Frequently Asked Questions (FAQ) Geotechnical

Earth Environmental & Geotechnical are an environmental, geological, and geotechnical practice that offer an expert driven, cost effective and pragmatic service to clients. Here we answer some of the questions we are often asked, to help you understand what support your development needs.

Frequently Asked Questions

The term geotechnical refers to the practical applications of geology, typically for the purposes of civil engineering and mining. Most geotechnical companies take this science and apply it to designing earthworks and structure foundations, monitoring site conditions, and foundation construction. Generally, these projects involve subsurface site investigation of bedrock, soil, and fault distribution.

Geotechnical investigation is a process in which the physical properties of a site are assessed for the purpose of determining which uses of the site will be safe. Before land can be developed or redeveloped, geotechnical investigation is often required. This process is also required or recommended in the wake of incidents like flooding, the emergence of foundation cracks on land which was thought to be solid, and so forth. The goal of such investigation is to confirm that the land is safe to build on. Here we answer some of the questions you may have on Environmental and Geotechnical services.

FAQ

A Phase 1 Desk Study is an interpretive report that details the likely presence of any contamination within the subsurface, and the potential risks that this may present to future site users, developments and the immediate environment.
The Phase 1 Desk Study collates information from a wide range of sources relating to the site setting and its previous historical uses. A Phase 1 Desk Study Report should always precede any ground investigation. Ideally it should also be accompanied by a walk over survey conducted by an experienced practitioner. to provide greater certainty in the report findings.

If you are planning on developing a site you will generally need a Phase 1 Desk Study Report as part of your Planning application set out by the Local Authority Planning Department.

Or you may be planning on purchasing a property or site for development, as part of the Property Transactions (Due Diligence) it is prudent to complete a Phase 1 Desk Study Report.

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A Phase 1 Desk Study Report collates information from a variety of sources.

At Earth Environmental & Geotechnical this may include.

  • Ordnance Survey, Town Plans, and Aerial Photographs to allow us to assess existing and former land uses
  • Flood risk potential by reference to Environment Agency mapping and British Geological Survey records
  • Solid and drift geology by reference to British Geological Survey mapping and borehole index
  • Groundwater vulnerability from Environment Agency classification of aquifer status
  • Earthquake records within 1km of the site by reference to British Geological Survey records
  • Consultation with local authority Environmental Unit
  • Assessment of potential subsidence issues from an examination of geological maps, boreholes index, and walkover survey
  • Assessment of slope stability for relevant areas during the walkover survey
  • Brine Subsidence search for sites within relevant areas
  • Active and historical surface and underground workings based on published information and internal records
  • Coal Authority Mining Report if the site is within the Mining District
  • Active and closed landfill search within 500m of the site boundary based upon local authority and Environment Agency records
  • Radon gas potential with reference to Heath Protection Agency records
  • Preliminary Ecological Assessment based upon walkover survey and references to English Nature database
  • Petroleum Licencing Officer record search for sites with evidence of petroleum storage
  • Planning history of the site by examination of local authority portal
  • Preliminary Invasive Plant survey based on walkover survey
  • Preliminary Archaeological Assessment based on reference to National Monument Records

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A Phase 2 assessment consists of an Intrusive Site investigation with quantitative risk assessment. Depending on what is highlighted in this assessment, a subsequent remediation strategy and verification report may then be required.
A Phase 2 assessment is only needed if it is identified in the initial Land Contamination Assessment or if it is part of the conditions the Local Planning Authority have attached to the planning approval.

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The site walk overs form an integral part of our Phase 1 Desk Study reports.  The purpose of the survey is to basically see a site in the flesh, to identify potential sources of contamination.During the walkover survey, we will assess areas identified within the desk study as potential development issues, environmental and cost liabilities. We also highlight potential remedial options or management considerations.
Following the desk study and walkover survey, a Site Conceptual Site Model can be developed. This will allow for environmental and geotechnical hazards to be individually assessed.  Any potential pollutant linkages can then be prioritised for any future Phase 2 Site Investigation.

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The Plate Bearing Test (or Plate Loading Test) is an in-situ field test used to find the ultimate bearing capacity of rocks and soils and predict the settlement beneath an imposed load.

An example of a Plate Bearing Test click here

Earth Environmental & Geotechnical  offer Plate Bearing Test (or Plate Loading Test)  for more information please click here

Design engineers need to know the bearing capacity of soil underneath the proposed construction when designing the traffic surface or shallow foundations.The Plate Bearing Test (or Plate Loading Test) is also useful for construction sites to establish ultimate bearing capacity and settlement of the ground for working platforms, crane outrigger pads and piling mats. At Earth Environmental & Geotechnical our engineers will advise on the plate size required to match the design load and reaction load required (i.e. size of excavator).

