Commercial Foundation Stabilization & Push Pier Underpinning in Aliso Viejo, CA

Friday, October 21st, 2022 by Keith Davis

Challenge

A commercial property in Aliso Viejo began experiencing severe foundation settlement that affected the structural performance of an approximately 38,000-square-foot, two-story office building originally constructed in 1991. By 2016, significant wall and floor slab movement had developed throughout the south and southeast portions of the structure.

A detailed manometer survey revealed approximately 4.5 inches of differential settlement, along with wall and ceiling cracks measuring up to 1.25 inches wide. The structure consisted of exterior concrete tilt-up wall panels and interior steel columns supported on shallow foundations. As settlement progressed, exterior glass wall panels became damaged due to structural movement, with several panels requiring replacement.

Geotechnical investigations performed around the building perimeter determined that nearly 30 feet of deep fill soil had been placed beneath portions of the site prior to construction. Additional monitoring conducted in 2018 confirmed that settlement was ongoing, with another 0.5 inches of differential movement occurring over a two-year period.

The combination of deep uncontrolled fill, ongoing settlement, and structural misalignment created a complex commercial foundation repair challenge. Additionally, difficult site access conditions along the south and southeast building perimeter limited the use of large construction equipment. The repair plan required a solution capable of stabilizing the structure, recovering lost elevation, providing lateral support during lifting operations, and filling resulting void spaces beneath the slab and footings.

Solution

To permanently stabilize the structure, the commercial foundation repair specialists at Saber Foundation & Concrete Repair designed a large-scale underpinning system utilizing a combination of Foundation Supportworks® push piers, helical anchors, and PolyLevel® polyurethane void filling technology.

The repair plan involved underpinning approximately 350 linear feet along the south and southeast exterior walls as well as a center patio area. Due to limited site access and challenging soil conditions, the team selected the Foundation Supportworks® Model 350 push pier system with side-load retrofit brackets to stabilize and lift the settling tilt-up panel foundations.

A total of 58 push piers were installed at approximately 6-foot intervals beneath the affected foundation areas. The steel push piers were hydraulically driven through the deep fill soils until stable load-bearing strata were reached. Final pier depths ranged from 34 to 73 feet to achieve the required structural capacities and specified safety factors.

To provide additional lateral support during the lifting process, 29 Foundation Supportworks® Model HA150 helical anchors were integrated into alternating push pier locations. These helical anchors were installed at approximately 20-degree angles and advanced to depths ranging from 10 to 38 feet until the required torque-correlated capacities were achieved.

Once the underpinning system was fully installed, controlled lift operations were performed to help recover lost elevation throughout the structure. The team successfully recovered approximately 1.75 inches of the original settlement, improving alignment of the building’s structural components and reducing stress on the tilt-up wall panels.

Following the lift procedures, approximately 2,900 pounds of PolyLevel® PL400 polyurethane foam were injected beneath the footings and interior floor slab to fill newly created void spaces. The high-density expanding foam was injected through small drilled access points where it expanded into a lightweight yet high-strength structural foam designed to stabilize the underlying support conditions.

Despite difficult access conditions and the complexity of the project, the entire commercial foundation stabilization system was completed within approximately 40 working days.