Floor Depth Research Articles

Prediction of Destroyed Floor Depth Based on Principal Component Analysis (PCA)-Genetic Algorithm (GA)-Support Vector Regression (SVR)

In order to prevent water inrush from working face floor, it is an urgent problem to predict destroyed floor depth. In this paper, based on the collected samples of floor failure depth of north China type coal fields, the factors that influence the development of floor failure depth were obtained by principal component analysis(PCA), that is, mine pressure, working face information, tectonic conditions, lithology, and sedimentary conditions of coal seam. Then, the parameters of support vector regression (SVR) were optimized by genetic algorithm (GA), the PCA-GA-SVR prediction model of floor failure depth was established, we put the last 4 samples into the model and verified its excellent generalization ability. Finally, we applied the PCA-GA-SVR model to the floor failure depth prediction of Zhaizhen coal mine, comparing the predicted value of the model with the field measured value using double side seal borehole water injection device, the effectiveness of the model was demonstrated.

Study on stress distribution under pillar floor of room in Potash mine with room and pillarmining technology

Room and pillar mining is a traditional mining method in the world. Carnallite/potash salt is easy to absorb water and has a strong cohesive force, its physical and mechanical properties are completely different from those of coal. The span of the room and pillar in the potash mine is small, generally ranging from 8 to 15m. Taking a solid potash mine in Laos as engineering background, basing on the elastic semi-infinite space theory, this paper sets up the mechanical model of room and pillar mining, adopts Flamant and Boussinesq solution under linear load to make research on the additional stress caused by mining in the transmission, distribution and impact depth of floor. The results indicate that depth 6 m under pillar bottom, the σz at various points is around 0.1 p. If 0.1p is used as the judgment basis for the critical impact depth of additional stress, it can be considered that the impact depth of stress concentration on bottom plate caused by mining is about 6b.

Research on Mechanism and Control of Floor Heave of Mining-Influenced Roadway in Top Coal Caving Working Face

The stability of the surrounding rock is the key problem regarding the normal use of coal mine roadways, and the floor heave of roadways is one of the key factors that can restrict high-yield and high-efficiency mining. Based on the 1305 auxiliary transportation roadway geological conditions in the Dananhu No. 1 Coal Mine, Xinjiang, the mechanism of roadway floor heave was studied by field geological investigation, theoretical analysis, and numerical simulation. We think that the surrounding rock of the roadway presents asymmetrical shrinkage under the original support condition, and it is the extrusion flow type floor heave. The bottom without support and influence of mining are the important causes of floor heave. Therefore, the optimal support scheme is proposed and verified. The results show that the maximum damage depth of the roadway floor is 3.2 m, and the damage depth of the floor of roadway ribs is 3.05 m. The floor heave was decreased from 735 mm to 268 mm, and the force of the rib bolts was reduced from 309 kN to 90 kN after using the optimization supporting scheme. This scheme effectively alleviated the “squeeze” effect of the two ribs on the soft rock floor, and the surrounding rock system achieves long-term stability after optimized support. This provides scientific guidance for field safe mining.

Stress distribution and failure characteristics of deep inclined seam and overhead mining along strike longwall floor

Based on a case study, this paper presents the stress distribution characteristics and plastic zone distribution characteristics of a deep inclined seam and overhead mining along strike longwall (ICMSL) floor by considering the results from numerical simulations, theoretical calculations, and field measurements. The results show that the vertical taper structure is formed by the roof, the interconnection, and the maingate. The vertical taper structure is formed by the floor, the face, and tailgate. The movement and deformation are mutually restricted by the vertical taper structure, which leads to the stress concentration of vertical stress and maximum shear stress. The maximum failure depth is 20 m, and the failure zone is mainly concentrated in the vicinity of the interconnection and face. The maximum failure depth of the coal seam floor is 21.32 m by theoretical calculation, and between 18.19 m and 20.24 m by in situ field tests.

