Search Results (101)

The strength mobilisation framework was adopted for the first time to describe the stress–strain responses for three different types of sands, including a total of 30 published drained triaxial tests—25 for Karlsruhe Fine Sand, 2 for Ottawa sands and 3 for Fontainebleau sand, under confining pressures ranging from 50 to 400 kPa. The peak shear strength ${\tau }_{peak}$ obtained from drained triaxial shearing of these sands was used to normalise shear stress. Shear strains normalised at peak strength ${\gamma }_{peak}$ and at half peak of shear strength ${\gamma }_{M=2}$ were taken as the normalised reference strains, and the results were compared. Power–law functions were then derived when the mobilised strength was between $0.2{\tau }_{peak}$ and $0.8{\tau }_{peak}$. Exponents of the power–law functions of these sands were found to be lower than in the published undrained shearing data of clays. Using ${\gamma }_{M=2}$ as the reference strain shows a slightly better power–law correlation than using ${\gamma }_{peak}$. Linear relationships between the reference strains and variables, such as relative density, relative dilatancy index, and dilatancy, are identified. Full article

To address the engineering challenges associated with Guilin red clay, such as its potentially low strength and unfavorable mechanical behavior, this study investigated the effectiveness of lignin and lime as modifiers. Consolidation undrained triaxial tests and scanning electron microscopy (SEM) were employed to evaluate the strength characteristics and microstructural changes in modified clay specimens with varying dosages. The results demonstrate distinct strengthening mechanisms: Lignin exhibits an optimal dosage (6%), significantly increasing cohesion and internal friction angle through physical reinforcement (“soil fiber” formation), but higher dosages (8%) lead to particle separation and strength reduction. In contrast, lime provides continuous and substantial strength enhancement with increasing dosage (up to 8%), primarily through chemical reactions producing cementitious compounds (e.g., C-S-H, C-A-H) that densify the structure. Consequently, lime-modified clay shows significantly higher cohesion and internal friction angle compared to lignin-modified clay at equivalent or higher dosages, with corresponding stress–strain curves shifting from enhanced (strain-hardening) to softening behavior. These findings provide practical insights into red clay improvement in geotechnical engineering applications. Full article

To investigate the slope instability caused by differential frost heaving mechanisms from the slope crest to the toe during frost heave processes, this study takes a typical silty clay slope in Xinjiang, China, as the research object. Through indoor triaxial consolidated undrained shear tests, eight sets of natural and frost-heaved specimens were prepared under confining pressure conditions ranging from 100 to 400 kPa. The geotechnical parameters of the soil in both natural and frost-heaved states were obtained, and a spatiotemporal thermo-hydro-mechanical coupled numerical model was established to reveal the dynamic evolution law of anchor rod axial forces and the frost heave response mechanism between the frame and slope soil. The analytical results indicate that (1) the frost heave process is influenced by slope boundaries, resulting in distinct spatial variations in the temperature field response across the slope surface—namely pronounced responses at the crest and toe but a weaker response in the mid-slope. (2) Under the coupled drive of the water potential gradient and gravitational potential gradient, the ice content in the toe area increases significantly, and the horizontal frost heave force exhibits exponential growth, reaching its peak value of 92 kPa at the toe in February. (3) During soil freezing, the reverse stress field generated by soil arching shows consistent temporal variation trends with the temperature field. Along the height of the soil arch, the intensity of the reverse frost heave force field displays a nonlinear distribution characteristic of initial strengthening followed by attenuation. (4) By analyzing the changes in anchor rod axial forces during frost heaving, it was found that axial forces during the frost heave period are approximately 1.3 times those under natural conditions, confirming the frost heave period as the most critical condition for frame anchor design. Furthermore, through comparative analysis with 12 months of on-site anchor rod axial force monitoring data, the reliability and accuracy of the numerical simulation model were validated. These research outcomes provide a theoretical basis for the design of frame anchor support systems in seasonally frozen regions. Full article

