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(a) Schematic of downward-traveling wave and measured reflections from PDA measurements; and (b) upward-traveling wave calculated using data from Fig. 6(a).
Contexts in source publication
Context 1
... t m was ≈21.2 ms, indicating a rise time of 2 ms. The force and acceleration data were measured on both sides of the pile; the averages of the F and Zv measurements from the two sets of gauges were adopted for input into the analysis. A schematic of the downward-traveling wave and measured reflections at the PDA gauges at the pile top is shown in Fig. 7, along with the upwardtraveling force F up calculated from the EOD hammer blow shown in Fig. 6(a). Taking a steel mass density ρ of 7.8 Mg=m 3 and Young's modulus E of 210 GPa leads to a pile impedance Z of 1,277 ...
Context 2
... matching was carried out by comparing the time series of the measured F up with the numerical upwave created using the downwave force signal from the hammer as input. The measured pile head displacement was also compared to the computed displacement. The reflections due to shaft and base resistance and the upward-traveling are shown previously in Fig. 7. Fig. 12 shows examples of the local shaft resistance with depth interpreted from the dynamic measurements made on the exemplar long pile LD05 at the end of, and during, driving and on the exemplar short pile LD13 at EOD. A trial signal match is illustrated in Fig. 13 for LD05 in terms of the measured (through PDA) trace for F versus ...
Context 3
... is worth considering independently the quality of the pile head match, which is traditionally used to assess pile capacity; Fig. 16 shows the match at the pile head obtained by both the manual and optimization process for the LD05 EOD blow. The manual case gives the best coincidence in the time up to first reflection from the tip (t mþ2L=c , see Fig. 7). Optimization using the G 1 case (1b and 2b) typically gives a good match at the pile head, although it leads to a lower mobilized resistance and a poorer match close to the pile tip. The optimization process using G ¼ G max gives a generally poorer match to the upward force at the pile head and a lower mobilized resistance (Table 5). ...
Context 4
... t m was ≈21.2 ms, indicating a rise time of 2 ms. The force and acceleration data were measured on both sides of the pile; the averages of the F and Zv measurements from the two sets of gauges were adopted for input into the analysis. A schematic of the downward-traveling wave and measured reflections at the PDA gauges at the pile top is shown in Fig. 7, along with the upwardtraveling force F up calculated from the EOD hammer blow shown in Fig. 6(a). Taking a steel mass density ρ of 7.8 Mg=m 3 and Young's modulus E of 210 GPa leads to a pile impedance Z of 1,277 ...
Context 5
... matching was carried out by comparing the time series of the measured F up with the numerical upwave created using the downwave force signal from the hammer as input. The measured pile head displacement was also compared to the computed displacement. The reflections due to shaft and base resistance and the upward-traveling are shown previously in Fig. 7. Fig. 12 shows examples of the local shaft resistance with depth interpreted from the dynamic measurements made on the exemplar long pile LD05 at the end of, and during, driving and on the exemplar short pile LD13 at EOD. A trial signal match is illustrated in Fig. 13 for LD05 in terms of the measured (through PDA) trace for F versus ...
Context 6
... is worth considering independently the quality of the pile head match, which is traditionally used to assess pile capacity; Fig. 16 shows the match at the pile head obtained by both the manual and optimization process for the LD05 EOD blow. The manual case gives the best coincidence in the time up to first reflection from the tip (t mþ2L=c , see Fig. 7). Optimization using the G 1 case (1b and 2b) typically gives a good match at the pile head, although it leads to a lower mobilized resistance and a poorer match close to the pile tip. The optimization process using G ¼ G max gives a generally poorer match to the upward force at the pile head and a lower mobilized resistance (Table 5). ...
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A novel pile-driving technique, named Gentle Driving of Piles (GDP), that combines axial low-frequency and torsional high-frequency vibrations has been developed and tested recently. During the experimental campaign, several piles were installed onshore, making use of the GDP shaker. Besides those, a number of additional piles were installed using...
