Drilled Displacement Piles Research Articles

Ultimate Capacity of Drilled Displacement Piles: Static Analysis and CPT-Based Methods

Ultimate Capacity of Drilled Displacement Piles: Static Analysis and CPT-Based Methods

Axial Load Capacity Predictions of Drilled Displacement Piles With SPT- and CPT-based Direct Methods

Drilled Displacement Piles (DDP) provide an ideal foundation solution that combines the benefits of ground improvement with traditional advantages of piling systems. This paper offers insights gathered from 55 construction projects in which nearly 130 DDPs were installed and tested axially. High quality site exploration data (e.g., Cone Penetration Test (CPT) and Standard Penetration Test (SPT)) were evaluated to derive geotechnical analysis parameters. The test sites consisted of mostly mixed soil types with strongly stratified layers of sand, silt, and clay. Pile diameters ranged between 35 and 61 cm (14 to 24 inches). Prior to analyzing the axial performance of DDPs, a variety of failure interpretation methods were assessed to confidently extrapolate failure loads when field testing was terminated prior to pile failure. Results of this study suggested the Van der Veen’s (1953) method to most closely estimate the load that triggers pile plunging behavior specific to DDPs, followed by the Butler & Hoy (1977) and L1-L2 methods (Hirany and Kulhawy, 1989). Hereafter, in-situ axial load test results were compared with a wide range of analytical methods, including those developed specifically for DDPs. Predictive accuracy was assessed in terms of total pile capacity and pile settlement and separated based on pile diameter, stiffness, and soil type. Most examined analytical methods underpredict the in-situ pile capacities for both, CPT and SPT -based analysis. It was also found that the difference between the experimentally determined and predicted capacities is related to the level of improvement in the surrounding soil following pile installation. A general comparison between predictive axial accuracy and the observed level of ground improvement is also discussed for sandy and mixed type of soils.

Experimental and field studies on the behavior of drilled displacement piles

Experimental and field studies on the behavior of drilled displacement piles

Measured end resistance of CFA and drilled displacement piles in San Francisco Area alluvial clay

Continuous Flight Auger (CFA) and drilled displacement (DD) piles in the San Francisco (California, USA) area are typically designed using a combination of side- and end resistances. For moderately...

Design of pile foundations by taking into account piling technology

AbstractThe article deals with design of pile foundations by taking into account piling technology, which has significant impact onto pile's resistance and settlement. The analysis is focused especially to design of a continuous flight auger pile and a drilled displacement pile. The results of fully instrumented static load tests were analysed and compared with the results of different computational methods. The numerical modelling using FEM, the Cavity Expansion Theory and the Limit Load Curve Method allowed modelling of load – settlement curve of the pile. The numerical modelling using “indirect” modelling of the technology impact led to very accurate determination of the load – settlement curve. Software based on the Cavity Expansion Theory allowed determining the load – settlement curve of total piles resistance as well as piles base resistance. The load – settlement curve calculated using this method was equal to the results of a static load test with more than 90 % degree of accuracy.

Reliability-based assessment of drilled displacement piles bearing capacity using CPT records

ABSTRACTDrilled displacement piles (DDPs) are known as an alternative to conventional foundations in coastal areas, given the elimination of environmental impacts and difficulties caused by installation process of driven piles and more consistency with environment. Despite increasing employment of these piles, the extent of research works does not yet suffice the requisites to reach a routine design. This paper aims to analyze six cone penetration test (CPT)-based methods of determining the bearing capacity of DDP. The statistical and reliability-based approaches were used in two parts of assessing performance of the methods with respect to soil–pile characteristics followed by evaluating reliability of the prediction outcome. A database is compiled including 65 DDP load tests with adjacent CPT profiles. Performance of the methods are analyzed. Finally, a reliability parameter, i.e., confidence interval, is introduced to demonstrate a more realistic insight into the evaluations by expressing performance of the methods in terms of a range for possible average values of the predictions ratios, rather than simply an arithmetic mean. The study reveals that the commonly used CPT-based methods which have not been specifically developed for DDP show great potential for design. The results indicate that the investigated methods can have promising performance if some modifications are applied.

