Unsaturated Permeability Research Articles

Characterization of textile permeability as a function of fiber volume content with a single unidirectional injection experiment

Textile permeability is a fundamental property to describe preform impregnation in Liquid Composite Molding (LCM) processes. It depends on textile architecture and fiber volume content (FVC). Conventional methods to measure in-plane permeability are based on radial or unidirectional injection experiments performed at fixed FVC. A complete characterization involves a series of tests and requires several material samples. This study presents a novel approach to characterize permeability as a function of FVC through a unique unidirectional injection experiment with a preform containing different FVC sections. The same experimental set-up as in conventional unidirectional unsaturated permeability measurements is used with a second pressure transducer embedded in the mold in addition to the one located at the inlet gate. A fast algorithm is developed to exploit the data from the two sensors and automatically derive the permeability distribution without any need of visual flow front observations. The methodology is validated with a random fiber mat and a woven fabric. Results show that accurate permeability characterization can be achieved for both kinds of textiles.

Effect of hydraulic properties of soil and fluctuation velocity of reservoir water on landslide stability

Water fluctuation is the main triggering factor of reservoir slope failures, especially in the area of the Three Gorges Reservoir of China. Fluctuation velocity of reservoir water and hydraulic properties of soil as defined by soil–water characteristic curve (SWCC), saturated permeability coefficient and unsaturated permeability function are key potential properties that control reservoir landslide stability. The effect of reservoir water fluctuation velocity and hydraulic properties of soil on landslide stability are investigated through a series of numerical simulations with different parameters. The results of simulations show that fitting parameters in the SWCC [i.e., a, n, m for Fredlund and Xing (Can Geo J, 31(3):521–532. doi: 10.1139/t94-061 , 1994) equations] have significant effect on the stability of landslide for reservoir water’s drawdown or impounding process. The saturated permeability coefficient of soil and velocity of water level fluctuation have comprehensive (defined as Impact Factor, α) and significant influence on the stability of reservoir landslide. A relative equation: m > α > n > a has been drawn for the susceptibility of effect on the stability of reservoir landslide for the parameters “a”, “n”, “m” and “α”.

A novel mold design for one-continuous permeability measurement of fiber preforms

One-continuous permeability measurement experiments allow measuring permeability of a fiber preform within a range of fiber volume fractions by conducting a single unsaturated (a.k.a. transient) flow experiment on a dry specimen at an initial thickness, and a set of saturated flow experiments on the wetted specimen by varying the thickness of the mold cavity. This approach allows quicker database construction and reduces the effect of inherent variation of fabric structure caused by inconsistent labor on permeability. In this study, the drawbacks of previous mold designs are eliminated by using appropriate sealing, gap thickness adjustment mechanism and features that allow straightforward and reliable manual operation. Experiments for three different fabric types are conducted and the results are discussed. It is mainly observed that the unsaturated permeability is higher than the saturated permeability.

Impact of carbonation on unsaturated water transport properties of cement-based materials

In unsaturated conditions, the durability of concrete structures is strongly dependent on the evolution of the amount of free water within concrete porosity. Reliable durability assessment of concrete structures in relation to their environment thus requires accurate unsaturated water transport description as well as reliable input data. The effect of carbonation on water transport remains poorly studied and data are lacking. It was then the purpose of this article to acquire all the data needed to describe unsaturated water transport in carbonated cementitious materials (porosity, water retention and unsaturated permeability). Four hardened pastes made with four different binders were carbonated at 3% CO2 to ensure representativeness with natural carbonation. Beyond the modification of the water retention curve and porosity clogging, significant microcracking due to carbonation shrinkage was observed. The consequence on permeability highlighted a competition between porosity clogging and microcracking that was dependent on the initial mineralogical composition.

