Soil-water Characteristic Curve Research Articles

Macroscopic Mechanical Properties and Microstructure Characteristics of Solid Waste Base Capillary Retarded Field Covering Material

In the practical operation of traditional landfills, compaction clay often experiences cracking, while the HDPE geomembrane may tear and bulge, resulting in a compromised performance of the landfill covering system. To address this issue, a capillary retarding covering material for landfill sites is proposed by utilizing municipal sludge and construction waste particles as substrates and incorporating a small quantity of calcium bentonite. The mechanical characteristics of the covering material were investigated using a standard consolidation test and a triaxial compression test. A permeability test and a soil water characteristic curve (SWCC) test were conducted to examine the permeability and capillary retarding effect of the covering material. Microscopic tests including SEM scanning, laser particle size analysis, and T2 NMR analysis were performed to investigate the connection mode, particle size composition, and pore structure characteristics of the covered particles. Based on the aforementioned research, the following conclusions can be drawn: The cohesion of the covering material ranged from 50 to 150 kPa, while the internal friction angle ranged from 24.23° to 31°. The cohesion was directly proportional to the content of construction waste, whereas the internal friction angle was inversely proportional to calcium bentonite content. The permeability coefficient ranged from 5.04 × 10−6 cm/s to 7.34 × 10−5 cm/s, indicating a certain level of impermeability. Both the sludge and the calcium bentonite contents jointly influenced the final permeability coefficient in a negative correlation manner, with a notable hydraulic hysteresis phenomenon observed. A higher content of construction waste leads to a more pronounced supporting force exerted by the formed skeleton structures within a load pressure range between 0 and 1600 kPa. When considering a mass ratio of municipal sludge: construction waste: calcium bentonite as 30:60:7, respectively, only a decrease in the pore ratio by approximately 13.20% was observed. This study provides valuable data support for designing and applying capillary retarding cover barrier systems in landfills.

A new mathematical model for the estimation of shear modulus for unsaturated compacted soils

Small-strain shear modulus ( G) is an essential parameter for many geotechnical analyses. Most of shallow foundations are constructed in an unsaturated soil and the shear modulus of the unsaturated soil fluctuates because of the precipitation, evaporation, and rising of ground water table. In this paper, a new mathematical model is proposed for the estimation of the shear modulus function, Gunsat, which defines the relationship between small-strain modulus of unsaturated soil and matric suction. In the proposed model, the soil-water characteristic curve in the form of the degree of saturation is used as the input information. There are additional two parameters named n and C, which can be calibrated with the experimental data, are adopted in the proposed model. The estimated results show good agreement with the experimental data from literature. The proposed method can be used to track the tendency of Gunsat and minimize the data points from the laboratory tests.

Combined influence of water-absorbing polymer and vegetation on soil water characteristic curve under field condition

Combined influence of water-absorbing polymer and vegetation on soil water characteristic curve under field condition

Reliability of Soil Water Characteristics Curve under Different Normal Stresses for Unsaturated Sand

The soil water characteristics curve (SWCC) demonstrates a link between soil moisture content and suction. The SWCC is almost treated as an index parameter in unsaturated soil. The soil permeability and shear strength can be linked to SWCC. SWCC is established using filter paper for the wetting path. This paper compares SWCC for both cases stress-dependent and no stress (reference) in the wetting path. The samples of soil are brought from Al-Najaf City with a gypsum content of 29%, Iraq. The stress-SWCC is studied using a modified Oedometer cell with controlled water and air entrance to apply a specific matric suction. While the reference SWCC is estimated using the filter paper method. Matric suction is conducted at a range of pressures from 90 kPa to 0 kPa. The tests use three net normal stresses of 100, 200, and 400 kPa. The results show that there are decreasing values of the SWCC with increasing normal stresses. An interesting result is that this decrease is high and has zero matric suction. The water entry value (WEV) with the most significant value of the water entry change is represented by the matric suction of 50 kPa.

