Frequent extreme weather events have exacerbated shallow soil erosion, which seriously threatens the stability and safety of engineering structures in coastal and reef areas. A sand stabilization technology is proposed using filamentous fungi and wheat bran. The growth conditions of fungal mycelium are optimized through single-factor experiments and response surface methodology, while the water stability and environmental impact of the reinforced soil are evaluated using disintegration and leachate toxicity tests. Experimental results reveal that temperature has a significant influence on fungal growth during the early curing stage, while nutrient solution concentration plays a more prominent role during the later stages. In contrast, moisture content exerts a consistent and significant effect throughout the entire curing process. Based on the desirability function method, the optimal curing conditions for fungal-reinforced soil are determined to be a temperature of 25℃, a moisture content of 10%, and a nutrient solution concentration of 10 mg/L. Compared to untreated samples, the incorporation of fungal mycelium results in maximum increases of 78.8% in peak strength and 369.2% in elastic modulus. The reinforced sand also exhibits significantly improved water stability, with a disintegration ratio of zero after 14 days of immersion and minimal environmental impact from the leachate. The experimental results confirm that the sand reinforcement technique based on filamentous fungal growth holds practical potential for applications in shallow soil stabilization and coastal slope protection.
To investigate the influencing factors of effective stress parameters for shear strength of unsaturated soils and to quantitatively examine their rationality, this study systematically analyzedate of 264 suction-controlled triaxial shear tests and 102 direct shear tests on unsaturated soils from both domestic and international sources. This research focuses on magnitude and influencing factors of effective stress parameters within the commonly encountered suction range (0-1500 kPa), and conducts quantitative examination and clear assessment of four types of effective stress parameters. The key findings are as follows: (1) Within the suction range of 25-400 kPa, more than 26.5% of triaxial test results show effective stress parameter values exceed the theoretical upper limit of 1, especially a maximum measured value of 2.63, breaking through its maximum limit of 1, which is not accidental. The reason is that the effective stress method simply attributes the influence of suction on the shear strength of unsaturated soil to friction and ignores the influence on cohesion; (2) In the suction range of 25-450 kPa, over 15.5% of triaxial tests and over 23.5% of direct shear tests yield effective stress parameter values within the range of 0 to 0.35, which is far lower than 1. The mechanism is related to the increase of the structural development of and internal friction angle of the undisturbed soil with the increase of suction. It shows that low suction does not necessarily correspond to high effective stress parameter values, which is also not a random occurrence; (3) Using a relative error threshold of ±10% as the accuracy criterion, there is a significant deviation of four effective stress parameters, i.e., saturation degree at failure, effective saturation degree at failure, and two published empirical equations including the equation suggested by Khalili, from the experimental values, with qualification rates below 20%. It is found that these four effective stress parameters severely overestimate or underestimate the contribution of suction to the shear strength of unsaturated soils, which seem unsuitable as effective stress parameters; (4) The effective stress parameter on shear strength depends complexly on soil type, suction magnitude, net confining pressure (or vertical net stress), and stress path, reflecting soil viscoplasticity hardening, dilatation and structural properties. Due to the absence of clear patterns, direct measurement of effective stress parameters via suction-controlled triaxial drained shear or direct shear tests remains the feasible method currently.
Soft soil has the characteristics of high water content and low shear strength.Under such geological conditions,the construction of foundation treatment is difficult and the construction period is long.In order to practice the concept of green foundation treatment and improve the effect of electro-osmotic consolidation of soft soil foundation,seven groups of laboratory tests are carried out by self-made model box using the electro-osmotic synergistic consolidation with recyclable carbonaceous materials.During the test,the variation regulations of the current,water discharge,shear strength and other parameters are monitored.At the same time,the microstructure pictures of the soil are obtained by SEM scanning electron microscope.The changes of soil pore characteristics after the reinforcement are analyzed by image processing software PCAS,and the mechanism of consolidated soil is explored from the microscopic point of view.The test results show that the electro-osmotic drainage effect can be effectively improved by adding recyclable carbon materials,and the composite conductor formed by carbon materials and soil particles could significantly improve the current transport capacity and bearing capacity.Compared with the control group,water discharge increases by 17.28%～79.77%after adding the recyclable carbon material,and the bearing capacity near the anode increases significantly by about 20～60 kPa.In addition,the concept of ecological efficiency foundation evaluation factor is presented innovatively,which could correctly evaluate the impact of the optimized electro-osmotic method on the environment,and is inversely proportional to the size of the material.
