Far-field Soil Research Articles

An analytical model for permeability coefficient of soil-structure interface composed of different capillaries

The soil-structure interface, representing the contact surface between soil and structures such as buildings or rocks, assumes critical importance in water-related projects like earth dams, cut-off walls, side slopes, foundation pits, and water tunnels. Monitoring reports and studies consistently identify this interface as a vulnerable zone susceptible to seepage-related accidents. Despite this recognition, research on the topic has been limited, with a predominant focus on experimental methods that tend to underestimate permeability. This paper presents an analytical model, grounded in capillary theory, for calculating the permeability coefficient of the soil-structure interface. The study explores the differences in permeability between the interfacial soil and far-field soil. The study concludes that the higher porosity of the interfacial soil (porosity ≥ 0.48) compared to the far-field soil (porosity: 0.26–0.48) is a key factor in rendering the soil-structure interface susceptible to seepage. The calculated permeability coefficient of the interface, in relation to experimental values, exhibits a consistent ratio of 2.5–2.6 when the soil porosity is below 0.43, indicating reliable predictive utility. Moreover, the permeability coefficient of the interfacial soil proves to be at least 4.05–6.67 times larger than that of the far-field soil, potentially leading to the creation of preferential seepage channels at the interface.

Numerical investigation of the seepage mechanism and characteristics of soil-structure interface by CFD-DEM coupling method

Interfacial seepage on soil-structure interface is common in water-related engineering, such as dam, culvert, water tunnel, foundation pit, etc. As a weak part in the project, seepage failure on soil-structure interface has caused many project accidents. However, there are few studies on the seepage mechanism analysis of soil-structure interface. In this paper, a series of numerical tests of interfacial seepage are carried out using CFD-DEM coupling method. The seepage mechanism and characteristics of different soil layers in the seepage device are analyzed and a formula for calculating the critical hydraulic gradient of the interface is discussed. The main conclusions are as follows: (1) The seepage flow on soil-structure interface will go through three stages: stability stage, transition stage and particle erosion stage; (2) The porosity and flow velocity of soil on the interface are greater than those in the far-field soil at the beginning of seepage flow; (3) The particle erosion on the soil-structure interface occurs earlier and the erosion degree is more serious than that of the far-field soil; (4) The critical hydraulic gradient of the interface rises nonlinearly with the increase of the degree of soil compaction; (5) The formula for calculating the critical hydraulic gradient of the interface could predict the numerical test results well.

Evaluation of the Performance of a Heat Pipe for Pre-Frozen Soil around a Solar Support by a Numerical Method

The base of solar collector systems is usually installed in soil that contains moisture. In cold regions, due to the low ambient temperature, the moisture in the soil freezes, creating a risk of frost heave. This study analyzed the frost heave mechanism of power transmission and transformation foundation, clarified the factors affecting soil frost heave and the way to solve soil layer frost heave, and proposed the use of heat transfer elements to pre-frozen soil layers to prevent the foundation of the solar collector system from freezing. A numerical model of the ground heat exchange pipes in soil was established. The effects of different soil types, soil moisture content, and the effective radius and operating time on the heat transfer performance of the system were investigated by the verified numerical model. The results show that the heat pipe pre-freezing technology can reduce the drop in soil temperature, thereby increasing the temperature difference between the ground heat exchange pipe and the far-field soil. In terms of the ability to delay the decline in soil temperature, reducing the water content and selecting certain clays can increase the degree and speed of the drop in soil temperature.

