Roof Conditions Research Articles

Trait-based green roof plant selection: Water use and drought response of nine common spontaneous plants

Plant health and cover are critical components of stormwater mitigation on green roofs. Green roof plants can be selected from analogous habitats (e.g. rocky outcrops) and/or by using plant traits associated with survival (e.g. succulence). Plants selected for stormwater mitigation should have high transpiration to replenish substrate storage capacity following rainfall, which is likely associated with ‘fast’ traits such as faster growth rate or higher leaf area. However, ‘slow’ traits such as slower growth rate or smaller biomass can help plants survive dry periods. Without routine maintenance, green roof plant communities are often replaced by ‘spontaneous’ vegetation. As spontaneous species can survive green roof conditions, they may contribute to stormwater mitigation and understanding how their traits relate to drought and water use strategies may help improve green roof plant selection. Therefore, we conducted an eight-week glasshouse experiment to determine the water use and drought response of nine spontaneous species commonly found on green roofs under well-watered (WW) and water-deficit (WD) conditions. Higher transpiration under WW conditions was related to ‘fast’ traits including greater biomass, leaf area and relative growth rate. There was a trade-off between water use under WW conditions and drought resistance under WD. While ‘fast’ species reduced transpiration by 57–72 % and biomass by up to 50 % under WD, this was insufficient to maintain leaf water status (leaf RWC < 90 %) and avoid drought stress. Whereas, ‘slow’ species with less biomass used less water under both WW and WD conditions, maintained their leaf water status and resisted drought stress. Diverse water use and drought responses of the nine spontaneous species reflects fluctuating conditions on green roofs that likely favour different strategies over time. While spontaneous species may not be desirable, they are likely to provide similar stormwater mitigation to planted species where good plant cover is achieved.

Rebound Mechanism and Control of the Hard Main Roof in the Deep Mining Roadway in Huainan Mining Area

Taking the occurrence conditions of the hard main roof in the deep 13-1 coal mining roadway in Huainan mining area as the research object, based on the mechanical parameters of the surrounding rock and the stress state of the main roof obtained by numerical simulation, a simply supported beam calculation model was established based on the damage factor D, main roof support reaction RA, RB, and critical range C (9 m) and B (7 m) at the elastoplastic junction of the solid coal side and mining face side (hereinafter referred to as “junction”). Considering that the damage area still has a large bearing capacity, the vertical stress of the main roof at the junction is K1γH (0.05γh, 0.15γh, and 0.25γh) and K2γH (0.01γh, 0.10γh, and 0.2γh). The maximum deflection is 21 mm, 324 mm, and 627.6 mm, respectively. According to the criterion of tensile failure, the maximum bending moment of the top beam is 209 mN·m at the side of the working face 3.1 m away from the roadway side when K1 = 0.15 and K2 = 0.10, and the whole hard main roof is in tensile failure except the junction. To control the stability of the top beam and simplify the supporting reaction to limit the deformation of the slope angle, RC and RD are used to construct the statically indeterminate beam. By adding an anchor cable and advance self-moving support to the roadway side angle, the problem of difficult control of the surrounding rock with a large deformation of the side angle roof is solved, which provides a reference for roof control under similar conditions.

Variation of Phytochemicals in Leaves of Seven Accessions of Hibiscus sabdariffa Grown under Field, Green Roof, and High Tunnel Conditions

Variation of Phytochemicals in Leaves of Seven Accessions of <i>Hibiscus sabdariffa</i> Grown under Field, Green Roof, and High Tunnel Conditions

The Comprehensive Identification of Roof Risk in a Fully Mechanized Working Face Using the Cloud Model

Roof accidents seriously affect the safe and efficient mining of the working faces. Therefore, it is necessary to assess and identify the possible and influencing factors on the occurrence of roof risk in a fully mechanized mining workface. In this study, based on the analytic hierarchy process and fuzzy comprehensive evaluation, a comprehensive standard cloud model was established through constructing a quantitative grade interval and calculating the weight of each index to achieve the aim of a roof risk assessment and identification. The accuracy of risk assessment was ensured by using the comprehensive analyses of various aspects, such as cloud digital features, risk assessment cloud image and standard cloud image. This showed that the main influencing factors on the occurrence of roof accidents were roof separation distance, weighting intensity and rib spalling followed by the coal body stress concentration, initial support force and geological conditions. Taking 42,115 fully mechanized working faces in the Yushen coal mining area as an engineering background, this model was adopted to assess and identify the risk of roof accidents through generating comprehensive assessment cloud images and introducing the Dice coefficient to calculate the similarity degree. The results showed that the overall risk of roof accidents in 42,115 working faces was regarded as grade II (general risk) through the overall index of comprehensive risk evaluation and a similarity degree of 0.8606. The impact of roof condition was mainly influenced by the risk of roof accidents, while the support status, personal working status and coal body condition had a limited effect on the risk of roof accidents. The comprehensive standard cloud model proposed in this study had strong visibility and discovered the key parts of risk indexes easily to solve the problems of ambiguity and quantitative identification in traditional roof risk evaluation methods. Therefore, this model was worth promoting, because it laid the foundation for the intelligent identification and early warning system of roof accident risk in a fully mechanized mining workface.

