Full-scale Lateral Load Tests Research Articles

FDEM analysis of deep rock mass failure and its impact on horizontal bearing capacity in offshore wind turbine piles

Rock-socketed single piles are integral components of offshore wind turbine foundations in rock-based sea areas. Traditional numerical models have been employed to analyze the failure modes and lateral interactions between piles and the rock medium. However, these do not simulate the decline in the horizontal bearing capacity due to rock breakage, posing potential safety risks. In this study, the combined finite-discrete element method (FDEM) was used to simulate the deformation process of submarine rock masses transitioning from an intact to a fractured state. A notable innovation in the proposed approach is the consideration of the effects of the rock mass fracture and pile-rock cohesion on the load-bearing behavior of single-pile foundations. The FDEM model was validated through full-scale lateral load tests. The results showed a distinctive sequence in failure mechanisms, with the tensile failure of the rock mass around the pile at significant depths preceding the compression failure. Local failure at the contact interface significantly reduced the horizontal bearing capacity—a phenomenon that is inadequately represented by conventional finite element models. Furthermore, the cohesion element embedding method was introduced and used to simulate the influence of the tensile properties inherent in grouting materials on the failure strength and mode of the pile-rock interface. This study highlighted the importance of considering the nuanced effects of rock failure in the design of horizontally loaded piles. Failure to do so could lead to nonconservative designs and compromise the safety and efficacy of offshore wind turbine foundations. By pushing the boundaries of numerical modeling with the FDEM, the study aims to provide a more accurate and reliable framework for the design and assessment of rock-socketed single piles for offshore wind energy applications.

Behaviour of bio-inspired grouped battered minipiles under lateral loading in clay

The field of bio-inspired geotechnics has been growing in response to the demand for foundations that are sustainable and yet have improved load-bearing capacities. This study aims to address the gap in a specialised adaptation of root system architecture for designing resilient foundations. The lateral load behaviour of one such novel grouped battered minipile configuration is evaluated in this study based on full-scale field testing and numerical modelling to report the unknown increase of load capacity caused by shape modification. First, three single minipiles battered at 0° and 25° were subjected to static lateral loading in fine-grained soil. The strain profiles along the individual minipile shafts were obtained using optic fibre sensors. Consecutively, full-scale lateral load tests on two types of minipile groups were also performed; one group had a configuration of two 25° battered minipiles perpendicular to the direction of loading mimicking a tree-root system, and another conventional group had two positive and negative battered minipiles. A numerical model was developed to investigate the effect of pile spacing and obtain soil pressures, bending moments and axial forces of the battered minipile groups. Results show that increased bearing area and higher engagement of soil volume for the novel minipile group with two perpendicular battered minipiles were larger than the conventional minipile group; thus, the former offered higher lateral resistance. The deflection pattern, bending moment and p-y curves showed a shadowing effect in stiff clay for battered minipile groups at a pile head spacing of three times the minipile diameter.

Nonlinear Stochastic Seismic Response Analysis of Three-Dimensional Reinforced Concrete Piles

A reliable assessment and design of engineering structures requires appropriate estimation and consideration of different sources of uncertainty. The randomness of seismic ground motion is one major uncertainty that needs to be considered from the perspective of performance-based earthquake engineering. To properly account for this uncertainty and its corresponding effect on pile foundations, a stochastic seismic response analytical framework based on a probability density evolution method and a stochastic ground motion model is proposed for the nonlinear stochastic seismic response analysis of pile foundations. A three-dimensional finite element model of a reinforced concrete pile with a large diameter embedded in the soil foundation is firstly established and calibrated using the full-scale lateral load test results from the literature, in which the nonlinear behavior of soil, the soil–pile interaction, the concrete damaged plasticity, and the steel yielding of the pile are properly modeled. Then, the calibrated three-dimensional numerical model is employed as an illustrative example for the stochastic seismic response analysis using the proposed framework. The mean, standard deviation, and probability density function of pile settlement and the dynamic reliabilities of the pile concerning various performance requirements are obtained in the present study. The settlements of the pile show great variability under the excitation of various stochastic ground motions, and the maximum mean value of the pile settlements is about 8 mm. The changing shape of the settlement probability density functions in every moment demonstrates that it is unreasonable to use assumed probabilistic distribution models to characterize the seismic responses of pile foundations during a seismic reliability analysis. Based on the proposed method, it is found that the dynamic reliabilities of the selected reinforced concrete pile concerning four different performance levels are 0, 0.1293, 0.8247, and 1, respectively. The proposed stochastic seismic response analytical method in the present study can provide a proper and comprehensive way to quantify various uncertainties and their corresponding effects on the seismic performance of pile foundations. It can also be used to estimate the actual reliability level of pile foundations that are designed by the current codes when they are subjected to seismic loads.

