Suction Measurements Research Articles

Real-time inference of compacted soil properties using deflection tests: An AI-driven solution informed by unsaturated soil mechanics principles

This paper presents a novel Artificial Intelligence (AI)-driven tool designed to convert deflection test results into crucial soil parameters essential for quality assurance in compaction projects. The accurate determination of these parameters, such as density and void ratio, is imperative for ensuring the structural integrity of infrastructures constructed on such soils. Moreover, it facilitates the utilization of modern non-destructive equipment in compaction endeavors. The determination of these parameters is notably challenging in unsaturated soils owing to the intricate interplay among factors such as suction, moisture content, void ratio, and resulting deflection.This paper presents a pioneering tool to address these challenges. By integrating unsaturated soil mechanics with advanced AI techniques, particularly reinforcement learning, the tool leverages a diverse array of inputs, including in-situ data, experimental observations, and physics-based modeling. This integration enables dynamic adaptation to changing field conditions and ensuring the tool’s real-time adaptability and predictive accuracy.Field trials validated the tool’s efficacy in predicting soil properties accurately without direct measurements of moisture content or suction, variables often unmeasured in practical soil compaction projects. This unique capability underscores significant advancements in real-time assessment of unsaturated soils, illustrating the transformative potential of AI in geotechnical engineering and unsaturated soil mechanics.

Exploring an eco-friendly approach to improve soil tensile behavior and cracking resistance

Soil tensile strength is a critical parameter governing the initiation and propagation of tensile cracking. This study proposes an eco-friendly approach to improve the tensile behavior and crack resistance of clayey soils. To validate the feasibility and efficacy of the proposed approach, direct tensile tests were employed to determine the tensile strength of the compacted soil with different W-OH treatment concentrations and water contents. Desiccation tests were also performed to evaluate the effectiveness of W-OH treatment in enhancing soil tensile cracking resistance. During this period, the effects of W-OH treatment concentration and water content on tensile properties, soil suction and microstructure were investigated. The tensile tests reveal that W-OH treatment has a significant impact on the tensile strength and failure mode of the soil, which not only effectively enhances the tensile strength and failure displacement, but also changes the brittle failure behavior into a more ductile quasi-brittle failure behavior. The suction measurements and mercury intrusion porosimetry (MIP) tests show that W-OH treatment can slightly reduce soil suction by affecting skeleton structure and increasing macropores. Combined with the microstructural analysis, it becomes evident that the significant improvement in soil tensile behavior through W-OH treatment is mainly attributed to the W-OH gel's ability to provide additional binding force for bridging and encapsulating the soil particles. Moreover, desiccation tests demonstrate that W-OH treatment can significantly reduce or even inhibit the formation of soil tensile cracking. With the increase of W-OH treatment concentration, the surface crack ratio and total crack length are significantly reduced. This study enhances a fundamental understanding of eco-polymer impacts on soil mechanical properties and provides valuable insight into their potential application for improving soil crack resistance.

Soil water potential measurement using fiber-optic sensing technique

Accurate measurement of soil water potential or suction is crucial for hydrology and geotechnical engineering. Inspired by recent advances in fiber-optic sensing techniques, we develop an innovative geophysical method for measuring the soil suction by using fiber Bragg grating (FBG), named FBG-suction method. In this study, working principles and theoretical background associated with the FBG-suction method are discussed. For verification purposes, a series of laboratory-scale tests including calibration, suction measurement, and evaporation monitoring are performed on two clayey soils of low to high plasticity under different degrees of saturation. The calibration and measurement results demonstrate the efficacy and accuracy of the developed method for measuring a wide range of soil suction. The curves of soil saturation with suction obtained by WP4C and FBG-suction method are comparable and reflect the difference in the water retention capacity of the tested soils. Additionally, the evaporation monitoring results show that the FBG-suction method can measure the low suction during the drying process and accurately obtain the high suction above the measuring range of the PST-55 psychrometer. The findings affirm the scientific viability of the fiber-optic sensing technique for acquiring the spatial distribution of water potential or suction in unsaturated soils and provide a novel perspective for future investigations into the spatiotemporal evolution characteristics of in-situ unsaturated soil under climate change. As interdisciplinary collaborations continue to advance, it becomes increasingly apparent that methods based on fiber-optic sensing have the potential to revolutionize traditional approaches to characterizing dynamic subsurface processes.

