Constant Head Permeability Tests Research Articles

Soil macropores induced by plant root as a driver for vertical hydrological connectivity in Yellow River Delta

Abstract The protection and management of the wetland should consider the changes in hydrological connectivity caused by the structural modifications of the soil macropores. The main purpose of our work is to clarify and quantify the influence of the soil macropores volume on vertical soil hydrodynamic process mechanically and statistically by taking the form of a case-study in Yellow River Delta (YRD), and further reveal the vertical hydrological connectivity in this area. Based on X-ray computed tomography (CT) and constant head permeability test, the results showed a highly spatial heterogeneity of the soil structure in the YRD, hydraulic parameter (Ks) was negatively correlated with bulk density (BD) and positively with soil macropore volume, soil aeration (SA), and maximum water capacity (MWC). Using Hydrus 1-D software and the Green-Ampt model, we estimated the characteristics of hydrodynamic process in the soil without macropores, then evaluated the effect of the soil macropore on soil hydrological connectivity by comparing the experimental results with the simulation results. We found that increasing soil microporosity improved the convenience of water movement, which would enhance the hydrological connectivity of the region. The results will further help to reveal the eco-hydrological process at vertical scale in soil and provide a theoretical guide for wetland conservation and restoration.

Bio-cementation practice on electric-arc steel slag and comparison with natural sand

In construction projects in Khuzestan province in Iran, electric-arc steel slag (EASS) materials are used as fill materials. In this research study, bio-cementation practice on EASS materials is examined and compared with that on natural sand. For this purpose, direct shear, unconfined compressive strength (UCS) and constant head permeability tests, together with scanning electron microscopy images obtained using an instrument equipped with an energy-dispersive X-ray spectroscope, were used to analyse and compare untreated and treated materials. The results showed that despite higher urease activity and higher calcite production of EASS materials compared with natural sand, the latter showed slightly higher UCS, higher cohesion intercept enhancement and higher permeability decrease after bio-cementation treatment.

Strengthening and permeability control in sand using Cr3+-crosslinked xanthan gum biopolymer treatment

Trivalent chromium (Cr3+), commonly used in reservoir conformance control, has recently been introduced as an innovative technique for enhancing the strength and durability of Xanthan gum (XG) biopolymer-based soil treatment via Cr3+-induced crosslinking. We investigated the effects of Cr3+-crosslinked XG (Cr-XG) biopolymer treatment on the strength, stiffness and hydraulic conductivity of sand through a comprehensive series of experiments, including unconfined compression, direct shear, constant-head permeability tests, and rheological yield stress measurements. The results revealed that gelation of Cr-XG hydrogel via crosslinking between cation and carboxyl groups in XG, leading to gel stiffening, enhances cohesion within the sand over time. Furthermore, the increased yield stress in the Cr-XG hydrogel, compared to clean XG hydrogel, contributes to a more enduring pore-clogging effect, particularly under elevated hydraulic gradient conditions. The addition of 1% Cr-XG biopolymer to the sand significantly increased the ultimate bearing capacity by 466% and resulted in a four-orders-of-magnitude reduction in hydraulic conductivity, in comparison to untreated sand. This study elucidated the soil strengthening mechanism and efficacy attributed to crosslinking-induced gelation in Cr-XG biopolymer treatment. It effectively addressed limitations inherent in previous biopolymer-soil treatments, thereby accentuating its potential as a rapid grouting material within geotechnical engineering.

Studying the Behavior of Asphalt Stabilized Gepseous Soil for Earth Embankment Model

