Soft Soil Research Articles

Research progress and prospects of seismic performance on underground structure embedded in soft soil foundation

For the complexity and difficulty of seismic research on subway station structure system embedded in soft soil foundation, the seismic research method is quite different from the ground structure. The methods of seismic research on subway station structures in soft soil were summarized, and relevant literature on this field in recent years were sorted out. The advanced progress of theoretical analysis and quasi-static simplification analysis, model test (shaking table test, centrifuge test), numerical simulation (the total stress method, the effective stress method), and dynamic reliability of underground structures were mainly introduced for seismic analysis of subway station embedded in the soft foundation. The advantages and disadvantages of each method and the development direction of this field were proposed briefly in order to better understand seismic analysis of underground structure engineering in soft soil.

Numerical modeling of site response at large strains with simplified nonlinear models: Application to Lotung seismic array

Abstract Site response analyses at large strains are routinely carried out neglecting the shear strength of soil and the stiffness degradation due to the increase in pore pressures, leading to unrealistic predictions of the seismic response of soil deposits. The study investigates the performance of a simplified nonlinear (NL) approach, implemented in the Deepsoil code, constituted by coupling a hyperbolic model incorporating shear strength with a strain-based semi-empirical pore pressure generation model. The first part of the study, based on a large one-dimensional parametric study, shows that above a shear strain of 0.1%, it is necessary to include shear strength in the site response modelling to get more realistic results. Then, the approach has been evaluated with reference to the well-known downhole Large-Scale Seismic Test array located in Lotung (Taiwan): numerical results have been compared with recordings in terms of acceleration response spectra and pore water pressure time histories at different depths along the soil profiles. The comparison shows that the NL simplified model is characterized by an accuracy comparable with more sophisticated advanced elasto-plastic NL analyses adopting essentially the same input data of the traditional equivalent linear approaches(shear modulus and damping curves) and simple physical-mechanical properties routinely determined during geotechnical surveys (i.e., shear strength, relative density, fine content). This approach is therefore recommended for site response analyses reaching large strains (i.e., soft soil deposits and moderate-to-high input motions).

Failure Probability-Based Optimal Seismic Design of Reinforced Concrete Structures Using Genetic Algorithms

Artificial intelligence (AI) has enabled several optimization techniques for structural design, including machine learning, evolutionary algorithms, as in the case of genetic algorithms, reinforced learning, deep learning, etc. Although the use of AI for weight optimization in steel and concrete buildings has been extensively studied in recent decades, multi-objective optimization for reinforced concrete (RC) and steel buildings remains challenging due to the difficulty in establishing independent objective functions and obtaining Pareto fronts. The well-known Non-Dominated Sorting Genetic Algorithm II (NSGA-II) is an efficient genetic algorithm approach for multi-objective optimization. In this work, the NSGA-II approach is considered for the multi-objective structural optimization of three-dimensional RC buildings subjected to earthquakes. For the objective of this study, two function objectives are considered: minimizing total cost and the probability of structural failure, which are obtained via several nonlinear seismic analyses of the RC buildings. Beams and columns’ cross-sectional dimensions are selected as design variables, and the Mexican Building Code (MBC) specifications are imposed as design constraints. Pareto fronts are obtained for two RC-framed buildings located in Mexico City (soft soil sites), which demonstrate the efficiency and accuracy of NSGA-II for structural optimization.

Modeling of Drain Consolidation in the Quick Triaxial Test and Its Analytical Solution

ABSTRACTSand columns have been widely used to accelerate drainage and then improving the mechanical properties of soft soil foundations. The sand column has also been introduced into the triaxial test by researchers, in the center of the cylindrical specimen, to greatly accelerate drainage and consolidation process. The objective of this paper is to evaluate the consolidation properties of the triaxial cylindrical specimen considering the presence of a sand column, and then to propose a consolidation model that simulates the consolidation process of the triaxial test. The consolidation equations were derived considering the drainage of the specimen with a sand column composed of both vertical and double‐radial flows. Then the analytical solution of the model was obtained based on specific initial and boundary conditions. The comparison between the consolidation model and the laboratory tests yielded highly consistent. The case study demonstrated that the proposed consolidation model accurately simulates the evolution of average pore pressure and degree of consolidation in triaxial specimens containing a sand column. The studies on the consolidation parameters showed that there were different effects on the drainage rate for the diameter of specimen, the permeability coefficients of specimen and sand column, as well as the radius of the sand column.

