Change Of Permeability Coefficient Research Articles

Changing law of permeability coefficient during compression for reconstituted sandy clays

Sandy clay is defined as a sand–clay mixture with the mechanical behavior dominated by fine clay but affected by coarse sand. Twenty sets of one-dimensional incremental load consolidation and falling head permeability coefficient tests were performed on sandy clays. The samples of sandy clays were prepared by mixing two hosted clays with different sand fractions from 0% to 60%. The interrelation between the change of permeability coefficient with void ratio and the compression curves is established. The results indicate that the effect of sand fractions on permeability coefficient can be attributed to the variation of void ratio at liquid limit induced by sand fractions. The initial void ratio affects permeability coefficient by changing the void ratio under the same effective vertical stress. These two findings highlight that the permeability coefficient-void ratio relationship of sandy clays is a function of void ratio at liquid limit and void ratio. An empirical method of estimating permeability coefficient is also proposed using two physical indices of void ratio and void ratio at liquid limit for sandy clays having void ratio at liquid limits ranging from 0.63 to 1.73 and initial void ratios varying from 0.72 to 2.67.

Influence of impact load on permeability of saturated calcareous sand

Due to the characteristics of geographical environment and many complicated factors, the seepage properties of calcareous sand are quite different from those of common continental and marine sediments. To investigate the change of permeability coefficient of calcareous sand under external load, a seepage test device equipped with an impact loading system was developed. The effects of particle size distribution, initial relative density and impact load on the permeability of calcareous sand were investigated with this device. The results showed that the larger the curvature coefficient and uniformity coefficient, the smaller the initial relative density lead to the greater the permeability coefficient of calcareous sand and the more obvious the change of permeability coefficient before and after loading. The permeability change of calcareous sand under impact load was greater than that of quartz sand.

Analytical Solutions of Steady a Seepage Field for Deep-Buried Tunnel with Grouting Ring Considering Anisotropic Flow

Difficulties related to seepage are frequently encountered in tunnel design and construction, especially in deep-buried tunnels. Nowadays, analytical solutions of steady seepage fields for deep-buried tunnel usually assume that the surrounding rock mass is homogeneous. In this study, analytical solutions of a steady seepage field for a deep-buried tunnel with grouting ring considering anisotropic flow are proposed. The proposed analytical solutions are verified by numerical simulations and parameter analysis are carried out. Results show that the seepage field of surrounding rocks around the deep buried circular tunnel is no longer uniformly distributed and presents elliptical distribution. The change of permeability coefficient of the lining structure has a great influence on the hydraulic head when the difference between permeability coefficient of lining structure and surrounding rock is not very large. The results show that the size of the grouting ring has more significant influence on the grouting effect.

A Study on the Generation Mechanism and Development Process of Piping Based on the Theory of Muddy Water Seepage

In the process of piping development, the sediment carried by seepage causes the change of porosity and then causes the change of permeability coefficient. Therefore, piping belongs to muddy water seepage (i.e., unstable seepage). Based on the theory of muddy water seepage, the new control equation of piping model is established. The generation mechanism and development process of piping for white fine sand and sand gravel are explored. The advantages for the new control equation of piping model are discussed. The results show that the new control equation of piping model is not only simpler in form but also easier to solve and can better describe the characteristics of piping generation, development, and stability. Compared with white fine sand (the initial relative density and porosity are smaller, and the initial permeability coefficient and critical gradient are larger), the porosity, permeability coefficient, seepage flow, and sediment volume of sandy gravel increase faster with time. When the porosity is the same, the permeability coefficient, seepage flow, and sediment volume of sand gravel are larger. The smaller the area affected by piping, the faster the increase of porosity, permeability coefficient, seepage flow, and sediment volume. When the porosity and permeability coefficient are the same, the seepage flow and sediment volume are smaller. The smaller the initial porosity and permeability coefficient, the later the generation, and development of piping. It can provide a reference for piping danger forecast and emergency response.