The study focuses on the issue of transient seepage of water in the unsaturated vegetated soil under a time-varying rainfall condition, based on a few assumptions, the corresponding analytical solutions are obtained using multiple mathematical methods. The solutions also consider two types of typical bottom boundary conditions and arbitrary initial water content distribution patterns. Furthermore, the expressions of analytical solution for several common rainfall patterns are provided. On this basis, the reliability of the obtained analytical solutions is verified through the comparison analyses. Eventually, taking a type of vegetation cover of landfill as the object, the analytical solutions are applied to study the impacts of several factors on its bottom leakage. The results show that when the total rainfall is the same, overall, the leakage amount is larger under the pattern with a larger rainfall intensity in the early stage. For different distribution forms with equal initial total water storage, the form with a larger bottom water content leads to a larger leakage amount, but its impact mainly occurs in the early stage of rainfall infiltration. Among the four typical root shapes considered, the vegetation cover with uniform root distribution has the best effect in blocking the bottom leakage, and the exponential root shape has the worst effect. However, the effect of root shape is relatively small. An increase in the transpiration rate can reduce the leakage amount, and this effect will gradually become more significant as the rainfall infiltration process proceeds.
There are a large number of cracks commonly distributed within expansive soil, which significantly affect the mechanical properties of the soil. To explore the influence of the crack penetration ratio on the creep properties of expansive soil, geomembranes are selected to simulate the internal cracks of the soil mass, and triaxial creep tests along unloading paths are carried out. The results show that cracks have a pronounced weakening effect on the strength of expansive soil. As the crack penetration rate increases, the failure deviator stress of the specimens shows a linear decreasing trend. During the unloading creep tests, under relatively low deviator stress, the creep curves exhibit the characteristics of attenuating creep and steady-state creep. With the increase in the deviator stress level, the creep curves start to display the characteristics of accelerating creep, and shear failure occurs within a short period of time, which results in relatively large axial deformation. During the creep process of expansive soil, the stress-strain isochronous curves show significant deviation gradually which transition from linear to nonlinear characteristics, and presenting obvious nonlinear characteristics. Before final failure of the specimens, the axial strain rates under deviatoric stresses at various levels gradually decrease from their initial values, and as the deviatoric stress increases, the initial creep rates at the corresponding levels show an increasing trend. Based on the isochronous curve method, the long-term strength value of expansive soil containing cracks is obtained. The results indicate that under long-term loads, the long-term strength of the soil mass is significantly reduced, which is approximately 54.5%-60.5% of the ultimate failure deviator stress. Based on the creep characteristics of expansive soil, an exponential creep empirical model is established, and the model fits the test results well. The fitting accuracy is above 0.97, indicating good applicability of the model. The results can provide valuable reference for the long-term stability problems of soil containing cracks.
This study derives an analytical solution for the scattering of plane waves from a cylindrical cavity in a half-space of unsaturated porous media, based on the wave function expansion method and the Hankel function integral transform. By introducing the Hankel transform, the orthogonality issue of boundary conditions at the half-space surface and cavity wall is effectively addressed, enabling accurate determination of surface displacements and cavity-induced stress responses. The effects of saturation, incident angle, frequency, and burial depth on wave propagation are systematically investigated, providing theoretical support for related analytical studies and engineering applications.
