Underpinning 101A Down & Dirty OverviewJohn Davis, PEDenise Richards, PEApril 25, 2016
Credit(s) earned on completion ofthis course will be reported to AIACES for AIA members. Certificates ofCompletion for both AIA membersand non-AIA members are availableupon request.CES for continuing professionaleducation. As such, it does notinclude content that may bedeemed or construed to be anapproval or endorsement by theAIA of any material of constructionor any method or manner ofhandling, using, distributing, ordealing in any material or product.Questions related to specific materials, methods, andservices will be addressed at the conclusion of thispresentation.This course is registered with AIA
Learning Objectives Learn the basic principles ofunderpinning. Understand the propertechniques of “approach pit”underpinning for wallfoundations. Understand how not to doapproach pit underpinning. Review techniques for individualspread footing underpinning. Review alternativeunderpinning/foundationmodification techniques.
Without a solid foundation Toronto, 2014London, 2014Toronto, 2014
On a Larger Scale Minard Hall,North Dakota State, 2009
un·der·pin·ning [uhn-der-pin-ing] –verb (used with object)1.the introduction of additional support to the foundation of astructure to deepen or increase its bearing value.a.if done because the foundation is inadequate, it is calledremedial underpinning.b.if done to deepen a foundation to enable adjacent, lowerconstruction, it is called precautionary underpinning.11. Edward E. White (1913-1988), Spencer White and Prentis, Inc.
In the Code2012 IBC Section 1804.1 - Excavations forany purpose shall not remove lateralsupport from any footing or foundationwithout first underpinning or protectingthe footing or foundation againstsettlement or lateral translation.
Historic Building Foundations Prevalent in Philadelphia housing Rubble stone foundations withoutfootings If exposed or undermined, moresusceptible to instability or suddenfailure
Most Common Type ofPrecautionary Underpinning“Approach Pit”:underpinning in order to lower the foundation bearing level toenable adjacent lower construction.
Theory of Approach Pit UnderpinningTYPICAL STRESSPATHARCHING OF WALL OVER APPROACH PIT
1. Plan the sequence
2. Initial Excavation
3. Start “Approach Pit”
4. Install Lagging and Extend Shaft Under Footing
5. Place Concrete and Drypack
5a. Or Extend Shaft to Depth Needed Then Placeand Drypack
Exceptions to the Rule
Non Continuous Approach PitUnderpinning
Individual Spread FootingUnderpinning
Temporary Footings & SupportBeams
How Not to Underpin
Third/FourthFloor WindowSecond/ThirdFloor Window
Fifth FloorWindow/ParapetFourth/FifthFloor Window
Cracking also appearedon the interior andthrough the wallfinishes.
Repairs completedtied the wall back tothe interior framingor the perpendicularwalls.