Axial cyclic loading of piles in low to medium density chalk (original) (raw)

Monotonic and cyclic lateral tests on driven piles in Chalk

Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2017

This paper describes the results of a pile-testing campaign on open-ended tubular steel instrumented piles driven into the Chalk formation in the UK. The testing campaign comprised the performance of both monotonic and one-way cyclic lateral load tests, performed at different times after pile installation. The tests were performed on five piles with uniform outer diameters of 762 mm and embedded lengths of 4 m and 10 m to investigate the difference in response between short and long piles. Lateral pile head load–displacement behaviour to failure has been analysed. The tangent stiffness evolution during monotonic loading has been evaluated at different times after pile installation and the chalk set-up has been found to have no effect on pile behaviour under lateral loading. The pile secant stiffness during cyclic lateral loading is also investigated. Accumulated pile head lateral displacements are discussed and their pattern is described by a logarithmic function that varies with nu...

The axial behaviour of piles driven in chalk

Géotechnique

This paper describes research into the poorly understood axial behaviour of piles driven in chalk. Comprehensive dynamic and monotonic axial testing on 27, mostly instrumented, piles undertaken for the ALPACA Joint Industry Projects is reported and interpreted covering: diameters between 139mm and 1.8m; lengths from 3 to 18m; different pile material types; tip and groundwater conditions, and ages after driving. The experiments show the factors that influence resistance most strongly are: (i) pile end-conditions, (ii) slenderness ratio and flexibility, (iii) shaft material, (iv) age after driving, (vi) relative water table depth, and (vii) whether loading is compressive or tensile. Varying the factors systematically identified a remarkable average long-term shaft resistance range from below 11 kPa to more than 200 kPa for piles driven at the same low-to-medium density chalk test site in Kent (UK). Dynamic and static analyses demonstrate that soil resistances to driving (SRD) were gen...

The behavior of a single pile under cyclic axial loads

Geotechnical Special Publication, 2010

Many piled foundations have been destroyed under significant cyclic loads in earthquakes. Centrifuge modelling of a single pile subjected to cyclic loads has been conducted to investigate the influence of cyclic loads on the axial performance of the single pile. Different pile installation procedures were applied to compare the axial behaviour of different piles under cyclic loads. Pile head permanent settlements accumulated due to cyclic axial loads, and these increased with the increasing load amplitude. Also the pile head axial secant stiffness decreased with the increasing number of axial load cycles, and with increasing amplitude. Furthermore, the axial pile performance is influenced significantly by different installation methods.

Improving the design of piles driven in chalk through the ALPACA research project

Revue Française de Géotechnique

Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. Large numbers of offshore wind turbines, bridges and port facilities rely on piles driven in chalk. Current European practice assumes ultimate shaft resistances that appear low in comparison with the Chalk’s unconfined compression strength and CPT cone resistance ranges and can impact very significantly on project economics. Little guidance is available on pile driveability, set-up or lateral resistance in chalk, or on how piles driven in chalk can sustain axial or lateral cyclic loading. This paper describes the ALPACA (Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing) project funded by EPSRC and Industry that is developing new design guidance through comprehensive field testing at a well-characterised low-to-medium density test site, supported by analysis of other tests. Field experiments on 36 driven piles, sixteen of which employ high resolution f...

Cyclic axial behaviour of piles and pile groups in sand

Canadian Geotechnical Journal, 2012

Piled foundations are often subjected to cyclic axial loads. This is particularly true for the piles of offshore structures, which are subjected to rocking motions caused by wind or wave actions, and for those of transport structures, which are subjected to traffic loads. As a result of these cyclic loads, excessive differential or absolute settlements may be induced during the piles’ service life. In the research presented here, centrifuge modelling of single piles and pile groups was conducted to investigate the influence of cyclic axial loads on the performance of piled foundations. The influence of installation method was investigated and it was found that the cyclic response of a pile whose jacked installation was modelled correctly is much stiffer than that of a bored pile. During displacement-controlled axial load cycling, the pile head stiffness reduces with an increasing number of cycles, but at a decreasing rate; during force-controlled axial load cycling, more permanent s...

