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The energy pile test at Lambeth College, London was first reported just over 10 years ago; however, the original appraisal of the test only looked at the thermal response at the end of extended cooling and heating stages, and did not examine the transient response within these stages or in the daily cyclic thermal loading stage that followed. This paper revisits the earlier results, allowing for concrete creep under sustained load and using a revised strain-dependent pile modulus. The strong influence of the latter and the possible importance of stiffness changes during load reversal is highlighted. Detailed evaluation of the long-term transient results suggests that within a given thermal loading interval the thermal effects are similar, but there is some further discrepancy in the results, possibly due to an underestimation of the concrete creep. This re-evaluation has mitigated pile head displacement and increased thermal stress in the cooling phase, with the reverse occurring in the heating phase, and appears to be in better agreement with back-analysis reported by others. The transient response within the thermal loading stages illustrates that the development of the thermal stress–displacement response is related to the time for heat to diffuse through the pile body – around 3 days in this case.

In geotechnical engineering, the transparent soil (also called transparent media) technique is an effective tool for conducting experimental tests and investigating the displacement characteristics and stress distribution of soils. It plays a vital role in the observation of internal soil deformations. This study aims to briefly review the current state of some of the common materials used to formulate transparent soil models and the application of the transparent soil technique to underground construction over the last 20 years. To this end, the basic concepts of transparent soils are introduced. Then, several representative applications of transparent soil in underground construction (i.e., soil deformations induced by the penetration of pile foundations, tunnel excavation-induced movements, and structural responses caused by braced excavations) are presented. Because some research gaps may exist, certain potential research topics are proposed. This review can serve as a guideline for researchers performing experiments using transparent soils.

Discretely spaced reinforced concrete (RC) energy pile rows have been proposed to be installed at the mid-height of soil slopes. Although the pile row can provide mechanical reinforcement to slopes, the piles can also potentially be used to (a) intercept solar energy from roadways for heat storage in the ground to mitigate extremely high carriageway temperatures and (b) to extract shallow geothermal energy for road surface de-icing. In this study, a series of centrifuge model tests was conducted to evaluate the shearing behaviour of unsaturated silt with and without reinforcement by conventional piles and energy piles. Three-dimensional finite-element coupled water–vapour–heat transport analysis was also performed to understand further the effects of pile heating on the responses of temperature and pore-water pressure of the soil. The measured and computed results revealed that the primary effect of pile heating was an increase in soil hydraulic conductivity due to the heat-induced reduction in water viscosity. The heated soil had enhanced water flow and hence developed higher suction. When subjected to translational slip, the silt reinforced by a row of closely spaced RC energy piles exhibited a more ductile shearing response and a lower peak shear resistance, compared to that reinforced by conventional piles. The peak bending moments mobilised in the energy piles in the stable stratum were also smaller. At larger shear displacements, however, the shear resistance converged to a similar value, regardless of the suction and temperature. These findings suggest that piles modified with additional energy transfer functionality can continue to act as reinforcement, potentially preventing soil from a sudden brittle failure, without attracting additional flexural stresses onto the piles.

One challenge for geotechnical centrifuge testing of soil–structure interaction problems is the reliable measurement of induced structural strains/forces. This paper presents a novel application of fibre Bragg grating (FBG) sensors for strain measurement within geotechnical centrifuge tests. FBG sensors have several advantages for centrifuge testing, in particular their small size and minimal self-weight. This paper gives an overview of recently developed installation and calibration procedures for FBG sensors within buried centrifuge model structures. The effect of thermal expansion/contraction of the materials (including both the fibre and structures) is considered and assessed. The precision and reliability of the FBG sensors are demonstrated using verification tests. The application of the FBG sensors is considered for two geotechnical problems, namely, pile jacking and a ‘retaining wall’ adjacent to a tunnel (acting as a protective wall to prevent an adjacent structure from tunnelling-induced ground movement). The results demonstrate that the FBG sensors can provide reliable measurements of pile axial strains/forces and protective wall bending moments. The paper provides evidence to support the routine adoption of FBG sensors for strain/force measurement of structures in geotechnical centrifuge modelling.

Three-dimensional finite-element analyses are performed to compute the interaction factors between two neighbouring piles, under both static and dynamic horizontal displacements. The fixed-head elastic piles are flexible, embedded in a homogeneous saturated clay stratum, and loaded under undrained conditions. Soil inelasticity and soil-pile interface separation are modelled in a rational way. With the aim of improving fundamental understanding of pile-soil-pile non-linear interaction mechanisms, it is found that the effect of a loaded ('source') pile on an adjacent ('receiver') pile diminishes rapidly with increasing amplitude of imposed displacement, at a rate which depends on the angle of departure from the direction of loading between source and receiver piles. Gap formation at the back of a displaced pile affects the response of the group. Using the interaction factors developed, the behaviour of 2 x 2 and 3 x 3 pile groups is analysed and compared with the three-dimensional analysis of the whole group. Under static conditions the differences between front ('leading') and back ('trailing') piles are illustrated. Under cyclic dynamic conditions, the separation gap forms on each side of a pile alternately, leading to the peaks in stiffness diminishing, and leading to larger (than the elastic) group efficiencies. Superposition using proper non-linear interaction factors offers reasonable approximation, but only for moderate amplitudes of load, smaller than about one-half of the ultimate lateral pile capacity. ISSN:0016-8505 ISSN:1751-7656

The design of pile foundations to accommodate horizontal loads is a complex soil−structure interaction problem. Current small-scale laboratory testing of pile foundations is mostly focused on metal piles, which raises the question of the validity of results from these tests, and the principles derived, for the use of analysing and designing reinforced-concrete piles, where not only the soil, but also the piles exhibit highly non-linear material behaviour. This paper describes centrifuge tests that were conducted on scaled aluminium and reinforced-concrete single piles, subjected to lateral loading, with the aim of establishing the suitability of using aluminium alloys for modelling scaled reinforced-concrete piles. With responses similar to literature, both pile types proved to model the behaviour of laterally loaded piles well as far as bending and deflection at low loads are concerned. At larger loads, the reinforced-concrete pile cracked, resulting in non-linear material response, which contributed significantly to the difference in the behaviour between the piles studied. It was observed that the behaviour of reinforced-concrete piles under serviceability loads would not be captured using materials that cannot replicate the reduction in stiffness resulting from crack formation in concrete.

