Minimal Excavation Foundations

Introduction to Minimal Excavation Foundations
What is a minimal excavation foundation?
A construction technique that minimizes disturbance of the natural soil profile within the
footprint of the structure
Common Foundation Types
perimeter / continuous / stem wall
pilings
post and beam
slab on grade
Perimeter / Continuous / Stem Wall
Typically constructed of reinforced concrete, masonry , or pressure treated lumber
Construction may require extensive grading with heavy equipment
Pilings
Elevated stilt pilings are commonly used in areas prone to flooding
Deep soil bore pilings are commonly used to support multistory high rise structures
Typically costly due to structural engineering
Post and Pier
Constructed of masonry, reinforced concrete, or lumber posts connected to girders
Posts are anchored to a concrete pier block or pad
Slab on Grade
Constructed of reinforced concrete and perimeter footings
Requires grading and / or filling to create a level foundation surface
How do minimal excavation foundations work?
Structural loads are transferred from a beam through a pin, pile, or post system, which
preserves the natural drainage patterns of the soil underneath the structure
Where can minimal excavation foundations be
used?
boardwalks
foot bridges
decks
ground-mounted solar panels
houses
observation platforms
pavilions
sheds
Types
Custom designed systems combine conventional piling and concrete components
Proprietary systems are pre-engineered, pre-fabricated, and assembled on site
Economic Benefits
Reduces consultant costs for preparing grading and drainage plans
Reduces excavation costs for constructing a continuous foundation
Controls cost of heavy machinery on sites that are not easily accessible
Reduces cost to transport fill and / or concrete to the building site
Reduces costs to transport excavated waste fill off site
Eliminates costs of constructing trenches or drywells
Environmental Benefits
Minimizes soil compaction and site disturbance from heavy equipment and machinery
Preserves rainwater infiltration and subsoil water flows
Allows rainwater to flow more naturally at shallow soil subsurface level
Social Benefits
Potentially useful for emergency housing construction due to ease of installation of preengineered proprietary systems
Design
Soils must be analyzed by a licensed geotechnical engineer
Structure must be designed by a licensed architect or engineer
• Pre-engineered systems for smaller projects likes decks or boardwalks may not require
additional engineering
Selection of an appropriate foundation system is dependent upon many factors:
• soil and groundwater conditions
• slope
• type of structure
Construction
Grade site by blading or surface terracing using light tracked equipment
Drive piles using a machine mounted, frame mounted, or hand-held automatic hammer
Install connection component (pre-cast or poured-in-place)
Install plastic vapor barrier in crawlspace
Costs
Costs are variable and dependent on
• Soil type
• Size and complexity of structure
• Structural load
Challenges
Building code barriers
• City of Seattle Department of Planning and Development issued a code interpretation
to allow small diameter pipe pile construction in May 2009
• City of Bellevue Utilities Department’s January 2012 Storm and Surface Water and
Engineering Standards encourages minimal excavation foundations
Architectural fees and structural engineering costs may be prohibitive
Case Study: Sol Duc Cabin, Olympic Peninsula
350 square feet fishing cabin on stilts to accommodate occasional river flooding
Most of the structure was pre-fabricated off-site to reduce construction waste and site
disturbance
Architect:: Olson Kundig
Case Study: Berkshire Boardwalk, Stockbridge MA
2700 feet long boardwalk along the edge of a 50 acre wetland on a residential property
Assembled by hand to limit construction disturbance
Design included a nine-month review process with biologists, permit specialists, contractors,
and conservation commissioners to ensure wetland protection
Landscape Architect: Reed Hilderbrand
Case Study: Mercer Slough Environmental
Education Center, Bellevue WA
Sited with minimal landscape disturbance, with buildings elevated on a sloping site
Cantilevered buildings are supported by steel framing anchored to concrete caps and helical piles
Site includes classroom and multipurpose buildings, a visitor center, and lab
Architect / Landscape Architect: Jones + Jones
Mercer Slough Environmental Education Center
Site Plan Illustrating Rainwater Flows
Case Study: Loblolly House, Taylor Island MD
Prefabricated 2220 square foot single family residence located on a barrier island
Sited between a loblolly pine forest and a shoreline meadow
Constructed on timber piles to minimize ground disturbance
Architect: Kieran Timberlake
Case Study: Clearwater Commons, Bothell WA
Residential co-housing community
House foundations are constructed with patented Diamond Pier Pin Foundations
Concrete pods are anchored by steel pins that hold them in place
Developer: Infiniti Real Estate & Development
Professional Resources
Built Green of Jefferson County
Federal Highway Administration Wetland Trails Design and Construction
Northwest Ecobuilding Guild
Peninsula College Green Construction and Remodeling program
WSU Extension LID Technical Workshop Series
References
City of Bellevue. Storm and Surface Water Engineering Standards. Bellevue, WA: January 2012.
City of Seattle. “Director’s Rule 10-2009.” Seattle, WA: Department of Planning and Development, 18 May 2009.
Clearwater Commons. http://clearwatercommons.com/
Hinman, Curtis. Low Impact Development: Technical Guidance Manual for Puget Sound. Olympia: Puget Sound Action Team, January 2005.
Hopper, Leonard J. Landscape Architectural Graphic Standards: Student Edition. 2nd Ed. Hoboken, New Jersey: John Wiley & Sons, Inc., 2007.