Stress distribution and failure characteristics of deep inclined seam and overhead mining along strike longwall floor

Based on a case study, this paper presents the stress distribution characteristics and plastic zone distribution characteristics of a deep inclined seam and overhead mining along strike longwall (ICMSL) floor by considering the results from numerical simulations, theoretical calculations, and field measurements. The results show that the vertical taper structure is formed by the roof, the interconnection, and the maingate. The vertical taper structure is formed by the floor, the face, and tailgate. The movement and deformation are mutually restricted by the vertical taper structure, which leads to the stress concentration of vertical stress and maximum shear stress. The maximum failure depth is 20 m, and the failure zone is mainly concentrated in the vicinity of the interconnection and face. The maximum failure depth of the coal seam floor is 21.32 m by theoretical calculation, and between 18.19 m and 20.24 m by in situ field tests.

Are There Gender-Specific Errors in Restoration of Hip Biomechanics That Affect Outcome Following Total Hip Arthroplasty?

BackgroundThere are morphologic differences between males and females, which are currently underappreciated during total hip arthroplasty. We sought to assess whether these differences affected surgical process and subsequent outcome. MethodsA total of 123 patients (75 females, 48 males) had preoperative and 1-year Oxford Hip Score (OHS) and pain scores recorded. Acetabular height and offset, femoral height and offset, and acetabular floor depth were measured on preoperative and postoperative X-rays and then compared to their normal opposite hip. Discrepancies between the replaced and normal hip X-ray measurements were then correlated with changes (the delta gain) in preoperative and 1-year postoperative OHS and pain scores. ResultsPostoperatively, females had significantly greater femoral height discrepancy (P = .023) which meant they were lengthened. This led to a reduced delta gain in OHS and pain score at 1 year. Males lost more acetabular offset than females (P = .002), leading to a medialized acetabular center and subsequently reduced delta gain in pain score at 1 year (P = .017). ConclusionFemales have a smaller femur leading to a bias toward a conservative (higher) neck cut compared with males and potential for femoral lengthening. Males have a greater acetabular floor depth compared with females and thus reaming to the true floor results in greater loss of acetabular offset. In this series, both scenarios led to reduced improvement in OHS and/or pain scores at 1 year.

¿Es sustentable el aprovechamiento de tierra de hoja en bosques de encino?

Se investigó si el esquema actual con el que se realiza el aprovechamiento de tierra de hoja es sustentable. Con este fin se evaluó la producción de hojarasca en un bosque de encino con aprovechamiento de tierra de hoja bajo tres condiciones: sin aprovechamiento (C1), aprovechamiento en los últimos dos años (C2) y aprovechamiento de más de dos años (C3). Se estimó la cantidad anual de nutrientes (N, P, K, Ca, Mg y S) que regresa al piso forestal mediante la caída de hojarasca. Se emplearon trampas de hojarasca de 0.5 m2 de área. La producción de hojarasca fue mayor en C2 y C3 [(9.36 ± 0.64; 10.04 ± 1.92) Mg ha-1 año-1, respectivamente], en comparación con C1 [(6.74 ± 0.45) Mg ha-1 año-1]. La cantidad de nutrientes que regresa al piso forestal es 40% mayor en los sitios bajo aprovechamiento que en los sitios sin aprovechamiento. Los resultados sugieren que el aprovechamiento de tierra de hoja estimula la producción de hojarasca. Sin embargo, aun cuando pueda haber un proceso de estimulación en la producción, se debe tener cuidado con el tiempo que se deja descansar un área bajo aprovechamiento, ya que, de acuerdo con los resultados de este estudio, se requieren 14 años de descanso para aprovechar en forma sustentable un mismo sitio; es decir, un tiempo al menos dos veces y media mayor al que se da actualmente. Un esquema sustentable implica que el tiempo entre dos fechas de aprovechamiento es igual al tiempo requerido para formar la capa orgánica retirada.

