Effect Of Vertical Stress Research Articles

Overlying Rock Activity Laws and Influential Ranges of Coal Seam Mining in Stubble Areas

This report applies theoretical analysis, similar material simulations, and numerical simulation methods to study the overburden strata movements and influential range of coal mining under pressure stubble conditions and to elucidate the relationship between adjacent coal seams. The pressure, failure, caving, stress, and displacement of crop conditions during coal seam mining were evaluated. The results show that the overlying W9-10 coal face and underlying J16-17 roof experience a long first pressure step, i.e., close to the periodic weighting distance. The working face of the W9-10 coal seam is located in the bending subsidence zone of the working face of the J16-17 coal seam. With the advance of the working face of the J16-17 coal seam, the development and range of overburden fracture of the W9-10 coal seam gradually increase. The supporting pressure and displacement caused by the mining process at the W coal seam have no impact on the coal seam of the stubble area, whereas the mining of the J coal seam leads to a continuous increase in the overburden displacement of the W coal seam; the latter also induces a shift in the maximum displacement to the rear, which is more significant for the stress concentration at the middle and front regions of the stubble area, thus presenting a superposition effect. The stress caused by mining at the coal seam decreases with increasing vertical distance from the roof or floor. For distant coal seams, the main contributing factor is the effect of vertical stress. The influential range of the vertical stress caused by mining in the overlying working face remains within 90 m, whereas the influential range of the stress caused by mining in the underlying working face is relatively large, i.e., it still affects the roadway at distances up to 160 m. The results and discussion presented herein provide significant practical value in terms of understanding the overburden strata activity and its influential range in adjacent mines’ stubble areas, which can be used to guide group mining efforts.

Experimental investigation on the monotonic, cyclic and post cyclic interfacial behavior of non-water reacted polymer and concrete

The safety performance of geotechnical engineering is obviously affected by the interface characteristics of geotechnical materials. With widely use of the polymer in geotechnical engineering, the investigation for interface characteristics of polymer and concrete structure is necessary. In this paper, to investigate the interfacial shear properties of non-water reacted polymer and cement concrete, a series of displacement controlled monotonic direct shear (MDS) tests, cyclic direct shear tests (CDS) and post cyclic direct shear (PCDS) tests were carried out by using a newly designed direct shear test apparatus. The compressive strength of the polymer and cement concrete blocks are 2 MPa and 20 MPa respectively. The effects of vertical stress (50 kPa, 100 kPa, 150 kPa, 200 kPa), shear rate (1 mm/min, 2 mm/min, 3 mm/min, 4 mm/min and 5 mm/min), and cycle number on the investigated interface characteristics were studied. The results show that, with the increase of the vertical stress, the average peak shear stress of the interface gradually increases. As the vertical stress increase from 50 kPa to 200 kPa, the average peak shear stress increased by more than two times under various conditions. While with the increase of the shear rate, the average peak shear stress of the interface gradually decreases, but the reduction is small. And the reductions are all not more than 10% when the shear rate increases from 1 mm/min to 5 mm/min under all conditions; with the increase of the number of cycles, the average peak shear stress of the interface gradually decreases, and the decrease rate gradually decreases. When the vertical stress is 100 kPa and the shear rate is 3 mm/min, the average peak shear stress is reduced by 4.4% as the number of cycles increases from 1 to 5, while that is reduced by 1.2% as the number of cycles increases from 5 to 10; Under the given shear rate and vertical stress, the interface between polymer and cement concrete shows the shear softening in both MDS test and PCDS test. However, under the same vertical stress and shear rate, the shear strength and shear modulus of the MDS tests are greater than those of the PCDS tests. While the differences for MDS and PCDS are almost all not more than 5 kPa; with the increase of vertical stress, the shear strength and shear modulus of MDS test and PCDS test increase gradually. The shear strength increased by more than two times and the shear modulus increased by more than one times as the vertical stress increases from 50 kPa to 200 kPa. The shear strength is reduced by not more than 6% and the shear modulus is reduced by not more than 11% as the shear rates increase from 1 mm/min to 5 mm/min. The apparent cohesions are obviously influenced by cyclic direct shear, while the effective friction angles are a little influenced by CDS.

