Geotechnical Engineering at Longleat Safari Park

Contaminated Land



Contract Overview

Delta-Simons, part of the wider Lucion Group, is a multi-disciplinary environmental and health and safety consultancy providing trusted advice and solutions to ‘Protect People and Planet’ through facilitating sustainable development.

As one of the UK’s leading teams of geoenvironmental consultants, we work with clients and their project teams to provide advice that is practical, commercially aware and technically robust with an outcome-focused approach. 

Our Client proposed to upgrade the western retaining wall of the Half Mile Pond reservoir at Longleat Safari Park by raising the crest level to account for overtopping in a 1:10,000 year event and to address some deterioration in the existing masonry and sheet pile walls.  The proposed new sheet piled wall would be constructed over a length of approximately 600m to depths of between 3m and 7 m depending on ground conditions.  The Half Mile Pond is home to a population of sealions and hippos.  Our team was appointed to provide ground investigation services within the reservoir and to undertake the design of the sheet-piled wall to ensure its stability.

Contract Challenges

The reservoir is believed to have been created in 1857 by Capability Brown, when an earthfill embankment was constructed approximately at 5m above natural ground. Our team was initially appointed to assess and investigate a small area of subsidence which had formed behind the existing retaining wall in the embankment supporting the reservoir.  The investigation indicated the embankment had locally softened due to water ingress from the reservoir, which increased the need for the new retaining wall to be constructed.  Our team then undertook a larger ground investigation along the full length of the western boundary of the Half Mile Pond to inform design parameters for the construction of the new sheet pile wall.  The overwater investigation was undertaken using a drilling rig mounted on a platform supported by an excavator located on the crest of the embankment, with minimal disruption to the wildlife in the pond.

Following the completion of the ground investigation works, our geoenvironmental team, in conjunction with the structural engineer for the scheme, undertook a series of geotechnical designs for the proposed sheet pile wall to determine its stability and deflections post-construction accounting for the operation of the miniature railway along the crest of the embankment.  Where necessary, the sheet pile wall was supported by ground anchors to minimise post-construction deflections.

Our Solution

Due to our swift response to undertaking the ground investigation, interpretation of the ground investigation and geotechnical design support:

  • Areas of soft ground within the embankment were identified for further stabilisation measures,
  • The construction of the new sheet pile wall was able to be commenced expediently,
  • A reduction in the overall number of ground anchors was possible with associated cost and programme savings


Get In Touch

Delta-Simons has extensive experience in undertaking site and ground investigations for a wide range of projects across multiple sectors, including residential, commercial, education, industrial and highways-related developments. 

Engaging with a nationally (and internationally) trusted provider of Geoenvironmental and Geotechnical services will help you reduce planning risks, identify challenges relating to noise and vibration impacts associated with your development and overall, reduce delays when submitting applications through the local planning process.

If you are looking to partner with an environmentally conscious, specialist services supplier, get in touch with our team by emailing