The owners of a beautiful contemporary 7,000-square foot dream home with a forever view in Murrieta near the Temecula wine country of Southern California awoke to a disturbing pool disaster a few years ago. Shortly after construction, their new pool, surrounded by a resort-like patio deck suddenly started to slip tragically down the slope below.
The movement of the patio/pool structure with large, visible cracks left no doubt about the unstable nature of the lot and hillside below. With the region’s often weak, compressible soils, and a proclivity for earthquakes, hillside homes in Southern California are often unstable and subject to more than a little shaking.
Analyzing the Causes
These tragic situations can generally be avoided by doing the proper geologic/geotechnical studies and structural engineering before the pool design is complete, costs are set and contracts are signed by homeowners. Those gorgeous blue infinity pool computer designed images showing an azure sky paradise make it all too easy to take the plunge prematurely.
In this case, the homeowners called Helfrich Associates to save their property from further damage before it was too late. As professional geotechnical and structural engineers licensed in multiple states, our first step was to conduct an engineering forensic review of the site. We then presented a full report to the homeowner about the causes and offered two repair options.
Our forensic review found the lot grading and soil compaction were both improper. The home’s lot had up to 20-feet of un-compacted fill soils under the house and pool. The slope below the building pad was also unstable, causing lateral and vertical movement of the site improvements. In addition, the retaining walls were not built properly, and they had settled and rotated.
Difficult Choices To Make
We gave the homeowner two options to resolve the many issues that were discovered in this situation. The labor and materials costs were going to be significant in either case, but the cost of the first option was significantly higher. Option 1 required full demolition of the improvements, excavation and re-compaction of the soil and then reconstruction of the patio/pool area. Option 2 required installing extensive structural supports for lot stabilization and then cosmetic and structural repairs to the patio/pool.
With the cost of Option 1 significantly higher (and taking much longer to complete) than Option 2, the homeowner decided the second option was the only viable, affordable solution to the problems. Helfrich-Associates then designed a system of reinforced concrete grade beams, helical anchors and helical tie-backs that anchored all the site improvements prior to making cosmetic repairs to the pool area.
Fixing The Problems
The swimming pool itself was underpinned by installing new helical piers. We also cut the pool bottom and installed a grade beam lengthwise and supported by the grade beam on helical piers. Lateral movement of the grade beam was restrained with tieback anchors. The perimeter pool walls were supported with helical piers. The spa area and pool equipment area were also supported on helical piers.
To address the pool’s cosmetic issues, the large cracks in the pool walls were repaired with epoxy injection and cutout repairs. The pool coping had to be replaced and leveled for safety and aesthetics. The pool equipment was installed in a new pool equipment vault. Nearby retaining walls were stabilized with helical piers and tiebacks. Other adjacent slopes were held in place by a new five-foot high below-grade wall supported on piers and restrained by tiebacks.
The differential settlement of the pool deck was corrected by replacing the affected areas with six-inch structural concrete slabs supported on grade beams and helical piers. Tiebacks were added as a lateral restraint on the fill slopes. To prevent erosion and deck damage, additional area drains were installed in the deck and planters to prevent standing water.
The decking slabs were also sloped to the new drains for further reduction of potential water penetration. With all that done, the water slide was secured with footings supported by helical piers. In addition, several modifications to the repair plan were made during construction that resulted in the installation of additional support beams and retaining wall construction.
Ready To Celebrate
The repair project took several months, and the owners were happy with the results that saved this home and outdoor entertaining paradise. Their advice to other homeowners in hillside areas is to start with a geologic survey of your property completed first by a licensed engineering firm before engaging the services of a pool design and construction contractor.
You’ll then be able to rely on your engineering firm to guide the construction company in designing a patio/pool that’s built to last. At Helfrich-Associates, we’re ready to help make your patio/pool dreams come true. With over 30-years geotechnical and structural engineering experience in Southern California hillside communities, you can count on us to help get it done right the first time.