Study on Gas Enrichment Mechanism of Coal Seam Influenced by Vertical Stress on Mountainous Region Condition

The controlling effect of vertical stress of mountainous region on gas occurrence of the coal seam below it has always been ignored. In order to clearly express its influence mechanism, the change laws of depth, stress, and permeability of coal seam pressurised by the overlying mountain were studied based on the Winkler elastic foundation beam theory and seepage theory in the paper. At the same time, the enrichment mechanism of the coal seam pressurised by the overlying mountain was analyzed. The results showed the following: (1) There was a significantly strong correlation between the stress, permeability change rule of the coal seam, burial depth, and surface elevation under such condition. (2) Under the action of the vertical pressure of the mountain, the stress and permeability distribution of the coal seam showed significant nonlinear characteristics. The stress was the greatest under the peak, and the permeability was the smallest. (3) The initial gas content value was controlled by the permeability and the stress of the coal seam in the situation. Moreover, the field practice showed that under the action of vertical pressure of the mountain, the evaluation law of gas content was coupling with the surface elevation of the overlying mountain. In addition, the gas emission change law during the excavation of the driving face also showed the same characteristics. The results might be of great significance for the development and utilization of coal-bed gas and the safe exploitation of coal resources.

Studies of the shear wave velocity in soil cement under the anisotropic stress state

Introduction. Deep soil mixing, that alters construction properties of foundations, allows to construct buildings and structures on the sites that have loose soils. As a rule, adverse geotechnical conditions are accompanied by dynamic forces that affect designed buildings and structures. The objective of these studies is to predict changes in mechanical properties of soils that follow the alteration of structural properties of a foundation. Soil cement is the focus of this study. Materials and methods. The findings of special laboratory tests of soil cement samples using the method of low amplitude torsional vibrations inside a resonant column in the anisotropic triaxial compression mode allowed to assess the effect of the supplementary vertical load on the velocity of shear elastic wave propagation. The co-authors present a description of the research method and provide an overview of the equipment used to conduct special laboratory tests. Tests were performed on undisturbed soil cement samples that had a natural water content. The anisotropic stress state of soil cement samples exposed to triaxial tests in the resonant column was caused by special behaviour features of the foundation. Results. In this study, laboratory tests had two stages. At the first stage, the effect of the vertical stress on the velocity of shear wave propagation was assessed. Correlation dependences between the shear wave velocity and the ratio of vertical and lateral stresses were obtained. At the second stage, shear wave propagation velocity values were identified at various combinations of lateral σ3 and vertical σ1 stresses. The results of the second stage are designated for the assessment of the effect of the anisotropic stress state and the projection of shear wave velocities at the stress levels anticipated on the site that will accommodate designed heavy structures. Conclusions. The findings allow to assess the effect of lateral and vertical stresses on changes of shear wave velocities in the triaxial compression mode. It was identified that at equal values of lateral stresses σ3, a 7-fold vertical stress σ1 increase leads to a 15 % increase in the shear wave velocity in soil cement Vs. At the same time, an increase in the ratio of vertical to lateral stresses σ1/σ3 by a factor of 15 causes an 11 % increase in the shear wave velocity. It is noted that the smaller the initial value of lateral stress σ3, the higher the rise in the shear wave velocity Vs in the course of testing. Correlation dependencies, presented in this study, can be used to assess the effect of the anisotropic state as the first approximation (for preliminary calculations) in the design of heavy structures on soil cement foundations.