The seepage barrier composed of cohesive soil is susceptible to local non-through or vertical through-cracks as a result of the arching effect and the uneven settlement. These cracks may trigger concentrated seepage erosion, thereby posing a threat to the safety of the dam structure. Remolded clay is adopted as the test material, with pre-fabricates vertical non-through and through cracks to simulate the cracking development of the dam core. The RST-300 multifunctional seepage piping test instrument is employed to investigate the influence of crack location, crack width, and filter gradation on the seepage deformation of the clay core. The seepage discharge, pore pressure, and turbidity of the seepage water are concurrently monitored to ascertain the self-healing or erosion-induced failure state of the cracks. Results indicate that under appropriate filter gradation conditions, non-through cracks with width ≤3 mm can self-heal through particle deposition within the crack, and the self-healing characteristics are associated with the relative position of the crack and the crack-free soil. Through cracks with width ≤3 mm are capable of self-healing, whereas those > 3 mm exhibit failure modes controlled by the filter gradation and are prone to layer-by-layer cracking, fork-shaped or step-shaped failure. During the seepage process in cracked clay, the critical condition for soil particles to pass through the filter varies dynamically with the hydraulic gradient, and the filter criterion needs to be transformed from a single geometric condition to a geometric-hydraulic coupling condition.
The electrical resistivity of soil is a key indicator of its conductivity and is influenced by factors such as testing methods (e.g., voltage, electrode insertion depth), sample conditions, mineral composition, particle size and shape, pore structure, water content, pore fluid composition, saturation, and temperature. However, the mechanisms by which soil properties and test configurations affect resistivity, and their interactions, remain insufficiently understood. This study investigates the resistivity of clayey and sandy soils, along with four types of electrolyte solutions, using the laboratory four-electrode method. The effects of water content, dry density, pore fluid concentration, voltage, electrode insertion depth, particle morphology and size, and media type are analyzed. An orthogonal testing combined with range and variance analyses is used to assess factor sensitivity. The linear correlations between electrical resistivity and intra-group factors are also examined. Results show that: (1) in sandy soils, resistivity is most sensitive to pore fluid concentration, followed by water content, dry density, particle size, electrode insertion depth, particle morphology, and voltage; (2) in clayey soils, water content and dry density dominate; (3) across media types, solution concentration has the greatest impact. (4) through Pearson linear correlation analysis, the linear correlation between the influencing factors is revealed, and the mechanism of state parameter single-factor and multi-factor coupling on resistivity is elucidated. This work supports the development of forward modeling of geotechnical resistivity and its application in engineering evaluation.
To address the instability of excavation slopes in tidal flat soft clays of the Yangtze River Delta after conventional dewatering, this study implements and evaluates an integrated ground improvement technique combining vacuum preloading with electroosmosis. The aim is to enhance drainage consolidation and strengthen low-permeability soils to ensure excavation stability. In the field, electric vertical drains (EVD) and ordinary prefabricated vertical drains (PVD) are installed in an alternating layout. Throughout the treatment process, real-time monitoring is carried out on electric current, temperature, vacuum pressure, surface settlement, and pore water pressure. Laboratory geotechnical tests are also conducted to determine key physico-mechanical properties of the treated soil. The results indicate that the combined method significantly accelerates the drainage and consolidation of the soft clay. Engineering properties such as strength and stiffness are markedly improved, and the subsequent excavation is completed smoothly with satisfactory slope stability. During energization, a noticeable thermal effect is observed within the soil mass, with its distribution varying according to the duration of electrification and depth. A vacuum-electroosmosis multi-field coupled numerical model is established and analyzed using the finite element method, which reveals the evolution patterns of pore water pressure and soil displacement. The simulation outcomes corresponded well with field monitoring data, confirming the reliability of the proposed model in simulating the multi-field coupling processes involved in soft soil improvement. This study demonstrates that the combined vacuum and electroosmosis method is an effective solution for stabilizing tidal flat soft clays and provides a reliable numerical tool for predicting and optimizing similar ground improvement projects.
