Small Diameter Piles Research Articles

Assessment of interfacial friction angles of sand-structural materials

This research evaluates the interfacial friction angles of sand-structural materials (i.e. concrete, steel, and wood) from direct shear and model pile tests data. Some variable parameters are considered for performing laboratory tests such as shearing rates (0.05, 0.5, 1.0, 2.0, and 2.5 mm/min.), pile diameters (38.1, 76.2, and 101.6 mm), and normal stresses (27, 55, and 81 kPa). The validated shearing rates are found to be 8.7% and 4.3% in cases of direct shear and model pile tests respectively, which may represent a good accuracy of experimental tests. According to the direct shear test results, the interfacial sand-concrete and internal friction angles are equal at shearing rate of 2 mm/min. The interfacial friction angles are increased with the increment of pile diameters because of slip dilation impact of small diameter pile. The interfacial friction angle of sand-wood pile shows the higher value because of lower self-weight and stiffness of wood compared to the other structural materials. There is a scope for further research by conducting numerical analysis and deriving analytical formulations for obtaining explicit solution.

Analysis of Soil Behavior by Constructing the Micro Pile

Micro piles are piles having a diameter of less than 300 millimeters. Due to small diameter piles, this may act as reinforcement in the soil. The deep foundation in places with limited access where it is impossible to utilize larger equipment, the micropile can also be deployed. Micro piles can provide tremendous support while reducing costs, environmental effects, and building vibrations. Micro piles have been widely used in a variety of engineering applications such as increasing bearing capacities, reducing settlements, underpinning, in situ soil reinforcing, seismic retrofitting, and foundation rehabilitation. The soil behavior was analyzed by using the Plaxis 2D software. The Saturated unit weight, unsaturated unit weight, friction angle, dilatancy angle, and cohesiveness are among the criteria taken into account when analyzing the behavior of the soil. The considered parameters were assigned to the software and the output will be the lateral displacement and stresses and also to know the cross-section. The micropiles Young’s modulus, diameter, and spacing are additional factors. The behavior of soil was observed by constructing the micropile.

Axial capacity ageing trends of large diameter tubular piles driven in sand

The paper examines dynamic pile test data from 25 high-quality offshore cases, where end-of-initial driving (EoID) and beginning-of-restrike (BoR) instrumented dynamic monitoring was undertaken on tubular piles driven in sands at well-characterised sites after known setup periods. The static resistances derived from signal matching by two independent specialist teams using different software are compared with CPT-based pile capacity calculations, providing the first axial capacity and setup dataset for large offshore piles driven in sand. Complementary re-analyses are made from three onshore/nearshore sites where dynamic and static testing was conducted on comparable piles. Open-ended tubular steel piles with 0.3–3.5 m diameters driven in (mainly dense) sands are all shown to develop marked setup, which is most active over the first 2–10 days. All piles show similar outcomes 20–30 days after installation. However, the larger diameter offshore piles’ dynamic tests indicate no further setup after 30 days, while smaller diameter piles at onshore/nearshore sites continue to display further marked capacity growth. Comparisons of the axial shaft capacities inferred from signal matching with CPT-based design methods provides insights into the performance of the design methods. A trend for long-term pile shaft set-up to decrease with increasing diameter is identified and ascribed principally to the diameter-dependent constrained dilatancy that develops under axial loading at the pile-sand interface.

Load capacity evaluation of different typologies of short and small diameter piles

It is common to observe residences with a high number of pathologies related to differential settlements in the municipality of Cruz Alta, Rio Grande do Sul, Brazil. Motivated by this perspective the first Geotechnical Engineering Experimental Field was implemented in the municipality. Standard penetration test and cone penetration test was conducted to characterize the subsoil and execute 17 excavated piles: nine compression piles and eight reaction piles. This technical note presents and discusses the results of the geotechnical load capacity obtained with the static load test in three different pile conditions: conventional piles, floating piles, and reinforced piles by inserting a crushed stone layer compacted at the bottom of the drilling. The piles evaluated have a length of 3 m and a diameter of 30 cm. The piles are immersed in a layer of unsaturated laterite soil. Conventional piles are extensively executed in the municipality due to the limited equipment of the companies offering this service. In summary, the piles presented low bearing capacity, however, the reinforced piles proved to be a viable alternative in terms of increased resistance. The conventional piles presented low load capacity and significant settlements. The insertion of the reinforcement at the tip of the pile resulted in a resistance gain in the range of 31%. The study of floating piles was important to understand the behavior of the pile base. This technical note will enable the geotechnical understanding for future researchers or designers who will work with this soil condition in the state of Rio Grande do Sul, Brazil.