Enhancing Deep Excavation Optimization: Selection of an Appropriate Constitutive Model

To minimize the impact on nearby structures during deep excavations, choosing an appropriate soil constitutive model for analysis holds significant importance. This study aims to conduct a comparative analysis of various constitutive soil models—namely, the Mohr–Coulomb (MC) model, the hardening soil (HS) model, the hardening soil small strain (HSS) model, and the soft soil (SS) model—to identify the most suitable model for the lacustrine deposit. To implement these models, the soil’s index properties and mechanical behavior were evaluated from undisturbed soil samples. The numerical simulation and verification of these properties were carried out by comparing the laboratory test results with the outcome of the finite element method; the most suitable constitutive soil model for the soil was identified as the HSS model. Upon analyzing the wall deflection and ground settlement profiles obtained from respective constitutive models, it was observed that the HS and HSS models exhibit similar characteristics and are well-suited for analyzing typical lacustrine soil. In contrast, the MC and SS models yield overly optimistic results with lower wall deflection and ground settlement and fail to predict realistic soil behavior. As a result, this research highlights the significance of selecting the appropriate constitutive soil model and refining the parameters. This optimization process contributes significantly to the design of support systems, enhancing construction efficiency and ensuring overall safety in deep excavation projects.

The Uses of Lightweight Material in Civil Engineering : A Review

A lightweight aggregate (LWA) is a group of aggregates with a relative density lower than normal density aggregates (natural sand, gravel, and crushed stone), sometimes referred to as low density aggregate. It is utilized for its reduced weight and exceptional qualities in sound reduction, fire resistance, insulation, and geotechnical applications LWA, or lightweight aggregate, is a cutting-edge construction material that is employed to decrease the overall weight of tall structures. Despite being lighter, it possesses a strength that is comparable to that of regular concrete. In recent times, there has been a significant surge in the use of lightweight aggregate in the field of building, mostly because of its exceptional performance in seismic situations. In addition, substituting natural aggregate with other industrial by-products and trash enables us to minimize the adverse environmental consequences. Laser wavelength ablation (LWA) has also been employed to address a wide range of geotechnical engineering challenges, including the transformation of soft and unstable soil into a suitable and usable property. Lightweight fillings have a weight that is around 50% less than fills made using typical materials. The load reduction, along with the high internal friction angle of the lightweight aggregate, can decrease vertical and lateral pressures by almost 50%, potentially resulting in less settling. This literature study examines the use of lightweight materials, including LECA, Bonza, and Thermostone, in geotechnical engineering applications. The results demonstrate a significant emphasis on improving slope stability and minimizing stresses on susceptible soils. Nevertheless, several knowledge gaps exist regarding the efficacy of these materials under challenging conditions and when subjected to dynamic loads. A growing inclination towards using these lightweight aggregates is observed because of their advantageous environmental and mechanical properties. Further investigation is needed to examine the extended-term performance and interactions of these materials with different soil types in order to enhance their performance in diverse geotechnical situations.

Data-driven forecasting of embankment settlements on soft soils using constant rate of strain test data

Geotechnical engineers continually seek accurate methodologies for predicting the time-dependent settlement of embankments on soft soils. This paper introduces a novel data-driven approach that utilises constant rate of strain (CRS) test data to forecast embankment settlements. The proposed framework circumvents the requirement to subjectively assign soil parameters used in traditional forecasting models by directly integrating CRS test data into an automated analytical process, thereby significantly reducing manual effort and user-dependent variation in forecast results. The accuracy of the method is demonstrated through applications to real-world trial embankments in Australia and the Netherlands. All data used in this study are freely available in digital format from Datamap.

Interparticle friction behaviors of kaolinite: Insights into macroscale friction from nanoscale

The friction behavior of widespread clay minerals is a major concern in many geo-engineering problems, such as the stability of soft soil foundations and the induction of seismic fault zones. The present work aimed to study the friction behaviors of kaolinite at the particle level using the molecular dynamics method. The effects of normal force (Fn), shear velocity (v), and interfacial water film on nanofriction were discussed. The “stick-slip” phenomenon and periodic evolution of friction forces (Ff) were observed in dry friction and became less pronounced with water lubrication. The dry Ff of kaolinite was found to be insensitive to Fn. However, wet Ff exhibited a linear increase with Fn and then transitioned to a non-linear relationship as slip displacement increases due to the continuous loss of water molecules from the interface during friction. Notably, at high loads (Fn ≥ 30 nN), the peak friction of wet kaolinite showed characteristics similar to dry friction. A velocity-strengthening behavior of kaolinite at high velocities was observed in both dry and wet conditions. The macroscale friction coefficients of kaolinite were predicted from nanofriction data and results showed good agreement with experimental values. This study lays the foundation for bridging micro- and macro-mechanical behaviors, suggesting a new pathway for acquiring precise macroscopic friction of minerals through cross-scale studies.