The study presents the test results of stabilizing gypseous soil embankment obtained fromAl- Faluja university Campus at Al-Ramady province. The laboratory investigation was dividedinto three phases, The physical and chemical properties, the optimum liquid asphalt (emulsion)requirements (which are manufactured in Iraq) were determined by using one dimensionalunconfined compression strength test.in the first phase , The optimum fluid content was 11%(6% of emulsion with 5% water content).. At phase two, the effect of Aeration technique wasinvestigated using both direct shear and permeability test. At phase three for the case of staticload , the pure soil embankment model under dry test condition was investigated, The testingprogram included the determination of the unconfined compressive strength, direct shearstrength, constant head permeability test, and one dimensional consolidation test for pure andasphalt stabilized gypseous soil. Testing was carried out in dry and absorbed conditions, themaximum pressure that can be supported before failure (ultimate sustained pressure) is 0.76MPa with vertical settlement (0.21 mm) . However, For the pure soil embankment model underabsorbed condition it was found that the maximum pressure before failure (ultimate sustainedpressure) is 0.3 MPa with vertical settlement (12 mm), Which reflects the reduction in bearingcapacity by (61%). Compression was made for absorbed stabilized soil and un-absorbed soiltested under hydraulic conductivity test for seven days, the results showed that a very lowmargin deffeneces in maximum pressure resistance and settlement were obtained (4.38 MPa ,0.11mm ) and (4.11MPa , 0.12mm).

A Novel Semi‐Analytical (Inertial) Solution for Determining Permeability of Highly Pervious Porous Materials Using the Two‐Reservoir Laboratory Setup

AbstractTwo conventional experimental procedures for determination of the water permeability of saturated porous medium are the constant and the falling head permeability tests. The first one is more applicable on more permeable materials where the outflow from the sample is measured at variety of constant water heads, while the second one is more convenient for low permeable materials, utilizing the continuous measurements of the water head falling due to filtration through the saturated sample. However, neither of the two is useful for materials of high permeability and large cross‐sectional area. The constant head permeability test faces technical issues since a significant and continuous water discharge is required, while the falling head permeability test has limitations due to neglection of the Forchheimer's high‐velocity flow through the sample, but also the influence of inertia on the fluid mass. Here we proposed an approach for determination of the water permeability of saturated porous medium based on the agreement between the measured water level change in two connected reservoirs containing a porous sample and the new semi‐analytical expression describing that change by accounting for the mentioned theoretical deficiencies. This efficient approach has been tested on four pervious paver samples, and results showed satisfactory agreement with the constant head permeability data. It has been also confirmed the proposed semi‐analytical solution is more accurate than the falling head permeability approach in case of highly pervious materials, while for low permeable materials it reduces to the conventional approach.

Environmental and geotechnical properties of lightweight aggregates made of reused solid wastes

This paper presents the environmental and geotechnical characterisation of new synthetic lightweight aggregates (SLAs) composed of reused biomass fly ash and waste plastics, namely high-density and low-density polyethylene (HDPE and LDPE), with a 50:50 fly ash-to-plastic ratio by weight. One-dimensional compressibility, creep properties, compaction features and stress-strain-strength behavior of SLAs were evaluated together with hydraulic conductivity and water absorbability. The fly ash–HDPE aggregate was found to be less compressible upon loading than the companion material made of fly ash and LDPE and similar to traditional natural lightweight expanded clay aggregate. The values of creep coefficient (C αε) were slightly higher than those expected for dense sands, but comparable, or even lower, than those measured for other recycled materials. Peak friction angle (ϕ′) and cohesion intercept (c′), determined by triaxial compression tests, were in the ranges 42.3–46.3° and 1.3–8.6 kPa, respectively with the highest values concerning the fly ash–HDPE aggregate. The hydraulic conductivity (k) was around 3 × 10−4–4 × 10−4 m/s, highlighting favorable permeability properties of both aggregates. Leaching tests and thermal stability analyses proved the sustainability of both aggregates from an environmental point of view. The results obtained in the present study demonstrate the suitability of the investigated aggregates for many geotechnical applications.

Improving sustainability of road construction by partial replacement of natural aggregates in subbase layer with crushed brick and reclaimed asphalt pavement

Reducing dependent on naturally sourced materials is among the priority in improving the sustainability of road construction. The subbase layer which provides strength and stability across the road profile, comprised mainly of natural aggregates. This study aims to explore the feasibility of partial replacement of natural aggregates in subbase layer with 20% Crushed Brick (CB) and 20 to 50% Reclaimed Asphalt Pavement (RAP). California Bearing Ratio (CBR) test and Constant Head Permeability tests were carried out to determine the effect of this partial replacement on the geotechnical properties of the subbase layer. The results obtained denotes that the combination of 20% CB and 50% RAP is the optimum partial replacement of natural aggregates in subbase layer with CB and RAP. The use of CB further complements RAP in improving the stiffness and compressibility of the subbase layer while contributing significantly toward sustainability in road construction.