Comparative study on suction obtained using the membrane filter method from triaxial apparatus and pressure plate apparatus

To investigate the stability of the earth embankments and slope failures during natural disasters, it is necessary to consider that soil is naturally unsaturated. Hence, it is essential to understand the variations of pore air pressure and pore water pressure, in terms of suction. The relationship between soil suction and soil moisture content is generally attained by soil water characteristic curve (SWCC), which is critically important in characterizing the mechanical behaviour of unsaturated soils. The SWCC is obtained from pressure plate apparatus by imposing the suction continuously by draining water from the saturated specimen and/or supplying water to unsaturated soil, which differs from the actual soil compaction process at the site. Therefore, the current study employs a methodology of suction measurement directly at a certain degree of compaction and degree of saturation using the membrane filter method in the triaxial apparatus, to meet the realistic conditions in the field. A comparative study has been done using SWCC with the imposed suction and the measured suction (Natural suction) at each compacted state. The results from both the methods exhibited an increase in the suction and air entry value with the increase in the degree of compaction, proving that an increasingly positive effect of suction contributed while increasing the density. Whereas the suction measured immediately after the compaction (Natural suction) in triaxial apparatus is more consistent with the suction imposed in the wetting process of SWCC. Further deep understanding of the microstructure behaviour of each compacted state and the SWCC is necessary.

Study on the Effect of Soil Type and Salinity on Water–Soil Characteristic Curves of Saline Soils Based on the Vapor Balance Technique

The soil–water characteristic curve (SWCC) describes the relationship between water content and soil suction, which is an important tool for determining the engineering properties of unsaturated soil. By measuring SWCC through vapor equilibrium technique, which could obtain soil suction up to 309 MPa, this paper explored the influences of the soil type and salt content on SWCC of saline soil. The experimental results illustrate that fine‐grained saline soil had a good water‐holding capacity, which had a higher air entry value and slower dehydrate rate. The study also brings out the observation that salt had negligible influence on soil suction and parameters effecting SWCC in low suction range; however, this effects was slight until it disappeared with the suction increasing.

Development of Pairwise Force Smoothed Particle Hydrodynamics for Capillary Rise Modelling

This research conducted a series of numerical experiments employing the Pair-Wise Force Smoothed Particle Hydrodynamics (PF-SPH) model to simulate the capillary action of water in the soil column. Initially, analytical relationships were formulated to connect various PF-SPH model parameters to surface tensions, static contact angles, and pore radius. Subsequently, the model was utilized to investigate PF-SPH equations and develop a modified function between numerical and physical parameters that incorporate the pore radius variable. The findings of this research reveal that capillary rise profiles in a steady state condition and Soil Water Characteristic Curve (SWCC) profiles closely align with empirical data obtained from published laboratory experiments. In conclusion, we observed that the PF-SPH model could simulate the capillary rise of water through the soil column by adjusting parameters such as surface tension, contact angle, and soil particle properties.

Studying Effect of Saturation Degree on the Bearing Capacity and Failure Mechanism of Sandy Soils

In this research, an experimental method was employed on samples of sandy soils from the Tartous and Palmyra regions. The objective was to investigate the impact of saturation degree on the bearing capacity of partially saturated sandy soil and the associated failure mechanism. To achieve the aim of the research, a series of tests were conducted to determine the basic physical properties of the soils. Additionally, a series of laboratory loading tests were conducted for a footing model atop sandy soil under various saturation degrees. Matric suction was measured, and soil water characteristic curves were determined using the filter paper technique. The results were subjected to analysis and discussion, and the experimental work demonstrated that saturation degree had a clear effect on the bearing capacity. It was observed that the bearing capacity of partially saturated soil is higher than that of fully saturated soil. The values of the increase were found to range between 2.3 and 9.7 times the bearing capacity in the fully saturated state. An empirical relationship was proposed to simulate the bearing capacity of partially saturated sandy soil based on the experimental results. Furthermore, the results indicated that the saturation degree exerted a discernible influence on the failure mechanism. In particular, a failure mode associated with dense soils was discerned in medium-dense soils at specific degrees of saturation for the tested soils.