Improvements in vacuum-surcharge preloading combined with electro-osmotic consolidation on soft clayey soil with high water content

This study conducted laboratory tests on soft clayey soils to investigate the effectiveness of the combinations of vacuum-surcharge preloading and electro-osmotic treatment (EOC-VPM-SPM). To minimize the loss of vacuum pressure and mitigate clogging of the drainage system during the consolidation process, two improved methods were developed by optimizing technical characteristics and geometric layout of drainage boards. In the EOC-Alternate VPM-SPM method, alternate vacuum pressure was incorporated using two drainage boards with different lengths in the VPM system, combined with EOC to improve consolidation efficiency. In the multiple-electrodes EOC-VPM-SPM method, a new design of multiple drainage boards in a square tube layout fabricated through 3D printing was employed to provide efficient connections of the consolidation system. Furthermore, electrokinetic geosynthetics (EKG) was utilized as the cathode in the EOC system to minimize erosion and passivation of electrodes for the enhancement in consolidation efficiency. The properties of tested soils were analyzed to evaluate the feasibility of the improved methods. Test results indicated that the consolidation effects were significantly improved, with effectively mitigated clogging of the drainage system. Compared to the traditional method, the water content of the tested soil was reduced through the improved methods, resulting in increased uniformity of strength distribution.

A metamodel for estimating time-dependent groundwater-induced subsidence at large scales

Construction of large underground infrastructure facilities routinely leads to leakage of groundwater and reduction of pore water pressures, causing time-dependent deformation of overburden soft soil. Coupled hydro-geomechanical numerical models can provide estimates of subsidence, caused by the complex time-dependent processes of creep and consolidation, thereby increasing our understanding of when and where deformations will arise and at what magnitude. However, such hydro-mechanical models are computationally expensive and generally not feasible at larger scales, where decisions are made on design and mitigation. Therefore, a computationally efficient Machine Learning-based metamodel is implemented, which emulates 2D finite element scenario-based simulations of ground deformations with the advanced Creep-SCLAY-1S-model. The metamodel employs decision tree-based ensemble learners random forest (RF) and extreme gradient boosting (XGB), with spatially explicit hydrostratigraphic data as features. In a case study in Central Gothenburg, Sweden, the metamodel shows high predictive skill (Pearson's r of 0.9–0.98) on 25 % of unseen data and good agreement with the numerical model on unseen cross-sections. Through interpretable Machine Learning, Shapley analysis provides insights into the workings of the metamodel, which alignes with process understanding. The approach provides a novel tool for efficient, scenario-based decision support on large scales based on an advanced soil model emulated by a physically plausible metamodel.

Experimental Study on Mechanical Properties of Recycled Aggregate Mixed Soil.

In the context of efforts aimed at reducing carbon emissions, the utilization of recycled aggregate soil mixes for soil stabilization has garnered considerable interest. This study examines the mechanical properties of mixed soil samples, varying by dosage of a soft soil curing agent C, recycled aggregate R content, and curing duration. Mechanical evaluations were conducted using unconfined compressive strength tests (UCS), field emission scanning electron microscopy (FESEM), and laser diffraction particle size meter tests (PSD). The results indicate that the strength of the mixed soil samples first increases and then decreases with higher dosages of recycled aggregate, reaching optimal strength at a 20% dosage. Similarly, an increase in curing agent dosage enhances the strength, peaking at 20%. The maximum strength of the mixed soils is achieved at 28 days under various proportions. The introduction of the curing agent leads to the formation of a flocculent structure, as observed in FESEM, which contributes to the enhanced strength of the soil mixes. Specimens prepared with a combination of 20% R and 20% C, maintained at a constant moisture content of 20%, and cured for 28 days exhibit a balance between economic, environmental, and engineering performance.