Unsaturated Permeability and Retention Curve Determination From In-Flight Weight Measurements in a Bench-Scale Centrifuge

Centrifuges have been used in many ways to determine permeabilities, as they can significantly shorten testing times in low-permeable soils. Typically equilibrium profiles, inflow–outflow measurements, or direct measurements from inside the sample—like from tensiometers or radioactive decay—are used. Recently, weight measurements of the sample outside the centrifuge were used effectively in an adapted setup. We present the results of the possibilities offered by doing transient weight measurements of a soil-sample during rotation in the centrifuge. We present the setup of such an experiment and how the unsaturated permeability and water retention curve can be recovered from it. This eliminates the overhead of doing measurements inside the sample.

Modification of triaxial apparatus for permeability measurement of unsaturated soils

Both the shear strength and the permeability of unsaturated soils are important engineering properties that are required in numerous geotechnical designs. Many studies on the shear strength of unsaturated soils have been reported; however, only a limited number of studies on the permeability of unsaturated soils have been presented. This might be due to the fact that the time and the costs associated with unsaturated permeability measurements are excessive. The purpose of this paper is to introduce the modification of a triaxial apparatus for the direct measurement of permeability in conjunction with shear strength tests on unsaturated soils under multiple cycles of drying and wetting. Detailed designs and modifications are carried out to allow the unsaturated permeability and the shear strength of a soil to be measured for the same soil specimen. The test results are found to be more consistent as both measurements are conducted on the same specimen. A series of unsaturated permeability tests and then a series of unsaturated consolidated drained (CD) triaxial tests, under multiple cycles of drying and wetting, are conducted on three different soils, and the results are shown to be compatible with the theory reported in literature.

An evaluation of the reproducibility of capacitive sensor based in-plane permeability measurements: A benchmarking study

A benchmark study for permeability measurement is presented. In the past studies of other research groups which focused on the reproducibility of 1D-permeability measurements showed high standard deviations of the gained permeabil- ity values (25%), even though a defined test rig with required specifications was used. Within this study, the reproducibility of capacitive in-plane permeability testing system measurements was benchmarked by comparing results of two research sites using this technology. The reproducibility was compared by using a glass fibre woven textile and carbon fibre non crimped fabric (NCF). These two material types were taken into consideration due to the different electrical properties of glass and carbon with respect to dielectric capacitive sensors of the permeability measurement systems. In order to deter- mine the unsaturated permeability characteristics as function of fibre volume content the measurements were executed at three different fibre volume contents including five repetitions. It was found that the stability and reproducibility of the pre- sented in-plane permeability measurement system is very good in the case of the glass fibre woven textiles. This is true for the comparison of the repetition measurements as well as for the comparison between the two different permeameters. These positive results were confirmed by a comparison to permeability values of the same textile gained with an older gen- eration permeameter applying the same measurement technology. Also it was shown, that a correct determination of the grammage and the material density are crucial for correct correlation of measured permeability values and fibre volume contents.

Effect of range of soil–water characteristic curve measurements on estimation of permeability function

The most commonly used indirect method to determine unsaturated permeability of soil is to estimate the unsaturated permeability function from soil–water characteristic curve and saturated permeability. The suction range that soil–water characteristic curve (SWCC) can be measured in the laboratory depends on the type of equipment used for measurement. As the estimation models use the available measured SWCC data to obtain the unsaturated permeability function, the estimated permeability function can be affected by the number of measured data of SWCC and the suction range over which the SWCC data are measured. Therefore, there is a need to investigate the effect of the range of SWCC measurements on the estimation of unsaturated permeability function. In this study, the effect of the range of SWCC measurements is investigated through different estimation models that are based on four different best-fit soil–water characteristic curve equations and three different relative permeability equations. It was found that the range of SWCC measurements greatly affect the estimated permeability functions. It was also found that the effect of the range of SWCC measurements is more significant than the selected best-fit SWCC equation used.

Modelling of unsaturated ground behaviour influenced by vegetation transpiration

Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots.

