Vintage at SLO is a luxury apartment complex located just two miles southeast of downtown San Luis Obispo, CA; offering its residents luxury living without sacrificing convenience. When the developer was designing this community, they realized they needed a solution to create the required parking spaces. Creating this parking area would prove to be quite the challenge though; an adjacent road 15 ft (4.5 m) above the proposed parking lot elevation was being widened to accommodate increased traffic loads. The developers originally looked at a cast-in-place retaining wall to create usable land but when faced with exorbitant costs, they turned to Allan Block for a better solution.

This area is geologically difficult to build on due to the poor clay soils, high seismic risk, tight space limitations and utility lines. The developers did not think a segmental retaining wall would even be an option on this project because the geogrid reinforcement would encroach the property lines and the excavation would have disturbed the roadway. The Allan Block Engineering team proposed a design using No-Fines Concrete (NFC) to reduce the overall structure depth. The estimated cost of the completed Allan Block retaining wall using NFC came out to be much less than the cast-in-place wall. The cast-in-place wall footing alone was about the same price as the whole Allan Block wall. Without the use of NFC and the support from Allan Block’s engineering team, the developers would have been limited to a cast-in-place wall, essentially doubling their expenses.

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Though Allan Block strongly recommends designing AB segmental retaining walls (SRW’s) using curves in lieu of corners, there are indeed options for incorporating corners into projects. Certain application steps, aspects, and regulations should be implemented for successful execution.

Corner design type – Is it an inside or outside variation? Inside corners require removing part of the section of the top lip from the first black making the lip line up with the adjoining block. This will allow the opposite wall to adjoin and subsequent courses to lay flush. Outside corners incorporate the AB Corner, with no need to cut blocks as the wall progresses.

Geogrid considerations – Placement and usage of geogrid is important with SRW corner design. Inside corners require alternating courses that extend the grid past 25% of completed height of the wall. Simply divide by four, use the result for the additional grid, and account for it in your planning. Outside corner grid applications require that each side is reinforced independently from each other. Also consider that geogrid should never be placed directly on top of each other when laying each segment.

Capping – With either option, cutting AB Capstones at a 45° angle will finish corners seamlessly.

Keep these considerations in mind when planning and designing walls with corners. Contact us at engineering@allanblock.com if you need preliminary assistance with corners, or give us a call at 800-899-5309 at ex. 3.

For decades, commercial site developments have commonly constructed cast-in-place reinforced concrete walls to retain soil. However, since the mid 1980’s, segmental retaining walls (SRW’s) like Allan Block have provided a better solution to these rigid walls. Some of the advantages SRW’s have compared to cast-in-place walls include the following:

• Lower installation cost (30-70%)
• Limited excavation for footing preparation since frost depth is not a factor
• Faster installation
• Easier to design elements to fit site conditions
• Better aesthetics options
• More reinforcement options (e.g. geogrid, no-fines concrete, wall anchors, etc.)
• Flexible vs. rigid system

SRW

Cast-in-Place

Aside from all the advantages listed above, what is often missed is the fact that SRW’s can also out-perform rigid walls, particularly in the most aggressive circumstances possible, such as during an earthquake. SRW’s ability to withstand seismic loading conditions has been proven in both the laboratory and the real world.

Allan Block’s full-scale seismic testing documented that SRW’s can withstand large seismic forces. The testing subjected the test walls to forces up to 0.8g and all experienced only minimal deflection and/or settlement. The tests showed the block facing, soil mass and geosynthetic reinforcement all moved together as a unit, in phase with the earthquake induced forces. It was suggested by Dr. Hoe Ling from the Columbia University that these structures, that are both flexible and coherent, are ideal for seismic conditions (AB Seismic Research Summary, Reference Document #R0505, August 2003).

In today's world, with Segmental Retaining Walls being tried and true for more than 30 years, there isn’t much of a market for traditional cast in place walls anymore. The next time you think you must use a cast in place wall on a project, just call Allan Block’s Engineering Department, 800-899-5309 x3, for a second set of eyes to see how we can find the most efficient design.

This time around for our engineer spotlight, we are highlighting Jeff Schwindt, a great wall engineer out of Portland, Oregon. Jeff started his engineering career at the University of Portland and graduated in 2004 with a degree in engineering. After college, Jeff worked for about a year for a Washington DOT structural and materials testing lab. Jeff was first introduced to segmental retaining wall design when he moved to a multidisciplinary firm doing structural design. After a few years, Jeff found himself at his current company, Harper Houf Peterson Righellis Inc., which specialized in civil design work. Jeff wanted to create his own firm after the 2008 market crash, but then decided to approach the company to create a partnership. Ever since then, Jeff has been a proud associate partner of Harper Houf Peterson Righellis Inc.

When asked, how has Allan Block contributed to his success, Jeff praises the support and literature supplied by Allan Block. Several of our older resources have been a great help year after year for him. For example, Jeff will consistently reference one of the technical newsletters on fences above retaining walls. For him, it has been an invaluable resource to help explain to DOT employees why we take a certain design approach or why extra reinforcement is needed. It is one thing when he tells the DOT employees, but it is another if he can provide a document from the block manufacturer that backs up his position. AB Walls has also been a great tool for him and his team. Jeff said that in comparison to other SRW design tools out there, AB walls is the easiest program to make quick adjustments as well as incredible flexibility. From geogrid reinforced walls to no fines concrete retaining walls, the availability of these options gives him the choice to choose which option he would like to design with.

Jeff had some advice to new engineers starting out in the retaining wall design industry: get your hands dirty. Jeff praises Allan Block’s Contractor Certification Class because it is one of the best opportunities to get a better understanding of the installation process, which helps speed up installation and reduce headaches when designed properly. It is one thing to understand the math behind the design equations, but it is another when you can see the principles in practice. Jeff has found that his hands on experience has provided him with the knowledge necessary to work as a team along with the contractors.