Project Background and Objectives
High Speed Two (HS2) Ltd is delivering a new high-speed railway linking London and the West Midlands. As part of Phase One enabling works, an attenuation tank was required at Grove Farm, Wendover, to manage surface water and provide controlled drainage within the main works civils package delivered by Eiffage Kier Ferrovial BAM (EKFB).
The objective was to construct a 96.6m long L-shaped temporary sheet piled retaining wall to facilitate excavation for the permanent attenuation tank, ensuring safe excavation support, protection of adjacent infrastructure, and compliance with HS2’s stringent safety and environmental standards.
Project Scope and SPI Involvement
SPI Piling Ltd was appointed to supply, install and subsequently extract AZ36-700 temporary sheet piles to form the excavation support system.
The scope comprised:
- 69nr AZ36-700 sheet pile pairs (10.0m average length) and one Omega 18 corner section
- Pre-augering along the 96.6m piling line
- Installation using an ABI TM17 leader rig with MRZV 30VV vibratory hammer
- Impact backdriving where required
- Future extraction using a 100t crawler crane and vibro hammer
The works formed part of EKFB’s Stage Two Main Works Civils package.
Methodology and Execution
A sequenced methodology was developed under a fully approved Work Package Plan.
Key stages included:
- Site mobilisation and working platform verification
- Pre-augering using VDW/MDBA auger systems to loosen structured chalk strata
- Installation of sheet piles via leader rig vibratory hammer
- Controlled impact driving to refusal criteria where required
- Daily monitoring, pile records and quality verification
The programme duration for installation was 18 days, with clear hold points, lift plans and permit controls embedded throughout.
Safety, Quality & Risk Management
The works were classified as high risk due to lifting operations, overhead power lines and vibratory plant. Controls included:
- Approved lifting plans and CPCS-qualified operators
- Exclusion zones and platform load certification
- Vibration assessment demonstrating <3mm/s PPV at 30m
- Section 61 consent and environmental controls
- ISO 9001 certified quality management procedures
Daily briefings, task-specific risk assessments and inspection records ensured compliance and traceability.
Challenges & Adaptive Collaboration
The site presented several constraints:
- Structured chalk ground conditions
- Proximity to overhead electrical lines
- Interface with live HS2 site logistics
SPI worked collaboratively with EKFB’s Temporary Works Coordinator, Engineering Manager and Appointed Person to sequence pre-augering, adjust vibration controls and maintain programme certainty. This proactive coordination prevented delays and eliminated rework.
Outcomes & Value Delivered
- 96.6m temporary retaining wall installed safely and to specification
- Delivered within the planned 18-day installation window
- Zero lost-time incidents
- Optimised sheet pile recovery strategy providing significant material credit value
SPI provided a complete temporary works solution that protected EKFB’s excavation programme and maintained HS2 compliance standards.
Lessons Learned & Strategic Strengths
- Early platform verification prevents downtime
- Integrated vibration assessment de-risks works near utilities
- Pre-augering significantly improves installation efficiency in chalk
- Strong coordination with principal contractor reduces interface risk
SPI’s strengths demonstrated: specialist plant capability, controlled methodologies, safety-led culture, and collaborative delivery within complex infrastructure environments.
Summary
The Grove Farm Attenuation Tank sheet piling works formed a critical enabling element of HS2 Phase One. SPI Piling delivered a fully compliant temporary works package—designed, installed and managed safely, on programme, and to required quality standards.
This project highlights SPI’s capability to deliver complex sheet piling solutions within major infrastructure environments, providing clients with certainty, control and measurable value.