A framework for estimating the matric suction in unsaturated soils using multiple artificial intelligence techniques

AbstractImplementation of the state‐of‐the‐art understanding of the mechanics of unsaturated soils into geotechnical engineering practice is partly limited due to the lack of quick, reliable, and economical techniques for matric suction measurement. Matric suction is one of the key stress state variables that significantly influences the hydro‐mechanical behavior of unsaturated soils. In this paper, to address this objective, two artificial intelligence (AI) models were developed for estimating matric suction in unsaturated soils based on the particle swarm optimization support vector regression (PSO‐SVR) and multivariate adaptive regression spline (MARS) algorithms. The results suggest that both these models can reasonably estimate matric suction. Compared to the MARS model, the PSO‐SVR model can achieve higher accuracy. Nonetheless, the MARS model facilitates the sensitivity analysis and the selection of essential inputs. A novel integrated framework is proposed and validated, leveraging the strengths, and alleviating the limitations of the PSO‐SVR and MARS algorithms for reliable and rapid estimation of matric suction in the range of 0–1500 kPa for low plastic soils (0 < Ip ≤ 7). Six inputs are required to use this model successfully; some can be measured using conventional laboratory tests, and others can be calculated from mass‐volume relationships.

Water Evaporation and Soil Suction Measurements of Different Soil Types in Jordan

Water Evaporation and Soil Suction Measurements of Different Soil Types in Jordan

Evolution of water content and suction of Opalinus Clay from recovery at the drilling site to handling in the laboratory

Advanced geotechnical engineering applications, such as shale gas extraction, CO2 geological sequestration, and geological radioactive waste storage, often involve various types of shales located at significant depths. Shales exhibit mechanical properties that are highly influenced by their hydration state and are exposed to substantial stress relief during extraction from considerable depths. This results in the development of elevated total suction (free energy per unit volume of pore water). While water content measurements are conventionally employed for characterizing these materials, ongoing discussions and uncertainties persist regarding the relevance and representativeness of laboratory suction measurements, particularly in light of potential influences stemming from core extraction and conditioning processes. A recent extensive borehole drilling campaign has provided a unique opportunity to offer scientific insights into specimens of Opalinus Clay shale, extracted from various locations and depths. These specimens were examined in their freshly extracted on-site condition and their freshly opened condition in the laboratory. Notably, it has been observed that suction and water content measurements acquired on-site immediately after core extraction differ from those obtained in the laboratory. The evolution of suction and water content from the field to the laboratory is closely linked to the main drying water retention behavior of the geomaterial.

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.

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.

Laboratory investigation of osmotic tensiometers filled with cross-linked polyacrylamide

Soil suction measurement is required for the analysis of slope stability and soil-structure interactions related to unsaturated soils below transportation infrastructures. Osmotic tensiometers (OT) can measure soil suction higher than 1000 kPa but suffer from the pressure decay problem. The OT filled with cross-linked polyacrylamide can maintain a stable pressure for a long time but the research on this type of OT is quite limited. In this study, the behaviors of OTs filled with synthesized non-ionic cross-linked polyacrylamide were investigated experimentally and explained in accordance with Flory-Huggins polymer theories. A generalized calibration equation was proposed to reduce the pressure fluctuation of OT caused by temperature. The pressure variations of two OTs were observed for more than 100 days and several cycles of drying tests were conducted. The results show that the pressure of the OT recovered after it was dried in the air for tens of minutes. In contrast, a slight pressure decay appeared when the OT was dried in the air for several days. However, as more cycles of drying tests were conducted, the pressure decay caused by the drying tests gradually became negligible. The relationship between the pressure of the OT at the end of observation and the volume fraction of the polyacrylamide inside the chamber of the OT was established by considering the confinement effect on the polyacrylamide hydrogel inside the OT. Finally, it is proved that salt solutions will not affect the pressure variation of OT filled with cross-linked polyacrylamide so the OT measures the matric suction of the soil.

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.

