Lateral Pressure Ratio Research Articles

Study on Distribution Law of Ground Stress in Main Coal Seam of Qinshui Coalfield

Abstract In order to investigate the distribution patterns of in situ stress in the main coal seams (3# and 15#) of the Qinshui coalfield, an in-depth analysis was conducted on the in situ stress measurement results obtained from 139 measurement points across 46 mines within the mining area. The findings indicate that the maximum horizontal principal stress in the coal mining area of both seams is generally higher than the vertical principal stress. The stress field exhibits characteristics of a tectonic stress field, while deeper regions display features of a vertical stress field. The in situ stress values in the mining area of coal seam 3# are predominantly characterized by moderate stress field zones, while those in the mining area of coal seam 15# are mainly composed of low to moderate stress field zones. The maximum horizontal principal stress in the Yangquan and Changzhi mining areas for both coal Seams 3# and 15# is concentrated in the NE direction, whereas in the Jincheng mining area, it is predominantly concentrated in the NW direction, indicating a clear directionality. With increasing depth, the following trends can be observed approximately: the maximum and minimum horizontal principal stress values generally exhibit an increasing trend, and the geological structures throughout the mining area are primarily dominated by horizontal tectonic movements; the lateral pressure ratio gradually decreases and tends to concentrate near the value of 1; the relative difference between the maximum and minimum principal stresses tends to increase, with the horizontal principal stress difference ratio concentrating near 0.5. The relationship between the average horizontal principal stress ratio (k) and vertical principal stress at different depths within the measured area follows Hawke-Brown’s general law for this relationship curve. The research results have important guiding significance for the design of coal mining engineering in this area.

The influence of flow pattern and hopper angle on static and dynamic pressures in slender silos

This paper focuses on the influence of flow pattern and hopper angle (β) on static and dynamic pressures in slender silos. The results were obtained using a test station developed by the authors, consisting of a silo (6 m high and 0.7 m internal diameter). Maize was used to generate the pressures. Five different hopper angles were tested by filling, static phase followed by complete silo discharge. Results are reported for pressure and flow analyses, and show that hopper angle influences normal pressures on the silo wall; Silos with transition flow do not have a concrete pattern of distribution of thrusts; pressure values are proportional to the variation of the hopper angle; and internal shear zones vary according to hopper angle, completely modifying the behaviour of static and dynamic pressures. Friction pressure and lateral pressure ratio values exceeded those calculated by the Eurocode 1, part 4.

Evaluation of pressures in slender silos varying hopper angle and silo slenderness

In this paper, we report the results for pressures in a full-scale silo obtained from assays performed on a test station using a free-flowing product. Six different types of silo geometry (slenderness and hopper angle) were tested by filling the silo to the height of interest and observing a static phase (10 min) followed by complete discharge. Our results show that discharge flow is not influenced by silo slenderness. The lateral pressure ratio and values obtained for vertical stress in the stored material at the transition were higher than those given in the Eurocode 1, part 4. In addition, the maximum frictional pressures in the cylinder showed peaks that exceeded the standard, as did the maximum normal pressure in the cylinder with maximum slenderness and mass flow (hopper β = 15°).

Comparative study of granular solid-structure interaction in a uni-axial compression system

Interaction between granular solids and confining structures is an elementary problem encountered in subsurface structural design and bulk solids storing and handling. A classic scenario is uni-axial compression of granular solids in a deformable cylindrical container. Despite being apparently simple in loading condition, the understanding of this scenario remains limited, mainly due to complex interactive deformation between the two components via frictional interfaces. This paper comparatively examines such a uni-axial compression particulate system by a laboratory experiment and two different numerical approaches, namely, continuum finite element method (FEM) and linked discrete-finite element method (linked DEM-FEM). In the continuum FEM approach, two intendedly chosen simple material models, linear elastic and porous elastic models, are attempted. The comparative study reveals that the majority of resultant characteristics show satisfactory agreement amongst the numerical predictions and the experimental measurements. The simple elastic continuum FEM models can hence be a useful alternative in modelling such problems with mild structural flexibility under a monotonic loading scenario. However, precise prediction of some characteristics, such as lateral pressure ratio, may demand more elaborated material model or parameter selection. The enhancements needed for each numerical approach in order to achieve an improved result are further discussed.

