Soil Behavior Research Articles

Photogrammetry-Based Method for Measuring Volume Changes of Soil Specimens During Critical Phases of Triaxial Testing

Triaxial tests has been routinely used to measure the stress–strain relationship for geomaterials. During triaxial testing, many sources of errors that cannot be completely avoided but are often ignored or approximated using empirical equations. This paper presents a systematic investigation of soil volume change, volume strain nonuniformity, and cross-sectional calculation along the specimen during triaxial testing using a photogrammetry-based method. Consolidated drained triaxial tests were performed in which two parallel measurements were taken: (1) relative volume using the conventional triaxial testing and (2) absolute volume using the photogrammetry-based method. The difference in the observed volume and void ratio measurements between the two methods highlighted the importance of absolute soil volume over the relative volume method. The results revealed the effect of soil volume change in the interpretation of triaxial testing findings. Various preparation steps and procedures during triaxial testing have influenced the initial measured volume and thus caused deviation of the subsequent associated measurements. This method would present a quality control approach for different aspects of triaxial testing to improve the test simulations to accurately measure the soil behavior. The proposed method is important for more refined simulations and identification of setup-induced errors. Additional applications of the current research would allow correct determination of the stress path followed during triaxial testing, the critical-state soil mechanics parameters, and the stress–strain relationship, including deformation and strength parameters.

Comprehensive analysis of cement-stabilised dredged marine soil: Evaluating physical, microstructural, and mechanical characteristics

This study evaluates the index, microstructural, and mechanical behaviour of cement-stabilised soft soil. The marine soil dredged from Hangzhou is taken for the study. Different percentages of ordinary Portland cement (OPC)by dry mass were added to the soils during reconstitution, i.e., 5, 10, 15, and 20%. The reconstituted samples were analysed in the laboratory to determine basic properties such as moisture content, void ratio, density, specific gravity, consistency limits, and particle size distribution. The microstructures of the reconstituted samples were also evaluated through scanning electron microscopy. Results inferred a significant impact on the physical properties of the soil. An increase in cement content increases the consistency limits. Additionally, the specific gravity, plasticity index, and density of the treated soil initially decreased but increased upon further addition of cement content. The microstructure of the soil transformed from a dispersed to a flocculated structure, with larger and denser particles. The change in microstructure was also evident in the particle size distribution, with an increase in cement content leading to larger size particles. Finally, the unconfined compression test conducted on the reconstituted soil indicates a substantial enhancement in strength with higher cement content and prolonged curing periods.

Evaluating the Compaction Behavior of Oil-contaminated Soils for Civil Engineering Applications

Evaluating the Compaction Behavior of Oil-contaminated Soils for Civil Engineering Applications

Equivalent state parameter dependency on gradation properties of medium sand-fines mixtures

Multiple studies confirm that determining the liquefaction resistance of sand-silt mixtures is more intricate compared to pure sand. Furthermore, it has been observed that the global void ratio fails to accurately predict the behavior of silty sand soils due to the fines particles, which can occupy voids between sand grains without significantly contributing to resisting external forces. To address this, a new parameter called equivalent void ratio (e*) has been proposed to better forecast the response of medium sand-fines mixtures. To investigate this further, a series of compression triaxial tests were conducted on mixtures comprising medium sand with low plastic fines. These mixtures were prepared in the laboratory with an initial relative density and subjected to varying confining pressures. The test results were utilized to assess the undrained shear strength of medium sand-silt mixtures based on the equivalent void ratio (e*) and to establish the equivalent granular steady-state line, which serves as a reference for calculating the equivalent state parameter (ψ*). Analysis of the obtained data suggests a correlation between the equivalent void ratio (e*) and the equivalent state parameter (ψ*) with the grading characteristics (such as D10, D50, Cu, D10R, D50R, and CUR) of the medium silty sand.