Relationship between Permeability Coefficient and Fractal Dimension of Pore in Ionic Rare Earth Magnesium Salt Leaching Ore

The change of permeability coefficient of ionic rare earth ore is one of the most important factors causing the uncontrollable flow of leaching solution, and the variation of pore structure of the ore body has a great influence on the permeability coefficient. The research on the evolution of the relationship between pore structure and permeability coefficient of ionic rare earths is of great significance for controlling water and soil pollution and improving the leaching rate of rare earths. In this paper, the column leaching test of ionic rare earth was carried out to study the evolution of the relationship between pore structure and permeability coefficient. In the process of MgSO4 solution and deionized water leaching, the T 2 spectrum and inversion image at each time were obtained by nuclear magnetic resonance (NMR). Based on the fractal theory, the pore structure change of the inversion image was quantitatively analysed, and the permeability coefficient of samples at each time of different leaching agents was calculated by using supercritical Dubinin-Redushckevich (SDR) model to analyse the nuclear magnetic resonance T 2 spectrum. The results show that in MgSO4 solution, the permeability coefficient of the sample changes significantly, and the growth rate of pore fractal dimension remains large. By discussing the evolution law of pore fractal dimension and seepage characteristics of ionic rare earth, the mathematical relationship between permeability coefficient and pore fractal dimension of mineral soil samples at different depths is fitted by polynomial function.

Development of Piping Analysis Method for Embankment Including Time-Dependent Change in Permeability Coefficient

Abstract The permeability of a saturated porous medium is regarded as a constant during the seepage process in traditional seepage analysis theory. However, it changes constantly during the piping ...

Study on Fracture and Permeability Characteristics of Unloading Rock with High Water Pressure

Research on the damage and seepage characteristics of unloading rock with high water pressure can help to further understand the mechanism of water inrush in deep mine floor and prevent water inrush. This paper used the RFPA2D-flow finite element software to study the failure and seepage characteristics of unloading rock with high water pressure and high stress and comparatively analyzed the failure modes and seepage characteristics of unloading rock with and without water pressure. The effects of different water pressure differences on the failure of unloading rock and the law of seepage were investigated by analyzing the change of acoustic emission and permeability coefficient with stress. The results showed that the unloading rock without water pressure was brittle failure, and the initial damage of the unloading model with water pressure was earlier than that of the model without water pressure and showed greater brittleness, and its cracks first break through at the bottom of the sample with higher osmotic pressure. With the increase in unloading, the permeability of rock increased gradually until it appeared an abrupt change. The failure mode and permeability law of the rock with different water pressure differences were basically the same, but the greater the pressure difference, the smaller the effective unloading capacity when the permeability coefficient changes suddenly, and the greater the possibility of water inrush in the rock.

A simple prediction method for the permeability coefficient of water-bearing sand layer after grouting compaction

Due to the particularity of the pumping of the compound paste slurry material, the traditional stress analysis method is difficult to apply. Based on the cylindrical hole expansion model of compacted grouting, the theoretical formula of the compacted grouting displacement field of soil is established on the basis of simplified body strain. Based on the displacement field theory, the analytical solution of the soil permeability coefficient after grouting and compaction is established according to the compressed porosity and Konzeny-Carman equation. The field test of compact grouting was carried out, and the water injection test was used to obtain the change of permeability coefficient before and after grouting under different grouting intervals. The obtained results are in good agreement with the theoretical solution and have certain engineering guidance significance.