A detailed investigation on thermal behaviour of slim floor beams with web openings at elevated temperatures

Purpose In recent times, the use of steel sections with web openings has become common as slim floor beams because they offer a reduction in weight of the steelwork, accommodate services within the floor depth and provide the composite action. The composite action in these beams is achieved either through the concrete dowels or through concrete plugs. Though these web openings offer several benefits in slim floor beams, they induce the material discontinuity in the steel web, which may affect their shear capacity and/or thermal behaviour. The purpose of this study is to investigate the thermal behaviour of slim floor beams with web openings in fire. Design/methodology/approach This research presents findings from experimental and analytical investigations conducted to study the thermal behaviour of slim floor beams with web openings in fire. For this purpose, an experimental investigation was conducted, which shows that the presence of web openings has a major influence on temperature development across the steel section as well as along the span of these beams. The behaviour of the tested slim floor beam is validated using finite element modelling. The validated finite element model is then used to conduct a sensitivity study to analyse the influence of different opening spacings, sizes and shapes on the thermal performance of slim floor beams in fire. Findings Test results show that the presence of web openings has a major influence on temperature development across the steel section as well as along the span of these beams. Temperatures on the web below the openings are found to be higher as compared to those recorded on the adjacent solid steel web. It is also observed that temperatures on the steel web above the openings are lesser than those on the adjacent solid steel web. Parametric studies conducted using the verified analytical modelling methods show that different opening spacings, sizes and shapes have a variable impact on the thermal behaviour of slim floor beams in fire. Closely spaced and larger opening sizes were found to have a more severe influence on their thermal behaviour in fire as compared to widely spaced and smaller openings. It was also found that the behaviour of these beams is influenced by the shape of the openings with rectangular openings resulting in more severe thermal distributions as compared to circular openings. Originality/value The findings from this research study are highly valuable as they contribute to the existing knowledge database. There is a lack of experimental and analytical investigation on performance of slim floor beams with web openings at elevated temperatures. The results and conclusions from this study will help in developing innovative designs for slim floor beams and will help in reducing the fire related risk associated with structures comprising of slim floor beams with web openings.

Study on failure depth of coal seam floor in deep mining

The year-after-year deepening of North China-type coal mines has resulted in frequent water inrush disasters at coal seam floors, causing significant casualties and property loss. The key factor for assessing water inrush hazards is the depth at which the coal seam floor will fail. It is therefore of great importance to predict this failure depth so as to evaluate the potential for floor water inrush incidents and establish effective controls in a timely manner. This paper takes a deep-mining mine in North China Coalfield, as an example, a comparative study is made using four methods: theoretical calculation method, back propagation neural network (BPNN) method, field measurement method, and empirical formula method. The results show that the new theoretical calculation method and the back propagation neural network method proposed in this paper are closer to the true floor failure depth under deep seam mining conditions. Therefore, this study has played an important reference role for prevention and control of water inrush from coal seam floor in deep mining.

Design of Cutting Depth of Artificial Dam of Underground Reservoir in Wulanmulun Mine

Rich in coal and lack of water is a remarkable characteristic of mining area in western China. The water storage technology of underground reservoir has become an important means of water resources protection in mining area of western China, and the cutting depth of artificial dam plays an important role in the design of underground reservoir. In order to study the influence of cutting depth of artificial dam on the stability of underground reservoir, the MB-1 dam of No. 2 reservoir in Wulanmulun mine is selected as the research object. The 3D calculation model is established by using FLAC3D, and several calculation schemes are made by changing the cutting depth of side, roof and floor, respectively. Then the influence of cutting depth of artificial dam on the stability of mine underground reservoir is deeply analyzed from the aspects of displacement field and stress field. The results show that the optimum cutting depths of MB-1 artificial dam in side, roof and floor are 0.6m, 0.5m and 0.4m, respectively.

Nutrient Allocation to Different Compartments of Age-Sequence Larch Plantations in China

Increased demand for forest-derived biomass has led to more intensive harvesting practices. However, the export of large nutrient quantities with the harvested biomass may lead to the depletion of soil nutrients. Therefore, improved knowledge concerning macronutrient allocation (N, P, K, Ca, and Mg) to different components in forests along age sequences is crucial for their sustainable management. In this study, we quantified nutrient allocation to different ecosystem components, including trees, understorey, forest floor, and different soil depths within a chronosequence (6-, 15-, 23-, and 35-year-old) of larch plantations in China. We then assessed the danger of significant nutrient losses from whole tree harvesting (WTH). Nutrient amounts in trees increased with stand age due to an increase in biomass. Stems accounted for 59%–72% of tree biomass and contained 40%–50% of total tree nutrients in the 15- to 35-year-old stands. The forest floor’s nutrient quantities increased from the 6- to 23-year-old stands and then decreased in the 35-year-old plantations. Conversely, most soil indicators initially declined from 15- to 23-year-old stands and then increased in the 35-year-old stand. The total nutrient stocks were greatest in the soil (0–40 cm), which accounted for about 93%–99% of total nutrients in the larch ecosystem. These data indicate that WTH causes nutrient losses about 2.0–2.5 times higher than stem-only harvesting, when thinning 15- or clear-cut harvesting 23- and 35-year-old stands. However, nutrient losses by WTH have little effect on the soil nutrient pools. Prolonging the crop cycle of larch plantations may be beneficial to improve nutrient return through litterfall and allow available soil nutrients to recover.