Analysis and effect of lateral forces on Micropiles

Micro piles are small diameter pile (less than 300mm). Micro piles are generally used when there are difficult ground conditions, such as natural or man-made obstructions, sensitive ground with adjacent structures, limited access/low headroom. Micro piles are small diameter drilled and grouted friction piles. Each pile includes steel elements that are bonded into the bearing soil or rock – usually with cement grout. The bearing stratum is logged during installation drilling to assure that bearing capacity is adequate. This chapter presents a summary of various parameters defining the computational models. The bearing capacity and spring constant values for different pile diameter and different length is studied in this paper. Also, lateral pressure is also checked on the pile. The software SAFE 2016 used for the analysis of model.

Holding Capacity of Suction Anchor in Cohesive Soils based on Soil-Spring Model

In this paper, a soil-spring model was applied to evaluate the holding capacity according to the loading position of the suction anchor. The API(2010) method, which is mainly applied to small-diameter piles, the PISA(2015) method, which recently introduced research results in offshore wind power design, and the Jeanjean(2009) method, which was presented as a model suitable for large-diameter piles in cohesive soil, were analyzed. A comparative review of the finite element analysis(ALE) was applied was performed for the conditions. A procedure for calculating the holding capacities for each loading position of the suction anchor was established using the soil-spring model, and it was confirmed that it was a method that could be used practically. When the soil-spring model of Jeanjean(2009) was applied, the results (5~10%) most similar to the FEM(ALE) analysis results in tendency and holding capacity could be obtained.

Cumulative cyclic response of offshore monopile in sands

Satisfactory performance of offshore wind turbines is governed by the cyclic response of its foundation under wind and wave. Most methods of evaluating the lateral cumulative deformation of monopile due to cyclic loading are based on small-diameter pile tests installed in dry sand. This paper investigates the cumulative deformation of large-diameter monopiles installed in saturated sand. A numerical model was developed employing FLAC3D and was validated by comparing its predictions with the results of triaxial tests and centrifuge tests. The validated numerical model was used to evaluate and compare the cyclic responses of monopiles between saturated case and no pore pressure case. To evaluate the cumulative deformation for offshore monopile due to cyclic loading, the numerical model was refined to account for the effects of number and amplitude and frequency of cyclic loading, soil permeability coefficient, soil relative density and pile diameter. It was found that the larger subsidence and the less capacity of soil around the pile is caused by accumulation and dissipation of transient excess pore pressure, thus the monopile in saturated sand would experience the larger cumulative deformation. Correspondingly, based on this parametric study, an analytical model was developed to calculate the pile-top cumulative displacement of offshore large-diameter monopile under lateral cyclic loading considering the effects of pile diameter. This analytical model was validated against the results of centrifuge tests and model pile tests in saturated sands.

Correlation of Clay-Bearing Capacity from Drop Hammer Test and Loading Test on Small Diameter Piles

The provision of foundation piles in small diameters to support load capacity is fundamental in enhancing the stability and safety of shallow foundations, retaining walls, and other medium-load structures. The ultimate load (Q_ult) of piles from soil investigations and CPT testing can be easily analyzed, but the facilities needed to determine this process in the form of test equipment are costly and time-consuming. This process makes it difficult to empirically calculate the ultimate load capacity on installing small diameter piles in the form of Cerucuk wooden piles. Therefore, this research aims to determine the correlation of clay-bearing capacity from drop hammers and loading tests on small diameter piles. This is based on the relationship between static and drop hammer test values on piles with varying diameter, depth, and curing time after piling. The method used in the drop hammer test is an analysis of the EN formula, technically and the calculation is a bit far from the analysis results from other in situ test results, but the use of simple tools in determining the ultimate load makes its reason to use it by correlating the Ultimate Load results from the loading test based on the Davison method. The analysis of the De Beer and Chin method is also shown to see significant results. As a benchmark in testing the Loading test on the pile, the soil investigations results, from analysis of the Meyerhof method and CPT calculations. As a result of the analysis of the relationship between the calculation of permitted bearing capacity pile from the drop hammer test and the loading test, it is displayed in a curve approaching an exponential equation <img src=image/14828384_01.gif> for 3 days of curing time after piling and <img src=image/14828384_02.gif> 30 days of curing time after piling. This research can be used as a reference for planners in determining the bearing capacity of foundation piles on soft soil for medium load structures.