불포화 사면의 포화 부근 침투 특성을 고려한 수리전도도 모델

불포화 수리전도도는 Mualem 모세관 모델에 의하여 이론적으로 함수특성곡선으로부터 적분된다. 하지만 예측된 수리전도도는 포화 부근에서 모관흡수력의 미소한 변화에도 극도로 민감하다. 원활한 형태의 함수특성곡선에 의한 Mualem 수리전도도는 포화 부근에서 급격하게 감소하며, 수리적 거동을 신뢰할 수 있게 모델하지 못하거나 수치해의 안정성을 저해 한다. van Genuchten-Mualem(VGM) 수리전도도를 개선하기 위하여, 낮은 모관흡수력 수준에 있는 임의의 공기함입치이내에서 van Genuchten 함수특성곡선을 수정하였다. 수정 VG 곡선은 대수축에서 임의의 공기함입치에서 포화상태까지 선형화된다. 수정 VG 함수특성곡선은 실제 함수특성거동의 회귀분석에 영향을 끼치지 않으며 원래의 VG 함수특성곡선의 계수를 그대로 사용한다. 수정 VG 곡선을 이용하여, VGM 수리전도도는 임의의 공기합입치를 기준으로 구간별 적분하여 수정되었다. 수정 VGM 수리전도도가 해석적 해로 제안되었으며, 포화부근 영역에서 수리전도도가 급격하게 감소하는 현상이 제거되었다. 실제 사면의 2차원 침투해석을 통하여 VGM 수리전도도와 제안된 모델에 따른 수리거동을 비교하였다. 제안된 모델은 여러 강우조건에 따른 해의 수렴성을 확보하였지만, VGM 수리전도도를 적용하면, 포화부근의 수리전도도가 급격하게 감소하여 강우량이 많은 경우 해가 수렴하지 않았다. 특히 선행강우에 의한 초기 안전율과 집중강우 후 최종 안전율을 크게 평가할 수 있었다. 제안된 수리전도도 모델은 침투해석과 안정해석을 통하여 실제 사면의 붕괴를 재현할 수 있었다. Unsaturated hydraulic conductivity (HC) is integrated theoretically from soil water retention curves (SWRC) by Mualem capillary model, but the prediction of HC is extremely sensitive to small variation of matric suction near saturation. Near saturation, the Mualem HC based on smooth SWRC decreases abruptly and has problems in the reliability of hydraulic behavior and the stability of numerical solutions. To improve van Genuchten-Mualem (VGM) HC, the van Genuchten SWRC model is modified within range of low matric suction (arbitrary air entry pressure). At an arbitrary air entry pressure, the VG SWRC is linearized in log scale until full saturation. The modified VG SWRC does not affect the fit of actual retention behavior and either the parameters of original VG SWRC fit. Using the modified VG SWRC, the VGM HC is modified to integrate for each interval decomposed by arbitrary air entry pressure. An analytical solution on modified VGM HC is proposed each interval, to protect the rapid change in HC near saturation. For silty soils, VGM models of HC function underestimate the unsaturated permeability characteristics and especially show rapid reduction near saturation. The modified VGM model predicts more accurate HC functions for Korean weathered soils. Furthermore, near saturation, the saturated HC is conserved by the modified VGM model. After 2-D infiltration analysis of an actual slope, the hydraulic behaviors are compared for VGM and the modified models. The prediction by the proposed model conserved the convergence of solutions on various rainfall conditions. However, the solution by VGM model did not converge since the conductivity near saturation reduced abruptly for heavy rainfall condition. Using VGM model, the factor of safety is overestimated in both initial and final stage during heavy rainfall. Stability analysis based on infiltration analysis could simulate the actual slope failure by the proposed model on HC.

