Phase 2 - SITE INVESTIGATION

Using various intrusive methods we produce high quality interpretative reports for our clients comprising both geotechnical and environmental assessments

Solmek undertake Phase 2 Site Investigations to assess each aspect highlighted by the Phase 1 Desk Study. This generally comprises a variety of exploratory methods such as boreholes and trial pits to sample potentially contaminated material. The Phase 2 Site Investigation is designed and implemented depending on a number of influencing factors such as the proposed end use, sensitivity of the area, ground conditions, size of site and type of contaminants identified by the desk study. A Phase 2 contamination assessment is a prerequisite for planning permission from statutory authorities such as the local authority, Environment Agency and NHBC.

Chemical analysis of soil and water samples for common contaminants is performed to establish the concentration and extent of any contamination present. All samples are sent for analysis to an accredited MCerts laboratory. From the results, a risk assessment using the “source-pathway-receptor” model in conjunction with the current widely accepted CLEA model would then be carried out and the Preliminary Conceptual Model created during the desk study updated to determine the risks to various receptors:

  • Human – Users of the proposed site after development. Infants are most at risk if a residential development is proposed and these are targeted in our assessments. Remedial measures are given to make the site safe for future development.
  • Construction Workers and surrounding areas – The health of the workforce during the construction phase of the development is considered in terms of the PPE that they wear and the facilities to be provided on site. Users in the surrounding area are assessed in terms of contamination prior to, during and after the development has taken place.
  • Vegetation – Plants and trees can be affected by contaminated sites. The risks to these receptors are considered and recommendations are given for topsoil and subsoil placement in soft landscaped and garden areas.
  • Controlled Waters – These include risks to water courses, bodies of water (e.g. Lakes or ponds) and aquifers. Water samples are tested along with leachate of the soil to determine the risks posed to these receptors.
  • Services – Concrete can be attacked by moisture and sulphates creating weakness and instability in foundations. We recommend the optimal concrete mix required to mitigate these circumstances. Some contaminants also attack plastic water pipe and we make an assessment of the ground in relation to service fabric upgrades.

 

The risk assessment may be Qualitative or Quantitative dependent upon the site.

INTRUSIVE SERVICES

The most appropriate methods of intrusive investigation are determined following completion of a desk study.

Understanding the behaviour of the underlying ground is an integral part of any site investigation.  It is important that the right combination of drilling, insitu testing, sampling, logging, laboratory testing and analysis are applied within the Phase 2 Intrusive Site Investigation.

Solmek uses a number of high quality drilling rigs and plant equipment to produce site investigation data which is tailored to our client’s needs. Following the soil retrieval, our experienced engineers can manage the samples from site and ensure they are transported safely and accurately for extensive ranges of geotechnical and contamination laboratory testing. This ensures we deliver the appropriate data for effective, factual and interpretative reporting.

Service Depth Range (>5m) Depth Range (>10m) Number per day Area Required Cost Reinstatement Costs Gas Installations Sample Types
Cable Percussive Rig Yes Yes Depth Dependent 6m² Mod Low-Mod Yes Undisturbed, disturbed, SPTs
Small Percussive Rig Yes No 5-6 4m² Low Low Yes Disturbed, SPTs
Rotary Rig Yes Yes Depth Dependent 8m² High Mod-High Yes Undisturbed, disturbed, SPTs, rock core
Trial Pits (Mechanical) Yes No 5-10 4m² Low High No Disturbed
Hand Held Machinery Yes No 5-10 2m² Low Low Yes Disturbed

What intrusive service would you like?

Cable Percussive Drilling

Cable percussion drilling, or shell and auger drilling, is the most popular method of retrieving soil samples from the ground whilst also undertaking insitu testing. The drilling technique allows the installation of casing inside the borehole to prevent loose soils collapsing into the hole, allowing the borehole to be advanced to depths of up to 100m. The rigs can be adapted to suit access and headroom requirements.

Insitu testing is undertaken in the borehole and includes Standard Penetration Testing (SPT), borehole shear vane testing & permeability testing.  The cable percussion drilling technique also allows for the retrieval of undisturbed samples used for laboratory geotechnical testing. 

Following completion of a borehole, ground gas and water monitoring standpipes can be installed. These allow future measurements of ground gases such as carbon dioxide and methane to be taken as well as long term monitoring of fluctuations in groundwater levels.

Small Percussive Drilling

The small percussive rig is a compact versatile rig which is tracked under its own power into locations with difficult access. It is an ideal method of drilling on smaller sites, e.g. gardens, offering minimal disruption.

Sampling, insitu testing and installations similar to the cable percussive rig are adopted.

Solmek also have dynamic probing equipment which can be fitted in place of the sampling tools. This allows dynamic probing to be alternated with fully sampled boreholes for a comprehensive investigation.

rotary Drilling

Solmek are required to check for shallow mine workings and can offer a range of rotary drilling techniques to assess the potential hazards to a development from subsidence due to shallow coal mine workings. The main technique to check for the presence of voids due to shallow mine workings is rotary drilling.

Solmek can undertake rotary coring to recover rock core samples of various diameters. These can be used to determine rock quality with information often required by piling contractors for deep foundation and tunnelling design. The cores are then logged by experienced engineering geologists in accordance with the relevant British and European standards.

trial pitting

In order to study the structure of shallow strata, machine excavated trial pits can also be carried out under the control and supervision of an experienced engineer. Our engineers have a thorough understanding and knowledge of geology and soil mechanics. Efficient excavation, spoil and reinstatement management ensures that the sites we work on remain hazard free.

Hand excavated trial pits can also be carried out where exposures are required to log and detail existing foundations at suspected subsidence problems. Services can also be exposed by this technique.

Soakaways and CBR’s

Within excavated trial pits Solmek can undertake soakaway testing in accordance with BRE 365 Soakaway design. The results can assess a site to determine whether sustainable drainage (SUDS) can be adopted. Solmek can also carry out insitu plate load and CBR testing using a wheeled excavator; these tests are normally carried out during the trial pitting investigation.

Concrete Coring

Solmek undertake coring of floor slabs in order to assess their construction and substrata. This is useful for the purpose of utilising existing rafts for internal construction e.g. mezzanine floors.

Difficult Access

Solmek have extensive experience of finding solutions for intrusive investigations with difficult access. Examples include mobilisation of cranes, drilling overwater via barge/pontoon, use of demountable/reduced size rigs and the use of handheld drilling equipment.