Study on Bidirectional Blasting Technology for Composite Sandstone Roof in Gob-Side Entry-Retaining Mining Method

The traditional gob-side entry-retaining mining method has problems such as difficulty in roof collapse and large deformation of the entry, which may affect the safety of mine production. In this study, we introduced a bidirectional blasting technology (BBT) to make the roof collapse smoothly and to improve the traditional gob-side entry-retaining mining method. A theoretical model of the BBT was established and the stress propagation of the BBT was analyzed by numerical simulation. The gob-side entry-retaining mining method was then applied in a composite sandstone roof condition. Compared with ordinary blasting, the concentrated stress and directional cracks can be generated in the set direction after using the BBT technology. Field monitoring data suggested that the deformation of the retained entry met the requirements of mining, verifying the effectiveness of the proposed technology for composite sandstone roof. The results of the study have an important significance in solving the high pressure and large deformation problems in the coal mine roadway and saving coal resources, which also provided a reference for similar geotechnical mines.

Failure Characteristics and Stability Control of Bolt Support in Thick-Coal-Seam Roadway of Three Typical Coal Mines in China

Roadways in thick coal seams are widely distributed in China. However, due to the relatively developed cracks and brittleness of coal, the support failure of thick-coal-seam roadways frequently occurs. Therefore, the study of bolt failure characteristics and new anchoring technology is very important for the safety control of thick-coal-seam roadways. Based on field observations, the failure mechanism of selected roadway failures under distinct conditions at three representative coal mines in eastern and western China was analyzed. Recommendations are provided for roadway safety control. The results show that the strength and dimension of the anchoring structure in the coal roof of thick-coal-seam roadways are the decisive factors for the resistance of the roadway convergence and stress disturbance. The thick anchoring structure in the roof constructed by flexible long bolts can effectively solve the problem of support failure caused by insufficient support length of traditional rebar bolts under the condition of extra-thick coal roof and thick coal roof with weak interlayers. The concepts and techniques presented in the paper provide a reference for the design of roadway support under similar geological conditions and dynamic load.

Stability Analysis and Control Measures of Large-Span Open-Off Cut with Argillaceous Cemented Sandstone Layered Roof

This paper is based on the condition where layered argillaceous cemented sandstone as an engineering background is met by the No. 207 fully mechanized working face open-off cut (Wanli No. 1 Coal Mine). Through mechanical theory analysis and field practice, the engineering safety problem of the large-span argillaceous cemented sandstone layered open-off cut roof supporting structure was analyzed. The roof caving arch height of the open-off cut roadway in 207 working face was obtained based on the mechanical mechanism of instability and caving of the layered surrounding rock mass roof. The anchor cable suspension and bearing stability of the open-off cut roof were analyzed in terms of the layered beam structure model. Meanwhile, combining with conditions, reasonable and effective support countermeasures and key parameters are proposed for such open-off cut roadway and enhance the actual supporting engineering on-site. These research results could provide engineering reference for an open-off cut roadway with composite roof conditions featured to weak cementation and weak interlayer.

Experimental Study on Presplitting Blasting of Roof Cutting Along Goaf with Thick and Hard Roof Plate

In order to explore the reasonable blasting parameters of the gob-side entry retaining technology under the specific conditions of thick and hard roof, and realize successful roof cutting and safe roadway retaining, the thick and hard roof of the XV1306 working face in the first panel of Yixin Coal Mine is used as the research background. The drilling parameters of blasting are analyzed, which contains the depth of slitting, angle of slitting and spacing of blasting holes. And the influence of charge structure and charge amount on the effect of presplitting blasting was studied through underground blasting tests. The results show that when the blast hole depth is 10m, the drilling angle is 15°, and the blast hole spacing is 500 mm, with adopting the “2+3+4+4+3+2” method to the deep-hole charge structure, the top-cut crack rate is more than 90%. the penetration effect of top-cut crack is good, which can meet the needs of roof cutting for pressure relief and control of surrounding rock in roadway retaining.