Efficacy of Design Methods for Predicting the Capacity of Large-Diameter Open-Ended Piles

Large-diameter open-ended piles (LDOEPs) are increasingly being used for support of infrastructure projects. Yet, many of the methods in current use for predicting their capacity are based on studies involving small-diameter piles. The efficacy of eight commonly used pile design methods was explored using a database of 64 load tests on full-scale LDOEPs. Capacities were computed using eight commonly used design methods based on both the standard penetration test (SPT) and cone penetration test (CPT). The calculated capacities were compared with capacities interpreted from load tests using several failure interpretation criteria. The study demonstrated that cone penetration test (CPT)-based methods are somewhat superior to SPT methods, but all methods exhibited scatter between measured and predicted capacities, with the computed capacity off by a factor of two in many load tests. Several plugging conditions were compared for each of these methods. Seven of the eight design methods better predicted pile capacity considering that the piles are unplugged, ignoring contributions of the soil internal friction on the pile inner diameter. These findings suggest that (1) LDOEPs do not plug during static loading, with little contribution of interior skin friction to pile capacity; and (2) LDOEPs do not develop significant end bearing.

Su-Based Shaft Friction Design Method and Evaluation for Pipe Pile

The shaft friction in clay is essential to bearing capacity of pipe piles. Reasonable selection of design methods and parameters is very important for offshore piles. This paper focuses on the current popular vertical load design methods based on undrained strength for pipe piles, especially for offshore piles. Based on the database, the accuracy and reliability of various pile design methods based on undrained strength su in clay were reviewed. The small-scale model tests were conducted to evaluate su-based methods. For the shortcomings of small-diameter piles in the database, a field test of full-scale offshore pile was carried out and analysed. By comparing the calculated and the measured capacity for each method, the reliability of various design methods is evaluated for large-diameter piles. For the design methods based on undrained strength, it demonstrates the importance and reliability of the determination of undrained strength parameters. In view of the vertical loading conditions of offshore large-diameter steel pipe piles, reasonable suggestions for design methods and parameters determination are given.

Experimental Study on the Mechanical Mechanism of Arch-Chord-Coupled Antisliding Structure

Arch-chord-coupled antisliding structure is a new type of structure composed of multiple small-diameter piles for strengthening small- and medium-sized landslides, especially suitable for the reinforcement of slopes that are sensitive to deformation. In order to further explore the mechanical properties of the antisliding structure, physical model tests under four cases were carried out to study the deformation and stress characteristics of the structure under different types, and the optimal structural type was determined. The displacement test results show that even if there is no crown beam at the top of the piles, all the piles can deform in coordination, and when the number of rear piles is large, all the piles can basically deform synchronously. The test results of the bending moment of the pile body show that the crown beam has a great influence on the extreme value of the bending moment of each pile. For the structural type with more piles arranged in the rear row, the standard deviation of the extreme value of the bending moment of the pile body before and after adding the crown beam decreases from 2.0 to 1.03; the presence of crown beams effectively adjusts the internal force of each pile. The comprehensive analysis results show that the arch-chord-coupled antisliding structure with more piles in the rear row is the best.

Investigation of soil plug formation in hollow piles using PIV technique

ABSTRACT The foundation systems for bridges and marine structures demand deep foundations like hollow driven open-ended piles, where hard-bearing strata exist on deep soil underneath loose inland and oceanic sea floors. During this driving process, a soil plug is formed near the hollow pile tip region, resulting in soil crushing and compression at the pile tip. The conventional methods fail to predict such volume changes and densification of the embedded soil. The present study utilised Particle Image Velocimetry (PIV) technique to assess the plugging at the pile tip and compare the penetration rate under different infill densities. The PIV results indicated that at a specific energy, pile geometric parameters and infill conditions strongly influenced pile drivability in a granular medium. Due to disturbance caused by pile driving at the base, high compressive strains are observed for large diameter piles, while large dilative strains developed soil plug during the penetration stage for small diameter piles. The plug surface profile was concave for larger diameter piles due to active arching mechanism, while it was convex for small diameter piles due to passive arching generated by lateral soil confinement within the pile wall surface.