Study of the effect of seismic performance measures on a metro station structure in liquefiable soil

After the concept of ‘resilient city’ was introduced, the anti-seismic and resilience enhancement of underground structures gradually became an important issue in engineering. In this study, a method for enhancing the resilience of a soil–structure system subjected to earthquakes is proposed. First, a water-soil fully coupled numerical model was established to analyse the seismic behaviour and enhancement effect of a station structure subjected to an earthquake in liquefiable ground. In the analysis, an elastoplastic cyclic mobility model was used to describe the soil behaviour, whereas an interface joint element model was used to consider the soil-structure interaction. Subsequently, a non-liquefied clay replacement method was designed, and the effects of the replacement position and thickness on the floating displacement and internal force of the structure were analysed. To fully utilise the cushioning effect of the liquefiable sand and the anti-floating drainage near the station structure, a unilateral drainage diaphragm wall that does not drain in the far-field soil and drains in the near-field soil is proposed around the station structure. Based on the analysis results of different cases considering the soil replacement position, replacement thickness, distance between the unilateral drainage diaphragm wall and station structure, and buried depth of the wall, combined measures of clay replacement with unilateral drainage diaphragm wall were examined. The results show that the combination of the two measures significantly reduced the floating displacement, restrained the additional internal forces of the structure, reduced the time for the structure to reach stability after an earthquake, which is helpful to enhance the ability of self-recovery and improve the seismic resilience of the underground structure.

2D and 3D soil finite/infinite element models: modelling, comparison and application in vehicle-track dynamic interaction

ABSTRACT In this work, 2D and 3D vehicle-track-soil (VTS) models are developed in a coupled manner. The VTS system is modelled as an integration of the multi-rigid-body vehicle sub-model, multi-scale finite element ballastless track sub-model and finite/infinite element (FE/IE) soil sub-model, where the IE method is introduced to deal with the boundary condition of the far-field soil. Particularly, the detailed approach for modelling the FE/IE soil sub-model is depicted in the 2D and 3D space domain, respectively. Through comparisons, it is proved that the IE method shows advantages in simulating the soil far-field region by meeting a soil boundary condition. Case studies are conducted to demonstrate the superiority and applicability of this model in improving the computational efficiency. Besides, the influence of vehicle speed on system dynamic performance is revealed, where the soil critical speed derived by the soil Rayleigh surface wave speed is explored by the vehicle-induced vibrations.

Towards disentangling heterogeneous soil moisture patterns in cosmic-ray neutron sensor footprints

Abstract. Cosmic-ray neutron sensing (CRNS) allows for non-invasive soil moisture estimations at the field scale. The derivation of soil moisture generally relies on secondary cosmic-ray neutrons in the epithermal to fast energy ranges. Most approaches and processing techniques for observed neutron intensities are based on the assumption of homogeneous site conditions or of soil moisture patterns with correlation lengths shorter than the measurement footprint of the neutron detector. However, in view of the non-linear relationship between neutron intensities and soil moisture, it is questionable whether these assumptions are applicable. In this study, we investigated how a non-uniform soil moisture distribution within the footprint impacts the CRNS soil moisture estimation and how the combined use of epithermal and thermal neutrons can be advantageous in this case. Thermal neutrons have lower energies and a substantially smaller measurement footprint around the sensor than epithermal neutrons. Analyses using the URANOS (Ultra RApid Neutron-Only Simulation) Monte Carlo simulations to investigate the measurement footprint dynamics at a study site in northeastern Germany revealed that the thermal footprint mainly covers mineral soils in the near-field to the sensor while the epithermal footprint also covers large areas with organic soils. We found that either combining the observed thermal and epithermal neutron intensities by a rescaling method developed in this study or adjusting all parameters of the transfer function leads to an improved calibration against the reference soil moisture measurements in the near-field compared to the standard approach and using epithermal neutrons alone. We also found that the relationship between thermal and epithermal neutrons provided an indicator for footprint heterogeneity. We, therefore, suggest that the combined use of thermal and epithermal neutrons offers the potential of a spatial disaggregation of the measurement footprint in terms of near- and far-field soil moisture dynamics.