Reliability of Chilled-Mirror Hygrometer (WP4C) for Soil Total Suction Measurement

Reliability of Chilled-Mirror Hygrometer (WP4C) for Soil Total Suction Measurement

Soil total suction sensing using fiber-optic technology

Measurement of the soil water suction is important for investigating geotechnical problems and mitigating associated risks; however, conventional high-range suction measurement techniques have some limitations for accurate, long-term, and quasi-distributed suction measurement in the field. Fiber-optic humidity sensors provide a viable solution due to their unique properties. Here, we present a novel microfabricated fiber-optic suction sensor for measuring the suction of water in unsaturated soils. We evaluated the performance of the sensor on four bentonite–sand mixtures by comparing it with two laboratory suction measurement methods (chill-mirror hygrometer, salt solution vapor equilibrium) and a capacitive relative humidity sensor. We determined that this sensor has a measurement range of 5–300 MPa with a root mean square error of less than 3.5 MPa, and a response time of 2–9 min over the tested suction variation range (6.5–80.5 MPa). The results of the evaporation model test showed that three fiber-optic sensors installed at different depths of bentonite could effectively capture changes in temperature, relative humidity in soil pores, and total suction during evaporation. Together, these results demonstrate the great potential of the fiber-optic suction sensor for in-situ, long-term, and quasi-distributed suction monitoring.

Empirical Equations Expressing the Effects of Measured Suction on the Compaction Curve for Sandy Soils Varying Fines Content

To effectively apply various soil types for embankments, understanding their compaction characteristics is crucial. One crucial factor affecting compaction is suction, which plays a significant role as it is typically performed under unsaturated conditions. Suction varies with soil density, water content, and fines content. This study directly measures suction after soil compaction using the triaxial apparatus, unlike the Soil water characteristic curve (SWCC), assessing its impact on compaction characteristics. Immediate suction measurement after compaction provides apparent suction, resembling on-site conditions with open pore air pressure. Comparing SWCC with apparent suction at each compacted state reveals that suction and air entry value increase with initial density, positively impacting compaction. Notably, apparent suction aligns better with wetting process suction from the SWCC due to added water during specimen preparation. Empirical equations are derived to obtain suction contours across various density and saturation ranges, aiding in understanding suction variations on the compaction curve. Even slight variations in saturation causes noticeable changes in apparent suction during higher compaction efforts, affecting soil compaction characteristics. Therefore, the precise control of saturation control is needed to achieve desired properties of compacted soil, especially at higher compaction efforts and with various soil types. This understanding significantly impacts the mechanical behavior of unsaturated soils.

Hydro–Mechanical Behaviour of a Rainfall-Induced Landslide by Instrumental Monitoring: Landslide–Rainfall Threshold of the Western Black Sea Bartin Region of Türkiye

Bartin City is located in the Western Black Sea Region of Türkiye, where rainfall-induced landslides are more frequently observed. Although it is known that many landslides are induced by rainfall, there is limited knowledge regarding how rainfall triggers these landslides in the city. To clarify the triggering mechanisms of rainfall-induced landslides, a detailed field monitoring program was performed on a chosen area to represent landslides in Bartin. The instrumentation included the measurements of site suction, volumetric water content, groundwater level, and rainfall amount over a period of two years. Various stability analyses were performed regarding pore pressures after both transient flow infiltration analysis and site-measured suction values. The rainfall intensity–duration thresholds were obtained for both dry and wet periods as a result of the numerical analyses performed by means of parameters obtained from field monitoring. The results show that the wet period conditions create more critical conditions before failure compared to the dry period conditions, so landslides occur more easily in wet periods. According to the landslide–rainfall threshold relations, landslide-risk limits are reached if the rainfall intensity is over 10 mm/h for the dry periods and lasts between 0.85 h and 17 h depending on the saturated hydraulic conductivity of the soil. When the rainfall intensities are less than 10 mm/h, longer rainfall durations are needed for a landslide to occur. For the wet periods, landslide-risk situations are encountered if the rainfall intensity over 1 mm/h continues for 0.36 h–3.67 h, depending on the saturated hydraulic conductivities.

