Now showing items 11691-11710 of 49060

    • D-distance Risk Factor for Transmission Line Maintenance Management and Cost Analysis

      Waraporn Luejai; Thanapong Suwanasri; Cattareeya Suwanasri (MDPI AG, 2021-07-01)
      In this paper, a D-distance risk factor was proposed to prioritize high-voltage transmission lines from high to low risk in transmission line maintenance and renovation management. Various conditions and importance assessment criteria together with the weighting and scoring method were proposed to calculate both the renovation and importance indices of transmission lines. The scores of different test methods and visual inspection were differentiated from zero to five as end-of-life to very good condition to evaluate the condition of the line and its components. Additionally, the scores of different importance criteria were modified to assess the line importance from low to high importance. Moreover, the analytic hierarchy process was applied to determine the important weight of all test methods and importance criteria, which were evaluated by utility experts. The renovation and importance indices were combined in a risk matrix to finally determine the risk of the line by using the D-distance technique. Later, the risk of every transmission line was plotted in a risk matrix to prioritize and manage maintenance tasks. Finally, a maintenance cost was analyzed by applying the D-distance risk factor and compared with the replacement cost of a new transmission line for maintenance planning and cost minimization. Twenty out of 115, 230 and 500 kV transmission lines fleet in Thailand were practically analyzed with actual data. The results were realistic to feasibly implement in a transmission system for sustainable management.
    • Da Nang Green Space System Planning: An Ecology Landscape Approach

      Duy Thinh Do; Jiayu Huang; Yuning Cheng; Thi Cat Tuong Truong (MDPI AG, 2018-09-01)
      Under the pressure of rapid urbanization, the development of urban land in Vietnam has invaded green lands and had a negative impact on their ecosystems and environments. The new urban development not only does not improve the demand for green urban space but makes the living environment worse. Studying the design seriously and putting forward solutions for green urban space is essential and urgent. Taking Da Nang as a case study, planning a network of multicenter urban green space would change ecological principles to create a sustainable urban ecosystem. This is based on a landscape metrics method to reveal the green space system characteristics and its spatial distribution, area, density, and shape. A set of shapes index including categories such as SHAPE, mean distance (m) between each cell (GYRATE) and mean Euclidean distance neighbour (ENN) was used to display the geometrical shape of patches and continuity. These indices stress the difference in spatial structure in various land-use types. This article draws upon ecological landscape theory to propose a green system of urban regions including green space wedges, greenways, corridors, greenbelts and green additions; these factors help to create a sustainable urban green space.
    • DAHP–TOPSIS-Based Channel Decision Model for Co-Operative CR-Enabled Internet on Vehicle (CR-IoV)

      Muhammad Arif; Venkatesan Dhilip Kumar; Loganathan Jayakumar; Ioan Ungurean; Diana Izdrui; Oana Geman (MDPI AG, 2021-12-01)
      The Internet of Vehicles (IoV) is an important idea in developing intelligent transportation systems and self-driving cars. Vehicles with various wireless networking options can communicate both inside and outside the vehicles. IoVs with cognitive radio (CR) enable communication between vehicles in a variety of communication scenarios, increasing the rate of data transfer and bandwidth. The use of CR can meet the future need for quicker data transport between vehicles and infrastructure (V2I). Vehicles with CR capabilities on VANET have a different appearance than regular VANET vehicles. This paper aims to develop effective spectrum management for CR-equipped automobiles. An improved channel decision model has been proposed with proven outcomes to boost the pace of transmission, eliminate end-to-end delays, and minimize the number of handoffs. Many high-bandwidth channels will be used in the near future to communicate large-sized multimedia content between vehicles and roadside units (RSU) for both entertainment and safety purposes. Co-operative sensing promotes energy-constrained CR vehicles for sensing a wide spectrum, resulting in high-quality communication channels for requesting vehicles. Our research on the CR-VANET focuses on channel decision instead of spectrum sensing and it differs from previous studies. We used the DAHP–TOPSIS model under multi-criteria decision analysis (MCDA), a sub-domain of operations research, to boost profits, i.e., transmission rate with less computing time. We constructed a test-bed in MATLAB and carried out several analyses to demonstrate that the suggested model performs better than other parallel MCDA models because there has been a limited amount of research work conducted with CR-VANET
    • Daily Accessed Street Greenery and Housing Price: Measuring Economic Performance of Human-Scale Streetscapes via New Urban Data