ОЦЕНКА ПОКАЗАТЕЛЕЙ РЕМОНТОПРИГОДНОСТИ АВТОМОБИЛЬНОЙ ДОРОГИ

The methods of managing the information model of the road at the operation stage are presented. A comprehensive methodology for checking transport and operational indicators is shown. It allows to predict the condition of the road surface, to determine the probability of deformations and destruction during the operation of the road. A software module is presented for assessing the maintainability of the road, taking into account all key transport and operational indicators. Based on this module, one can calculate the real overhaul service life for certain sections of the road. In the algorithms of the developed program, data transmission at various stages of the life cycle is provided, the stage of creating a general data environment, interaction with the IFC attributes is laid. This approach ensures the interoperability of the information model of the road and allows to evaluate current condition and planned measures to eliminate construction flaws or defects formed during operation, which ensures the extension of the road service life. Popular rheological models have been investigated for predicting residual deformations of road clothing based on the analysis of various models of the soil behavior of nonlinear soil mechanics. It is revealed that the most adequate model is a model that uses the theory of hereditary creep, which takes into account the calculation of non -rigid road clothing, which is exposed to short-term load from moving cars. Some aspects of the maintainability of the road facility affecting the environmental and economic indicators of the environment are given.

Numerical investigation of artificial ground freezing–thawing processes in tunnel construction

Artificial ground freezing is a frequently used method for temporary support of the soil in geotechnical interventions, such as tunneling. Besides the time required to form a supporting frozen soil structure during freezing, the prediction of temperature evolution during the thawing process and the final thawing time are also relevant, since settlements induced by thawing of the frozen soil can pose a risk to sensitive structures in urban tunneling. The freezing and thawing process of soils depends strongly on the unfrozen liquid content. The unfrozen liquid content during the freezing and thawing cycles is known to have a pronounced hysteresis response, whose effect on the temperature distribution and groundwater flow, especially at the structural level has not been extensively studied. In this work, we present a thermo-hydraulic finite element model for freezing soils and incorporate the hysteresis behavior of soil. We aim to investigate the suitability of the presented numerical model for tunnel construction on the one hand, and quantify the extent of the influence of the hysteresis response of the unfrozen liquid content at the structural level on the other. To this end, the model is first validated with the help of experimental data from a soil test subjected to a freezing–thawing cycle and subsequently used to analyze three problems of artificial ground freezing in tunnel construction during the freezing phase or freezing–thawing phases. The results show a good agreement with the experimental measurements. We show that the computational model is capable of providing accurate prognosis of the temperature profile as well as broader metrics such as the thickness and shape of the frozen body for tunneling applications under hydrostatic and seepage flow conditions. The hysteresis response is shown to have a significant influence on the coupled thermo-hydraulic process, with thawing times differing depending on whether hysteresis is considered. It is concluded, that the inclusion of the hysteresis response is crucial for obtaining an accurate representation of the freezing process.

A novel framework for deriving water retention behavior of multimodal unsaturated soils based on pore size distribution data

AbstractThe soil water retention curve (SWRC) strongly influences the hydro-mechanical properties of unsaturated soils. It plays a decisive role in geotechnical and geo-environmental applications in the vadose zone. This paper advances a novel framework to derive the water retention behavior of multimodal deformable soils based on the pore size distribution (PSD) measurements. The multiple effects of suction on the soil pore structure and total volume during SWRC tests are considered. The complete picture of soil microstructure is quantitatively described by the void ratio (for the pore volume) and a newly defined microstructural state parameter (for pore size distribution) from a probabilistic multimodal PSD model. Assuming a reversible microstructure evolution, a unique PSD surface for wetting and drying links the SWRC and PSD curves in the pore radius-suction-probability space. A closed-form water retention expression is obtained, facilitating the model's implementation in particle applications. The model is validated using the water retention data of four different soil types, showing a strong consistency between the measurement and the reproduced curve. The proposed method provides new insights into the pore structure evolution, the water retention behavior and the relationship between them for multimodal deformable soils.