The m-method is widely used to analyze laterally loaded piles, with extensive data available for recommended values of m. However, it currently lacks an analytical solution and typically requires numerical methods. Numerical methods require model meshing and iterative computations, and they can only compute one set of input parameters at a time, which results in inefficiencies for tasks demanding extensive computations. Recently, Physics-informed neural networks (PINN) have been proposed, which do not require meshing and can solve high-dimensional partial differential equations (PDEs). Based on these advantages, a PINN model that considers all input parameters of the m-method, including loads, pile parameters, and soil parameters, is proposed to analyze arbitrary input parameters without the need for re-modeling or re-training. The model normalizes the input parameters and employs a hard constraint method, significantly enhancing training efficiency. The dimensions of the loss terms are unified, addressing the issue of large differences among them. The accuracy of the PINN model is validated by comparison with the dimensionless coefficients obtained from the tabular method. The advantages of the PINN model include: it is trained directly on differential equations without requiring labeled data; it provides higher accuracy than the tabular method and greater computational efficiency than FEM when evaluating large sample sets; it enables efficient parallel computations for multiple parameter sets without re-modeling, making it highly advantageous for reliability analysis; it efficiently computes input-output derivatives, offering significant benefits for optimization design; and it demonstrates excellent scalability, allowing application to other pile analysis models, such as the c-method.
Grouting in soft clay for ground improvement generates significant excess pore water pressure and damages structure destruction, resulting in slight improvement of soil strength and appreciable settlement after grouting. This paper proposes a new method named "capsule expansion combined with electro-osmosis" for ground improvement. The capsule expansion is design to control the uncontrollable flow of grout, while synchronous electro-osmosis dissipates the generated excess pore water pressure. Two small-scale model tests are carried out to investigate the behavior of mud with sand improved by capsule expansion combined with electro-osmosis. The difference between the two tests is the content of sand within the mud of the model. Excess pore water pressure, ground vertical displacement, and compression modulus are monitored during the tests. It is found that electro-osmosis can effectively dissipate the excess pore water pressure caused by capsule grouting. The soil structure significantly affects the evolution of the excess pore water pressure. The lower the sand content in the soil, the greater the excess pore water pressure generated by grouting, and the more significant the dissipation effect of electro-osmosis. The ground vertical displacement of the ground surface shows a small and uniform characteristic under the synergistic action of capsule grouting and electro-osmosis. Moreover, the combined action can significantly enhance soil stiffness, with the compression modulus of the soil reaching up to 2.3 times the initial value. The reinforcement effect is more pronounced in areas closer to the grouting zone.
This study investigates the mechanisms of fines migration and deposition in porous media by using a particle-seepage coupling method. A cylindrical porous media model is constructed by PFC3D, and a seepage program is developed in Python to achieve two-way fluid-solid coupling. The particle flow governing equation under saturation state is derived, and the microscopic parameters of the model are calibrated and verified through microfluidic experimental data. The particle migration process in cylindrical saturated porous media is simulated, and the impact of interparticle adhesion on the migration process is analyzed. In the simulations, the JKR contact model is employed in the simulations to characterize the interparticle forces. The results indicate that when considering interparticle forces, aggregates are easily formed, leading to more adsorption and deposition of fines on the surface of porous media. Arching structures due to particle accumulation appear in the pores, resulting in significant pore clogging. The evolution of permeability is affected by interparticle forces. A large number of fines are captured by solid skeleton, resulting in pore clogging and the permeability curve decreases and eventually tends to stabilize. Finally, the particle distribution inside the model exhibits spatial heterogeneity: a barrier layer is formed in the middle region (L2) of the model, while stable clogging occurs in the bottom region (L3) when interparticle attractive forces are considered. In contrast, models considering only linear contact show a dynamic equilibrium of particle entry and exit.
Based on the discrete element method (DEM), this study investigates the evolution of mechanical stability in granular materials during shearing within the framework of the second-order work theory. Using meso-loop structures as the fundamental analysis units, a meso-scale second-order work index is developed to reveal the stability, to reveal the distinct stability characteristics inside and outside the shear band, as well as the contribution of different loop types to both local and global stability. The results show that the negative value of the macroscopic second-order work of the dense specimen appears at the peak stress state with the initial formation of shear band, making a bifurcation from a stable to an unstable state. As shearing progress, the instability of loop elements intensifies significantly, leading to the spatial concentration of localized failure. In contrast, the region outside the shear band retains a high level of overall stability. The vanishing pattern of second-order work within the shear band is highly consistent with that of the whole specimen, indicating that the global instability is predominantly governed by local instability within the shear band. Moreover, distinct differences in stability are observed among loop types: 3-cycle loops exhibit higher stability, while 4-cycle, 5-cycle, and especially high-order 6+-cycle loops are more prone to instability. The synchronized destabilization development of these higher-order loops can further amplify local instabilities within the shear band, ultimately triggering global structural failure.