Ankle joint pressure change in varus malalignment of the tibia

BackgroundVarus malalignment of the tibia could alter ankle biomechanics, and might lead to degenerative changes of the ankle joint. However, previous studies failed to report the detailed changes of ankle biomechanics in varus malalignment of the tibia. The aim of this biomechanical study was to evaluate how the ankle joint pressure would change in response to the incremental increases in varus malalignment of the tibia.MethodsEight fresh-frozen human cadaver legs were tested in this study. Varus malalignment of the tibia and a total of 600 N compressive force was simulated using a custom made fixture. Intra-articular sensors (TeckScan) were inserted in the ankle joint to collect the ankle joint pressure data. The testing sequence was 0°, 2°,4°,6°,8°,10°,12°,14°,16°,18°,20° of tibial varus.ResultsAs the tibial varus progressed, the center of force (COF) shifted laterally both for the medial and lateral aspect of the ankle joint. For the medial aspect of the ankle joint, the lateral shift reached its maximum at 8° [2.76 (1.62) mm, p = 0.002] of tibial varus, while for the lateral aspect of the ankle joint, the lateral shift reached its maximum at 12° [2.11 (1.19) mm, p = 0.002] of tibial varus. Thereafter, the COF shifted medially as the tibial varus progressed. For the lateral aspect of the ankle joint, The Pmean increased from 2103.8 (625.1) kPa at 0° to 2295.3 (589.7) kPa at 8° of tibial varus (p = 0.047), significant difference was found between the Pmean at 0° and 8° (p = 0.047) of tibial varus. Then as the tibial varus progressed, the Pmean decreased to 1748.9 (467.2) kPa at 20° of tibial varus (p = 0.002). The lateral joint pressure ratio also increased from 0.481 (0.125) at 0° to 0.548 (0.108) at 10° of tibial varus (p = 0.002), then decreased to 0.517 (0.101) at 20° of tibial varus (p = 0.002) .ConclusionsFor mild tibial varus deformities, there was a lateral shift of COF and lateral stress concentration within the ankle joint. However, as the tibial varus progressed, the COF shifted medially and the lateral stress concentration decreased.

Gob‐Side Entry Retaining Technology with Advanced Empty Hole Butterfly‐Shaped Weakening in Three‐Soft Coal Seam in China

China has a large number of coal resources in “three‐soft” geological conditions. The roof of these coal seams is soft and has low strength. Under this condition, gob‐side entry retaining can be carried out under the guidance of roof leading holes to achieve the goal of nonblasting roof cutting and roadway retaining. In this paper, the technology of void weakening, roof cutting, and pressure relief along gob retaining roadway is investigated. The force model of void is established, and the stress concentration of void and interference effect of stress superposition between holes is simulated by COMSOL numerical simulation software. The influence of different factors on stress distribution surrounding round holes is then studied by orthogonal experiment. The results show that the distribution of the plastic zone in circular holes varies with the lateral pressure ratio. With the increase of lateral pressure ratio, the shape of the plastic zone will gradually change from circular to elliptical, and eventually to butterfly, and the size of the butterfly plastic zone is positively correlated with the aperture. On this basis, the technology of “empty hole weakening + dense pillar” roof cutting and gob‐side entry retaining is presented. The methodology is then applied to an auxiliary air intake roadway of 21309 working face in the Xiangshan Mine. Industrial testing of three‐soft seams using advanced empty hole without blasting roof cutting and gob‐side entry retaining is then successfully carried out. The advanced weakening hole replaces the original blasting cutting technology, omits the blasting cutting link in the existing gob‐side entry retaining technology, shortens the retaining time, solves the problems such as large coal dust concentration and bad construction environment in the blasting process, and provides scientific theoretical basis for the gob‐side entry retaining technology without blasting under such geological conditions.