The role of soil structure on the cracking and cadmium leaching behavior of biochar-amended fine-grained soils

Biochar has shown promising potential for soil remediation, yet its impact on heavy metals (HMs) immobilization often overlooks soil structure, which could influence soil cracking behavior and HMs transport. To address this gap, this study investigates the role of soil structure (dry density and aggregate size) on the cracking and cadmium (Cd) leaching behavior of biochar-amended fine-grained soils. A series of semi-dynamic leaching tests were conducted on samples with and without wetting-drying (W-D) cycles. Based on the proposed improved method for quantifying the effective diffusion coefficient (De) of Cd in unsaturated soils and microstructural analyses, we found that: (1) Higher dry density and larger aggregate generally resulted in smaller De by decreasing soil pore volume. (2) Biochar could connect isolated pores within large aggregates through its internal pores, yielding greater increases in De (294.8%–469.0%) compared to small aggregates (29.1%–77.4%) with 3% biochar. However, further increases in biochar dosage led to decreased De, primarily due to the dense pore structure. (3) Biochar effectively inhibited soil cracking, achieving the highest reduction of 36.8% in surface crack ratio. (4) After W-D cycles, samples exhibited higher De with increasing dry density, with aggravated cracking being the primary cause, suggesting preferential flow within the cracks, particularly those penetrating the soil. This study highlights the importance of careful consideration of soil structure and cracking potential before in situ field application of biochar as a remediation agent for HMs-contaminated fine-grained soils.

Landscape Drivers of Floods Genesis (Case Study: Mayo Mizao Peri-Urban Watershed in Far North Cameroon)

Landscape has significant effects on hydrological processes in a watershed. In the Sudano-Sahelian area, watersheds are subjected to a quick change in landscape patterns due to the human footprint, and the exact role of the actual landscape features in the modification of the hydrological process remains elusive. This study tends to assess the effects of landscape on the genesis of the runoff in the Mayo Mizao watershed. To achieve this goal, 62 infiltration tests were performed at different points and depths (5 cm and 20 cm) using the double-ring method and the Porchet method. The results show that the combination of many factors (soil type, land use, and farming practices) can guide the hydraulic conductivity behavior of soils. For example, at 5 cm depths, clayey-evolved soils, such as vertisols and halomorphic soils, inhibit infiltration, as opposed to non-evolved mineral soils, such as lithosols and clayey-sandy soils. However, at 20 cm depths, gray soils with halomorphic tendencies followed by vertisols have a low sensitivity to infiltration, as opposed to soils derived from loose materials and halomorphic soils. For a given soil type, rainfed crops are the primary land use that runs against infiltration. However, the effect of tillage varies according to the soil type. Finally, given the extent of vertisols and halomorphic soils in the Far North region of Cameroon in general, and in the Mayo Mizao watershed in particular, and regarding the increase in cultivated areas, a probable reduction in the infiltration capacity of soils in this region is to be expected in the medium term. The results of this study can be used as a basis for land-use planning and sustainable watershed management in semi-arid tropical zones.

Analysis of pile end bearing capacity in Holocene interlayered silty deposits based on CPT soil behavior type index

The existing correlations between pile and cone penetration test (CPT) results often lack versatility for silty geomaterials, as they were primarily developed for clays or sands. To establish meaningful correlations, it is essential to understand the geology of the environment under examination. The CPT and its derived parameters, including the Soil Behavior Type (SBT) index, have proven to provide reliable soil information, particularly in the field of pile foundation engineering. This paper presents the findings and interpretations from several pile load tests conducted alongside field cone penetration tests on a Holocene saline interlayered silty formation, a distinct condition encountered in practice. Various CPT-based pile design methods were employed to evaluate pile capacity based on CPT results. As observed, predictions for pile shaft resistance in this geological formation remained consistent across all methods, while notable variations emerged in estimating pile end bearing. This was inferred to be a result of limited research on pile end bearing capacity in the literature, leading to proposals of broad ranges for pile influence zone and toe coefficient values, as well as various CPT tip resistance averaging techniques across different methods. Consequently, to improve accuracy, modifications based on site-specific test data may be necessary. Drawing from the assessments, effective modifications involved considering the SBT index near the pile tip. Subsequently, the current study introduces a new region-specific adjustment to the widely recognized Enhanced Unicone method based on the SBT index, resulting in a more accurate estimate of pile end bearing in such interlayered silty contexts, with less scatter compared to other available approaches.