Discrete element method is used in this work to examine the mechanisms determining powder deposition efficiency during powder spreading in powder bed fusion additive manufacturing. The results reveal that powder flow in the powder pile is critical for the formation and break of transient jamming. The forces on the underlying part increase first with spreading speed then decrease with a large fluctuation. For varied spreader shapes, a small inclined angle of the spreader surface makes the force barrier farther from the discharging gap, creating a larger region which ensure enough powder supply to the gap. Furthermore, a small inclined angle of the spreader surface close to the gap results in less particle motion conflicts at the gap and ensures larger discharging rate through the gap. This mechanism explains why spreaders with inclined or round surfaces help increase powder deposition efficiency.

This study aims to solve the problem of locating charging stations for public electric vehicles. We take into consideration the factors affecting charging station locations including mileage, electric vehicles distribution, and passenger distribution. A Non-deterministic Polynomial model aiming to minimize the total vehicle service distance is developed. We use an agent-based model to simulate the optimized charging station location based on Anylogic. Through a case study of Beijing, we test the model in five situations. The results of one situation show that the existing layout of the charging stations is unreasonable when charging frequency is sharply variant (basic model); this paper optimizes the existing location by improving the constraint for the smallest number of charging stations (improved model); compared with the basic model, the improved model has a shorter response time to passenger demand, shorter service time for passengers but more mileage for electric vehicles.

This study investigates the thermo-mechanical behavior of energy piles equipped with a spiral pipe configuration. The analysis is based on the results of a full-scale energy pile as well as three-dimensional thermo-mechanical finite element analyses. The thermo-mechanical behavior of two energy piles with five U-shaped pipes connected in series and parallel, characterized by the same total length of the piping network, is also analyzed numerically for comparison purposes. The results of this work highlight that energy piles equipped with a spiral pipe configuration are characterized by the lowest trends of average temperature variation and thermally induced vertical stress within their volume, as compared to energy piles equipped with five U-shaped pipe configurations connected in series or parallel. Considerable variations in temperature and thermally induced vertical stress arise in the vicinity of the piping network embedded in all of the considered energy piles. Nevertheless, energy piles equipped with a spiral pipe configuration appear the best solution for practical applications in comparison with U-shaped pipe configurations of the same total length, because they maximize the heat exchange that is achieved with the ground and minimize the associated thermally induced variations of their mechanical response.

Ever-increasing scarcity of land and demand for high-rise structures has significantly contributed to the use of combined piled raft foundations (CPRF) in soft ground. However, utility, design constraints and aesthetic considerations bring asymmetry to superstructures, making structures more vulnerable during seismic excitations. Traditional design practices involve designing superstructure elements and foundation considering fixity at the base of the superstructure and ignoring soil-structure interaction (SSI) which may result in under-estimation of forces and displacement in the system. Hence, the present study aims at developing new seismic design guideline pertaining to asymmetric single and multi-storied structure supported on CPRF embedded in soft clay. Some important parameters, such as torsional coupling mode of vibration and multi-storey idealisation involving the effect of higher modes are investigated incorporating seismic SSI effect. The study broadly reveals that the torsional to lateral period ratio considerably influence the seismic response of asymmetric structural system on the piled raft foundation due to the incorporation of SSI. Furthermore, multi-storey building idealisation gives a higher estimation of response compared to single storey idealization in superstructure and pile head which may be due to the effect of higher modes of vibration and SSI

Transmission tower foundations experience large vertical uplift forces during their lifetime. These forces can be resisted by providing anchor foundations below the tower. In this study, laboratory experiments were conducted to investigate the pullout capacity of inclined plate anchors in dry sand. The capacity of inclined anchor significantly improved in the presence of geogrid reinforcement on top of the anchor plate. Besides, the pullout capacity increased with the inclination angle (30°, 45°, 60°) both in unreinforced and reinforced soil. It was observed that the ultimate pullout load is significantly influenced by the embedment depth of the anchor plate and relative density of the backfill material. The experimental results were compared with a three-dimensional numerical model developed in F L A C 3 D . The comparison shows good agreement between the experimental and numerical results, and the numerical model can predict the pullout behaviour of the inclined anchor plate both in unreinforced and reinforced soil. Comparison of uplift resistance of pile and anchor foundations are shown through a design example of a transmission tower foundation. Results indicate that inclined anchors embedded in reinforced soil can resist the uplift forces at shallow depth compared to piles.

Lateral responses of a pile are governed by its mutual interaction with the supporting soil, known as the Pile-Soil Interaction (PSI), which in turn influences its structural limit states. The present study evaluates the seismic limit states for bridge pile in sand, while incorporating the parametric influences of pile and soil assessed through PSI. Such influences have not been dealt with in the past, except for the p (soil-pile reaction) – y (pile deflection) responses (though with only few pile parameters). Pile cross sectional size, grades of concrete and reinforcement, longitudinal and transverse reinforcement ratios, axial load ratio and the sand effective friction angle are observed to affect the PSI and consequently the limit states. Thus, limit states are proposed as parameterised expressions, generated through regression on the limit state data obtained by analysing the damage model (developed herein) for the pile-soil system samples generated over wide ranges of the influential parameters. These expressions, validated through the compliance with the expected trends and a fair agreement with a test result, can be readily used to obtain the expected values of the limit states over a broad range of parametric combinations and without requiring analysis repetition. These, in turn, can contribute to reliable estimation of fragility of a bridge system with the given properties for its pile foundation.