Hypersonic flow characteristics and relevant structure thermal response induced by the novel combined spike-aerodome and lateral jet strategy

Huge aerodynamic drag and severe aeroheating are the inevitable challenges for hypersonic vehicles, this paper proposes a novel combined spike-aerodome and lateral jet strategy for drag reduction and thermal protection. Meanwhile, the hypersonic flow characteristics and structure thermal response are numerically investigated by an in-house code. The obtained results demonstrate that this novel strategy not only further reduces the total drag, but also provides excellent thermal protection for both the blunt body and spike rod. Then the effects of lateral jet pressure ratio, spike length and aerodome diameter on the flow properties, drag and heat reduction performance are thoroughly explored. Increasing the lateral jet pressure ratio can effectively enhance the thermal protection. Surprisingly, in a certain range, higher lateral jet pressure ratio even leads to larger pressure peak value on the blunt body. Increasing the spike length would enhance the heat transfer along the blunt body surface, and the total drag changes non-monotonically as the spike length varies. The total drag rises significantly when the aerodome diameter increases, and it can be increased by 40.1% when the aerodome diameter ratio increases from 0.15 to 0.5. Besides, increasing the aerodome diameter is beneficial to remarkably enhance thermal protection.

Novel Combinational Aerodisk and Lateral Jet Concept for Drag and Heat Reduction in Hypersonic Flows

Hypersonic vehicles have attracted lasting and worldwide attention in recent years. Considerable aerodynamic drag and severe aerothermal loads are major challenges for hypersonic vehicles. A novel combinational aerodisk and lateral jet concept is proposed for drag reduction and thermal protection in hypersonic flows. The flow field characteristics have been numerically investigated with in-house code. The Reynolds-averaged Navier-Stokes (RANS) equations were adopted to simulate the flow field, and the shear stress transport (SST) k−ω turbulence model was used to present the turbulent nature. Fluid–thermal interaction is also taken into consideration in this paper. The influences of the lateral jet pressure ratio and its location on the flow field have been thoroughly studied using numerical methods. The obtained results demonstrate that the novel concept is beneficial for drag reduction and thermal protection in hypersonic flows. Increasing the lateral jet pressure ratio can further improve drag reduction performance. In addition, the heat flux can be significantly reduced by increasing the lateral jet pressure ratio. The lateral jet location also has important effects on the flow properties. The peak values of the Stanton number and wall static pressure can even be reduced by 19.76% and 22.15%, respectively, with different lateral jet locations.

Effect of aspect ratio on the mechanical behavior of packings of spheroids

This paper presents measurements of the mechanical response of assemblages formed by spheroid particles. Sets of such particles in the form of thin, cylindrical samples were subjected to uniaxial confined compression. The particles were flattened and elongated, with aspect ratios ranging from 0.5 to 2.5. All particles were fabricated using a 3D printer and each had the same volume. Because the particles had well-defined shapes, it was possible to experimentally observe how the mechanical response of the anisotropic and highly constrained samples depended on the elongation of the particles. In particular, we showed how the sample density, lateral pressure ratio, and work done to compact a sample of elongated or flattened particles changed with change in particle aspect ratio. Furthermore, we found that the evolution of packing density in subsequent loading–unloading cycles followed a stretched exponential law regardless of particle aspect ratio.

Investigation of drag and heat reduction induced by a novel combinational lateral jet and spike concept in supersonic flows based on conjugate heat transfer approach

When flying at supersonic or hypersonic speeds through the air, the drag and severe heating have a great impact on the vehicles, thus the drag reduction and thermal protection studies have attracted worldwide attention. In the current study, the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k−ω turbulence model have been employed to investigate the flow behavior induced by a novel combinational lateral jet and spike concept in supersonic flows. A coupling conjugate heat transfer (CHT) approach has been applied to investigate the thermal protection, which takes the heat transfer of structure into consideration. After the code was validated by the available experimental results and the gird independency analysis was carried out, the influences of the spike length ratio, lateral jet pressure ratio and lateral jet location on the drag and heat reduction performance are analyzed comprehensively. The obtained results show that a remarkable reduction in the drag and heat flux is achieved when a lateral jet is added to the spike. This implies that the combinational lateral jet and spike concept in supersonic flows have a great benefit to the drag and heat reduction. Both the drag and heat reduction decrease with the increase of the lateral jet pressure ratio, and the heat flux is more sensitive to the lateral jet pressure ratio. The lateral jet should not be located in the bottom of the spike in order to realize better drag and heat reduction performance. The drag and heat flux could be reduced by about 45% by reasonable lateral jet location. The drag decreases with the increase of the spike length ratio whereas the heat flux is affected by the spike length ratio just in a certain range.