Determination of soil–water characteristic curves by using a polymer tensiometer

Determination of soil–water characteristic curves by using a polymer tensiometer

Experimental Design of Measuring Soil-Water Characteristic Curve of Unsaturated Soil Using Bayesian Approach

Experimental Design of Measuring Soil-Water Characteristic Curve of Unsaturated Soil Using Bayesian Approach

Analytical and Finite-Element-Method-Based Analyses of Pile Shaft Capacity Subjected to Rainfall Infiltration

The presence of unsaturated soil is critical in geotechnical engineering since the matric suction may aid in accommodating the pile shaft capacity. The design of piles can be optimized by incorporating unsaturated soil mechanics principles. Hence, the amount of waste materials can be reduced, the duration of pile installation can be expedited, and the amount of energy used for casting the pile can be optimized, resulting in more sustainable design and construction of piles. Conventional α, β, and λ methods and modified α, β, and λ methods are the common models that are used for calculating the shaft capacity by incorporating soil–water characteristic curves (SWCCs). However, in our opinion, we feel that the investigation of the influence of seepage infiltration due to rainfall on the shaft capacity of piles, calculated using both analytical means and numerical analysis, has been dealt with inadequately in past studies. The objective of this study is to investigate changes in the shaft pile capacity according to suction changes due to rainwater infiltration for the greater reliability of the pile design, using both analytical and numerical studies with the finite element method (FEM). Sand and kaolin, which are typical components of coarse-grained and fine-grained soil, are used in this study. The laboratory results were incorporated into PLAXIS 3D (Version 22), and a coupled analysis was carried out, utilizing the meteorological conditions in Astana. The results showed that the decreases in matric suction in sand and kaolin are similar after their subjection to rainfall, yet sand produces a higher shaft capacity compared to kaolin. The modified β method offers a higher shaft capacity compared to the other methods due to the effective stress factors being taken into account. The modified α and λ methods are recommended for short piles because they are more sustainable, whilst the modified β method is preferable for long piles. Overall, unsaturated soil conditions should be applied to optimize the foundation design since they generate a higher shaft capacity.

General Properties of Commingled Materials for Mix Designs

Tailings volumes continue to collectively increase worldwide, leading to larger dams and tailings management facilities. With numerous high-profile dam failures in the past decade, the risks of these management practices are also growing. A potential shift to waste management practices at mineral mines is to commingle waste rock and dewatered tailings. This blended material should have superior physical strength properties provided by the waste rock together with improved chemical stability characteristics associated with the low permeability of the tailings. Ideally, commingled tailings and waste rock can be used to construct various mined earth landforms that are both physically and chemically stable, which will enhance operational performance and ultimately provide for the sustainable decommissioning and closure of the mining facility. To study these materials, the University of Alberta Geotechnical Centre is working with global industry partners to test commingled materials from several mine sites with varying ore and host rock types and climate regimes. The first stage of this study is described here and is focused on the optimum density, saturated hydraulic conductivity, and soil–water characteristic curves of various blend ratios, performed at laboratory scale.

Prediction of Soil–Water Characteristic Curves in Bimodal Tropical Soils Using Artificial Neural Networks

Prediction of Soil–Water Characteristic Curves in Bimodal Tropical Soils Using Artificial Neural Networks

Hydraulic characteristics and incubation methods for enhancing durability of Fungi- Mycelium treated silica sand using Rhizopus oligosporus and Rhizopus oryzae combination

Nowadays, the application of Fungi as a bio-mediated soil improvement technique is developing. The hydraulic properties of Rhizopus Fungi-Mycelium Treated Soil are unknown, and the treated sample tends to have low durability. This article presents experimental results on the hydraulic conductivity and shear strength of Fungi-mycelium-treated silica sand. The fungi used in the experiments are a combination of Rhizopus oligosporus and Rhizopus oryzae, which are popular for making Tempeh, a local soybean cuisine from Indonesia. The samples were prepared by mixing the sand with Tempeh inoculum at various treatments and Tempe inoculum and rice flour dosages for enhancing the durability of the treated soil. The results showed that the saturated permeability of the treated soil could be reduced by about 10 times compared to the untreated soil. In addition, the Soil-Water Characteristic Curve of the treated soil also developed. The effect of the fungi appears to fill the void of soil and hence increases the Air Entry Value and residual suction of soil. The curing method outside the mold (O-method) with 10% Tempeh inoculum, and 5% Tempeh inoculum with 5% rice flour is proven can extend the durability of the treated sample, the undrained compressive strength is about 40 kPa on day 14. Scanning electron microscope was performed on the samples, which lasted for 4 months. The mycelium and hyphae are still clearly seen covering all sand particles with different percentages of Tempeh inoculum and rice flour. When the mycelium covered all the sand particles and filled the pores, the water flow was partially blocked. It might be attributed to the strong hydrophobicity of the fungi, which could prevent water from penetrating the soil.