Sub-structure-based ‘three-tiered’ finite element approach to soil-masonry-wall interaction for light seismic motion

Recent, light earthquakes induced by the extraction of gas in the north of the Netherlands have been linked to light, mostly aesthetic damage of the traditional masonry structures in the region; this is also connected to economic losses and societal unrest. To be able to accurately assess the light damage, detailed finite element models are necessary and need to include realistic soil movement, wave propagation, and soil-structure interaction boundaries. Moreover, the minute deformation of the soil, including the rocking and translational components of seismic ground motion, has shown to be influential to light damage. Consequently, this study has pursued the definition of efficient soil-structure interaction boundaries to implement in finite element models of buildings.A methodology, following the sub-structure method for the seismic Soil-Structure-Interaction (SSI) is defined and presented. The soil-structure-system is divided into three sub-systems: the far-field soil, the near-field soil and the superstructure. First, a 3 km deep and 8 km wide, plane-strain model of the soil is employed to study the behaviour of the soil at the surface due to deep, simplified seismic events. The soil model is linear-elastic since only light seismic excitations are considered. Next, a smaller, 30 × 300 m (shallow) soil model with a building on top, is given boundary elements calibrated to replicate the behaviour observed at the surface in the larger model. Finally, 2D models of masonry façades set on the intermediate soil model are used to reduce the soil-structure interaction to representative interface elements. The models are matched in terms of dynamic behaviour, strains, cracking, and displacements, and the behaviour is compared to existing ground motion data for the Zeerijp and Westerwijtwerd earthquakes. It is demonstrated that the equivalent interface allows efficient modelling of seismic excitations considering a detailed soil-structure interaction for complex, smeared non-linear, time-history analyses of wall models to assess (light) damage in probabilistic studies. Models with this equivalent interface show greater damage than comparison models without it.

Modal analysis of coupled soil-structure systems

This paper presents an efficient approach for the modal analysis of coupled soil-structure systems, for which the dynamic response is strongly influenced by the embedment in the soil. The methodology is based on a finite element-perfectly matched layer model that allows for the derivation of frequency-independent system matrices and the computation of the modal properties of the coupled system. This is achieved by solving a nonlinear eigenproblem using a Compact Rational Krylov (CoRK) eigensolver. A procedure is developed to sort the computed eigenpairs, filter out the spurious modes of the system which are related to the near-field and truncated far-field soil subdomains and select the physical structural modes of system. The proposed method can be used in the dynamic assessment and structural identification of strongly coupled soil-structure systems such as fully or partially buried structures and allows for the interpretation of experimentally identified modal properties of these systems, especially in the presence of highly damped or closely spaced coupled modes. The applicability and the scalability of the proposed approach for 2D and 3D problems is demonstrated in two case studies.

Shaking table test and numerical simulation on seismic performance of prefabricated corrugated steel utility tunnels on liquefiable ground

The seismic failure mechanism of a shallow-buried prefabricated corrugated steel utility tunnel on the liquefiable ground was investigated by the shaking table test and numerical simulation. Firstly, A scaled model of prefabricated corrugated steel utility tunnel, inside pipelines, and three kinds of brackets were designed and fabricated. The model system was then excited by two seismic ground motions on a shaking table. Various dynamic responses of the model system were measured and the interface slip of tunnel and surrounding soil was also tested by a self-designed transducer. The experimental results demonstrated that the near-tunnel soil was more likely to liquefy than the far-field soil, and the liquefied soil had a remarkable damping effect. The bottom bracket was more vulnerable to be affected by excitations with high-frequency than the suspending and standing bracket. Both the utility tunnel and the suspending bracket yielded under the mainshock, but only slight deformations were observed with the model. Finally, the tunnel-ground system was simulated numerically using the FLAC 3D program. The comparison of experimental records with simulated results was carried out for validation of research outputs. The results provide valuable insight into the seismic performance of shallow-buried underground structures and the safe design of prefabricated corrugated steel utility tunnels.

About Contemporary Seismic Analysis of Underground Structures

This paper is devoted to actual problems of seismic analysis of underground structures. Brief classification and overview of corresponding methods of analysis (force-based methods, displacement-based methods, numerical methods of seismic analysis of coupled system “soil – underground structure” and approaches to problems of soil-structure interaction) is presented. Special static finite element method with substructure technique for seismic analysis of underground structures is described. Dynamic soil-structure interaction system can be decomposed into three sub-structures: structure, near-field and far-field soil. The first stage of static finite element method is solving the free field shear stress, acceleration, velocity and displacement, when the moment that the relative displacement of the soil that the underground structure located in reaches the maximum. The second stage is computing of internal forces and parameters of boundary conditions. The third stage is construction of the static finite element model and imposing the loads and constrains computed at the second stage and then making a static analysis.

