Answer: The Denver area and surrounding counties in Colorado have expansive soil problems. We have found that when a structure is built on this type of soil a drilled concrete pier properly designed by an engineer with the proper steel installed, locked deep into bedrock will resist the skin friction uplift of expansive soil. However, the void area in between the piers under the foundation wall must be sufficient and stay in tact.
When we repair or install new piers on existing structures we believe in the helical piers for the following reasons: (1) The helical pier has a 1 ½ inch square galvanized shaft; (2) There are single, double, and triple helical piers used – they are installed into and lock into bedrock holding the structure up as well as down. Any type of pier that is pushed in soil to refusal can be lifted by expansive soil if present as it is not locked into bedrock. As a result your structure will lift.

Question:   What causes soil to swell?

Answer:

(Figure #2)

The change in rock or soil volume is caused by the chemical and physical attraction of water molecules to the tiny clay plates that make up the expandable, montmorillonite clay material often called "bentonite." As moisture or water comes in contact with the clay, the flat plates are pushed farther apart.

In a sample of pure montmorillonite the plates may expand so much that the sample increases up to 15 times its original volume. While most montmorillonite soils will not expand over 35-50 percent, the pressure and movements created on a building foundation or floor by this tremendous volume increase are responsible for most swelling soil damage.

Answer: Do not use plastic under the landscape because it traps moisture. Use a landscape fabric that allows the soil to dry. It is also important the soil slopes away from the foundation wall at least a minimum of 1 inch per foot, or more if possible. Most engineers prefer 10 inch drop in 10 feet sloping away from the foundation.

Question: Does it hurt if water stands behind my landscape border edging around my house?

(Figure #3)

Allowing water to stand behind your landscape border edging could cause problems as pictured in figure #3. When the hole in your lot was excavated for your foundation to be installed, it was made larger by 2-5 feet around all sides. This additional area allows room for the workers to place and remove the foundation forms as needed. After the foundation was constructed and water proofed this 2-5 feet area was then backfilled. Over time this area has a tendency to settle and compact. This backfilled area is porous allowing water to seep to the bottom of the foundation.

Question: What kind of landscape border edging should be used?

Answer: Any edging may be used if drilled or modified with 3/8 inch or larger drain holes every 1-2 feet, in the center width of the edging. This will allow the water to bleed through the edging. Normal edging is usually 3-4 inches in width.

Question: If I get water in my basement why can’t I just install a sump pump only?

Answer: If your house is on caissons and the void under the foundation wall is still somewhat in tack it may work for a while. If this void closes up it will only pick up water immediately around the sump pit and pump area only. A sump pump and pit is only to collect water and pump it out of your basement. With out an interior drain system there is no way for the water to get from the opposite side of the basement to where the sump pit and pump are. A proper drain system design is very important. Please see information listed under Water Problems Page (Figure 3)

Question: Should I be concerned if I start to see cracks in my foundation wall or retaining wall?

Answer:

(Figure #4)

(Figure #4) There is a reason why cracks appear in concrete foundation walls or retaining walls. You may have a problem developing. Sometimes these cracks don’t worsen and sometimes they happen so slowly you don’t notice the subtle progressive change. It is best to have this problem looked at and monitored by an experienced structural contractor and a professional structural engineer.

(Figure #5)