Installation of Large-Diameter Monopiles: Introducing Wave Dispersion and Non-Local Soil Reaction

During the last decade the offshore wind industry grew ceaselessly and engineering challenges continuously arose in that area. Installation of foundation piles, known as monopiles, is one of the most critical phases in the construction of offshore wind farms. Prior to installation a drivability study is performed, by means of pile driving models. Since the latter have been developed for small-diameter piles, their applicability for the analysis of large-diameter monopiles is questionable. In this paper, a three-dimensional axisymmetric pile driving model with non-local soil reaction is presented. This new model aims to capture properly the propagation of elastic waves excited by impact piling and address non-local soil reaction. These effects are not addressed in the available approaches to predict drivability and are deemed critical for large-diameter monopiles. Predictions of the new model are compared to those of a one-dimensional model typically used nowadays. A numerical study is performed to showcase the disparities between the two models, stemming from the effect of wave dispersion and non-local soil reaction. The findings of this numerical study affirmed the significance of both mechanisms and the need for further developments in drivability modeling, notably for large-diameter monopiles.

The Environmental Effects Induced by a Metro Shield Tunnel Side-Crossing on Adjacent Pile Foundations and Its Impact Partition

With the advantages of fast construction speed and small disturbance to stratum, shield tunneling is becoming the preferred construction scheme for metro construction. However, if the disturbance of stratum cannot be clearly understood, it will affect the safety of adjacent underground structures and aboveground buildings. Based on the construction of the interval tunnel between Shizishan station and Chuanshi station of Chengdu metro line 7 project, this paper proposed a simplified calculation method to analyze the impact of shield excavation on adjacent pile foundation. A two-stage method of modified Peck formula and Winkler elastic foundation model was used to investigate the additional displacement and internal force of pile. A three-dimensional numerical model validated with the field test data was performed to compare with the theoretical results. The impact factors and their impact degree were discussed. The results show that the additional displacement and internal force are at a reasonable and acceptable level. The permanent pile foundation should adopt the small diameter pile as far as possible. When the small diameter pile foundation cannot meet the stress requirements, the design scheme of the pile group should be adopted. The area around shield tunnel is divided into strong impact area of pile foundation (S ≤ 0.75 D), slight impact area (0.75 D ≤ S ≤ 1.5 D), and no impact area (S &gt; 1.5 D). The pile researched in this paper (S = 0.83 D) is in the slight impact area.

Ground Stability Analysis in Non-Open-Cut Tunneling Method Using Small-Diameter Steel Pipe Piles

The non-open-cut method is used for constructing tunnels under existing roads without blocking traffic. Various non-open-cut methods use pipe roofs made of medium- and large-diameter steel pipe piles. However, the risk of ground settlement or heave is involved during the application of such piles. Therefore, research is conducted through model tests and numerical analysis on the non-open-cut method to investigate these problems using small-diameter piles. The progress of tunnel construction is divided into two repetitive steps. The first step (Stage 1) involves pulling back the pressure panel, and the second step involves propelling the precast structure (Stage 2). The behaviors of the pipe piles and ground displacement are analyzed according to the cover depth, tunnel size, existence and nonexistence of the shoe structure, and progress of tunnel construction. Small-diameter piles reduce the displacement during both stages. With a decrease in cover depth, the stress acting on the pile decreases during Stage 1 and increases during Stage 2. The presence of the shoe structure reduces the stress on the pile during both stages. The ground behavior based on the construction progress indicates that the ground settlement increases during Stage 1; however, no correlation is observed during Stage 2 at low depth.

Analysis of the Behaviour of Very Slender Piles: Focus on the Ultimate Load

The paper aims to analyse the influence of slenderness on the ultimate behaviour of piles with a very small diameter (less than 10 cm) that are often employed in soil reinforcement and for which the slenderness can significatively influence the failure behaviour, reducing the ultimate load. The aim is reached by means of numerical analyses on small-diameter piles of different geometries, embedded in clayey soil. The critical load is evaluated numerically in undrained conditions and then compared to the bearing capacity estimated by the classical approaches based on limit equilibrium method. The numerical model is first calibrated on the basis of the results of experimental laboratory tests on bored piles of a small diameter in a cohesive soft soil (average undrained shear strength cu = 15 kPa). The comparison between the critical load and the bearing capacity shows that their ratio becomes less than 1 for critical slenderness LCR that decreases, nonlinearly, with the decreasing of the pile diameter. The results of the analysis show that varying the diameter of the pile from 0.06 to 0.18 m, LCR varies from 65 to 200. The aforementioned evidence suggests that the evaluation of the ultimate load of piles of very small diameter has to follow the considerations on the critical load of the pile, especially if it is embedded in soft soil; on the contrary for piles of greater diameters (bigger than 20 cm) the buckling is not meaningful because LCR is so big that the common slenderness does not exceed it.