This study aims to comprehensively explore the thermomechanical characteristics of energy pile-raft foundations through in situ full-scale field tests. The foundation of interest was subjected to the joint effect of building loading and cooling thermal loading. The temperature, strain, and stress variability in both the employed pile and raft were measured and analysed. The basement of the building acted as an insulator, and the near-surface ground temperatures under the basement were affected less by seasonal changes in the air temperature. The stabilized heat exchange rate of the energy pile was approximately 75.0 W/m. The overlying raft and building at the pile head and the expanded foot and sandstone at the pile toe imposed greater restraints than those observed at other parts of the pile. The thermally induced stress per centigrade near the pile head and toe was approximately −0.160 MPa/°C and −0.202 MPa/°C, respectively. The thermally induced stresses of this kind of pile were mostly stabilized after 16 days of heating operation. When the pile was under thermomechanical loading, the axial tensile stress was mobilized along the lower half of the pile, and the maximum measured tensile stress was approximately 0.25 MPa, which did not exceed the tensile strength of the employed concrete. The cooling (contracting) of the energy pile also influenced the nearby raft. The raft temperature decreased by 6.2 °C, and the additional tensile stress was approximately 0.88 MPa (40.0% of the upper bound).

The thermal response of an energy field scale pile that is part of a pair of energy piles spaced at a centre-to-centre distance of 3.5 m (i.e., 6D, where D is the pile diameter), was examined experimentally and numerically. Three field tests were conducted to assess the axial and radial thermal responses of the energy pile: (i) heating of the energy pile alone, (ii) heating of both energy piles simultaneously, and (iii) heating of the other energy pile while the considered energy pile was not heated. Good agreement was obtained between the experimental and numerical evaluations of the energy pile during the tests. A parametric study of the validated numerical model was performed for each of the three tests to understand the effects of varying soil thermal conductivity, thermal expansion coefficient, and elastic modulus on the thermal response of the considered energy pile. The numerical results confirmed the field results that radial thermal stresses in the energy piles were insignificant compared to axial thermal stresses. The impact of elastic modulus of the soil was more significant on the thermal stresses of the energy pile compared to the effects of soil thermal conductivity and thermal expansion coefficient. The thermal stresses of the considered energy pile were not significantly affected when both energy piles were heated simultaneously, even though ground temperature changes between the energy piles were more significant due to thermal interaction. Only minor thermal effects on the non-thermal pile were observed during heating of one of the energy piles for different soil properties.

To investigate the behavior of piles and the performance of the mechanically stabilized earth (MSE) walls under static and cyclic lateral loading, six reduced-scale model tests of single and group piles within the MSE walls were conducted inside a test box. In the single pile tests, a hollow aluminum tube as a pile was placed at a distance of 2D or 4D (D is pile diameter) behind the wall facing, while in the group pile tests, the piles were only placed at the distance of 2D with a spacing of 3.3D between the piles. The piles were subjected to static lateral loading only and cyclic lateral loading followed by static loading until failure. The test results showed that the lateral load capacity of each pile in the group pile test was approximately 60% that of the single pile, while the wall facing displacements and the geogrid strains in the group pile test were larger than those in the single pile test. The lateral pile capacity, the wall facing displacement, the strain in the geogrid, and the lateral earth pressure behind the wall facing in the static and cyclic loading tests were evaluated at the pile head displacement equal to 20%D.

This paper presents a series of laboratory tests on cemented soil with high water content, and the water content of cemented soil samples were all larger than the liquid limit. A group of model PHC pile-cemented soil interface shear tests were then conducted to investigate the interface frictional capacity. Finally, a group of full-scale tests on PHC pile-cemented soil columns were conducted to study the frictional capacity of cemented soil-soil interface. The test results show that: the cohesion of cemented soil with high water content had a linear relationship with the unconfined compressive strength; the cemented soil strength had a large effect on the frictional capacity of PHC pile-cemented soil interface, and the peak skin friction of PHC pile-cemented soil interface increased linearly with the increasing cemented soil strength; the frictional capacity of cemented soil-soil interface was better than the frictional capacity of conventional pile-soil interface.

To investigate the load transfer mechanism of open and closed Pre-stressed High-strength Concrete (PHC) piles jacked into layered soil, a full-scale in-situ test was conducted. In this test, the axial stress experienced by one open and two closed PHC pipe piles during jacking into layered soil was monitored using Fiber Bragg Grating (FBG) sensors mounted on pile shaft. The test results showed that (1) The jacking force on pile depended on the soil mechanical properties at the end of pile; (2) The variation of axial force on pile reflected that the compaction effect of soil for closed pile was larger than that for open pile; (3) At the beginning of penetration depth, the variation of shaft and end resistances on the open pile were different from those on the closed piles; (4) The variation of average shaft resistance relied on the mechanical properties of soil at the side of pile.

Pile foundations are widely designed extending principles of saturated soil mechanics assuming drained conditions (i.e. effective stress) even in expansive soil deposits despite the fact the soil around the pile is in a state of unsaturated condition. The mechanical behavior of in-situ pile foundations are significantly influenced by suction changes associated with water infiltration. In this paper, a single model pile mechanical behavior variations associated with suction changes in an unsaturated expansive soil under a service load were investigated. Experimental results suggest pile settlement increases due to water infiltration. Such a phenomenon can be attributed to pile shaft friction reduction in the active zone associated with suction reduction due to water infiltration and volume expansion of the soil. Experimental results were also simulated and interpreted using a computation program, PEI (i.e. Pile behavior in Expansive soil upon Infiltration), which was proposed based on principles of unsaturated soil mechanics. A theoretical model was proposed for the estimation of threshold pile head load which distinguishes whether the pile would experience upward or downward movement upon water infiltration. The theoretical model and the numerical modeling approach presented in this are valuable for practicing engineers in the rational design of piles taking account of the mechanical behavior of expansive soils.

Y-shaped piles are a new type of pile whose cross-section is like the letter Y: they are often used in ground improvement for road or train subgrades in the eastern coastal region of China. To investigate the bearing behaviour of Y-shaped piles in saturated sand, a series of model tests under compressive and horizontal load for Y-shaped piles, C 1 circular pile (the same cross-sectional area of Y-shaped pile), and C 2 circular pile (the same perimeter of Y-shaped pile) were carried out. Comparative analysis was conducted on bearing capacity, axial force and side resistance distribution, load sharing ratio, bending moment, and lateral soil pressure distribution along the embedded length. The results show that the bearing capacity of a Y-shaped pile does not increase in proportion, and the shaft resistance is weakened to some extent in saturated sand; Y-shaped pile can effectively improve the compressive bearing capacity for the same amount of concrete. The lateral bearing capacity of a Y-shaped pile has directionality, and hanging a circular section into a Y-shaped section may improve the horizontal bearing capacity for the same amount concrete, but cannot give full play to the advantage of the larger side area for horizontal bearing capacity in saturated sand.

