Martin R. Owen PE, GE

Geotechnical Engineer

 

San Diego County, California

Tel: (619) 813-8462, Fax: (858) 273-1652

Email: martinowen@geotechengineer.com

 

 

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DISTRESSED PROPERTY EVALUATIONS

Many older homes in San Diego County are founded on poorly compacted fill soils, constructed before modern grading standards and practices were implemented.  Graded lots in hillside areas may be underlain by 10 to 30 feet of fill, or more.

When loosely compacted fills become wet from infiltration of rainfall or landscape irrigation, they can settle excessively, as shown in the diagrams below, causing buildings to tilt, doors and windows to bind, and walls, ceilings, foundations and floor slabs to crack.

1.  WATER REDUCES THE STRENGTH BETWEEN THE SOIL PARTICLES AND ACTIVATES THE FILL   SETTLEMENT PROCESS

Pic1

2.  THE FILL SETTLES IN THE DIRECTION OF ITS GREATEST  WEIGHT OR THICKNESS

pic2

HOW MUCH SETTLEMENT IS NORMAL OR EXCESSIVE?

Residences are typically built with a floor elevation difference of up to about 1 inch, including normal settlement during construction.  A floor differential over 1 inch usually indicates excessive fill settlement or other ground movement. 

Some buildings may continue to perform reasonably well even with a floor differential of several inches.  However, excessive ground settlement can rupture water and sewer pipes, subjecting the subsurface soils to even more water infiltration and settlement. 

OTHER TYPES OF GROUND MOVEMENT

AND GEOTECHNICAL PROBLEMS

Homes may also incur distress from other types of ground movement, such as soil expansion.  Expansive soils are clay soils which absorb water and swell (like a sponge) when they get wet, and can be either fill or natural soils.  The swell pressure can cause uplift damage to foundations, floor slabs, driveways and patio slabs, and other exterior improvements.

Landslides and shallow slope failures are another, relatively common problem in San Diego, especially during periods of heavy rainfall.  Many homes are located in hillside areas comprised of slide-prone or erodible soils and bedrock.  Fortunately, San Diego's average rainfall is low (about 10 inches per year) otherwise the number of slope problems would be even higher.  Leaking water and sprinkler pipes can also result in slope failures.

Basement and foundation seepage problems (which can lead to mold and mildew issues) are also fairly frequent in San Diego County.  Over-irrigation of planter areas next to foundations and poor surface drainage are often the cause of these problems.   In addition, basement retaining walls may have been constructed with inadequate waterproofing or drainage. 

HOW ARE FILL SETTLEMENT AND

OTHER SOIL PROBLEMS RESOLVED?

If the fill is old, most of the potential settlement may already have occurred and relatively minor foundation or slab repairs may be all that are necessary.  Improving lot and roof drainage, so that water does not pond next to foundations and infiltrate into the subsurface soils is a good way to help reduce the potential for soil/foundation movement.

However, some additional settlement may still be possible, and the risk of more building damage may be considered unacceptable by homeowners. In this case, foundation underpinning or other, more extensive, foundation repairs may be necessary.

Foundation underpinning consists of supporting the building on concrete caissons, piers or pipe piles extending through the fill into dense, natural soil or bedrock.  Other foundation repairs include structural mats (thick slabs), compaction grouting, ground anchors etc.

Landslides and shallow slope failures may require regrading the hillside, or other structural forms of slope stabilization, such as concrete pile walls, pipe and board retaining systems, slope guniting etc.

EVALUATION OF PROBLEM

A distressed property evaluation typically starts with a physical site inspection and a review of topographic maps, geologic maps and other published and unpublished, soil and geologic information.  I may research original building construction documents, such as soil reports and grading plans, at the City or County Engineering Offices.  

From my many years of experience, I can usually tell what the cause of the problem is after my initial inspection and research, and advise you as to possible repair options.   This information can then be given to a foundation repair contractor or other specialist contractor, who can provide you with a cost estimate for repair.

It may also be necessary to undertake a subsurface soil investigation, requiring test borings or test pits, to more thoroughly evaluate the subsurface conditions.  A soil investigation is also usually required to obtain a building repair permit.  A structural engineer may also be needed to help design more complex foundation repairs.  This information is then used to refine the cost of the repairs, and is presented by the contractor to the City or County, along with a repair plan.