Coastal marine soft clays subjected to long-term storm wave loading often exhibit inclined initial principal stress orientation (α₀) and subsequent cyclic principal stress rotation (PSR). These stress states critically influence soil mechanical behavior and failure mechanisms, threatening offshore structural stability. This study employs hollow cylinder apparatus testing to investigate the undrained cyclic loading behavior of reconstituted soft clay under controlled α₀ and PSR conditions, simulating storm wave-induced stress paths. Results demonstrate that α₀ governs permanent pore pressure and vertical strain accumulation with distinct mechanisms, e.g., a tension-dominated response with gradual pore pressure rise at α₀ < 45° transitions to a compression-driven rapid strain accumulation at α₀ > 45°. Rotational loading with PSR significantly intensifies permanent strain accumulation and stiffness degradation rates, exacerbating soil’s anisotropic behavior. Furthermore, the stiffness degradation index tends to uniquely correlate with the permanent axial or shear strain, which can be quantified by an exponential relationship that is independent of α₀ and PSR, providing a unified framework for normalizing stiffness evolution across diverse loading paths. These findings advance the understanding of storm wave-induced degradation behavior of soft clay and establish predictive tools for optimizing marine foundation design under cyclic loading. Full article

Climate-induced wetting and drying (WD) cycles significantly affect the long-term performance of geotechnical structures. This study explores expansive Oxford clay’s mechanical and volumetric responses stabilised with ordinary Portland cement (OPC) and guar gum (GG) under repeated WD cycles. We prepared 108 samples in total—36 untreated, 36 treated with OPC, and 36 treated with GG. These samples were compacted to 90% of their maximum dry density and subjected to 1, 5, 10, and 15 WD cycles, with nine samples for each treatment at each cycle. During the WD cycles, we monitored volumetric strain and moisture content. Mechanical performance was assessed through unconsolidated undrained triaxial tests conducted at matric suctions of −1500 kPa, −33 kPa, and under saturated conditions. We evaluated the undrained shear strength (S_u), secant modulus of elasticity (E₅₀), and modulus of toughness (U_t). The results showed that OPC-treated samples consistently exhibited the highest S_u at −1500 kPa across all WD cycles, followed by untreated and GG-treated samples. At −33 kPa, OPC-treated samples again outperformed the others in S_u, while GG-treated samples performed better than the untreated ones. Under saturated conditions, GG-treated samples displayed a similar S_u to OPC-treated samples, significantly higher than untreated samples. Energy absorption capacity, measured through U_t, peaked for OPC-treated samples at −1500 kPa but favoured GG treatment at −33 kPa and under saturation. X-ray computed tomography (CT) revealed severe degradation in untreated samples, characterised by extensive cracking, minor cracking in OPC-treated samples, and minimal damage in GG-treated samples. This highlights the superior resilience of guar gum to wetting–drying cycles. These findings underscore the potential of guar gum as a sustainable alternative to cement for enhancing the WD resilience of expansive soils, particularly under low-suction or saturated conditions. Full article

The rapid expansion of land reclamation necessitates a fundamental understanding of the strain rate effects on structured clays. While the rate effect has been widely studied in various soils, the interplay between bond structure and strain rate sensitivity remains unclear. This study investigates these mechanisms using artificially cemented kaolin (ACK) with controlled curing periods (2 and 30 days) to simulate naturally bonded clays. A series of undrained triaxial tests was conducted under low (100 kPa) and high (600 kPa) confining stresses, employing constant strain rates (0.01–5%/h) pre-peak and stepwise rate changes post-peak. The results reveal that the strain rate effects are governed by the bond structure maturity and drainage mechanisms. For the 30-day curing ACK, the pre-peak strength under low confining stress shows minimal rate sensitivity due to the rigid bond, while high confining stress induces a “negative” rate effect attributed to localised drainage along shear planes. The post-peak behaviour consistently exhibits a positive isotach-type rate effect (+3%/log-cycle) driven by viscous sliding. In contrast, the 2-day curing ACK displays negative rate effects pre-peak influenced by ongoing curing and post-peak strength reductions (−8%/log-cycle) linked to stick-slip dynamics. These findings establish a framework for predicting rate-dependent behaviour in structured clays, offering insights into land reclamation and subsequent construction work. Full article

