The next DFI / ADSC Joint Micropile Committee meeting will take place at the DFI 36th Annual Conference on Deep Foundations in Boston, MA on Wednesday, October 19th from 10AM to 12PM. All committee members are encouraged to attend. The venue location is below:
The Seaport Hotel and World Trade Center
One Seaport Lane
Boston, MA 02210
To see a copy of the latest Chairman’s report for the Joint Committee, click HERE.
More information on the 36th Annual Conference on Deep Foundations can be found HERE. See you in Boston!
The following upcoming events are good places to learn about micropiles and stay up to date on what is going on in the micropile industry. Some are micropile specific while others are more general deep foundations oriented with micropile components or associated events. Click on the individual links for more information:
Now there is no major Social Media space that is untouched by Micropile Design and Construction! FACEBOOK users can now get their fair share of Micropile Design and Construction industry information and will be able to provide feedback and interact with the site.
Check out our page HERE! Be sure and LIKE us to show your enthusiasm for Micropiles!
If you missed the last one, there is another ASCE Continuing Education webinar coming up on LRFD for Geotechnical Engineering Features: Micropile Foundations. The date is advertised as Friday, July 29, 2011 at 11:30AM to 1:00PM. You get the best bang for your buck if you register and make it available to a group because for one registration fee, you can have an unlimited number of people from your organization attend at your site. I have seen this webinar and it is worthwhile if you are new to AASHTO LRFD Design for Micropiles or if you just want to get a bunch of geotechnical engineers together on a Friday to have fun talking about Micropiles. I know of one group that registered an entire local ASCE Geotechnical Chapter for it.
Find out more and register for the event HERE. The webinar description is below:
This webinar focuses on micropile foundations. Micropile foundations are often a technically sound and cost-effective foundation choice where a deep foundation solution is appropriate based on site conditions, applied loads and project schedule and performance requirements. The Load and Resistance Factor Design (LRFD) platform offers a rational framework for consideration of micropile foundation systems. The webinar will use the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge and Structures Specifications as a basis for the technical content. The webinar will include discussion on the terminology and construction of micropiles. It will also focus on topics such as: identification of limit states and resistance factors, axial compression and uplift resistance of a single micropile, estimation of grout-ground bond resistance and tip resistance, and group efficiency factors for evaluation of axial resistance of micropiles in groups. It is assumed that the participant has a basic working knowledge of design and construction of deep foundations.
The 2011 DFI / ADSC Micropile Seminar held last week in Little Rock, AR was an exciting whirlwind tour of micropile technology and featured presentations from the leading micropile practitioners in the United States and worldwide. The next Micropile Seminar will occur sometime in either Spring, Summer or Fall of 2012. Keep an eye out for information on this event that is likely to be combined with an Anchored Earth Retention seminar to boot.
If you are interested in LRFD for Micropiles, I have posted my presentation on the subject from the seminar on my Scribd page. You can view that presentation and others I have given in the past at http://www.scribd.com/jonbennett. If you have questions or comments as to other aspects you would like to see covered, let me know as I will be presenting a revised version at the next seminar.
In terms of upcoming Micropile industry events, don’t miss SuperPile this week in Charleston, SC. The next ADSC / DFI Joint Micropile Committee meeting will be held at the ADSC Summer Meeting also in Charleston, SC. Check ADSC’s website for information on that. Hope to see you at one of these events.
Load and Resistance Factor Design (LRFD) is the predominant design method utilized today for reinforced concrete and structural steel, and is the primary focus of the relatively new AASHTO LRFD Bridge Design Specifications. Historically, micropile design has been performed mainly with Service Load Design (SLD) and Allowable Stress Design (ASD) methodologies and most of the design manuals and specifications in existence prior to 2008 were based on SLD and ASD concepts. The AASHTO LRFD Bridge Design Specifications document offers the most comprehensive LRFD guidance for geotechnical engineering features in the United States (and maybe the World) today. The use of this LRFD design specification is mandated by the majority of State DOTs for use in designing highway bridges and highway structures governed by it. The AASHTO LRFD specification adopted a micropile design section in 2008.
In recent DFI / ADSC Micropile Seminars, there have been a number of questions regarding the proper use of LRFD for micropiles. On May 4, 2011, at the DFI / ADSC Micropile Seminar in Little Rock, AR, I will give a presentation that will cover the fundamentals of LRFD as it applies to micropiles, and will provide a comparison with SLD methodology. We will work through an example analysis problem where we will see how every aspect of micropile axial design compares between SLD and LRFD. We will be looking specifically at FHWA and IBC Service Load Design compared to AASHTO LRFD design. This covers pretty much all the current bases for mainstream micropile design. I have never seen this type of comparison presented so don’t miss out.
Details have been finalized for the 2011 DFI / ADSC Micropile Seminar to be held in Little Rock, AR. Complete information and registration details are available on the ADSC website.