In-situ stress measurements by hydraulic fracturing and its implication on coalbed methane development in Western Guizhou, SW China

Based on data independently measured and collected within depth from 135.9 to 1243.6m in Western Guizhou, SW China, the distribution of in-situ stress was analyzed systematically. Maximum horizontal principal stress (σHmax), minimum horizontal principal stress (σHmin), vertical stress (σv) and lateral pressure ratio variations with depth were obtained by regression analysis. Results show that the growth rate of horizontal stresses is higher than that of vertical ones. Three types of stress field distribution have been noted that σv⩾σHmax⩾σHmin mainly occurs in shallow and intermediate to deep coal seams (<400m and 600–1000m), the σHmax⩾σv⩾σHmin mainly occurs in deep and shallow to intermediate coal seams (400–600m and >1000m). The ratio of maximum and minimum horizontal principal stress versus depth shows linear relationships with a correlation coefficient of 0.77 and 0.85, separately. The ratio of the maximum horizontal principal stresses to vertical stress is usually between 0.5 and 2.0 in coal seams, and decreases as the depth increases and approaches 1.0. The coefficient of average lateral stress versus depth (λ) is also illustrated, which shows a wide range at shallow sites from 0.48 to 1.80, and then gradually decreases to a fixed value as the depth increases. Coal permeability obtained during injection/falloff tests shows that the permeability is damaged with a trend difference under a depth of 550–750m for the in-situ stress belting change and other reasons.

Mechanical behaviour of a granular solid and its contacting deformable structure under uni-axial compression – Part I: Joint DEM–FEM modelling and experimental validation

This paper proposes an exquisite confined compression experiment to validate a recently developed numerical method (Joint DEM–FEM approach). A uni-axial compression apparatus was designed to investigate the mechanical behaviour of a granular solid under vertical loading and the load transmission to the containing wall. This tester consists of an instrumented thin-walled circular cylinder, two platens, a commercial dynamic material test machine (MTS 810), a bottom load cell and twelve bi-axial strain gage rosettes. Experiments were conducted on polystyrene beads. The delicately-designed confined compression test provides abundant experimental data for proving the validity of the proposed modelling technique.The corresponding simulations were performed by the developed numerical approach with the linking of discrete element method (DEM) and finite element method (FEM). To attain a high level of quantitative validation, the important particle properties required for DEM simulation were not simply assumed but measured directly in laboratory tests. Characteristics of the compression system, such as load–displacement response, force transmission to boundary surfaces, lateral pressure ratio, bulk wall friction, and stress distribution in the cylindrical wall, were evaluated. A comparison between the numerical and experimental results was made and discussed in this paper. The majority of compared physical quantities show reasonable to good agreement, thus giving a convincingly quantitative validation for the developed Joint DEM–FEM modelling technique. This proposed linking methodology is shown to give plausible results and can be used as a first step to solve the particulate solid–structure interaction problems.

Multivariate Analyses of Selected Mechanical Properties of Dry Bean Grain

Abstract The direct shear test are widely used to measure the bulk material properties for economical design of bulk handling equipment and to estimate wall pressure inside storage structures, namely their bulk density, the angle of internal friction, shear strength, Poisson ratio, and lateral pressure ratios are required. Tests were conducted at thirty six different shear speeds (between 0.30-1.00 mm min-1) and three different normal stresses were applied (60, 120 and 180 kPa). The angle of internal friction, Poisson ratio, and lateral pressure ratios demonstrated fluctuations depending on the shear speeds. The results of the principal component analysis indicated that the first three principal components accounted for 97.40% of the total variability among the thirty six different shear speeds for all the traits investigated. The first principal component was the most important. In the result of principal component analysis, the shear speeds were divided into seven clusters. The pressures were decreased and increased with the change of the angle of internal friction and the lateral pressure ratio. The data obtained from the study will be useful in the structural design of dry bean bins to calculate loads on bins from the stored material and grain handling equipment.