To overcome the challenge of real-time acquisition of in-situ stress during drill-and-blast tunnel construction, the authors develop a high-precision synchronous acquisition equipment for drilling parameters using an impact rotary drilling system and a three-dimensional controllable stress loading platform. Twelve while-drilling tests are conducted under different surrounding rock stress states, systematically revealing the response laws between drilling parameters and ground stress, and between ground stress and wave velocity. Based on this, a five-dimensional while-drilling feature-wave velocity sample library of 6000 multi-condition features is constructed, and a Bagging decision tree integrated model is designed to achieve intelligent prediction of triaxial wave velocity. The magnitude of principal stress is then inverted based on acoustoelastic theory. Meanwhile, an analytical algorithm for principal stress direction based on wave velocity ellipsoid regression is proposed. Results show that the prediction accuracy of the triaxial wave velocity model ranges from 84.44% to 88.21%, and the principal stress magnitude inverted using the predicted wave velocity agrees well with the loading value. The maximum principal stress direction error analyzed by the wave velocity ellipsoid method is ≤0.1°, and the errors of other principal stress directions are ≤18.3°. The research findings provide a new approach for the rapid and intelligent analysis of the stress field of tunnel surrounding rock and provide a methodological reference for stress analysis in high-stress tunnels.
Variations in the flow field of the surrounding of liquefiable seabed have a significant impact on the dynamic stability of subsea pipelines. The motion of seawater (waves) and the pore fluid within the seabed are described using the Reynolds-Averaged Navier-Stokes (RANS) equations and Biot's dynamic consolidation equation, respectively. Based on the extended Masing's rule, a visco-elastoplastic constitutive model capable of simulating cyclic softening and large deformation due to liquefaction of the seabed is constructed. By achieving real-time transfer of hydrodynamic pressure at the seawater-seabed interface, an integrated numerical model for wave-seabed-pipeline interaction is established. The model is validated against Sumer et al.'s wave flume experiments. Based on a typical borehole in the Jinqimen area, numerical analysis is conducted on the dynamic response of pipelines under long-term wave loading. The results show that: (1) The presence of pipelines alters the spatial distribution of liquefied zones in the seabed. Liquefaction initiates at the seabed surface and beneath the pipeline, with subsequent liquefied areas evolving upwards along the outer wall of the pipeline; (2) The rate of reduction in deviatoric stress is more pronounced in the near-field compared to the far-field, leading to significant strain concentration around the pipeline. Additionally, the cyclic shear stress ratio (CSSR) near the pipeline is higher than in the far-field, resulting in faster liquefaction rate in the near-field; (3) Intense seabed-pipeline interactions increase the depth and extent of liquefaction in the near-field seabed, increasing buoyancy forces on the pipeline while reducing frictional resistance. Plastic flow of soil within the affected zone causes soil accumulation and compression under the pipeline, collectively resulting in pipeline uplift and lateral displacement.
For municipal solid waste (MSW) embedded in shallow depths within landfills, its temperature is susceptible to atmospheric temperature fluctuations that exhibit periodic change. Impact of temperature cycles on the volume change behavior of MSW remains unknown, the latter impacts the long-term stability of landfills and its further utilization as land resources. To address this issue, temperature-controlled triaxial tests are conducted to examine the temperature-cycling effect on the volume change behavior of both fresh and aged MSW under different stress levels. The test results indicate that temperature-cycling- induced elastic and plastic volume changes of MSW are much larger than those of clayey soils. The accumulated plastic volumetric strain appeares to increase with the number of temperature cycles and gradually stabilizes. The temperature-cycling induced volume change of MSW was dependent on stress level and MSW age, fresh MSW under a lower stress tended to yield a larger volume change. Neverthelexs, temperature-cycling induced volume change of the aged MSW is still significant and cannot be ignored. Based on the triaxial test results, a method is proposed to estimate the thermoelastic-plastic compression index λT and thermoelastic compression index κT of MSW. A thermo-elastoplastic constitutive model in the form of λT and κT is developed, incorporating the number of temperature cycle, stress level, and MSW age. The feasibility of the proposed model is validated against the experimental results.
