. In this study, we demonstrate that a “focused drop-casting” of h-PDMS (hard PDMS) on nanostructured regions, provides the necessary stiffness to avoid roof collapse, without increasing the probability of deep cracks formation, a drawback that shows up in the peel-off step, when h-PDMS is used all over the device area. With this new approach, we efficiently fabricate working devices with reproducible sub-100 nm structures. We verify the absence of roof collapse and deep cracks by optical microscopy and, in order to assess the advantages that are introduced by the proposed technique, the acquired images are compared with those of cracked devices, whose top layer, of h-PDMS, and with those of collapsed devices, made of standard PDMS. The geometry of the critical regions is studied by atomic force microscopy of their resin casts. The electrical resistance of the nanochannels is measured and shown to be compatible with the estimates that can be obtained from the geometry. The simplicity of the method and its reliability make it suitable for increasing the fabrication yield and reducing the costs of nanofluidic polymeric lab-on-chips.

Design of the Key Bearing Layer and Secondary Mining Technology for Previously Mined Areas of Small Coal Mines

In many underground coal-mine fields, where small scale coal mining had been performed, the available resources were not extracted fully. To extract the remaining coal, it is necessary to perform secondary mining. In this paper, a novel secondary mining technology is suggested incorporating a novel concept of building a key bearing layer (KBL) through backfilling in the previously mined areas to increase the extraction ratio, prolong the mine life, and avoid undesirable impacts on the limited coal resources and ecological environment. To analyze the influence of previously mined areas of small coal mines on the secondary mining, two new methods of determining the thickness of the KBL, choosing of the backfilling material, the slice backfilling method, ABAQUS finite-element analysis, field monitoring of displacement, and secondary mining technology were implemented. The results show that a minimum thickness of 5 m is required for the KBL in B909 panel of Pingshuo No. 2 underground coal mine to ensure stability of both the roof and coal walls during the secondary mining process. Ruimi-backfilling material was used to construct the cutting layer and KBL with different compressive strengths in the previously mined areas to carry out the slice backfilling, which met the mining requirements of the normal coal seam with reduced cost. Numerical simulation results showed that, when the secondary mining face was 20 m away from the previously mined areas, the secondary mining stress overlapped with the stress which was there from the previously mined areas to result in roof collapses. When the secondary mining face approached the previously mined areas, the roof of the goaf had a large area of collapse, which was beneficial to the stability of the KBL. It was possible to use the field-monitored displacements to validate the numerical-modeling results. The proposed novel secondary mining technology with backfilling in the previously mined areas of small coal mines turned out to be a safe, high-yielding and efficient mining method.

Behaviour of H-section purlin connections in resisting progressive collapse of roofs

When a truss roof is subjected to sudden local damage, purlins are capable of bridging the damaged truss unit, thereby increasing the robustness of the integrated roof system. To investigate the bridging capacity purlins can provide, experiments were carried out on bolted fin plate connections that join thin-walled H-section purlins to the main truss, investigating their behaviour under a main truss-removal scenario. Eight specimens with varied connection details were tested. Results of all experiments are provided in detail, including the full-range vertical resistance versus displacement curves, the collapse-resisting mechanisms, and the failure modes, being either bolt shear failure or combined bolt bearing and net-section tensile failure. Experimental results showed that better bridging capacity can be achieved by adopting relatively larger diameter bolts, reducing the bolt group height, applying higher preloading force when installing bolts, and increasing the end distance for the bolt holes. Meanwhile, a theoretical model is proposed to predict the vertical resistance versus displacement response of the purlin-to-connection assembly. This model is capable of capturing the slip of bolts, and the gradual yielding and failure of the connection components, and thus gives predictions that are in reasonably good agreement with the experimental results.

Field study on the load transfer mechanics associated with longwall coal retreat mining

The two-entry longwall panel system is frequently used in underground coal mines in China. One of these entries serves only the current longwall panel while the other serves both current and subsequent longwall panels. The latter entry is built to survive the continuously high mining-induced stress generated by mining the current panel throughout the longwall mining process. The failure of the entry is controlled by the load transfer mechanics associated with the advancement of the longwall face. This paper presents a field study of the response of the entry during driving and longwall retreat phases. Extensive field data including entry convergence and changes in principal stresses are obtained for the Pingshu coal mine, China. A careful analysis of these data shows that the influence zone of the front abutment load on the trail entry can reach as far as 120 m outby the longwall face during panel mining. Bed separation can occur in competent fine-grained sandstone, which is 7.4 m deep into the trail entry roof. It is also found that the periodic collapse of the main roof above the mined-out area can continue when the longwall face has advanced 120 m away.

