NASCLA Accredited Commercial General ContractorSite WorkHard
A construction site requires the installation of a new 36-inch diameter storm drain pipe at a depth of 15 feet in unstable, granular soil. Due to adjacent structures and limited access, open-cut excavation with sloping is not feasible. Which shoring system would be most appropriate for this scenario?
- ATrench shields (boxes)
- BSoldier pile and lagging
- CAluminum hydraulic shoring
- DSlurry wall
Show answer & explanationAnswer & explanation
Correct answer: B. Soldier pile and lagging
Soldier pile and lagging is a robust shoring system suitable for deep excavations in unstable granular soils where space is limited and adjacent structures require protection. It provides continuous earth retention and can be designed for significant depths and loads.
Why the other options are wrong
- A. Trench shields are primarily for worker protection in trenches, not for providing structural support to prevent face collapse in deep, wide excavations near structures.
- C. Aluminum hydraulic shoring is typically used for shallower excavations (up to 20 feet) and may not be robust enough for 15-foot deep unstable granular soils with adjacent structures.
- D. A slurry wall is a permanent cutoff wall, typically used for groundwater control or deep foundations, not primarily as temporary shoring for a pipe installation.
Soldier Pile and Lagging
A shoring system consisting of vertical steel H-piles (soldier piles) driven or drilled into the ground, with horizontal timber or precast concrete lagging placed between the piles as excavation proceeds.
- Suitable for deep excavations and unstable soils.
- Provides earth retention and can be tied back.
- Commonly used when adjacent structures are present.
Memory trick: Soldiers Lagging in Trenches, Shields for Safety, Hydraulics for Shallow.