Investigation, Remediation & Validation of a Residential Development in the Lake District

Project Overview

ERGO were commissioned to provide ongoing Consultancy from outline design through construction as part of the development of apartment blocks and residential bungalows on a predominantly greenfield site adjacent to the Lake District National Park.

Appointed by the developer as an independent Geoenvironmental Consultant, our remit was to undertake preliminary desk based geoenvironmental site assessment, with subsequent intrusive investigation to facilitate the development of a remediation and enabling works strategy to support the planning application.

During the design process additional support was required from ERGO to assess the geotechnical stability of a proposed crib wall structure within the vicinity of proposed properties and the site boundary which included a rock slope stability assessment.

While during construction, ERGO provided validation works and the production of a detailed report to ensure the satisfaction of the relevant planning conditions, Building Control/ warranty providers and the future adoption of infrastructure by the Highways Authority and statutory service providers.

Site Background

Prior to redevelopment, the site comprised a predominantly undeveloped parcel of agricultural land with a historic reservoir feature present within the northern area. The site had significant topographic variation requiring assessment at design stage for proposed levels. It was also underlain by Karstic limestone, with an assumed potential for subjacent voids and cave systems.

Client

Engie

Project type

Residential

Scope of works

Phase 1 Desk Study, Phase 2 Intrusive Investigation, Remediation & Enabling Works Strategy, Slope Stability Assessment & Verification/Validation

Site Works

ERGO provided a comprehensive assessment of both geoenvironmental and geotechnical aspects of the works, which included initial site assessment to inform the design of suitable ground investigation. An initial focus on the former reservoir feature was determined, although subsequent assessment determined geotechnical liabilities including karstic cave systems, foundation proposals, slope and retaining wall design to be of greater potential concern.

Following identification of a cave entrance within a cutting adjacent to the site, additional specialist information was obtained from the BGS and the British Caving Society to assess the potential for instability, 3D models of the feature were able to be obtained which were used to assess interaction with the proposed development and necessitated additional rotary coring investigation.

Following completion of the intrusive phases of investigation, a remediation and enabling performance specification was developed for the site which facilitated the securing of planning permission for the scheme. Detailed design was completed by others, with ERGO utilising cut/fill modelling capabilities to determine earthwork volumes for the Client to support Earthworks and Construction costings and ensure regulatory compliance through development of a CL:AIRE Materials Management Plan.

During construction ERGO were requested to provide support to assess the construction of a crib wall through geotechnical slope stability modelling, determining whether outlined proposals and temporary works solutions were suitable for installation. Utilising cored borehole information, we were able to determine the potential for instability and provided recommendations on appropriate mitigation to facilitate installation.

We completed validation of the remediation and enabling works strategy, providing verification of the required works and management of the limited Made Ground deposits, localised contamination hotspots and placement of suitable clean cover systems within required soft landscaping areas.

Key Issues and Solutions

During the project, several key issues were identified which required detailed assessment, investigation and determination of appropriate management. The main issues associated with site redevelopment were noted to be geotechnical, primarily related to the site topography, the underlying karstic limestone deposits and geotechnically variable drift deposits.

The proposed earthworks resulted in geotechnically complex foundation designs with a partial engineered piled solution and partial traditional foundation methods utilised.

Furthermore, as part of the enabling works a significant cut face was proposed which required appropriate retention. We worked with key stakeholders and other specialists to determine a safe, pragmatic solution which maximised the developable area of the site. This involved a series of detailed slope stability assessments to determine a safe solution upon which each party agreed.
ERGO were involved at every project stage to support the delivery of development from scheme conception to planning sign off.