Cohesion provided by pore ice is a critical component influencing the mechanical behavior of frozen soil, as it not only cements soil particles together but also shares the external loads with them. In view the crucial role of cohesion in developing an elastoplastic model for frozen soil, this paper employs triaxial tensile strength (TTS) to characterize cohesion and proposes a TTS degradation expression driven by plastic shear strain. By directly incorporating TTS into the yield function, a framework for a Non-Orthogonal Elastoplastic (NOEP) constitutive model that accounts for cohesion degradation in frozen soil is developed. Furthermore, a hardening parameter incorporating TTS is introduced and used in conjunction with the modified yield function to determine the magnitude of the plastic strain increment. The non-orthogonal plastic flow rule is used to determine the direction of the plastic strain increment based on the modified yield function. Ultimately, by combining the elastic strain increment determined by Hooke's rule, a NOEP constitutive model incorporating cohesion degradation for frozen soil is established. The validity and rationality of the proposed NOEP model in representing the stress-strain relationship of frozen soil are confirmed through comparisons with test results of frozen soil under the triaxial compression conditions. The proposed constitutive model provides a more comprehensive and precise representation of frozen soil's response to external loading, enhancing the understanding of its shear deformation behavior and providing a robust theoretical foundation for engineering design and construction in cold regions.

Characterising the mechanical properties of minor bodies is essential for understanding their origin and evolution. Past missions such as Hayabusa2 have landed on asteroids to sample and discover what these bodies are made of. However, there has been conflicting evidence and reports into the physical properties of the granular surface material of these bodies. With future missions such as Japan Aerospace eXploration Agency's Martian Moons eXploration mission landing on Phobos, the understanding and identification of these physical properties is crucial to maximising the scientific output from these missions. Penetrometry, the determination of the reaction force that an object experiences as it penetrates a surface, can help to understand the essential properties of regolith, such as grain size, porosity and cohesion. Results of penetrometry experiments are largely analysed based on empirical models, which presents us with a challenge if we want to apply them to understand granular materials on asteroid surfaces because gravity cannot be eliminated in the laboratory. Hence, it is essential to verify penetrometry as a method and validate penetrometry instrument designs in microgravity. For this purpose, we conducted a microgravity experiment onboard a parabolic flight campaign. Our experiment tested the use of penetrometry in asteroid-analogue environments by investigating samples with varying properties, such as grain size distribution and shape, and then compared to 1 g experiments to understand the role microgravity plays. The experiment provided a substantial database for future analysis. This paper will focus on the design of the experiment and the parabolic flight campaign in which the experiments were conducted. The design decisions and the variables adjusted during the experiment will be discussed, evaluating how these influenced the campaign and its outcomes. We will also provide a snapshot of preliminary results of the data captured during this experiment. For example, we show the effect of cohesion on penetrometer reaction force, with more cohesive materials providing larger reaction forces nearly of the same magnitude of their 1 g counterparts. We also show that penetrometer tip shapes provide different reaction forces and that flat tips provide the largest reaction force compared to the others. The influence of penetration velocity will be investigated further with the aid of theoretical models. Early indications from the results seen so far are promising for future analyses and will provide key information for the analysis of penetrometry data on future missions.

The demand for tunnels in densely populated urban areas is growing rapidly to address mobility challenges. Mechanized tunneling is widely adopted in urban environments due to its high productivity and the relatively small ground deformations it induces. However, urban tunneling is highly complex because of the typically shallow depths and interactions with aboveground structures. Therefore, accurately predicting ground deformations induced by mechanized tunneling at the design stage is crucial for assessing potential building damage. To investigate these deformations, a series of centrifuge tunnel tests have been conducted at academic institutions such as the Universities of Cambridge and Nottingham to study the behavior of shallow mechanized tunnels in cohesionless soil. These tests serve as excellent benchmarks for numerical model calibration. Once calibrated to replicate centrifuge test results, numerical models can efficiently analyze a wide range of scenarios at a fraction of the time and cost. This paper investigates ground deformations induced by shallow tunneling in cohesionless soil using numerical models calibrated against selected centrifuge tunnel tests, which encompass varying tunnel diameters, depths, and sand relative densities. The numerical modeling results presented in this paper provide extensive insights into tunnel behavior, illustrating how tunnels respond to different relative densities and depths under tunnel volume losses of up to 5%, approaching failure conditions. Additionally, a comprehensive analysis of ground deformations caused by shallow tunnels in sandy soils and their potential impact on buildings is presented.

