Model Piles Research Articles

Effect of the Slenderness Ratio of Piles on Ultimate Lateral Resistance in Sandy Soil

This research presents the results of 14 tests, where the pile is subjected to static lateral loads. The tests are carried out on pile models with different length / diameter ratios embedded in sand with different relative densities. The influence of embedment length to diameter ratios (L/D), relative density and mode of failure of the pile on the ultimate lateral resistance of piles are investigated. A series of different ratios of embedded length to constant diameter ranging from 12 to 30 was used to perform this study. From the results of the experimental models, it is found that, the length to diameter ratio is a significant variable that influences the ultimate resistance of the piles, where lateral static loads were employed to the single pile by a static lateral load using a device designed for this purpose, and due to the static lateral load the pile was deflected. The ultimate lateral resistance of a pile is investigated to specify the behavior of the pile under the effect of lateral loads as a rigid or flexible pile.

Effect of Seismic Loading on Variation of Pore Water Pressure During Pile Pull-Out Tests in Sandy Soils

Experimental model was done for pile model of L / D = 25 installed into a laminar shear box contains different saturation soil densities (loose and dense sand) to evaluate the variation of pore water pressure before and after apply seismic loading. Two pore water pressure transducers placed at position near the middle and bottom of pile model to evaluate the pore water pressure during pullout tests. Seismic loading applied by uniaxial shaking table device, while the pullout tests were conducted through pullout device. The results of changing pore water pressure showed that the variation of pore water pressure near the bottom of pile is more than variation near the middle of pile in all tests. The variation of pore water pressure after apply seismic loading is more than the variation before apply seismic loading near the middle of pile and near the bottom of pile and in loose and dense sand. Variation of pore water pressure after apply seismic loading and uplift force is less than the variation after apply seismic loading in loose sand at middle and bottom of pile.

Effect of Dynamic Earth Vibration on the Behavior of Laterally Loaded Single Pile Embedded within Unsaturated Soil

Most of the studies of laterally loaded piles focused on the behavior for piles subjected to static or cyclic lateral loading embedded within dry or saturated soils, few studies investigate the behavior of piles embedded within partially saturated soils and subjected to dynamic loads. In this research, an experimental study presents an aluminum pile model embedded within dry, fully saturated and partially saturated soils, subjected to dynamic load with the El Centro 1940 NS acceleration data (0.05g, 0.15g, and 0.32g) accelerations. Three different lowering levels of the water table for fully saturated soils model is achieved to get partially saturated soils of three different values of matrix suction. During an earthquake model, a liquefaction phenomenon is observed by boiling of sand and completed collapse in the soil as shown in the results. It is concluded that the resisting to the bending moment reduced by 22%, 50%, and 57% after 1st, 2nd and 3rd lowering of water level respectively, than that of the saturated condition. This reduction approaches to 28% for completely dry soil. It is worth to mention, that, the deflection of the pile reduced as the lowering of water level increased. The soil resistance increases with the increasing of dynamic load acceleration. The soil resistance increases about 35% when the acceleration increase from 0.05g to 0.15g and an increase of about 22% when the acceleration increases from 0.15g to 0.32g.

Damage effect of pile wharf under underwater explosion load

According to the relevant data of reinforced concrete pile test under underwater explosion load in the near-field range of the cooperative company, the corresponding numerical model is established through the explicit finite element analysis program AUTODYN. The accuracy of the required parameters and the calculation method in the numerical simulation process is verified by comparing shock-wave load with reinforced concrete pile damage. Considering the influence of charge quality on the dynamic response and damage mode of reinforced concrete single and group piles, the collapse conditions of the high-pile wharf are analyzed from static and dynamic aspects based on the reinforced concrete pile model of a typical high-pile wharf structure. Results show that the reflected pressure of shock wave is unevenly distributed along the pile with different explosive equivalents, that is, large in the middle and small on both sides. The damage modes of single piles can be divided into bending, bending shear, and shear failures. The study of the continuous collapse condition of piled wharf reveals that the concrete pile and the cap contact part of the first coagulant crushing failure.