A new hybrid model for rigorous analysis of buried pipelines under general faulting accounting for material and geometrical non-linearities with focusing on corrugated HDPE pipelines

Earthquake-induced Permanent Ground Deformations (PGD) can be occurred due to fault movements, land sliding or liquefaction-induced soil displacements. This kind of deformation could significantly affect underground lifelines, such as buried pipelines. To assess the integrity of the pipelines against fault deformations, it is important to quantitatively evaluate the interaction between the pipelines and the surrounding soil. The simplified analysis procedures for buried pipelines crossing active faults given in the major seismic design guidelines for pipelines consider some bilinear force-displacement relationship curves to represent the soil-pipeline interaction. In a case of fault's large movement or existing relatively soft soil, the soil adjacent to the pipe could behave more in a nonlinear fashion and then affects the pipe's response and also changes the pipeline-soil interface behavior significantly. In this study, the effect of soil non-linearity as well as pipe's geometric and material non-linearities due to large ground deformations on seismic performance of buried pipelines were investigated. A new hybrid approach was developed to reduce the number of degrees of freedom of the soil-pipeline system accounting for rigorous soil-pipeline interaction. The approach combines the finite-element method (FEM) which models the pipe itself as well as the near-field soil around the pipe and the scaled boundary finite element method representing the far-field soil beyond the soil near-field. The behavior of pipeline embedded in the near field soil is modeled using large deformation shell elements, while the segment located far away from the fault, is considered as elastic beam elements. The proposed method was used to evaluate the maximum strains for the fault-crossing steel and High Density Polyethylene (HDPE) plane and corrugated pipes subjected to various fault movements. Parametric responses for different fault crossing angles, fault displacements and pipe diameters have been presented.

Finite element modelling and seismic behaviour of integral abutment bridges considering soil–structure interaction

A comprehensive non-linear finite element (FE) model of integral abutment bridges (IABs) is presented to facilitate the analysis of such bridges using commercial software, especially under seismic loading. The presented model is capable of capturing non-linearity in both the structure and soil, in addition to considering far-field soil response. The model is simple enough to be used for practical purposes. On the other hand, many aspects of seismic behaviour of IABs are unclear, due to complicated soil–structure interaction. Using the presented model, a parametric study is performed to identify the effects of bridge length, abutment type and soil type on seismic behaviour of IABs. Non-linear direct integration FE analyses are performed on the IAB models. The results of the parametric analyses demonstrate the importance of non-linear modelling of soil and pile in capturing a realistic seismic response of IABs.

Ground Motion Intensity Measures to Evaluate I: The Liquefaction Hazard in the Vicinity of Shallow-Founded Structures

When evaluating the liquefaction hazard within a performance-based framework, whether using simplified procedures or advanced numerical tools, the hazard and its effects on structures need to be evaluated under a range of ground motions. Choice of an optimum intensity measure (IM) in the selection and scaling of ground motions will reduce variability in the predicted response, dependence on source characteristics, and uncertainty in the prediction of the IM. This paper presents the results of a numerical parametric study, validated against centrifuge results, to evaluate the influence of different IMs on the liquefaction hazard in the far-field and near shallow-founded structures. Pore pressure redistribution and soil-structure interaction were considered in estimating the liquefaction hazard in terms of peak excess pore pressure ratio ( r u,peak). The IMs at the base rock, far-field soil surface, and foundation with the best combination of efficiency, sufficiency, and predictability were evaluated and identified as: (1) pseudo-spectral acceleration at the site's initial fundamental period ( PSA Base[ T So]) for predicting r u,peak in the far-field; (2) peak ground acceleration, ( PGA Base); and Arias intensity ( AI Base) for predicting r u,peak under the foundation.