A predictive model to determine shear strength and mechanical properties of soil-mix material (soil reinforcement) is required in many geotechnical projects especially when the weight of geomaterial is important for stability or drainage purposes. In this paper, several matching learning (ML) techniques namely Chi-squared Automatic Interaction Detection (CHAID), Classification and Regression Trees (CART), Random Forest (RF), Artificial Neural Network (ANN), Support Vector Machine (SVM), and Generalized Linear Mixed Model (GLMM) were used to predict the effects of reinforcement on cohesion (C) parameter in sandy soil. To establish an appreciate database for prediction purposes, several laboratory tests were planned and conducted on sandy soil mixed with fiber and subsequently, soil properties together with their shear strength parameters were measured. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and then, the mentioned parameters were set as inputs. According to the most effective parameters of predictive ML techniques, many models were constructed to predict C of the soil. The modelling results showed that the CHAID model provides the best prediction performance of cohesion in the short term and long term. Coefficient of determination of one and system error of zero for both train and test stages of CHAID have confirmed that this model is a perfect, powerful and applicable ML technique. The design process and model development presented in this study can be considered and used by the other researchers or engineers in resolving their complicated issues.

This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens. The hoop stresses are caused by normal viscous stress. The rheological dynamics theory (RDT) is used, with the mechanical parameters being determined by P- and S-wave velocities. The angle of internal friction is determined by the ratio of Young's modulus and the dynamic modulus, while dynamic viscosity defines cohesion and normal viscous stress. The effect of frequency on cohesion is considered. The initial stress state is defined by the minimum cohesion at the elastic limit when axial splitting can occur. However, as radial cracks grow, the stress state becomes oblique and moves towards the shear plane. The maximum and nonlinear cohesions are defined by the rock parameters under compressive strength when the radial crack depth reaches a critical value. The efficacy and precision of RDT are validated through the presentation of ultrasonic measurements on sandstone and rock specimens sourced from the literature. The results presented in dimensionless diagrams can be utilized in microcrack zones in the absence of lateral pressure in rock masses that have undergone disintegration due to excavation. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The number of studies concerning the shear strength of resedimented alluvial soils is extremely limited compared to the studies conducted on fine-grained marine sediments, since alluvial soils are generally tested in remolded or reconstituted state especially in the studies investigating their liquefaction potential. In this study, estimation models were developed to predict cohesion (c) and internal friction angle (phi) parameters of a fine-grained alluvial soil using resedimented samples. A total of 60 undisturbed soil samples were obtained from Bafra district of Samsun province (Turkiye) by core drilling. A cone penetration test with pore water pressure measurement (CPTu) was also carried out alongside each borehole to determine the over-consolidation ratios of the samples. Physical-index property determinations and triaxial tests were conducted on the undisturbed samples. 20 sample sets were created with known physical, index, and strength characteristics. The samples are classified as CH, CL, MH, and ML according to the Unified Soil Classification System, with liquid and plastic limits ranging from 31.6-75% and 19.3 to 33.6% respectively. The c and phi values of the samples varied from 4.1 to 46.1 kPa and 26 to 35 degrees respectively. The samples were then resedimented in the laboratory under conditions reflecting their original in-situ properties, and triaxial tests were repeated. The c and phi values of the resedimented samples ranged from 5.3 to 24.5 kPa and 28 to 32 degrees respectively. The results indicate that the c values of the resedimented samples are generally lower than those of the undisturbed samples, whereas upper and lower bounds for phi values are similar. Multivariate regression analyses (MVR) were utilized to develop estimation models for predicting c and phi using strength and physical properties of 20 soil samples as independent variables. Three estimation models with R-2 values varying between 0.723 and 0.797 were proposed for c and phi which are statistically significant for p <= 0.05. Using artificial neural networks (ANN), the estimation models developed by MVR were replicated to validate the models. ANN yielded very similar results to the MVR, where the R-2 values for the correlations between c and phi values predicted by both methods varied from 0.852 to 0.955. The results indicate that c and phi values of undisturbed samples can be estimated with acceptable accuracy by determining basic physical and index properties of the disturbed samples and shear strength parameters of the resedimented samples. This approach, which enables the reuse of disturbed soil samples, can be used when undisturbed soil samples cannot be obtained from the field due to economic, logistical, or other reasons. Further research on the shear strength parameters of resedimented alluvial soils is needed to validate the estimation models developed in this study and enhance their applicability to a wider range of alluvial soils.