Thermo-hydraulic behaviour of the vadose zone in sulphide tailings at Iberian Pyrite Belt: Waste characterization, monitoring and modelling

Unsaturated conditions favour the oxidation of sulphide minerals from mine wastes, which results in the release of contaminant products into groundwater. An abandoned high-sulphide impoundment in the Iberia Pyritic Belt, wherein tailings have undergone oxidation for more than 28years, was investigated for hydrological purposes. The objective was to understand the interactions between those mining tailings and the atmosphere under natural semiarid conditions (wet and dry seasons, short intensive rain events and strong daily temperature differences during the dry season).After the deposition, the sequence of waste textures that results from the sedimentation process is strongly dependent on the distance to discharge point. The spatial continuity of the sedimentation layers was studied by means of small scale dynamic penetration tests.The thermo-hydraulic characterization of the waste includes the determination of the water retention curve, saturated and unsaturated permeability, pore size distribution and thermal properties for the different textures.Atmospheric and waste physical measures, from 2002 to 2006, were performed using different techniques. The important changes in the salinity of the waste avoided the use of a single calibration for the electromagnetic sensors; a valid alternative was the evaluation of the water content from thermal conductivity estimations.Finally, a numerical model using the HYDRUS-1D software is presented. Model results reasonably fit the in-situ measures of soil moisture, soil temperature, soil water potential and soil heat flux in the vadose zone of tailings impoundment. Moreover, they provide information for energy and water balance determinations.

Temperature effects on unsaturated hydraulic property of bentonite-sand buffer backfilling mixtures

The influence of temperature on the engineered properties of bentonite-sand mixtures (B/S) is of major concern in the design of engineered barriers in underground repositories for high-level radioactive waste disposal. We experimentally studied the influence of temperature on soil unsaturated hydraulic properties related to water holding capacity and permeability of GMZ B/S in China. The vapor equilibrium method and water infiltration apparatus were used to measure the soil water characteristic curve (SWCC) and unsaturated hydraulic conductivity (k u). The results show that the SWCC under different temperatures from 20 °C to 60 °C tends to be the same. Temperature influence on unsaturated permeability is more relevant at low suctions, no clear effect is detected below a degree of saturation of 74%, and experimental data show that temperature dependence on unsaturated permeability is small.

화강풍화토의 확률론적 불포화 지반정수 특성에 따른 사면안정해석

함수특성곡선, 불포화투수곡선, 불포화전단강도와 같은 불포화 지반정수는 필연적으로 불확실성을 내포하기 때문에 사면안정해석에 사용될 대표적인 값을 획득하기 힘들다. 결정론적인 방법은 하나의 대표적인 값을 사용하기 때문에 분산이 심한 지반정수일 경우 잘못된 평가를 초래할 수 있다. 이를 해결하기 위해 확률론적 해석방법이 이용되고 있다. 하지만 지반정수에 대한 확률론적 특성 연구가 확률론적 해석을 위해 선행되어야 함에도 불구하고, 불포화 지반정수에 대한 확률론적 특성 연구는 아직 부족한 실정이다. 따라서 본 연구에서는 국내 화강풍화토의 불포화 지반정수에 대한 확률론적 특성을 파악하고, 이를 바탕으로 사면안정해석을 위한 불포화지반정수를 획득하기 위한 간단한 절차도를 제안하였다. 또한 불포화 화강풍화토 사면에 대하여 몬테카를로 시뮬레이션 방법을 사용한 확률론적 사면안정해석을 수행하였다. The unsaturated soil properties such as soil-water characteristic curve, unsaturated permeability and unsaturated shear strength, always involve uncertainties associated, making it hard to obtain a representative value in analyzing the stability of slopes. Because a deterministic approach use a representative value, soil properties with severe variance sometimes lead to misestimate and hence the consequence also varies from person to person. To address this problem, a probabilistic approach to the analysis of slope stability has been adopted. Even though the probabilistic characteristics of soil are essential for probabilistic approach, it has not been established. Therefore, in this paper, the probabilistic characteristics of the unsaturated soil properties were defined. A simple procedure for the probabilistic approach was proposed to obtain the unsaturated soil properties for the slope stability analysis. Finally, the probabilistic analysis of unsaturated slope stability using monte-carlo simulation method was conducted for the Korean weathered granite soil.