Ground Motion Intensity Measures to Evaluate II: The Performance of Shallow-Founded Structures on Liquefiable Ground

A reliable mitigation of the liquefaction hazard requires an accurate estimation of the consequences of liquefaction in the context of building performance. Knowledge and use of an optimal intensity measure (IM) will reduce variability and improve accuracy of the predicted measure of performance. This paper presents the results of a three-dimensional, fully coupled, nonlinear, dynamic parametric numerical simulation of shallow-founded structures on layered, liquefiable soils, previously validated with centrifuge results. The generation and redistribution of excess pore pressures as well as soil-structure interaction effects were directly considered in the simulations. The influence of different IMs recorded at the base rock, far-field soil surface, and foundation was evaluated and compared on engineering demand parameters (EDP) that relate to structural performance and damage potential, such as foundation settlement and peak, transient, inter-story drift ratios. The IMs identified with the best combination of efficiency, sufficiency, and predictability in predicting the structural EDPs of interest were identified at the base rock as: CAV and CAV5 for permanent settlement, PSA[ T STo] for total and flexural drift ratios, and PGV for rocking drift ratio.

Field testing and numerical investigation of streetscape vehicular anti-ram barriers under vehicular impact using FEM-only and coupled FEM-SPH simulations

This article presents two field-scale crash tests of Streetscape Vehicle Anti-Ram barrier systems and LS-DYNA simulations to predict the global response of each system under vehicular impact. Tests 1 and 2 consisted of a five-post welded bus stop and a welded bollard, respectively; both were in a steel and concrete composite foundation embedded in compacted American Association of State Highway and Transportation Officials aggregate. Test 1 resulted in a P1 rating, where minimal foundation uplift and rotation were observed. Test 2 failed to result in a P1 rating, where significant foundation uplift, rotation, concrete cracking, and large deformation of surrounding soil were observed. For each test, two LS-DYNA models, namely, a finite element method–only model and a hybrid finite element method–smoothed particle hydrodynamics model, were created to predict the global response of the system. In the finite element method–only model, traditional finite element method approach was used for the entire soil region; in the hybrid finite element method–smoothed particle hydrodynamics model, the near-field soil region was modeled using the smoothed particle hydrodynamics approach, whereas the far-field soil region was modeled using the finite element method approach. For Test 1, both the finite element method–only model and the hybrid finite element method–smoothed particle hydrodynamics model were able to match the recorded global response of the system. For Test 2, however, the finite element method–only approach was not able to accurately predict the global response of the system; on the other hand, the hybrid finite element method–smoothed particle hydrodynamics approach was able to capture the global response including the bollard pullout, soil upheaval, and vehicle override. This research suggests that the hybrid finite element method–smoothed particle hydrodynamics approach is more appropriate in simulating the field performance of embedded structures under impact loading when large deformation of the surrounding soil is expected.

Numerical evaluation on the effects of soil freezing on underground temperature variations of soil around ground heat exchangers

Freezing of soil around ground heat exchangers (GHE) is a common problem for a ground coupled heat pump (GCHP) operated in the cold district, which will affect the underground soil temperature variation and its heat transfer performance. In this paper, a two-dimensional model for heat transfer with freezing-thawing phase change in soil around GHE is developed and numerically analyzed by apparent heat capacity method. The influences of soil freezing, soil water content, and soil type on soil temperature variations and long term underground thermal imbalance of GCHP with GHE array are investigated. The results indicate that the soil freezing can lessen the soil temperature drop and thus increase the temperature difference between the fluid inside GHE and far-field soil. This helps to shorten the GHE design length and cut down the initial system cost. The soil freezing characteristics are mostly affected by the soil thermal diffusivity. From the view of the ability in delaying soil temperature drop, the sandstone is preferable to sand, and sand is better than clay. Additionally, increasing water content can reduce the drop degree and speed of the soil temperature, as well as, accordingly alleviate the underground thermal imbalance of GCHP.

