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Numerical derivation of CPT-based p–y curves for piles in sand
Abstract and Figures
The formulations for the lateral load-displacement (p-y) springs conventionally used for the analysis of laterally loaded piles have been based largely on the back-analysis of the performance of small-scale instrumented piles subjected to lateral load. Although such formulations have been employed with much success in industry, their applicability to large-diameter piles, such as those used to support offshore wind turbines, is uncertain and has necessitated further research in this area. Moreover, with the growth in popularity of in-situ cone penetration tests (CPTs), there are demands for a theoretically supported direct method that can enable the derivation of p-y curves from the CPT end resistance (q c). In this paper, a numerical derivation of CPT-based p-y curves applicable to both small- and large-diameter laterally loaded single piles in sand is presented. Three-dimensional finite-element analyses are performed using a non-linear elasto-plastic soil model to predict the response of single piles in sand subjected to lateral loads. The corresponding CPT q c profile is derived using the same soil constitutive model by way of the cavity expansion analogue. An extensive series of computations of the lateral pile response and CPT q c values is then employed to formulate a direct method of constructing p-y curves from CPT q c values. The proposed method is shown to be generally consistent with existing empirical correlations and to provide good predictions in relation to the measurements obtained during lateral load tests on instrumented piles in an independent case study.
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... A variety of approaches have been proposed to derive p-y curves using CPT data. One such method by Suryasentana and Lehane (2014) proposes an exponential function for p-y curves in sand derived as a function of CPT cone resistance. ...
... These typically require the input of parameters such as angle of friction or relative density and require that soil layers be discretized with average layer properties. More recently, methods have been developed to characterize these p-y curves using CPT data (Suryasentana and Lehane 2014), which provides an improved estimate of the inherent soil properties and its variability. A schematic of a monopile modelled using discretized BNWF elements is shown in Figure 2, whereby the super-structural loads can be reduced to a set of pile head loads and moments. ...
The increasing demand for renewable energy has led to the rapid growth of the offshore wind sector, leading to larger Offshore Wind Turbines (OWT) being developed in deeper water locations further offshore. The geotechnical design procedures therefore become increasingly uncertain as ground investigations become more challenging, and the use of traditional design methodologies are applied to configurations outside of the datasets from which they were originally derived. This paper evaluates the influence of certain elements of geotechnical uncertainty on the monotonic load-displacement behaviour of laterally loaded monopiles. A traditional Beam on Nonlinear Winkler Foundation (BNWF) model is used to characterise the lateral pile-soil interaction, and the p-y springs are informed using Cone Penetration Test (CPT)-based functions. Geotechnical uncertainty is evaluated through the spatial variability of the CPT end resistance profile. Results suggest that spatial variability in end resistance profiles has limited effect on the pile head displacement predictions, highlighting a potential issue whereby local variations in soil properties may not be captured in p-y only models. This implies other spring-type components associated with diameter-dependency are necessary in the BNWF model to capture rigid pile behavior.
... Capacity defined at maximum padeye displacement of 0.1D or plastic hinge. CPT-based p-y curves in sand (Suryasentana and Lehane, 2014) and API in clay (API, 2007). ...
A rapid expansion of the anchor market is required to meet the increasing demand for floating offshore wind. This paper, which is aimed at a broad readership within and beyond geotechnical engineering, summarises the current state-of-the-art and discusses future developments of anchor types and geotechnical design methods. Current anchor technologies are presented via comparative analytical assessments of performance across a range of practical scales and seabed conditions. This analysis demonstrates the relative merits and performance of different anchor types, using simplified cost-performance indicators for each anchor technology. An example outcome is the large differences in anchor efficiency (capacity per unit weight), that are linked to the different ways anchors achieve their holding capacity. Potential improvements in the performance-cost response for each anchor type, through future enhancements, are then explored. These enhancements are categorised as (1) unlocking higher anchor performance through improved design methods with a better understanding of the geotechnical response, (2) upscaling or (3) com-moditising of the anchor type, by making larger versions or enabling more efficient mass production and installation, or (4) invention of new anchor technologies. Finally, findings of the different sections are summarised within a single table to enable a quick selection of anchoring solutions.
