Shoring Systems for Excavation: Types, Selection Factors and Safety Controls
Excavation shoring holds back the surrounding ground so work can happen safely below the natural surface level. A well-designed shoring system controls lateral earth pressure, limits ground movement that could affect nearby structures, keeps water out of the excavation, and gives the site team safe, predictable access. Get it wrong, and the consequences range from program delays to serious safety incidents, so shoring is rarely an area where projects should cut corners.
Every shoring system is a response to the same underlying question: how much ground needs to be held back, for how long, and with what margin for error. The answer shapes everything from the system selected to the monitoring regime used once excavation begins.
When Ground Support Is Needed
Ground support becomes necessary whenever an excavation exceeds the depth at which unsupported soil can safely stand, which varies with soil type, groundwater and site conditions. In practice, most excavations near boundaries, roads, existing buildings or underground services need some form of shoring well before reaching that theoretical limit, simply to protect people and assets nearby. Basement construction, road and rail cuttings, service trenches and staged bulk excavation all commonly require engineered ground support.
Common Shoring Systems
Soldier Piles and Lagging
Soldier piles are steel or concrete piles installed at regular centres, with timber or steel lagging boards placed between them as excavation proceeds. This system suits stiffer soils where some ground movement between piles is acceptable, and it is often chosen for its speed of installation and relatively low cost.
Sheet Piles
Sheet piles are interlocking steel sections driven or vibrated into the ground to form a continuous wall. They work well in soft to medium soils and where groundwater control matters, since the interlocking sections limit water ingress. Sheet piles can often be extracted and reused, which suits temporary works on tighter budgets.
Secant and Contiguous Pile Walls
Secant pile walls use overlapping bored piles to form a near watertight barrier, making them suitable for deep excavations with high groundwater. Contiguous pile walls use closely spaced but non overlapping piles, offering strong ground support without the added cost of secant construction, though they allow more water and fines through the gaps between piles.
Soil Nails, Anchors and Shotcrete Facing
Soil nailing and ground anchoring reinforce the ground in place rather than building a separate retaining structure. Nails or anchors are drilled and grouted into the slope or cut face, and a shotcrete facing is sprayed over the surface to tie the reinforcement together and protect against erosion. This approach suits steep cuts, rock faces and sites where a conventional piled wall is not practical.
Selection Factors
Choosing a shoring system means weighing up soil type and groundwater conditions, the depth and duration of the excavation, proximity to boundaries and existing structures, access for plant, and program and budget constraints. A system that performs well in stiff clay may be entirely unsuitable in loose, water bearing sand, so ground investigation data should always drive the decision rather than habit or convenience.
Cost is rarely the only factor. A cheaper system that requires more monitoring, slower staged excavation or additional dewatering can end up costing more overall than a system with a higher upfront price but faster, lower risk installation.
Monitoring and Hold Points
Once a shoring system is installed, monitoring confirms it is performing as designed. This typically includes survey monitoring of nearby structures, inclinometers or strain gauges on piles or anchors, and regular visual inspection for signs of movement, cracking or water ingress. Hold points are usually set before each excavation stage proceeds, so the design engineer can confirm ground behaviour matches expectations before the dig goes deeper.
Access, Plant and Sequencing
Shoring installation depends heavily on getting the right plant to the right place at the right time, whether that is a piling rig, a sheet pile driver or a drill rig for anchors and nails. On constrained urban sites, access sequencing often drives the entire program, since the plant may need to work from a single side of the excavation or in a specific order to avoid clashing with adjoining retaining works. Coordinating retaining and shoring wall installation with soil nailing and ground anchoring packages under one contractor reduces the number of handovers and access conflicts on site.
Safety Duties and Competent Person Input
Excavation work carries specific legal duties in every Australian state, and shoring design and installation should always involve a competent, suitably qualified person. Safe Work Australia’s excavation hazards guidance sets out the general risks associated with excavation work, including collapse, falling objects and service strikes, while state regulators publish more detailed codes of practice covering specific control measures. Reviewing this guidance early in design, rather than after an excavation has started, gives project teams time to plan realistic controls rather than reactive fixes.
Frequently Asked Questions
Soldier piles and lagging are often the lowest cost option in stiff, dry soils, but cost depends heavily on ground conditions, depth and program. A system chosen purely on price without checking suitability for the ground can end up costing more once delays or rework are factored in.
Yes. Many projects combine systems, for example, using secant piles along a boundary with high groundwater and soil nails with shotcrete facing on a lower-risk cut elsewhere on the same site.
Groundwater is controlled through a combination of shoring system selection, such as sheet piles or secant walls that reduce water ingress, along with dewatering measures like well points or sump pumping where needed.
The geotechnical and structural engineer typically specifies the system based on ground investigation data, while the civil contractor advises on constructability, program and cost during design development.
Planning a Shoring Package for Your Site?
Every excavation has its own mix of ground conditions, access constraints and program pressure. Contact Terracon Civil to request a constructability discussion for your retaining, anchoring and shotcrete facing works, and our team will help you match the shoring system to your site before design is locked in.