A New Osmotic Oedometer with Electrical Resistivity Technique for Monitoring Water Exchanges

This article presents a new osmotic oedometer that is able to measure changes in the degree of saturation (Sr) during suction-controlled drying-wetting and oedometric tests. A circular four-electrode cell made of polyvinyl chloride was developed. The geometric factor of the cell was determined by numerical simulation and validated by calibration tests. A total of 29 samples was statically compacted in the oedometric cell at different moisture contents and dry densities. Based on these measurements, the normalized electrical resistivity was defined and correlated with the Sr. After that, three suction-controlled drying-wetting and oedometric tests were performed on the samples statically compacted at the water content of 21 % and dry density of 1.62 g/cm3, which corresponds to the standard Proctor optimum conditions. The results show (i) the potential of the new oedometer for the study of the hydromechanical behavior of unsaturated soils, (ii) the ability of the electrical resistivity technique to estimate the variation of the Sr in unsaturated oedometric tests, with a relative error smaller than 5 %, and (iii) the coupled effect of vertical stress and suction on the change in void ratio (e) and Sr shown in the (e - suction pressure [s] - vertical total stress [σv]) and (Sr - s - σv) state surfaces.

The Effects of Vertical Stress on the Liquefaction Potential Originated from Buildings in The Urban Areas

Main purpose of this paper is to study the influence of vertical stress on soil liquefaction in urban areas. The literature provides limited information on vertical stress analysis of multiple footings, and, as a result, there is no accurate way to account for the effect of the foundation depth on liquefaction. Additionally, practical methods do not exist for considering the interaction between the neighboring foundations vertical stress and seismic forces in the urban area. Vertical stress distribution was calculated in examining the soil liquefaction potential exhibited by building foundations as a case study. The vertical stresses were chosen randomly for some buildings with foundation depths of 3.00 m; 4.50 and 6.00 m at the Burkent site (Burdur-Turkey). The influence of 5-storey buildings on the liquefaction potential of sandy soils was evaluated in terms of the safety factor (FS) against liquefaction along soil profile depths for different earthquakes. Standard Penetration Test (SPT) results were used based on simplified empirical procedure.

Thermal conductivity of geosynthetic clay liners

The thermal conductivities of powdered and granular bentonite based needle punched geosynthetic clay liners (GCLs) were investigated at different gravimetric water contents under 25, 50, 75, and 100 kPa vertical stresses. Both types of GCLs exhibited an increase in thermal conductivity with increasing vertical stress at all water contents. The effect of vertical stresses was more pronounced for the specimens hydrated at lower gravimetric water contents and this was attributed to their high initial volumetric air content. The variability of water distribution in partially hydrated GCLs has been identified as a factor that may affect their thermal conductivity. The forms of bentonites (i.e., powder or granular) affected their thermal conductivities; however, this effect was less apparent at higher gravimetric water contents due to the reduced air content and gel formation in the bentonites. Finally, the GCL thermal conductivity calculated from the measured thermal conductivities of its various constituents (i.e geotextile and bentonite) components differed from the measured values. This was attributed to the nonuniform water distribution across the GCL specimen and change in material properties when components of GCL were disassembled.

Effect of Stress Level and Binder Composition on Secondary Compression of an Artificially Stabilized Soil

This paper examines the effect on the compressibility of a Portuguese soft soil stabilized with binders, with a special emphasis on creep characteristics. The effects of vertical stress during curing time and binder composition (type and content) on the creep behavior of a sta- bilized material are analyzed with oedometer tests. The results show the decrease of the secondary compression index with the decrease of the vertical stress applied during creep phase and with the increment of the binder content. The best binder type for this soil, in terms of creep be- havior, iscomposedof portland cement and flyash witha dryweight proportionof 75/25, becausethis promotes thedevelopment of secondary pozzolanicreactions.Theresultsalsorevealthatthebindercompositionshouldhaveaminimumquantityofcementtoimprovethecompression characteristicsofthestabilizedsoiladequately.DOI:10.1061/(ASCE)GT.1943-5606.0000762. © 2013 American Society of Civil Engineers. CE Database subject headings: Mixing; Columns; Creep; Soil consolidation; Soft soils; Soil stabilization; Compression; Soil stress. Author keywords: Deep mixing columns; Creep; Secondary consolidation; Oedometer creep tests; Soft soils.