... When using a more practical complex constitutive model, numerical analysis is often required for simplified calculations. A spherical cavity expansion was modelled in the Plaxis 2D to simulate the penetration process, following similar procedures described by Xu and Lehane (2008) and Suryasentana and Lehane (2014). Considering the symmetry of spherical cavity expansion, the model dimension is x = 12 m, y = 24 m. ...
Deformation analysis and control of underwater large-diameter shield tunnels is a prerequisite for safe tunnel construction. Reasonable selection of constitutive model and its parameters is the key to accurately predicting the deformation induced by underwater shield tunnelling. In this paper, the finite element analysis of cavity expansion during the piezocone penetration test (CPTU) based on the hardening soil model with small strain stiffness (HSS) model was carried out, and the correlation model of the normalized cone tip resistance Q with the reference secant modulus E 50 ref and the effective internal friction angle φ ’ was established and verified using mini CPTU chamber test. Then, a Bayesian probability characterization approach for E 50 ref of silty clay based on CPTU was proposed. Furthermore, the deformation analysis of Jinan Yellow River tunnel crossing the south embankment was carried out to verify the reliability of the proposed approach. The good agreement between the field measurement and numerical simulation confirms that the parameters obtained by the Bayesian approach are reliable. Finally, a sensitivity analysis was performed to study the law of riverbed settlement induced by underwater large-diameter shield tunnelling. The results show that the increasing support pressure could effectively reduce the riverbed settlement, but there is an upper limit. The optimal support pressure of established model is between 0.45 MPa and 0.5 MPa. The uphill section causes greater riverbed settlement than the downhill section. Under the same condition, increasing buried depth and water level will lead to a more significant settlement.
... Pile foundations are commonly used to resist the lateral loads applied to structures. Numerous experimental and theoretical research on the lateral pile-soil response in silica sand [8,9,16,20,25] and coral sand in the Australia Sea [6,22,36] were conducted, but the most existing design methods for laterally loaded pile were derived from silica sand [1,26,43]. The lateral response of the pile is mainly determined by the properties of the surrounding soil [4]. ...
This paper presents the lateral pile-soil response occurring in coral and silica sand foundations through comparative numerical studies. In this study, the Hypoplastic constitutive model was implemented into Abaqus software to simulate the stress–strain relationship of coral sand and silica sand with the same particle gradation. The validation of numerical model was verified by centrifuge test results. Afterward, forty-eight numerical analyses were employed to assess the influence of pile diameter, embedment length, loading eccentricity, and relative density on the lateral response of piles in two kinds of sands. The load–displacement response, pile deflection, bending moment, and p-y curves were compared and analyzed in detail. The results showed that, with the increase in displacement level and relative density, the load responses of piles in coral sand gradually became greater than that in silica sand, the p-y curves in coral sand were also significantly higher than that in silica sand, and the bending moment and deflection profile of pile in silica sand were larger than that in coral sand. The difference in pile response between the two kinds of sands became more significant as the density and load level increased. Finally, a multi-parameter modified p-y model for coral sand was proposed, and its applicability and rationality were validated.
... The design of monopiles is a very complicated problem. During their service period, monopiles are mainly subjected to lateral loads imposed by wind, wave and current loads (Abadie et al., 2019;Truong et al., 2019;Doherty and Gavin, 2012;Suryasentana and Lehane, 2014) . With the gradual development of the construction of wind power farms to the deep sea field (water depth >30 m), the requirement of foundation bearing capacity has increased. ...