The progression of marine resource exploration into deepwater and ultra-deepwater regions has intensified the requirement for precise quantification of the undrained shear strength of clay. Although diverse in situ testing methodologies—including the vane shear test (VST), cone penetration test (CPT), T-bar penetration test (TPT), and ball penetration test (BPT)—are widely utilized for the assessment of clay strength, systematic discrepancies and correlations between their derived measurements remain inadequately resolved. The aim of this work is to provide a systematic comparison of strength interpretations across different in situ testing methods, with emphasis on identifying method-specific biases under varying soil behaviors. To achieve this, a unified numerical simulation framework was developed to simulate these four prevalent testing techniques, employing large-deformation finite element analysis via the Coupled Eulerian–Lagrangian (CEL) approach. The model integrates critical constitutive behaviors of marine clays, specifically strain softening and strain rate dependency, to replicate in situ shear strength evolution. Rigorous sensitivity analyses confirm the model’s robustness. The results indicate that, when the stain rate and softening effects are neglected, the resistance factors from the CPT and VST remain largely insensitive to shear strength variations. However, T-bar and ball penetrometers tend to underestimate strength by up to 15% in high-strength soils due to the incomplete development of a full-flow failure mechanism. As a result, their application in high-strength soils is not recommended. With both the strain rate and softening effects considered, the interpreted strength value S_ut from the CPT increases by 13.5% compared to cases excluding these effects, while other methods exhibit marginal decreases of 4–5%. The isolated analysis of strain softening reveals that, under identical softening parameters, the CPT demonstrates the least sensitivity to strain softening among the four methods examined, with the factor reduction ratio N_s/N₀ ranging from 0.76 to 1.00, while the other three methods range from 0.65 to 0.88. The results indicate that the CPT is well suited for strength testing in soils exhibiting pronounced softening behavior, as it reduces the influence of strain softening on the measured results. These findings provide critical insights into method-specific biases in undrained shear strength assessments, supporting a more reliable interpretation of in situ test data for deepwater geotechnical applications. Full article

The construction industry is a major contributor to the global climate crisis, prompting increasing interest in minimising the embodied carbon of structures, whether through material production regulations or the optimisation of structural elements. While a wide body of literature addresses the reduction of embodied carbon in superstructures, limited attention has been devoted to the optimisation of foundations, particularly piles. This research introduces a hybrid genetic algorithm optimisation tool designed to minimise the embodied carbon of tension piles in different soil conditions. Six different pile types are analysed: solid and hollow concrete piles, steel pipes, universal column (UC) sections, and timber piles in both square and circular forms. The optimal design parameters for each pile type on undrained clay and loose sand are presented and compared. The results demonstrate the potential for reducing the embodied carbon of tension piles when utilising optimised designs. Finally, a case study involving an 8-metre-high cross-road signpost is presented, illustrating the practical application of the proposed optimisation algorithm for reducing embodied carbon in future designs. Full article

Gassy clay, commonly encountered in coastal areas as overconsolidated deposits, demonstrates distinct mechanical properties posing risks for submarine geohazards and engineering stability. Consolidated undrained triaxial tests combined with cyclic simple shear tests were performed on specimens with varying overconsolidation ratios (OCRs) and initial pore pressures, supplemented by SEM microstructural analysis. Triaxial results indicate that OCR controls the transitions between shear contraction and dilatancy, which govern both stress–strain responses and excess pore pressure development. Higher OCR with lower initial pore pressure increases stress path slope, raises undrained shear strength (s_u), reduces pore pressure generation, and induces negative pore pressure at elevated OCR. These effects originate from compressed gas bubbles and limited bubble flooding under overconsolidation, intensifying dilatancy during shear. Cyclic tests reveal gassy clay’s superior cyclic strength, slower pore pressure accumulation, reduced stiffness softening, and enhanced deformation resistance relative to saturated soils. Cyclic pore pressure amplitude increases with OCR, while peak cyclic strength and anti-softening capacity occur at OCR = 2, implying gas bubble interactions. Full article