It is typically assumed that the strength of individual particles deteriorates with time when using the discrete element method(DEM)to model the creep behaviour of rockfill materials under loading.Quantifying the time-varying degradation characteristics of actual particle strength is essential for a quantitative analysis.However,effective means to measure these characteristics are currently lacking.To address this issue,a measurement method that integrates experimental testing with theoretical analysis is proposed in this paper.In this method,the creep compliance of individual particles is determined by a uniaxial compression test with a multiple-stage constant loading history.Moreover,theoretical analysis is employed to obtain the spatiotemporal evolution of the strain field in individual particles under a single-stage constant loading history.The calculation equation for the particle failure time is then derived based on the maximum tensile strain theory.Finally,the time-varying degradation process of the particle strength is characterized by a quantitative relationship between the load level and the failure time.Preliminary applications on limestone particles(10-50 mm)verify the effectiveness of this method.The results also exhibit that the relationship between the load level and the failure time follows an exponential function.Meanwhile,the decay parameter shows a lognormal distributional randomness,and the randomness of the load level corresponding to the long-term strength obeys a beta distribution.The proposed method provides a viable solution to quantitatively measure the time-varying degradation characteristics of rockfill particle strength.
The development of offshore wind turbines (OWTs) is gradually moving toward deeper seas, where jacket foundations serve as the preferred support structure for large OWTs in deep seas. To investigate the seismic failure modes of multi-caisson jacket foundations in liquefiable interlayer ground, dynamic centrifuge tests are conducted using the TK-C500 large-scale geotechnical centrifuge-shaking table system installed at the Tianjin Transport Engineering Research Institute. Based on non-equal stress similarity theory, a scaled model of the multi-caisson jacket foundation supporting a large OWT is designed. The study presents a method for applying equivalent horizontal cyclic loading in the centrifuge model tests. Technical details are described, including the preparation process of the layered soil, the installation method of three-caisson jacket foundation using continuous negative pressure penetration, and other aspects. The tests ultimately yield satisfactory results and fulfill the experimental objectives. This paper systematically describes the centrifuge model test design for OWT structures in complex site conditions, which can provide technical insights and methodological references for similar tests in the future.
The nonlinearity and inhomogeneity of rock mass are manifested at any scale. Geometric equations and constitutive equations based on the continuity assumption cannot accurately characterize the post-peak deformation and failure processes of engineering rock masses. Considering the practical shortcomings of continuum mechanics in solving the stress and deformation in surrounding rock, this study employs only boundary conditions and equilibrium equations, and describes the stress distribution in the surrounding rock softening zone via an averaging approximation. Furthermore, the initial radius of the softening zone of circular openings estimated, and the softening law of the post-peak internal friction angle is back-calculated. The results show that the softening law can be well described by the Boltzmann function. In addition, the mass conservation law is applied to analyze the deformation of the surrounding rock. The research results can provide theoretical reference for the design of long-term stability support in deep underground engineering.
To investigate roof deformation and overburden failure, this study combines theoretical modeling with physical simulation to compare full and partial backfilling. Results show that, based on elastic foundation beam theory and the initial parameter method, roof subsidence increases and then stabilizes, reaching 0.52 m for partial backfilling and 0.38 m for full backfilling. In the simulation, full backfilling results in one overburden fracture and minor roof caving with a maximum displacement of 3 mm, indicating good integrity. In contrast, partial backfilling leads to multiple fracture and caving events, with a maximum roof displacement of 5.5 mm. Delayed filling may induce localized roof collapse and more developed fractures; however, the backfill body effectively restricts overburden rotation and prevents overall cutting failure. Overall, partial backfilling presents favorable surrounding rock control performance, with advantages in backfilling cost and mining efficiency, and possesses broad application prospects.