Effects of microplastic contamination on the hydraulic, water retention, and desiccation crack properties of a natural clay exposed to leachate

Microplastic (MP) can significantly affect soil behaviour and the ecosystem. This paper presents an experimental study to investigate the effects of MP contamination and leachate exposure on the desiccation cracks, hydraulic conductivity, and water retention properties of the natural black clay. The leachate was from a landfill in Australia. The black clay was incorporated with up to 2.0% MPs by weight (w/w) with diverse dimensions and mixed with water/leachate. The measured properties include saturated hydraulic conductivity (ksat), soil-water characteristic curves, moisture evaporation rates, and crack intensity factors. The results suggest that the inclusion of MPs significantly increases ksat, and this increase is more obvious for soils with larger dimensions and contents of MPs, e.g., ksat of the black clay with 2.0% of 500 μm MP increases significantly by 206% (p < 0.05). The black clay exposed to leachate exhibits a slight increase in ksat due to the low viscosity of leachate. The existence of MPs decreases the residual moisture contents and air-entry pressures, and so does the water retention capacity (v/v %) of the black clay. The exposure to leachate increases the air-entry pressures by 6.0%–15.8% of the clay. The evaporation rates increase with the dimensions and concentrations of MPs. The highest evaporation rate (0.96 g/h) can be observed in samples exposed to 2.0% 500 μm MP with water addition. For all samples, the crack intensity factors increase when MP content is between 0.2% and 1.0% and decreases slightly after that. After being exposed to leachate, the evaporation rates and crack intensity factors of the black clay are decreased by 2.4%–12.6% and 3.6%–13.7%, respectively.

Effect of the Mid-Layer on the Diversion Length and Drainage Performance of a Three-Layer Cover with Capillary Barrier

The capillary barrier is a type of soil cover system commonly used in various geotechnical applications, such as limiting infiltration for slopes or landfills or providing cover for solid waste. It serves to prevent the movement of water through the soil layers by utilizing contrasting particle sizes. This paper focuses on investigating the effect of the granular layer on the performance of a three-layer cover with a capillary barrier, integrating the granular layer within clayey sand. The investigation involved one-dimensional infiltration tests utilizing four uniform granular soils with varying grain sizes. These tests were instrumental in calibrating soil water characteristic curves and hydraulic conductivity curves via back analysis. Subsequently, numerical analyses were conducted using a 15 m long model for each of the four distinct cover types. The results indicated that the fine gravel significantly improved the barrier performance beyond one-dimensional tests, owing to its high permeability and the influence of the slope. After the capillary barrier failure, the intermediate layers transitioned into efficient drainage layers, particularly in the gravel layer with the highest lateral drainage capacity. Clayey sand at the bottom delayed percolation, thereby supporting the conversion of the intermediate layer into an effective drainage component. Overall, the multi-layer system showed superior percolation performance compared to the clayey sand cover lacking a granular layer.

