Foundation Issues Related to Foundation Lateral Movement
When most folks think of Colorado’s expansive soil, they think of heaving and settling structures, like we described in the “Vertical Movement” pages. It is important to remember that when soil expands, it expands in all directions. When soil is confined by more soil next to it, the only way it can expand is vertically. If this expansive force is too great for your foundation, it can push your foundation walls sideways, causing them to lean out of plumb, bow in the middle, crack, and, if left uncorrected, eventually fail. A few telltale signs of this type of failure are cracking in the wall itself, a long horizontal crack about halfway up the wall is typical. Often the horizontal crack will turn down at the foundation corners. Leaning of the foundation inwards, as frequently with older homes the connection between the foundation wall and the floor diaphragm is poor. This allows the wall to tilt inwards, rather than crack in the middle. If the basement is finished, you may see drywall cracking where the wall meets the ceiling or in the middle of the walls. Often you will see the interior walls that are perpendicular to the foundation walls pushed sideways. If you have brick veneer on your house, you may see the brick overhanging the foundation wall in the middle of a long wall and sitting flush with the edge of the foundation at the corners.
If the house is sided, you will still be able to observe this overhang, and it is just not as easy to spot as it is with brick houses.
Another common symptom of a bowing or leaning foundation wall is the center floor support beam ‘punching-out’ the side of the foundation wall. The beam, of course, didn’t move, the wall leaned in against the end of the beam and the foundation failed at the beam.
Arvada Foundation Lateral Movement Video #1
How we fix these issues
Catching a leaning or bowing wall when it first starts to move will save you money! If the wall has moved less than two inches, or if the bow has resulted in a horizontal, mid-wall crack less than two inches, the wall can likely be braced with steel or carbon-fiber.
Carbon fiber bracing applied to a leaning foundation wall.
Two examples of steel bracing applied to leaning foundation walls.
While steel or carbon-fiber bracing may seem expensive, it is many times less expensive than repairing a wall that has moved more than 2”!
If the wall has moved more than about 2”, it is typically necessary to return the wall to vertical and provide permanent exterior anchors to prevent the wall from moving again. Van Matre Construction has successfully re-plumbed dozens of walls leaning more than 9”. We typically install helical piers running sideways, angled about twenty degrees downward from horizontal, with the aim of placing the bearing plate of the pier at least 20’ away from the house and with a pull-out strength of about 25,000 per pier (about 5000 foot-pounds of torque applied to the pier to anchor it into stable, dense soil).
Piers are typically placed about every six feet along the wall. After the piers are placed, the stems of the piers are placed through the walls, passing through large steel ‘washers’.
The wall is plumbed, the bolts tightened, and the wall is secure, guaranteed not to move. The foundation wall pictured below had broken free of the attachment to the floor diaphragm and leaned in a little more than 8” (remember, most foundation walls are only 8” thick). With very little rebar in the wall, there was not much keeping the wall from falling over. After temporarily bracing the wall so that we could work safely without the wall collapsing in on us, we went to work.
First, the wall is excavated, relieving the soil pressure so that we can straighten the wall. After that, we cored holes in the walls at 6’ intervals and installed the helical piers until our designed capacity was reached.
Temporary support is placed under the floor of the house and the house’s weight taken off the foundation. With the helicals installed and the house on temporary supports, it is time to start moving the wall back to vertical! Once we returned the walls to plumb, we put the house’s weight back on the foundation, re-attach the framing to the foundation, patch the cored holes in the foundation and any other cracks, waterproof the foundation wall and backfill. After backfill, the lot is graded to allow any surface water to drain away from the home.
Here are a couple more videos showing progress and final completion of the foundation lateral movement repair on this Arvada home.
The problem with buried deadman anchors: Another common method of stabilizing a leaning foundation wall is with buried deadmen anchors placed in the yard. Placing deadmen is by far less labor intensive and invasive than placing helical piers. Deadmen are typically installed by auguring a 3 or 4 foot deep hole in the yard outside of a leaning wall, a steel plate is placed in the hole and a threaded rod is driven through the foundation wall to the buried plate, a washer placed over the rod on the inside of the foundation and a nut tightened. Conceptually, the deadman is not unlike the helix of a helical pier: it is a plate placed in the soil to resist any leaning of the foundation wall. The problem with them is the limitation of the depth which they can be placed. Because we screw a helical pier in at a downward angle, the bearing plate ends up deeper than the basement floor: typically about 15’ below ground surface and 20’ away from the house. The soil at this depth tends to be of a more constant moisture content, it tends to be dense, and it has the pressure of 15’ of overburden keeping it in place. A deadman seldom is placed deeper than 4’ below the surface and typically about 12’ away from the house. Soil this shallow has typically been disturbed or is fill, so it is not very dense. At this shallow depth, the moisture content is constantly fluctuating and there is not adequate overburden to resist lateral load. Furthermore, if placed close to the foundation wall, the deadman is in the unit of soil that moves when the foundation wall leans.
Though deadmen anchors are more economical, Van Matre Construction feels they are too risky and will not install them.
Pictures of a Failed Attempt to Repair a Leaning Wall with deadman anchors