Multilayered Soil Research Articles

Bio-inspired branch structure seismic metamaterial: attenuating low-frequency Rayleigh waves

This study investigates the transmission characteristics of natural forests with branches and introduces a bio-inspired branch structure seismic metamaterial (SM) designed to create bandgaps for low-frequency Rayleigh waves. Employing the finite element method, we reveal the mechanism behind the generation of these Rayleigh wave bandgaps and their transmission properties. A distinct ‘collectivization mode’ within the bio-inspired branch structure SM is identified, effectively attenuating Rayleigh waves. A collectivization coefficient is introduced for quantitative characterization, and we extend the analysis to multi-layered soil mediums, demonstrating an interface with the metamaterial’s bandgaps. The frequency-domain analysis highlights the difference between using the collectivization mode and traditional methods for attenuating surface waves, offering a novel approach to low-frequency Rayleigh wave reduction with implications in seismology and related engineering fields.

Development of a multi-way coupled discrete-finite element method simulation procedure for modelling soil-passive vibration tool interaction

Among the energy-saving tillage solutions, a promising technology is the application of passive vibration-based soil tillage tools. If the appropriate tillage parameters are applied, a tillage tool which involves vibration-based motion can reduce the draught force and energy requirements of the tillage process while enhancing its quality. The main focus of our research was on developing a coupled discrete-finite element procedure to investigate the interaction between passively vibrating tools and the soil. To validate this method, a soil bin measuring system was constructed to investigate the operation of a highly rigid structural steel (S235) tool along with a more flexible polymethyl methacrylate (PMMA) tool, with the soil bin at working depths of 18, 30, and 42 mm, tool velocities between 28 and 37 mm s−1, in sandy soil with 1 ± 0.1 % dry based moisture content. Soil bin measurements with the highly rigid S235 tool were simulated using the discrete element method (DEM) along with a coupled discrete-finite element (DEM-FEM) procedure, while the soil bin measurements applying the more flexible PMMA tool were simulated using the coupled DEM-FEM procedure. In the case of DEM calculations the hysteretic spring and linear cohesion contact models were applied, and in the case of FEM calculations the transient, linear elastic model was utilised with Rayleigh damping. During the parameter calibration process it was observed that the soil properties depend on depth, therefore a multi-layered soil model was created. After parameter calibration the simulated mean force and deformation values matched the measured values with less than 15 % difference. Furthermore the simulation results also supported the assumption that passively vibrating tillage tools loosen and mix the soil more effectively. Based on these results, it can be concluded that the coupled DEM-FEM procedure enabled the accurate modelling of passively vibrating tillage tools.

Lightning Response Transient Characteristics of Substation Grounding Grid in Multilayer Horizontal Stratified Earth Model Considering Soil Ionization Effect

This article proposes a new time-domain partial element equivalent circuit method mathematical model. The mutual impedance matrix between the potential on the discrete node and the leakage current on the conductor connected around the discrete node is adopted. To reduce the amount of calculation, the matrix equation that minimizes the unknown quantity is derived and adopted. The model can accurately calculate the lightning current distribution and lightning impulse response in a horizontal multilayered soil model considering the soil ionization effect. To improve computational efficiency, the quasi-static complex image method and its closed form of Green's function in the time domain are introduced into the model.

Evaluation of Overall Response of Driven Pile in Multi-layered Soil

Evaluation of Overall Response of Driven Pile in Multi-layered Soil

Probabilistic analysis of ground settlement induced by tunnel excavation in multilayered soil considering spatial variability

Accurately evaluating and predicting the ground settlement during tunnel excavation are crucial for ensuring the stability of tunnel structures. However, the traditional methods always use representative (or average) values for deterministic analysis and rarely consider the spatial variability of soil properties. In this study, a probabilistic analysis of ground settlement under uncertain soil properties was performed based on random fields combined with the finite-difference method. The random fields of Young’s modulus and friction angle of multilayered soils were generated based on the Cholesky decomposition in a manner consistent with a specified numerical mesh. The effects of spatial variability and cross-correlation in random fields on the ground settlement were investigated in detail. The results demonstrate that spatially variable soils significantly influence the probability of failure, magnitude, and longitudinal profile of ground settlement in the vertical direction. It can be found that the allowable ground settlement of the limit state function also dominated the degree of the vertical scale of fluctuation on stability. Neglecting the cross-correlation between the two random fields results in an overestimation of the probability of failure compared with an independent analysis. Subsequently, the failure mechanisms of ground settlement in spatially random soils were discussed.

