Borehole – Page 3

16 March, 201616 March, 2016

When is an SPT not an SPT?

SPT Calibration - 2 — SPT Hammer Calibration

The answer is when it’s not calibrated.

The Standard Penetration Test, or SPT, has been the mainstay of geotechnical site investigations in the UK for decades. The test is simple, quick and cheap and it’s particularly suited to the light cable percussion drill rigs that are so widely used in the UK.

What isn’t generally appreciated is that even a low tech test such as this requires proper calibration in order to yield consistent, reliable results. In fact Eurocode 7 requires the SPT hammer to be calibrated annually. Unfortunately very few drilling contractors bother to do this and, in our experience, few consultants know that they should be asking for it. Given that results from out of spec hammers can vary by as much as 50%, we think this is something that should be given more attention.

We’ve put our money where our mouth is and now all our SPT hammers are correctly calibrated and all our drill rigs come with up to date LEAA inspection certificates. If you’d like to know more about our drilling capabilities please contact Angus Gale – 01296 739433.

14 March, 2016

Bulldog Spirit?

We are accustomed to working for the big hitters of modern industry. However, today we were handed the opportunity of working around one of the big hitters from history. This WWII machine gun bunker holds listed status, and rightly so. It’s one of 18,000 built, around the coastal areas of the UK during Churchill’s defence against Operation Sea Lion.
Our plucky little rig was able to negotiate perimeter fencing, dense undergrowth, steep inclines, tank traps and machine gun bunkers just to get on site. It all sounds more “Band of Brothers” than “geotechnical site investigation”. In all 28m of dynamic windowless sampling with SPTs (and 2″installs) plus 80m of dynamic probing were effortless completed.

Now that’s the spirit…………..

17 February, 201617 February, 2016

When Horizontal Just Won’t Do

A prominent pipeline client came to us with a problem. A ‘positive’ problem that is. A section of their pipeline runs underground next to a railway line. The railway’s overhead high voltage power lines were causing an amplified positive electrode potential in the ground, which in turn was leading to increased corrosion of their pipeline. In these cases, cathodic protection is the usual solution.

A typical cathodic protection system would comprise a series of shallow earthing rods installed at regular intervals along the pipeline. However, this requires access for maintenance in the future to the entire pipeline. But these pipelines run for hundreds of miles through agricultural land, some of which is only accessible during certain periods of the year. The solution was to design a single anode string capable of achieving the required negative electrode potential in a vertical design. Thus saving on space, maintenance and cost

The client’s senior cathodic protection engineer approached us to see if we could drill a 75m deep borehole and undertake the (negative) anode installation. We took the challenge and set about devising a safe method for installing a multi core anode string weighing more than 300kg! The borehole was installed through 18m of gravel into underlying mudstone. Just to complicate matters further, our environmental appraisal identified a potential risk of penetrating into a sandstone aquifer beneath the mudstone. To mitigate these risks and achieve the required potential we had to install a vent pipe to the base of the borehole, a tonne of coke, gravel and a bentonite seal at the top of the mudstone to ensure the underlying aquifer was protected.

Exactly how we did all this is our secret but needless to say it involved a large rig, and unusually for us, a lot of “negativity” ………….But happy pipeline equals happy client – now that’s positive.

5 February, 2016

Earth, Wind and Fire…mostly Fire

It’s never good when your business premises are reduced to ash in a raging inferno. But this was just the scenario faced by one of our clients, when their car showr0om and repair workshop has burnt down overnight.

We were on hand the next day, working closely with both the fire brigade and the demolition crew. We were able to obtain the vital geotechnical data necessary to allow design for the new buildings to progress.
Here you can see our Terrier rig taking soil samples and completing in situ standard penetration tests and dynamic probes to depths of up to 15m.

Now the flames have died out, the demolition has been completed and the new structure has been designed. Our client is well on the way to be back in business.

7 October, 20157 October, 2015

A Week in the Life…..