Hydraulic behaviour of sand-biochar mixtures in water and wastewater treatment applications

• Influence of biochar on hydraulic behaviour of sand-biochar systems were investigated. • Inclusion of dual porosity system provided more accurate prediction against experimental data. • By creating 3D models of biochar-sand system, the interparticle porosity and tortuosity were calculated. • Excluding intraparticle porosity improves the accuracy of hydraulic conductivity prediction calculations. Interest in using biochar in environmental engineering applications has substantially increased with strong evidence emerging for its applicability in water and wastewater treatment, the containment of hazardous gases, carbon dioxide sequestration and the filtration of microplastics. Understanding the hydraulic behaviour of sand-biochar mixtures is critical for designing biochar-based water and wastewater filter systems. We present an investigation on the impact of the biochar microstructure on the hydraulic conductivity of sand-biochar mixtures, focusing on where there are gaps in existing knowledge on how the biochar affects the hydraulic properties. A dual-porosity concept for sand-biochar mixtures is introduced and included in four existing constitutive models for the hydraulic conductivity of soils. We have experimentally investigated the hydraulic properties of sand-biochar mixtures for uniformly graded sand with three representative grain sizes, and one type of hardwood biochar in the UK market. Based on a series of constant-head permeability tests, the hydraulic conductivity of the mixtures with biochar content from 0 to 50% has been measured. We used randomly generated spherical 3D models representing the same particle distribution of sand biochar systems to characterise the biochar's intraparticle porosity and tortuosity. By employing the dual-porosity concept and effective porosity instead of the total porosity, the accuracy of the four models' predictions was considerably improved when compared with the experimental measurements. We show that by excluding biochar's intraparticle porosity, the hydraulic conductivity prediction accuracy can be significantly improved, thus providing a more accurate prediction of the hydraulic behaviour of the soil-biochar filters.

Effects of basalt fibres on strength and permeability of rice husk ash-treated expansive soils

The application of stabilised soil in agricultural construction works such as shallow foundation fills and subgrade material for farm roads is in demand due to the improved geotechnical properties. This study focused on improving the compressive capabilities and the permeability characteristics of rice husk ash (RHA)-treated clayey soils using basalt fibre. Basalt fibres are made from naturally occurring basalt rock, yet their use in soil stabilisation has not been realised due to limited research for its validation in ground stabilisation. Essential variables in the stabilised soil matrix included basalt fibre length (3 mm, 6 mm, and 12 mm), RHA percentages (5%, 10%, and 15%), and cement percentage (3%). In addition, the optimum moisture content of each admixture was determined by standard proctor compaction tests and reduced by 3% to prepare the specimens for unconfined compression strength test, constant head permeability test, and scanning electron microscope (SEM) test. It was observed that the unconfined compression strength of the RHA-basalt fibre stabilised clayey significantly increased when the specimens wet cure for 28 days. Similarly, adding fibres into the soil improved the permeability coefficient. The SEM test showed a porous morphology that increased permeability. Furthermore, through SEM, the randomly oriented basalt fibres’ portrayed the reinforcing phenomenon related to improved compressive strength and sufficient bearing capacity to support structures built upon this class of soils.