Permeation and diffusion of nutrient ions in poly (vinyl alcohol) hydrogel membrane

Poly (vinyl alcohol) (PVA) hydrogel membrane has transport properties because of their cross-linked network structure, which had been used in soilless cultivation of plants. This work revealed the permeability and diffusion ability of nutrient ions in the PVA hydrogel membrane, such as K+, Na+, Ca2+, and Mg2+, which were based on the solution–diffusion model and free volume theory. The microstructure of the membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction, and scanning electron microscopy. From experimental results, the process of ion diffusion was a steady-state diffusion. With the increase in temperature and concentration, ion permeability was enhanced. However, compared with divalent ions, permeability increase for monovalent ions is more pronounced due to its smaller hydrated radius. At the concentration of 0.01 mol/L, the permeability coefficient of K+ was 3.5 × 10−7 cm2/s at 30 °C, which was nearly three times of Mg2+. The nutrient ion permeability coefficient was more strongly dependent on the temperature than the ion concentration. For the permeability of K+, the temperature increases from 20 to 50 °C, the permeability coefficient changes from 1.54 to 8.64 × 10−7 cm2/s, and when the concentration increases from 0.01 to 0.08 mol/L, the permeability coefficient changes from 4.53 to 6.8 × 10−7 cm2/s.

A Fractal Model for Characterizing Hydraulic Properties of Fractured Rock Mass under Mining Influence

In this paper, two basic assumptions are introduced: (1) The number and length distribution of fractures in fractured rock mass are in accordance with the fractal law. (2) Fluid seepage in the fractures satisfies the cubic law. Based on these two assumptions, the fractal model of parallel seepage and radial seepage in fractured rock mass is established, and the seepage tensor of fracture network which reflects the geometric characteristics and fractal characteristics of fracture network under two kinds of seepage is derived. The influence of fracture geometry and fractal characteristics on permeability is analyzed, and the validity and accuracy of the model are verified by comparing the calculated results of the theoretical model and physical model test. The results show that the permeability coefficient K of fracture network is a function of the geometric (maximum crack length Lmax, fractured horizontal projection length L0, diameter calculation section porosity Φ, fracture strike α, and fracture angle θ) and fractal characteristics (fracture network fractal dimension Df and seepage flow fractal dimension DT). With the increase of fractal dimension Df, the permeability coefficient increases. With the increase of DT, the permeability coefficient decreases rapidly. And the larger the Df (Df>1.5), the greater the change of permeability coefficient K with DT.

Study on the Permeability and TSS Removal Efficiency of Permeable Pavement Using Constant Head Particle Loading Test

Kim, J.Y.; Choi, Y.S.; Kim, T.Y.; Lee, S.H., and Kwon, S., 2019. Study on the permeability and TSS removal efficiency of permeable pavement using constant head particle loading test. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 236-240. Coconut Creek (Florida), ISSN 0749-0208.Climate changes cause extreme disasters frequently such as storms, floods and tsunmai in lowlands and coastal areas. A new paradigm for the prevention of disaster damages has been required. To date, LID technologies using porous materials has been paid attention to control direct runoff, floods and NPSs. Permeable pavement among LID technologies which prevent floods and reduce NPSs can be actively applied to sidewalks, parking lots and driveways in lowlands and coastal areas. However, the loss of permeability in the material matrix has been considered as a critical issue when pore is clogged by particles for maintaining the constructed facility in the field. Herein, we conducted particle loading test at constant head to obtain the permeability coefficient and TSS removal efficiency to evaluate the cyclic performance of the permeable pavement system, and further determine their correlation. We found that the change of permeability coefficient was 273 ∼ 72 mm/s when the ∼ 4.2 kg/m2 particles were loaded for 60 minutes. Trend of permeability coefficient depends on amount of particle per time. This means that loading particles in a short time make more clogging than a long time. The TSS removal efficiency was >80% at different hydraulic gradient and inflow concentration. Trend of TSS removal efficiency increased as particles were loaded. The correlation between the permeability coefficient and TSS removal efficiency is inversely proportional. Although the results will vary depending on the specification of the pavement system, this method can be used to estimate the effective replacement period with further researches.