Analysis of Fracture Mechanics Theory of the First Fracture Mechanism of Main Roof and Support Resistance with Large Mining Height in a Shallow Coal Seam

Because the first-weighting of a main roof with a large mining height has obvious sudden characteristics and is more severe, which causes large-scale support crushing and has a great impact on the ecological environment of the mining area, it is necessary to conduct an in-depth analysis. This paper studies the mechanical mechanism and asymmetric fracture conditions of a main roof with a large mining height, with the first-weighting occurring in a shallow coal seam. In combination with an asymmetric three-hinged arch structural model, the main roof was regarded as a finite plate model with a crack, and a fracture-mechanics model was established. The conditions and main controlling factors of main roof fracture asymmetry were analyzed, and the determination methods of the first-weighting interval and support resistance were further analyzed. The results show that the stress concentration and the stress-intensity factor increase at the crack tip with the advancement of the face; when the stress-intensity factors increase beyond the critical value, the crack expands until the first-weighting. The sufficient condition for modeling the instability was the length s of the branch crack reaching the protection thickness H of the main roof, and the necessary condition was the activation of the crack. The calculation equations of the first-weighting interval and the support resistance were obtained. The influence weights of each parameter on the support resistance are ordered as follows: overburden load q &gt; rock fracture toughness KC &gt; crack length a &gt; main roof thickness h &gt; weighting interval l. Finally, the theoretical analysis results were verified by an in situ monitoring case of the no. 33,206 working face in the Bulianta coal mine, China. On this basis, a reasonable value of the support resistance is further calculated. The results mentioned above can provide a new method for researching the first-weighting of the main roof and can improve the accuracy of the roof control analysis. The research on the mechanisms of first-weighting and the support resistance can effectively promote the safety production of mine, which is in line with the concept of green and sustainable development of the mine.

Research on Non-Pillar Coal Mining for Thick and Hard Conglomerate Roof

This article introduces a new non-pillar coal mining technology (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) under the condition of thick and hard roofs. First, we theoretically analyzed the solution to the large suspension span of the thick and hard roof in coal mining. Three-Zone pre-split blasting design in non-pillar coal mining for thick and hard roofs was proposed, based on the principles of rock mechanics. After field experiments, the technology was successfully applied to the non-pillar coal mining of a huge thick conglomerate roof. This research supplements the non-pillar mining technology system. The proposed technologies and methods have strong applicability and have certain guiding significance for the safe and efficient mining of related coal mines.

Electrotomography of the roof rocks in coal seams

A comparative analysis of boundaries determined by the initial and integrated geoelectric section with the results of engineering-geological wells drilling and sampling has been performed. Taking into account the refined boundaries, electrical conductive properties and mining and geological information, geological and geophysical sections were built and the roof condition in the study area was determined.

Research on theory, simulation and measurement of stress behavior under regenerated roof condition

To determine ground stress behavior under the special condition of a regenerated roof, we established a model of elastic rectangular cantilever thin plates. Moreover, the critical conditions for bending and fracturing the regenerated roof during mining were analysed. Meanwhile, by applying continua FLAC-3D numerical simulation, this research simulated changes in the stress and strain on a regenerated roof during mining and proposed prevention and control methods for dynamic disasters. The results show that: (1) the thinner the regenerated roof, the larger the tensile stress on the roof based on analysis using the theoretical model. Furthermore, the longer the advance distance during mining, the greater the tensile stress on the regenerated roof. (2) By analysing simulation results, during the fracturing of the regenerated roof, roof displacement firstly suddenly increases and then gradually decreases to be stable. Floor-heave-induced displacement presents a divergent state, that is, increases outwards in an elliptical manner. (3) For control of the regenerated roof, monitoring on activities of the roof should be strengthened and stress should be relieved timeously. Moreover, effective support methods should be taken to prevent development of hazards on working faces and roadways caused by the widespread behavior of the roof.

