Design Responsibility for Support of Excavation

What is SOE?

Support of Excavation (SOE) is a system of earth retention used to protect streets, buildings, and other structures near the excavation of a project. As a property owner, your goal is to install the below grade structure safely, and in a manner that limits soil displacements which could cause damage to the surrounding properties.

For the owner or developer of a project, the decision to perform the design of SOE or to delegate the design to the contractor’s engineer, depends on the nature of the structures around the site. The more sensitive the structures around the site are, the more the owner should consider performing the design.

Designing an SOE System

When delegating design work, the owner must confirm that the contractor’s objectives are the safety of individuals and surrounding structures as well as minimizing soil displacements. The contractor has the added pressure of trying to provide a system economical enough to win the bid. Generally, the more economical the system, the more likely it is to displace and provide risk to the surrounding property. To address this, owners can require that the SOE system be designed to produce a displacement that won’t cause damage to the surrounding property.

On lower risk projects the owner often leaves the decision of the actual displacement limit value to the contractor’s engineer. This limits the owner’s options if the submitted design shows a questionable displacement limit. Some specifications will prescribe a maximum displacement; by doing so the owner takes on the responsibility of determining what that displacement becomes and should consult with the geotechnical engineer of record for this additional work.

Regardless, the specification should include a quality control requirement for monitoring the displacements in the field to verify compliance. Some specifications will note the frequency of measurements and the instrumentation required to perform them, such as inclinometers, settlement plates, vibration monitors or survey measurements.

Consulting an SOE Engineer

Since the below grade structure is installed first, the contractor’s engineer may feel pressured to produce a design quickly. As a result, the contractor’s engineer will often adapt the geotechnical information obtained for the design of the building to use in the design of the SOE without performing any other geotechnical exploration and make assumptions about the soils where information may be lacking.

To avoid this, it’s best to consult with an SOE engineer during geotechnical exploration. SOE Engineers can help prescribe the required testing specific to these systems. The American Institute of Architects recently published AIA document C202 – 2015, a standard form of consultant’s services. This form helps owners incorporate geotechnical services into their projects, including SOE and other services.

For more information about our SOE capabilities or our other geostructural services, contact Jeff Segar.

Jeff Segar Senior Engineer

P: 952.995.2340