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GSP 131 Contemporary Issues in Foundation Engineering

Practical Advice for Foundation Design – Micropiles for Structural Support

D.A. Bruce1, Member; A.W. Cadden2, Member; and P.J. Sabatini3

1Geosystems, L.P., P.O. Box 237, Venetia, PA 15367; PH (724) 942-0570; FAX (724) 942-1911; email: dabruce@geosystemsbruce.com Schnabel Engineering, 510 E. Gay Street, West Chester, PA 19380; PH (610) 696- 6066; FAX (610) 696-7771; email: acadden@schabel-eng.com. GeoSyntec Consultants, 55 W. Wacker Drive, Suite 1100, Chicago, IL 60601; PH (312) 658 0500; FAX (312) 658 0576; email: psabatini@geosyntec.com 2 3

Abstract

Certain details of micropile design remain unresolved between various practitioners and such disagreements have limited the acceptability of micropiles in certain

quarters.

subject,

Detailed micropile design is an extremely lengthy and

especially

when

micropile

groups

are

concerned

or

seismic

often

complex

issues

must be

addressed.

The

paper

provides

a

simplified

step-by-step

design

approach

discussing

initial evaluation of feasibility,

considerations.

Thereafter

the

review of data, loading combinations and

final

design

steps

are

discussed.

These

general include

geotechnical strength limit states, other structural

considerations, service limit states,

corrosion protection, and some seismic considerations.

Introduction

Through the efforts of many authors it is now well established that micropiles have been used throughout the world since their development in Italy in 1952 (FHWA, 1997). In North America, the use is somewhat more recent, and as is typical with a relatively new specialty geoconstruction technique, most of the technical knowledge has resided with the contractors. Not surprisingly therefore, and even given that such contractors have displayed admirable skill, knowledge, and zeal in their developments, there still tends to be more certainty and consensus within the industry with respect to issues relating to construction and testing than to design.

Following the FHWA State of Practice review in 1997, there have been major efforts made in the quest for a “unified” design approach. Such efforts include the FHWA Implementation Manual (2000), the efforts of the Micropile committees of both the

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