Dynamic characteristics and microscopic mechanism of graphene oxide modified coastal soft soil under small strain

Graphene oxide (GO) has been shown to improve the static mechanical properties of cement soils. However, the dynamic mechanical properties of GO-modified cement soils are rarely investigated. Therefore, in this study, the effects of different confining pressures, GO contents, and curing ages on the small-strain dynamic shear modulus (G) and damping ratio (D) of GO-modified coastal cement soil (GOCS) are investigated via resonant column tests. The results show that the G of GOCS increases with the confining pressure, GO content, and curing age, whereas D decreases. Moreover, the GOCS indicate the highest stiffness improvement when 0.05 % GO is used as a modifier. The variation patterns of the maximum dynamic shear modulus and maximum damping ratio with the increase in the confining pressure, GO content, and curing age of the GOCS are consistent with the measured results. Microstructural analysis shows that the incorporation of GO can promote the early cement hydration of GOCS and increase its internal calcium-silicate-hydrate gel as well as its crystal types and numbers. The filling and bridging effects of GO not only enhance the stiffness of GOCS, thus increasing its G value, but also effectively reduce the energy consumption of the vibration wave in the sample, thus reducing its D value. The results of this study can provide important references and guidance for the design and construction of coastal soft-soil roadbed projects.

Numerical study on Slurry-induced Fracturing Pressure of Cohesive Soil

The stability of the tunnel face during the slurry shield tunnelling is controlled by the slurry pressure in the slurry chamber, and excessive slurry pressure will cause fracturing on excavation face. In order to prevent the occurrence of slurry fracturing, it is necessary to conduct a detailed study on the slurry support pressure when the slurry fracturing occurs. In this study, the hydraulic fracturing experiment of cohesive soil samples was carried out by the self-developed hydraulic fracturing device, and the improved XFEM was used to simulate the experiment process. The influence of various factors on the fracturing pressure was analyzed, and the accuracy of the numerical simulation method was also verified. In addition, the calculation method of fracturing pressure of soft cohesive soil is obtained by fitting the influence of each factor. The results show that the improved XFEM can accurately simulate the shear failure of soft cohesive soil. The fracturing pressure increases linearly with the increase in the circumferential pressure, indicating that a higher overburden of the tunnel can help resist the initial fracturing induced by shield tunneling. The fracturing pressure increases with an increase in the unconfined compressive strength as well as the slurry viscosity. Based on the regression analysis of the numerical results, an empirical approach was proposed for estimating the slurry-induced fracturing of soil.

Fully coupled finite strain consolidation analysis for soft clay treated by prefabricated horizontal drain with vacuum and heat preloading

This paper established a one-dimensional fully coupled finite strain consolidation analysis for soft clay treated by thermal prefabricated horizontal drain under vacuum and heat preloading with the consideration of thermal elastic viscoplastic (TEVP) behaviors of soft clay. Firstly, the governing equations for finite strain consolidation, heat conduction, and heat convention process have been carefully derived based on the well-established Gibson’s large strain consolidation theory and TEVP constitutive model. Secondly, the accuracy and reliability of the numerical method have been verified with benchmark cases and three physical model tests. Then, improvement of consolidation efficiency rate (IER) was defined and used to study the effect of three variables on consolidation efficiency. Last but not least, a graphical user interface (GUI) was provided to support researchers and engineers in utilizing the proposed numerical method for conducting consolidation analysis of soft soil treated in the same or similar fashion.

A Numerical Investigation on the Sinkage of the Deep-Sea Mining Vehicle Based on a Modified Constitutive Soil Model

Abstract The seabed soil of the polymetallic nodule mining area is relatively thin, soft, and fluid, which will produce large deformation under external disturbance. Its undrained shear strength is related to strain-rate and strain-softening effect. It is an important engineering safety problem for the deep-sea mining vehicle (DSMV) to travel in the soft seabed, and its sinkage is a vital index affecting the traction performance. It is necessary to study the sinkage performance of the DSMV under the characteristics of large soil deformation, but there are only few existing studies. This study established a numerical model of seabed soft soil with Tresca constitutive considering strain-rate and strain-softening effects. First, a numerical simulation study was carried out on the interaction between the DSMV track plate and the seabed soil, and the influence of track plate structures on the pressure–sinkage characteristic was obtained. Then, a simplified three-dimensional model of the “PIONEER-I” DSMV was established. Under the condition of wet weight and initial vertical velocity, the influence of different initial bottoming velocities, weight, and soil parameters on the sinkage of the DSMV was obtained. An empirical prediction model of the DSMV sinkage was established based on the energy method and numerical calculation results.