The stress and displacement boundary conditions of excavation retaining structures affect the deformation mechanism and movement of the retained soil mass. The soil movement disturbs the load sharing performance and structural integrity of cement-fly ash-gravel (CFG) pile composite foundations existing in the vicinity, which merits considerable research work. This article presents results from 3D finite element analyses performed to study the influence of retaining wall rotation on the load sharing characteristics of adjacent CFG pile composite foundation comprising long and short piles. To verify the numerical model, a relatively large-scale 1 g physical model test was conducted. It is revealed that to arrive at a new static equilibrium during progression of wall rotation, the percentage load sharing ratios of the long and short piles change increasingly while the load proportion carried by the upper soil reduces remarkably. The percentage load sharing characteristics of CFG pile composite foundation are more affected in immediate proximity to the wall than those located at far distance. For the foundation having 3 × 3 long and short piles placed at 3.0–15.0 m away from the wall, the location resulted in a reduction of soil bearing capacity ranging between 1.4 and 7.5% of the total imposed load while the corresponding increase in the % load borne by the long and short pile range was 0.83–4.15 and 0.59–3.36%, respectively. For the other parameters considered in this article viz. pile spacing, subsoil stiffness, cushion stiffness and thickness, and applied working load, the increment in % load sharing of the long and short pile range was 3.45–4.15, 1.3–5.79, 1.48–3.36, 4.15–4.79, and 3.67–4.15% and 3.36–4.67, 1.43–4.99, 1.48–3.36, 3.36–3.64, and 1.38–3.36% of the imposed load, respectively. Moreover, the long piles’ load sharing proportion was higher than that of short piles, and peripheral piles received larger load proportion.

PurposeDelays in projects execution due to improper structural design lead to substantial losses to the owners. Little guidelines are available in practice that deals with structural design of Delayed Coker Units (DCUs). This work describes effective structural criteria for design of DCU used in hydrocarbon industry. Economical procedures are described for steel and concrete design. Design of pump houses supporting DCU is also described.Design/methodology/approachNumerical procedures are developed to model pipelines and mechanical equipment loadings. Soil restraints are simulated using horizontal and vertical springs along the pile embedded length. Concrete pile-caps are integrated with steel structure in the analysis model.FindingsThe proposed design approach is cost effective to use in practice. The paper offers economical footprint for design of DCUs that can be used for multiple projects.Practical implicationsThe paper provides useful guidelines that can be utilized by engineers for design of coker heater and coker fractionation stacks, steel modules, coke pump house, deluge building, etc.Originality/valueCurrently, there are no guidelines in practice that deal with structural design of DCU. The present work bridges this gap and describes novel strategies that can be utilized for industrial projects.

Compaction operations have a vital role in embankments or rock fills to avoid settlement, but in some projects, such as marine ones, it is hardly possible to accomplish compaction operations due to the problems and executive limitations. In situations with no possibility of compaction, it is recommended to use single-size or self-compacted materials. From a theoretical point of view, self-compacted materials consist of coarse aggregates with no vast domain of gradation. In this case, the porosity of the materials in the dense state is not significantly different from the loose one, and a relatively dense condition occurs after it is poured; thus, the mass of materials will undergo lower volumetric changes in the future. In this study, the self-compacted characteristic of materials has been investigated using real aggregates with different gradations (the ratio of the largest to the smallest aggregate size of 1, 2, 4, and 8). The gradation and shape of aggregates are the main variables examined in the research. Real aggregates have been used in order to compare the study of self-compacted idea with ideal aggregates and the effects of sphericity and angularity of them. According to the experiments carried out on samples in the present work, it was observed that, without compaction operations, even ideal materials would not be in fully self-compacted state. However, relatively denser conditions can be achieved by observing the necessary points. Moreover, aggregates with high sphericity have better self-compacted property. Furthermore, the more uniform gradation and bigger size of materials lead to more self-compacted pile of materials.

This paper presents the results from a comprehensive experimental study on the Quadrant Face Pile Supported Breakwater (QPSB) in two different water depths exposed to three different oblique wave attacks. The results are compared with that for a Vertical face Pile Supported Breakwater (VPSB) for identical test conditions. The paper compares the reflection coefficient, transmission coefficient, energy loss coefficient, non-dimensional pressure, and non-dimensional run-up as a function of the relative water depth and scattering parameter. The results obtained for QPSB are validated with existing results. The salient observations show that QPSB experiences better hydrodynamic performance characteristics than the VPSB under oblique waves.

Purpose This paper aims to investigate single pile and pile group responses due to deep braced excavation-induced soil movement in soft clay overlying dense sand. The analysis focuses first on the response of vertical single pile in terms of induced bending moment, lateral deflection, induced axial force, skin resistance distribution and pile settlement. To better understand the single pile behaviour, a parametric study was carried out. To provide further insights about the response of pile group system, different pile group configurations were considered. Design/methodology/approach Using the explicit finite element code PLAXIS 3 D, a full three-dimensional numerical analysis is carried out to investigate pile responses when performing an adjacent deep braced excavation. The numerical model was validated based on the results of a centrifuge test. The relevance of the 3 D model is also judged by comparison with the 2 D plane strain model using the PLAXIS 2 D code. Findings The results obtained allowed a thorough understanding of the pile response and the soil–pile–structure interactions phenomenon. The findings reveal that the deep excavation may cause appreciable bending moments, lateral deflections and axial forces in nearby piles. The parametric study showed that the pile responses are strongly influenced by the excavation depth, relative pile location, sand density, excavation support system and pile length. It also showed that the response of a pile within a group depends on its location in relation to the other piles of the pile group, its distance from the retaining wall and the number of piles in the group. Originality/value Unlike previous studies which investigated the problem in homogeneous geological context (sand or clay), in this paper, the pile response was thoroughly studied in a multi-layered soil using 3 D numerical simulation. To take into account the small-strain nonlinear behaviour of the soil, the Hardening soil model with small-strain stiffness was used in this analysis. For a preliminary design, this numerical study can serve as a practical basis for similar projects.