A Capillary Model for Predicting Saturated Hydraulic Conductivity of Ion-Adsorption Rare Earth Ore Based on Improved Kozeny–Carman Equation

During the in-situ leaching process of ion-adsorption rare earth ore, the seepage velocity of the leaching solution is one of the core problems in studying the leaching efficiency. The determination of the saturated hydraulic conductivity is of great significance to reveal the leaching process. The classical Kozeny–Carman (KC) equation is widely employed to predict the hydraulic conductivity of sandy soils. However, in the equation, the effect of tortuosity on the hydraulic conductivity is not considered, and the specific surface area is difficult to determine in practice. In this study, the capillary model for predicting the saturated hydraulic conductivity of ion-adsorption rare earth ore was established. First, we assumed that all the pores in the ore body are a series of parallel and tortuous capillaries with equal diameters. Based on the assumption and Hagen–Poiseuille’s law, the KC equation was improved by introducing the tortuosity. Second, the constant head permeability tests were carried out to derive the seepage velocity and hydraulic head loss under the steady seepage state. According to the experimental results, the diameter of the capillary was calculated with Darcy's formula. Then we obtained a linear-fit relationship between capillary diameter and porosity to express the specific surface area variation with porosity. Third, by validating with experimental data, when the pore shape coefficient is 0.4, the saturated hydraulic conductivity calculated by the capillary model is in good agreement with the tested value. The proposed model can be considered to have a satisfactory capability to predict the saturated hydraulic conductivity of ion-adsorption rare earth ore.

Predicting the permeability coefficient of polydispersed sand via coupled CFD–DEM simulations

Permeability is one of the most fundamental properties of soil, which governs many geotechnical engineering problems. However, among the published equations that predict the permeability coefficient k, the influence of a wide range of particle size distributions (PSDs) on k was not considered accurately. This research aims to quantify the influence of PSD on k and propose a prediction equation for k. Coupled computational fluid dynamics–discrete element method (CFD–DEM) simulations were conducted to reproduce the constant head permeability tests of different soil samples. The results show that among the various drag models implemented in the CFD–DEM, the Syamlal–O’Brien drag model leads to the highest accuracy in simulating sand permeability. The permeability coefficient is proportional to the square of the Sauter mean diameter of the polydispersed particle system. Therefore, the prediction equation for k considering the PSD of the particle system is proposed based on the particle gradation and the size characteristics Cu, Cc, and d10. The proposed equation is verified well by published experimental data. Additionally, the proposed equation can calculate the k of irregular calcareous sand by representing the effect of particle irregularity with the Kozeny–Carman (KC) constant.

Hydraulic and morphological characterization of clogged pervious concrete (PC)

In pervious concrete (PC), the permeability decreases as a consequence of the clogging phenomenon that have been widely studied in recent years; however, there is a gap in the knowledge of how this phenomenon affects the internal morphology (micro-scale studies) of the PC, mainly related to pores distribution. Therefore, an experimental program was defined to evaluate the permeability variation caused by the clogging, and the variation of the internal morphology of the PC using 3D microtomography (before and after analysis). For this, three sediments were used to clog the PC (Sand, Clay, and an S + C mixture), adapting the constant head permeability test. All the tests performed globally on the material (porosity, permeability, and clogging) were defined as a macroscale study, and as micro-scale studies the evaluation of internal morphology using 3D microtomography. The macro-scale results showed that the most damaging sediments for PC were the fine sediments (clay and S + C) that achieved permeability reductions of more than 90%. On the other hand, 3D microtomography was shown as a powerful tool in the study of the variation of the morphology of the clogged PC. Through this test, it was possible to identify the variation in porosity depending on the type of sediment, increased frequency of smaller pores (<1 mm) and their influence in permeability variation, their spatial distribution, and finally, the decrease in accessible porosity (connection throats) and this relation with permeability decrease, when fine sediments always being the most damaging.

Study on permeability characteristics of soil and marble dust soil composite as a eco-friendly building material

The major goal of this research is to compare the permeability characteristics of soil after adding marble dust (MD). Materials and Methods: To investigate the variations in permeabilities, a constant head permeability test is performed on two sets of soil samples (group 1: soil without MD, N = 17; group 2: soil with 5 % MD, N = 17). For sample size calculation, the pre-test power and confidence intervals were set at 80 % and 95 %, respectively. Result: The findings of a constant head permeability test reveal that when marble dust is mixed with soil, the permeability of the soil reduces. Because the value of p is 0.0001 (p0.05) for the permeability values observed, there is a significant difference (2 tailed) between two groups of soil. Conclusion: Even when the permeability decreases slightly, it still meets the design code permeability criteria. As a result, marble dust can be utilised as a novel additive material for sustainable construction.

