Multilayered Soil Research Articles

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

An Overview of Sandbox Experiment on Ground Heat Exchangers

As an energy-efficient and low-carbon technology, ground-source heat pumps are promising to contribute to carbon neutrality in the building sector. A crucial component of these systems is the ground heat exchanger, which has been extensively studied through sandbox experiments. These experiments play a vital role in understanding heat transfer characteristics and validating simulation results. In order to facilitate the improvement of ground heat exchangers and the development of ground-source heat-pump systems, this article provides a comprehensive summary of existing sandbox experiments. The borehole sandbox experiments are classified into the single borehole experiment, borehole group experiment, seepage experiment, and multi-layer soil experiment. It was observed that the heat transfer efficiency of a single spiral tube is only 80% compared to that of a double spiral tube. Moving on to energy-pile sandbox experiments, they are further divided into mechanical performance, thermal performance, and thermal-mechanical coupled performance tests. It was revealed that the heat transfer distance of a single U-shaped energy pile in the radial direction is three times greater than in the vertical direction. For the mentioned sandbox experiments, the sandbox design, experiment conduction, testing conditions, and result analyses are summarized. To improve the sandbox experiments, there are still some difficulties in building a similarity experiment, testing the temperatures in a small error, controlling the boundary conditions accurately, and testing the thermophysical properties of soil accurately. Furthermore, the perspectives of sandbox experiments of ground heat exchangers are also proposed. The sandbox experiments under complex environment conditions or with novel composite energy geo-structures or ground heat exchangers with new materials and new technologies would be further investigated. By addressing these aspects, this review aims to provide guidelines for the design, construction, operation, and optimization of sandbox experiments for different ground heat exchangers, ultimately promoting the wider adoption of ground-source heat pumps in achieving carbon neutrality.

Measured Rainfall Infiltration and the Infiltration Interface Effect on Double-Layer Loess Slope

It is of great theoretical and engineering significance to carry out field rainfall tests and research on double-layer soil slopes in loess areas. Based on the developed rainfall simulation system with slow-moving injection, field rainfall tests were carried out on a natural double-layer loess slope. The characteristics of volumetric water content were monitored, and the rainfall infiltration characteristics and infiltration effect at the interface of the soil layer were analyzed by numerical simulation. The results showed the fastest infiltration at the top platform of the slope, followed by that at the upper surface of the slope, and the slowest infiltration at the lower surface of the slope during rainfall. Under various rainfall intensities, the erosion of the upper silty loess slope was greater than that of the lower clay loess slope, and the erosion patterns were quite different at the end of rainfall. During the infiltration process in the double-layer loess slope, a stagnant transition area was formed near the interface of the soil layer. The equipotential line of water content in the stagnant transition area of the upper region was roughly parallel to the slope surface, and the equipotential line in the lower region was roughly parallel to the interface of the soil layer. With an increase in rainfall intensity, the upper transition area at the interface of the soil layer continued to extend from the slope surface inward, showing the interface infiltration effect that became increasingly significant with the intensification of rainfall. The infiltration effect at the soil layer interface could provide an evaluation basis for rainfall infiltration analyses of multi-layer soil slopes.

Assessment of p-y response of a laterally loaded single pile embedded in two-layered cohesionless substrata with inclined interface

ABSTRACT Laterally loaded piles embedded in multi-layered soil strata comprising inclined substratum presents a complex soil-structure interaction problem. Based on three-dimensional finite element analysis, this paper reports the response of a laterally loaded single pile embedded in two-layered cohesionless medium comprising inclined substrata. The overlying soil wedge is considered relatively weaker than the underlying stratum, and that the inclination of the wedge is considered varying along the direction of the applied lateral load. The pile-soil interaction is portrayed through p-y response at specified depths, load-deformation behaviour of the pile head and the lateral deflection profile of the pile. The outcomes manifest that the behaviour of laterally loaded pile, especially the p-y responses, is significantly influenced by the interface inclination angle, direction of loading and length-to-diameter ratio of pile. Further, the marked influence of strength and stiffness of the multi-layered strata on the p-y response of the laterally loaded pile are elucidated.