정수슬러지 혼합토의 함수특성곡선과 불포화 투수 특성

In this paper, in order to solve high water content of water sludge and promote its recycle, sludge mixtures with various mixing ratios were produced. Sludge mixture consisted of water sludge and weathered granite soil. Their physical properties and unsaturated characteristics (soil-water characteristic curve, and unsaturated permeability function) were investigated by laboratory tests. Experimental test results indicated that at a given matric suction volumetric water content of sludge mixture increased as water sludge content increased. Air entry values of sludge mixture increased from 0.9 kPa to 2.4 kPa with an increase in water sludge content or fine content. In addition, unsaturated permeability function, which is an important factor for performing infiltration analysis, was predicted using saturated permeability and soil-water characteristic curve of sludge mixture.

Impact of pit-toilet leachate on groundwater chemistry and role of vadose zone in removal of nitrate and E. coli pollutants in Kolar District, Karnataka, India

Assessment of chemistry of groundwater infiltrated by pit-toilet leachate and contaminant removal by vadose zone form the focus of this study. The study area is Mulbagal Town in Karnataka State, India. Groundwater level measurements and estimation of unsaturated permeability indicated that the leachate recharged the groundwater inside the town at the rate of 1 m/day. The average nitrate concentration of groundwater inside the town (148 mg/L) was three times larger than the permissible limit (45 mg/L), while the average nitrate concentration of groundwater outside the town (30 mg/L) was below the permissible limit. The groundwater inside the town exhibited E. coli contamination, while groundwater outside the town was free of pathogen contamination. Infiltration of alkalis (Na+, K+) and strong acids (Cl−, SO4 2−) caused the mixed Ca–Mg–Cl type (60 %) and Na–Cl type (28 %) facies to predominate groundwater inside the town, while, Ca–HCO3 (35 %), mixed Ca–Mg–Cl type (35 %) and mixed Ca–Na–HCO3 type (28 %) facies predominated groundwater outside/periphery of town. Reductions in E. coli and nitrate concentrations with vadose zone thickness indicated its participation in contaminant removal. A 4-m thickness of unsaturated sand + soft, disintegrated weathered rock deposit facilitates the removal of 1 log of E. coli pathogen. The anoxic conditions prevailing in the deeper layers of the vadose zone (>19 m thickness) favor denitrification resulting in lower nitrate concentrations (28–96 mg/L) in deeper water tables (located at depths of −29 to −39 m).

An analytical solution for rainfall infiltration into an unsaturated infinite slope and its application to slope stability analysis

SUMMARYSurficial slope failures in residual soils are common in tropical and subtropical regions as a result of rainfall infiltration. This study develops an analytical solution for simulating rainfall infiltration into an infinite unsaturated soil slope. The analytical solution is based on the general partial differential equation for water flow through unsaturated soils. It can accept soil–water characteristic curve and unsaturated permeability function of the exponential form into account. Numerical simulations are conducted to verify the assumptions of the analytical solution and demonstrate that the proposed analytical solution is acceptable for the coarse soils with low air entry values. The pore‐water pressure (pwp) distributions obtained from the analytical solution can be incorporated into a limit equilibrium method to do infinite slope stability analysis for a rain‐induced shallow slip. The analysis method takes into account the influence of the water content change on unit weight and hence on factor of safety. A series of analytical parametric analyses have been performed using the developed model. The analyses indicate that when the residual soil slope, consisting of a completely decomposed granite layer underlain by a less permeable layer, is subjected to a continuous heavy rainfall, the loss of negative pwp and the reduction in factor of safety were found to be most significant for the shallow soil layer and during the first 12 h. The antecedent and subsequent rainfall intensity, depth of a less permeable layer and slope angle all have a significant influence on the pwp response and hence the slope stability. Copyright © 2012 John Wiley & Sons, Ltd.