Design and Construction Validation of Pile Performance through High Strain Pile Dynamic Tests for both Contiguous Flight Auger and Drilled Displacement Piles

Design and Construction Validation of Pile Performance through High Strain Pile Dynamic Tests for both Contiguous Flight Auger and Drilled Displacement Piles

Numerical analysis of bearing capacity of drilled displacement piles with a screw-shaped shaft in sand

ABSTRACTDrilled displacement (DD) piles with a screw-shaped shaft (referred to as DD piles) are installed using a continuous full thread hollow rod (without a displacement body) inserted and advanced in the soil by both a vertical force and a torque. As a type of newly developed pile, current understanding of the bearing mechanism of DD piles is unsatisfactory, which restricts their further applications in engineering. The primary aim of this paper is to study the bearing mechanism of this type of pile using a numerical method. First, a numerical model for calculating the bearing capacity of the DD piles was created and validated by a laboratory test. Then, the effects of the parameters of pile–soil interface, soil strength, and pile geometrical parameters on the bearing mechanism of the DD piles were investigated in parametric studies. The results of parametric studies show that the limit shear stress on the pile–soil interface, the friction angle of surrounding sand, screw pitch, and thread width significantly influence the bearing capacity of the DD piles, whereas the friction coefficient at the pile–soil interface and the thread thickness have little effect. Based on the results of the parametric studies, the failure mechanism of the DD piles under vertical load is analyzed. Finally, an equation for predicting the ultimate bearing capacities of helical piles based on cylindrical shear failure was used for estimating the bearing capacity of the DD piles, and the calculated results were verified with the numerical results.

Installation Effects of Controlled Modulus Column Ground Improvement Piles on Surrounding Soil

AbstractThe installation of foundations and ground improvement systems alters soil stresses affecting their soil-structure interaction and behavior under vertical loading. The installation effects have been investigated for several foundation types, especially for driven piles; however, experimental full-scale investigations of drilled displacement piles are very limited. This paper focuses on investigating the short-term installation effects of controlled modulus columns (CMCs) using an instrumented full-scale field test unit. The soil was instrumented using push-in pressure sensors (PS) and shape acceleration arrays (SAAs) to monitor the evolution of soil horizontal stresses, pore water pressures, and lateral displacements during installation and vertical load test. These sensors were installed at approximately 1D, 2D, 3D, and 4D from the outside surface of the CMC shaft, where D is the diameter of the CMC. The measurements presented in this paper clearly show that the soil experienced an increase of ho...

Field Tests to Investigate the Installation Effects of Drilled Displacement Piles with Screw-Shaped Shaft in Clay

AbstractThis technical note presents a detailed field study to investigate the installation effects of drilled displacement (DD) piles with a screw-shaped shaft in Shanghai soft clay. Horizontal soil displacements and pore water pressures were measured in the vicinity of two DD piles with a screw-shaped shaft during their installation and subsequent soil consolidation periods. The results show that the horizontal soil displacements induced by the installation of a DD pile with a screw-shaped shaft are mainly concentrated within a circular region with a radius smaller than six times the pile external diameter and that the maximum horizontal soil displacements decrease by 10–20% one day after concreting and then tend to be stable. The excess pore water pressures reach their maximum when the drilling rod reaches the design depth or the concreting is completed and then start to decrease with time following approximately an exponential decay function.

Influence of shear stress on cylindrical cavity expansion in undrained elastic–perfectly plastic soil

The conventional cavity expansion method is based on the assumption of uniform radial pressure applied at the cavity wall boundary without considering the shear stress. However, in practice, shear stress may exist at the cavity wall, such as during the drilling process of drilled displacement piles. This note presents an analysis of the influence of shear stress on cylindrical cavity expansion in an undrained elastic–perfectly plastic soil. The problem is formulated by assuming large strain in the plastic zone and small strain in the elastic zone around the cavity, with a plane-strain condition under the cavity expansion process. Plastic yielding is determined by the Tresca failure criterion and an associated flow rule. A closed-form solution for the pressure–expansion relation is given to modify the conventional pressure–expansion relation without considering the influence of the shear stress. The plastic zone radius, cavity wall limit pressure, stress and excess pore pressure are also obtained. Furthermore, parametric studies are carried out to investigate the influence of shear stress on the cavity wall limit pressure, stress, excess pores pressure distributions around an expanding cylindrical cavity and the plastic zone radius. The results show that shear stress at the cavity wall boundary has a significant influence on the pressure–expansion relation and cannot be neglected when deriving the cavity wall pressure or excess pore pressure. However, the plastic zone radius is not sensitive to the shear stress. The present work provides a more general solution and improves the conventional cavity expansion theoretical framework.

