We were asked to perform a geotechnical investigation at a property in Temecula, CA, to assess damage and prepare repair recommendations for a pool, retaining wall and patio system. Damage was caused by settlement of improperly compacted fill dirt and the movement of slope soils. Cracks and separations in the retaining walls up to about 1.5-inches wide were visible.
Based on our observations and testing of the soils, we concluded that the pool, retaining walls and pool patios were constructed on inadequately compacted fill soils, which had compressed and moved laterally and downslope. The cause of the movement was a combination of: (1) improper preparation of the building pad and (2) improper design and construction of the pool and retaining walls. Investigation of the subsurface conditions was not performed before the design and construction of the pool.
The Bad News
We concluded that the original geotechnical company did not adequately research the grading history of the site. The geotechnical company did not inform the owner or the pool company of the likelihood of slope and fill movement that could affect the future performance of the pool.
The pool contractor also should have informed the owner of the risks associated with pools that are supported on inadequately fill soils next to a descending slope, and that movement of the pool should be expected if the pool is not properly supported. It is so important that hired contractors meet the due diligence standard of care on each project. This situation has created an additional expense for the homeowner.
Difficult, Expensive Choices
Based on the results of our study to date, we developed the following three options for the homeowner to repair the pool and associated improvements:
Remove and replace the pool, the walls, patios, and the improperly compacted fill. This option would involve significant grading to remove and replace the approximately 16-feet-thick fill. The new pool will need to be supported on a deepened footing below the top of the slope to provide required slope setback distances.
Remove the pool shell and all backyard improvements, and build a helical anchor and pier-supported, concrete grade beam system to support the pool. Build the new pool shell and improvements on the new grade beams.
Build a helical pier and anchor-supported grade beam through the pool to withstand future lateral and vertical fill movement. Support the retaining walls on helical anchors and tiebacks. Support the new patios on helical anchors that support concrete grade beams. Inject lightweight grout below the pool, patios, and appurtenant structures to densify and strengthen the fill soils.
The owner selected Option 3 as the most appropriate way of repairing conditions. There are two expensive lessons to learn here:
(1) Homeowners living in hill-side or canyon areas with sloping properties should always strongly consider contracting with an independent professional engineering firm before accepting bids from pool and patio contractors to ensure their construction plans will not compromise the stability of their lot.
(2) Pool and patio contractors should always strongly recommend to their clients with hill-side or canyon homes that they enlist the services of a professional engineering firm to analyze the stability of their lot before construction.
In Southern California, the earth beneath us moves frequently. Over time, there is always the possibility that hill-side, canyon or cliff homes could experience movement.
Asking a professional engineering firm to evaluate the stability of your property before making home additions or improvements is always money well spent. It provides peace-of-mind when you consider the high cost of construction and the potential high cost of dealing with slippery slopes later on.