Study on structural simplified method for specific target ranges in multi-layered soil

Study on structural simplified method for specific target ranges in multi-layered soil

Amplitude-frequency characteristics of the "structure–pile foundation" layered model

Taking into account the interaction between a structure and the soil bed during an earthquake is a vital task of the seismic resistance theory. Despite a large amount of research, there is no satisfactory solution of this problem at the time being. The "platform model" applied in engineering practice can be used only for homogeneous soil beds. However, the surface stratum of soil, as a rule, has a multilayer structure, in which each individual layer has its own physical and mechanical characteristics determining the resonant properties of the entire system. The standard methods of analysis do not take into consideration the heterogeneity and layered nature of a soil bed using the averaged stiffness characteristics, which does not allow evaluating the specific features of resonance processes during the joint oscillation of a building and its soil bed. In addition, the dynamic characteristics of soils have a rather high statistical variability even within the same layer, and this can significantly affect the distribution pattern of the resonant frequencies of the system.
 The present article is aimed at investigating the dynamic response of the “building – multilayer soil bed” system based on the analytical model of a horizontal layered medium.
 The following tasks were solved:
 – an analysis of a layered system under the action of a complex sinusoidal signal was carried out with regard to damping;
 – the amplitude-frequency characteristics were constructed both for individual layers and for the system as a whole;
 – the influence of the statistical variability of the velocity of transverse seismic waves propagation on the resonant frequencies of the layered system under consideration was assessed.
 The analytical methods for the solution of the wave problem of seismology were used.

Dynamic Diffusion Model of Stray Current in DC Traction Power Supply System

The dynamic fluctuation of stray current is the main characteristic of the metro causing harm to surrounding buried metal structures. While establishing the equivalent circuit model of the return system, not only mainline but also metro depot should be considered. The diffusion models of the dynamic stray current of the DC traction power supply system (DTS) in multi-layer soil medium and massive texture soil medium are established. They are co-simulated with the DC traction power supply return system. The massive texture model (MTSM) is verified by an on-site experiment of ground potential distribution. In the case study, the direct grounding of the rail in the depot will deteriorate the ground potential gradient and stray current. When considering the impact of the river or lake, the stray current easily flows to the low resistivity texture soil, the maximum ground potential gradient increases.

Comparative Experiment and Analysis of a Base-Isolated Structure with Small Aspect Ratio on Multi-Layered Soft Soil Foundation and Rigid Foundation

Through conducting a comparative experimental study of small-aspect-ratio isolated structure models on multi-layered soft soil foundations and rigid foundations, this paper investigates the influence of soil–structure interaction (SSI) effects on the seismic response of small-aspect-ratio isolated structures on multi-layered soft soil foundations. An energy balance equation for isolated structure systems considering SSI effects is proposed, and the impact of SSI effects on the energy dissipation response of small-aspect-ratio isolated structures on multi-layered soft soil foundations is analyzed in depth. The analysis results reveal that SSI effects on multi-layered soft soil foundations reduce the first-order natural frequency of the isolated structure system and significantly increase the damping ratio of the system. Furthermore, the rotational effect of the isolated structure foundation is significant on multi-layered soft soil foundations, and the isolation layer has a certain amplification effect on the rotational effect of the foundation. The study shows that SSI effects on multi-layered soft soil foundations may either increase or decrease the seismic response of isolated structures. Moreover, due to the influence of SSI effects, the ratios of kinetic energy, damping energy dissipation, and hysteresis deformation energy dissipation of the isolated structure on multi-layered soft soil foundations are significantly different from those on rigid foundations. The research concludes that the influence of SSI effects is more significant during large earthquakes, where the ratios of kinetic energy and damping energy dissipation of the isolated structure increase, the hysteresis deformation energy dissipation ratio of the isolation layer decreases, and the magnitude of the decrease is related to the characteristics of the input seismic motion. This research has significant implications for improving the seismic design theory of small-aspect-ratio isolated structures on multi-layered soft soil foundations.