Lateral Responses of a Model Pile in Biocemented Sand

Abstract This technical note aims to investigate the effects of biotreatment on the response of a concrete model pile embedded in poorly graded sand through lateral loading tests. The bending momen...

Study on Bearing Mechanism of Split Grouting Pile Based on Finite Element Simulation

In order to realize the directional and controllable splitting of splitting grouting, the field grouting test was carried out. Using a new grouting pipe designed, the splitting direction and size of the branch vein are effectively controlled through the control of grouting pressure and grouting amount. In order to explore the bearing characteristics of split grouting pile and provide necessary parameters for the design of split grouting pile composite foundation in engineering practice, the field static load test and indoor geotechnical test of split grouting pile are designed, and the ultimate bearing capacity of single pile and necessary soil parameters are obtained. In order to make up for the limitations of field static load test, the three-dimensional finite element model of pile, soil and branch vein of split grouting pile is established by using the finite element analysis software ABAQUS. The finite element analysis results are compared with the measured values of field test, and the variation laws of pile shaft axial force, stress and displacement of branch vein at different depths, pile side friction, etc. are further explored, Through these changes, the interaction and load transfer mechanism between pile and soil are analyzed, which provides a reference for optimal design.

A cyclic p-y model for the whole-life response of piles in soft clay

It is evident from model testing, field studies and theoretical considerations that the strength of a soft clay can reduce and then recover – potentially to above the initial value – as a result of cyclic loading followed by consolidation. For piled foundations and well conductors, these changes in soil strength and the resulting lateral resistance affect their stiffness, capacity and fatigue. This paper introduces a new model for the cyclic lateral ‘p-y’ response of a pile in soft clay, using concepts from critical state soil mechanics, combined with a parallel Iwan model to capture the hysteric response. Example analyses show that the model can capture the general forms of behaviour observed in model tests, and is rapid and simple to implement. The model provides a new basis for whole life modelling of piles and well conductors, allowing changes in stiffness and capacity to be simulated, as well as improved modelling of fatigue accumulation. This approach allows more reliable design, quantifying the benefits and risks associated with evolving soil strength.

Assessment of Stress in the Soil Surrounding the Axially Loaded Model Pile by Thin, Flexible Sensors.

Foundation piles transfer the applied vertical load to the surrounding soil by skin friction and base resistance. These two components induce stress in the soil. The load transfer is still not fully recognized, and some pile load tests analyses have raised many doubts. The present paper aimed to measure the stress levels during pile load tests in laboratory conditions. This research examined the possibilities of using thin, flexible sensors in measuring the stress in soil. Two sensors were used: tactile pressure sensor with mapping system and color film pressure sensors with digital analyzing. Calibration and preliminary tests of the sensors have been described. This calibration proved that this kind of sensor could measure the stress in the soil in laboratory conditions. The results of stress distribution in the soil, shown as pressure maps, have been presented. Significant stress changes were observed in pile load tests. Rough and smooth piles were compared in the analyses. Stress distribution was the result of simultaneous interaction of pile skin and base. The knowledge about stresses surrounding the pile allows us to carry out a deeper analysis of the pile–soil interaction.

A simplified approach for the response of pile groups composed of dissimilar piles

In practice, saddle-shaped settlement is often investigated in the pile group foundation with identical piles. For the purpose of decreasing the differential settlement, uneven-distributed pile groups can be used. This paper provides a simplified approach to capture the behaviour of pile groups with dissimilar pile length or pile diameter. The hyperbolic function was adopted to express the mechanism of the interface between pile and soil. Considering the interaction of piles with dissimilar length, the hyperbolic load-transfer model of individual pile in pile groups composed of dissimilar piles were proposed. The related parameters of load transfer function of pile shaft or pile base of dissimilar piles were determined. To clarify the deformation mechanism of pile-soil system, an iterative approach for the analysis on the behaviour of non-uniformly arranged pile groups was proposed. Comparisons between the present computation results and the finite element simulation results were drawn to check the dependability of the proposed approach. Moreover, taking 3 × 3 pile groups as an example, the bearing characteristics of the centre pile, the edge pile and the corner pile in pile groups with different pile arrangements were analysed. For practical purposes, some suggestions on the pile groups composed of dissimilar piles were given to alleviate differential settlement among each individual pile and decrease the cost of pile groups and the construction difficulties.

