Temporary Works Engineering
When the ground does not stay put on its own
Deep excavations are among the highest-risk activities on any construction site. The moment you dig below natural ground level, the surrounding soil wants to move. It wants to slide, slump, heave, or flow into the hole you have just created. Without properly engineered shoring, that movement can collapse the excavation, damage neighbouring buildings, rupture underground services, and put lives at serious risk.
That is why deep excavation support is classified as temporary works, and why it requires specific engineering design by a qualified structural or geotechnical engineer. In NSW, any excavation deeper than 1.5 metres that is not battered back to a safe angle requires an engineered shoring system. In practice, most basement and underground car park excavations in Sydney fall well beyond that threshold.
Our team designs shoring systems for excavations of all scales, from single-basement residential projects through to multi-level commercial basements in congested urban sites. Every design starts with the geotechnical report and a clear understanding of what sits next to the excavation, because protecting adjacent structures is just as important as holding the ground back.
A braced excavation with soldier pile shoring, steel walers, and internal propping supporting surrounding ground during basement construction.
Choosing the right shoring system
There is no universal shoring solution. The right system depends on excavation depth, soil type, groundwater conditions, proximity to adjacent structures, and the construction programme. Here are the systems we design most frequently:
Sheet Piling
Interlocking steel sheets driven or vibrated into the ground to form a continuous retaining wall. Sheet piles are effective in soft to medium soils and provide good groundwater control because the interlocks create a near-watertight barrier. They are commonly used for excavations near water tables, along waterfront sites, and where the soil is too weak for cantilever-type solutions.
Soldier Piles & Lagging
Steel H-piles installed at regular centres (typically 1.5 to 3 metres apart) with timber or concrete lagging spanning between them. This is one of the most versatile and economical shoring systems available. It works well in stiff clays and sands where the ground can stand unsupported for short periods while the lagging is installed. We design soldier pile systems for depths up to around 12 metres, with tie-back anchors or internal bracing where needed.
Contiguous & Secant Piles
Bored concrete piles installed in a continuous line to form a retaining wall. Contiguous piles have small gaps between them and suit sites with low groundwater. Secant piles overlap, creating a watertight wall for high water table conditions. Both systems can be designed as cantilever walls for shallow excavations or propped and anchored for deeper digs. They are the preferred choice for urban sites where vibration from driven piles is not acceptable.
Diaphragm Walls
Reinforced concrete walls constructed in slurry-filled trenches before the main excavation begins. Diaphragm walls serve a dual purpose: they provide temporary shoring during excavation and become the permanent basement wall in the finished structure. This makes them cost-effective on large commercial projects where the basement perimeter wall would need to be built anyway.
Bracing & Propping
Internal steel struts, walers, and raking props that provide lateral support to the shoring wall. Bracing is used where ground anchors are not feasible, either because the neighbour will not grant permission to drill under their property or because underground services or rock prevent anchor installation. The bracing layout needs to be coordinated with the construction sequence so that basement slabs and walls can be built around the props.
"Every deep excavation is a race against the ground. The shoring design needs to stay ahead at every stage."
IA Engineering Design Team
What makes deep excavation engineering complex
Shoring design is not just about holding the ground back. It is about controlling ground movement within acceptable limits, managing groundwater, protecting adjacent structures, and providing a safe working environment for the trades who need to work inside the excavation.
Ground movement and displacement
Every shoring system deflects under load. The question is how much, and whether the neighbouring structures can tolerate that movement. We calculate wall deflections at every stage of the excavation and compare them to allowable limits, which are typically set by the sensitivity of adjacent buildings, underground services, and road pavements. On tight urban sites, the displacement limits can be as low as 15 to 25 millimetres.
Groundwater management
Water is the single biggest complication in deep excavations. If the excavation extends below the water table, the shoring system needs to either cut off the water (using secant piles, sheet piles, or grout curtains) or the excavation needs a dewatering system. Dewatering can cause ground settlement outside the excavation if not carefully managed, so we assess the drawdown effects on neighbouring properties and services before specifying the approach.
Staged construction sequences
Deep excavations are not dug in one go. They are excavated in stages, with each stage requiring the shoring to be propped or anchored before the next stage begins. The design must account for every intermediate stage, not just the final depth. In some cases, the most critical load condition occurs during an intermediate stage rather than at the bottom of the dig.
Protecting what is next door
On most urban sites in Sydney, the excavation boundary sits right on or very close to the property line. That means the shoring system is the only thing standing between your excavation and your neighbour's building, their footings, their underground services, and their peace of mind.
Dilapidation surveys are carried out before excavation begins to document the existing condition of adjacent properties. We use this baseline to assess whether any movement caused by the excavation has resulted in damage, and to defend against unrelated claims.
Monitoring programmes track wall deflection, ground settlement, and building movement throughout the excavation. We specify monitoring points, trigger levels, and response actions so that any unexpected movement is detected early and addressed before it becomes a problem.
Underpinning assessments determine whether adjacent footings need to be deepened or strengthened before excavation proceeds. If the new excavation will expose the base of a neighbouring footing, underpinning is required to maintain the footing's bearing capacity and prevent settlement.
Standards & Compliance
Every shoring design is certified to Australian Standards
All temporary works designs are prepared in accordance with the relevant Australian Standards, WorkSafe requirements, and state regulations. Documentation includes design certificates, construction drawings, monitoring specifications, and staged excavation sequences.
How we work with you
We start with the geotechnical report and the architectural basement drawings. The soil profile, groundwater level, and proximity to adjacent structures drive the shoring system selection. We work closely with your builder and geotechnical engineer to develop a solution that is buildable, cost-effective, and safe.
The design output includes full structural drawings of the shoring system, a staged excavation sequence, monitoring specifications with trigger levels, and a structural design certificate. For anchored systems, we provide anchor load schedules and testing requirements. For propped systems, we detail the prop sizes, connections, and removal sequence.
We remain involved through construction, reviewing monitoring data, responding to site queries, and carrying out inspections at critical stages. Deep excavation is not the kind of work where you hand over drawings and walk away. We stay engaged until the basement structure is complete and the temporary works are removed.