Let’s Talk Dirt by Walt Keaveny, Risk Manager, MS, PE, PG

Does this Sound at all Familiar? A home builder puts up a side sign that reads “Clean Fill Dirt Wanted.” A row of trucks arrive and dump dirt in a ravine located under one area of a planned . A dozer spreads the dirt to make a level pad for the foundation. Clean Fill Dirt Wanted Fast forward one year. The homeowner has been moved into their new home for a couple of months. The builder is surprised to get a call from the homeowner was found to be non-uniform, varying 2-10 Home Buyers Warranty indicate that expressing concerns about some from to . The dirt thickness was fill dirt is the leading cause of new home inoperable doors and windows, noticeable also non-uniform, varying from zero structural failures! When placed under a floor slopes, cracks in floor tile, and to several feet under portions of the foundation, fill dirt is arguably the most separations in trim. The quality conscious foundation. The fill density was low, since important structural component of a builder wonders what could be causing a dozer is not designed to compact fill. home. If the dirt that supports the home the significant foundation movement This all resulted in both excessive total settles excessively, then every structural and related structural distress? After all, and differential settlement, and a very element located above it is at risk of the builder used a reputable structural expensive repair. failure. Structural engineers do not take engineer, built in accordance with the into account the potential for unexpected plans, and passed all building department fill settlement in their structural designs. inspections. How often is Dirt to Blame? Alarmingly, nationwide it costs an Unfortunately fill dirt-related structural average of over $50,000 to investigate A subsequent forensic investigation failures like this are all too common. In and repair a structural failure caused by determined the cause of the structural fact, the ground-breaking findings from fill dirt. In some states the average cost failure to be the fill dirt. The dirt quality over 40 years of forensic investigations by exceeds $100,000.

Fill dirt is the leading cause of new home structural failures! When placed under a foundation, fill dirt is arguably the most important structural component of a home. Let’s Talk Dirt

or tilt in the foundation which in turn developed just prior to site development. causes distortion in the superstructure. Engineered also means that the What is Engineered Fill? engineer’s representative observes fill placement operations, and conducts “Fill Dirt” as it is broadly called in the a sufficient number of tests to confirm construction industry, is formally referred compliance with specifications. The test to as “engineered fill” when used below results are reviewed by the engineer foundations. The need to engineer this and documented in a fill certification important fill is required by governing report. The report should be archived so construction authorities. For example, that in the event of a structural failure the International Residential Code (IRC) builders can protect their liability states “Fill that support footings and by demonstrating that the fill met foundations shall be designed, installed, engineering specifications. and tested in accordance with accepted engineering practice.” HUD Sheet 79G, with Controlled Most often Foundations Don’t Fail Like Playing Jenga® on Jello® Earthwork, states “For any development - People Do in which buildings are to be placed on Foundation failures caused by fill are graded areas, all earthwork shall be Building a home on improper fill dirt avoidable. Most often foundations designed, engineered, and constructed is a bit like playing Jenga® on Jello®! don’t fail - people do. Unfortunately, in such a manner that there will be no Geotechnical engineers recommend it is relatively common to overlook the adverse differential movement which may that footings bear on either undisturbed fill under foundations. In part because cause damage to the structure.” natural or on “engineered fill.” Most building departments in most states don’t natural soils were deposited over 10,000 require confirmation of fill compaction. What is actually “engineered” about years ago during the last ice age, and The fill located under foundations should fill? Isn’t it all basically the same and have had plenty of time to densify. On be engineered - just like structural just compacted to 95% of maximum the other hand, fill relies on mechanical concrete and structural framing are density? No -- there are countless types compaction to achieve high density like engineered. of fill, fill applications, and natural soil. If fill is not densified initially conditions. “Engineered” means that by the weight of proper compaction a professional geotechnical engineer equipment, unfortunately it will develops site-specific specifications eventually be compacted by the weight of for fill quality, subgrade preparation, the home. fill thickness uniformity, placement on slopes, lift thickness, moisture content Structural failures caused by fill are a and density (expressed as a percent of very severe type of foundation failure max. density of a lab Proctor sample). The due to the high potential magnitude of engineer also ensures that the natural both total and differential settlement. soils that underlie the fill can safely bear Since fill is often placed under the entire the weight of both the fill and the home. foundation, all areas of the home are These specifications can be found in the It all starts with the dirt. potentially impacted. Settlement causes site geotechnical report, if available, or damaging deflection (i.e., bending) and/

About the author: Walt Keaveny, MS, PE, PG is the Risk and Underwriting Manager for America’s leading new home warranty company, 2-10 Home Buyers Warranty. Mr. Keaveny is licensed as both a Professional Engineer and Professional Geoscientist with over 30 years of engineering and construction experience. His articles have been broadly distributed by the NAHB and local HBAs.