Comparison of permeabilities of quarry dust soil composite for application as eco friendly backfills

The principal objective of this research is to compare permeability properties of soil after inclusion of quarry dust into it. Two categories of soils are subjected to Constant head permeability test to study the differences in their permeabilities (group 1: soil without RHA, N = 17; group 2: soil with 5 % RHA, N = 17). The pre-test power and confidence intervals were chosen as 80 % and 95 % respectively for sample size calculation. Test results show that the permeability of soil decreases as a result of inclusion of quarry dust. A significant difference (2 tailed) between two groups of soil exists as the value of p is 0.0001 (p < 0.05) for the permeability values obtained. The permeability of novel quarry dust soil composite meets the permeability requirements of the design codes. Hence quarry dust has the potential to be utilized as a novel material which can be added with sandy soils in place of costly good quality earth fills for sustainable construction of civil infrastructures.

Influence of Gradation of Coarse-Grained Soil on the Permeability Coefficient

A constant head permeability test of the coarse-grained soil of an earth-rockfill dam was carried out and the gradation of the tested soil was determined based on the continuous gradation equation. Based on the test results, an empirical formula of permeability coefficient considering the influence of gradation was established. The formula can be used to assess the influence of gradation on permeability coefficient with respect to the area under the gradation curve. The applicability of the formula was verified based on the results of the permeability test from other studies. It was found that the empirical formula of permeability coefficient based on gradation area was suitable for coarse-grained soil. This paper provides a new perspective for the study of permeation behavior of coarse-grained soil.

Predicting the permeability of consolidated silty clay via digital soil reconstruction

Numerical modelling of the pore structure of porous media is still one of the most powerful tools for predicting the soil’s permeability and transport properties for geoengineers. However, that approach relies heavily on both the availability and accuracy of microstructural information, which is often challenging to acquire. In this study, statistically equivalent 3D micropore structures of soil samples were reconstructed using a digital soil model, which generated the 3D microstructures using a probabilistic map derived from 2D cross-section images and parameter sets calibrated via a deep learning neural network. The reconstructed images of the 15 micropore structures generated for each of two soil samples with different consolidation pressures (no disturbance and 3200 kPa) indicated that the pores become homogeneous with the consolidation process. The tortuosity factor was found to have a linear correlation with voxel size for simulation. The permeability of each soil sample was computed using the ABAQUS CFD module, and the results of the simulation were comparable to those for the constant head permeability test.

An Improved Large-Scale Stress-Controlled Apparatus for Long-Term Seepage Study of Coarse-Grained Cohesive Soils.

Clay–gravel mixture has been widely used in high embankment dams and understanding its seepage characteristics is critical to dam safety. From the instrumental perspective, the realization of continuous pressurized water supply becomes a key technical challenge, significantly restricting the working conditions replicated in previous seepage apparatuses. To this end, a novel water provision system, relying on parallel-disposed sensor-based pressure devices, was introduced, so that the application of an existing large-scale stress-controlled apparatus can be expanded to long-term seepage tests regarding coarse-grained cohesive soils. Constant-head permeability tests were conducted on original-graded clay–gravel mixtures to investigate their hydraulic properties, incorporating the influence of stress relaxation. Test results show that with 35% gravel content, the clay–gravel mixture is suitable for dam construction as the core material. The stress relaxation holds a marginal effect on the hydraulic conductivity of soil. The functionality of this improved apparatus is verified, especially under long-term seepage conditions.