Physical modeling the formation of roof collapse zones in Vorkuta coal mines

Collapse of the roof during mining is a constant threat to the lives of miners and equipment performance. To predict it, different numerical and physical approaches are used. Physical modeling of the massif region from -951 m to -841 m using equivalent materials were undertaken in this investigation. Various options for mining the Vorkuta coal deposit were considered: mining only the upper industrial seam, mining the lower coal seam as a protective layer to the upper one, and assessing the impact on the collapse zone of the complex structure of the upper coal seam roof while maintaining an upward order of mining. The main results were as follows: calculated collapse zone is approximately 30% larger than theoretical; collapse zone decreased when using mining with lower protective coal seam; the largest collapse zone was observed when pinching the rocks in upward mining order. Therefore, the research has shown the need to adjust the project for a larger methane yield. Further large-scale modeling is needed for understanding the characteristics of the collapse zone.

Contributions for the Rehabilitation of the Castro da Senhora do Bom Sucesso - Mangualde (Portugal)

Portugal is undoubtedly, a destination for the practice of Nature Tourism, containing a vast and rich natural, historical and cultural heritage. This settlement, Castro of Senhora do Bom Sucesso is a place where the surrounding landscape stands out with several mountains around it, in an environment where the flora and fauna, characteristics of this region, stand out. The whole history of the place, refers to a certain period of the past, valuing it and able to make the experience that the Nature Tourism can provide even better. Being one of the highest places in the central region of Portugal, it is for many people, a special place of enjoyment and relaxation. In this place, hundreds of years ago, there were between 80 and 100 houses of ancient people from the Celtic culture. Later, due to the abandonment by Men, these houses became disused, falling into a rapid decay process with the collapse of walls and roofs, making the roads impassable and the place covered with vegetation. Thus, in this work, in methodological terms, based on literature review, the collection of cartographic elements of the place, and in the field and cabinet studies, it was possible to develop an investigation on the Military Heritage of the region, in order to analyze in detail, the relation of the nature of the place with the architecture. This work resulted in a proposal for the site of the former Castro do Bom Sucesso, with the main objective of creating an Ecotourism Park, around the Celtic culture and autochthonous nature, organized in the following main equipment: i) Reception of the Ecotourism Park; (ii) “Celtic Bungalows”; iii) Celtic Interpretation Center; iv) biological pool and v) Camping. The paper presents the main elements developed, from the design to the form and location of the equipment that, to be built, is believed to improve the regional economy through a scientific, didactic, cultural and sustainable tourism.

The Roman Eifel Aqueduct: archaeoseismological evidence for neotectonic movement at the transition of the Eifel to the Lower Rhine Embayment

The Lower Rhine Embayment and adjacent areas are characterised by neotectonic deformation resulting in differential crustal movement. Slip rates along the fault systems are very low (< 0.1 mm/a). Significant earthquakes are known to have occurred in the past but the faulting behaviour is not adequately known which hampers the risks assessment. We analysed the archaeological record of the largest Roman aqueduct north of the Alps. This so called Eifel Aqueduct is 95.4 km long, has its source in the Eifel mountains and supplied the ancient city of Cologne with calcareous fresh water. The aqueduct crosses major faults of the Lower Rhine Embayment perpendicular. Analyses of the aqueduct´s gradient gives weak evidence for creep along the Kirspenich Fault resulting in differential movement of hanging and foot wall in the order of a few centimetres. Vertical offsets of 15 and 35 cm are documented exactly where the aqueduct crosses the Holzheim Fault system close to the city of Mechernich. Here, also structural damage of the aqueduct is recorded and archaeological evidence exists for repair works on the aqueduct. We interpret these observations as well as the construction of a 4 km long deviation as necessary measures to keep the aqueduct operational after earthquake damage. The timing of the event falls within the period of aqueduct operation which is reconstructed to be between 80 ± 10 and 270 ± 10 CE. Supporting evidence for earthquake activity within this period is seen in the roof collapse of the nearby Kakus cave.

