We offer site investigation contracting with factual reporting, cross consultancy services.

Geotechnical  Consultancy

Geotechnical Consultancy

Geotechnical risk is one of the main considerations developers and engineers need to manage in order to deliver a successful project.

In-situ Testing  Earthworks

In-situ Testing Earthworks

Working closely with the laboratory and the consultancy teams, we specialise in working with contractors delivering the placement of engineered fill.

Laboratory  Testing

Laboratory Testing

Our modern testing facilities paired with qualified and experienced staff enables our clients to choose independent testing services, or testing as part of the overall site investigation package.

Contaminated Land

Contaminated Land

Our investigations range from Phase 1 reports, developing the conceptual site model to detailed quantitative risk assessments.



South West Geotechnical Ltd works within a wide variety of sectors.Clicking here will take you to case studies, by sector type, that demonstrate our capabilities and innovative approach.



 Glastonbury, Somerset

Peat Permeability

It was proposed to exploit a new peat working close to an existing isolated house on the Somerset Levels. Due to concerns of the impact of groundwater drawdown due to the workings on the house foundations, it was necessary to model what would occur in this process.


Peat Permeability


Fundamental to establishing this impact was determining the permeability of the peat. This was achieved by long term full scale pump tests.


The test set up, including control console and monitoring boreholes are shown in the graphic below: 


Peat Permeability


Graphical data was produced that could be read to establish permeability values by a number of different methods:


Peat Permeability




Methods of Analysis

Data from all the monitoring wells was analysed using the Thiem-Dupuit method given in Kruseman and de Ridder (2000). Classical equation given in all text books; Q = pk (h22 – h12)/ (ln (r2/ r1) or k = (2.3Q/ p (H22 – h12)) x log (r2/ r1)


Some were analysed using the Theis Analysis (BS5930,, which uses a plot of observation well drawdown compared or superimposed on a Theis 'type-curve’. Depending where the test curve falls on the type curve, parameters are read off the type curve, and substituted in equation to determine k.


The four nearest monitoring holes were also analysed using the Cooper-Jacob Time Drawdown Method (BS5930,  Using this method, the drawdown over a log cycle of time on a straight line portion of the graph is determined, and substituted into an equation to derive k.


The same method can be used plotting drawdown against log distance Cooper-Jacob Distance Drawdown Method from the well at a given time.  Drawdown/ distance between the four nearest holes to the pump well were plotted to determine the unit drawdown value. 


The recovery phase of PW01 and near wells was analysed using Theis’s Recovery Method (Kruseman and de Ridder, 2000, 13.1.3). A semi log plot of residual drawdown against time after pumping ceased is plotted, which gives a straight line, the slope of which = 2.30/ 4pKD


The recovery of PW01 after the step test was also analysed by this method. 


Rising head permeability tests (BS 5930) were carried out in all of the boreholes put down as part of this exercise both to determine k, but more importantly to check uniformity of conditions across the site.


Peat Permeability




Once a characteristic permeability value was determined, the extent of drawdown could be accurately predicted, and modelled.


Peat Permeability

The testing demonstrated that the nearest property to the working would in fact remain unaffected, and this permitted the extraction to proceed safely.



Peat Permeability



South West Geotechnical
South West Geotechnical
South West Geotechnical