Single piles under monotonic lateral loads-Full scale tests and numerical modelling

This paper aims to present the results of the analysis of full-scale lateral loading tests of a single pile driven into a bi-layered soil located in Plancoet (France). The pile was subjected to a monotonic sequence of loads, and the P-Y curves along the pile were derived and compared to those recommended by the current design methods. Displacement analysis was then undertaken by inputting these P-Y curves, as well as those currently recommended in the literature, into the software SPULL to predict the load-deflection curve. The calibration process was conducted by a 3D finite element model using Abaqus software based on the elastic-perfectly plastic Mohr–Coulomb constitutive model, and the surface-to-surface contact method was used to take into account the nonlinear response at the pile/soil interface. The determined soil elastic modulus was used to predict the pile deflections by using some usual elasticity-based methods, which led to good prediction of the small pile deflections.

Analytical model for laterally loaded pile groups in layered sloping soil

The historic canal wall structures in many Northern European cities have been built as masonry walls on a timber deck founded on timber piles. For analysis of the resistance of those structures and assessment of their remaining service life, suitable and accurate calculation models are needed. Thereto an analytical method was developed for modelling laterally loaded pile groups in layered sloping soil. In the proposed method, the bending of a pile, which is subjected to a lateral load and axial load, is described by a beam on a Winkler elastic foundation in which the soil behaviour is represented by a series of independent p-y springs, idealized with a bilinear elastic-perfect-plastic approximation. The plastic limit was computed with Brinch Hansen ultimate soil resistance and the elastic soil response by the Ménard stiffness. The plastic limit was corrected for each depth, based on the reduction of the passive soil wedge due to pile group effects and the presence of a sloping surface. The analytical model was calibrated and validated with three field experiments, one full-scale lateral load test of a 3 × 5 pile group in soft clays and silts (Snyder, 2004), one full scale lateral load test of a single pile located on a slope in layered soils (Mirzoyan, 2007) and one small scale lateral load test of a single pile located near a slope in sand (Abdelhalim et al., 2020). The proposed method can adequately predict bending moment distributions and pile deflections and in addition, a good consistency between the analytical model and experimental tests was observed. The method is very fast, making it suitable for probabilistic, Monte Carlo type, simulations and reliability updating to determine the probability of failure of quay walls or other structures with horizontally loaded piles.

Laterally loaded single piles – construction of the P–Y reaction curves from the DPT test in sandy soils

ABSTRACT The Dynamic Penetration Test (DPT) is one of the simplest and least expensive in-situ tests, used in geotechnical projects. However, in the literature, there is no available practical method for constructing the P–Y curves based on the DPT test (P is the soil-pile reaction and Y is the pile deflection). This paper is aimed at suggesting a new practical method of constructing the P–Y curves on the basis on the DPT data in sandy soils. This method was derived from the interpretation of five full-scale lateral loading tests on fully instrumented piles in sandy soils. Simple analytical formulation of the P–Y curves parameters, as well as design practical charts were proposed as function of the number of blows Nd of the DPT test. The results predicted by the proposed DPT based P–Y curve agreed relatively well with measured results within the margin of small to medium deflection.