Three-Dimensional Nonlinear Seismic Analysis of Pile Groups Using FE-CIFECM Coupling in a Hybrid Domain and HISS Plasticity Model

AbstractThis paper reports the three-dimensional (3D) nonlinear dynamic analysis of floating pile groups subjected to seismic loading. For the nonlinear dynamic analysis of foundations in general, and pile foundations in particular, a perfect accuracy in modeling the frequency dependence of the unbounded soil support, as well as the local temporal nonlinearities, was ensured. In the current work, the finite elements (FEs) and boundary FEs were coupled in a hybrid domain of alternating frequency-time domains, to analyze the nonlinear dynamics of pile foundations in a 3D space. The frequency dependence of the stiffness and the damping of the unbounded far-field soil were completely accounted for by the consistent infinitesimal finite-element cell method (CIFECM) in the frequency domain, whereas the nonlinearities and transient conditions of the near-field were accounted for by the FE in the time domain. The hybrid frequency time domain algorithm is used for coupling the two domains. For the evaluation of no...

지반의 고유진동수에 따른 면진 원전 격납건물의 지진응답 특성

According to natural frequency of soil, characteristics of earthquake responses of an isolated containment building in nuclear power plants are examined. For this, earthquake response analysis of seismically isolated containment buildings in nuclear power plants is carried out by strictly considering soil-structure interactions. The structure and near-field soil are modeled by the finite element method while far-field soil by consistent transmitting boundary. The equation of motion of a soil-structure interaction system under incident seismic wave is derived. The derived equations of motion are solved to carry out earthquake analysis of a seismically isolated soil-structure system. Generally, the results of this analysis show that seismic isolation significantly reduces the responses of the soil-structure system. However, if the natural frequency of the soil is similar to that of the soil-structure system, the responses of the containment buildings in nuclear power plants rather increases due to interactions in the system.

DYNAMIC SOIL-PILE-RAFT INTERACTION IN NORMALLY CONSOLIDATED SOFT CLAY DURING EARTHQUAKES

This paper examines the seismic response of clay pile-raft system with flexible and stiff piles using centrifuge and numerical studies. Centrifuge studies showed that interaction between pile-raft and clay will cause a significant softening in the clay adjacent to the pile-raft which produced a lengthening of resonance period in near-field soil compared to the far-field soil. The difference of response among the raft and the soil at both near- and far-field indicates that ground motion at both near- and far-field cannot be representative of raft motion. There is also significant difference between flexible and stiff pile response. It has been shown in a previous study that, for stiff pile, the soft clay acts as an inertial loading medium rather than a supporting medium. For this reasons, the bending moment diagram extends deep into the soft soil stratum. However, for flexible pile, the supporting effect of the surrounding clay is much more significant than in stiff pile. As a result, the bending moment envelope for flexible pile under earthquake shaking is very similar to the head-loaded test results, with an active length of pile below which no significant bending moment occurs.

Electrogenic capacity and community composition of anodic biofilms in soil-based bioelectrochemical systems

Although a number of bacteria are known to be capable of generating an electrical current, the diversity of electrogenic bacteria in soils and the commonality across soil types is relatively unknown. Simple bioelectrochemical cells were constructed to measure the electrogenic capacity and community composition of bacteria originating on cell anodes from three biogeochemically distinct soil types. All three soils supported electrogenic activity, amounting to a maximum sustained current of 1.5-2.1mA over 55days. Analysis of fatty acids identified differences in microbial community composition between anode biofilms and far-field soil materials. Anode communities showed greater percentages of fatty acids indicative of Gram-negative bacteria and Actinomycetes. By analysis of anode biofilm genomic DNA via terminal-restriction fragment-length polymorphisms, commonalities in community composition across the three soil types were identified, specifically, the putative presence of bacterial species belonging to the α- and ß-Proteobacteria and the Firmicutes. Subsequent culture and isolation of bacteria from the anodes confirmed the presence of similar classes of bacteria. Results showed that, under saturated conditions, different soils can support electrogenic activity and that the bacterial communities that develop on the anodes share certain common inherent community traits.