Unified approach for describing rheological behavior of soil and mineral substrates modified with polymers

Studies in the rheology of natural aqueous dispersions (soils and their mineral substrates) as well as the approaches to control rheological parameters of these systems are of the prime importance to progress in the modern agricultural technologies, geoengineering, construction, etc. To advance in these fundamental and applied directions both original processing of the experimental results and search for the promising modifying agents are required. In this paper, rheological behavior of a representative range of virgin and modified aqueous soils, quartz sand and clays was studied. Modification of the above aqueous dispersed systems with polyelectrolytes and their complexes provided variation of the basic viscoelastic parameters corresponding to the linear viscoelastic region (initial storage modulus G0′, initial loss modulus G0", and strain γ0) and to the transition to steady-state flow (storage modulus Gin′ and strain γin) within 1 – 2 orders of magnitude. For samples studied, correlations for these mechanical characteristics were found – with the growth in the values of G0′ and G0′′, the increase in the values of Gin′ and decrease in the values of γ0 and γin were observed. Based on these correlations the master curves for the strain dependences of storage and loss modulus as well as for loss tangent were constructed. The appearance of the master curves reflected the unified regularities of the rheological response of dispersed systems which were attributed to the general features of structural evolution caused by the mechanical loading. Procedure for prediction of the rheological behavior of aqueous soil samples based on the experimental measurement of only two experimental characteristics (initial values of storage and loss modulus G0′ and G0′′ respectively) was proposed. The validity of this approach was tested using independent experimental data. The original approach obtained can be used for express analysis of the rheology of natural aqueous dispersed materials.

Monitoring of early curing stage of cemented soil using polymer optical fiber sensors and microscopic observation

Deep cement mixing (DCM) piles are widely utilized for reinforcing soft clay foundations, particularly in coastal regions where soil stability is critical. Monitoring the quality and early-stage behavior of cemented soil is essential to ensure the effectiveness of DCM pile projects in meeting design requirements. Innovative methods for on-site monitoring are necessary to enhance the reliability and efficiency of these reinforcement techniques. In this study, a novel approach is proposed utilizing polymer optical fiber (POF) sensors based on physical optical sensing principles to monitor the initial hydration degree and overall quality of cemented soil during the early curing stage. The proposed method relies on the principle of physical optical sensing, where POF sensors are employed to measure changes in reflected light intensity (LI) and temperature in cemented soil. Two crucial variables, namely the initial water content and the amount of cement, are considered in analyzing their impact on the LI and temperature changes over time. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis are conducted on cemented soil samples with varying water-cement ratios to investigate their mechanical properties and microstructure evolution. The results of the UCS tests indicate that higher initial water content prolongs the initial hydration reaction time required for cemented soil with different cement contents. Analysis of LI curves reveals a rapidly rising trend as the hydration reaction progresses, particularly evident in samples with higher initial water content. SEM analysis further demonstrates that a stable POF LI corresponds to the completion of the hydration process, with hydrated gel formation resulting in a more compact microstructure and smaller voids. The findings highlight the significant influence of cement quantity and initial water content on the mechanical strength and microstructure of cemented soil. By analyzing changes in reflected LI and temperature, the proposed monitoring method provides valuable insights into the early-stage behavior and quality of cemented soil during the curing process. This innovative use of POF sensors for on-site monitoring offers a novel approach to evaluating cemented soil in DCM pile projects.