      Yu Ye; Hanting Xie; Jia Fang; Hetao Jiang; De Wang (MDPI AG, 2019-03-01)
      The protective effects of street greenery on ecological, psychological, and behavioral phenomena have been well recognized. Nevertheless, the potential economic effect of daily accessed street greenery, i.e., a human-scale and perceptual-oriented quality focusing on exposure to street greenery in people’s daily lives, has not been fully studied because a quantitative measuring of this human-scale indicator is hard to achieve. This study was an attempt in this direction with the help of new urban data and new analytical tools. Shanghai, which has a mature real estate market, was selected for study, and the housing prices of 1395 private neighborhoods in its city center were collected. We selected more than forty variables that were classified under five categories—location features, distances to the closest facilities, density of facilities within a certain radius, housing and neighborhood features, and daily accessed street greenery—in a hedonic pricing model. The distance and density of facilities were computed through a massive number of points-of-interest and a geographical information system. The visible street greenery was collected from Baidu street view images and then measured via a machine-learning algorithm, while accessibility was measured through space syntax. In addition to the well-recognized effects previously discovered, the results show that visible street greenery and street accessibility at global scale hold significant positive coefficients for housing prices. Visible street greenery even obtains the second-highest regression coefficient in the model. Moreover, the combined assessment, the co-presence of local-scale accessibility and eye-level greenery, is significant for housing price as well. This study provides a scientific and quantitative support for the significance of human-scale street greenery, making it an important issue in urban greening policy for urban planners and decision makers.
    • Daily Average Wind Power Interval Forecasts Based on an Optimal Adaptive-Network-Based Fuzzy Inference System and Singular Spectrum Analysis

      Zhongrong Zhang; Yiliao Song; Feng Liu; Jinpeng Liu (MDPI AG, 2016-01-01)
      Wind energy has increasingly played a vital role in mitigating conventional resource shortages. Nevertheless, the stochastic nature of wind poses a great challenge when attempting to find an accurate forecasting model for wind power. Therefore, precise wind power forecasts are of primary importance to solve operational, planning and economic problems in the growing wind power scenario. Previous research has focused efforts on the deterministic forecast of wind power values, but less attention has been paid to providing information about wind energy. Based on an optimal Adaptive-Network-Based Fuzzy Inference System (ANFIS) and Singular Spectrum Analysis (SSA), this paper develops a hybrid uncertainty forecasting model, IFASF (Interval Forecast-ANFIS-SSA-Firefly Alogorithm), to obtain the upper and lower bounds of daily average wind power, which is beneficial for the practical operation of both the grid company and independent power producers. To strengthen the practical ability of this developed model, this paper presents a comparison between IFASF and other benchmarks, which provides a general reference for this aspect for statistical or artificially intelligent interval forecast methods. The comparison results show that the developed model outperforms eight benchmarks and has a satisfactory forecasting effectiveness in three different wind farms with two time horizons.
    • Daily Emotional Labor, Negative Affect State, and Emotional Exhaustion: Cross-Level Moderators of Affective Commitment

