Soldier piles and lagging

This is the most common type of temporary earth retention solution for urban construction, especially when space is an issue. It is comprised of wide-flange steel beams, and thick timber lagging. The wide flange beams, known as soldier piles, are placed vertically in the perimeter of the excavation. These piles can be driven with a vibratory pile driver or drop a hammer and sometimes need to be drilled and concreted below the base of excavation. Thick timbers are then placed between the soldier piles to retain the soil. Depending on the soil condition, different angles may be needed for the piles. The lagging is most commonly installed in 4’ lifts.

The depths of excavation, soil type and loading forces from proximity buildings may determine the need for additional shoring components, including tiebacks, rakers, walers, and struts.

Secant Wall

When excavating in close proximity to an existing structure, or when excavation is close to the water table, a secant wall is usually required. Secant walls may be preferable to soldier piles and lagging when minor losses of soil, during lagging operations, might be detrimental to adjacent footings.

These walls can be used to restrict water from entering the excavation. Secant walls are more common in urban areas than sheet piling as the piles are drilled and not vibrated into place, allowing them to be more readily installed close to adjacent buildings.

Sheet Piling

Sheet piles are interlocking steel sheets typically driven into the ground with a vibratory pile driver. They are designed for work close to or within the water table. The interlocking sheets form a continuous barrier that permits excavation below the water table. The vibratory installation of sheet piles can significantly effect nearby structures and therefore is not commonly used in urban areas. Stable Ground has the expertise and equipment for more limited sheet piling projects in Toronto.

Caissons/drilled shafts

A drilled shaft filled with concrete is known as a caisson. The diameter of these shafts range in size from 16”- 48’’. The hole is drilled to a suitable bearing stratum or is drilled to a depth where there is sufficient friction to the sides of the hole. The bottom of the shaft must be pristine, prior to concrete pouring to avoid future settlement concerns. Caissons may be reinforced or unreinforced, depending on load conditions.

Stable Ground has the equipment, tooling and experience to install straight shaft caissons in both cohesive and noncohesive soils, and angled/belled caissons in cohesive soils.


Underpinning is a viable option when an excavation will undermine the adjacent footings of an existing building. It can be a cost effective solution when there is not sufficient clearance to install a caisson wall, or your excavation depth is not significantly lower than the neighbouring footings.

Underpinning is carried out by excavating the soil beneath the structure to a new depth, and replacing it with concrete. The process is repeated in sections to ensure there is adequate soil bearing during the underpinning. This results in the structure’s footings to be extended to a depth where they will not be affected by the excavation.

Other reasons to underpin include:

- To achieve additional headroom below grade, creating more useable space
- Increase a structures footing width to increase allowable loading of the structure
- Support a building that is experiencing differential settlement
- Provide frost protection to a buildings foundation, if not already protected
- Provide stability to a structure that is resting on fill and unstable ground by extending the footings down to virgin soil