The Oaks at Portola Hills
Belgard® Wall Systems Crucial to Creating Nearly 100 Buildable Acres in Harsh Geological Conditions
Every Project Starts with a Purpose
In 2014, California-based developers Baldwin & Sons planned a housing complex on 99 acres of land in the city of Lake Forest, California, at the base of the Santa Ana Mountains. The Oaks at Portola Hills is comprised of seven neighborhoods of both single-family and multi-family residences with many amenities. Located in one of the fastest-growing yet safest cities in the state, it has easy access to restaurants, shops and interstates.
Developing the site required transforming steep hillsides and natural valleys into acres of buildable land. The project faced complex challenges, including seismic conditions, poor soil quality and multiple failure planes—weak clay layers that can cause landslides, particularly during periods of heavy rainfall. Additional requirements included the City of Lake Forest’s mandate that most retaining walls be plantable.
These thin layers are like grease which, once exposed, cause landslides as dirt and rock slip over them. This is especially the case when there is significant rainfall, as there was throughout the fall and winter of 2015/2016. There were also design requirements the team had to meet for the project, including the city’s demand that most of the walls be plantable.
The Solution
Solving for Style, Function, and Durability
To create buildable space, the team implemented an expansive segmental retaining wall system. Baldwin & Sons partnered with Geogrid Retaining Wall Systems, Inc., the largest segmental retaining wall installer in Southern California, to develop acres of flat “super pads” suitable for residential construction.
The project was completed in three phases—Portola Northwest, Portola Northeast and Portola South—using a combination of Belgard Diamond Pro blocks along with Vertica Virtual Joint and Plantable block systems to meet both structural and aesthetic requirements.
Geogrid’s in-house design engineer, Matthew Merritt, P.E., of Red One Engineering, designed walls comprising the entire perimeter of the project to develop “super pads,” acres of flat land for Baldwin to build on. Many of these walls reached up to 49 feet tall and 1,000 feet long.
“We worked with the geotechnical engineer on the global stability analysis and incorporating Mirafi global stability geogrids into the wall design. Portola South had a long (100’+) and very strong geogrid for global stability. Portola NE had two walls incorporated into a large landslide buttress,” said Merritt. “We also worked with a shoring contractor to incorporate the Diamond Pro block facing over the shoring elements.”
To address global stability in the seismic areas, the team designed a system of secondary geogrids, placed between the standard grid layers. A grid’s length is usually equal to 100 percent of wall height. At the Portola site, between every layer of standard-length grid and compacted fill was another, smaller grid of only four feet long. These strata provided the necessary additional stability in the seismic area.
Geogrid’s choice of Belgard plantable blocks gave Baldwin & Sons the maximum amount of space on which to build homes. This is because Belgard’s Plantable system has an 8:1 batter and the competitor’s block has a 4:1 batter.
“The wall batter is a ratio of vertical feet to horizontal feet, so 8:1 means for every eight feet vertical the wall slants backwards one foot so one foot of useable property is lost to the wall batter. The competition at 4:1 loses one foot every four feet of height, or two feet for every eight of height,” explained Merritt. “Using the various Belgard products provided the client with an additional 66,500 SF (1.5 acres) of usable land compared to using the competition at 4:1 batter.”
Featured Products
The Result
A Lasting Impression:
The Final Transformation
The final phase of the project, Portola Northeast, is scheduled for completion in December 2023. By using a full range of Belgard retaining wall products, the team delivered plantable and non-plantable walls that blend seamlessly into the surrounding landscape while meeting the City of Lake Forest’s requirements and providing long-term structural confidence.
“The result was great-looking walls that provide excellent aesthetics and, most importantly, lasting confidence in their structural capabilities,” said Matthew Merritt, P.E., of Red One Engineering.
“The fact that Belgard offers so many complementary products that we could use both as vertical and plantable walls was a huge asset. The manufacture of the product was also outstanding. We were installing more than 1,000 square feet of block a day, and delivery was always timely,” said Mike Stevenson, Owner of Geogrid Retaining Wall Systems, Inc.
PLAN + DESIGN
Smarter Planning. Better Design.
Belgard isn’t just here to provide the product—we’re your partner in planning and design. From first ideas to final layout, we make it easy to bring your outdoor vision to life.
Outdoor Living Awaits
Let’s build something beautiful together
Outdoor living solutions for homeowners, contractors, and designers.
We’ll listen to your needs, help identify the right products and design approach, and guide you toward a tailored solution that brings your outdoor vision to life.