Prediction of flow patterns during silo discharges using a finite element approach and its preliminary experimental verification

Obtaining a reliable discharge of particulate solids from a storage silo is a prerequisite to securing operational adequacy in solids handling processes. If a silo is poorly designed, an unreliable interrupted discharge often occurs. In this study, an in-house finite element (FE) program was modified to predict the particulate solids flow patterns during discharges from silos, and the effect of a double-cone insert on such flow patterns. In FE modeling, a Eulerian approach was adopted with an assumption of steady-state flow—a state that greatly facilitated investigations on the effects of double-cone inserts on the flow of particulate solids. Predictions were carried out on whether the discharge was in mass flow or funnel flow, associated with the inclination angle of the silo's hopper. Predicted results were in agreement with the Jenike Chart, and proved that an upper lateral pressure ratio value gave a better critical hopper half angle to achieve mass flow (EN 1991-4, 2006). The shape and size of the stagnant zone were further discussed to address the flow channel boundary between the flowing and static solids if the discharge was in a funnel pattern. Results also showed the effects of a double-cone insert on the flow patterns which converted silos from funnel flow to mass flow up to a certain hopper inclination angle and would improve the flow pattern even for shallower angles. Experiments were carried out to verify some of the predicted results. Some qualitative comparisons were made between the predicted results and experimental measurements, which indicated that further efforts are needed in predicting the shape of the stagnant zone (flow channel boundary) during funnel flow discharges.

In-situ stress distribution and its implication on coalbed methane development in Liulin area, eastern Ordos basin, China

Abstract Based on well test parameters independently measured within depth from 400 to 1100 m in Liulin area, eastern Ordos Basin, China, the distribution of in-situ stress was analyzed systematically. Maximum horizontal principal stress ( σ Hmax ), minimum horizontal principal stress ( σ Hmin ), vertical stress ( σ v ) and lateral pressure ratio variations with depth were obtained by regression analysis. Results show that the growth rate of horizontal stresses is higher than that of vertical ones. Three types of stress fields were found and calculated: the type of σ v ≈ σ Hmax ≈ σ Hmin mainly distribute in relatively shallow coal seams from 400 to 700 m; the σ Hmax > σ v > σ Hmin type ranges from 700 to 850 m; and, the σ v > σ Hmax > σ Hmin type is dominant in depth from 850 to 1100 m. Coal permeabilities obtained during injection/falloff tests showed that the permeability was damaged under a depth of 700–850 m for the relatively high σ Hmax and σ Hmin . The correlation between strata temperature and depth was also illustrated, which showed three linear relationships in depth of 400–700, 700–850, and 850–1100 m, separately. The gas content and gas/water production data were also plotted, showing that the strata shallower than 700 m is of better gas resources and recovery rate than the deeper strata.

Monotonic triaxial experiments to evaluate steady-state and liquefaction susceptibility of Babolsar sand

In this study, drained and undrained triaxial tests under isotropic and anisotropic consolidations were conducted on reconstituted samples of Babolsar sand, which underlies a densely populated, seismic region of the southern coast of the Caspian Sea, Mazandaran, Iran. It was demonstrated that the sand experienced all possible states of liquefiable soil: flow failure, limited flow, and dilation. The steady-state and flow liquefaction lines of this sand were presented and compared with previously tested sands. It is shown that the initial stress anisotropy can affect the potential of volume change and pore pressure generation. The steady-state line (SSL), however, remains identical for the isotropically and anisotropically consolidated specimens under drained and undrained conditions. The tests data were then analyzed in order to investigate the liquefaction susceptibility of this sand in terms of parameters such as the state parameter, relative state parameter index, and lateral earth pressure ratio at failure.

