A Texas (and maybe elsewhere) Problem With Foundations
 

Here in Tejas, you will be hardpressed to find a house built with a basement - the soil expands and contracts too much or so I have been told. I had a conversation over the phony with a civel eng and he told me the following - interesting stuff:

Foundation movement may result from a wide range of factors, which can include: • Shrinking or swelling of clays caused by changes in moisture content
• Compression of a soft layer in the ground as a result of the applied foundation loads
• Soil softening
• Frost heave
• Improper back filling
• Variation in groundwater levels
• Erosion
• Vibration from nearby construction
• Hydrostatic Pressure

Inadequate design of basement walls and footings, before construction, traditionally account for 75 to 85 percent of all problems in residential structures built upon expansive clay soils. These failures are generally divided between two broad classes - lateral pressure and differential settlement. Both classes of failure generally have few primary causative factors.

Lateral pressures on basement walls have four likely sources:
• Pressure from soil weight
• Pressure from soil swell
• Hydrostatic pressure
• Pressure from frost

Identifying lateral pressure damage is not difficult, but accurately quantifying the contributing sources is very difficult and should only be handled by a qualified engineer. The inward bowing of a basement wall is the simplest indication of lateral pressure. The bowing generally occurs when the external forces exceed the wall strength. The maximum bowing will often occur near the center of the wall because the adjoining perpendicular walls provide support in the corners. If bowing becomes severe, these walls can collapse inward.

Cracking can also occur when lateral pressure exceeds the strength of the concrete or block wall. The most common crack pattern begins in the corners and move up or down at 45 degree angles in concrete walls. For block walls, the cracks move along the mortar joints in a stair step pattern. Often these cracks end at a long horizontal fracture that parallels the basement floor.

Lateral pressure can affect the overall integrity of a house. Severe damage results in a visible opening between the top of the basement wall and the structure. Since water is one of the main causes of these cracks, water infiltration becomes significant in the largest of the cracks. Filling these cracks with epoxy, without solving the water problem, only moves the lateral pressure to another section of the wall.

The difference of the outside ground level and the basement floor creates a mass of soil that must be retained thus causing a lateral pressure. The pressure of soil weight is typically considered during the design of an engineered wall using theoretical earth pressures.

Clay soils undergo a change in volume when the moisture content of the soil changes. When expansive clays are placed against basement walls, the swelling of these soils can induce lateral pressures not accounted for in the original design. Cyclic shrink/swell can also reduce the shear strength of the backfill and thus increase the lateral pressures . The solution to this problem can be as easy as replacing clay backfill with gravel or other non-swelling material. When used in conjunction with a footing drain, gravel will prevent increased lateral pressure.

Hydrostatic pressure is pressure exerted by a fluid due to its weight. Hydrostatic pressure against a basement wall develops when water fills voids or "ponds" within backfill immediately adjacent to the wall. This water buildup can cause dripping, seepage, dampness or efflorescence (salt residual). Leakage during heavy rains or poorly designed/maintained drainage increase hydrostatic pressure. Like soil swell, hydrostatic pressure is not typically considered during design and construction of basement walls.

Water that accumulates in backfill and then freezes may cause large lateral pressures on basement walls. Severe damage can result from frost causing lateral pressures much greater than even hydrostatic pressure. The expansive natures of water crystals have been know to create catastrophic structural damage.

Backfill, that is heavily clay laden, present long term lateral soil pressure problems. Their cohesive nature makes it practically impossible to re-compact them to a uniform moisture content and density. Clay backfills require significantly stronger basement walls to withstand the larger horizontal pressures. The obvious solution is to backfill with non-cohesive aggregate with proper drainage.

Structural settlement is characterized as either total and /or differential settlement. Total settlement is a complete structure downward movement. Differential settlement is the difference in vertical movement between various locations causing structure distortion. Generally, total settlement is not a critical factor as long as it is uniform. Utility connections are affected to the greatest degree by total settlement. Even relatively small differential settlements can cause cracks in floor slabs, brick walls and drywall.

Settlement can be tolerated in most homes provided it is within specified limits. Small amounts of settlements are anticipated in most design work. When homes experience excessive settlement special procedures must be employed to stop or limit the amount of settlement. These special procedures usually employ the use of resistance piers or helical anchors. To determine the best course of action for your home the hiring of a foundation engineer is recommended. Do you have a potential foundation failure?

Let us try ALL of North and NW Las Vegas as one big expansive soil area. The Prez of KB Homes was interviewed by CNBC a few years back, where he stated that "That in some of our developments the soil of every home is tested (for expansive soil issues)." Yep tey are such good citizens, it just so happens the City of N LV REQUIRES that every lots has its soil tested and appropriate measures taken are taken to obviate expansive soil issiues.

Let us come to my own little development of homes...172 of them....Beofre i ever bought this home...13 homes filed Class Action suit against Rhodes Homes for Construction defect mostly concerning expansive soil issues. Ten of those homes were in buy back mode when I moved in in 2003. People do not believe what I tell them about the look of a home that has suffered expansive soil issues, it looks as if a bomb went off in a home. Drywall that is tearing multiple cracks that one could follow through out the house. Wall seperating from Base Boards and Ceilings. If one owned such a house there is NO WAY ONE COULD SELL IT...They look like wrecks....

Anyway faced with that prospect and upon hearing the 2 year history of my neighbors case across the street I filed suit within a month of purchase along with those neighbors against Rhodes HOmes and 1 1/2 years later I settled with them and proceeded to make substantial repairs around the foundation of my home. My neighbors settlement was for over $1M USD...after atorneys fees were paid. their hosue included a buy back, and said house is still empty after 3 years. Several other homeowners also filed suit in this time period as well, one case settled out for $290K with an estimated repair of $235K. These people had been reluctant to sue, Rhodes even moved them out of their home during their effort to make repairs. Two weeks after returning to a repaired home the situation was worse then before said repairs were made.

After my neighbors and I settled at least 50 other home owners have belatedly filed Class Action Suit against Rhodes Homes. They have reached a settlement of $2,000,000.00, but Rhodes Homes has filed BK so only the Rhodes Insurance Company is on the hook for its portion of the settlement...I estimate about 3/4 of it. That leaves in limbo another purported Class Action of some 20 odd homes whose disposition I don't know anything about as I have stopped following the cases very closely.

So the moral of this tale of woe is to be aware of an soil issues pertaining to a home purchase..better to be knowledgable then to be sorry.

So if I build an inground pool in my backyard, I gotta figuer it will actually look to help stabilize any shifting no?

i thought the tornado belt in texas all had basements? i think most foundations get beat up by the ground heaving. differential swelling from the water mixing with the clay in the soil.

basement or not, even slab foundations get lifted by swelling soil. the key is to keep the water draining away.

this is a great topic.

No. A lot of older houses had "Storm Cellars" which are not part of the house.

I wish.

In NY all we ever got was , "err, err, err, the following is a test of the emergency broadcast system, this is only a test."

Moved to TX, 3x's in the first month driving home, "err, err, err, tornados have been spotted near xxx, seek immediate shelter, YOUR GONNNA DIE"

We get that fairly regularly. Freaks me out.