Experimental Analysis on Permeability Characteristics of Iron Tailings

The permeability characteristics of iron tailings are one of the important factors affecting the stability of the tailings dam. The permeability properties of undisturbed iron tailings and disturbed iron tailings were analyzed from various aspects such as FC value, gradation, particle size, specific surface area, and interparticle void ratio with water head test in laboratory. The results show that the permeability coefficients of undisturbed iron tailings and disturbed iron tailings are affected by the fine particles content (FC). The threshold of fine content is about 40%. The traditional formulas for calculating the permeability coefficient are applied. But the results are inaccurate. The relationship between permeability coefficient of the iron tailings (undisturbed iron tailings and disturbed iron tailings) and the nonuniform coefficient (Cu), the curvature coefficient (Cc), the average particle size, the weighted average particle size, the specific surface area, and the skeleton void ratio (es) is nonlinear. It is difficult to characterize the change of permeability coefficient when the fine content is large. However, the relationship between permeability coefficient of the iron tailings (undisturbed iron tailings and disturbed iron tailings) and the effective particle size and silt particles void ratio (ef) is linear. A formula was developed for the determination of permeability coefficient of iron tailings by analyzing the effective particle size and silt particles void ratio. And it is more accurate. The permeability coefficients of disturbed samples are slightly larger than the permeability coefficients of undisturbed sample. This is due to the destruction of the sedimentary structure of the tailings and increasing e. Maybe the R in the new formula is affected by the structure of iron tailings. This requires further research.

Seepage Field-Strain Field Coupling Analysis for Rock Masses of Coal Seam Floor during Mining Based on COMSOL

Based on the fluid-solid coupling theory, The fractured rock mass was described as a continuous porous medium, and consider the rock mass permeability coefficient has a relationship with the stress and strain. The dynamic change of permeability coefficient was achieved using the multi-physics coupling analysis software COMSOL, and found that the stress and strain of surrounding rocks changes a lot due to mining. The maximum stress and strain in the mudstone area reaches 2-3 times of the original one, which happened at the immediate roof of mined-out area. According to the analysis of seepage field, mining does not destroy water resistance of floor aquifer. Mining fissures do not connect limestone aquifers, and water in the limestone is less likely to flow into stop to cause damage.

Study of Coal and Rock Floor Failure Characteristics of Upper Protective Layer Mining

For less study on coal rock floor fracture distribution of upper protective layer mining process, by numerical simulation and similarity simulation combined to get failure characteristics of distribution on the floor with the protective layer mining ,divided into deformation-failure zone and plastic deformation zone of seam floor, with the same time divided each zone height of "upper three zone". Regional outburst prevention measures as the most effective, a mine protective layer mining practice, investigated the protective effect of the protective layer on the protected layer after mining coal seam gas pressure, gas content, permeability coefficient changes, Because of the protective layer at the plastic deformation zone of seam floor, the gas release have a good effect .By numerical simulation and similarity simulation test combined, get protective layer mining floor failure distribution. Keywords: upper protevtive layer;Similar simulation;numerical simulation; failure characteristics ;protection effect.

Laboratory tests of filtration coefficient of selected materials used in liquidating shafts in collieries

There are a lot of dangers associated with closing mine shafts which may emerge during its liquidation works, and after liquidation of a shaft. The most important of them are: methane hazard, water hazard, and public safety hazard, which are commonly connected with occurrence of sinkholes. In the process of shaft liquidation it is extremely important to choose the right backfill materials, which determine stability of the backfill column and proper drainage of the backfill, which will match or exceed potential flow of water into a shaft. When the water flows into a liquidated shaft the main problem is a change in permeability coefficient of the used backfill materials due to grain degradation resulting from the fall into a shaft and the pressure within the backfill column. The article presents results of laboratory tests on the influence of vertical pressure on filtration coefficient and compressibility of the most commonly used backfill materials. During the tests, samples of the materials were loaded in a hydraulic press, simulating in this way the increase in vertical pressure within the backfill column. Compressibility of a given material and the change in filtration coefficient were assessed.