Prediction of maximal water bursting discharge from coal seam floor based on multiple nonlinear regression analysis

Aimed at the influences of various complicated factors for water inrush from a coal seam floor during coal seam mining, the prediction of the maximal water bursting discharge from a coal seam floor is regarded as a problem of pattern identification with nonlinear, high dimensions, and finite samples. Based on information fusion theory and regarding the prediction of maximal water bursting discharge from a coal seam floor as a process of multisource information fusion and state estimation, an evaluation system of the main controlling factors for predicting the maximal water bursting discharge from a coal seam floor was established. An evaluation model for forecasting the maximal water bursting discharge from a coal seam floor was also structured according to multiple nonlinear regression theory. Considering the major coal mines of Xinwen coalfield as the research background, six factors are selected as the basic discriminant factors, i.e., aquifer thickness, unit water inflow, water pressure, aquiclude thickness, fault influencing factor, and depth of a coal seam floor destroyed by rock pressure. Deng’s grey relational theory was used to analyze the correlation degrees between each main controlling factor and the maximal water bursting discharge from a coal seam floor. A structural equation model was adopted to reveal the internal connecting links among the key influencing factors and determine the weights of each main controlling factor for predicting the maximal water bursting discharge from a coal seam floor. An SPSS scatter plot and MATLAB functional programming were applied to fit the correlativity curves between each main controlling factor and the maximal water bursting discharge from a coal seam floor in the Xinwen Mining Area. The optimal unitary nonlinear regression models between the maximal water bursting discharge from the coal seam floor and each main control factor were established. A multiple nonlinear regression–modified model for predicting the maximal water bursting discharge from the coal seam floor was acquired using a multiple nonlinear regression analysis with the combined weights of each main control factor. Compared with the bivariant multiple regression equation and the measured data, the results showed that the average values of forecasting errors predicted by the multiple nonlinear regression–modified model and bivariant multiple regression equation are 10.53% and 16.76%, respectively, which indicates that the multiple nonlinear regression–modified model and the bivariant multiple regression equation have higher prediction accuracy and relatively smaller error ranges, with comparatively better application value in the prediction of maximal water bursting discharge from a coal seam floor.

Research on the required width of a fault waterproof coal pillar based on underground pressure control theory

Based on underground pressure control theory, this paper expounds the distribution characteristics of abutment stress and the resulting damage to a coal seam in front of a working face. In addition, the distribution and propagation features of vertical underground pressure in floor strata is characterized by simulation results obtained from 2D-σ finite element analysis software. Numerical simulation reveals that the peak stress line of the vertical underground pressure is inclined toward the coal mining direction of the working face. Based on the establishment of a mechanics model for water inrush from floor aquifer through a fault in a stope, a formula for calculating the distance between the bottom of the coal seam and the intersection point of the peak stress line with the fault is derived. The condition allowing water inrush from a floor aquifer through a fault is described as follows: the destroyed floor depth caused by underground pressure is not less than the distance between the bottom of the coal seam and the intersection point of the peak stress line with the fault. The water inrush pathway is composed of the fault and the floor strata destroyed by underground pressure. Based on gray multivariate nonlinear regression analysis, the formula for calculating the destroyed floor depth with four main factors is deduced: these factors are the mining depth, dip angle of the coal seam, inclination width of the working face, and Platts’ coefficient of the floor strata. According to the mechanics model for water inrush from a floor, the formula for a fault waterproof coal pillar in a stope is presented, and the rationality of the model and formula has been verified by cases of water inrush from floor aquifers in the Suncun Coal Mine and the Xiaoyun Coal Mine, China.