Large-diameter piles in chalk – part 2, design and construction

Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2018

The design of a 60-storey tall residential tower with a two-level basement in East London has had to take account of two London Underground tunnels which pass beneath the centre of the site resulting in "working" pile loads of up to 45 MN. The foundation solution comprised of a stiff raft with cast-in-situ bearing piles up to 2.4 m in diameter and 61 m long founding in the Grade A/B chalk stratum. Some piles, using bentonite support fluid, needed to be constructed within the tunnel exclusion zones which required a concession from London Underground. This paper presents the Osterberg cell preliminary pile load test and results, foundation design, working pile construction and limitations on piles constructed in the LU exclusion zones. The paper also discusses the control on the bentonite support fluid properties and monitoring of its properties during pile construction.

Lateral Response of a Single Pile under Combined Axial and Lateral Cyclic Loading in Sandy Soil

Civil Engineering Journal

According to practical situation, there have been limited investigations on the response of piles subjected to combined loadings especially when subjected to cyclic lateral loads. Those few studies led to contradictory results with regard to the effects of vertical loads on the lateral response of piles. Therefore, a series of experimental investigation into piles in dense sand subjected to combination of static vertical and cyclic lateral loading were conducted with instrumented model piles. The effect of the slenderness ratio (L/D) was also considered in this study (i.e. L/D= 25 and 40). In addition, a variety of two-way cyclic lateral loading conditions were applied to model piles using a mechanical loading system. One hundred cycles were used in each test to represent environmental loading such as offshore structures. It was found that under combined vertical and cyclic lateral loads the lateral displacement of piles decreased with an increase in vertical load whereas it causes ...

Estimates of shaft and end loads in piles in chalk using strain gauge instrumentation

Geotechnique, 1976

Since the end of 1973, eight test piles in chalk have been instrumented in order to determine detailed information on their behaviour under test. Of these eight, four were bored and four were driven, and the distributions of load with depth have been determined for the first time in chalk in a similar manner to that previously used in sands and clays. The driven piles were instrumented with strain gauges only, while the bored piles were instrumented with strain gauges and rod extensometers. All were tested under maintained loads to at least twice the working load, and some were subjected to cychc loadings. From the detailed strain profiles now available, together with information on the crosssectional area and on the modulus from strain results over a control length, it has been possible to determine load variations with depth. By considering depth increments and integrating strain profles it has been possible to determine relationships between the loads mobilized both in shaft load transfer and in end-bearing, and the differential movements between pile and soil which produced them. Graphs are produced giving quantitative relationships calculated from the above mentioned tests for three sites in the Upper and Middle Chalk at various depths, and some of the implications on design procedure are discussed. Comparison between bored and driven piles shows much higher creep strains in the higher stressed conditions of the latter, and the efsects of this and other aspects of the loadprofiles are discussed. Depuis la fin de 1973, huit essais de pieu dans de la craie, ont été effectués, de manière à obtenir des informations détaillées sur leur comportement pendant les essais. Sur ces huit pieux, quatre furent fores et quatre battus, les distributions des charges en profondeur ont été déterminées pour la première fois dans la craie, de la même façon que celles précédemment utilisées dans les sables et argiles. Les pieux battus furent équipés uniquement de jauges de déformation, tandis que les pieux forés furent équipés avec des jauges de déformation et des extensomètres à tige. Tous furent testés sous des charges maintenues à, au moins, deux fois la charge de travail, et certains furent soumis, à des chargements cycliques. Grâce aux profils détaillés de déformation maintenant disponibles, et aux informations sur le module de déformation sur une longueur bien définie, il a été possible de déterminer les variations de charge en profondeur. En considérant les augmentations de profondeur et en intégrant les profils de déformation, il été possible de déterminer les relations entre les charges mobilisées respectivement par le frottement latéral et par la résistance depointe, et les mouvements différentiles entre pieux et sol qui les ont produits. Des abaques sont fournis, donnant des relations quantitatives calculées à partir des essais mentionnés cidessus, pour trois chantiers dans la Craie Supérieure et Moyenne, à des profondeurs diverses, et quelquesunes des implications sur la méthode de calcul, sont discutées. La comparaison entre les pieux forés et les vieux battus, montre pour ces derniers déformations de fluage beaucoup plus importantes pour les contraintes élevées, et les conséquences de cela et d'autres aspects desprojils de chargement, sont discutés.