Determining the Bimodal Soil–Water Characteristic Curve of Fine-Grained Subgrade Soil Derived from the Compaction Condition by Incorporating Pore Size Distribution

The soil–water characteristic curve (SWCC) is a key constitutive relationship for unsaturated soil which can be unimodal or bimodal. For the fine-grained compacted subgrade soil with a bimodal pattern, the determination of SWCC is complicated and needs a wide-range suction measurement. In this paper, the bimodal SWCC of a subgrade soil derived from the compaction condition was measured and determined by incorporating pore size distribution. For this purpose, a series of laboratory tests were conducted, including the pressure plate method, filter paper method, and vapor equilibrium method, which were used to measure SWCC at the low, medium, and high suction range, respectively. The pore size distribution (PSD) data were obtained by mercury intrusion porosimetry (MIP) tests and used to predict SWCC. Based on the analysis of hydraulic paths and SWCC-PSD correlations, the SWCC of the subgrade soil should be determined to follow the actual hydraulic path. SWCC within a low suction range can be filled by PSD-based data to improve the fitting accuracy. Then, a graphical method is applied to predict the bimodal SWCC by combining the filter paper method, vapor equilibrium method, and PSD-based data. The prediction curves fit well with the test data for all selected compaction conditions. Furthermore, the prediction method can still provide good prediction performance in the absence of high suction section data, which is beneficial for the application of bimodal SWCC.

High-suction polymer sensor for measurement of soil suction under freezing and thawing conditions

Soil-water characteristic curves (SWCC) are one of the most essential elements of unsaturated soil properties, yet the instruments employed for acquiring them have distinct limitations, for example, the tests are time-consuming, tedious and costly. High-suction polymer sensor (HSPS) with modified polyacrylamide (PAM) polymer is an alternative of measuring soil suction that relies on osmosis pressure rather than capillary pressure alone. The sample examined originated in Astana and was defined as clayey sand (SC). The ambient temperature of the Astana soil (sample 1) was used to assess soil suction using HSPS, which was verified by typical unsaturated equipment such as the Tempe Cell and dew-point potentiometer (WP4C). Once confirmed and SWCC was formed, the HSPS was utilized to detect soil suction during freeze-thaw cycles to simulate the climate in Astana. Based on the durability test, with the anticipated outcome lasting up to a year, PAM can resist the pressure for >200 days. Additionally, the modified PAM generated a stable response compared to the conventional PAM. The results from laboratory testing indicated that sample 2 has a greater average suction during freezing, while sample 3 has a higher average suction during thawing. In general, freezing cycles should produce more suction than thawing; yet, in sample 3, the water was still in supercooling stage, resulting in freezing having a lower suction average than thawing.

Hysteresis in Soil, Its Causes and Influences

Soil hysteresis is a natural phenomenon that occurs in soil water retention curve (SWRC) and soil water characteristic curve (SWCC), the mismatch of the drying (drainage or desorption) and wetting (sorption or adsorption) curves in each curve is called hysteresis in soil, i.e., At any potential (Ψ), there is a discrepancy between the soil water content (Θ or ű) in the curve of desorption and adsorption, this indicates that the amounts of water collected during the desorption cycle are not the same as the amount of water for adsorption the soil at the same applied pressure (suction Ψ). So, this relationship between soil water content (Θ or ű) versus soil water potential (Ψ) is non-unique. The difference is caused by a number of mechanisms, including: Contact Angle (θ), Adsorption, Bubble-form, Matric potential, Ink-Bottle Effect, Entrapped Air, Wetting and Drying History and Pore Size... etc. The explanations concern both (water and soil). Soil hysteresis has a degree, that varies depending on the type of clay minerals and pore size... etc. In this review paper, what are the causes of soil hysteresis, the hysteresis degree, and what does it influence? will be discussed.

Suction Variation of Natural and Treated Unsaturated Gypseous Soils During Wetting

Abstract The current work is directed to study the variation of suction with time and soil water characteristics curve (SWCC) for natural and treated gypseous soil treated with two types of additive (lime and silica fume) compacted at different initial degrees of saturation S0 = 20 and 50 %. Soil subjected to wetting in an upward direction. Three types of gypsum soils were experimented with different gypsum content 15, 35, and 60 % taken from various sites in Salah Al-dean government, Iraq. The main results show that the air-entry value, residual values, and the time required for the entire saturation stage increases with increasing gypsum content and treatment with lime and silica fume and they for soil treated with silica fume are greater than for soil treated with lime. The rate of flow for soil treated with silica fume is less than that of soil treated with lime. The treated soil is more effective in increasing the time required for the entire saturation stage and decreasing the rate of flow when compacted at an effective degree of saturation S0 = 50 %.