Monopiles are the most commonly utilized foundation type for offshore wind turbines. Due to continuous growth in the capacity of offshore structures, increasing the diameter of piles is a relatively simple but costly method. How to improve the bearing capacity of monopile foundations without increasing the pile diameter is the research purpose of this paper. A series of laboratory model tests of laterally loaded monopiles in clay were carried out considering different foundation reinforcement methods (i.e., annular point post-grouting, distributed post-grouting and jet-grouting) to investigate the lateral monotonic and cyclic response of unreinforced and reinforced piles. As a result, the three foundation reinforcement methods improve the lateral capacity of piles, among which jet-grouting-reinforced piles have the greatest improvement. After the monotonic test is completed, an excavation test is carried out. It is determined that the cement slurry injected by the annular point post-grouting reinforcement mainly diffuses in the clay by splitting, while the reinforcement body formed by the distributed post-grouting and jet-grouting more evenly covers the outer surface of the pile, and the effect of improving the lateral capacity is improved. The accumulated displacement calculation formulas of different reinforced piles are obtained. The accumulation coefficient of distributed post-grouting and jet-grouting reinforced piles is small, which means that they can more effectively reduce the cumulative displacement of the pile.
... where K and n are constants and set to 150 and 0.5 for sands in all the FE analyses following Suryasentana and Lehane [58], Ullah and ...
This paper reports the lateral – moment bearing capacity of bucket foundations under lateral loading in sand. The Modified Mohr-Coulomb (MMC) model is adopted to capture the hardening – softening behaviour in medium dense and dense sands within a finite element (FE) modelling framework. The FE model performance is assessed against available field test data as well as analytical solutions showing a relatively good agreement. A series of parametric study is conducted to investigate the effects of bucket aspect ratio, bucket diameter, load eccentricity, vertical load and relative density of sand on the lateral - moment bearing capacity of the bucket. Comparisons are drawn between the conventional Mohr-Coulomb (MC) model and the stress dependent MMC model highlighting the role of sand dilatancy in mobilising the lateral moment capacity. Based on the FE results, a simple stepwise calculation framework is proposed for two scenarios: (i) to predict the lateral - moment bearing capacity of the bucket if the bucket dimensions are known, and (ii) to design the bucket dimensions for a known required bucket capacity.
The aim of this paper is to present a simple method of construction of the load-transfer P-Y curves for the design of laterally loaded piles in sand based on the cone penetration test (CPT). The proposed method was developed on the basis of interpretation of 5 field tests on single instrumented piles conducted in sandy sites in France and shows a simple relationship linking the P-Y curve parameters, the cone penetration resistance and the lateral pile/soil stiffness ratio. The validation process was carried out by direct comparison of the predicted load-deflection curves based on the proposed method to those obtained from a worldwide case history of field lateral loading tests on piles and showed a very good quality of the prediction using the proposed method. KEYWORDS: Piles, Lateral load, Sand, Full-scale loading, P-Y curves, CPT test.
The right selection of soil model parameters is essential to make good predictions in geo-engineering projects where the Finite Element Method (FEM) is used. In order to support geotechnical engi-neers with soil model parameter selection, empirical formulas have been developed to derive the model para-meters of the Plaxis Hardening Soil model with small-strain stiffness (HSsmall), on the basis of a characteris-tic property (relative density for sands and plasticity index for clays). This paper shows a validation of formulas for sands which have been derived from published soil testing data. The main goal of the empirical formulas is to give a reasonable first order approximation of soil behaviour in FEM calculations, covering a wide range of sands. In a case study it is demonstrated that the empirical formulas work reasonably well to get a first estimate of deformations and stress developments for a real project.
Methods are presented for the calculation of deflections, ultimate resistance, and moment distribution for laterally loaded single piles and pile groups driven into cohesionless soils. The lateral deflections have been calculated assuming that the coefficient of subgrade reaction increases linearly with depth and that the value of this coefficient depends primarily on the relative density of the supporting soil. The ultimate lateral resistance has been assumed to be governed by the yield or ultimate moment resistance of the pile section or by the ultimate lateral resistance of the supporting soil. The ultimate lateral resistance is assumed to be equal to three times the passive Rankine earth pressure. The deflections and lateral resistance, as calculated by the proposed methods, have been compared with available test data. Satisfactory agreement was found.