Flexural behaviour of composite slim floor beams

Composite slim floor beams consist of a steel section embedded in a concrete slab, offering the advantages of a steel-concrete composite structure combined with a reduced floor depth. Several mechanisms contribute to the shear connection in this type of beam, such as headed studs, friction and clamping effects and the using of reinforcement bars passing through holes in the steel beam web. However, to date, nobody has systematically identified these mechanisms and Eurocode 4 does not provide specific design guidance for slim floor beams. A series of shear beam tests and flexural beam tests, using different arrangements of shear connectors, were carried out in order to assess the degree of shear connection and connector capacity in these beams. Most of the specimens used a novel shear connector, comprising a transverse steel bar surrounded by concrete, passing through a hole in the steel section web. This paper presents the findings from the flexural beam tests and draws comparisons with those from the previous shear beam tests. Numerical models will be developed in future to extend the data and include a wider range of parameters. The data will also be used to improve understanding of this type of beam and will lead to the provision of specific design guidelines for slim floor beams.

Study on Failure Law and Failure Depth of Floor in Deep Mining

Aiming at the problem of floor failure in deep mining nowadays, taking a certain working face of a deep mine in Shandong, China as the engineering background, the method of numerical simulation and similar simulation are used to study the failure law of floor in the mining process. The numerical simulation results show that the vertical stress increasing area of deep mining is “bubble-shaped”; shearing stress is generally “butterfly-shaped”; plastic zone distribution is “rectangular-shaped”, shearing failure is dominant in the surrounding and middle parts, the range of plastic zone decreases with the increase of the depth from the coal seam; when the working face is advanced to 100 m, the floor failure depth reaches 30 m and tends to be stable state no longer increase. The similar simulation results show that that with the increase of floor rock depth, the stress value decreases, and the stress propagation of floor rock mass to deep depth has a lag effect, and the lag time is longer with the increase of depth. Finally, the depth of floor failure in working face is measured by the method of subsection water injection in the downhole. The measured result shows that the maximum floor failure depth is 31.6 m, which is similar to the result of numerical simulation. The two results were verified each other. The numerical simulation can provide a reference for the study of floor failure law in similar mines, and it can also provide some guidance for the prevention and control of water inrush in deep mines.

Study on Mechanism of In-Situ Stress Control on the Coal Floor Damage During Deep Coal Seam Mining

In order to study on mechanism of in-situ stress control on the coal floor damage during deep coal seam mining, the internal relationship among ground stress, mine pressure and floor water inrush was analyzed base on the increasing distribution rule of ground stress with the increasing depth of stratum. It is shown that the stress on the deep coal seam has obvious control effect on the depth of the floor damage and failure through the numerical simulation and the statistical analysis of the measured data of the mining damage depth of the coal seam floor. And the calculation formula for the depth of the floor failure in the deep seam mining and the influence coefficient of the ground stress were put forward.

Dynamic monitoring the deformation and failure of extra-thick coal seam floor in deep mining

With the increasing depth of mining, the disasters of water inrush above confined aquifers tends to increase annually, which seriously threatens the safe mining of coal seam, especially the extra-thick coal seam floor in deep mining. This research is to study the characteristics of deformation and failure of extra-thick coal seam floor in deep mining, the field measurement is carried out by the distributed fiber optic sensing technology (BOTDR) and the 3D resistivity method of studying coal field in China. The axial strain curves and resistivity distribution characteristics of the mining face at different depth under the coal seam floor are obtained by extending the working face. Through the comprehensive comparison and analysis of monitoring data in the monitoring boreholes, the characteristics of deformation and failure of extra-thick coal seam floor in deep mining can be ascertained. The results indicate that the comprehensive monitoring technology can effectively distinguish the characteristics of stress excess, distortion and failure of rock during the process of the working face mining. The influence range of mining advance stress is about 36 m, the failure depth of coal seam floor is about 12 m and the depth of mining disturbance deformation is about 26 m. The formation of the deformation and failure of the coal seam floor have obvious stratification, which are mainly influenced by the formation structure and the lithology of the rock strata. The comprehensive monitoring technology can effectively capture the fine features of the deformation and failure of the coal seam floor, which is valuable for extra-thick coal seam floor in deep mining.