Modeling of Large Diameter Piles in Soil Formations Including Soft Clay

In Egypt, large diameter piles are used in some sites with diameters exceeding 2 m. In some cases, these piles carry foundations of heavy structures and/or large vertical and lateral loads. The analysis and design methodologies of large diameter piles are mainly controlled by the relatively smaller diameter piles, usually ranging between 60 and 120 cm. However, there is a special need for the analysis and design of larger diameter piles (i.e., larger than 120 cm) to assess their actual load carrying capacities. This paper presents numerical modeling of end bearing piles constructed in thick layer of soft to very soft clay underlain by a dense sand layer, typical to large zones in Northern and North Eastern zones in Egypt. The finite element analysis software ADINA (2018) [2] is used to simulate the behavior of the large diameter bored piles. Results showed that increasing the pile diameter cause a corresponding increase in pile capacity. It is also noticed that increasing pile embedded length in the end bearing sand layer has an enormous effect on pile capacity especially for larger diameter piles.

Carga de ruptura de estacas de pequeno porte escavadas com trado manual em solos tropicais colapsíveis

O objetivo deste trabalho é analisar a carga de ruptura de seis estacas escavadas com trado manual de 25 cm de diâmetro, de 3 m e 6 m de comprimento, executadas no Campo Experimental de Engenharia Geotécnica (CEEG) da Universidade Estadual de Londrina. As cargas de ruptura foram determinadas pelos métodos semi-empíricos de Aoki-Velloso (1975), Décourt-Quaresma (1978) modificado por Décourt (1996), Ranzini (1988) modificado por Peixoto (2001) e Alonso (1996). As estacas foram submetidas a ensaios de prova de carga estática com carregamento misto sem inundação e reensaiadas com pré-inundação por 48 h para a verificação do efeito do colapso no solo tropical de Londrina-PR. A partir das curvas carga versus recalque obtidas das provas de carga foram determinadas as cargas de ruptura das estacas pelos critérios de ruptura de Van der Veen (1953) modificado por Aoki (1976) e da NBR 6122 (ABNT, 2010). Os resultados das provas de carga mostraram que os métodos semi-empíricos são de maneira geral conservadores em relação aos critérios de ruptura e que o método de Ranzini (1988) modificado por Peixoto (2001) apresentou valores mais próximos aos obtidos em campo. A perda da carga de ruptura das estacas no solo do CEEG após a inundação foi confirmada por efeito do colapso e as curvas apresentaram formato de ruptura nítida com predominância de resistência lateral.

Scour Effects on the Lateral Behavior of a Large-Diameter Monopile in Soft Clay: Role of Stress History

Scouring of soil around large-diameter monopile will alter the stress history, and therefore the stiffness and strength of the soil at shallow depth, with important consequence to the lateral behavior of piles. The existing study is mainly focused on small-diameter piles under scouring, where the soil around a pile is analyzed with two simplified approaches: (I) simply removing the scour layers without changing the strength and stiffness of the remaining soils, or (II) solely considering the effects of stress history on the soil strength. This study aims to investigate and quantify the scour effect on the lateral behavior of monopile, based on an advanced hypoplastic model considering the influence of stress history on both soil stiffness and strength. It is revealed that ignorance about the stress history effect (due to scouring) underestimates the extent of the soil failure wedge around the monopile, while overestimates soil stiffness and strength. As a result, a large-diameter pile (diameter D = 5 m) in soft clay subjected to a souring depth of 0.5 D has experienced reductions in ultimate soil resistance and initial stiffness of the p-y curves by 40% and 26%, and thus an increase of pile head deflection by 49%. Due to the inadequacy to consider the stress history effects revealed above, the existing approach (I) has led to non-conservative estimation, while the approach (II) has resulted in an over-conservative prediction.

Numerical study of diameter effect on accumulated deformation of laterally loaded monopiles in sand

The design of offshore monopile is generally governed by the accumulated deformation under lateral cyclic loading, e.g. loads induced by winds and waves. Although methods have been proposed to predict the accumulated deformation of laterally loaded monopiles under cyclic loading, these models are mainly based on small diameter pile test results with number of load cycles far less than that experienced by an offshore wind turbine during its lifetime. Additionally, the effect of monopile dimension, e.g. diameter effect, on the cyclic response of monopile is not well examined. Based on the degradation stiffness model, this paper investigates diameter effect of monopiles on the accumulated deformation via a finite difference program, which shows that pile diameter has a remarkable influence on the development rate of the accumulated deformation of laterally loaded monopiles. A design model, which takes account of the effect of loading cycle numbers, load amplitudes and monopile diameter, is proposed based on a series of numerical simulation. The proposed design model is validated against measured results from field test and centrifuge test on cyclically loaded monopiles, which proves the validity of the proposed design model.