Shear Strength and Drainage Characteristics of Elastomeric Polyurethane Treated Coal-Fouled Ballast

The shear behavior and drainage characteristics of coal-fouled ballast when treated with elastomeric polyurethane are assessed by means of large-scale direct shear and permeability tests. The results from direct shear tests confirmed that the shear strength of both stabilized and unstabilized coal-fouled ballast was highly influenced by the extent of fouling (VCI: void contamination index). The performance index (PI) of elastomer-stabilized coal-fouled ballast (ESFB), determined as the fraction of shear strength of fouled ballast to the shear strength of fresh and unstabilized ballast, lies in the range of 1.23 to 0.84. Moreover, the performance of ESFB having VCI ≥30% was found to be either similar to or poorer than that of clean ballast without any treatment, thus indicating that the elastomer treatment may be provided only to ballast with VCI ≤30%. The results from constant head permeability tests indicate that the hydraulic conductivity of ballast ( k) is highly influenced by the presence of fouling materials but is only slightly reduced as a result of the elastomer stabilization. The k of ballast decreased from 43 to 0.18 mm/s as the VCI increased from 0 to 75%. For VCI ≥ 45% the k of ballast was found to be lower than that recommended for sub-ballast. On the other hand, the k of ballast reduced slightly from 43 to 37 mm/s because of the elastomer stabilization. Furthermore, an empirical relationship is established between k and e to determine the k of both stabilized and unstabilized fouled ballast.

Saturated hydraulic conductivity (Ks) of earth materials in a weathering profile over the Kuantan Basalt, Pahang, Malaysia

Three broad morphological zones can be differentiated at the weathering profile; the top, 3.80 m thick, pedological soil (zone I with sub-zones IA, IB and IC) comprising soft to stiff, brown clays and the bottom bedrock (zone III) being an outcrop of vesicular olivine basalt. The intermediate zone II (saprock) is 1.12 m thick and consists of brown, very stiff, sandy clayey silt with many lateritic concretions. Laboratory constant head permeability tests show the saturated hydraulic conductivity (Ks) to vary with depth; sub-zone IB having a conductivity of 0.007 cm/hr, and sub-zone IC (saprolite), and zone II (saprock), having conductivities of 0.147, and 0.447, cm/hr, respectively. The conductivity values show no correlation with physical properties of the earth materials, but increase with increasing sand, gravel, and silt, contents. The conductivity values also decrease with increasing clay and colloid contents. The low hydraulic conductivity of sub-zone IB will lead to surface runoff and ponding over natural ground surfaces during rainfall events, though over disturbed ground surfaces, infiltration is anticipated in view of exposed saprolite and saprock earth materials with relatively high conductivity

Saturated Hydraulic Conductivity (Ks) Of Earth Materials In The Weathering Profile Over A Porphyritic Biotite Granite At The Kuala Lumpur - Karak Highway In Peninsular Malaysia

Three broad zones can be differentiated within the weathering profile over porphyritic biotite granite at Km 31 of the Kuala Lumpur - Karak Highway. The top Zone I (pedological soil) is 12 m thick and comprises A, B and C soil horizons; the C horizon (saprolite) being a clayey sand with indistinct relict bedrock textures. The intermediate Zone II (saprock) is some 30 m thick and consists of silty sands that indistinctly to distinctly preserve the minerals, textures and structures of the original granite. Zone II can be differentiated into four sub-zones; the upper II A and II B sub-zones marked by an absence of core boulders, whilst the lower II C and II D sub-zones have some to many core-boulders. The bottom Zone III (bedrock), whose upper surface is marked by an unconfined groundwater table, is a continuous granite outcrop with effects of weathering along and between discontinuity planes. Constant head permeability tests show saturated hydraulic conductivity (Ks) to vary with depth and texture; clayey sand from saprolite having a conductivity of 0.2420 cm/hr and silty sand from sub-zone II B, a conductivity of 0.7464 cm/hr. Silty sands from sub-zone II D have saturated hydraulic conductivity values of 1.5313, and 1.9585, cm/hr, whilst a silty sand from sub-zone II C has a conductivity of 4.1131 cm/hr due to it being collected at a relict pegmatite pod. Regression analyses show variable trends with low to moderate correlation coefficients (R2 &lt;0.600) for hydraulic conductivity versus index properties as clay and sand contents, but large correlation coefficients (R2 &gt;0.820) for hydraulic conductivity versus physical properties as dry unit weight and void ratio.