Citations
... Table 1 summarises the axial-cyclic subset of eight nominally identical 508mm OD open-tubular 'LD' piles driven to 10.15m tip depths, with 41% of their shaft lengths below the water table and L p /D ≈ 20. The piles' 20.6mm wall thicknesses (giving relatively low D/t w ≈ 25) were instrumented with opposing strings of optical fibre Bragg grating (FBG) strain gauges (Buckley et al., 2020b). Axial-cyclic tests were also conducted on six new 'SD series' 139mm OD piles, one of which also carried FBG gauges. ...
Comprehensive field investigations into the axial cyclic loading behaviour of open-steel pipe piles driven and aged in low-to-medium density chalk identify the conditions under which behaviour is stable, unstable or metastable. Post-cycling monotonic tests confirmed that stable cycling enhanced pile capacity marginally, while unstable cases suffered potentially large losses of shaft capacity. Metastable conditions led to intermediate outcomes. The patterns by which axial deflections grew under cyclic loading varied systematically with the normalised loading parameters and could be captured by simple fitting expressions. Cyclic stiffnesses also varied with loading conditions, with the highest operational shear stiffnesses falling far below the in-situ seismic test values. The monotonic and cyclic axial responses of the test piles were controlled by the behaviour of, and conditions within, the reconsolidated, de-structured, chalk putty annuli formed around pile shafts during driving. Fibre-optic strain gauges identified progressive failure from the pile tip upwards. Large factors of safety were required for piles to survive repetitive loading under high-level, two-way, conditions involving low mean loads, while low amplitude one-way cycling had little impact. A simple ‘global’ prediction procedure employing interface shear and cyclic triaxial tests is shown to provide broadly representative predictions for field behaviour.
... Iterative wave matching analyses, which applied the shaft and base resistance models in IMPACT (Randolph, 2008), indicated how shaft shear stresses evolved locally as pile tips advanced. Buckley et al. (2020b) considered both FBG and PDA measurements and describe how modelling parameters were selected and shaft resistances taken as applying over only the outside shaft areas. The FBG measurements agreed well with high-frequency conventional PDA measurements and the end-of-driving (EoD) datasets provided key information on the piles' initial axial resistance profiles. ...
... The FBG measurements agreed well with high-frequency conventional PDA measurements and the end-of-driving (EoD) datasets provided key information on the piles' initial axial resistance profiles. Buckley et al. (2020b), Cathie et al. (2022 and Wen et al (2023) show that rigorously conducted stress wave matches provide the best available proxy means of measuring instantaneous EoD resistances, which cannot be measured statically in cases where set-up progresses rapidly. These authors show that, if conducted and interpreted carefully, stress-wave analyses of instrumented dynamic re-strike tests provide shaft capacity estimates that are compatible with trends inferred from static testing. ...
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 generally well-predicted by the Chalk ICP-18 short-term formulation. Considering the piles’ long-term behaviour, the Chalk ICP-18 approach over-predicted capacity, while the widely used CIRIA approach proved over-conservative for most cases. The research enabled the development of a revised ‘ALPACA-SNW’ long-term capacity assessment method that matches the test outcomes far more faithfully.
... Recent research into improving the design of axially loaded piles in chalk through field studies with impact driven and highly insturmented jacked model piles is reported by [6][7][8][9]. A new effective stress-based approach to predict axial pile capacity has been proposed, which is currently being calibrated and checked through additional testing in the ALPACA Joint Industry Project (see [8] or [39]). The proposed method builds from the key phenomena identified during the field experiments, namely (i) the use of CPT cone resistance to track and allow for local variations in properties (ii) the marked effect of the relative distance, h from the pile tip below any given chalk horizon, normalised by effective pile radius (iii) the interface effective stress shear failure characteristics and (iv) incorporation of dilation-induced changes in radial effective stresses during axial loading. ...