A Multi-Layer Blowout Model for the Tunneling Face Stability Analysis

The stability of the tunnel face during tunneling is one of the major criteria for the design and construction of the tunnel. Collapse and blowout are two modes of tunnel face failure during the excavation. The cover-to-diameter ratio is one of the main parameters controlling these failure modes. Several analytical solutions have been proposed to estimate the range of support pressure applied on the tunnel face to avoid both the collapse and the blowout. However, most of those models deal with homogeneous soils. This paper aims at proposing an analytical model to predict the blowout of the tunneling face of a tunnel in multi-layered soils. The derivation is based on a limit equilibrium analysis, which considers the water tCiable. The proposed model is validated against the real blowout data reported from the tunneling in the Second Heinenoord Tunnel project in the Netherlands. Then, the maximum support pressure exerted on the tunneling face is predicted as a function of the cover-to-diameter ratio, the tunnel diameter, and the water table level for five representative soils. Finally, the model is applied to an underground segment of the Hanoi Metro Line 3 project (in Vietnam) to show the role of the multi-layer aspect.

Applicability Assessment of Passive Microwave LST Downscaling over Semi–Homogeneous Desert Underlying Surface Based on Machine Learning

The spatial and temporal resolution of remote sensing products in land surface temperature (LST) studies can be improved using the downscaling method. This is a crucial area of research as it provides basic data for the study of climate change. However, there have been few studies evaluating the applicability of downscaling methods using underlying surfaces of varying complexities. In this study, we focused on the semi–homogeneous underlying surface of Gurbantunggut Desert and evaluated the applicability of five classical, passive microwave, downscaling methods based on the machine learning of Catboost, using 365 days of AMSR–2 and MODIS data in 2019, which can be scanned once during the day and night. Our results showed four main points: (1) The correlation coefficients between feature vectors and the LST of the semi–homogeneous underlying surface were clearly different from those of the surrounding oases. The correlation coefficient of the semi–homogeneous underlying surface was high, and that of the surrounding oases was low. (2) At the same frequency, the correlation coefficient between vertically polarized BT and LST was greater than that between horizontally polarized BT and LST. Considering the semi–heterogeneous underlying surface, 23.8 GHz and 36.5 GHz may be more suitable for passive microwave LST retrieval than 89 GHz according to physical mechanisms. (3) The fine–scale LST downscaling accuracy achieved with all BT channels of AMSR–2 was higher than that achieved with the other four classical models. The day and night RMSE values verified with MYD11A1 data were 2.82 K and 1.38 K, respectively. (4) The correlation coefficients between downscaled LST and the soil temperature of the top layer of the site were the highest, with daytime–nighttime R2 values of 0.978 and 0.970, and RMSE values of 3.42 and 4.99 K, respectively. The all–channel–based LST downscaling method is very effective and can provide a theoretical foundation for the acquisition of all–weather, multi–layer soil temperature.

Study on Stability of Excavation Surface of Shield Tunnel in Clay Layer

If an excavation surface becomes unstable, it will cause damage such as soil collapse or surface uplift. Through field investigations and tests, the stability of the shield tunnel excavation surface and its influencing factors are studied in this paper. Equations for solving the limit support pressure of the excavation surface of the overlying multilayer soil tunnel and for the safety factor of the excavation surface are deduced. The single reduction method and the double reduction method are respectively used to solve the safety factor of the excavation face under the basic working conditions, and the numerical simulation method of the safety factor of the excavation face is clarified. Based on FLAC3D numerical simulation software, the ultimate support pressure and safety factor were used as the evaluation criteria for the stability of the excavation face to analyze the response of objective factors such as internal friction angle and cohesion, as well as engineering factors such as hole diameter to the stability of the excavation face. The greater the internal friction angle and cohesion, the smaller the hole diameter, the more stable the excavation surface, and the internal friction angle has the greatest impact on the stability of the excavation surface.

Analytical solution for laterally loaded non-uniform circular piles in multi-layered inhomogeneous soil

ABSTRACT Non-prismatic piles are typically used in cases where large lateral loads must be resisted. In many applications, piles are partially or fully embedded in multi-layered non-homogeneous soil, with each layer having its own set of properties. Analytical, simple solutions to study this problem are more limited and complex than that of prismatic ones. The analysis becomes even more complicated when both the variation of the cross-sectional area of the element and the soil inhomogeneity are included in the formulation. This work presents the derivation of the stiffness matrix and load vector of a non-uniform section of pile partially or fully embedded in non-homogeneous soil. The analysis of non-uniform piles in multi-layered soil is carried out by dividing the pile into multiple sub-elements and then assembling them using conventional matrix methods. Four examples, encompassing partially and fully embedded piles, are presented to validate the simplicity and accuracy of the proposed solution.