Jones + Jones Architects and Landscape Architects. http://www.jonesandjones.com/
Kieran Timberlake Architects. http://www.kierantimberlake.com/
Northwest EcoBuilding Guild. http://www.ecobuilding.org/
Olson Kundig Architects. http://www.olsonkundigarchitects.com/
Image Credits
Slide 1, left to right:
http://www.pinfoundations.com/
http://www.asla.org/2011awards/351.html
http://www.olsonkundigarchitects.com/Projects/1909/Sol-Duc-Cabin
http://media.treehugger.com/assets/images/2011/10/matalicrasset1.jpg
http://www.djc.com/stories/images/20081010/MercerSlough_big.jpg
Slide 2: http://www.jetsongreen.com/images/old/6a00d8341c67ce53ef010536e9df2b970c-500wi.jpg
Slide 3, left to right:
http://www.libertynaturepreserve.com/user/cimage/6-28-6-29-09-003small.jpg
http://www.ecoboot.nl/artikelen/WeblogFloatingCommunitiesGraphics/TiesCambodiaHouseOnStilts640x447.jpg
http://4.bp.blogspot.com/_EO8kdjHDWTI/SvyNf1-6cZI/AAAAAAAAEZ0/k-j-TixX11g/s400/crawlspace_new_floorbeam.jpg
http://www.esogrepair.com/images/slab_foundation_repair.jpg
Slide 4, left to right:
http://www.asilverweb.com/img/house-foundation2.jpg
http://blog.buildllc.com/wp-content/uploads/2012/01/BUILD-LLC-Foundation-Vent.jpg
http://www.eisenhourhomeimprovements.com/pb/wp_45224b20/images/img29195461f83c46f701.JPG
http://nbbd.com/npr/preservation/OliversCamp/Stemwall0004.jpg
Slide 5, left to right:
http://thisfacade.com/wp-content/uploads/2011/01/house-on-stilts4s.jpg
http://densitykatrina.files.wordpress.com/2009/03/house-on-stilts.jpg?w=460
http://www.nottingham.edu.my/Engineering/Research/images-multimedia/Matmechstru/Geomechanics/pilefoundation.jpg
Slide 6, left to right:
http://www.frontierbasementsystems.com/core/images/foundation-repair/foundation-problems/sagging-crawl-space/crawl-space-post-shimming-lg.jpg
http://inhabitat.com/wp-content/blogs.dir/1/files/2010/05/holyoke-cabin.jpg
http://www.backwoodsconstruction.com/mediac/450_0/media/IMG_0605.JPG
http://www.countryplans.com/images/lemay-3.jpg
Slide 7, left to right:
http://upload.wikimedia.org/wikipedia/en/thumb/1/10/Raft-slab.jpg/220px-Raft-slab.jpg
http://www.dropyourenergybill.com/wp-content/uploads/2010/10/tmp883D.tmp_tcm10-267609.jpg
http://upload.wikimedia.org/wikipedia/en/1/10/Raft-slab.jpg
http://www.esogrepair.com/images/slab_foundation_repair.jpg
Image Credits
Slide 8: http://www.cusa-dds.net/seed/?tag=foundation
Slide 9, left to right:
http://www.asla.org/2011awards/351.html
http://sonsdevelopment.com/images/products_pin2.jpg
http://www.freewatt.co.uk/images/page/16_9369c53872.jpg
http://lakeshorepreserve.wisc.edu/photo-gallery/1918marsh/lg/CLASS%20OF%201918%20MARSH%20OBSERVATION%20PLATFORM,%20CRONON,%20DSC_0196_800.jpg
Slide 10: http://www.buildinggreen.com/cgi-bin/scale.cgi?width=200&src=/productimages/1627_diamondpier.jpg
Slide 11: http://www.flickr.com/photos/tracy_olson/61056391/sizes/l/
Slide 12: http://media.dwell.com/images/480*384/a-lot-to-love-house-exterior-from-hillside.jpg
Slide 13: http://graphics8.nytimes.com/images/2008/04/13/us/13trailers.600.jpg
Slide 14: http://cdn.freshome.com/wp-content/uploads/2010/10/architect_drawing-e1287585143184.jpg
Slide 15, left to right:
http://netdrive.bobcat.com/attachments/mediawidget-landscape_rake.jpg
http://www.djc.com/stories/images/20010712/pin2.jpg
http://www.capitalcleanspace.com/core/images/home/vapor-barrier-system-lg.jpg
Slide 16: http://www.flickr.com/photos/tracy_olson/61056391/sizes/l/
Slide 17: http://www.archithings.net/wp-content/uploads/2010/08/Tyler-Engle-Raised-House-Plan-Budget-588x399.jpg
Slide 18: http://www.olsonkundigarchitects.com/Projects/1909/Sol-Duc-Cabin
Slide 19: http://www.asla.org/2011awards/351.html
Slide 20, left to right:
http://www.djc.com/news/en/11205540.html
http://www.seattlepi.com/ae/article/On-Architecture-Mercer-Slough-center-treads-1298476.php#photo-719119
http://www.flickr.com/photos/premiersips/5219476512/in/photostream/
Slide 21: http://www.flickr.com/photos/premiersips/5219476016/sizes/l/in/set-72157625500929970/
Slide 22: http://www.kierantimberlake.com/featured_projects/loblolly_4.html
Slide 23, left to right:
http://clearwatercommons.com/houseplans.php
http://www.ecobuilding.org/green-building/project-spotlights/clearwater-commons
http://clearwatercommons.com/gallery.php?gallery=Houses
Slide 24: http://2aem.files.wordpress.com/2009/07/oska-rollinghuts1.jpg
Acknowledgements
This project has been funded wholly or in part by the United States Environmental
Protection Agency under assistance agreement PO-00J08601 to Jefferson County
Department of Community Development. The contents of this document do not
necessarily reflect the views and policies of the Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.