Effect of Vertical Stress on Seismic Performance of Autoclaved Aerated Concrete Block Composite Walls with a Door Opening

Non-linear analysis of autoclaved aerated concrete (AAC) block masonry composite walls with a door opening was conducted with finite element software ABAQUS in order to study its seismic performance. The finite element results were firstly verified with laboratory results and then the effects of vertical stress on seismic performance of the wall was investigated using finite element analysis. This study indicates that seismic performance can be improved with the increase of vertical stress; however, the effect of vertical stress on ultimate load is less than that on the displacement under ultimate load.

Finite Element Analysis of Horizontal Reinforcement Ratio's Effect on Seismic Performance of Autoclaved Aerated Concrete Block Masonry

Non-linear analysis of autoclaved aerated concrete (AAC) block masonry composite wall with column has been conducted using finite element software ABAQUS. First, the finite element results were verified with laboratory results of full-scale specimens. Effects of horizontal reinforcement ratio on seismic performance were investigated. The analysis indicates that shearing strength of the wall is affected by the openings greatly. Seismic performance is improved with the increase of horizontal reinforcement ratio. The effect of vertical stress on wall without openings is more than that on wall with openings. Bearing capacity of walls without openings has a linear relationship with the horizontal reinforcement ratio. And bearing capacity of walls with openings is related to the place where the reinforcements are installed as well as the horizontal reinforcement ratio.

Finite Element Analysis of Vertical Stress's Effect on Seismic Performance of Autoclaved Aerated Concrete Block Masonry Walls

Non-linear analysis of autoclaved aerated concrete (AAC) block masonry composite wall with reinforced concrete (RC) core columns has been conducted using finite element software ABAQUS. First, the numerical results from finite element analysis were verified with laboratory results of full-scale AAC masonry wall specimens. Effects of vertical stress on seismic performance were investigated. The analysis indicates that lateral load capacity of the wall is affected by the openings greatly and increased with the increase of vertical stress. The effect of vertical stress on the wall without openings is more obvious than that with openings.

A new aspect of mechanical stress effects in scaled MOS devices

Deviation in device characteristics due to mechanical stress is investigated experimentally and analytically from the viewpoints of scaling and hot-carrier effects. A stress analysis program, SIMUS (stress analysis program for multilayer structure) 2D/F, which can analyze the stress state of thin multilayer structures such as LSI devices throughout their manufacturing process, was used. In scaled MOS devices, the effect of uniaxial stress is reduced. However, the effect of vertical stress, such as mold stress, becomes a serious problem when the vertical stress causes compressive surface stress. Compressive stress has a serious effect on electron trapping, in SiO/sub 2./ These results provide important guidelines for the manufacture and package design of deep submicrometer devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of vertical stress, temperature and density on the dielectric properties of lunar samples 72441,12, 15301,38 and a terrestrial basalt

The dielectric properties of lunar soil samples 72441,12 and 15301,38 have been measured as a function of vertical stress to 2 bars, temperature to 200°C and density, in vacuum, over the frequency range 200–10 5 Hz. It was found that the dielectric constant varies not only with density, but also with stress at constant sample density. The loss tangent was found to be insensitive, within experimental limits, to both stress and density variations over the ranges measured. A solid terrestrial basalt sample has been ground and the dielectric properties of the powder and a remaining portion of the solid sample have been measured in vacuum. The measured dielectric constants for the basalt soil at different densities are compared with calculated values using the solid sample data in conjunction with the Lichtenecker, Rayleigh and Krotikov-Troitskiy mixing formulas. Qualitative behavior of the dielectric properties of the lunar regolith with depth is discussed.