Installation Of Displacement Piles Research Articles

Influence of residual stress and soil dilatancy on the load capacity of jacked pile

ABSTRACT Pile jacking is one of the commonly adopted techniques for installation of displacement piles. The present study investigates the evolution of residual stresses during the pile jacking process and its subsequent impact on the pile load capacity with a particular emphasis on the soil dilatancy angle. The simulations have been carried out following an updated Lagrangian-based finite element framework employing ABAQUS. The magnitude of radial to vertical residual stress ratio coincides with the passive earth pressure coefficient within a radial zone of 6D and reduces to the at-rest coefficient beyond 20D. Owing to the enhanced stress-state, the load capacity of jacked pile is markedly higher than the in-place one with a predominant contribution from the shaft resistance. A small increase in soil dilatancy results into significant enhancement of residual radial stress and extent of influence zone, which further leads to increased load capacity in jacked pile through enhanced shaft resistance.

Numerical investigation of displacement pile installation in silica sand

The penetration of deep foundations into sand is a classic geotechnical engineering problem that carries not yet fully understood aspects of the soil-pile interaction. The complexity of rigorous numerical and experimental studies of these foundations is well-stated in the literature. Extensive measurements of the properties of the soil that surrounds the pile are difficult to obtain experimentally. In this paper, the analysis of the installation of closed-ended, displacement piles in two silica sands is undertaken. Centrifuge tests from the literature on loose and dense dry sand samples are employed for validation of the numerical models, based on the Arbitrary Lagrangian-Eulerian (ALE) method. To capture the constitutive behaviour of the sand, the hypoplastic constitutive law with intergranular strain is adopted. After successful validation, an investigation on the variation of the initial conditions of the soil mass surrounding the pile during its installation is undertaken, and their influence on the tip resistance, the radial stresses, and the void ratio at the target penetration depths are identified. This paper illustrates the effect of cone apex angle on the state of sand after installation. Flat-ended piles tend to create clear zones of dilated material around the shaft.

Large-Deformation Finite-Element Simulation of Deformation and Strain Fields Resulting from Closed-End Displacement Pile Installation in Sand

Large-Deformation Finite-Element Simulation of Deformation and Strain Fields Resulting from Closed-End Displacement Pile Installation in Sand

Effects of full displacement pile installation on the stress and deformation state of surrounding soil: review

Effects of full displacement pile installation on the stress and deformation state of surrounding soil: review

MPM modeling of pile installation in sand: Contact improvement and quantitative analysis

The material point method (MPM), which is known to be advantageous in modeling large deformation and contact problems, is utilized in this study to simulate displacement pile installation in sand. A modified Bardenhagen’s contact algorithm is proposed that calculates the node-to-surface distances between the deformable soil mass and the rigid pile surface more effectively, along with a smoothing factor for the change of momenta between the contacting bodies. The modified algorithm is shown to produce more accurate and stable contact results. Three tests, namely, the rolling cylinder, the penetrating wedge, and the strip footing, are first conducted to demonstrate the validity of the modified algorithm. It is then applied to analyze the installation of a closed-ended pile, employing a state-dependent Mohr–Coulomb model to capture the sand’s state-dependent shearing behavior. Detailed analyses of the stress and deformation fields developed around the pile during steady penetration reveal quantitative agreement between the MPM predictions and published experiments, indicating that the approach holds promise for use in more sophisticated analyses designed to improve the understanding of industrially driven piles.

DEM investigation of sand response during displacement pile installation

Previous experimental and numerical studies indicate that the stress state of sand at a specific depth changes significantly during the installation of a displacement pile. At a given depth level, the horizontal stress in sand increases as the end of pile approaches and reduces as the pile continues to penetrate and go past the sand element. This horizontal stress reversal, together with the large-strain deformation of the sand at the pile shaft, may cause a reduced accuracy in the calculation of pile capacity. In this paper, the micro-mechanical behaviour of sand developed around pile shaft during the installation of a closed-ended pile was studied using the two-dimensional Discrete Element Method (DEM). Sand assembly was modelled as uncrushable discs, and the closed-ended pile was modelled as a rigid clump which was made of a large number of overlapped discs with a fixed distance. The sand responses in terms of stress, strain and volume changes during the monotonic jacking of the closed-ended pile were investigated. Simulation results revealed micro-mechanical behaviours of the sand in both the interface zone “B” adjacent to the pile shaft and the far field zone “A” away from the pile. It was shown that the sand along the pile shaft at a small normalised distance to pile tip was subjected to a volume reduction as the pile goes past. As the pile drives deeper, the sand at a larger normalised distance to pile tip exhibited dilation. This captured process will give insights to the degradation of shaft friction at a given sand horizon.