Numerical simulation for the nonlinear behavior of laterally loaded barrettes

Full-scale lateral static load tests performed on rectangular barrette sections are commonly limited due to their large capacity and high testing cost. The soil–barrette system behaves nonlinearly, making it convoluted to understand its real behavior. In the present study, finite element analysis is utilized to simulate the soil–structure interaction of a full-scale lateral load test carried out on a large-section rectangular reinforced concrete barrette in Hong Kong. The effect of the tension cracking, in the reinforced concrete sections, on the flexural stiffness of the rectangular barrette under static lateral loading–unloading cycles is explored. A proposed approach of sequential decreasing the flexural stiffness, based on the ratio between the affecting and the cracking bending moment of the concrete section, to simulate the real concrete behavior resulting from the cracking effect, is applied in the developed numerical model for the case study. The conducted study showed that the proposed approach adopted to simulate the decrease in the concrete stiffness based on the bending moment level is reasonable to represent the actual response of the barrette to lateral loads and provides a practical alternative to the costly field loading tests.

Equivalent diameter of grouted micropile embedded in marine soft clay under lateral load

Grouted micropiles are widely used in transmission tower foundations and in situ reinforcement in China. This paper deals with the grouting effect on the lateral performance of grouted micropiles embedded in marine soft clay, especially with an external driving shoe. Full-scale lateral loading tests on both grouted and non-grouted micropiles were conducted. The equivalent diameter of a grouted micropile was determined using the cylindrical cavity expansion method and the empirical value of the equivalent diameter was also calculated. The test results showed that, compared with a non-grouted micropile, the lateral bearing capacity of the grouted micropile was improved by 3·75 times. The empirical equivalent diameter was determined to be about 1·5 times the diameter of the steel pipe used, and this was used to predict lateral load–displacement responses of the grouted micropile.

Lateral Performance and p-y Curves for Large-Capacity Helical Piles Installed in Clayey Glacial Deposit

AbstractThe lateral performance of large-capacity helical piles is of significant interest. This study presents the results of five full-scale lateral load tests conducted on 6.0 and 9.0 m large-ca...

Full-Scale Tests on Effects of Slope on Lateral Capacity of Piles Installed in Cohesive Soils

AbstractA series of full-scale lateral load tests of fully instrumented piles in cohesive soils were carried out to assess the lateral response of piles in free-field and near a slope condition. Th...

DEVELOPMENT OF A SEISMIC FITTING FOR WOODEN BUILDINGS

Japanese wooden buildings are vulnerable to large earthquakes, and ensuring their seismic safety is a significant issue. However, many owners of wooden buildings hesitate to install seismic reinforcement because of the long construction period and high expense. There are many sliding doors in wooden buildings, which can be used for efficient seismic reinforcement. The objective of this study is to develop a seismic fitting for Japanese wooden buildings. Full-scale lateral loading tests were conducted for wooden frames that include a seismic fitting. The fittings can be constructed quickly and at a low cost. The parameters of the full-scale lateral loading tests were chosen in order to examine the effect of the fitting and the restriction condition surrounding a fitting on the seismic performance of a wooden frame. The relationships between the lateral load and deformation angle, the collapse mechanism, and the quantitative effect of seismic reinforcement for a wooden frame were clarified. From the results of the full-scale tests, it is found that the lift up of a seismic fitting should be restricted by a hanging wall for the seismic reinforcement of wooden frames.

Nonlinear Load-Deflection Behavior of Reinforced Concrete Drilled Piles in Stiff Clay

AbstractThe results of three full-scale lateral load tests of cast-in-drilled-hole RC piles are evaluated to provide insights into the soil-pile interaction behavior as represented by p-y curves (p = soil reaction/length; y = lateral pile deflection) spanning from elastic conditions to mobilization of the soil capacity. The test sequence enables evaluation of the diameter effects on the p-y behavior as a result of testing two otherwise similar specimens, but with different diameters (0.6 and 1.8 m), and evaluation of the head-fixity effects as a result of testing similar specimens (with a 0.6 m diameter) under flagpole and fixed-head conditions. A constrained exhaustive search procedure that facilitates data interpretation even in the presence of severe shaft nonlinearity is introduced, which was needed because the testing was performed to full structural failure conditions. The p-y curves obtained with the present test data differ from the predictions of a standard (American Petroleum Institute) model, i...

