Category Archives: Geotechnical

Site Investigation – Bristol

Site Investigation – Bristol

Just to the south of Bristol actually in Thornbury!

This was a geotechnical investigation. We needed to provide geotechnical information for foundation design.

The site was to the left (or west) of a establishes educational site . The coring went well, and there was good core recovery, once we were in competent rock.

The results will be written up in a report, with load bearing calculations provided to the client.

If you require a site investigation in Bristol, London, Exeter or elsewhere please give us a call and we will get it sorted out for you.

Site Investigation Bristol

Site Investigation Bristol

Southwest Environmental Limited were commissioned to undertake a reduced scope geo-environment assessment at a site in Bristol. The investigation was retrospective in that construction work had already started.

Bristol City Council  are one of the few council nationally who will accept a reduced scope investigation for geo environmental risk assessment. Ordinarily it is required to take a high frequency of samples even of smaller sites, often including ground gas investigations including deep boreholes which can prove very costly. The cost of such investigations when considering build costs for smaller projects can be approaching 10% of project value, which is some cases in inhibitive.

Below is a panoramic photograph of the site at the time of the investigation. The bedrock has been exposed to some depth by excavations for the foundations. You can clearly see the angle of the bedding and the more coal rich bed to the left of the photograph.

Photograph of Outcrop (or Incrop!)

Just 2 samples were requested by Bristol Site Council. This is a very low number. The samples retrieved showed no exceedances of established “safe” levels. Although Total Organic Carbon Levels in one sample were above those mentioned in CIRIA guidance, likley owing to the presence of coal.

The whole of Bristol is now considered a brown field area. This may seam an overreaction, but SWEL have been surprised by contamination found on “innocent” looking sites in the past. Despite best efforts to categorise a site as low risk without soil sampling it is often the case that if SWEL are pushed to investigate, post Phase 1 Desktop Study will find high levels of some contaminants.

BRE 365 Soak-Away Report – Brinkworth, Chippenham

BRE 365 Soak-Away Report – Brinkworth, Chippenham

On site geology is the Oxford Clay Formation. Which is described as:
“Silicate-mudstone, grey, generally smooth to slightly silty, with sporadic beds of argillaceous limestone nodules.”
BGS Borehole 398037 which is situated to the south west of site shows considerable thicknesses of Clay, extended to the base of the borehole at 44.81 mBGL.
BGS describe the Oxford clay formation as being blocky and fissile in certain areas, so there is potential the clay in to pervious (support of flow through fissures) in certain localities.
Trial pits showed varying thicknesses of made ground resting over the Oxford Clay. 
Site works comprised of 2no. trial pits with soak away tests conducted in each on. The positioning of these pits were sited in anticipation of a fairly large soak away being required. Clay typically being assumed to have a low infiltration rate.
Holes were dug using an excavator, with care being taken to keep the side vertical. This is important so as to be able to deduce an accurate volume, and pit internal surface area. 
The location of the pits can be viewed on the location plan in Appendix 1. Dimensions of the trial pits were chosen so as to representative of the final soak-away. Trial pit dimensions can be seen on the Trial Pit Log sheets in Appendix 3.
Calculations show that based on a 1 in 10 year rainfall event, allowing for a 20% increase in rainfall events owing to climate change, that a trench or pit soak-aways could provide adequate infiltration drainage for surface water from the proposed development. Results from Trial Pit 1 are adopted as a worst case scenario.
Detailed Calculations – To BRE 365

BS9530 –  Logging of Trial Pits

Geotechnical Investigation Belluton near Bristol

Geotechnical Investigation Belluton near Bristol 

In support of some road stabilisation work SWEL have carried out a geotechnical investigation at Belluton near Bristol.

Despite tight access, drilling works started in a timely fashion, with recovered of some excellent core samples. Holes were advanced to a depth of 15 meters, with dynamic sampling in soils and weathered rocks, and coring in rock proper.

Dynamic Samples from Ground Level in c. 3 Meters Depth

Core Samples from Weathered Rock Head

Close Up of  Core Fragment

SPT results and disturbed samples from Soils. 

The investigation is to provide data for a cutting for road widening. The rock seems very competent, but soil nails are proposed for further strengthening. Samples were tested for aggressive ground characteristics, and a variety of classification and strength tests.

Geotechnical Investigation Bristol

Site Investigation Bristol

Site Investigation Bristol

Acting on instruction from a property owner in Bristol. Southwest Environmental Limited are currently undertaking a Geo-environmental site investigation in Bristol.

The site is an dis-used petrol filling station, there are concrete filled tanks on site, and various buildings with above ground tanks and assicoated storage.

Site Investigation Bristol – Buried Services and Pipework were Present

Site Investigation Bristol – Site Works were completed in One Day

The site works were undertaken in December 2015, with reporting no being progressed.

A full report will be prepared to collate finding of investigation and to compare soil quality against various guide values. 

Site Investigation Bristol

Geotechnical Investigation & Design for Solar Park – Somerset

Geotechnical Investigation & Design for Solar Park – Somerset

A renewable energy company approached Southwest Environmental as they were concerned that transformer bases incorporated within a new solar park in Somerset were sufficient to meet structural loading.

The solar park which extends to approximately 12 hectares was well under construction with the majority of panels installed, and the transformer bases constructed.

The site was heavily trafficked and access was difficult


most of the solar panels were already installed


lots of solar panels just what the UK needs


again – a large number of solar panels

The site was on the peats and silts of the Somerset levels, these are very challenging areas in which to build, with soils typically exhibiting very low strength values, and owing to the thickness of they superficial silts are infeasible for piled foundations.

Using an established method for the determination of soil strengths SWEL found that the proposed structural loading was very similar to the max allowable loadings for the soil conditions encountered on site. To that end a program of monitoring was suggested for a period of 18 months to span a wet season, and observed for movement, as a secondary option a piled foundation solution was recommended.

The above work was turned around with a 15 day working window, with sampling, dynamic probing, laboratory analysis and reported delivered within a tight time frame.

Geotechnical Somerset

Geotechnical Investigation Bristol

Geotechnical Investigation Bristol

SWEL were engaed to undertake a geotechnical investigation within an existing reatial unit, structural engineers required ground data so as to construct a mezzanine floor.

There was restrict access on site but with the help of an expert crew from Stunt Drilling Services,  3 rotary boreholes were advanced 10 meters below ground level in to the Sandstones and Coal measures that underlie the site.

Core recovery improved with depth, and rock core logging was used to give empirical rock mass strength estimates.

Below is a video of site works (drilling rig) underway.

Running a drilling rig in a building can cause a build up of fumes and as such an extractor system was used to suck exhaust gas outside the building via lots of ducting.

Site Investigation Bristol

Geotechncial Consultants Bristol