Analysis of Laterally Loaded Drilled Shafts in Rock

Yang Ke, University of Akron
May 2006

Drilled shafts socketed into rock are widely used as foundations for bridges and other important structures. Rock-socketed drilled shafts are also used to stabilize a landslide. The main loads applied on the drilled shafts are axial compressive or uplift loads as well as lateral loads with accompanying moments. Although there exist several analysis and design methods especially for rock-socketed drilled shafts under lateral loading, these methods were developed with assumptions without actual validations with field load test results. Some of the methods have been found to provide unsafe designs when compared to recently available field test data. Therefore, there is a need to develop a more rational design approach for laterally loaded drilled shafts socketed in rock.

A hyperbolic non-linear p-y criterion for rock is developed in this study that can be used in conjunction with existing computer programs, such as COM624P, LPILE, and FBPIER, to predict the deflection, moment, and shear responses of a shaft under the applied lateral loads. Considerations for the effects of joints and discontinuities on the rock mass modulus and strength are included in the p-y criterion. Evaluations based on comparisons between the predicted and measured responses of full-scale lateral load tests on fully instrumented drilled shafts have shown the applicability of the proposed p-y criterion and the associated methods for determining the required input of rock parameters.

In addition to the development of a hyperbolic p-y criterion for rock, a method for predicting lateral capacities of drilled shafts in rock and/or soils is developed for assessing the safety margin of the designed shafts against the design loads. A computer program LCPILE is developed using VC++ to facilitate computations. An elastic solution based on a variational approach is also developed for determining drilled shaft elastic deflection due to applied lateral loads in a two-layer soil layer system. The computational algorithm was coded in a Mathematica file for easy application.

Finally, Briaud’s method for deriving p-y curves of rock from pressuremeter or dilatometer test results is evaluated using available field test data. A modification to the Briaud’s method is recommended for applications in rocks.

Design and Construction of Continuous Flight Auger (CFA) Piles

Dan A. Brown, Ph.D., P.E., Steven D. Dapp, Ph.D., P.E.,
W. Robert Thompson, III, P.E., and Carlos A. Lazarte, Ph.D., P.E.
FHWA Geotechnical Engineering Circular 8
April 2007

This manual presents the state-of-the-practice for design and construction of continuous flight auger (CFA) piles, including those piles commonly referred to as augered cast-in-place (ACIP) piles, drilled displacement piles, and screw piles. CFA pile types, materials, and construction equipment and procedures are discussed. A performance-based approach is presented to allow contractors greater freedom to compete in providing the most cost-effective and reliable foundation system, and a rigorous construction monitoring and testing program to verify the performance. Quality control (QC)/quality assurance (QA) procedures are discussed, and general requirements for a performance specification are given.

Methods to estimate the static axial capacity of single piles are recommended based on a thorough evaluation and comparison of various methods used in the United States and Europe. Group effects for axial capacity and settlement, and lateral load capacities for single piles and pile groups are discussed. A generalized step-by-step method for selecting and designing CFA piles is presented, along with example calculations. An Allowable Stress Design (ASD) procedure is used.

Drilled Shafts: Construction Procedures and LRFD Design Methods
(pdf format)

We also have the previous document, Drilled Shafts:
Construction Procedures and Design Methods (FHWA IF-99-025), available for download. It was the last version to be written by Michael W. O'Neill and Lymon Reese, both of whon passed away the following decade.

Federal Highway Administration
Dan A. Brown, Ph.D, P.E., John P. Turner, Ph.D, P.E., and Raymond J. Castelli, P.E.
FHWA-NHI-10-016
FHWA Geotechnical Engineering Circular #10
May 2010

This manual is intended to provide a technical resource for engineers responsible for the selection and design of drilled shaft foundations for transportation structures. It is used as the reference manual for use with the three-day National Highway Institute (NHI) training course No. 132014 on the subject, as well as the 10th in the series of FHWA Geotechnical Engineering Circulars (GEC). This manual also represents a major revision and update of the FHWA publication on drilled shaft foundations co-authored by the late Michael O’Neal and late Lymon C. Reese, published in 1988 and revised in 1999. This manual embraces both construction and design of drilled shafts, and addresses the following topics: applications of drilled shafts for transportation structure foundations; general requirements for subsurface investigations; construction means and methods; LRFD principles and overall design process; geotechnical design of drilled shafts for axial and lateral loading; extreme events including scour and earthquake; LRFD structure design; field loading tests; construction specifications; inspection and records; non-destructive integrity tests; remediation of deficient shafts; and cost estimation. A comprehensive design example (Appendix A) is included to illustrate the step-by-step LRFD design process of drilled shafts as foundations for a highway bridge.