Foundation piles have the potential to improve the economic and technical feasibility of ground source heat pump (GSHP) systems. They simultaneously provide structural support and energy for space heating and cooling. In this study, a thoroughly verified and validated numerical model of a novel in-ground heat exchanger for GSHP systems is developed and used to simulate and optimize performance. Commercially available helical steel casings with nominal sizes according to the American Petroleum Institute (API) of API 13.5, API 23, API 29, API 53, API 60, and API 68 were considered. The flow rates considered were 1 L/min, 2 L/min and 4 L/min for laminar flow and lower pressure drops. Results show the performance to increase with increasing pile size owing to improved heat transfer and longer residence times. Optimizing performance with an API 68 steel casing, (with a 2” nominal plastic pipe) gives a capacity increase of 0.01 ton/pile (or 8.3%), which would reduce the approximate pile array required for a 3 ton cooling system from 13 to 12. Doubling the size of this pile while keeping other parameters constant gives an 18.5% capacity improvement with an output capacity of 0.28 ton/pile, and an 11, 20 m pile array requirement to meet a 3 ton cooling load. With a maximum heat exchange rate of 58.6 W per meter depth, this shallow in-ground heat exchanger has the potential to minimize energy and costs for small-scale implementation. In addition, the possible low flow rates help reduce pumping power requirements. This study provides a foundation for sizing and design of helical steel piles. Moreover, the study also gives insights into pile performance in multi-layered soils where the thermal conductivity varies with depth.

There is an increasing interest and use of energy foundation worldwide. Full-scale tests, physical model tests at one Earth’s gravity and at elevated gravity in a geotechnical centrifuge and numerical simulations have been widely reported in the literature. Almost all studies have focused on single energy piles (EPs) and pile groups subjected to symmetrical thermal loads, although it is not unusual to have energy pile groups stressed by non-symmetrical thermal loads. In this study, a series of non-symmetrical thermal loading centrifuge model tests were conducted in saturated soft clay (OCR = 1.7), which is much vulnerable to temperature changes. The tests aim to investigate the effects of pile spacing on the serviceability of floating energy pile groups. Fifteen cycles of non-symmetrical thermal loading are applied to three EPs in 2 x 2 elevated energy pile groups with 3D and 5D (D denotes pile diameter) pile spacing. The thermally induced irreversible settlement and tilting in the 3D-pile group are 200% and 300% larger than those in the 5D one, respectively. Contrary to the 5D-pile group where the serviceability criteria (EN 1997-1:2004) are satisfied, the settlement and tilting are 30% and 200% larger than the criteria in the 3D one, respectively.

The picking of one or more objects from an unsorted pile continues to be non-trivial for robotic systems. This is especially so when the pile consists of a granular material (GM) containing individual items that tangle with one another, causing more to be picked out than desired. One of the key features of such tangle-prone GMs is the presence of protrusions extending out from the main body of items in the pile. This work characterises the role the latter play in causing mechanical entanglement and their impact on picking consistency. It reports experiments in which picking GMs with different protrusion lengths (PLs) results in up to 76% increase in picked mass variance, suggesting PL to be an informative feature in the design of picking strategies. Moreover, to counter this effect, it proposes a new spread-and-pick (SnP) approach that significantly reduces tangling, making picking more consistent. Compared to prior approaches that seek to pick from a tangle-free point in the pile, the proposed method results in a decrease in picking error (PE) of up to 51%, and shows good generalisation to previously unseen GMs.

An important source of time-dependent pile deformation is creep behavior at pile-frozen soil interface in permafrost regions. A creep model for pile-frozen soil/ice interfaces was proposed based on a series of multistage creep tests. The test results show that the creep behavior of the pile-frozen soil/ice interfaces is easily observed at a steady rate larger than 0 even at a small load level, which increases as the increase of load level. The elastic shear modulus increases at a slowing down rate with the increase of load level. The interfaces are mainly strengthened during the creep process until the occurrence of the accelerating creep, which is more obvious for frozen soil. A large amount of ice in frozen soil can enhance the creep rate and reduce the carrying capacity of pile foundation. The viscosity [Formula: see text] reflecting steady creep rate, the instantaneous shear modulus [Formula: see text], and the critical stress [Formula: see text] required for describing damage behaviors distribute in the form of Bigaussian asymmetric peak function with ice content. The Burger model considering ice effect and damage effect is feasible to describe the entire creep behavior of the interfaces. Sensitivity analysis reveals that ice content in frozen soil has a marked influence on pile deformation, a cooling method can probably adjust the creep deformation of pile in frozen soil with high ice content.

The aim of this paper is to analyze the buckling stability problem for piles in the slope foundation based on cusp catastrophe theory. Formulation of critical buckling load of piles in the slope foundation is obtained. The influential factors of slope angle, distribution of landslide thrust behind the pile, pile-embedded ratio, pile constraints, pile-side friction, pile-side soil resistance, and pile socketed ratio upon buckling stability characteristic for piles in the slope foundation are examined. The results reveal that when pile diameter remains unchanged, critical buckling load increases with the increase of pile length when pile-embedded ratio reaches 60%. When pile length remains unchanged, critical buckling load increases with the increase of pile diameter. Critical buckling load with the assumption of nonlinear horizontal elastic resistance of pile-side soil in the paper is more close to the value based on horizontal elastic resistance of pile-side soil suggested in the code. When slope angle increases, decreased extent of buckling critical load for piles 30–60 m in length is more obvious than the piles which are 10–30 m in length. Strengthening of pile constraints and increase of pile-embedded ratio and socketed ratio are helpful to pile critical buckling load increase. The influential factors of pile-side friction and landslide thrust behind the pile upon pile critical buckling load are tiny and can be neglected.