근접병설터널의 안정성 평가를 위한 모형실험 연구

본 연구에서는 <TEX>$30^{\circ}$</TEX> 경사진 층리면을 가진 풍화암 물성의 이방성 암반에서 필러 폭이 0.5D와 0.25D로 매우 작은 근접병설터널을 시공할 경우에 대한 터널 안정성을 조사하였다. 이를 위해 터널간 이격거리와 지보조건이 서로 다른 6가지 모형을 제작하고 측압계수 1의 하중조건으로 축소모형실험을 실시하였다. 모형별 균열개시압력, 최대압력, 필러 및 터널의 변형거동을 조사하였으며, 복공지보와 필러보강 여부가 터널의 안정성에 미치는 영향을 알아보았다. 필러 폭이 큰 모형일수록 균열개시압력이 더 크게 나타나 터널 안정성은 증가하였으며, 복공지보를 설치한 모형은 무지보 모형에 비해 균열개시압력와 최대압력이 더 크고 내공단면의 변형량은 적어 풍화암 근접병설터널에서 복공지보의 필요성을 확인하였다. 복공지보와 더불어 필러보강을 실시한 모형은 다른 모형에 비해 터널 안정성이 더 크게 나타났으며, 특히 필러 폭 0.25D인 근접병설터널은 복공지보뿐 아니라 필러보강도 실시해야 터널 안정성이 확보됨을 알 수 있었다. In this study, scaled model tests were performed to investigate the stability of twin tunnels with small clearance, where the pillar widths were 0.5D and 0.25D, respectively. The tunnels were supposed to be constructed in anisotropic weathered rocks with <TEX>$30^{\circ}$</TEX> inclined bedding planes, and the model tests were conducted under the condition of lateral pressure ratio, 1. Six types of test models which had respectively different pillar widths and support conditions were experimented, where crack initiating pressures, maximum pressures, failure modes of pillar and deformation behaviors around tunnels were investigated. The models with wider pillar were cracked under higher pressure than the models with shallower pillar. The models with lining support were cracked under higher pressure and showed less tunnel convergence than the unsupported models. The models with both lining and pillar reinforcement were proved to be most stable among the tested models. In particular, as the model of 0.25D pillar width with only lining support showed shear failure of pillar according to the existing bedding planes, so both lining and pillar reinforcement were thought to be indispensable in that case of tunnel.

이방성 암반내 쌍굴터널의 안정성에 대한 모형실험 연구

Abstract In this study, scaled model tests were performed to investigate the stability of twin tunnels constructed in anisotropic rocks with 30° inclined bedding planes under the condition of lateral pressure ratio, 2. Five types of test models which had respectively different pillar widths and shapes of tunnel sections were experimented, where both crack initiating pressures and deformation behaviors around tunnels were investigated. The models with shallower pillar width showed shear failure of pillar according to the existing bedding planes and they were cracked under lower pressure than the models with thicker pillar width. In order to find the effect of tunnel sectional shape on stability, the models with four centered arch section, circular section and semi-circular arch section were experimented. As results of the comparison of the crack initiating pressures and the deformation behaviors around tunnels, the semi-circular arched tunnel model was the most unstable whereas the circular tunnel model was the most stable among them. Futhermore, the results of FLAC analysis were qualitatively coincident with the experimental results.

Study on Effect of Silo Wall Elasticity on Lateral Pressure Ratio

Lateral pressure is a key parameter to silos’ design. It has an important effect on the safety and efficiency of silos. The lateral pressure ratios that recommended by some overseas design codes and literatures have been analyzed. These ratios didn’t take into account the elasticity of silo wall, one of which is 28% smaller than the measure value, but another goes up to super pressure ratio. A new lateral pressure ratio is derived by considering the elasticity of silo wall, which is relevant to Passion ratio of stored material and relative stiffness coefficient . The coefficient of usual metal silo varies from 0.01 to 0.2, so it has significance to consider the wall elasticity.

Distribution Laws of in-Situ Stress in Deep Underground Coal Mines

Abstract With depth and intensity of coal mining increasing, effects of in-situ stress on deformation and failure of the surrounding rock are increasingly growing. Through data independently measured and collected within 600-1500m, this paper summaries distribution laws of in-situ stress in deep underground coal mines of our country, main existing types of in-situ stress and its directional characteristics. Maximum horizontal stress, minimum horizontal stress, vertical stress and lateral pressure ratio variation laws with depth are obtained by using regression analysis. Generally, in-situ stresses increase with depth. With increasing depth the rate of increase in horizontal stresses decreases. A considerable scatter in the in-situ stress test data may be due to distinct differences in both the strength and deformation moduli of strata located in varying geological environments and different coal districts. Two types of stress field distribution have been noted with σHvh (σHmax>σv>σhmin) and σvHh(σv>σHmax>σhmin) found mainly in deep coal mines. The ratio of the maximum horizontal principal stresses to vertical stress is usually between 0.63 and 2.42 in the deep coal districts.