The shear strength and compression properties of stiff Boom clay from Belgium at a depth of about 16.5 to 28 m were investigated by means of cone penetration and laboratory testing. The latter consisted of index classification, constant rate of strain, triaxial, direct simple shear and unconfined compression tests. The Boom clay samples exhibited strong swelling tendencies. The suction pressure was measured via different procedures and was compared to the expected in situ stress. The undrained shear strength profile determined from cone penetration tests (CPTs) was not compatible with the triaxial and direct simple shear measurements, which gave significantly lower undrained shear strength values. Micro-computed tomography (μCT) scans of the samples showed the presence of pre-existing discontinuities which may cause inconsistencies in the comparison of the laboratory test results with in situ data. The experimental data gathered in this study provide useful information for analyzing the mechanical behaviour of Boom clay at shallow depths considering that most investigations in the literature have been carried out on deep Boom clay deposits. Full article

The development of marine energy requires reliable foundations, which may be located near submarine slopes. This paper utilizes the lower bound limit analysis (LBLA) to analyze the undrained bearing capacity of foundations on slopes with anisotropy and linearly increasing strength with depth. The anisotropic undrained strength (AUS) model is employed to simulate the anisotropy of the slope soil. This study considers five variables that affect the bearing capacity: the normalized foundation setback (L/B), load angle (θ), strength ratio (s_uc/γB), heterogeneous index (ρB/s_uc), and anisotropy ratio (r_e). Here, s_uc represents the soil strength obtained from triaxial compression tests, while ρ denotes the strength gradient. The results indicate that the bearing capacity increases with the increase in L/B, s_uc/γB, ρB/s_uc, and r_e, while the maximum bearing capacity corresponds to a load angle ranging from 75° to 90°. The failure modes of foundations under different boundary conditions were presented and discussed. To establish the relationship between the foundation bearing capacity and each variable, the multivariate adaptive regression splines (MARS) is introduced. The MARS results indicate that θ is the most significant variable, while the relative importance of L/B is the lowest; neither can be neglected in practical engineering. The empirical equation based on the MARS algorithm can accurately predict the bearing capacity of foundations in non-homogeneous and anisotropic clay. These results offer critical guidance for engineering practice, enabling efficient design of marine foundations near slopes while accounting for soil anisotropy and heterogeneous strength gradients, thereby reducing risks of instability in offshore energy infrastructure. Full article

Cone penetration test often uses the cone factor to calculate the undrained shear strength of silty clay base on the cone tip resistance data, but the accurate determination of the cone factor is challenging due to its wide range of values. This study conducted a laboratory cone penetration test and vane shear test to investigate and calibrate the cone factor for evaluating the undrained shear strength of silty clay at various depths. The cone factor is first identified based on the laboratory cone penetration test and vane shear test, and it is compared with the cone factor generated from the cavity expansion theory. Cone factor calibration has been performed by integrating laboratory model tests with the cavity expansion method, unlike conventional approaches relying on singular methodologies. The proposed cone factor is validated by the in situ undrained shear strength of Shanghai silty clay based on the in situ cone penetration test data. The results indicate that the cone factor varies significantly, ranging from 3 to 27. The cone factor from laboratory results shows good agreement with that based on the cavity expansion method. The calibrated cone factor predicts reasonable undrained shear strength measured from in situ tests. The refining method enables ±30% accuracy in predicting field-measured undrained shear strength values, establishing region-specific guidelines for East China Sea investigations. Full article

This study addresses the critical issue of basal heave stability in deep excavations within Bangkok’s soft clay, particularly under conditions of confined groundwater recovery. Historical failures in excavation projects highlight the urgent need for effective stability assessments that account for fluctuating groundwater levels. Utilizing a comprehensive dataset derived from case studies and numerical simulations, this research employs the finite element method (FEM) to analyze the interactions between excavation depth, undrained shear strength, and groundwater dynamics. The findings reveal that groundwater recovery significantly influences effective stress, leading to increased uplift pressures that can destabilize excavation support systems. The numerical analyses indicate that Terzaghi’s method overestimates safety factors, while Bjerrum and Eide’s and Chang’s methods closely match numerical results, emphasizing the need for robust analysis that integrates groundwater effects to enhance stability assessments in urban excavations. Grouting techniques applied 10 m below the diaphragm wall significantly improved stability, with safety factors increasing by 63.47%, 87.86%, and 138.72% over various periods. This study contributes valuable insights into excavation design practices and provides empirical data that can inform future research aimed at mitigating hydraulic heave risks in urban environments. Ultimately, the findings advocate for the integration of advanced modeling techniques in geotechnical engineering to improve safety and structural integrity in excavation projects. Full article