Experimental study on the control effect of ground stress on the damage of coal seam mining floor

In order to study on mechanism of in-situ stress control on the coal floor damage during deep coal seam mining, the internal relationship among ground stress, mine pressure and floor water inrush was analyzed base on the increasing distribution rule of ground stress with the increasing depth of stratum. It is shown that the stress on the deep coal seam has obvious control effect on the depth of the floor damage and failure through the experimental study and the statistical analysis of the measured data of the mining damage depth of the coal seam floor. And the calculation formula for the depth of the floor failure in the deep seam mining was put forward.

Does a Low-shrink Resin Composite Induce Less Stress at the Adhesive/Dentin Interface in High C-factor Cavities?

Objective: The aim of this in vitro study to compare µTBS of two low shrink, TCD- based and dimer acid-based and one flowable SDR-based bulk-fill, resin composites; on the bottom of high C-factor cavities. Materials & methods: Thirty extracted noncarious human mandibular molars were used in the study. The occlusal enamel, in each tooth, was cut parallel to the occlusal surface, to expose a flat dentin surface. The cut teeth were randomly divided into two main groups (n=15), depending on the preparation of dentin i.e., group I: high C-factor occlusal class I cavity, and group II: flat dentin surface at the same depth of the cavity floor. Single Bond Universal adhesive was used to bond the resin composites to dentin in the two groups. Teeth in each group were further subdivided into three subgroups (n=5) according to the restorative materials used. In subgroup a: Surfil SDR flow, bulk-fill flowable resin composite. In subgroup b, TCD-DI-HEA based, Charisma Topaz, nano-hybrid resin composite. In subgroup c, DDCDMA based, N’Durance, nano-hybrid resin composite. All the samples were subjected to 5000 cycle, thermocycling. Each specimen was sectioned longitudinally in both mesio-distal and bucco-lingual directions to obtain four beams per each sample. A total of 20 sticks were collected from each subgroup and subjected to µTBS evaluation using universal testing machine and the results were then subjected to statistical analysis. The fractured surfaces were inspected under a stereomicroscope to determine the failure modes. Results: The collected data were subjected to two way AOVA, followed by Tuky’s post hoc test. Dentin preparation factor afforded insignificant higher µTBS values with samples prepared in flat dentin surface compared to Samples with high C-factor class I cavities, when TCD- based, restorative material was used. DDCDMA based, ND, nanohybrid and SDR-based restorative material resulted in significant increase in the µTBS when applied to the flat dentin surfaces in comparison with the high C-factor class I cavities. The three restorative materials were arranged in a descending order from TCD- based, DDCDMA based, followed by SDR resin, with no significant difference, when applied to the flat dentin surfaces. Yet, with high C-factor class I cavity restorations, µTBS in SDR-based resin revealed the lowest significant values. Most of the failure modes are adhesive in nature. Conclusions: Under the conditions of the present study, it might be concluded that TCD-based low-shrink resin composite investigated in this study perform well, in terms of compensation of polymerization shrinkage at the restoration/dentin interface and µTBS in high C-factor cavities. Conversely, the investigated Dimer acid-based and low-viscosity bulk-fill material based on SDR technology demonstrated unfavorable performance in high C-factor cavities.

Abrasi dan Sedimentasi Pantai di Kawasan Pesisir Kota Bengkulu

<strong>Coastal Abrasion and Sedimentation Kota Bengkulu Coast Area.</strong> Coastal environment of Kota Bengkulu is typified by strong wave energy, which caused coastal abrasion and sedimentation. This paper intends to discuss the abrasion and sedimentation processes in the coastal area of Kota Bengkulu. Bathymetry survey has been employed to measured the depth of ocean floor, together with turbidity of water, and tide and wave currents. The erosion in the coastal Kota Bengkulu occurred as a result of the strong waves which hit coastal cliffs intensively and high rainfall conditions that weaken the bond-forming material at the foot of the cliff coast. On the other hand, sedimentation occured due to the supply of sediment from the collapsed material of the coastal cliffs that are transported by the current in the Coastal Waters of Kota Bengkulu together with Jenggalu River and Air Bengkulu River.