Development of the thermophysical parameter tester for measuring the soil matrix suction and optimization of the calibration function

The accurate measurement of the soil matrix suction is the prerequisite for understanding the mechanism of unsaturated soil. In this study, the in-situ thermophysical parameter tester was developed for measuring the soil matrix suction. The determination of the soil–water characteristic curve (SWCC) is a key step in the determination of the calibration function. Therefore, the simulation performances of three theoretical models and three machine learning models on SWCC were compared. It was concluded that the particle swarm optimization extreme learning machine (PSO-ELM) model outperforms the other models. The calibration function was obtained by combining the PSO-ELM model with the line heat source theory, and the coefficient of determination (R2) of the calibration model was greater than 0.95. The calibration function was then applied to a field test in order to verify the performance of the designed instrument and compare it with the tensiometer. Finally, the error propagation and synthesis theory based on random error was adopted, and it was deduced that the theoretical systematic error of the instrument is 9.85 %. Considering that the tensiometer also has a test error, it is believed that the relative measurement error of the two instruments is reasonable. Therefore, the instrument designed with the optimal calibration function can effectively measure the soil matrix suction. It also allows to determine the temperature, thermal conductivity, and thermal diffusion coefficient, providing an accurate measurement method for the soil matrix suction.

TOTAL AND MATRIC SUCTION MEASUREMENT OF UNSATURATED SOILS IN BAGHDAD REGION BY FILTER PAPER METHOD

Soil suction is one of the most important parameters describing the moisture condition of unsaturated soils. The measurement of soil suction is crucial for applying the theories of the engineering behavior of unsaturated soils.The filter paper method is one of the soil suction measurement techniques In this paper, five soil samples were collected from five sites within Baghdad city – al-Rasafa region. These soils have different properties and they were prepared at different degrees of saturation. For each sample, the total and matric suction were measured by the filter paper method at different degrees of saturation. Then correlations were made between the soil properties and the total and matric suction. It was concluded that the suction increases with decrease of the degree of saturation. The relationships between the total and matric suction and the filter paper water content are approximately linear and indicate decrease of suction with increase of the filter paper water content. The total and matric suction increase with the decrease of the soil shear strength.

Calibration of the root water uptake spatial distribution of a young Melaleuca styphelioides, an Australian-native plant, by means of a large-scale apparatus experiment

The stability of slopes is greatly influenced by seasonal variations in pore water pressures (pwp) induced by rainfall infiltration and evapotranspiration processes. Despite that, the prediction of the hydrological effects of long-stem planting is often simplified or neglected because it is challenging to address. Its computation requires a proper definition of the plant root water uptake spatial distribution, which depends, in turn, on geometry and spatial root density. A well-suited case study in this field of application has been provided by a soil-filled embankment, close to an important traffic artery in Newcastle (Australia), which experienced shallow instability. The implementation of long-stem planting has been suggested as a remediation intervention. Based on this, an experimental study focusing on the effects of plant roots on the distribution of pwp in the site soil has been performed by means of a large-scale laboratory experiment on a 2-year-old native plant. Suction measurements were recorded within the vegetated soil mass under controlled boundary conditions and used to calibrate two different root spatial distributions in a seepage simulation. One is based on a flexible RWU spatial distribution function, and the other, specific for the plant RWU pattern, is simpler in its formulation and requires the definition of a lower number of parameters. A comparison between their performances in reproducing pwp distribution suggests that the second one is a better alternative. The methodological approach adopted has proven to be suitable for representing the hydraulic behaviour of a vegetated hillslope, to be eventually implemented in a proper stability assessment problem.