      Hyewon Kong; Joo-Eon Jeon (MDPI AG, 2018-06-01)
      Employees’ emotional-labor strategies, experienced affects, and emotional exhaustion in the workplace may vary over time within individuals, even within the same day. However, previous studies on these relationships have not highlighted their dynamic properties of these relationships. In addition, although the effects of surface and deep acting on emotional exhaustion have been investigated in emotional-labor research, empirical studies on these relationships still report mixed results. Thus, we suggest that moderators may affect the relationship between emotional labor and emotional exhaustion. Also, this study examines the relationship between emotional labor and emotional exhaustion within individuals by repeated measurements, and verifies the mediating effect of a negative affect state. Finally, our study confirms the moderating effects that affective commitment has on the relationship between emotional labor and emotional exhaustion. Data was collected from tellers who had a high degree of interaction with clients at banks based in South Korea. A total of 56 tellers participated in the survey and responded for five working days. A total of 616 data entries were collected from the 56 respondents. We used a hierarchical linear model (HLM) to examine our hypothesis. The results showed that surface-acting emotional labor increases emotional exhaustion; furthermore, the relationship between surface acting emotional labor and emotional exhaustion is mediated by a negative affect state within individuals. In addition, this study verified that affective commitment buffers the negative effects that surface acting emotional labor has on emotional exhaustion. These results suggest that emotional labor is a dynamic process within individuals, and that emotional exhaustion caused by emotional labor differs among individuals, and is dependent upon factors such as the individual’s level of affective commitment.
    • Daily Mobility in Urban Peripheries: The Role of Clandestine Taxis in Dakar, Senegal

      Gaele Lesteven; Dramane Cissokho; Pascal Pochet; Momar Diongue; Pape Sakho (MDPI AG, 2022-06-01)
      Background: This study addresses the mobility practices of the inhabitants of the peripheries of Dakar and the transport services they use to meet their mobility needs, in particular the unlicensed shared taxis (“Clandos”). In the peripheries, which suffer from a lack of jobs and amenities, mobility is essential to meet household needs and for social integration. Current transport policies focus on formalizing supply and organizing the system around high-capacity transport facilities, such as the Regional Express Railway (TER) or Bus Rapid Transit (BRT), but they have difficulty in dealing with the mobility problems facing the outskirts of the city. Methods: The study is based on secondary analysis of the 2015 Household Travel Survey and on a survey on the activity of Clandos conducted in 2021 in Dakar. Results: The analysis highlights the daily mobility practices of the inhabitants of the peripheral areas. These residents, who are on average poorer than the others, travel mainly on foot. Their access to public transport remains limited and, when they use it, a significant proportion of their trips are made by Clando. Clandos have a dual function. On one hand, they are used for long trips to the center, in competition with buses, but more often they operate as a complement to buses. On the other hand, they are mostly used for local mobility within the peripheries. Conclusions: Although relatively expensive, Clando services are valuable for the inhabitants of the peripheries and their daily mobility. They should be better integrated into transport and planning strategies for the peripheral areas.
    • Daily Monitoring of Shallow and Fine-Grained Water Patterns in Wet Grasslands Combining Aerial LiDAR Data and In Situ Piezometric Measurements

      Sébastien Rapinel; Nicolas Rossignol; Oliver Gore; Olivier Jambon; Guillaume Bouger; Jérome Mansons; Anne Bonis (MDPI AG, 2018-03-01)
      The real-time monitoring of hydrodynamics in wetlands at fine spatial and temporal scales is crucial for understanding ecological and hydrological processes. The key interest of light detection and ranging (LiDAR) data is its ability to accurately detect microtopography. However, how such data may account for subtle wetland flooding changes in both space and time still needs to be tested, even though the degree to which these changes impact biodiversity patterns is of upmost importance. This study assesses the use of 1 m × 1 m resolution aerial LiDAR data in combination with in situ piezometric measurements in order to predict the flooded areas at a daily scale along a one-year hydrological period. The simulation was applied over 663 ha of wet grasslands distributed on six sites across the Marais Poitevin (France). A set of seven remote sensing images was used as the reference data in order to validate the simulation and provide a high overall accuracy (76–94%). The best results were observed in areas where the ditch density was low, whereas the highly drained sites showed a discrepancy with the predicted flooded areas. The landscape proportion index was calculated for the daily steps. The results highlighted the spatiotemporal dynamics of the shallow flooded areas. We showed that the differences in the flooding durations among the years were mainly related to a narrow contrast in topography (40 cm), and occurred over a short period of time (two months).
    • Daily Photovoltaic Power Generation Forecasting Model Based on Random Forest Algorithm for North China in Winter