Numerical Modelling and Full-Scale Testing of Concrete Piles Under Lateral Loading

Full-scale lateral loading tests were carried out on hollow-pre-cast-pre-stressed concrete piles embedded into the ground. The results from the tests were used as the basis for the analysis where soil was modelled as 20-node solid elements; and for the modelling of piles comparison was done between 3-node beam elements and 20-node solid elements. It showed that the 3-node beam element modelling for pile largely underestimates its lateral capacity. The 20-node solid element modelling can, however, accurately simulate the experimental results when interface element between pile and soil, and the degradation of shear stiffness of soil in cyclic loading is considered.

Numerical modelling and full-scale testing of concrete piles under lateral loading

Full-scale lateral loading tests were carried out on hollow-pre-cast-pre-stressed concrete piles embedded into the ground. The results from the tests were used as the basis for the analysis where soil was modelled as 20-node solid elements; and for the modelling of piles comparison was done between 3-node beam elements and 20-node solid elements. It showed that the 3-node beam element modelling for pile largely underestimates its lateral capacity. The 20-node solid element modelling can, however, accurately simulate the experimental results when interface element between pile and soil, and the degradation of shear stiffness of soil in cyclic loading is considered.

Full scale lateral behaviour of monopiles in granular marine soils

Monopiles are used in piers as mooring or berthing dolphins. This article reports the results of full-scale lateral loading tests on monopiles constructed as dolphins in the Pars Special Economic Energy Zone in southern Iran. The length and diameter of the monopiles were approximately 40 m and 2 m, respectively. Lateral loading tests of such large monopiles are not commonly undertaken, thus there is limited data available. This research developed a lateral analysis of piles computer code to examine analytical methods for pile analysis. Appropriate models were introduced resulting in accurate predictions in the analysis of lateral loaded piles. The results showed that traditional p–y curves and strain wedge models calculate larger pile head deflection in comparison to the field test data and therefore local calibration is essential.

Field behaviour of stiffened deep cement mixing piles

Full-scale pile load tests were performed on soft Bangkok clay improved by stiffened deep cement mixing (SDCM) piles and deep cement mixing (DCM) piles installed by jet-mixing to compare their performance. The SDCM pile is a DCM pile with a precast reinforced concrete core pile inserted in the middle. A series of full-scale tests consisting of axial compression, lateral and pullout interface between the concrete core pile and surrounding DCM material were performed. The length of the concrete core pile influenced both the ultimate axial bearing capacity and the settlement of the SDCM piles more than its section area. Furthermore, the section area of the concrete core pile affected both the lateral ultimate bearing capacity and the lateral displacements of SDCM piles significantly. Moreover, the SDCM piles with area ratio (Acore/ADCM) of 0·17 and length ratio (Lcore/LDCM) of 0·85 increased the axial and lateral ultimate bearing capacities so that they were as much as 2·2 and 15 times higher than the corresponding values of DCM piles, respectively. The flexural strength of the DCM pile obtained from the laboratory was 16% of its unconfined compressive strength whereas that obtained from full-scale lateral load tests was much lower at 4–7% of its unconfined compressive strength. The strength reduction factor, Rinter, at the interface between the concrete core pile and DCM pile in the field averaged 0·40, which agreed with the data from laboratory tests of 0·38–0·46.