Assessing the risk of E. coli contamination from manure application in Chinese farmland by integrating machine learning and Phydrus

This study aims to present a comprehensive study on the risks associated with the residual presence and transport of Escherichia coli (E. coli) in soil following the application of livestock manure in Chinese farmlands by integrating machine learning algorithms with mechanism-based models (Phydrus). We initially review 28 published papers to gather data on E. coli's die-off and attachment characteristics in soil. Machine learning models, including deep learning and gradient boosting machine, are employed to predict key parameters such as the die-off rate of E. coli and first-order attachment coefficient in soil. Then, Phydrus was used to simulate E. coli transport and survival in 23692 subregions in China. The model considered regional differences in E. coli residual risk and transport, influenced by soil properties, soil depths, precipitation, seasonal variations, and regional disparities. The findings indicate higher residual risks in regions such as the Northeast China, Eastern Qinghai-Tibet Plateau, and pronounced transport risks in the fringe of the Sichuan Basin fringe, the Loess Plateau, the North China Plain, the Northeast Plain, the Shigatse Basin, and the Shangri-La region. The study also demonstrates a significant reduction in both residual and transport risks one month after manure application, highlighting the importance of timing manure application and implementing region-specific standards. This research contributes to the broader understanding of pathogen behavior in agricultural soils and offers practical guidelines for managing the risks associated with manure use. This study's comprehensive method offers a potentially valuable tool for evaluating microbial contaminants in agricultural soils across the globe.

Cyclic cumulative strain of coarse-grained soil under large cyclic stress amplitude

The deformation behavior of coarse-grained soil under large cyclic stresses, such as those induced by strong earthquakes, has received limited attention. This study aims to investigate the cyclic accumulation behaviors and hysteresis loops of coarse-grained soil during drained cyclic triaxial tests, spanning a range from small to large cyclic stresses. The cyclic triaxial tests were primarily conducted under anisotropic consolidation conditions, with an axial-to-radial stress ratio of 2.0, confining pressures ranging from 100 to 500 kPa, and cyclic stresses varying from 0.01 to 1.85 times the confining pressure. Additionally, cyclic triaxial tests under isotropic consolidation conditions and constant mean stress conditions were performed for comparison and validation. The test results reveal that the properties of the hysteresis loops exhibit significant nonlinear behavior as cyclic stress increases, particularly concerning their shape, symmetry, degree of closure, and initial tangent modulus of elasticity. The cumulative axial strain displays three stages: strain increases slightly and gently at small cyclic stress, increases rapidly and substantially at medium cyclic stress, and decreases at large cyclic stress. The delineation of these phases is largely governed by the behaviors observed during the first cycle. Moreover, the cumulative volumetric strain increases monotonically with the increase of cyclic stress, with a more rapid increase at large cyclic stress. This study provides valuable insights into the cyclic deformation and constitutive modeling of coarse-grained soil under significant cyclic stress.

The difficult task of teaching shear strength of soils

Shear strength is a classical topic in Soil Mechanics and generally there is little concern about the inconsistencies behind the theories used to predict its value. In fact the debate on this issue is rather limited as the geotechnical community considers this a well-established concept. This note intends to highlight the difficulties that arise when teaching that concept in an undergraduate Soil Mechanics course. Those difficulties are related to the drained/ undrained behavior of soils, but also to the fact that cohesion is a tricky parameter, with a misleading physical meaning, depending not only on the properties of the contacts between particles, but also on external conditions (i.e., saturation or unsaturation). All these aspects are not analyzed in detail in many textbooks, but they should be considered in a modern Soil Mechanics course.

Derivation of Contour Plots for the Characterization of the Behaviour of Sand under Undrained Loading

The soil response under the inherent cyclic loading conditions when dealing with offshore foundations can be considered by using contour plots. These plots are derived from several cyclic laboratory tests and characterize the general cyclic soil behaviour. In the design process with explicit numerical methods, such plots are needed in order to assess the soil behaviour under arbitrary loading conditions and hence estimate the cyclic foundation response. In the paper, excess pore pressure contour plots for a poorly graded medium sand are derived from numerous constant volume (CV) cyclic direct simple shear (DSS) tests and a new approach for parametrization of the plots is presented. Subsequently, the data are assessed regarding scaling for other sand soils, i.e., construction of contour plots with only a small number of test results by using the general trends observed.