Little attention has been paid to investigating borehole deformation characteristics during drilling in soil and rock mixtures commonly encountered in the construction of ground anchors, micropiles, etc., raising questions as to the pile quality. This unique study investigates the deformations of micropile boreholes during rotary drilling in a compacted soil-limestone mixture (S-LM) by developing model tests. Three sets of experiments were carried out, in which three groundwater conditions (no water flow, 40 cm water level, and 80 cm water level) were applied at each of the three boreholes, which had diameters of 32, 44, and 56 mm. The variations in vertical displacement, deep horizontal displacement, pore water pressure, and soil pressure were recorded during the drilling stage. The test results showed that, in general, the vertical displacement at the ground surface, radial horizontal movement, and soil pressure induced by rotary drilling were strongly correlated with the borehole diameter. It was observed that the larger the borehole diameter was, the higher the values of these parameters. Furthermore, the 80-cm water level resulted in borehole collapse during the drilling stop periods since a negative displacement area and a soil pressure varying from negative to zero were observed. This research broadens the limited study of borehole deformation conducted on soil and rock mixtures via model tests. Additionally, it can provide a reference for micropile designers and contractors planning to drill in similar soil-rock mixtures.

Pile foundations are often exposed to vertical and lateral loads. In common pile analysis, it is assumed that the effect of these two load types do not depend on each other, and designing is usually done individually for each of the vertical and lateral loads. The influence of vertical load on the response of the pile lateral load can be extracted via finite element analysis in a variety of soils. AllPile is a commercial program that has been utilized in many executive tasks and because of its ease of use in engineering, and in particular the analysis of different pile types under the influence of vertical, lateral, and bending loads and their combinations, as a single pile or pile group. It is one of the most popular and practical programs among geotechnical engineers. The results of the single-pile analysis under the lateral load and lateral load with vertical load in Allpile and Abaqus software are presented to compare their results. Then for layered soil, a comparison has been made between the results of Allpile analysis and numerical modeling with the finite element method in Abaqus. The results generally indicate that as the lateral load increases, the pile head displacement increases. Also, by increasing lateral load and applying a vertical load, the amount of displacement is reduced compared to the situation with the absence of a vertical load.

In collapsible loess area, the negative skin friction of pile foundation will cause many engineering problems such as failure of pile strength and reduction of bearing capacity of pile foundation, which will bring great harm to engineering construction. In order to study the change and distribution law of negative friction of pile foundation in collapsible loess area, the scale model test of negative friction of pile considering loess collapsibility was designed and completed. Through finite element numerical simulation, the test results are verified, and the distribution law of negative friction of pile and the number and position of neutral points are obtained. The test results show that under the condition of immersion, the loess has layered settlement, and there are both negative friction and positive friction on the pile surface, and there are two neutral points. Negative friction drags the pile downward, which makes the axial force of the pile increase obviously. The numerical simulation results verify the feasibility and validity of the test results. The research results of this paper have certain guiding significance for pile foundation design in collapsible loess area.

Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability method (FORM) based on a support vector machine (SVM) and uniform design (UD) is proposed to investigate the reliability of a pile-stabilized slope. A deterministic model considering soil-pile interaction and using a strength reduction method based on the displacement criterion is employed to calculate the factor of safety and the corresponding pile-bending moment. The uncertainties involved in both the soil and the stabilizing pile are taken into consideration in the proposed method. Two typical failure modes, namely the insufficient factor of safety of a pile-stabilized slope and the insufficient flexural bearing capacity of stabilizing piles, are investigated from a probabilistic viewpoint. The proposed method is illustrated with an artificial homogeneous slope and a real slope engineering case. The influence of stabilizing pile installation locations on the reliability results were studied. The sensitivity of random variability was also investigated. The results of the proposed method show high accuracy while having a smaller computational time requirement when compared with the polynomial response surface method. The case study of a real highway slope shows the feasibility of the proposed method applied to practical engineering problems.

This study investigates the disturbance of bridge piles caused by the adjacent deep excavation of a metro station in Guangzhou while considering the existence of underlying karst caverns. Ground treatment was adopted to reduce the effects of the deep excavation on the surrounding environment, including metro jet system (MJS) technology and karst treatment. Considering the presence of karst cavern and an inhomogeneous limestone layer, three-dimensional nonlinear finite element analysis (FEA) was implemented to investigate the excavation-induced effects on the surrounding ground and structures. Coupled pore fluid diffusion and stress analysis were adopted for the excavation simulation, and comparative analyses between the field data and FEA results were used to verify the numerical model. A series of parametric studies were conducted by varying the parameters of the MJS piles and karst cavern filling. This study reveals that: (1) increasing the Young’s modulus of the MJS pile leads to a decrease in ground and wall settlement; (2) the optimal buried depth of MJS piles is the depth that reaches the rock stratum; (3) the optimal MJS pile–wall distance is 0.225H (H denotes excavation depth); (4) increasing the piles diameter leads to a linearly decrease in wall and piles settlement; and (5) varying the Young’s modulus and permeability coefficient of the karst cavern filling has little effect on the surrounding environment. MJS treatment can be used as an effective measure for protecting the surrounding environment from disturbance by deep excavations.

The seepage phenomenon (uplift pressure - flow rate - exit gradient of hydraulic structures) is one of the main causes of failure or collapse of hydraulic structures, so it has been reduced using sheet piles under floor of hydraulic structures. In this study, effect of mutual interference piles were studied on seepage phenomenon by using finite elements program ANSYS. The results were verified with the practical results L-SAYED which given a good correlation. It was found that the use of the pile in the upstream reduced the uplift pressures by 8.36%, and the pile in the downstream increased it by 11.66%, the flow rate reduced by 66.8% and exit gradient of the hydraulic structures reduced by 28.28%. http://dx.doi.org/10.30572/2018/kje/090419

Stone columns (or granular piles, GPs) are progressively being utilized for ground improvement, mostly for pliant edifice such as road mounds, oil depot, and so forth. The present analysis is done by introducing strengthening at both the ends of GP, i.e., bottom and top end so that the bulging problem will be solved and the beneficiary effect of the bearing stratum can be utilized by the bottom strengthening feature. Analysis of a single partially strengthened, at both top and bottom, end-bearing GP is presented in this article in terms of displacement affecting component for the top (DACT) of GP, percentage load transferred to the base (PLTB) of strengthened GP, and normalized shear stress (NSS). The PLTB of the strengthened GP was found to increase considerably. The NSS was found to reduce at the top end of GP and is found to be redistributed along the length of GP.