To achieve environmental and economic goals in ground improvement, a one-part geopolymer (OPG), synthesized from binary precursors (fly ash [FA] and granulated blast furnace slag [GGBFS]) and a solid activator (solid sodium silicate [NS]), was used to replace ordinary Portland cement (OPC) for stabilizing high-water-content soft clay. The effects of different initial water content (50%, 80%, 100%, and 120%) and various OPG binder content (10%, 20%, 30%, and 40%) on the strength development of the OPG-stabilized soft clay were investigated through unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial tests. Additionally, the microstructure evolution and the distribution of pores in the OPG-stabilized soft clay were examined by the utilization of mercury intrusion porosimetry (MIP) and scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) techniques, respectively. The life cycle assessment (LCA) methodology was then used to analyze the environmental and economic advantages of employing an OPG binder for soil stabilization. It was revealed that the optimal content of OPG binder was contingent upon the water content of soft clay, with variations in requirements for strength development. Specifically, for soft clay not demanding early strength, a maximum binder content of 20% is proposed. Conversely, for soft clay that necessitated rapid strength gain, the OPG binder content escalated with increasing water content of the soft clay, in which soft clays with different water contents had corresponding required amounts of OPG binder. For soil with water content ranging from 50% to 80%, the recommended OPG binder content is 20%. While for soil with 100% and 120% water content, the designed OPG binder content is suggested to be 30% and 40%, respectively. The environmental assessment demonstrated that the utilization of OPG as a binder for the stabilization of soft clay reduces costs and carbon emissions in comparison to OPC. The present study provides substantial theoretical validation for the utilization of OPG as a novel binder to stabilize soft clay with elevated water content, which holds promise as an eco-friendly and cost-effective solution in ground improvement. Full article

In recent decades, rapid urbanization has generated a large amount of waste soft soil and construction debris, resulting in severe environmental pollution and posing significant challenges to engineering construction. To address this issue, this study explores an innovative approach that synergistically applies recycled fine aggregate (RFA) and soil stabilizers to improve the mechanical properties of soft soil. Through laboratory experiments, the study systematically examines the effects of different mixing ratios of RFA (20%, 40%, 60%) and soil stabilizers (10%, 15%, 20%) with red clay. After standard curing, the samples underwent water immersion maintenance for varying durations (1, 5, 20, and 40 days). Unconfined compressive strength (UCS) tests were conducted to evaluate the mechanical performance of the samples, and the mechanisms were further analyzed using scanning electron microscopy (SEM) and particle size distribution (PSD) analysis. The results indicate that the optimal performance is achieved with 20% RFA and 20% stabilizer, reaching the highest UCS value after 40 days of water immersion. This improvement is primarily attributed to the formation of a dense reticulated structure, where RFA particles are effectively encapsulated by clay particles and stabilized by hydration products from the stabilizer, forming a robust structural system. Unconsolidated undrained (UU) tests reveal that peak deviatoric stress increases with confining pressure and stabilizer content but decreases when excessive RFA is added. Shear strength parameter analysis demonstrates that both the internal friction angle (φ) and cohesion (c) are closely related to the content ratios, with the best performance observed at 20% stabilizer and 20% RFA. PSD analysis further confirms that increasing stabilizer content enhances particle aggregation, while SEM observations visually illustrate a denser microstructure. These findings provide a feasible solution for waste soft soil treatment and resource utilization of construction debris, as well as critical technical support and theoretical guidance for geotechnical engineering practices in high-moisture environments. Full article