Effects of Uncertain Soil Parameters on Seismic Responses of Fixed Base and Base-Isolated Liquid Storage Tanks

ABSTRACT Effects of soil-structure interaction (SSI) on the seismic performance of cylindrical ground-supported liquid storage tanks are studied. The present study attempts to investigate the effects of uncertainties, associated with the critical soil parameters, on the seismic behavior of liquid storage tanks. Random multi-layered soil models coupled with the fixed base liquid storage tank are developed and analyzed. Further, the tank structure is considered base-isolated with lead rubber bearing and analyzed with the same set of soil models, to investigate the seismic behavior of base-isolated tank under uncertain soil condition. A set of three ground motions are selected from a large suite through a mean spectral matching scheme for investigating the effect of soil uncertainties on the seismic response. Distributions of the peak seismic response quantities observed herein show that the uncertainties in soil parameters critically affect the seismic responses of fixed base and base-isolated liquid storage tanks. Sloshing displacement of fixed base and base-isolated tanks is affected by both uncertainty in the soil parameters and ground motion characteristics. Nevertheless, for ground-supported tank, relatively larger dispersion or variability of base shear and overturning moment, as compared to that of the sloshing response, is observed.

Case study of spudcan punch-through in layered soil with interbedded thin stiff clay

Punch-through failure may occur when the spudcan is installed in layered soil, which can result in a detrimental effect to the jack-up unit and jeopardize personnel. This paper introduced a practical case of spudcan punch-through which occurred in a kind of multi-layer soil which has a thin stiff layer and a transition layer locating between soft layers. The existence of the transition layer blurs the difference of soil strength. To explore the failure mechanism set behind the field case, LDFE analyses were conducted with the Coupled Eulerian-Lagrangian (CEL) method. The results indicated that the failure of soil changes between three failure mechanisms of general shear, punch-through and squeezing with the penetration of spudcan. The transition point of failure mechanism can be identified through the depth of failure surface based on the LDFE results. According to the failure mechanism, a modified approach was set out in estimating the spudcan penetration resistance in the multi-layer soil, which matches the field data well on the basis of the soil strength obtained by laboratory element tests.

Applying the strength reduction method to study of stability of residual mountains: A particular application

Due to huge disaster-caused force, seismic geological disasters primarily induce residual landslide, collapse and debris flow disasters with far higher hazard extent than that of earthquake disasters. Wherefore, this paper, with various vibration slopes caused by the most representative Wenchuan earthquake as research objects, introduces the strength reduction method to the stability study of residual mountains in a certain area, puts forward dynamic stability slope evaluation method based on dynamic and overall strength reduction method to obtain the mountain slope stability situation in the process of gradual instability, searches out the sliding surface of progressive expansion making use of dynamic strength reduction method and calculates dynamic safety index in the process of gradual slope instability pursuant to the calculation advantages of dynamic strength reduction method, so as to realize the analysis and regulation of the whole process of slope instability. The results show that in the stability analysis of a homogeneous slope, the safety index of slope stability calculated by strength reduction method is 6.7%, 8.8% and 10.5% higher than that calculated by finite element limit equilibrium method, Bishop method and Janbu method respectively. In the stability analysis of a multi-layer soil slope, the safety index of slope stability calculated by strength reduction method is 4.8%, 4.3% and 9.4% higher than that calculated by other three algorithms. While in the stability analysis of soft interlining slope, the safety indexes of slope stability calculated by the method proposed in this paper are increased by 26.10%, 29.11% and 26.46% respectively compared with other three algorithms, indicating that the stability of landslide residual mountains calculated by strength reduction method proposed in this paper is the highest.