Geosynthetic-reinforced and pile-supported (GRPS) embankments are becoming more and more popular as this technique showed good performances in practice. Various design methods were introduced to analyze GRPS embankments. However, the applicability of these design methods was not always fully validated. This paper focuses on the review of projects containing field observations of GRPS embankments. The comparison results showed that the assumptions related to the subsoil support, geosynthetic, arching shape, and its evolution are not consistent in the analytical methods. Comparison results with twenty-five full-scale cases and six series of experiments emphasize that these available design methods produce significantly different results in predicting loads transfer mechanism. The analytical models predict arching for cohesionless fill better that for cohesive fill soils. Besides, the analytical methods which consider subsoil support such as the CUR226 and EBGEO methods give results that are in a better agreement with experimental data as compared to other methods which do not consider the subsoil support. The CUR226 (2016) analytical model seems to be able to give the best performance with measured data when compared to other design methods. Finally, the results pointed out that the limit equilibrium model is adequate and has good performance.

An analysis of combined piled raft foundations could be performed by means of a special geotechnical finite element software that utilizes 3D modeling and advanced constitutive models for the soil. However, a foundation is generally included in the structural models in a structural design program. The least advanced part of finite element software that has been developed for structural FEM modeling are the tools used for modeling behaviour. A method is required with which the input parameters of the structural design software that are used for modeling the soil structure interaction as well could be determined so that the results calculated by means of a geo-technical software that approximates realistic soil behaviour the best can be reproduced by structural design software as well. The procedure outlined in this paper by means of a cluster analysis provides a tool for a substantial and innovative improvement in subsoil modeling, to which not enough attention is generally paid in the structural FEM software, thereby resulting in a reduced amount of work associated with the task of inputting data.

The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed, resulting in water leakage or even ground collapse. To establish a more realistic simulation and provide guidelines for designing a safe and cost-effective secant-pile wall, a three-dimensional model of a secant pile, considering the geometric imperfections of the diameter and direction of the borehole, is introduced. An ultrasonic cross-hole test was performed during the construction of secant piles in a launching shaft in Beijing, China. Based on the test results, the statistical characteristics of the pile diameters and orientation parameters were obtained. By taking the pile diameter D, inclination angle β, and azimuth angle α as random variables, Monte Carlo simulations were performed to discuss the influence of different design parameters on the probability density functions of the overlap of secant piles. The obtained results show that the randomness of the inclination angle and pile diameter can be well described by a normal distribution, whereas the azimuth angle is more consistent with a uniform distribution. The integrity of the secant-pile wall can be overestimated without considering the uncertainty of geometric imperfections. The failure of the secant-pile wall increases substantially with increasing spatial variability in drilling inclination and diameter. A design flowchart for pile spacing under the target safety level is proposed to help engineers design a safe and economical pile wall.

Hollow auger piles are a new solution technique being used more often in recent years as a foundation for buildings of 15 floors or less in the coastal region of Joao Pessoa, Brazil. Designed on “piled raft” type systems, the hollow auger substitutes well the traditional soil improvement solution with compaction piles, in which the ground vibration, inherent to the pile driver process, is no longer admissible in densely populated areas of the city. Hence, this paper addresses the in-situ behavior of this new pile technique in foundation groups of hollow auger piles in a sandy soil deposit, typical of the region. The analyses are based on load tests performed in the actual-size foundations, also scarce for this foundation type. The results indicate that the efficiency factors (η) of the pile groups is greater than one and close to typical values in the geotechnical literature for sandy soils. For the 2-piled group, η varied between 1.10 and 1.33. For the 4-piled group, η varied between 1.05 and 1.25. Settlement ratios (Rs) found experimentally show that the effects of the interaction are more intense at the group with more piles. The results obtained for Rs were 1.08 and 2.01, for 2-piled group and 4-piled group, respectively. The distribution of a load on a pile is analyzed using instrumentation with strain gages, allowing the perception of the division of loads between the shaft and tip. The analyses carried out through the laws of Cambefort show that the average unit lateral friction is fully mobilized and reached a maximum value of 52 kPa, corresponding to a settlement of 18.7 mm. The bearing pressure of the tip was not fully mobilized and reached a value of 5531 kPa, equivalent to a displacement of 83.5 mm.

Understanding the interaction between the star wheel arm and coal particles is important to efforts for improving the loading efficiency and reducing the energy consumption of the feeder star wheel. The interaction mechanism between the star wheel arm and coal particles is the theoretical basis of the research. First, the design method of the star wheel arm shape was provided, then a model of the star wheel was constructed with EDEM and a simulation structure. Finally, the influence of the parameters on loading efficiency and energy consumption was determined. Results have been shown that the coal particles in the active zone of the material pile exerts a fluidity effect on loading efficiency and torque. The loading efficiency and energy consumption have been increased with increase in the number of arm and height of the arm. The feeder inclination angle 14° is the best coal loading angle.

Transmission towers are critical components of electrical transmission systems, whose damage and failure during earthquakes may cause extensive economic losses and significantly hinder the post-seismic rehabilitation. Seismic fragility analyses of pile-supported transmission towers are usually performed without regard for the influences of soil-structure interaction (SSI) and the site amplification of ground motions from the pile end to ground surface, which may lead to inaccurate structural performance evaluation results. In this context, the present study numerically investigates the seismic fragility of a typical pile-supported transmission tower considering SSI and depth-varying ground motion (DVGM) inputs. Specifically, a three-dimensional finite element model of the transmission tower is created in ABAQUS software, and SSI is simulated by adopting soil springs at the end of pile nodes. The three-dimensional DVGMs are stochastically synthesized to be used as seismic inputs. Moreover, the pushover analysis is employed to identify the threshold values of different limit states of the transmission tower. Then, probabilistic seismic demand models (PSDMs) are developed by nonlinear time history analyses and linear regression fitting, which are used to generate fragility curves. Furthermore, parameter studies are carried out to discuss the effects of SSI, DVGMs and structural parameter uncertainties on the seismic fragilities. Numerical results show that the seismic fragilities of the transmission tower can be affected substantially by the above mentioned three influencing factors. This research is expected to serve as an exploration to reliably and effectively evaluate the seismic fragility of a transmission tower with SSI.