Micropile Design and Construction Guidelines Implementation Manual

Tom Armour, P.E., Paul Groneck, P.E., James Keeley. P.E. and Sunil Sharma, P.E., PhD.
FHWA-SA-97-070
June 2000

The use of micropiles has grown significantly since their conception in the 1950s, and in particular since the mid-1980s. Micropiles have been used mainly as elements for foundation support to resist static and seismic loading conditions and less frequently as in-situ reinforcements for slope and excavation stability. Many of these applications are suitable for transportation structures. Implementation of micropile technology on U.S. transportation projects has been hindered by lack of practical design and construction guidelines.

In response to this need, the FHWA sponsored the development of this Micropile Design and Construction Guidelines Implementation Manual. Funding and development of the manual has been a cooperative effort between FHWA, several U.S. micropile specialty contractors, and several State DOT’s This manual is intended as a “practitioner-oriented” document containing sufficient information on micropile design, construction specifications, inspection and testing procedures, cost data, and contracting methods to facilitate and speed the implementation and cost effective use of micropiles on United States transportation projects.

• Chapter 1 provides a general definition and historic framework of micropiles.
• Chapter 2 describes the newly developed classifications of micropile type and application.
• Chapter 3 illustrates the use of micropiles for transportation applications.
• Chapter 4 discusses construction techniques and materials.
• Chapter 5 presents design methodologies for structural foundation support for both Service Load Design (SLD) and Load Factor Design (LFD).
• Chapter 6, which was supposed to present a design methodology for slope stabilization, is not included in this version.
• Chapter 7 describes micropile load testing.
• Chapter 8 reviews construction inspection and quality control procedures.
• Chapter 9 discusses contracting methods for micropile applications.
• Chapter 10 presents feasibility and cost data.
• Appendix A presents sample plans and specifications for Owner Controlled Design with Contractor Design Build of the micropiles, and/or micropiles and footings.

Minipiling and Soil Anchors

Martin Jones, Groundation
Presented at the Annual Meeting of the Deep Foundations Institute, Hamilton, Ontario, 1987

This paper outlines the development of small diameter grouted piling, to deal with foundation problems in difficult soils conditions and in very restricted access areas. A number of applications are outlined to show the way in which these piles have been used over the last sixteen years in Canada.

P-y Curves for Laterally Loaded Drilled Shafts Embedded in Weathered Rock

(click on the title above to download)

M.A. Gabr, R.H. Borden, K.H. Cho, S.C. Clark, and J.B. Nixon
North Carolina State University
FHWA/NC/2002-008
December 2002

In areas of weathered and decomposed rock profiles, the definition of soil parameters needed for the analysis and design of laterally loaded drilled shafts poses a great challenge. The lack of an acceptable analysis procedure is compounded by the unavailability of a means for evaluating the weathered profile properties, including the lateral subgrade modulus, which often leads to the conservative design. Results from this research revealed that currently proposed P-y approaches to design drilled shafts embedded in weathered Piedmont profiles do not provide reasonable estimates of load-deflection response. Results in this report are used to develop and validate a procedure for the analysis of laterally loaded drilled shafts embedded in a weathered rock mass. The developed procedure is based on the P-y method of analysis in which the shape and magnitude of the P-y function are defined. The research proceeded along four complementary tracks: i) Finite Element modeling , ii) Laboratory work, iii) Field testing using full scale shafts; field work also included estimation of in situ modulus of subgrade reaction using “rock” dilatometer, and finally iv) Performance predictions. The proposed P-y curves are developed as hyperbolic functions. A method to evaluate in situ stiffness properties of the weathered rock by utilization of the rock dilatometer, as well as by using geologic information of joint conditions, RQD, and the strength properties of cored samples, is proposed. A computational scheme for lateral behavior is advanced by which different lateral subgrade responses are assigned in the model based on the location of the point of rotation. Above the point of rotation, a coefficient of lateral subgrade reaction is assigned on the basis of evaluated modulus as computed from rock dilatometer data or from index geologic properties. A stiffer lateral subgrade reaction is assigned below the point of rotation in order to model the relatively small shear strains in this region. Predictions based on the proposed Py model for weathered rock show good agreement with field test results, which were performed in various rock profiles. The proposed method is also verified by comparisons with published results of an additional field test. Concepts of the proposed weathered rock model have been encoded into the computer program LTBASE.