Project Description

Jarvis Contractors

Services Supplied on this Project:

  • A site walkover survey of the site, set-out and supervision of the field works.
  • Basic desk study.
  • Window sampling/dynamic probing.
  • Soakage tests.
  • Geotechnical testing.
  • Analysis of samples of soil for a comprehensive suite of common zootoxic and phytotoxic contaminants, SVOCs and VOCs.
  • The provision of an interpretive site appraisal report including an assessment of environmental issues pertaining to the site and its redevelopment.

Project Details:


Housing Development
Approximately 23k
November 2013 – December 2013

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The Project

Geo-Environmental Services Limited was instructed by Jarvis Contractors Limited to undertake a desk study and intrusive ground investigation to assess the geotechnical and geoenvironmental issues pertaining to the proposed redevelopment of eight separate sites in a Watford housing estate.

What were the issues?

When undertaking the investigation there were a number of issues highlighted by the desk study that needed to be taken into account in the intrusive investigation:

  • The possible presence of deep Made Ground on the site, which may affect foundation design and construction.
  • The possible presence of shrinkable soils and the impact this could have on foundation construction.
  • The presence of laterally and vertically variable strata and the impact these could have on construction.
  • The desk study and PRA also identified a limited number of possible sources of contaminants.

What did we consider?

The investigation was to comprise a desk study of geotechnical and environmental factors pertaining to the site, including a site walkover survey, a review of available historical maps and an examination of other sources of geo-environmental and geotechnical information. Subject to the findings of the desk study, an intrusive investigation was to be undertaken into the geotechnical and geo-environmental conditions pertaining to the site.

The data from the geotechnical investigation was to form the basis of an interpretation with

respect to foundation design, pavement construction, soakaways, concrete specification and excavation stability. In terms of the environmental investigation, a Preliminary Risk Assessment (PRA) was undertaken as part of the desk study in accordance with CLR11, in order to provide a basis for the scope and rationale of the subsequent Phase II ground investigation. The data from Phase I and Phase II were then to form the basis of a subsequent Generic Quantitative Risk Assessment (GQRA).

The objective of the risk assessments was to evaluate the risks posed to the proposed redevelopment, adjacent land uses, and the wider environment, in the context of the development options, immediate liabilities under the Environment Act 1990, and risks posed to Controlled Waters under the Water Resources Act.

What were the key challenges?

The key challenge on this project was the timescales, with all the sites requiring turnaround in the space of a few weeks. Within a day of the site visit, risk assessment and method statements were produced and a preliminary investigation plan was then drawn up which detailed each of the investigation points, and whether a cable percussive rig, window sampler rig or trial pit was required. The risk assessments and method statements were submitted to the Clients Health and Safety representative for review prior to the works commencing.

Progress was monitored on the project using our online project management system (see screenshot below) and any potential delays identified and mitigated. The rapid transfer of investigation data from the site to the Project Manager enabled testing to commence at an early stage of the investigation and facilitated an effective logistical control in terms of supplies to site, transfer of samples to testing laboratories and management of personnel and operations on site.

Successful delivery of such a project in those timescales and working conditions requires quality procedures and a strong health and safety methodology. Geo-Environmental have invested in ISO9001, ISO14001 and OHSAS 18001 to ensure that our clients know that when we undertake site investigations is reduced. Our approach reduces issues later in development and this can save our clients time and money.

What were the outcomes?

The report provided recommendations to support the construction of foundations, excavations, pavements and soakaways, as well as advice on the design and specification of sub-surface concrete. In addition advice was also provided on gas protection measures, depths of topsoil, backfill and reuse of materials and waste.