Numerical analysis of the set-up around the shaft of a closed-ended pile driven in clay

When a pile is driven into the ground, soil standing in the path of the pile is heavily distorted as it has to cede for the penetrating pile. At the end of installation, this soil is left in a distressed state, which progressively evolves to an equilibrium with time. As a result, for lightly overconsolidated clays, soil resistance generally decreases during driving but increases after installation; the latter phenomenon is referred to as set-up. Correct assessment of pile set-up is one of the most important considerations of displacement pile design, especially offshore. Indeed, underestimation of set-up leads to unnecessary expense and overestimation of set-up leads to a precarious overestimation of the pile capacity. This paper presents a numerical model, the aim of which is to predict set-up around the shaft of a driven pile in clay. The model was conceived after a careful literature review of the relevant field data, in order to support its assumptions. It is used to predict the stress and pore pressure distributions around the shaft of a driven pile during installation and subsequent equalisation. Numerical results are then compared to the literature results. Although the model underestimates the excess pore pressure created around the pile, it captures a key feature of displacement pile installation in clay: at the end of installation, the radial distribution of excess pore pressure presents a peak located a few radii away from the pile wall. This implies that, during equalisation, the radial effective stress at the pile wall decreases to a short-term minimum, leading to a short-term minimum in pile capacity, before eventually increasing.

Numerical simulations of deep penetration problems using the material point method

Penetration problems in geomechanics are common. Usually the soil is heavily disturbed around the penetrating bodies and large deformations and distortions can occur. The simulation of the installation of displacement piles is a good example of the interest of these types of problems for geomechanics. In this paper the Material Point Method is used to overcome the difficulties associated with the simulations of problems involving large deformation and full displacement type penetration. Recent modifications of the Material Point Method known as Generalized Interpolation Material Point and the Convected Particle Domain Interpolation are also used and evaluated in some of the examples. Herein a footing submitted to large settlements is presented and simulated, together with the processes associated to a driven pile under undrained conditions. The displacements of the soil surrounding the pile are compared with those obtained by the Small Strain Path Method. In addition, the Modified Cam Clay model is implemented in a code of MPM and used to simulate the process of driving a pile in dry sand. Good and rather encouraging agreement is found between compared data.

Numerical investigation of pile installation effects in sand using material point method

The installation of displacement piles in sand leads to severe changes in the stress state, density and soil properties around the pile tip and shaft, and therefore has a significant influence on the pile bearing capacity. Most current numerical methods predicting pile capacity do not take installation effects into account, as large deformations can lead to mesh distortion and non-converging solutions. In this study, the material point method (MPM) is applied to simulate the pile installation process and subsequent static pile loading tests. MPM is an extension of the finite element method (FEM), which is capable of modelling large deformations and soil-structure interactions. This study utilizes the moving mesh algorithm where a redefined computational mesh is applied in the convective phase. This allows a fine mesh to be maintained around the pile tip during the installation process and improves the accuracy of the numerical scheme, especially for contact formulation. For the analyses a hypoplastic constitutive model for sand is used, which takes into account density and stress dependent behaviour. The model performs well in situations with significant stress level changes because it accounts for very high stresses at the pile tip. Numerical results agree with centrifuge experiments at a gravitational level of 40g. This analysis confirms the importance of pile installation effects in numerical simulations, as well as the proposed numerical approach’s ability to simulate installation and static load tests of jacked displacement piles.

Shearing resistance during pile installation in sand

This paper examines the detailed stress changes recorded by surface stress transducers equipped on model piles during jacked installation of various piles at sand sites with different groundwater regimes and sand characteristics. Three separate types of shear stress–displacement characteristics are observed and these are explained using findings from existing laboratory and field-based studies on soil-pile–penetrometer interface friction. The findings advance understanding of factors influencing the shearing resistance developed during displacement pile installation in sand, which is an important consideration for pile driveability assessments.