Improving the Safety of Concrete Structures on Soft Soils by Changing the Properties of the Bed

Improving the Safety of Concrete Structures on Soft Soils by Changing the Properties of the Bed

Disintegration behaviors of red clay under wet-dry cycles

Cyclic wetting-drying alternation has a significant influence on the strength and structure of soils. It is prone to causing soil softening and disintegration, highlighting the importance to improve the soil's resistance to disintegration. This paper utilizes a self-developed disintegration test apparatus to analyze the disintegration characteristics of improved red soil under wet-dry cycles, focusing on the disintegration amount and ratio. Furthermore, XRD (X-ray diffraction), SEM (scanning electron microscope), tensile test, and contact angle test are employed to investigate the anti-disintegration behaviors of the improved red soil. The results show that the disintegrating amount and ratio of undisturbed and improved red soil are distinctly different under wet-dry cycles. Linear, stepped, constant and concave but perfect "S" shapes of the disintegrating ratio are observed in the cyclic tests. Cement and lime strengthen the red soil primarily through hydration reaction. The drop experiment confirms that cement plays a crucial role in restraining the disintegration. When the ameliorant content is low, the correlation between pore parameters and disintegration duration of red soil follows the order: mean shape coefficient > fractal dimension > probability entropy > area probability distribution index. With a high ameliorant content, the correlation remains similar, with slightly higher correlation for probability entropy. Under wet-dry cycle conditions, sludge and kaolin can improve the soil through the bonding of clay particles. The improved water repellency greatly enhances the resistance to disintegration of the altered red soil. The research provides valuable insights for the practical application of soil.

Enhancement of Shear Strength Properties of Soft Clay Using Coir Fiber-Coconut Husk Ash-Wood Ash Mixture

Soft clay is a problematic type of soil because it has high water content, low shear strength, low bearing capacity, and high compressibility. This study explores the effectiveness of stabilizing soft clay using a combination of coir fiber, coconut husk ash, and wood ash. This research investigated the impact of incorporating 0.75% coir fiber and varying levels of a coconut husk ash-wood ash mixture (ranging from 0% to 10%) on the shear strength properties of soft clay. The study applied two different curing times: seven and 21 days. An unconsolidated-undrained triaxial test was conducted following ASTM D2850-03. The results demonstrated that combining coir fiber reinforcement with chemical stabilization through the ash mixture significantly enhanced the deviatoric stress, cohesion, internal friction angle, shear strength, and elastic modulus of soft soil. Specifically, an 8% ash content with a 21-day curing time achieved the highest deviatoric stress and shear strength. This highest shear strength value was 210% greater than soil solely reinforced with coir fiber.

Application of non-stationary shear-wave velocity randomization approach to predict 1D seismic site response and its variability at two downhole array recordings

Accounting for uncertainties in seismic site response is crucial to improving the performance of one-dimensional (1D) ground response analyses (GRAs) at downhole array recording sites. In addition to site effects, uncertainties in 1D-GRAs can also be contributed from the seismic source and/or path. Though often representing not more than one percent of the distance (path) from the source, site conditions are known to have an enormous influence on ground shaking. In this study, we focus on the site shear-wave velocity (VS) structure, which is the main ingredient for estimating the variability of site response. As such, VS can manifest aleatory uncertainties related to the effects of small-scale spatial heterogeneities within the near surface, thus VS can substantially modify ground shaking during earthquakes. We apply a novel VS randomization approach to propagate the small-scale heterogeneities of VS to estimate seismic site response within a non-stationary probabilistic framework. The randomization approach generates samples of VS profiles that are used to perform several 1D-GRAs and obtain an averaged site response and related variability. The proposed method is implemented on data recorded at two downhole array sites with different subsurface soil conditions: a soft soil site on Treasure Island (California, United States of America) and a rock outcrop site in Cadarache (South-East France). We show that synthetic surface-to-borehole transfer functions from 1D-GRAs provide an acceptable fit to the empirical transfer functions from low-motion earthquake records and succeed in reproducing most of the site-specific seismic response variability. The remaining mismatch between transfer functions is likely due to insufficient precision on the seismic bedrock and the impedance contrast. The variability in site response is discussed with emphasis on the role of VS small-scale heterogeneities, attenuation, and input motion incidence angle in ground motion variability for the site and soil conditions at both locations.

Analysis of factors affecting the groundwater level during foundation pit dewatering in the soft soil area: a review

Analysis of factors affecting the groundwater level during foundation pit dewatering in the soft soil area: a review