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Here is an example of a Plate Bearing Test (or Plate Loading Test). The objective of the test is to obtain a load-settlement curve of a soil at a particular depth, to estimate the ultimate bearing capacity of the foundation.

Example of Plate Loading Test

The load intensity and settlement observation of the plate load test are plotted. The graph shows the load settlement curve. The ultimate bearing capacity is taken as the load at which the plate starts sinking at a rapid rate, i.e. when the curve drops down to a vertical line.

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A Basement Impact Assessment (BIA) combines risk-based assessments and ground investigation information to determine if a basement development can be completed successfully at any given site. During every BIA potential development risks are identified and advice on how to mitigate those risks is provided.

A Basement Impact Assessment (BIA) is undertaken to ensure the proposed development will not adversely impact on current development or adjoining / neighbouring developments. The BIA will evaluate the direct and indirect impacts of the proposed basement and the specific risks involved.

At Earth Environmental and Geotechnical our Basement Impact Assessment (BIA) involve three key stages:

Stage One: Desk Study and Screening & Scoping Report

Initially a desk based screening and scoping report will be completed alongside a Phase I Desk Study. At this initial stage, the proposed development is reviewed in the context of the site’s history, its geological and hydrogeological conditions, potential for contamination and any risks posed by surface and groundwater flooding.

A  Flood Risk Assessment may also be required if the proposed development resides within a defined flood zone area. If the development site is in a Flood Zone 1, this may be of limited scope, however if the property is in a more vulnerable flood zone, detailed further investigation is likely to be required.

The desk study and screening and scoping report will conclude by outlining any areas of concern which require further investigation.

Stage 2 : Site Investigation

The second stage of a BIA is to undertake a Site Investigation / Ground Investigation tailored to investigate the potential issues highlighted within stage one and to provide design information to allow the safe construction of the basement.

The site investigation will help to highlight any potential hazards beneath a site which are unknown and determine the engineering properties of the underlying soils. Ground investigation works also allow the installation of ground gas and groundwater monitoring standpipes and subsequent recording of ground gas and groundwater data. This data will in turn be used to determine if waterproofing / dewatering will be required as part of the development and if ground gas protection measures will need to be installed.

The type of ground investigation techniques used will be dependent on the proposed basement design and the access constraints present at the assessment site.

Given that basement developments are often required on sites with restricted access, specialist limited access investigation techniques may be required.

The following is a list of intrusive investigation techniques often used as part of a BIA.

  • Hand Pits (often used to expose current foundations and the presence of known underground utilities)
  • Trial Pits (used to visually inspect shallow ground conditions to depths of around 3.5m)
  • Boreholes (used to inspect ground conditions and undertake insitu testing on underlying soils and rock)
  • Modular / Limited Access Boreholes (used on sites where access for a standard drilling rig is not possible. Several specialist drilling rigs are available with rigs being able to be carried into position by hand)

Once the ground investigation works are complete, a factual and interpretive report will be produced. This report will provide detailed of the works undertaken, alongside geotechnical design information for the basement’s construction. Other influencing factors such as contamination will also be discussed within the ground investigation report and any mitigating measures required will be produced.

Stage 3 : Basement Impact Assessment Report

Finally, after the Site Investigation stage, a detailed Basement Impact Assessment report will be produced.

This report combines the information from both stages 1 & 2 and provides a complete assessment of the risks and mitigation measures required to successfully complete the basement development.

An example of the topics covered within Stage 3 include:

  • A summary of the ground conditions identified beneath the assessment site.
  • Recommendations on the type of construction methods required, including recommendation on foundation depths and types.
  • Recommendations Regarding Structural Monitoring.
  • The Potential for Hydrological Impacts.
  • The Potential for Hydrogeological Impacts. And
  • The Potential for Flood Risk Issues

Geotechnical Resources

Here we have some of the examples of reports to help you understand what the different documents cover.

Geotechnical Resources

Report Examples

Coal Mining Risk Assessments identify site specific coal mining risks and set out the proposed mitigation strategy to show that the site can be made safe and stable for the proposed development.

The Plate Bearing Test (or Plate Loading Test) is an in-situ field test used to determine the ultimate bearing capacity of rocks and soils and anticipated settlement beneath an imposed load.

Click here for example of Plate Bearing Test (or Plate Loading Test)

For more information on Plate Bearing Test (or Plate Loading Test) examples please click here