Hydro-Mechanical Coupled Analysis of the Variable Permeability Coefficient of Fractured Rock Mass

Based on the fluid-solid coupling theory, we describe the fractured rock mass as a continuous porous medium and consider the rock mass permeability coefficient a function of the stress and strain. By using the multi-physics coupling analysis software COMSOL, we achieved the dynamic change of permeability coefficient, and found that serious damage due to micro cracking occurred in the excavated damage zone of rock mass due to the yield and failure of rock mass. Corrodingly, permeability will remarkably increase, which is basically consistent with the experimental results. The simulations indicated the "indirect coupling" effect of seepage and stress. Therefore, the coupled analysis of the seepage and stress in fractured rock masses is important for the practical rock mechanics and rock engineering.

Reuse of dewatered sewage sludge conditioned with skeleton builders as landfill cover material

High water and organic content of sewage sludge constricts its reuse and disposal. It is often necessary to solidify/stabilize the dewatered sludge with solidifying agents before landfill disposal. In this study, the sewage sludge was conditioned with skeleton builders, i.e., fly ash and lime combined with ferric chloride for the purpose of improving the dewatering efficiency. The dewatered sewage sludge was then directly reused as landfill cover materials since the skeleton builders also play a role in solidification of sludge. The geotechnical properties of the dewatered sewage sludge were investigated. The results show that the plasticity index of the dewatered sludge increases compared to that of the dewatered sludge without any conditioner, and the permeability coefficient changes from 10−8 to 10−5 cm s−1. Furthermore, the strength of specimens increase with curing days. Microstructure analyses reveal that the main hydrated products are calcium silicate hydrate and ettringite, which contribute to the solidification/stabilization of the dewatered sludge. The results indicate that the dewatered sewage sludge conditioned with skeleton builders can be used as landfill covers. This study provides an alternative for traditional sewage sludge treatment and disposal.

Study on the Nitrogen Removal Capacity and Mechanism of Bioretention Tanks with Different Engineered Soils

Under continuous observation of the TN, NH3-N and NO3-N levels of the influent and effluent, as well as the changes in permeability coefficients of bioretention tanks with different engineered soils, the nitrogen removal capacity and mechanism of bioretention tanks were investigated. The research showed that the bioretention system had advantages in the nitrogen removal of rainfall runoff, and the average removal rate rose from 50% during the stabilization stage to up to 70% after running for 9 months. In addition, the permeability coefficients of bioretention decreased as the nitrogen removal capacity increased, with the permeability coefficients decreased by as much as 50% or even up to 90%. This study is of great importance for further exploration on the mechanism and application of bioretention technology in the purification of rainfall, and may play a positive role in promoting an environmentally-friendly society as well as sustainable development.

The Analysis of Soil Slope Transient Seepage Consider the Change of Permeability Coefficient in Rainfall Condition

In order to study the transient seepage field of soil slope when the saturated permeability coefficient changes under rainfall infiltration condition, the finite element software is used to build the numerical analysis model, the influence of slope seepage field and pore water pressure caused by the change of saturated permeability coefficient are emphatically discussed. The results show, under the condition of the certain sustained rainfall strength and rainfall duration, the rain water infiltration rate and infiltration depth are proportional to slope soil saturation permeability coefficient; Pore water pressure along the elevation direction shows the characteristic of “two big heads, among small” under the influence of rainfall infiltration.

The Analysis of Soil Slope Transient Seepage Consider the Change of Permeability Coefficient in Rainfall Condition

In order to study the transient seepage field of soil slope when the saturated permeability coefficient changes under rainfall infiltration condition, the finite element software is used to build the numerical analysis model, the influence of slope seepage field and pore water pressure caused by the change of saturated permeability coefficient are emphatically discussed. The results show, under the condition of the certain sustained rainfall strength and rainfall duration, the rain water infiltration rate and infiltration depth are proportional to slope soil saturation permeability coefficient; Pore water pressure along the elevation direction shows the characteristic of “two big heads, among small” under the influence of rainfall infiltration.