Retaining Wall ($100 Thousand Dollar Project) – Slope Remediation at Similk Bay, Anacortes

anacortes-wall-2Merit Engineering has strong expertise in retaining wall design. The walls we designed include both walls under the jurisdiction of WSDOT and walls for private sectors. The highest geogrid reinforced retaining wall we have designed and being built was the wall in Similk Bay, Anacortes, Washington. The total height of the two step wall was 50′ with 25′ each. The following two projects demonstrate the experience of Merit Engineering possesses in retaining wall design.

As prime consultant, Merit Engineering provided full-scale geotechnical engineering services for this project. A landslide almost hit the residence on a bluff of 50 feet high overlooking Similk Bay. Merit Engineering conducted dynamic cone penetration test to investigate soil conditions, evaluated slope stability conditions, and designed a retaining wall – a two steps 25′ high anacortes-walleach. The wall was geo-grid reinforced with UltraBlock face.

We also managed the construction of the project including obtaining all the permits needed: shoreline, hydraulic, SEPA checklist, critical area checklist, Army Corps of Engineers checklist, building and grading permits and septic system permit.

The significant achievement in this project is the successful design of the two step with limited horizontal spaces. The site is very limited in available space. Using currently popular computer programs which are widely distributed within geotechnical engineers such as that by Tensar for geogrid reinforced retaining wall design, the available space in the property is far too short for reinforcement for the height of the wall. This is because most computer programs were written with the most simplified assumptions anacortes-wall-3that the sols in the reinforced zone and the soils retained by the wall are all cohesionless granular soils. Therefore, the calculation is greatly simplified, and the result is obtaining a much more conservative wall in most situations. However, in the case that the retained soil is cohesive with a high cohesion value (as in this case), the reinforcement depth obtained from the computer program is way too high than necessary because the computer program totally ignored the cohesion of the soil. We have conducted a traditional analysis by hand calculations to design the wall in the limited space with successful results.