Nonlinear Settlement Calculation of Composite Foundation Based on Tangent Modulus Method: Two Case Studies

The tangent modulus method of undisturbed soil is a new method in settlement calculation, which is mainly applied to hard soil with a strong structure, such as silty clay, completely weathered rock, and granite residual soil with an SPT blow count greater than 8. The tangent modulus is mainly obtained from a field plate load test, which can consider the influence of the soil stress level and reflect the nonlinear characteristics of the foundation settlement. In a multi-layer soil foundation, since the deep plate loading test is difficult, a method was proposed to determine the tangent modulus of deep soil. It is assumed that the ratio of the initial tangent modulus to the deformation modulus is equal to the ratio of the unloading–reloading modulus Eurref to the secant modulus E50ref obtained by triaxial unloading–reloading test. Since there are corresponding empirical formulae for SPT counts and the deformation modulus of different types of soils in many regions, the initial tangent modulus can be derived by the above method. In two cases of a composite foundation, the compression modulus and tangent modulus were used to calculate the settlement of the foundation, which is then compared with the measured results. The results show that the proposed method for determining the tangent modulus of deep soil is feasible in theory, and the calculating accuracy of the tangent modulus is significantly higher than that of the traditional compression modulus.

Inversion of one‐dimensional parameters of horizontal multi‐layer soil model based on dynamic state electromagnetic field theory and ant colony optimization algorithm

AbstractBuilding a reliable soil model is a prerequisite for accurately calculating the ground potential distribution of the grounding grid. Research shows that the soil electrical parameters are frequency‐dependent, so frequency domain inversion of soil parameters should consider the soil inhomogeneity and the frequency characteristic of parameters. A method for retrieving parameters of horizontal multilayer soil model is proposed. The theoretical formula of apparent complex resistivity with considering dynamic state electromagnetic field theory is derived from Green's function. Discrete dynamic state complex image method is introduced to solve the infinite integral in Green's function. Ant colony optimization algorithm is applied to optimize the inversion process of soil parameters. In the first stage, applicability of this method is confirmed by interpreting field data under DC field. DC parameters including DC resistivity, thickness and number of layer are determined. The performance of different optimization algorithms in terms of computational efficiency is compared at this stage. In the second stage, soil resistivity and relative dielectric constant are retrieved by inverting frequency domain experimental data. Different representations based on quasi‐static electromagnetic field and dynamic state electromagnetic field theories are taken into account. The frequency characteristic of soil parameters is concluded by discussing the inversion results. In the study of parameter inversion of horizontal multi‐layer soil model, our method has shown strong performance in computational efficiency and accuracy of inversion results.

Liquefaction behavior evaluation of a multi-layered site with fines-dominated soils

Characterization of liquefaction response in terms of triggering and manifestation at sites with soils containing significant amounts of fines is critically important. Saturated fines-dominated soils, that are known as liquefaction-susceptible materials, would represent a range of extreme responses to earthquake excitations from cyclic mobility to cyclic liquefaction causing excessive displacements. In a multi-layered soil profile, the interaction of adjacent layers in porewater pressure redistribution along the site profile plays an important role in liquefaction response. In this study, an advanced Nonlinear Dynamic Analysis (NDA) procedure in predicting the liquefaction mechanism and manifestation at a site with multiple fines-dominated soil layers is presented. The procedure specifically aims at simulating the interactions in a multi-layered system containing both sand-like and clay-like materials. The liquefaction data recorded by Wildlife Liquefaction Array (WLA) in 1987 Superstition Hills Earthquake (M = 6.6) was deployed to validate the NDA procedure. WLA site consists of sandy silt, silty sand, clayey silt, silty clay, and silt deposits in its upper 20 m and has provided invaluable records of porewater pressure and ground motions. Two critical-state-based constitutive models, PM4Silt and PM4Sand, in a coupled dynamic-fluid finite difference platform were employed. Calibration of the constitutive models was conducted using Cyclic Direct Simple Shear (DSS) test single-element modeling. The simulated response of the site from the proposed approach was compared with those of other NDA procedures conducted on this case history in terms of liquefaction parameters such as excess porewater pressure ratio and maximum shear strain. These comparisons revealed that incorporating multi-layer effects in an advanced NDA procedure can enhance the liquefaction behavior predictions at sites with fines-dominated materials.