Bypass shotcrete is an excavation support system unique to the HCM group and consists of piles installed in vertically drilled holes with shotcrete lagging. Steel piles are installed at regular intervals and shotcrete is installed in lifts between piles to retain the soils behind the excavation and transfer the loads to the piles. The piles are embedded below the depth of excavation to provide the necessary passive resistance. Similar to traditional shoring systems, piles can be cantilevered or braced with walers, rakers, struts and/or tiebacks.
RWH Engineering Inc. was able to work together with HCM to develop the by-pass shotcrete shoring system through the Scientific Research and Experimental Development (SR&ED) program. In addition to finite element modelling, an empirical design approach was taken and extensive field testing was completed to prove the structural adequacy of the connection. The result was a mesh and clip connection exclusively implemented by HCM.
Advantages of bypass shotcrete systems:
- Cost effective shoring solution with less labour and material requirements
- Eliminates voiding behind the shoring as shotcrete is shot directly onto the soil face
- Can be used next to existing structures replacing traditional caisson wall systems and eliminating the wood rot issue associated with lagging
- Excavation activities can be expedited as vertical drilling requirements are significantly reduced in comparison to a caisson wall
Challenges associated with bypass shotcrete systems:
- Installation in poorer soils can be challenging due to the time required for the soil to stand open to place reinforcing steel and mesh
- May require additional face-saving measures between the piles for the soil to stand vertically