232 Street Underpass
By John Meissner | August 28, 2025
Excavation Shoring
While D.H. Charles Engineering, Inc. is based in the United States, we also provide engineering services in many Canadian provinces. We recently had the opportunity to help a customer in British Columbia value-engineer a slide rail excavation shoring system on a large bridge construction project. The shoring was originally slated as internally braced sheet pile, so being able to offer a slide rail solution came at a substantial cost and time savings to the Contractor.
Our specific scope of work on the project entailed shoring design for the center bridge pier. The pier was sandwiched between existing eastbound and westbound freeway lanes and was approximately 95’-long x 28’-wide. To provide adequate working room to construct the pier, the inside dimensions of the shoring were ~104’-long x 37’-wide x 16’-deep. The pier was also founded on (30) 3’-diameter steel pipe piles, installed prior to the shoring.
The size of the shoring presented numerous challenges for a slide rail solution. Most slide rail panels cap out at a length of 24’. With the required shoring width of 37’, slide rail panels could not be used to close the ends of the excavation. Instead, custom beam struts were engineered to not only support the axial load from the sides of the shoring, but also support the lateral load from sheet piling bearing against them for their full length. The other challenge specifically related to the crossing struts was the potential conflict with the existing 3’-diameter pipe piles. The location of each strut had to be carefully positioned to pass between the pipe piles.
A phased approach to the shoring installation was used due to the 9’-2” thickness of the pier cap. The shoring was initially installed in a standard braced configuration to the final 16’ depth. Then I-beam sacrificial struts were installed at the base of excavation between each interior slide rail middle post to provide a point of support at the bottom of the post. The sacrificial struts were also snaked between the pipe piles and allowed the crossing struts to be raised up and out of the way of the new pier cap.
While the sheer size of the pit added complexity to the design, the most substantial hurdle was the engineering approach to the soil conditions. The geotechnical information initially provided for the project indicated extremely soft silt and clay for the lower half of the excavation depth. Soft silt and clay are among the worst soil conditions we often run into in temporary shoring design. They can produce very high earth pressures against shoring, while also heaving into the bottom of the excavation, increasing the risk of settlement of the ground surface around the shoring and potential for damage to surrounding utilities and structures. The closest boring provided to the shoring location was taken about 300’ away. With the potential savings of slide rail over sheeting and bracing, we proposed reengaging with the geotechnical engineer to have a soil boring taken at the pit location, in addition to having them provide geotechnical parameters for shoring design. The project team agreed with this approach and in the end, the additional investigation paid off. The accurate design parameters specific to the pit location were the saving grace to engineering approval of the slide rail solution on this project.
This project was a testament to collaboration between all parties involved, and leaving no stone unturned in pursuit of an innovative solution. It is always rewarding to be a part of projects like this, and through our extensive experience with slide rail shoring, be able to safely push the limits of its capabilities.