Willenhall & Darlaston

March 18, 2026 - Adele Smith

Darlaston Station

Project Background and Objectives.

The Darlaston Station scheme forms part of the West Midlands Combined Authority HS2 Connectivity Programme, designed to enhance regional rail infrastructure and support economic regeneration. The new station is located on the Walsall–Wolverhampton line at approximately ELR PBJ 10m 198yds.

The objective of the project was to deliver a new, fully accessible railway station comprising:

Two single-face platforms.
A footbridge with lifts.
A 300-space car park.
Associated drainage and flood mitigation measures.
Given the site’s industrial legacy, proximity to the River Tame, historic mining activity, and variable ground conditions, robust geotechnical solutions were required to enable safe construction and long-term performance.
SPI Piling Ltd, were engaged to deliver the sheet piling elements forming part of the permanent retaining solutions.

Project Scope and SPI Piling Ltd Involvement

The retaining structures package comprised:

A sheet pile wall at the rear of Platform 2 to retain approximately 3.0m of fill.
Retaining walls associated with the raised car park area.
Integration with flood bund and attenuation measures.

The site ground model identified:

Made Ground (0.8–2.3m thick).
Alluvium (soft to firm).
Glacio-fluvial deposits (loose to medium dense sands and gravels).
Pennine Coal Measures with recorded historic shallow workings.

SPI Piling’s scope focused on the installation of permanent sheet pile retaining structures to:

Provide vertical retention at the back of the platform.
Facilitate excavation and platform construction.
Integrate with permanent works and fencing.
Preliminary design identified 9m long AZ26 sheet piles as suitable for retained heights up to 3.0m.

Methodology and Execution

Ground Preparation & Constraints

The site presented several technical challenges:

Made Ground requiring excavation and replacement with piling platform material.
High groundwater risk.
Historic coal workings at shallow depths.
High UXO risk classification.
Proximity to operational electrified railway.

SPI Piling worked collaboratively with the Principal Contractor and Designer to confirm:

Pile lengths adequate to achieve embedment within competent strata
Installation methodology compatible with overhead line equipment (OLE) constraints
Temporary works integration with permanent sheet pile design

Sheet Pile Installation

Given the sensitive ground conditions and proximity to operational railway infrastructure, a conventional driven-only solution was not appropriate for this site. The presence of Made Ground, soft alluvium, loose granular deposits and potential historic mining features required a controlled, low-vibration approach.

SPI Piling Ltd, adopted a two-stage installation methodology combining:

VDW cased auger pre-drilling.
Leader rig sheet pile installation.

Ground Loosening – VDW Cased Auger

A VDW rotary cased auger rig was used to pre-drill along the pile line to design depth.

The purpose of the VDW was to:

Loosen and remove soil within the pile alignment.
Provide temporary ground support in soft and granular strata.
Reduce resistance prior to pile driving.
Minimise vibration transfer to the live railway.

The casing prevented collapse in soft alluvium and controlled ground behaviour within loose sands and gravels. This approach also reduced the risk of disturbing any potential shallow mining influences.

Sheet Pile Installation – Leader Rig

Following pre-drilling, the AZ26 sheet piles (approximately 9m length) were installed using a leader-mounted vibratory hammer rig.

The leader rig provided:

Controlled vertical alignment.
Accurate positioning along the wall line.
Reduced deviation risk.
Consistent embedment to design depth.

Because the ground had been pre-loosened by the VDW system, the leader rig was able to install the sheet piles with significantly reduced driving resistance and lower vibration levels than traditional driven methods.

Completion Works

Once installation was complete:

Line and level checks were carried out.
A reinforced concrete capping beam was constructed to tie the wall together and support the rear platform interface works.
Backfilling was undertaken in controlled layers to manage lateral loading.

Results

This combined methodology allowed SPI Piling Ltd to:

Maintain tight tolerances.
Minimise vibration adjacent to live rail infrastructure.
Safely manage variable ground conditions.

Deliver the permanent retaining wall efficiently and in programme.

Safety, Quality & Risk Management

This was a technically constrained brownfield rail site. Key risks included:

Historic mining activity: Documented shallow workings in the Bottom and New Mine seams.
Contamination: Made Ground containing hydrocarbons, PAHs, VOCs and hazardous materials in places.
Ground gas potential: Moderate/low risk identified.
UXO risk: Identified as very high during desk study.

SPI Piling’s approach included:

Full review of the Ground Investigation Report and Geotechnical Parameters.
Controlled piling platform construction over Made Ground.
Method statements aligned with Network Rail standards.

All works were delivered in compliance with the GRIP 4 design intent documentation for retaining structures.

Quality assurance included:

Monitoring installation tolerances.
Verification of pile depth.

Challenges & Adaptive Collaboration.

Variable Ground Conditions.

Soft alluvium and loose glacio-fluvial deposits required careful embedment design to control deflection. SPI Piling Ltd, ensured pile toe embedment extended into suitable bearing strata.

Design Evolution.

Earlier consideration of alternative retaining systems (e.g., king post wall) was superseded by sheet piling due to groundwater control and long-term movement concerns. SPI supported this transition through constructability input.

Working Adjacent to Live Railway.

Installation required coordination with rail possession planning, OLE constraints, and restricted access.

SPI Piling’s collaborative engagement ensured early resolution of these constraints before mobilisation.

PILING CONTRACTOR OF CHOICE

Outcomes & Value Delivered

SPI Piling Ltd, successfully delivered:

Permanent sheet pile retaining solution.
Controlled installation within a high-risk brownfield rail environment.
Safe integration with platform and car park works.

The retaining system:

Provided structural stability for 3.0m retained heights.
Supported raised car park and flood mitigation measures.
Addressed challenging ground conditions identified in the GIR.

The works were delivered:

Safely.
In accordance with Network Rail approval in principle documentation.
To the required quality and tolerances.
In programme alignment with overall station delivery.

Lessons Learned & Strategic Strengths.

Early Geotechnical Engagement is Critical.
Historic mining, contamination and soft ground conditions required early review of the GIR. SPI Piling’s proactive engagement reduced design risk.

Permanent/Temporary Works Integration Adds Value.
Utilising sheet piles as both temporary excavation support and permanent structure reduced programme interfaces and duplication.

Constructability Input at GRIP 4 Improves Outcomes.
Collaboration during the design stage ensured practical installation methods were embedded within the F001/F002 retaining structure submissions.

Brownfield Rail Sites Demand Controlled Execution.
The combination of UXO risk, contamination, groundwater and mining history required disciplined methodology and communication.

Summary

Summary

The Darlaston Station project demonstrates SPI Piling’s, capability to deliver technically complex sheet piling works within a live rail, high-risk brownfield environment.

Through:

Thorough geotechnical understanding.
Collaborative engagement with the design team.
Safe and controlled installation practices.
Commitment to programme and quality.

SPI Piling Ltd, successfully delivered the permanent retaining structures required to support the new station infrastructure.

The scheme provides a strong reference for future rail infrastructure and urban regeneration projects requiring specialist sheet piling solutions under challenging ground and operational constraints.

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