Theoretical prediction of ground settlements due to shield tunneling in multi-layered soils considering process parameters

This paper conducts a theoretical analysis of ground settlements due to shield tunneling in multi-layered soils which are usually encountered in urban areas. The proposed theoretical solution which is based on the general form of the Mindlin's solution and Loganathan-Poulos formula can comprehensively consider the in-process tunneling parameters including: unbalanced face pressure, shield-soil friction, unbalanced tail grouting pressure, unbalanced secondary grouting pressure, overloading during tunneling and the ground volume loss. The method is verified by comparing with the field data from the Qinghuayuan Tunnel Project in terms of the ground surface settlements along the longitudinal and transverse direction. Due to the local settlement or heave caused by the certain tunneling parameters, the ground surface settlements calculated using current solution along the longitudinal direction presents an irregular S-shaped curve instead of the traditional S-shaped curve. Results also find that the effect of the unbalanced secondary grouting pressure and the overloading during tunneling cannot be ignored.

Fluid and Thermal Analysis of Pre-Columbian Tiwanaku (500–1100 CE) Raised-Field Agricultural Systems of Bolivia

Raised-field agricultural systems have received attention from scholars involved in the analysis of prehistoric agricultural intensification in the New World. This paper discusses the function of raised fields associated with the Tiwanaku society (500–1100 CE) located on the southern rim of Lake Titicaca in Bolivia. The overnight internal heat storage capacity of Tiwanaku raised-field berms located at the high-altitude (~3810 masl) Bolivian altiplano is analyzed through ANSYS (version 4.2B) finite difference methods to provide an understanding of ancient agricultural engineers’ knowledge regarding how to protect crops from nightly subzero freezing temperatures and water saturation. The present analysis concludes that enhanced berm heat storage capacity derived from solar radiation into multi-layered moist berm agricultural soils, together with radiative heating of berm-surrounding swale water (swale water depth determined from excavation into the groundwater aquifer), was an essential Tiwanaku design element of raised-field agriculture to protect crops from freezing damage during both wet and dry seasons. This paper reports the ANSYS temperature distribution results derived from a raised-field berm swale computer model of ancient excavated raised fields in the form of a 24 h heat input and cooling cycle, which indicates the presence of an internal berm heat storage effect designed to protect crops from freezing damage. The calculations performed use specific hydrological and climatological conditions characteristic of the littoral and near-shore environment of Lake Titicaca. The use of the ANSYS finite element code to investigate the source of internal berm heat storage protecting crops from freezing temperatures, compared to the field test results from experimental use of reconstructed ancient, raised fields, provides an understanding of the technologies developed by Tiwanaku agricultural engineers to increase raised-field agricultural production.

Modelling smear effect of vertical drains using a diameter reduction method

Vertical drains are used to accelerate consolidation of clays in ground improvement projects. Smear zones exist around these drains, where permeability is reduced due to soil disturbance caused by the installation process. Hansbo solution is widely used in practice to consider the effects of drain discharge capacity and smear on the consolidation process. In this study, a computationally efficient diameter reduction method (DRM) obtained from the Hansbo solution is proposed to consider the smear effect without the need to model the smear zone physically. Validated by analytical and numerical results, a diameter reduction factor is analytically derived to reduce the diameter of the drain, while achieving similar solutions of pore pressure dissipation profile as the classical full model of the smear zone and drain. With the DRM, the excess pore pressure u obtained from the reduced drain in the original undisturbed soil zone is accurate enough for practical applications in numerical models. Such performance of DRM is independent of soil material property. Results also show equally accurate performance of DRM under conditions of multi-layered soils and coupled radial-vertical groundwater flow.