Effect of model scale on helical piles response established from shake table tests

This paper investigates the effect of model scale on seismic response of prototype helical pile (HP) groups employing finite element modelling approach verified by the results of single gravity shaking table models of piles installed in dry and saturated sands. The prototype shaking test configuration was established from model shake table tests by adopting a set of similarity and dimensional laws. The results demonstrated that the scaled models exhibited generally similar responses. The HPs' response in the saturated sand bed was dominated by the rocking behaviour, while the flexural behaviour dominated the response in the dry tests. In addition, the HPs' lateral response followed the lateral soil uniform deformation in the dry tests, while they did not follow the nonuniform soil deformation in the saturated tests. However, the prototype models' axial and lateral responses were different from the results of the shaking table scale. The HP exhibited less scaled lateral deformation, bending moments, and settlement in the prototype models than those at the shaking table scale in the dry and saturated tests. Meanwhile, the prototype helices’ stress was higher than the shaking table helices in the saturated tests and less than them in the dry tests. A set of scaling factors was suggested for extrapolating the soil and HP responses from 1 g shake table model tests. Based on the obtained results, the soil and HP responses may be extrapolated from 1 g shake table model tests employing the following scaling factors: soil displacement increase factor, SDIF = 0.8n in the saturated tests, and SDIF = 0.6n in the dry tests, while the pile displacement increase factor, PDIF = 0.7n in the saturated test and 0.5n in the dry test.

Study on Heat Transfer Model and Applicability of Energy Piles in Nanning Basin under Subtropical Climate

In order to meet the requirements of peak carbon dioxide emissions, energy pile systems have been widely used in more and more regions because of their low-carbon, energy-saving, and emission-reducing characteristics. To explore the applicability of the energy pile project in Nanning, which has typical subtropical climate characteristics with warm winters and hot summers, some research work has been carried out in this paper. Firstly, through indoor thermophysical property tests, the geotechnical thermophysical parameters of typical composite strata in this area are obtained. Then a transient heat transfer model of the energy pile is established, which can fully reflect the heat transfer characteristics of the pile and the soil. On this basis, the superposition principle and stepped heat flow theory are used to analyze the temperature recovery characteristics of typical strata in Nanning area under different intermittent operation conditions. The results show that: the rock-soil mass of the typical stratum in Nanning area has good heat transfer characteristics, which is conducive to the promotion of energy pile engineering. The heat transfer model proposed in this paper has higher accuracy than the classical linear heat source model, which can reflect the material characteristics of energy pile system and avoid overestimating or underestimating the temperature field of energy pile system. The operation of energy pile system in a subtropical climate will produce an unbalanced heat load, and corresponding measures need to be taken to achieve the balance of heat load. The research results can provide a reference for energy pile engineering design in different climate regions.

Performance Analysis on Heat Transfer Enhancement of Energy Pile with Nanofluid

Energy pile is a novel ground heat exchanger with the pipes buried within building piles. The heat transfer performance of energy piles is essential for the ground source heat pump system’s efficiency, economy, and reliability. Nanofluids can improve the convective heat transfer inside the heat exchange pipe and the heat transfer of ground heat exchangers. The improvement of the thermophysical properties of nanofluids has been studied previously. However, only a few research studied the heat transfer performance analysis of a spiral coil energy pile with nanofluids as the heat carrier. Hence, this study will investigate the heat transfer enhancement of the energy pile contributed by a nanofluid. The analytical model of a spiral coil energy pile with seepage and the correlations of thermophysical properties of the nanofluid were employed. The heat transfer capacity, wall temperature, and the outlet temperature of an energy pile under different factors were studied. The results showed that by adopting the nanofluid, the heat transfer of the energy piles increased by 1.21 % ∼ 3.12 %, and the pile wall temperature increased by 0.22 °C–0.47 °C. The increase in the outlet temperature caused by the nanofluid is more significant than that caused by increasing the spiral pitch. It is also is more constant than that caused by increasing the seepage velocity. This work can contribute to improving the heat transfer performance of energy piles.