Investigation on Surrounding Rock Stability Control Technology of High Stress Roadway in Steeply Dipping Coal Seam

There are a large amount of steeply dipping coal seams deposited in China, the safe and effective extraction of which are the challenge for coal operators due to the complicated geological characteristics, in particular, when the underground roadway is excavated in the steeply dipping coal seams with limited seam distance. The Universal Distinct Element Code (UDEC) was adopted in the present research to explore the stress distribution of surrounding rock of the roadway. Based on the numerical simulation, the damage coefficient was proposed and then used to classify the roof conditions into four groups. After that, the asymmetric support technique was proposed and put into practical applications. It is indicated that the stress concentration on the floor is the main feature of the extraction of steeply dipping coal seams. Moreover, the distributions of the maximum vertical stress and horizontal stress which are much different from each other mainly attributed to the effect of the large dip angle. This research also verified the feasibility of using the asymmetric and partition support technique to maintain the integrity of the surrounding rock, as from the case study conducted at the 12032 longwall coal face of Zhongwei coal mine.

Underground mine stream crossing assessment: A multi-disciplinary approach

Underground mine designs typically try to avoid extraction beneath streams and rivers of any significant size, especially when the overburden rock thickness between the stream bed and the mine is thin. Potential issues with mining beneath streams include excessive groundwater inflow to the mine, weak ground (roof, floor, and pillar) conditions, horizontal stress effects, as well as stream loss and other potential adverse environmental effects. However, there are times when crossing beneath a stream or river is necessary to move into a new area of mineral reserve without creating additional mine access points from the ground surface. Often, stream crossings are completed without thorough assessment, potentially resulting in increased costs, decreased safety, and, in some cases, failure to advance the mine. Selection of the most favorable location(s) to cross the stream must account for numerous factors and the associated assessment often requires a multi-disciplinary approach. Stream crossing investigations often require geological, hydrogeological, geotechnical, and geophysical expertise. Phases of stream crossing investigations include desktop evaluation of maps and aerial photography, stream bed observations, drilling, detailed rock core logging, downhole geophysical surveying, hydraulic conductivity testing (packer testing), geotechnical laboratory testing, assessment, and reporting. The deliverables from a stream crossing assessment typically include geological, geotechnical, and hydrogeological characterization of potential stream crossing locations, classification of favorable and unfavorable crossing locations, recommendations for entry design and pillar sizing, and recommendations for if, and how, to conduct pre-grouting activities. Examples of technical aspects of data collection and assessment are provided based on decades of industry experience conducting stream crossing assessments in various underground mining scenarios.

Study of hydraulic fracturing for gas drainage in a coal mine in Iran

Hydraulic fracturing (HF) is one of the methods for making the coal mining operation safer and more economical. The most important parameters affecting the HF process of a coal seam are dip, thickness, uniformity, roof and floor conditions, reserve and strength. This paper presents the development and application of a fuzzy model for predicting the efficiency of HF, considering the aforementioned factors. In the developed model, the efficiency of HF of coal seams is calculated as a dimensionless numerical index within the range 0–100. The suggested numerical scale categorises the efficiency of HF of seams to very low, low, medium, high and very high, each one being specified by a numerical range as a subset of the mentioned range (0–100). The model is used to study the potential of HF in Parvadeh 4 coal mine in Iran. The mine consists of five different seams C1, C2, B1, B2 and D. The results show that seams C1 and B2, with predicted 94·6 and 81·2% efficiency, have high potential for gas drainage. The B1 seam, with 31·8% efficiency, has low potential for gas drainage by HF. HF would not be appropriate for both C2 and D seams, with 7·5% efficiency.

Cooperative Automatic Control for the Canopy Posture of a Four-Leg Hydraulic Support

The contact state between the canopy and roof of a hydraulic support considerably influences the bearing capacity and stability of the support. To ensure a secure contact between the canopy and roof in the setting stage, this paper proposes a cooperative double closed-loop automatic control technique for the canopy posture, with MATLAB used to simulate the canopy posture under different roof conditions. First, a cooperative double closed-loop automatic control model was established. Second, the method to determine the target value of the canopy posture and constraint conditions of the rising process were formulated. Finally, by simulating the canopy posture under three roof conditions, the response curve of the canopy posture and the leg length were obtained. The results show that the front and rear legs can rise through either synchronous or asynchronous coordination, and the canopy posture can approach the target value. The presented findings can guide the realization of the automatic control of the canopy posture of hydraulic support.