Metagenomics insights into the performance and mechanism of soil infiltration systems on removing antibiotic resistance genes in rural sewage

The removal of antibiotic resistance genes (ARGs) in sewage is of great concern, but advanced sewage treatment technologies are not suitable for rural areas, so the multi-layer soil infiltration system (MSL) has been developed for rural sewage treatment. However, little is known about the performance and function of MSL in the treatment of ARGs in rural sewage. Here, we optimized the matrix composition and structure of MSL and explored the efficacy and mechanism of MSL systems for ARG removal under different hydraulic conditions. The ARGs removal rate of MSL ranged from 41.51% to 99.67%, in which MSL with the middle hydraulic load, high pollution load, and continuous inflowing conditions showed the best removal performance. In addition, this system can operate stably and resist the temperature fluctuation, which showed an equivalent removal rate of ARGs in warm and cold seasons, amounting to 69.0%. The structural equation model revealed that microorganisms in sewage could significantly affect ARG removal (path coefficient = 0.91), probably owing to their interspecies competition. As for the internal system, the reduction of ARGs was mainly driven by microorganisms in the system matrix (path coefficient = 0.685), especially soil-mixture-block (SMB) microorganisms. The physicochemical factors of the matrix indirectly reduce ARGs by affecting the microorganisms that adhere to the matrices. Note that the pairwise alignment of nucleotide analysis demonstrated that the system matrix, especially biochar in the SMB, adsorbed ARGs and their hosts from the sewage, and in turn eliminated them by inhibiting the spread and colonization of hosts, thereby reducing the abundance of ARGs. Collectively, this study provides a deeper insight into the removal of ARGs from rural sewage by MSL, which can help improve sewage treatment technologies.

Numerical solution for nonlimit-state earth pressure considering interlayer shear stress and the soil arching effect

The earth pressure of multilayer cohesive soils is affected by interlayer interaction and the soil arching effect. However, only the soil arching effect is considered in the existing methods for calculating earth pressure, and the interlayer shear stress caused by principal stress deflection is ignored. For a vertical rigid retaining wall with a horizontal backfill surface, the trajectory of the minor principal stresses in the soil behind the wall takes the form of an arc of a circle. On this basis, the horizontal and vertical stress equilibrium equations of the differential soil elements behind the wall are derived. The interlayer shear stress, wall displacement and soil arching effect are incorporated into the horizontal slice model, and the numerical scheme of the nonlimit-state earth pressure, the resultant force and the location of the action point are determined with the numerical solution method. Furthermore, the rationality of the proposed solution is demonstrated through comparison with experimental data and other solutions.

The Efficiency of Belled Piles in Multi-Layers Soils Subjected to Axial Compression and Pullout Loads: Review

Multi-belled piles are piles with enlarged ends; these piles have one or further bells at the lower third part of the pile. These piles are suitable for many soils with problems such as softening clay, the variation of groundwater table, expansive soils, black cotton soil, and loose sand. The current study reviewed the behavior of belled piles in multi-layer soils subjected to axial compression and pullout loading. The review covered the experimental and theoretical works on belled piles in multi-layered soils. These piles were subjected to static and dynamic loadings in compression and pullout cases. Most theoretical results focused on software such as PLAXIS 3D. The axial load applied on the piles comes from the upper structure built above these piles, and negative skin friction comes from groundwater. The results obtained from previous studies showed the validity of using such piles in different types of soil and multilayer soils. According to previous studies, this study aims to find all the things about the belled piles, including the best shape of the belled pile being the half cone and the worst state being when the bell is fully cone. The best number of belled piles is two bells because the bearing capacity increases when the number of bells increases but does not exceed two due to hard work and high cost. The best location of a bell is at the base of the pile. The current study showed that the bearing capacity increased from 40% to 73.75% compared with ordinary piles.

Displacement-based finite element approach on analysing flexible combined pile–raft foundation in layered soil

The present study proposes a new finite element methodology to analyse the behaviour of flexible combined pile–raft foundation (CPRF) situated in layered soil, in a displacement-based framework. The soil medium is idealised as an advanced elastic Pasternak medium and the piles and raft are modelled as bar and plate element, respectively. The two components of CPRF are analysed simultaneously and displacement compatibility is satisfied at the pile–raft junctions. A number of soil–structure interaction factors, which govern the behaviour of CPRF, are suitably subsumed in the analysis scheme. The proposed method is validated with available analytical and experimental studies. Further parametric studies, investigating the effects of soil layering and raft flexibility on the behaviour of CPRF, are explored. It is observed that the load sharing proportion between the components and the raft deformation pattern depend upon the thickness and position of the soft soil layer in a multilayered soil system. The thickness of the flexible raft plays a pivotal role in determining the behaviour of CPRF, founded in a multilayered soil profile. Thus, this research manifests notable advancement in understanding the behaviour of flexible CPRF in layered soil.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3mm and 0.4-0.6mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experimentsdepicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.