The Analysis of Soil Resistance During Screw Displacement Pile Installation

Abstract The application of screw displacement piles (SDP) is still increasing due to their high efficiency and many advantages. However, one technological problem is a serious disadvantage of those piles. It relates to the generation of very high soil resistance during screw auger penetration, especially when piles are installed in non-cohesive soils. In many situations this problem causes difficulties in creating piles of designed length and diameter. It is necessary to find a proper method for prediction of soil resistance during screw pile installation. The analysis of screw resistances based on model and field tests is presented in the paper. The investigations were carried out as part of research project, financed by the Polish Ministry of Science and Higher Education. As a result of tests and analyses the empirical method for prediction of rotation resistance (torque) during screw auger penetration in non-cohesive subsoil based on CPT is proposed.

Sand grain crushing and interface shearing during displacement pile installation in sand

Particle crushing, shear banding, interface abrasion and migration of crushing products all have the potential to influence the behaviour of displacement piles in sands. This paper considers these particulate processes, reporting experiments with model displacement piles installed in uniform pressurised sand and parallel interface ring shear tests. The findings offer new insights into the mechanics of displacement piles in sands.

Field measurements of the stiffness of jacked piles and pile groups

INTRODUCTION This Technical Note presents a back-analysis of the axial response of some field-scale tubular displacement piles installed by jacking. This study was motivated by the recent development of large pile-jacking rigs. These rigs are sufficiently strong to offer an alternative to bored piling in urban areas where conventional dynamic methods of displacement pile installation are not permitted (White et al., 2002). The most notable feature of the axial response was the very high stiffness. Some pile jacking machines ‘walk’ along the pile wall under construction, so all piles must necessarily be installed at close centres, or indeed touching. This geometry is in contrast to conventional design guidance, which suggests that a separation of typically two or three diameters is required between piles, to prevent harmful interaction effects (BSI, 1986; GEO, 1996). Load test results from jacked piles installed closer than this recommended minimum spacing are presented. The study comprised a series of field tests carried out in Kochi, Japan. Full details are provided by Yetginer et al. (2003), and brief details are repeated below. Test piles were installed singly and in groups forming a ‘cell foundation’, comprising jacked piles at close centres around an enclosed soil block. In this Technical Note, pile group efficiency is defined as the average performance per pile (strength or stiffness) when a group is loaded in unison, divided by the performance of a single pile tested alone. Using this definition, the behaviour of trial piles installed prior to the main group can be linked to the group response. This definition is used by Vesic (1969) and Fleming et al. (1992), and is shown in equation (1) for strength and stiffness. Group strength efficiency, GROUP, is defined in equation (1a), where QSINGLE and QGROUP represent the capacity of a single (isolated) pile and the capacity of a group of n piles respectively. Group stiffness efficiency, GROUP, is defined in equation (1b), where KSINGLE and KGROUP represent the stiffness of a single (isolated) pile and the stiffness of a group of n piles respectively.

Bearing capacity of rigid piles under eccentric and inclined loads

The ultimate bearing capacity of instrumented vertical single rigid model piles in homogeneous loose sand and soft clay under vertical eccentric and central inclined loads has been investigated. The results of these load tests provide a more realistic lateral soil pressure distribution on the pile shaft and better theoretical estimates of pile capacity under pure moment and under horizontal load. For intermediate eccentricities and inclinations of the load, the bearing capacity can be obtained from simple interaction relationships between the axial load and moment capacities and between the axial and horizontal load capacities, respectively. The influence of lateral soil pressures due to installation of displacement piles in clay is examined in relation to the ultimate load of the pile. The analyses are compared with the results of model tests and some field case records. Key words: bearing capacity, clay, eccentric loading, horizontal load, instrumentation, model test, pile, sand.

Survey of problems associated with the installation of displacement piles : Healy, P R; Weltman, A J DOE and CIRIA Piling Development Group report PG8, Oct 1980, 54P

Survey of problems associated with the installation of displacement piles : Healy, P R; Weltman, A J DOE and CIRIA Piling Development Group report PG8, Oct 1980, 54P