Evaluating innovative direct and indirect soil suction and volumetric measurement techniques for the determination of soil water retention curves following drying and wetting paths

Soil Water Retention Curves (SWRC) are a main characterising component in constitutive models developed for describing unsaturated soils behaviour. Their determination requires establishing a combination of accurate soil matric suction measurements and volumetric measurements. While direct suction methods are always preferred, current methods, such as high capacity tensiometers, are limited to a measuring range of only 1.5 MPa. In this work, the novel Northumbria High Capacity Tensiometer, with an extended measuring range of up to 3.5 MPa, is used in a simplified continuous-drying setup, with proposed modifications to enhance the equalisation times and volumetric measurements. The results are then compared and validated with direct and indirect methods in both drying and wetting paths. At the same time, different volumetric measurement techniques were assessed in order to establish an understanding of Soil Shrinkage Curves (SSCs) that describe the moisture-voids relationship during drying and wetting and has the potential to be used for indirect determination of volumetric dimensions of soil specimens. Hysteresis was observed in the water retention behaviour but not in the volumetric behaviour. An established SSC model is proposed in this work and is fitted to experimental data in order to indirectly estimate volumetric measurements from the water content of small-scale specimens. The proposed novel approach standardises volumetric measurements determination, leading to uniform and complete-range SWRCs.

Laboratory Study on Entire Range Suction Measurement and Microstructure Change of Granite Residual Soil

The shear strength of unsaturated granite residual soil (GRS) will decline rapidly when moisture content increases, because of loss of matric suction in the soil. This can lead to slope instability and embankment collapse during rainfall. Determining the matric suction of GRS accurately at different conditions can improve the accuracy of stability analysis. Generally, matric suction can be characterized as the soil–water characteristic curve (SWCC), and it is closely related to soil microstructure. In this study, the entire range of matric suction was measured using a combination of pressure plate method, filter paper method, and vapor equilibrium method. Microstructure change was investigated based on mercury intrusion porosimeter tests, in which the pore size distribution (PSD) curves of GRS samples with different initial densities and moisture content were measured. The PSDs of samples before and after wetting were also measured and compared to investigate the influence of water intrusion. Test results indicate that the combination of measurement methods can cover the entire matric suction range. The microstructure of GRS with different initial conditions presents a clear bimodal PSD. At the same density, the increase in initial moisture content can increase intra-aggregate pores and decrease inter-aggregate pores. When initial density increases, only the volume of inter-aggregate pores decreases. Wetting can decrease inter-aggregate pores and increase intra-aggregate pores. Finally, the Li model is applied in SWCC fitting for tested samples, the result of which performs well with a high correlation coefficient (R2 > 0.95) and is recommended for GRS analysis.

Long-term decay of the water pressure in the osmotic tensiometer

Matric suction is an important state variable required for the assessment of unsaturated soil properties. Tensiometers are commonly used for direct matric suction measurement but have a limited measuring range up to 90 kPa due to the cavitation problem. Osmotic tensiometer (OT) can improve the measuring range of tensiometers by increasing the osmotic pressure of water to avoid the cavitation. However, the long-term water pressure decay that appeared in OTs caused a gradual decrease in their measuring range. In this study, crosslinked poly(acrylamide-co-acrylic acid) potassium salt (PAM-co-PAAK) was used for the preparation of OTs (five in total) to explore the mechanism of water pressure decay of OTs. The maximum water pressure in the OT versus the volume fraction of polymer filled in the OT was described based on the Flory-Huggins polymer theories and validated using WP4C dewpoint hygrometer. The long-term pressure decay of OT-1, OT-2, and OT-3 was observed for 130 d and constant pressures were found for OT-1 and OT-2, indicating that the pressure decay of OT was mainly caused by the stress relaxation of the polymer hydrogels, and standard linear solid (SLS) rheological model was appropriate to fit the decay data. For OT-1, OT-2 and OT-3, the theoretical osmotic pressure that was calculated based on the mass of retrieved polymer from OTs after 130-d pressure observation was higher than the actual osmotic pressure as observed, indicating that polymer leakage cannot explain the pressure decay of the OT. The ultraviolet–visible (UV–visible) spectrophotometry examined the change in polymer concentrations in the water containers of OT-4 and OT-5 and demonstrated that there was no increase in polymer leakage during the period of pressure decay of OT-4 and OT-5. As a result, the pressure decay of OT was not caused by polymer leakage. The results of this research suggested that the viscoelastic properties of polymers should be taken into consideration in further OT development. • Water pressure versus volume fraction of the polymer filled in OT was validated. • Pressure decay in OTs was mainly due to stress relaxation of polymer hydrogels. • No increase in polymer leakage during the period of pressure decay of OTs. • Development of new OTs should consider rheological properties of polymers.