      Ming Meng; Chenge Song (MDPI AG, 2020-03-01)
      North China is one of the country’s most important socio-economic centers, but its severe air pollution is a huge concern. In this region, precisely forecasting the daily photovoltaic power generation in winter is essential to improve equipment utilization rate and mitigate effects of power system on the environment. Considering the climatic characteristics of North China, the winter days are divided into three classifications. A forecasting model based on random forest algorithm is then designed for each classification. To evaluate its performance, the proposed model and three other methods are separately used to forecast the daily power generation at the Zhonghe PV station, which is located in the center of North China. Empirical results show that, because of its ability to reduce the risk of overfitting by balancing decision trees, the proposed model obtains mean absolute percentage errors as low as 2.83% and 3.89% for clear and cloudy days, respectively. For days in which weather conditions are unusual, forecasting errors are relatively large. On these days, enlarging training samples, performing subdivision, and imposing manual intervention can improve the forecasting precision. Generally, the proposed model is better than the other three methods for nearly all error evaluation indicators in each classification.
    • Daily Positive Affect and Job Crafting: The Cross Level Moderating Effects of Individuals’ Resources

      Nayoung Kwon; Mihee Kim; Min-soo Kim (MDPI AG, 2019-08-01)
      Whereas past research on daily job crafting has tended to focus on how job crafting affected employee behaviors, we extend this study by examining the antecedents of job crafting and cross-level moderators such as leader-member exchange (LMX) and resilience. Using experience-sampling methodology, we examined the within-person level relationship between positive affect and job crafting as well as the moderating role of individuals’ LMX and resilience on this relationship. Finally, 105 employees completed surveys over 10 days. Results of hierarchical linear models revealed that daily positive affect was positively associated with job crafting. Also, results revealed moderating effects of LMX: the relation between positive affect and job crafting strengthened when employees had low-quality LMX relationship.
    • Daily Precipitation Threshold for Rainstorm and Flood Disaster in the Mainland of China: An Economic Loss Perspective

      Wenhui Liu; Jidong Wu; Rumei Tang; Mengqi Ye; Jing Yang (MDPI AG, 2020-01-01)
      Exploring precipitation threshold from an economic loss perspective is critical for rainstorm and flood disaster risk assessment under climate change. Based on the daily gridded precipitation dataset and direct economic losses (DELs) of rainstorm and flood disasters in the mainland of China, this paper first filtered a relatively reasonable disaster-triggering daily precipitation threshold (DDPT) combination according to the relationship between extreme precipitation days and direct economic loss (DEL) rates at province level and then comprehensively analyzed the spatial landscape of DDPT across China. The results show that (1) the daily precipitation determined by the combination of a 10 mm fixed threshold and 99.3th percentile is recognized as the optimal DDPT of rainstorm and flood disasters, and the correlation coefficient between annual extreme precipitation days and DEL rates reached 0.45 (<i>p</i> < 0.01). (2) The optimal DDPT decreases from southeast (up to 87 mm) to northwest (10 mm) across China, and the DDPTs of 7 out of 31 provinces are lower than 25 mm, while 5 provinces are higher than 50 mm on average. These results suggest that DDPTs exist with large spatial heterogeneity across China, and adopting regional differentiated DDPT is helpful for conducting effective disaster risk analysis.
    • Dairies in Germany: Key Factors for Grassland Conservation?