Slope failure, as a natural disaster, can cause extensive human suffering and financial losses worldwide. This paper introduces a new soil moisture extended cohesive damage element (SMECDE) method to predict railway slope failure under heavy rainfall. A correlation between rainfall intensity and soil moisture content is first established to create an equivalence between the two. Considering slope failure mechanisms dominated by the loss of soil or the cohesion of slope materials due to heavy rainfall infiltration, the soil moisture decohesion model (SMDM) is developed using previous experimental data to express how soil cohesion varies with different soil moistures and depths. The SMDM is incorporated into the extended cohesive damage element (ECDE) method to fundamentally study slope failure mechanisms under varying soil moisture levels and depths. The proposed SMECDE approach is used to predict the failure propagation of a selected railway embankment slope at the critical soil moisture or rainfall intensity. This SMECDE failure prediction is validated using relevant data from previous fieldwork and meteorological reports on the critical rainfall intensity at the site. Additionally, the corresponding slope damage scale prediction is validated with a large plastic deformation analysis using the commercial FEM package ABAQUS.

This study investigates the shear parameters of sand modified with varying percentages of Portland cement and polyvinyl alcohol (PVA) fibers. Seventy-two static strain-controlled consolidated-drained (CD) triaxial compression tests were conducted on saturated samples. The study evaluated the effects of various factors, including relative density (50% and 80%), cement content (0%, 2%, and 4%), fiber content (0%, 0.5%, and 1%), and confining pressures (50, 100, 300, and 500 kPa), on the peak and residual shear strength parameters of the samples. The findings revealed that increasing the cement content enhances the peak internal friction angle and peak cohesion, while cementation has minimal impact on residual cohesion and residual internal friction angle. Fiber reinforcement improved peak cohesion, peak internal friction angle, residual cohesion, and residual internal friction angle of the sand. The rate of improvement in peak internal friction angle due to fiber addition decreased with higher cement content and dry density, whereas the increase in peak cohesion was more pronounced at higher cement percentages. Furthermore, the influence of cementation on shear strength parameters was more significant in denser samples. These results provide valuable insights for improving the design methodologies of reinforced soil structures such as retaining walls and foundations.

This study used Persian gum (PG) as a sustainable anionic hydrocolloid to alternative traditional stabilizers to stabilize this soil. For this purpose, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), and direct shear tests were performed after freeze-thaw cycles. The results show that biopolymers can improve UCS by creating stronger bonds between soil particles and effectively reducing the adverse effects of freeze-thaw cycles compared to unstabilized clayey soil. Also, the accumulative mass loss by adding 2% of Persian gum to unstabilized clayey soil decreased by about 70% due to the adhesive property and interaction of Persian gum hydrogel with soil grains. In addition, the moisture loss is reduced with the addition of biopolymer compared to the unstabilized sample. The UPV of the samples under the freezing phase is higher than in the thawing phase. The internal friction angle and cohesion of unstabilized and stabilized clayey soil with 2% Persian gum increased and decreased under freeze-thaw cycles. Overall, the findings show that anionic hydrocolloids such as Persian gum can effectively improve the performance and durability of CH clayey soil under severe freeze-thaw conditions.

In cold regions, the performance, safety, and serviceability of engineering facilities overlying on freeze- thaw susceptible soils are being compromised to varying degrees due to the alternate seasonal freezing and thawing cycles (FTCs). FTCs induce temporary and permanent microstructural deterioration of the underlying soils, especially fine-grained soils. In this study, we investigate the shear strength and stiffness behavior of low-compressibility silt subjected to alternate FTCs. Four series (S1 to S4) of unconsolidated undrained triaxial compression tests were performed on moist tamped solid cylindrical soil specimens. The specimens were prepared at four compaction states by changing dry unit weight and moisture content. At each compaction state, unfrozen (normal) specimens and specimens subjected to different number of FTCs were tested at total confining pressures ( 63 ) of 100 kPa, 200 kPa, and 300 kPa. At lower moisture content and increased 63, strain-hardening behavior was more obvious in the stress- strain response. The strain-hardening behavior was subdued with the number of FTCs. Higher moisture content and lower dry unit weight make the silt susceptible to frost action and thaw weakening. Percentage reduction in peak shear strength ranged from 20 to 32% for specimens subjected to 16 FTCs in S1 and S2, 8 FTCs in S3, and 04 FTCs in S4. The reduction in resilient modulus ( MR) with the number of FTCs ranged from 2 to 48% for the four compaction states. The reduction in apparent cohesion value was in the range of 23-64%. After an initial decrease in the range of 16-59%, the angle of internal friction showed a net increase in the range of 8-142%. The current study reveals that low- compressibility silt is susceptible to frost action and thaw weakening. The results show that the S4 with the highest moisture content and void ratio (lowest dry unit weight) aggravates the frost action in the soil.