M11 Slip Road, Northbound between J5 & J6
Project Background and Objectives
M11 motorway northbound between Junctions 5 and 6 experienced progressive embankment instability at Earthwork ID EW2319, near Marker Post 21/4A. Historic defects included tension cracking at the crest, subsidence behind the vehicle restraint system (VRS), and undermining of gantry and communications assets .
Connect Plus Services commissioned a permanent remediation scheme to stabilise approximately 150m of embankment, protect critical highway infrastructure, and restore long-term safety and serviceability. The objective was clear: deliver a durable solution with minimal disruption to live motorway operations.
Project Scope and SPI Piling Ltd’s Involvement
SPI Piling Ltd were appointed under NEC3 Subcontract SH1040/003 with a subcontract value of £296,908.50.
SPI’s scope included:
- Offloading and storage of GU27N sheet piles within the Jackson compound
- Installation of approximately 151m of permanent sheet pile wall (average 11.7m length)
- Working within full night-time motorway closures
- Use of silent piling techniques to protect adjacent infrastructure
SPI had no design responsibility but delivered strictly in accordance with the Geotechnical Design Report and Works Information.
Methodology and Execution
Installation was undertaken using a Kowan WP150 silent and vibrationless press to mitigate risk to unstable ground and sensitive assets. Starter piles were installed using a 35t excavator with Movax attachment before pressing commenced.
Where difficult ground conditions were encountered, controlled water jetting and pre-auguring were introduced via approved method statement addenda to maintain programme while protecting the embankment.
Works were completed during night possessions with minimum five-hour working windows, requiring precise logistics, daily mobilisation from compound, and disciplined execution.
Safety, Quality & Risk Management
The design risk assessment identified hazards including live carriageway working, buried services, steep gradients and adjacent assets.
SPI operated under detailed RAMS, lift plans, plant inspection regimes and workforce briefings.
Working platforms were specified to accommodate crane and rig ground bearing pressures, ensuring stability throughout installation.
The use of silent piling significantly reduced vibration risk to the gantry and surrounding infrastructure.
Challenges & Adaptive Collaboration
Key challenges included:
- Restricted 5-hour night shifts
- Unstable ground conditions
- Working adjacent to live motorway infrastructure
- Protection of existing gantry and drainage assets
SPI responded with proactive collaboration, introducing controlled jetting and auguring only when required and agreed, maintaining compliance while protecting programme.
Outcomes & Value Delivered
SPI successfully installed the permanent sheet pile retaining wall, stabilising the embankment and protecting motorway infrastructure.
The works were delivered safely, within the constrained possession windows, and in accordance with the design intent.
The solution provides long-term structural stability and resilience to the M11 corridor.
Lessons Learned & Strategic Strengths
- Early planning of compound logistics is critical for motorway night works.
- Silent piling offers measurable risk reduction on sensitive infrastructure.
- Adaptive methodology (jetting/auguring) preserves programme certainty.
- Strong coordination under NEC frameworks ensures clarity of responsibility and efficient decision-making.
SPI demonstrated technical capability, disciplined safety management, and flexibility under pressure.
Summary
The M11 EW2319 embankment remediation demonstrates SPI Piling Ltd’s ability to deliver complex motorway sheet piling works safely, efficiently and to specification.
Through controlled methodology, rigorous safety standards and collaborative delivery, SPI provided a permanent stabilisation solution that protects critical national infrastructure and maintains operational resilience for future users of the M11.