Chalk, a soft, white, variable, high porosity, rock has been the focus of recent research into pile behaviour following the rapid expansion of offshore windfarms in Northern Europe and the advancement of other major infrastructure projects in areas where foundations are installed in chalk. An overview of recent in-situ testing (cone penetration tests and geophysical tests) at low-medium density chalk sites is presented. Typical cone penetration test profiles are discussed, which illustrate that while cone resistance and friction ratio in chalk lie within the typical ranges for sands and clays, pore pressures are remarkably high and dissipate quickly, leading to partial drainage occurring during cone penetration tests conducted at standard velocities. The CPT cone resistance increases markedly with reducing penetration rate due to increasing degrees of drainage developing around the advancing cone tip. While both cone resistance and friction ratio have been shown to increase with improving chalk grade, a consistent method to classify chalk grade using CPT parameters has not yet been developed. Shear wave velocities measured in the field through geophysical testing fall below the trends interpreted from laboratory tests on intact samples, which may be attributable to the presence of fractures in the chalk mass or differences in applied effective stress levels. However, the cone resistance profiles developed in struc-tured chalk provide sensitive indicators of local variations in key factors that affect mass shear strength and density. This observation has encouraged the authors to propose CPT based design methods for piles driven in chalk.
... Such a low rate was intended to allow for fully drained penetration. In comparison, the fullsize piles (D o = 508 mm) impact-driven by Buckley et al. (2020) at the St Nicholas-at-Wade site were installed at rates of about 1500 mm/min. ...
Penetration of open- and closed-ended model piles into intact chalk, a soft calcareous rock, was investigated using microfocus X-ray computed tomography (XCT). Three-dimensional images of the specimens showed that the piles crushed and densified the chalk in their path, creating a crushed chalk annulus around the shaft, a region of compressed destructured chalk below the tip, and fractures across cemented regions of the specimen. Laser-diffraction particle-size analyses of the crushed chalk annulus after exhumation showed limited difference with laboratory-remoulded chalk, which suggested thorough de-cementation. Installation stresses and XCT-derived densities were paired using a simplified cylindrical cavity expansion solution to estimate effective radial stress–void ratio states at the pile tip during penetration. More complex numerical solutions could not be applied using the available data. This approach posed significant problems, as it could not suitably incorporate hardening and non-linear stiffness behaviours of chalk during pile penetration, nor account for the creation of discontinuities. However, effective radial stress–void ratio estimates were found to converge with the reconstituted critical state line of the material at high stresses and low void ratios. This partially supported the use of a critical state framework to characterise pile penetration in chalk, as proposed in recent literature.
Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). After presenting the development of a purpose-built GDP driving device and the geotechnical characterisation of the site, this paper covers the execution of GDP installation tests. Focus is on the installation performance of GDP-driven piles, which is discussed with the aid of structural and ground monitoring data. The comparison between piling data associated with GDP and standard axial vibro-driving points out the potential of the proposed installation technology, particularly with regard to the beneficial effect of the torsional vibration component. The findings of this study encourage further development of the GDP method and its future extension to offshore full-scale conditions.
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Larger-diameter open-ended pipe piles are widely used as foundation for offshore structures. The lack of high-quality inner wall axial stress measurement results in difficulties in loading analysis of open-ended pipe piles during penetration and service period due to the effect of soil plugging. In this paper, two groups of model tests to assess the feasibility of bare fiber Bragg grating (FBG) sensing technology in monitoring the inner wall axial stress profile of open-ended aluminous pipe piles during penetration and horizontal loading are presented. One open-ended aluminous pipe pile was instrumented with bare FBG sensors and then penetrated into the sand bed with the rate of 20 and 30 mm/min, respectively. Two horizontal static loading tests were also conducted after 24-h penetration. The installation process of bare FBG sensors along open-ended aluminous pipe pile is introduced. The distribution profiles of axial stress and unit shaft resistance on inner wall and outer wall along model pile is discussed in detail. Model test results indicated that the bare FBG sensing technology was feasible to measure the axial stress of inner wall along open-ended pipe piles during penetration and horizontal loading in sand. During horizontal loading, the average values of qso/qsi are 0.717 and 0.727, respectively, for model pile with penetration rate of 20 and 30 mm/min. The axial stress difference of inner wall and outer wall along model pile in penetration and horizontal loading is the result of a combination of the inside and outside soil friction as well as of the pipe in-wall shear stiffness.