      Nicolas Schoof; Rainer Luick; Karin Jürgens; Gwyn Jones (MDPI AG, 2020-05-01)
      Germany is the largest milk producer of the 28 EU Member States (statistically still including Great Britain) and dairying is the most important single sector in German agriculture. Dairies are of central importance in the value chain, but very little is known about their objectives and perspectives in relation to grassland management, feedstuffs deriving from grassland and towards resource conservation issues. This study gives an insight on the way German dairies think about and act in such topics by using a standardized survey method. The survey revealed little to no linkage between the size of dairies and their interest in conservation issues on grassland and very little consideration of extensive grasslands. Dairies are divided over questions of governance for a more sustainable milk market and on the nature of their relationships with farmers. There is evidence that the German dairy industry is willing to contribute to a more sustainable and more robust milk market, but the enterprises mostly regard other market actors as more important. According to this survey, consumers will tend to opt for more sustainable milk products in future and there are possibilities to raise the willingness to pay.
    • Dairy Buffalo Life Cycle Assessment (LCA) Affected by a Management Choice: The Production of Wheat Crop

      Elio Romano; Pasquale De Palo; Flavio Tidona; Aristide Maggiolino; Andrea Bragaglio (MDPI AG, 2021-10-01)
      Life cycle assessment (LCA) was performed in dairy buffalo farms representative of Southern Italian farming systems, similar due to several characteristics, with the exception of wheat production. This work evaluated the impacts derived from this management choice, comparing farms with wheat crop (WWC) or not (NWC). In agreement with the literature, economic allocation was chosen as a useful strategy to attribute equivalents to by-products, i.e., culled animals; the same criterion was also adopted to assign pollutants to wheat grain, limited to WWC farms. Environmental impacts in terms of Global Warming Potential (GWP, kg CO<sub>2</sub> eq), Acidification Potential (AC, g SO<sub>2</sub> eq), Eutrophication Potential (EU, g PO<sub>4</sub><sup>3-</sup>eq), Agricultural Land Occupation (ALO, m<sup>2</sup>y) and Water Depletion (WD, m<sup>3</sup>) were estimated. The production of wheat crop significantly affected (p < 0.05) the Agricultural Land Occupation (ALO) category as WWC farms need adequate land. WWC farms could allow a significant reduction in eutrophication (EU) compared to NWC farms (p < 0.05).
    • Dairy Farms and Life Cycle Assessment (LCA): The Allocation Criterion Useful to Estimate Undesirable Products

      Elio Romano; Rocco Roma; Flavio Tidona; Giorgio Giraffa; Andrea Bragaglio (MDPI AG, 2021-04-01)
      In this study, the life cycle assessment (LCA) principle was performed to estimate the environmental impact of three dairy farms that operate using different farming systems, namely, conventional (CON), organic (ORG), and high-quality (HQ) modes. In Italy, the typical style of high-quality (HQ) farming is commonly included in the conventional system but is more strictly regulated by the Decree of the Italian Ministry of Health N° 185/1991. Although the farms are not fully representative of each conduct, they showed intrinsic peculiarities, e.g., the cow-culling rate of each system. This rate requires a quantification as it may be related to loss of income. Allocation criteria were applied to attribute the quantities of pollutants to the co-products: wheat, involved in the congruence and number of cows culled, the latter being undesirable and therefore necessary to quantify. Analysis of variance (ANOVA) highlighted that the no-dairy products significantly mitigated (<i>p</i> < 0.05) some of the impacts’ categories. The allocation of culled cows decreased the impacts of the CON and particularly those of the ORG farms when the mass mode was adopted. HQ showed values similar to the results without allocation. Overall, the objective of identifying a “marker” of undesirable products, estimated by the culling rate, was partially achieved.
    • Dam Removal Effects on Benthic Macroinvertebrate Dynamics: A New England Stream Case Study (Connecticut, USA)