Feasibility Analysis of Utilization of Shallow Geothermal Energy through LNG Tank Pile Foundation

Liquefied Natural Gas (LNG) needs an additional heat source to meet its heat demand in the process of gasification. Based on the background of using shallow geothermal energy, the feasibility of using LNG tank piles as heat exchangers for LNG gasification was studied. A two-dimensional finite element heat transfer model of energy piles was established, and the heat transfer capacity and long-term stability of different buried pipe options were analyzed. The results show that the LNG tank energy piles can meet part of the heat demand for LNG gasification to a certain extent.

Probabilistic Seismic Response and Capacity Models of Piles for Statewide Bridges in California

This study develops the probabilistic seismic response and capacity models for the broad collection of standard pile designs that are routinely incorporated into bridges in California. A review of the state bridge inventory indicates considerable variations in design details for different standard pile types used across multiple eras. For each pile type, fiber-section-based pile models attached with p-y soil springs are built to incorporate nonlinear behaviors of soil materials, a wide array of heterogeneous soil profiles, full-range damage states of piles, and realistic connection details between piles and footings (i.e., pile caps). Moreover, force-displacement responses of pile-soil systems under a large number of pushover analyses are regressed as response models consisting of five parameters [termed as response five parameter (R5P) models], which can capture all essential behaviors of laterally-loaded piles. Capacity damage states and limit state models are defined for different pile types by linking pile global responses to fiber-scale material behaviors at plastic hinge locations. Procedures are further provided to expand R5P models to pile foundation models at the regional scale, taking into account the pile group effect and capacities of pile cap backfills. R5P models for all distinct pile types are further summarized in an Excel workbook to facilitate their practical implementations. In general, this study provides a comprehensive and consistent set of response and capacity models to quantify the seismic damage potential of regional pile foundations, as well as to capture their dynamic interplays with other crucial bridge components, such as columns and abutment components. The proposed pile models are expected to significantly enhance the existing modeling capability toward improved seismic risk assessment of California’s bridge infrastructure.

BEHAVIOUR OF PILES SUBJECTED TO LATERAL FORCES IN COHESIVE SOIL

Although piles are elements designed primarily to support vertical loads, They are subjected to horizontal loads by serval sources such as earthquake, wind, impact loads and lateral earth pressure. Large number of studies have been carried out to investigate the effect of different parameters on the behavior of piles. These parameters are summarized as i) effect of pile diameter, ii) angle of the pile with the vertical, iii) piles slenderness ratio and soil type. In the present study an experimental program was carried out to identify the deflection of vertical and inclined piles subjected to a lateral force in cohesive soil. The experimental program comprised pile lateral load tests performed on model of single pile driven in cohesive soil. Using the experimental model results, relations were utilized to estimate the lateral deflection of piles.

Automated High-Speed S-Wave Velocity Tomographic System for Laboratory Geotechnical Engineering Process Monitoring – A Study on Pile Installation

Abstract This paper reports the innovative development of a flexible, multiple-layer, economical but robust, and automated high-speed shear wave (Vs) tomographic control and data acquisition system for process monitoring in the laboratory and the associated validation for monitoring the dynamic process of model pile installation. This tailor-made tomographic system consists of four major parts: (i) the control unit built with a microcontroller board, (ii) a signal generating unit, (iii) three layers of bender element sensing arrays (including 14 source and receiver bender elements per layer), and (iv) a signal receiving unit. The system allows for sampling rates up to 1 GS/s (20 MS/s were used in this study); the required total measurement time is 2.94 seconds (i.e., for 196 ray path measurements) to allow for dynamic process monitoring. The obtained time-lapse Vs tomographic images during pile installation show that Vs first gradually increases when the pile toe is approaching the sensing layer and gradually decreases afterward as the pile toe penetrates through the layer. The validity of the Vs tomographic images is supported by similar responses in variations of the circumferential stress σc′ and radial stress σr′, measured by the tactile pressure sensors.