Closure to “Design Methodology for Axially Loaded Auger Cast-in-Place and Drilled Displacement Piles” by Sungwon Park, Lance A. Roberts, and Anil Misra

Closure to “Design Methodology for Axially Loaded Auger Cast-in-Place and Drilled Displacement Piles” by Sungwon Park, Lance A. Roberts, and Anil Misra

Discussion of “Design Methodology for Axially Loaded Auger Cast-in-Place and Drilled Displacement Piles” by Sungwon Park, Lance A. Roberts, and Anil Misra

The authors propose to employ t-z functions for estimating the load-movement response of a pile subjected to a static loading test. Judging by the authors’ Fig. 1, the proposed t-z functions are springslider relations, that is, they model the shaft and toe resistances as bilinear with an elastic initial part followed by a plastic part representing the ultimate resistance (capacity). The authors state that the capacity is mobilized at a pile-head movement of 5% of the pile diameter, which they also apply as the definition for the pile-toe load-movement response. First, the discusser would expect that themovement should be the movement at the pile element considered—a pile does not have to be very long before a substantial portion of the movement at the pile head is attributable to pile axial compression. It is not logical to assume that the length of the initial elastic response decreases with depth, all other factors being equal. Second, applying an elastic-plastic model for the pile-toe response is incorrect. The response of the pile toe—usually denoted as the q-z function to separate it from the t-z function expressing the shaft response—does not show an ultimate resistance but is a gently rising curve showing no kinks or explicit changes in curvature. Third, the pile diameter has nothing to do with the changeover from elastic to plastic response nor, indeed, anything to do with the ultimate shaft resistance. The magnitude of the movement at the point of transition from elastic to plastic response may differ in different soils. However, it is usually also much smaller than the authors’ mentioned range of 10–20 mm. Moreover, it is independent of the pile diameter, be the pile a small-diameter pile, say, 300mm, or a large one, say, 3,000mm, and be the pile shape circular or square or rectangular, such as a barrette, which can have one side about 1 m in length and the other between 3 and 8 m in length. Fourth, the elastic-plastic response is too simplified a model for the shaft resistance. Although it can occur, a strain-hardening response is more common, particularly in sand that includes silt and clay.Other soil types can exhibit strain-softening response, particularly in soft clays. The mathematical expressions for four common t-z functions are given in Eqs. (1)–(4) (Fellenius 2012). Eq. (1) presents the relation for the ratio function, so called because it states that the ratio between two values of unit shaft resistance (or load) is equal to the ratio between the movements produced by the same loads raised to an exponent

Design Methodology for Axially Loaded Auger Cast-in-Place and Drilled Displacement Piles

AbstractWith the increasing use of augered cast-in-place and drilled displacement piles in new construction, it is important that proper design parameters be incorporated when evaluating pile performance using reliability-based design methods. Although augered piles can be distinguished from bored piles, including drilled shafts, and driven piles by the magnitude of the effective stress changes they produce in the vicinity of the pile during construction, the current design methods for augered piles generally use the same design methods as those used for bored or driven piles. To enhance the efficiency of the augered piles, a unique design method must be developed. This paper focuses on developing a design methodology for axially loaded augered piles installed in predominately sandy soils using the t-z method. To develop the design parameters for augered piles, back-calculation of the t-z parameters was conducted using static load–test data. The data from 17 static pile load tests conducted on augered pil...

Static load test interpretation using the t-z model and LRFD resistance factors for auger cast-in-place (AC IP) and drilled displacement (DD) piles

Static load test data for augered cast-in-place (ACIP) and drilled displacement (DD) piles were interpreted using the <i>t-z</i> model method. Eighteen load tests consisting of load-settlement and load transfer data were obtained from two different construction sites. A series of back-calculations were performed using the <i>t-z</i> model method to enhance the static load test data, which were then analyzed to obtain resistance bias factors for the currently used ACIP and DD pile design methods. The <i>t-z</i> model method enhanced load test data provides the ability to interpret field data for loading conditions beyond those measured during test. The resistance bias for the various design methods were then used to obtain the resistance factors based upon the traditional calibration approach. Furthermore, resistance factors were also obtained using probabilistic analysis based upon the <i>t-z</i> model method. The comparison of these two sets of resistance factor indicates that those obtained from the traditional calibration approach contain a wide range of magnitudes, while the resistance factors from the <i>t-z</i> model method design result in a consistent level of reliability.

Drilled Displacement Piles – Current Practice and Design

AbstractDrilled displacement piles are being increasingly used as foundation elements, particularly in projects requiring fast construction. Different types of drilled displacement (DD) piles are available in practice. DD piles are classified according to the drilling tool design and installation method. The capacity of a DD pile, depending on its type, is between the capacities of geometrically similar nondisplacement and full-displacement piles installed in the same soil profile. This paper provides an overview of the different types of DD piles and their installation techniques and describes three design methods used in practice. It also compares DD pile capacities obtained with these design methods for two different sites.