      Helen M. Poulos; Kate E. Miller; Ross Heinemann; Michelle L. Kraczkowski; Adam W. Whelchel; Barry Chernoff (MDPI AG, 2019-05-01)
      Dam removal is an increasingly common stream restoration tool. Yet, removing dams from small streams also represents a major disturbance to rivers that can have varied impacts on environmental conditions and aquatic biota. We examined the effects of dam removal on the structure, function, and composition of benthic macroinvertebrate (BMI) communities in a temperate New England stream. We examined the effects of dam removal over the dam removal time-series using linear mixed effects models, autoregressive models, non-metric multidimensional scaling, and indicator and similarity analyses. The results indicated that the dam removal stimulated major shifts in BMI community structure and composition above and below the dam, and that the BMI communities are becoming more similar over time. The mixed model analysis revealed that BMI functional groups and diversity were significantly influenced by sample site and several BMI groups also experienced significant interactions between site and dam stage (P < 0.05), while the multivariate analyses revealed that community structure continues to differ among sites, even three years after dam removal. Our findings indicate that stream restoration through dam removal can have site-specific influences on BMI communities, that interactions among BMI taxa are important determinants of the post-dam removal community, and that the post-dam-removal BMI community continues to be in a state of reorganization.
    • Damage Assessment of Historical Masonry Churches Subjected to Moderate Intensity Seismic Shaking

      Nicola Ruggieri (MDPI AG, 2021-04-01)
      An earthquake of magnitude 4.3 MW struck Cosenza (Calabria region, South Italy) and its immediate area on 24 February 2020. Although no damage was reported to ordinary masonry buildings, the ancient masonry churches suffered widespread damage. The herein article presents an analysis of the failures suffered by monumental buildings (e.g., churches) following a moderate seismic action. The contribution is based on the in situ damage observation of 14 churches, with a dating ranging from the 12th to 20th century. The study consists of a first phase, in which the different damage modes are identified, describing their causes and effects, and a second phase that correlates the damage detected to the main parameters that influence the seismic response of the churches (geometric characteristics, boundary condition, masonry and floor organization, past interventions, etc.), regardless of the state of conservation that was discrete for all buildings before the telluric event. From the rapid visual survey, the “weight” of each seismic parameter on the type of damage detected was then established. The past “retrofitting” interventions were decisive in the response of the ancient structure, with particular regard to those that made an aggravation of seismic mass and an increase in stiffness.
    • Damage Data Analysis of Deep Coal Roadway Roof and Application of Long Anchorage and Zone Linkage Support Technology

      Yang Wang; Nong Zhang; Wenda Wu; Juncai Cao; Yu Guo; Donghong Duan (MDPI AG, 2022-07-01)
      China’s energy structure mainly depends on coal resources, which will still play the dominant role in economic development in the future. With the mining depth increasing, the deep roadway construction will be exposed to a complex stress environment, increasing the difficulty of roof control and further hindering the mining activities. The problem of deep roadway excavation causing significant fracture scope of surrounding rock in and outside the anchorage zone has attracted much attention. For the large crack scope existing in the roadway roof of deep underground openings, this paper focuses on the exploration of upgrading the support system. In order to solve this problem, we investigated the zone damage of the roadway roof with the discrete element model using the UDEC trigon method and damage quantified evaluation with data analysis. The long anchorage and zone linkage support technology was proposed based on the damage control effect of varying lengths of supporting bolts. The purpose of extending the length of bolts is to link the more severely damaged rock mass in the shallow part to the minimum damaged part in the deep place, aiming to form the thick anchor zone to mobilize the rock mass in each zone to participate and bear the load together. Furthermore, the onsite application of long anchorage and zone linkage technology gained good control effects in the selected typical roadway with different geological conditions. The results show obvious resistance in cross-section shrinkage, integrity maintenance, and minimization of crack scope in the roadway roof. The promotion of long anchorage zone linkage technology can help the mine with similar situations uplift the efficiency of working and guarantee the safety of miners during mine service life in the deep coal roadway.
    • Damage Indices and Photogrammetry for Decay Assessment of Stone-Built Cultural Heritage: The Case Study of the San Domenico Church Main Entrance Portal (South Calabria, Italy)