Evaluation of through-thickness permeability and the capillary effect in vacuum assisted liquid molding process

Through-thickness penetration under vacuum assistance is crucial for resin film infusion (RFI) and vacuum assistant resin transfer molding (VARTM) process. In this paper, values of the through-thickness unsaturated permeability (TTUP) and capillary pressure (Pc) are estimated based on the infiltration velocity in preforms of carbon fiber fabric and glass fiber fabric, respectively, measured by a specially designed apparatus. It reveals that, for the through-thickness permeation, the Pc values generally decrease with increasing fiber content. Relatively accurate TTUP can be obtained by counting Pc into the permeation dynamics. If Pc is neglected, liquids with good-wettability, such as silicone oil, tend to result in larger TTUPs. The corrected TTUPs show good agreement according to Carman–Kozeny, Gutowski modified Carman–Kozeny equation, and Gebart model, respectively. The resultant permeability resistance parameters of the preforms indicate that the penetration in carbon fabric bed is slower than in glass fabric bed. However, for fiber volume fraction more than 60%, the corrected TTUPs show no significant difference for all the preforms.

Chloride ion ingress distribution within an alternate wetting-drying marine environment area

Concrete structures in an alternate wetting-drying area often suffer from severe chloride ion ingress more than those in other areas. Field tests of marine structures were conducted, and chloride concentration is found to reach a maximum value at a certain elevation. The surface concentration and diffusion coefficient of chloride ions at different elevations exhibit Gaussian unimodal curve distributions. Using the chloride ion unsaturated permeability model, the distribution regularity mechanism is analyzed. Finally, an improved indoor accelerated simulation experiment is proposed to simulate the rules governing chloride ion ingress into concrete structures in an alternate wetting-drying area.

Temperature effects on the unsaturated permeability of the densely compacted GMZ01 bentonite under confined conditions

In this study, temperature controlled soil-water retention tests and unsaturated hydraulic conductivity tests for densely compacted Gaomiaozi bentonite — GMZ01 (dry density of 1.70Mg/m3) were performed under confined conditions. Relevant soil–water retention curves (SWRCs) and unsaturated hydraulic conductivities of GMZ01 at temperatures of 40°C and 60°C were obtained. Based on these results as well as the previously obtained results at 20°C, the influence of temperature on water-retention properties and unsaturated hydraulic conductivity of the densely compacted Gaomiaozi bentonite were investigated. It was observed that: (i) water retention capacity decreases as temperature increases, and the influence of temperature depends on suction; (ii) for all the temperatures tested, the unsaturated hydraulic conductivity decreases slightly in the initial stage of hydration; the value of the hydraulic conductivity becomes constant as hydration progresses and finally, the permeability increases rapidly with suction decreases as saturation is approached; (iii) under confined conditions, the hydraulic conductivity increases as temperature increases, at a decreasing rate with temperature rise. It was also observed that the influence of temperature on the hydraulic conductivity is quite suction-dependent. At high suctions (s>60MPa), the temperature effect is mainly due to its influence on water viscosity; by contrast, in the range of low suctions (s<60MPa), the temperature effect is related to both the water viscosity and the macro-pores closing phenomenon that is supposed to be temperature dependent.

Parameters of Muzhuping Landslide in the Shuibuya Reservoir

Landslide is common geological hazards to the hydropower reservoir. Reasonable parameters are the key to design and prevent the landslide. After geological exploration, a few laboratory tests (uniaxial compression test, unsaturated permeability test, unsaturated direct-shear test) were conducted for the sliding mass. In order to obtain reasonable strength parameters of sliding mass, basing on the experimental results, some researches (such as engineering analogy, parametric inversion) were performed by using limit equilibrium method. The mechanical parameters of the slope were proposed.