Expansive soils

Expansive soils

Geo Craft Builders — Swelling Soils – foundation settlement and movement.

A small amount of foundation settlement is normal and some cracking may occur.  Excessive foundation movement will not only compromise the value of your business or home, but can also compromise the structural integrity.  The typical warning signs of excessive foundation movement that any home or business owner should be aware of are excessive cracking (both in quantity and size of crack) or buckling in walls or floor slabs, windows or doors that stick, uneven floors.  

The clay soils of Denver and the Front Range love water and will absorb incredible amounts of water which causes the clay soil to expand.  Similarly, when allowed to dry out, the clay soil will contract.  Cyclic wetting and drying of these clay soils are often the cause of excessive foundation movement, but not always.  There are other mechanisms that can cause excessive foundation movement. 

Regardless, ALL foundation movement is caused by water!  Ideally any surface water readily drains away from the structure as quickly as possible and does not have the opportunity to pond and seep into the subsurface. 

Any home or business owner that suspects foundation movement is an issue is advised to first and immediately take the following corrective measures to eliminate, if possible, or minimize the opportunities and pathways for water to seep into the soils near the foundation:

  • Establish positive drainage slope of at least 2%-5% away from the structure.
  • Install rain gutters and downspouts with drainage extensions. The longer the extension the better.
  • If downspouts empty into buried extension, make sure the extensions daylight and actually drain (buried extensions pipes may be broken and caved in or may not daylight). Asinine as it seems, the most practical way to do this is to stuff a garden hose in the downspout, turn it on, and locate if and where the water daylights.  If you can’t locate
  • Observe that gutters and downspouts adequately drain and don’t overflow during rain or snow melt event – if they do not they may be clogged, have them cleaned.
  • If you have an irrigation system:
    • Turn it off, leave it off. If this is not an acceptable option,
    • Reduce watering duration and frequency to the bare minimum, i.e. don’t over water.
    • Check for any leaks in irrigation system and repair.
  • Monitor water bills and water meter for any signs of a broken water line.
  • If you have a sump pump in your basement, make sure it is working and if you can locate the drain pipe make sure it daylights.

If one or more of these corrective measures are taken It will take time for soil moisture to reach a new equilibrium (months to a year or more).  Installing crack monitoring gauges across visible cracks in the structure is always a good idea, even if you do nothing else – record the crack monitoring gauge readings at regular intervals.  The quantitative data is a better indication than observing the size and length of cracks. 

Taking the necessary corrective drainage measures will reduce foundation movement.  If the movement has been reduced to the point that it is not noticeable or to an acceptable point-congratulations, you likely saved yourself at least $20,000, likely more had you called a foundation repair service.

For more information we highly recommend these online resources:

Guide to Swelling Soil for Colorado Homebuyers & Homeowners ($7), older resources available for free

https://store.coloradogeologicalsurvey.org/product/swelling-soils-guide-colorado-homebuyers-homeowners/

Abandoned coal mine maps

http://coloradogeologicalsurvey.org/geologic-hazards/subsidence-mine/

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