Physical model experiment and numerical analysis on innovative gob-side entry retaining with thick and hard roofs

Gob-side entry retaining is a common method in underground coal mining. Conventional gob-side entry retaining (CGER) always causes stress concentration and large deformation around roadways under the condition of thick and hard sandstone roofs. Thus, an innovative method of no pillar gob-side entry retaining (NPGER) in longwall mining is proposed in this paper. First, a physical model was established to explore the mechanism of the new method. The modeling results indicate that the progressive caving of the strata in the middle of the stope is consistent with CGER. The major difference between NPGER and CGER is that CGER collapsed with a structure of a long arm beam, but NPGER collapsed with a structure of a short arm beam near the roadway. In the end, a new roadway with a gangue rib was formed when the immediate roof and main roof slipped along the pre-cutting plane. Subsequently, the numerical simulation software Universal Distinct Element Code (UDEC) was adopted to establish the numerical model of the 8501 working face in Tangshangou coal mine. The NPGER process is simulated. The evolution of the roof structure and stress characteristics were clearly demonstrated. The results showed that the roof structure noticeably changed from a long beam to a short beam after roof fracturing. The retained roadway was under low stress conditions, and the stress was transferred to the deep rock. In the end, the NPGER method was applied in the field, and the results showed that the retained roadway could meet the requirements of the next working face, which may provide guidance for longwall mining with thick and hard roofs.

Performance of Green Roofs for Rainwater Control

Green roofs can be an effective tool for sustainable urban drainage, since they reduce and retain runoff by delaying its peak. Most studies analysing the retention capacity of green roofs are usually referred to a specific place and roof condition and do not consider the possibility that the roof could be partially pre-filled from previous rainfalls at the beginning of the given event. The aim of this paper is to develop an analytical probabilistic approach to evaluate green roof performance for stormwater control in terms of runoff that could be applied for different sites and climate conditions. To this end, the possibility that the green roof retention capacity could not be completely available owing to pre-filling from previous rainfall events has been considered and equations for an optimum green roof design, relating the runoff average return interval to the water retention capacity, have been proposed. The influence of parameters affecting the runoff process has been examined in depth and a case study to test the goodness of fit of the resulting equations has been developed.

Roof bolt identification in underground coal mines from 3D point cloud data using local point descriptors and artificial neural network

ABSTRACT Roof bolts are commonly used to provide structural support in underground mines. Frequent and automated assessment of roof bolt is critical to closely monitor any change in the roof conditions while preventing major hazards such as roof fall. However, due to challenging conditions at mine sites such as sub-optimal lighting and restrictive access, it is difficult to routinely assess roof bolts by visual inspection or traditional surveying. To overcome these challenges, this study presents an automated method of roof bolt identification from 3D point cloud data, to assist in spatio-temporal monitoring efforts at mine sites. An artificial neural network was used to classify roof bolts and extract them from 3D point cloud using local point descriptors such as the proportion of variance (POV) over multiple scales, radial surface descriptor (RSD) over multiple scales and fast point feature histogram (FPFH). Accuracy was evaluated in terms ofprecision, recall and quality metric generally used in classification studies. The generated results were compared against other machine learning algorithms such as weighted k-nearest neighbours (k-NN), ensemble subspace k-NN, support vector machine (SVM) and random forest (RF), and was found to be superior by up to 8% in terms of the achieved quality metric.

Research on Plastic Zone Evolution Law of Surrounding Rock of Gob-Side Entry Retaining under Typical Roof Conditions in Deep Mine

To solve the control problem of the surrounding rock of gob-side entry retaining under typical roof conditions in deep mines, we conduct theoretical analysis, numerical simulation, and actual measurements. Starting from the plastic zone of the surrounding rock, the serious damage area, the degree and scope of damage, and the dynamic evolution process of the surrounding rock of the gob-side entry retaining are systematically analyzed under four typical roof conditions in deep mines; the expansion and evolution laws of the plastic zone of the surrounding rock are expounded; and a key control technology is proposed. The results indicate that (1) the plastic failure of surrounding rock was concentrated mainly on the coal side and on the floor, especially in the filling body. The plastic zone of the surrounding rock of the gob-side entry retaining with the thick immediate roof was widely distributed and deep, but the plastic failure of the filling body was not obvious. The plastic failure of the surrounding rock of the gob-side entry retaining with the compound roof was mainly concentrated on the roof, filling body, and floor of the filling area. (2) According to the typical roof conditions of the deep gob-side entry retaining, the order of the degree of damage to the surrounding rock was as follows: thick immediate roof, compound roof, thin immediate roof, and thick-hard roof. (3) A “multisupport structure” control system is proposed for the gob-side entry retaining in a deep mine, including measures for enhancing the bearing performance of the anchorage system, increasing the strength of the cataclastic coal-rock mass, enhancing the bearing capacity of the filling body, and increasing the bearing capacity on the tunnel side. The proposed technology was applied to the deep gob-side entry retaining project in the east area of Panyi Mine, and it effectively fulfilled the reuse requirements of gob-side entry retaining in deep mines.