Capacity prediction and design optimization for laterally loaded monopiles in sandy soil using hybrid neural network and sequential quadratic programming

Data driven methods have gained momentum in recent years in solving highly non-linear engineering problems that are challenging to solve using conventional methods. In this paper, we present a hybrid neural network model to predict the lateral response of large-diameter monopiles in multi-layered soil. The hybrid neural network consists of a mixture of convolutional and fully-connected layers, which capture the impacts of the soil profile, the pile geometry, and loading conditions on the lateral load response of monopiles. To train the neural network model, we produced data from high-fidelity three-dimensional (3D) finite element (FE) models that are validated against full-scale pile load tests. To ensure consistent model performance across the entire range of pile capacities considered in the dataset (ranging from approximately 100 kN to 100,000 kN), we utilize the relative error (percentage error) as the criterion for training the model. To achieve this goal, we explored six different combinations of data transformation methods (i.e., natural logarithm and root transformations) and cost functions. Among these models, the model trained with Mean Squared Error (MSE) using natural logarithm transformation yielded the most accurate and consistent predictions of the lateral capacities of monopiles. To demonstrate the strengths of the developed neural network model, it was used as a surrogate model to perform pile design optimization using sequential quadratic programming. In addition, a design example is provided to show how the developed method can be easily implemented.

Field Testing and Numerical Simulation of the Effectiveness of Trench Isolation for Reducing Vibration Due to Dynamic Compaction

Dynamic compaction is a widely used method to strengthen the foundation, which can cause significant impacts on surrounding structures, making vibration control measures necessary. This study investigates the effectiveness of isolation trenches in reducing ground vibration caused by dynamic compaction in a typical multi-layered alluvial soil foundation adjacent to the Yangtze River. A combination of field testing and numerical simulation was employed to evaluate the vibration isolation effect of trenches at different depths and locations. The results show that trenches have a significant vibration isolation effect on the side away from the tamping point, but they can have an amplifying effect between the trench and tamping point. The effectiveness of the isolation trenches increases with deeper trenches and distance from the tamping point, but the amplification effect decreases with increasing depth. Therefore, when employing trenches, reinforcement measures must be adopted, and a suitable trench depth should be selected. The closer the isolation trench to the dike, the better the protection will be. The study provides effective guidance for designing isolation trenches in similar dynamic compaction processes, emphasizing the importance of considering spatial attenuation characteristics and selecting appropriate trench depths and locations.

Probabilistic analysis of tunnel face stability in spatially variable soil

the limit analysis incorporated with the random field theorem is an effective approach for the probabilistic analysis of tunnel face stability. However, the existing incorporation procedure is not sufficiently efficient and accurate. A modified random field model, which is directly superimposed onto the rotational failure mechanism, is proposed to address this issue. In comparison with previous methods, the proposed approach avoids the generation of redundant random field elements and evades the inaccurate matching procedure of the elements, thereby enabling efficient and accurate estimation of the failure probability of a tunnel face. Moreover, cross-correlated random fields with the rotated anisotropy are readily generated with the proposed approach. Parametric sensitivity analysis is performed with Monte Carlo simulations to investigate the effects of the coefficient of variation, the scale of fluctuation, cross-correlation coefficient, and rotated anisotropy on the failure probability of a tunnel face. It is found that: (1) the failure probability is more sensitive to the scale of fluctuation in the vertical direction than that in the horizontal direction; (2) neglecting the cross-correlation of soil shear strength parameters leads to a slightly conservative design for tunnel face stability; (3) the influence of rotated anisotropy on the failure probability of a tunnel face is limited unless the soil exhibits high levels of uncertainty in its friction angle. Application of the proposed approach to multi-layered soil demonstrates its superiority in the probabilistic analysis of tunnel face stability in spatially variable soil.