Numerical modeling of earthen dam breach due to piping failure

Based on model tests of earthen dam breach due to piping failure, a numerical model was developed. A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section. A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability. Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively. The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe. After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped. In addition, incomplete and base erosion, as well as one- and two-sided breaches were taken into account. The USDA-ARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model. Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process. Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge. Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model.

Structural control on karst water circulation and speleogenesis in a lithological contact zone: The Bossea cave system (Western Alps, Italy)

Geological surveys, structural mapping, and thin section analysis helped to unravel the speleogenesis and water circulation in the Bossea cave (Northern Italy), an unconventional karst system at the contact between carbonates and underlying insoluble rocks. The surveys within the cave and in the surrounding surface outcrops revealed a complex structural setting caused by the coupling of lithological-mechanical heterogeneities with two major regional left-lateral ESE-WNW strike-slip faults. Transpression associated with the faults led to a disharmonic deformation, accommodated by a detachment surface, between the buckled basement meta-volcanics and the disharmonically-folded-marble sequence laying on top. Low-angle shear zones, recumbent or drag folds, and small stacks of duplexes are localized next to this detachment. The preferential pathways for water circulation inside the vadose zone are the folded bedding interfaces in the meta-carbonate sequence. Fracture clusters at slipping bed terminations, on the other hand, provide through-sequence connectivity. Once underground stream water flow reached the cataclastic and highly deformed meta-volcanics of the detachment core and damage zones, erosion started, removing large volumes of rocks. The downward erosion of the Permian basement rocks caused gravitational instability and subsequent roof collapses, aided by structural control in the damage zone above the detachment surface (slip surfaces in between duplexes or drag folds). This gravitational instability ultimately led to the formation of the giant halls that are characteristic of the downstream part of the Bossea cave.

CONTROL TECHNOLOGY FOR COAL ROADWAY WITH MUDSTONE INTERLAYER IN NUI BEO COAL MINE

The insufficient effect of traditional supports (e.g. the U-shape structural steel support) has been verified from various vital accidents in terms of roof collapse in Vietnam coal mines. The situation is becoming more complex, particularly, where the overlying strata consist of series weak interlayers such as mudstone and/or coal gangue. This paper starts with the summary of the failure mode of existing supports used in Vietnam coal mines, followed by the FE simulation (RS2 programming) based on the given geological conditions. Then, a case study conducted at Nui Beo coal mine by using the high strength prestressed bolt to prevent the separation of mudstone interlayer is presented. The design based on systematic numerical simulation and careful discussion of the failure mode of traditional support technology has been successfully verified from practical application. The results revealed that the rheological strain is closely related to time, it is about 60 days from the firstly caving to be stable, the maximum displacement of the roof and ribs to ribs are 14 mm and 35 mm respectively. The first ever practical application of prestressed bolt in Vietnam coal mine roadway associated with mudstone interlayers indicated that, compared with current widespread passive support, it is an effective support technology for some other coal mines in Vietnam with similar geological conditions.

Devil Landforms as Resources for Geotourism Development: An Example from Southern Apulia (Italy)

The landscape of Murge Tarantine limestone ridge (southern Apulia, Italy) is marked by the presence of an isolated relief showing a singular shape and name, the Monte del Diavolo (i.e., the Devil’s Mount). The Monte del Diavolo is located in a very interesting area from a geological point of view since it shows an E–W trending high-fault scarp, the morphological effect of the right-lateral transtensive North Salento Fault Zone. The Monte del Diavolo is a small isolated conical relief reaching at its top 115 m above m.s.l.; it elevates about 20 m from the surrounding plain surface, stretching at about 95 m altitude. Its evolution has been influenced by the occurrence of strongly cemented breccia deposits, most likely due to cave roof collapse and calcite precipitation, which are more resistant to the karst denudation process than surrounding limestones. This paper would be the first step towards the cultural promotion of the Monte del Diavolo area, which is marked by geological and geomorphological peculiar features and by a relevant archaeological and natural heritage as well.