Cone tip resistance is the most widely measured quantity in the cone penetration test. A brief review is made of presently available theories for the analysis of cone resistance. The theories are presented in farms that enable direct comparisons among them. The simplifying assumptions made in the analysis using various theories are emphasized. In the light of experimental evidence and the fundamental principles of mechanics, the limitations and advantages of each theory are: assessed. Comparison with limited experimental data indicates that cavity expansion theories give the closest overall agreement between predicted and measured penetration resistance.
Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this paper, the seismic performance of such slopes in non-liquefiable granular soils is considered, focusing on permanent movement and dynamic motion at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge, numerical (finite-element, FE) and analytical (sliding-block) modelling, the centrifuge tests being used to validate the two non-physical approaches. The FE models focus on the specification of model parameters for existing non-linear constitutive models using routine site investigation data, allowing them to be used routinely in design and analysis. Soil-specific constitutive parameters are derived from shearbox and oedometer test data, and are found to significantly outperform existing empirical correlations based on relative density, highlighting the importance of specifying a suitably detailed site investigation. An improved sliding-block ('Newmark') approach is also developed for estimating permanent deformations during preliminary design, in which the formulation of the yield acceleration is fully strain-dependent, incorporating both material hardening/softening and geometric hardening (re-grading). The site-specific (improved) FE models and the new sliding-block approach are shown to outperform considerably existing FE parameters and sliding-block models in capturing the permanent deformations of the slope under virgin conditions, and further, only the improved FE and sliding-block models are found to capture correctly the behaviour of the 'damaged' slope under subsequent earthquakes (e.g. strong aftershocks). The FE models can additionally accurately replicate the settlement profile at the crest and quantify the dynamic motions that would be input to supported structures, although these were generally overpredicted. The FE procedures and sliding-block models are therefore complementary, the latter being useful for preliminary design and the former for later detailed design and analysis.
The behavior of displacement piles in uncemented calcareous sand is investigated using field piles instrumented with a sensor that simultaneously records the radial stress and shear stress at specific locations on the pile shafts. These tests are interpreted with the assistance of data from adjacent self-boring pressuremeter tests and from monotonic and cyclic direct shear interface tests performed on reconstituted samples. The existence of extremely low radial stresses on the pile shafts is verified. Although dilation during shear is seen to compensate for such low radial stresses, short-term shaft capacities are much lower than capacities of equivalent piles in siliceous sands. The development of a bonded or welded crust to the pile shaft was seen to be the primary contributor to the setup observed at the test site; this crust forced failure to take place at a sand-sand rather than a sand-steel interface and also gave rise to higher levels of dilation during monotonic loading. The welded sand crust did not, however, give rise to a higher long-term cyclic capacity.
Cavity expansion analysis plays a significant role in modem soil mechanics. The analysis o f many o f the most important problems in the practice o f geotechnical engineering (such as cone penetration testing, pile loading, or pressuremeter testing) rely to a large extent on cavity expansion analyses. Cavity expansion processes are o f two basic types: expansion from a finite radius and expansion from zero initial radius. It is usual to use a different type o f analysis for each o f these problems. Analysis o f the cavity creation problem yields only the limit pressure, but not necessarily information on the pressure-strain relationship during expansion. Analysis o f expansion from an initially finite cavity radius gives a pressure-strain curve, but no information on the limit pressure. In this article, we present a simple numerical analysis that provides the solution to both problems simultaneously. The analysis takes full account of the flow rule and dependence o f the friction angle on stress state, providing a rigorous solution for the cavity expansion problem throughout the plastic zone. The analysis can be used for both spherical and cylindrical cavities. As illustration o f the versatility o f the analysis, plots o f limit pressure versus soil state, cavity pressure versus strain for various soil states, and evolution o f soil state within the plastic zone are provided.