Consolidation of multilayered soil with fractional derivative viscoelasticity due to surface loading and internal pumping

Classical Terzaghi’s solution provides a useful tool to predict the one-dimensional consolidation of homogeneous elastic soil layer with fully drained/undrained boundary condition under instantaneous loading. Due to the sedimentation process and complex internal structure, natural soils usually exhibit multilayered inhomogeneity and viscoelastic behavior. In practical cases, the drainage capacity of the boundaries can change with time. Thus, these practical factors should be well in considered for accurate prediction of the consolidation. This paper extends the classical Terzaghi’s solution to multilayered viscoelastic soil with continuous drainage boundaries and subjected to time dependent loading. The fractional derivative Kelvin-Voigt model is used to describe the viscoelasticity of soil. Two loading cases namely surface loading and internal pumping are considered. The consolidation problem is solved by Laplace transform technique and a transfer matrix formulation. Analytical solutions for excess pore water pressure, effective stress and settlement are given. The present solution is general and can reduce to existing solutions available in the literatures. Numerical studies are conducted to investigate the effects of viscoelastic parameters, boundary drainage capacity and loading rate on the consolidation behavior. It is shown that the multilayered soil system with large viscosity coefficient and small fractional order can consolidate fast. For the consolidation due to internal pumping, the drainage parameters have no influence on the consolidation process.

Study of seismic vulnerability of steel frame structures on soft ground considering group effect

Earthquakes have caused increasingly severe casualties and economic losses in coastal urban areas where soft soils are widely distributed. To mitigate disaster losses, this paper aims to investigate the mechanism of the group effect, the interaction between a group of buildings (at least three) through the foundation, on seismic vulnerability in coastal urban areas. Firstly, the analysis models are established, and the validity is subsequently verified. Meanwhile, a self-built automatic iterative calculation program for multilayer soils is adopted to consider the nonlinearity of the soft soils. On this basis, probabilistic seismic demand analyses are further performed using ten earthquake ground motions. The seismic vulnerability formulas of the structures are obtained in combination with the probabilistic seismic demand models. Finally, the influence of the group effect on the seismic performance of the structures is evaluated from different perspectives based on the vulnerability formulas. The results indicate that the group effect of the steel frame structures makes the performance margin ratio (PMR) significantly higher and reduces the seismic vulnerability of the structures in coastal urban areas. The mechanism revealed in this paper presents a more accurate way to conduct earthquake-resistant design, provides guidelines for setting the criteria, and is likewise instructive to the seismic design of other structural forms.

Offshore Wind Turbine Monopile Foundation Systems in Multilayered Soil Strata under Aerodynamic and Hydrodynamic Loads: State-of-the-Art Review

Due to the large demand to produce clean and renewable energy, offshore wind farms are extensively being used to help with economic development. Offshore Wind Turbine (OWT) structures are usually supported by various types of foundations and its selection depends on several factors such as water depth, economic costs, construction methodologies, seabed bathymetry, soil characteristics, and load characteristics. The present State-of-the-Art review focuses on OWT-monopile foundation systems embedded in multi-layered soil strata subjected to aerodynamic and hydrodynamic loading conditions. The purpose of this study is to carry out a comprehensive review on the performance of OWT-monopile foundation structures to support the design and drafting choices and thereby provide an understanding to reduce the costs. Two specific subject areas are addressed in this paper: (1) Factors affecting the performance of OWT-Monopile Foundation Systems; and (2) Experimental modeling and numerical analyses of OWT-Monopile Foundation Systems. The immediate challenge to the design of OWTs is to analyze the dynamic response of the foundation structure when exposed to both aerodynamic and hydrodynamic loads acting simultaneously. The limitations of the existing guidelines point to the need for improved design methods to obtain an economical design of OWT-monopile foundations. The use of Finite Element (FE) models is effective in studying the functioning of OWT-monopile structures. The present study suggests the development of further numerical models and modifications to the existing ones to properly assess soil-monopile interactions. This study also suggests further investigations on the design and analysis of OWT-monopile foundations considering the effect of (i) aerodynamic and hydrodynamic loading conditions with soil-monopile interactions, and (ii) multi-layered seabed characteristics.

Parametric Analysis of Conductive Coupling of Transmission Line Tower Grounding and Pipeline in Multilayer Soil

Parametric Analysis of Conductive Coupling of Transmission Line Tower Grounding and Pipeline in Multilayer Soil