Field Testing and Analyses of a Batter Pile Group Foundation under Lateral Loading

Much of the new I-10 Twin Span Bridge, built over Lake Pontchartrain between New Orleans and Slidell, Louisiana, is supported by driven batter pile group foundations. To assess the methodology used to design and analyze batter pile foundations and to evaluate their performance under lateral loading, a full-scale lateral load test was conducted on an M19 eastbound pier of the new bridge. The M19 pier foundation consisted of 24 precast, prestressed concrete 110-ft-long batter piles; eight piles were instrumented with in-place inclinometers (IPIs), and 12 piles were instrumented with strain gauges. The test was conducted by pulling the M19 eastbound and westbound piers toward each other with high-strength steel tendons. A maximum 1,870-kip lateral load was applied in increments. A high-order polynomial curve-fitting method was applied for each load increment to fit the measured rotation profiles from the IPIs, and the fitted rotation curves were used to deduce the bending moment, shear force, and soil reaction profiles on the basis of specific mathematical derivations. The calculated moments from curve fitting were compared with the moments calculated from strain gauge measurements, and the results showed good agreement. The soils’ p-y curves at different depths were backcalculated from the derived soil reaction profiles. The resulting p-y curves showed no evidence of group effect. The FB-MultiPier program was also used to analyze the behavior of the M19 pier foundation under lateral loading. Comparison of FB-MultiPier results with measured values as well as values calculated from polynomial curve fitting showed that FB-MultiPier overpredicted the lateral deformations of batter pile group foundations.

Lateral Performance of Two-Section Helical Piles in Soft Soils

AbstractA Two-Section Helical Pile (TSHP) is a steel pipe with two shaft sections of different diameters and with one or more helix plates near the bottom of each shaft section. TSHPs are used regularly in western Canada as foundation pockets for single and double circuit distribution power line poles. The results of a comprehensive lateral pile load test program and the field monitoring of TSHPs installed in organic soil (muskeg) over soft clay are presented in this paper. A total of nine full scale lateral load tests were carried out, including seven tests using TSHPs with different diameters and embedment depths, and two tests using one-section helical piles. The prime objective of the study was to evaluate the lateral resistance of TSHPs installed into very soft organic soil (muskeg) overlying soft clay soils, to compare their lateral resistance relative to one-section helical piles and to compare the measured and the estimated lateral resistances using p-y curves. In order to provide sufficient soil ...

P-y Criterion for Rock Mass

Drilled shafts socketed in rock mass have been used frequently as a foundation system to support both vertical and lateral loads. Traditionally, the lateral interaction between the drilled shaft and the surrounding rock medium has been characterized by means of nonlinear p-y curves; however, there is a lack of well verified p-y criterion for rock mass. In this paper, a hyperbolic p-y criterion is developed based on both theoretical derivations and numerical (finite element) parametric analysis results. The methods for determining pertinent rock parameters needed for constructing the proposed p-y curves are presented in the paper. Two full-scale lateral load tests on large diameter, fully instrumented drilled shafts socketed in rock conducted by the writers, together with additional four load test results reported by Gabr et al. were used to validate the applicability of the proposed hyperbolic p-y curves for rock mass. The comparisons between the computed shaft responses (both deflections and bending moments) and the actual measured responses are considered acceptable.

Design of Drilled Shafts Supporting Sound Walls

AbstractDrilled shafts are widely adopted as the foundation for sound walls. However, there has been a lack of uniformity in design and analysis methods and design criteria, in terms of factor of safety against ultimate capacity failure as well as the allowable deflection. In order to establish a uniform design methodology for the drilled shafts supporting sound walls in cohesive and cohesionless soils, respectively, a database of fullscale lateral load tests on fully instrumented drilled shafts was collected. Based on the compiled database, existing design methods and design criteria of laterally loaded drilled shafts were evaluated. Broms method and COM624P (or LPILE) are suggested as the design methods for drilled shafts supporting sound walls in both cohesive and cohesionless soils. Additionally, the corresponding design criteria, including factor of safety and permissible deflection, for both design methods are recommended. Two full-scale lateral load tests on fully instrumented drilled shafts were s...