Shear behaviour of E-UHPC containing recycled steel fibres and design of E-UHPC screw piles

The shear behaviour of Eco-Efficient Ultra-High Performance Concrete (E-UHPC) has not been investigated until now and this limits the potential applications for this material that uses low-cost and sustainable constituent materials including Recycled Tyre Steel Fibres (RTSF) and Recycled Tyre Steel Cords (RTSC). The potentially high shear resistance of E-UHPC could enable its use in more complex applications such as screw piles, something not easily achievable with conventional concrete. This study presents experimental and numerical work to address this research gap. It provides a detailed account of the experimental testing of 13 E-UHPC mixes containing various dosages of recycle steel fibres. Prismatic specimens are tested under an asymmetric four-point loading configuration and their deformation response is used to investigate the shear performance of the studied mixes. The shear stress – strain behaviour as well as shear modulus is determined. The results show that mixes containing RTSC can develop a high shear strength at the level of their flexural strength and comparable to that obtained from mixes with manufactured steel fibres. While mixes containing RTSF overall have lower shear strengths, high shear strengths can be achieved by using higher dosages of RTSF or using hybrid mixes of RTSF and RTSC. Shear strength prediction models based on flexural properties and fibres dosage are proposed for design purposes. An E-UHPC screw pile design model is developed for screw pile use in foundations of light and medium weight structures. Theoretical and physical modelling of the E-UHPC screw pile model is carried out and a design guideline is proposed. E-UHPC screw piles can offer various practical advantages, including rapid installation, immediate load carrying capability, minimal site disturbance, resistance to wide load applications, i.e. compression and tensile loads, and will solve the corrosion vulnerability of steel screw piles.

Comparison of plugging impact of open-ended with closed-ended model piles in clayey soils

Comparison of plugging impact of open-ended with closed-ended model piles in clayey soils

In Situ Test Research on Friction Resistance of Self-Anchored Test Pile

The traditional static load test method has been considered as the most direct and reliable method to determine the bearing capacity of single pile, but it has some disadvantages, such as inconvenient operation, laborious test, high cost, and being time-consuming. In this paper, a new type of pile testing method, self-anchored pile testing method, was proposed, and the in situ test was carried out for the first time. This method allows the upper and lower piles to provide force to each other and does not occupy other construction spaces. It had the advantages of simple operation and being economical and practical. Based on the Q-w curve, axial force distribution curve, and hyperbolic function model of load transfer, this paper studied the evolution law of friction of self-anchored test pile and the load transfer process of self-anchored test pile. The results show that the load transfer process of self-anchored pile-soil interface can be divided into three stages: elastic, elastic-plastic, and limit state. The friction of the upper and lower piles starts from the bottom of each pile and then gradually increases. The soil around the upper and lower piles gradually undergoes nonlinear deformation and shear failure, and the pile soil reaches the yield state. By analyzing the hyperbolic function model of load transfer, it shows that the hyperbolic function model can be better applied to the self-anchored test pile, which has reference value for the selection of the function model of self-anchored test pile in the future.

An elastoplastic solution for cylindrical cavity expansion under constant water content conditions in anisotropic unsaturated soils

In this paper, an elastoplastic solution is developed for cylindrical cavity expansion in anisotropic unsaturated soils under constant water content conditions. The most prominent features of the solution can be attributed to 1) the stress–strain behaviour of unsaturated soil is subtly coupled with the saturation-suction behaviour; 2) both the mechanical and hydraulic behaviours are modelled as elastoplastic processes; and 3) an anisotropic critical state soil model for saturated soil is extended to an unsaturated situation to consider the effects of the initial stress anisotropy and stress-induced anisotropy of the natural unsaturated soils. The problem is formulated as a system of first-order differential equations and solved as an initial value problem. A numerical code that can judge the hydraulic yield condition of soil particles during the cavity expansion process is developed based on the Runge-Kutta algorithm to solve the governing equations. Parametric analyses, which cover a wide range of suctions, overconsolidation ratios, degrees of initial stress anisotropy, are conducted to investigate the effects of these important factors on the expansion responses in unsaturated soils. The proposed solution could potentially be applied to interpret pressuremeter tests and model pile installation effects in anisotropic unsaturated soils.