Novel Insights in Soil Mechanics: Integrating Experimental Investigation with Machine Learning for Unconfined Compression Parameter Prediction of Expansive Soil

This paper presents a novel application of machine learning models to clarify the intricate behaviors of expansive soils, focusing on the impact of sand content, saturation level, and dry density. Departing from conventional methods, this research utilizes a data-centric approach, employing a suite of sophisticated machine learning models to predict soil properties with remarkable precision. The inclusion of a 30% sand mixture is identified as a critical threshold for optimizing soil strength and stiffness, a finding that underscores the transformative potential of sand amendment in soil engineering. In a significant advancement, the study benchmarks the predictive power of several models including extreme gradient boosting (XGBoost), gradient boosting regression (GBR), random forest regression (RFR), decision tree regression (DTR), support vector regression (SVR), symbolic regression (SR), and artificial neural networks (ANNs and proposed ANN-GMDH). Symbolic regression equations have been developed to predict the elasticity modulus and unconfined compressive strength of the investigated expansive soil. Despite the complex behaviors of expansive soil, the trained models allow for optimally predicting the values of unconfined compressive parameters. As a result, this paper provides for the first time a reliable and simply applicable approach for estimating the unconfined compressive parameters of expansive soils. The proposed ANN-GMDH model emerges as the pre-eminent model, demonstrating exceptional accuracy with the best metrics. These results not only highlight the ANN’s superior performance but also mark this study as a groundbreaking endeavor in the application of machine learning to soil behavior prediction, setting a new benchmark in the field.

Biocalcification of Sandy Gypseous Soil by Bacillus Pasteurii

Microbial-induced carbon precipitation (MICP) is one of the most recent treatment methods for soil stabilization. The present work employs this technique in improving the collapsing behavior of sandy gypseous soil with 35% gypsum content under one-dimensional loading to 100 kPa and leaching conditions. A bacterial strain, Bacillus pasteurii was used for this purpose. A set of collapse tests was performed inside a modified oedometer on specimens, prepared with 25% bacterial solution and 0, 0.25M, 0.5M, or 1M cementation solution molarities, cured to 7, 14, or 21 days. The results indicated that the bacterium was able to produce a considerable amount of calcium carbonate ranging from 3% to 15%. This carbonate was also observed by microscopic imaging of the specimens at the interparticle contacts and also on the surfaces of soil grains. Consequently, the soil gained additional bonding and the voids became smaller. Therefore, the soil became more resistant to water flow and leaching, where the treated specimen maintained nearly the same permeability with the progression of leaching, unlike the untreated specimen which showed a 7-fold increase over the same water flow condition. Over the examined load, the MICP treatment provided almost no change in the strains caused by external loading, unlike the wetting strains which exhibited a considerable reduction of 11% to 80%. The results of leaching strains appeared to be sensitive to the rate of flow and the cementation solution molarity

An effective stress-based DSC model for predicting hydromechanical shear behavior of unsaturated collapsible soils subjected to initial shear stress

Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.

A vector sum analysis method for stability evolution of expansive soil slope considering shear zone damage softening

Slope stability analysis is a classical mechanical problem in geotechnical engineering and engineering geology. It is of great significance to study the stability evolution of expansive soil slopes for engineering construction in expansive soil areas. Most of the existing studies evaluate the slope stability by analyzing the limit equilibrium state of the slope, and the analysis method for the stability evolution considering the damage softening of the shear zone is lacking. In this study, the large deformation shear mechanical behavior of expansive soil was investigated by ring shear test. The damage softening characteristic of expansive soil in the shear zone was analyzed, and a shear damage model reflecting the damage softening behavior of expansive soil was derived based on the damage theory. Finally, by skillfully combining the vector sum method and the shear damage model, an analysis method for the stability evolution of the expansive soil slope considering the shear zone damage softening was proposed. The results show that the shear zone subjected to large displacement shear deformation exhibits an obvious damage softening phenomenon. The damage variable equation based on the logistic function can be well used to describe the shear damage characteristics of expansive soil, and the proposed shear damage model is in good agreement with the ring shear test results. The vector sum method considering the damage softening behavior of the shear zone can be well applied to analyze the stability evolution characteristics of the expansive soil slope. The stability factor of the expansive soil slope decreases with the increase of shear displacement, showing an obvious progressive failure behavior.