Date: Tuesday and Wednesday, May 3-4, 2011
Location: Peabody Hotel, Little Rock, AR, USA
DFI / ADSC Micropile Seminar
A day and a half event to discuss the history of micropiles, design and construction, industry challenges, load testing, material and equipment, quality control, and selected case histories. This seminar will include a presentation on LRFD for micropiles in response to increased interest in the subject. The event will feature presentations from the leading North American and worldwide experts on micropile design and construction.
Presentations will include:
History and Overview
Lateral Loads on Vertical Micropiles
Hollow Bar Micropiles
Local Micropile Design
Materials and Equipment
LRFD for Micropiles (by yours truly)
Exhibitor spaces and sponsorship opportunities are available.
The first use of micropiles dates back to the early 1950’s in Italy, where new methods of underpinning for existing structures were needed to restore structures and monuments damaged during World War II (Lizzi, 1982). Dr. Fernando Lizzi is commonly recognized as the inventor of micropiles in the form of the root pile or palo-radice.
Dr. Lizzi was a civil engineer and Technical Director with the Italian specialty foundation contractor Fondedile and obtained the first patents for root piles in Italy in 1952. This early form of micropile technology was used extensively in Europe for the restoration of various structures and monuments.
Fondedile introduced micropiles into North America in 1973 by performing a number of projects, mainly in the Northeastern United States. By the mid 1970’s a number of US specialty foundation contractors previously engaged in drilled and grouted anchor work had developed their own variants of the technology. There was slow growth of the technology in the time period between the mid 1970’s and the mid 1980’s with Fondedile closing their North American venture for economic reasons. (Bruce and Juran, 1997)
There has been a rapid growth in the specification and use of micropiles in the United States since the mid 1980’s to early 1990’s partly as a result of FHWA research efforts, trade association promotion efforts and the development of various publications offering standardized design and specification guidelines.
In the early 1990’s, the Intermodal Surface Transportation Efficiency Act (ISTEA) provided massive funding for the rehabilitation of highway infrastructure in the United States. As part of this effort, the FHWA undertook a number of research and development projects associated with specialty geotechnical construction to encourage innovation in geotechnical applications and produced several design manuals including the first on micropiles. This was the beginning of the surge in micropile use in the United States.
In 2006 and 2007 respectively, the International Building Code and the AASHTO LRFD Bridge Design Specifications incorporated design code sections for micropiles thus making way for further expansion of applications in both building and highway construction. Micropiles currently are widely specified and used in all construction sectors worldwide.
Micropiles can be installed at various angles from vertical and are capable of resisting both axial and lateral loads. The unique structural makeup of micropiles has an effect on the way in which they develop their load resistance and how they behave in response to these loads at various inclinations.
Micropiles develop their axial capacity primarily through the bond between grout and soil or rock in the bonded zone of the pile. Because of this, micropiles provide both tension and compression resistance thus making them useful in a variety of applications, particularly where resistance to uplift is needed in addition to resisting compression or gravity loads.
With the majority of micropile axial load being resisted by steel casing or internal reinforcing core, micropiles exhibit relatively high axial stiffness and are capable of resisting large axial loads. Micropiles that are fully bonded exhibit even higher apparent stiffness than those that are partially unbonded for the same steel area.
Because of the installation methods (down-hole hammer and rotary-percussive drilling) and equipment used, micropiles can be installed in soil and rock conditions where the use of other conventional deep foundation systems are not a reasonable alternative, such as in Karst topography or where modest subsurface obstructions or boulders are present. Micropiles can be installed through modest obstructions and boulders that would be problematic for installation of helical piles, driven piles, drilled shafts or augercast piles. They can also be drilled into pinnacled rock where achieving acceptable anchorage or bearing for other deep foundation types might be questionable.
Micropiles can be easily installed in caving soils and below the water table by either using casing or hollow bar micropile installation methods. Caving soils and elevated water can be problematic for deep foundation systems that rely on open hole drilling such as drilled shafts.
Compact and low headroom drilling equipment is available such as to make installation of micropiles possible in low-headroom or limited space applications where the installation of other types of conventional deep foundation systems is not possible. Examples of this are applications where supplemental foundation support is required in basements or areas with overhead restrictions or otherwise small or space restricted areas where relatively large equipment cannot fit.
The drilling and installation equipment used for micropiles does not produce an amount of vibration that would be harmful to structures as opposed to driven piles which can produce magnitudes of vibration that have the potential for causing settlement of adjacent structures resulting in structural damage. For this reason micropiles are well suited for use in close proximity to existing structures.
Micropiles are ideal for retrofit applications in that they can easily be installed through a core drilled hole in an existing foundation or footing and anchored to the existing foundation for load transfer.
A new video has been uploaded to my YouTube Micropile page: Limited Access Hollow Bar Micropile Installation. Hollow bars can be the ideal foundation solution in this application because they do not require as much hardware and equipment as conventional cased micropiles. Hollow bar segments can easily be carried by hand whereas casing and downhole hammer equipment often will require a forklift or other mechanical assistance to move. WARNING: The US Surgeon General has determined that smoking is hazardous to your health. You can view my videos at http://www.youtube.com/user/JonathanBennettPE. Let me know if there are particular things you want to see.