Root pile is a new type of pile that improves the load carrying capacity by roots penetrating into soils. To carry out the nonlinear settlement analysis of such a root pile in multilayered soils, the hyperbolicity-based load transfer model is in this paper reformulated to account for the discontinuities between the segments with and without roots. The procedure to determine the model parameters for root piles is presented accordingly. The feasibility and reliability of such a proposed modified hyperbolic model for nonlinear settlement analysis of root piles in multilayered soils are verified by a numerical case and two real experimental cases. The numerical case study shows that the root pile does increase the pile load carrying capacity to some extent. In a parametric study based on this numerical case, it can be found that the bearing capacity of root piles increases along with the increase in the root number, size, depth and the elastic modulus of the surrounding soil. The loading test results on two real root piles sited in Chizhou Yangtze River Bridge, China, are used to further verify the proposed method. Comparing with other analytical methods, it is demonstrated that the proposed method incorporated with the proposed modified hyperbolic model can achieve a better agreement with the measured ones especially in a large loading stage.

Due to the acceleration of urbanization in China, the land use and new building construction in mining subsidence areas are increasing. However, a large high-rise building (100 m × 80 m × 100 m) was planned to be built above gob areas in the Xiangcheng Mine subsidence area. According to the analysis of the borehole exploration data, borehole TV observations, and theoretical calculations, there were broken bedrock and developmental fractures in the fracture and caved zones above the gob areas. In addition, the depth affected by the building load is less than 9 m from the top of the fracture zone; thus, the stabilities of the gobs are low. Then, through the theoretical analysis of the space stress, compression settlement of foundation soil, and residual settlement of the gob and coal pillar under loads, combining the similar simulation study on settlement characteristics of foundation soil and gobs, the total settlement of the foundation can be regarded as the vector superposition of the compression settlement and residual settlement; then, the maximum settlement is calculated as 555 mm and the maximum tilt is 14.9 mm/m under the building load, which are greater than the permissible values of 200 mm and 2 mm/m, indicating that the foundation’s stability is inadequate. Therefore, the treatment measures of the deep pile group foundations in the soil layer and grouting reinforcement in the gobs were simultaneously put forward to effectively improve the stability of the building foundations.

To propose a simplified semi-empirical method for predicting the additional stress on the underlying layer of the rigid pile-net composite foundation, a finite element analysis, which verified by a...

In this study, liquefaction mitigation potential of improved ground using pervious concrete column is being investigated. The seismic performance of pervious concrete column improved ground is compared with conventional stone column improved ground. Three-dimensional finite element analysis using OpenSeesPL software is conducted to study the ground lateral deformation and excess pore water pressure generation of pervious concrete column improved ground on a mildly sloping soil strata of infinite extent under seismic loading. The soil strata considered is fully saturated sand with an inclination of 4°. The parameters influencing seismic performance of improved ground like area ratio, founding depth of columns, diameter of columns and hydraulic conductivity of columns are considered. It is found from various response parameters that the pervious concrete column improved ground has better seismic performance than conventional stone column improved ground. The lateral deformation profile of pervious concrete column is found to be similar to that of concrete pile, allowing excess pore water pressure to dissipate through the pores of pervious concrete column. It is also concluded that pervious concrete columns could be used as an alternative to conventional stone columns to mitigate liquefaction to a larger extent.

Pile foundation settlement is a kind of foundation form. In recent years, because of the increasing population and economic development in China, high-rise buildings have emerged in people’s vision. Due to the development of engineering construction, the type and technology of pile foundation, as well as the control and detection of the single pile and pile group have been greatly improved. In view of the influence of pile foundation settlement on the surrounding environment of high-rise buildings, this paper mainly studies from the angle of single pile settlement and pile group settlement. According to the construction method of pile foundation, the static pressure sinking pipe cast-in-place pile can produce soil squeezing effect in pile foundation construction. The experimental analysis was carried out. According to the engineering example, finite element numerical simulation is used to analyze the influence degree of pile foundation settlement on adjacent buildings with and without raft, and the feasibility and correctness of numerical simulation are analyzed by comparing the simulation results with the measured values. This paper mainly studies the influence of pile foundation settlement of high-rise buildings on surrounding buildings from the aspects of problems and solutions.

The lateral deformation behaviour of inclined piles in calcareous sand is investigated with model testing and numerical analysis. A model pile is instrumented with quasi-distributed strain sensors ...

The rigid long-short-pile composite foundation has been increasingly used as an effective and low-cost reinforcement method. The pile-soil interaction in this foundation type is more complicated than that in the equal-length pile composite foundation. In this study, several physical model tests were conducted to investigate the pile-soil synergistic mechanism of the rigid long-short-pile composite foundation. A comparative analysis was conducted of the static load test data of single-pile and long-short pile composite foundations to assess the load-bearing characteristics and stiffness evolution of the composite foundation and pile-soil unit. The result indicated a positive correlation between the pile length and the overall bearing capacity of the single-pile composite foundation. The overall stiffness of the four-pile composite foundation was lower than that of the single-pile composite foundation due to an increase in the areas of the soil stress and the pull-down effect caused by multiple piles. The long pile exerted a greater influence on the overall settlement than the short pile. In addition, the correction coefficients were obtained to determine the pile-soil stiffness of the four-pile composite foundation based on that of the single-pile composite foundation, providing a theoretical reference for the optimal design of composite foundations.

Based on the nonlinear Winkler theory, a simplified method for evaluating the lateral bearing capacity of the caisson-pile foundation (CCPF) considering the effect of scour-hole dimensions was prop...