Throughout the years, we at FSGC have been faced with numerous situations where we’ve been called in to advise our clients and trade partners in instances for Support of Excavation (SOE) or also known as earth shoring. We’ve found several instances where SOEs have been excluded from the design and quoting phase of a new structure, leading to potentially detrimental problems down the road. This may be from a lack of understanding of this complex solution, but this is where we come in and add value as Subject Matter Experts!
Our team has found that unless the structural or geotechnical engineer calls out the unique need for an SOE on a project, the general contractor quoting the project can easily miss this very important (and costly) portion of the project. In addition to potentially adding significant cost to the project, it will impact the build schedule as well. Many times, the support of the excavation system is paired with an underpinning solution when excavation occurs adjacent to structural foundations.
Below are some factors to consider in determining if support of excavation and/or underpinning may be needed during the design or bid phase – Ideally, identifying the need for an SOE and underpinning system is optimal during the design phase.
- What areas of excavation will be deeper than 5 feet? In those areas, is there room to bench or lay-back the soil on a 1:1 slope? (If the geotechnical report allows, it could be a steeper slope)
- Are there adjacent underground utilities that cannot be moved along the excavation area?
- Are any adjacent structures with shallow foundations that may be undermined by the excavation? Excavations less than 5 feet can still be compromising to an adjacent structure’s foundation if the excavation is within 5 feet. (NOTE: The levels of footings of adjacent structures should be indicated on plans or, if the adjacent structures are pile supported, this should be noted)
- Is there heavy off-road traffic (surcharge loads) close to the excavation? (railroads, construction equipment, etc.) If so, what are the loads, and how often do they occur?
- Is there a high probability of groundwater when you excavate? Does the SOE need to cut-off the water flow?
- Would a permanent SOE wall provide cost savings in the design of new foundation walls? If an earth shoring system is needed, it may be beneficial to choose an SOE technique that can be permanent and handle the lateral loads, reducing the need for reinforcement, concrete and smaller footings for the walls. (This needs to be identified in the design phase).
- In reviewing the Geotechnical report, are the soils being excavated non-cohesive (or ‘free-running’ kind of soil)?
The primary purposes of Support of Excavation (SOE) systems are:
- Provide a safe working area for personnel working by keeping sides of deep excavation stable (“An unprotected trench is an early grave”)
- Minimize the excavation area for new construction. (i.e. Construction inside an existing structure or a constrained area)
- Ensure adjacent structures (buildings or utilities) will not move or settle
The performance of support of excavation system is a soil and structural interaction challenge. The SOE system needs to address many factors that are site and soil dependent. Due to the many and varying factors, there is no one-size-fits-all approach to SOE problems. Depending on the site and soil, some of the SOE techniques that may be utilized include the following:
– Soil Nails and Shotcrete Walls (Permanent and Temporary)
– Soldier Pile and Lag
– Soldier Pile and Shotcrete
– Soldier Pile and Sheeting
– Sheet Piling – Cantilever
– Sheet Piling with Tiebacks
– Rakers and Braces
– Tangent Walls
– Secant Walls
– Compressed Ring Wall
Our team at Foundations Specialties has the necessary experience designing many types of SOE walls, and we’re available to provide insight on the best approaches to utilize for your construction project.