Let's Talk Dirt

• By Pieter van der Have
• 10/01/18

I’m not of the inclination to “talk dirt,” like the stuff that custodians must deal with regularly. Not this time, anyway. For the purpose of this column, I use the word “dirt” as a layperson’s synonym for “soil.”

Like many of you, I’ve witnessed some avoidable disasters that befell some of our buildings because of inadequate or bad testing of soils. For instance, I watched what happened when a 200,000-gross-square-foot hospital-in-waiting started to settle unevenly. Apparently, the footings constructed under this new building were inadequate for the type of soils upon which it was erected. The solution to this crisis was to jack up the south end of the structure, using hundreds of hydraulic jacks, after which they built additional spread footings under the original ones. I can only imagine how much time and money were wasted having to correct that avoidable problem. Very likely, dedicating more money to proper testing and engineering would have been a profitable investment.

Water, Water Everywhere

During this same time frame, a dormitory was constructed that ultimately developed serious issues, allegedly because of inadequate testing or poor interpretation of the results (or both). In this case, the problem surfaced after the first few years of occupancy. The foundation walls in one corner of the building started to show numerous significant cracks. Whenever there was substantial precipitation, or heavy snow thaw, or a sprinkler valve was stuck open, water poured in through those cracks, flooding the basement storage areas. That part of the building was sinking. Research that might have been performed during the early planning stages did not discover or consider that an abandoned creek bed was located under the proposed footing. It had been covered over when the U.S. Army had control of the property (until the 1950s), after they finished using the area as a garbage dump.

There were other buildings that leaked badly through foundation walls on the uphill sides because of inadequate consideration of hydrostatic pressure, in combination with the wrong backfill materials, and/or the wrong selection of waterproofing materials. One building complex with underground connecting pedestrian tunnels leaked so badly that the media published images of students paddling canoes in those tunnels.

I eventually learned enough about soils to understand why mistakes were made, though not to the point of saying they were unavoidable. Soils are more complex than most people realize. All soils are comprised of a mix of one, some, or all of these: gravel, sand, silt, clay, and/or organic matter. (Rocks are not considered “soil.”) Expansive soils can “grow,” while compressible soils might shrink under the weight of a building—even small ones. Soil’s chemistry must be assessed to avoid corrosion of building materials. In northern zones, buildings constructed on permafrost can potentially have a detrimental impact on soils, just by the heat generated within and by the building. Arguably, climate change is generating its own impact on buildings constructed on permafrost—mitigatable with appropriate engineering and designs.

Start With Testing

Soils testing is one of the first activities that should occur before any substantial planning occurs. It can be costly, but will potentially generate tremendous cost avoidances during and after construction. Testing activities should include the following: moisture content, Atterberg limits test (looking at shrinkage, plasticity, and liquidity of fine-grained soils), specific gravity of soil test, test for dry density of soil, and a Proctor’s test (compaction).

The USDA Natural Resource Conservation Service website offers access to soils information. Though not the most user-friendly website, it is a great place to start when we’re not familiar with soils compositions in the area where we’re proposing to build. However, it should not be the only source of information consulted when starting construction planning. It is not at all uncommon for a building with a large footprint to find itself located over two or more different types of soil (or bedrock). Several soil tests must be performed, at carefully specified locations.

How should those tests be performed? Boring is considered by professionals to be the most obvious answer. If it is properly performed, this method can provide the clearest image of what is located below each site, down to the desired depth or beyond. One risk associated with this approach is to underground utilities. Unless an organization has accurate maps that locates all underground utilities within inches, this method can be risky. We insisted on potholing, performed at our cost by our own staff. We thereby avoided boring into a HTHW pipes or other direct buried utilities.

This article originally appeared in the College Planning & Management October 2018 issue of Spaces4Learning.