      Luciana Randazzo; Matteo Collina; Michela Ricca; Loris Barbieri; Fabio Bruno; Anna Arcudi; Mauro F. La Russa (MDPI AG, 2020-06-01)
      In recent decades, increasing attention is being paid to the multidisciplinary approach that allows the performance of both a preventive conservation and a more invasive restoration action. In this context, the present study aims to acquire information and data from field surveys undertaken in San Domenico Church, Southern Calabria, in order to provide a tool for the recording and the inventory of damage and decay phenomena, and assess their causes and scale. The subsequent calculation of damage indices also provided useful information in order to allow the prioritization of conservation and preservation responses.
    • Damage Management of Concrete Structures with Engineered Cementitious Materials and Natural Fibers: A Review of Potential Uses

      Mehran Dadkhah; Jean-Marc Tulliani (MDPI AG, 2022-03-01)
      The importance of the safety and sustainability of structures has attracted more attention to the development of smart materials. The presence of small cracks (<300 µm in width) in concrete is approximately inevitable. These cracks surely damage the functionality of structures, increase their degradation, and decrease their sustainability and service life. Self-sensing cement-based materials have been widely assessed in recent decades. Engineers can apply piezoresistivity for structural health monitoring that provides timely monitoring of structures, such as damage detection and reliability analysis, which consequently guarantees the service life with low maintenance costs. However, concrete piezoresistivity is limited to compressive stress sensing due to the brittleness of concrete. In contrast, engineered cementitious composites (ECC) present excellent tensile ductility and deformation capabilities, making them able to sense tensile stress/strain. Therefore, in this paper, first, the ability of ECC to partly replace transverse reinforcements and enhance the joint shear resistance, the energy absorption capacity, and the cracking response of concrete structures in seismic areas is reviewed. Then, the potential use of natural fibers and cellulose nanofibers in cementitious materials is investigated. Moreover, steel and carbon fibers and carbon black, carbon nanotubes, and graphene, all added as conductive fillers, are also presented. Finally, among the conductive carbonaceous materials, biochar, the solid residue of biomass waste pyrolysis, was recently investigated to improve the mechanical properties, internal curing, and CO2 capture of concrete and for the preparation of self-sensing ECC.
    • Damage Mechanism and Stress Distribution of Gypsum Rock Pillar Subjected to Blasting Disturbance

      Shuli Wang; Zhihe Liu; Kaizhi Zhang; Huaichang Zheng (MDPI AG, 2022-04-01)
      The room-pillar mining technology of underground gypsum resources results in numerous gypsum rock pillars for controlling and supporting mined gobs, which forms a large area of roof hanging gobs. Owing to weathering and mining activities, gypsum rock pillar damage and failure will occur, thereby inducing a large area of gypsum mined-gob collapse accidents and disasters. Blasting is vital to the stability of gypsum rock pillars and is indispensable in mining engineering. Based on field blasting tests and using wave velocity as the basic parameter to characterise the integrity of gypsum rock, the damage mechanism of gypsum rock pillars subjected to blasting disturbance is investigated. With ten blasting tests, the maximum damage rate is 7.82% along the horizontal direction of pillar, and 3.52% along the vertical direction. The FLAC numerical simulation calculation software is used to analyse the stress distribution law of gypsum rock pillars with disturbances of different strengths from different distances. As the disturbance strength increased, the stress increased with no clear linear relationship; as the disturbance distance increased, the stress decreased gradually with a linear relationship. All stress after disturbance is greater than the original static stress, and lower than the ultimate compressive strength. However, the correlation between blasting tests results and numerical simulation results is poor and is discussed for many factors. The results can provide important guidance and reference for clarifying the damage mechanism of gypsum rock pillars subjected to blasting disturbance, as well as reveal the collapse mechanism of gypsum mined gobs.