Temporary Propping in Deep Excavations: Strut Systems, Sequencing, and Safe Basement Construction

 

Deep excavations in tight urban environments are some of the most complex temporary works challenges in civil engineering. Excavating a multi-level basement isn’t simply a matter of removing soil — it’s a controlled operation where ground movement, structural stability, and construction sequencing must be managed simultaneously.

On constrained sites, where adjacent buildings, roads, utilities, and infrastructure sit just metres away, temporary propping systems are often the critical element that allows excavation to proceed safely and efficiently.

This article explains how temporary propping works in deep excavations, why high-capacity modular strut systems are widely used, and what makes them especially effective when integrated early with the permanent structure programme.

What Is Temporary Propping in Deep Excavations?

Temporary propping refers to the use of structural support systems installed during excavation to restrain retaining walls and control lateral ground movement.

In deep basements, retaining walls such as:

• diaphragm walls

• secant pile walls

• sheet piles

• contiguous bored piles

…can experience significant lateral deflection as excavation progresses. Without temporary restraint, these deflections can lead to:

• excessive ground settlement

• damage to adjacent structures

• cracking or overstressing of retaining walls

• instability or collapse risk

• programme delays due to redesign or remediation

Temporary propping systems prevent this by introducing horizontal bracing, typically using steel struts spanning between opposite retaining walls.

Why Strut-Based Propping Is So Effective on Urban Basement Projects

On projects where excavation is deep and the footprint is constrained, strut systems provide a powerful balance between:

• strength

• speed of installation

• modularity

• adaptability to sequencing

• high load capacity

In the project referenced, the temporary propping solution was based on high-capacity modular struts, combined with:

• waling beams

• jacks (hydraulic or mechanical)

• bespoke steel connections

This type of system is particularly valuable in urban sites where excavation cannot rely on wide open slopes or large working areas.

Key Advantages of Modular Temporary Propping Systems

1. Simple, Modular Support from Shallow Trenches to Deep Basements

Modern propping systems are designed to be modular, meaning the same core components can be adapted for:

• shallow temporary trenches

• multi-stage deep excavations

• partial basements and complex footprints

• projects with irregular wall geometry

This modularity reduces fabrication time and allows rapid adjustment when site constraints evolve.

2. Adjustable Strut Systems for Long Spans and High Loads

High-capacity strut systems can be engineered for very large spans (up to ~41 m) and significant axial loads.

This unlocks major benefits:

• fewer struts required (more working space)

• staged excavation can continue without over-propping

• compatibility with basement slab pours and permanent frame works

• reduced obstruction for cranes, plant, and logistics

This becomes critical on deep basement builds where construction is happening in parallel — excavation, slab casting, steel erection, and fit-out preparation may overlap.

3. Engineered Design + On-Site Coordination with Civil & Structural Teams

Temporary propping is not a “supplier-only” activity. It requires strong integration between:

• temporary works engineers

• permanent works designers

• the contractor’s construction management team

• site supervisors and lifting teams

A successful propping system is one that is:

• structurally correct in design

• practical to install

• safe to load and pre-load

• compatible with excavation sequencing

• coordinated with permanent structure elements (columns, slabs, cores)

4. Collaboration Between Temporary Works Supplier and Contractor

One of the most overlooked success factors in deep excavation temporary works is sequencing collaboration.

Even the best propping design can fail in practice if:

• installation sequencing is unclear

• excavation proceeds too fast before props are loaded

• temporary connections are not installed correctly

• pre-load requirements are missed

• access constraints prevent correct lifting operations

In this project example, the temporary works supplier and contractor worked closely to tailor the propping sequence to site constraints — which is exactly how deep excavations should be managed.

Typical Components of a Temporary Propping System

A high-performance strut propping package usually includes:

Steel Struts

Primary compression members spanning between walls. Often modular for fast assembly.

Waling Beams

Steel beams fixed to the retaining wall to distribute strut loads across the wall section.

Jacks

Used for pre-loading and adjustment. Pre-load reduces wall movement and improves stiffness.

Bespoke Connections

Custom brackets, stiffeners, gussets, and wall fixings designed around wall type, load path, and site geometry.

The Real Purpose of Temporary Propping: Sequencing Without Compromise

Temporary propping is not just steel and hydraulics.

Its real purpose is to enable a controlled sequence where excavation and permanent works can progress without compromising:

• stability

• safety

• programme

• adjacent structures

• structural integrity of the retaining wall

In deep basements, the excavation is rarely “complete first, structure later.”

Instead, the reality is phased:

1. Excavate to first stage

2. Install props

3. Excavate deeper

4. Install next stage props

5. Begin permanent works (slabs, cores, columns)

6. Remove props progressively as slabs take load

This interaction between temporary and permanent works is why early temporary works planning is essential.

Best Practice: Temporary Propping Should Be Engineered Early

Deep excavation temporary works should be treated as a design discipline — not an afterthought.

When engineered early, propping can:

• reduce wall thickness requirements

• improve programme predictability

• minimise movement and settlement risk

• reduce redesign cycles

• simplify permanent works integration

• improve safety and lifting planning

This is especially true on tight urban projects where any delay creates knock-on impacts across logistics, traffic management, and stakeholder approvals.

Final Thoughts: Temporary Propping Keeps Deep Excavations Safe and Buildable

Temporary propping systems — especially modular, high-capacity strut solutions — remain one of the most reliable methods for supporting deep excavations in urban environments.

When the system is:

• designed by engineers

• coordinated with civil and structural teams

• sequenced with the contractor

• installed safely and correctly

…it becomes more than a temporary measure. It becomes the backbone of a safe excavation strategy and a predictable basement construction programme.