No-one can say that our workload isn’t varied. Last week one of our drilling crews completed the following schedule:
Monday – Geotechnical investigation including U100 sampling and SPT testing with our Terrier drill rig;
Tuesday – Water well installation using rotary rock roller with our Commachio 205;
Wednesday – Environmental investigation at a filling station using hollow stem augering, again with our Comacchio 205, while a new canopy was being installed;
Thursday and Friday – Deep water well installation using down the hole hammer to penetrate into a limestone aquifer.
We love a bit of variety in life and this week has proved it so. Time for a rest…….next week looks busy………

12 May, 2015

Greek Myth?

Actually, there is nothing mythical about Subadra being commissioned to install shallow monitoring wells at the Daedalus Airfield Development! We constructed several shallow wells over the course of two days using our Hollow Stem Auger drilling system.

Lee-on-Solent is known for its sand and a dense gravels which are more or less guaranteed to make drilling difficult. So to avoid this we used our powerful Comacchio drilling rig which ensure we reached the target depth at all the drilling locations with minimal disruption to the site. We then installed 50mm diameter wells to allow future groundwater sampling. All our materials were sourced locally to enable us to take the minimum of equipment and vehicles thus reducing our carbon footprint for the works.

We even had time to the collect soil samples for the Principal Contractor and get them
analysed for WAC by our in house lab facility. As a result of our prompt and efficient service the client retained us to carry out a more detailed geotechnical investigation at the site. No myth there then!

13 April, 2015

Everybody Breathe In

Terrier - Restricted Access — Terrier – Restricted Access

The combination of restricted head room and a ‘confined space’ presents major obstacles to any site investigation. However, our Terrier rig was able to gain access and complete a geo-environmental investigation in such a space. Its quite amazing where this little rig can get.
Access was through a standard doorway working with an overhead ceiling clearance of
less than 30mm with the machine set up. Precision operation was required to ensure we completed five boreholes, each to 6 metres in depth, with SPTs every metre, all in a safe and efficient manner.
The nature of the confined space meant that exhaust gases from the Terrier’s engine had to be vented to an outside area. We used an extendable sectional exhaust pipe to ensure a safe working environment. But just in case we also carried out carbon monoxide monitoring to ensure our crew’s safety.
Even better, our work was completed without the need to close the car repair workshop we were working in. allowing our client to continue panel bashing, filling and spraying to his hearts content.

6 March, 20156 March, 2015

Big Old Tanks

Have you ever wondered what is below your feet when you’re filling up at a petrol station? Big old tanks, that’s what! We’ve investigated the ground at more filling stations in the UK than anyone else and so, not surprisingly, we have a have a pretty detailed understanding of how they are put together. This sort of experience is invaluable when
it comes to assessing potential environmental risk – we know how and where problems
can occur…

Obviously owning our own specialist drilling systems, UKAS and MCerts accedited
laboratory and remediation equipment also has benefits, both in terms of cost and speed of turnaround.

For pragmatic advice and cost effective assessment strategies for the assessment
of filling station sites please contact James Skinner on 07770 611554.

6 March, 20156 March, 2015

When You Need to Know Fast

Our Geoprobe Drilling Systems offer something a little special when it comes to rapidly investigating a site. And when coupled with the fast turnaround from our UKAS and MCerts laboratory, our clients benefit from the best of all worlds.

We were asked to investigate a large industrial site that had a history of fuel contamination issues. The question was: how far had the contamination spread and was it migrating under the neighbouring properties. Our solution was to carry out a groundwater probing survey, comprising driving a re-useable probe into the ground to the underlying groundwater and then taking a sample of the groundwater for laboratory analysis.

We completed 54 probes in two days, accurately delineating the hydrocarbon plume. Forensic analysis of the samples by our laboratory then confirmed that there were three separate sources of the hydrocarbons, two of which were ongoing leaks, and not just the one known historic source.

We now know what the problems are, how far the contamination has spread and how to clean it up. Isn’t that better than endless phases of investigation last months and costing £££s.

Project value: £10-£15k

26 January, 2015

Free Water Supply?

We’ve recently completed construction of a water well to supply a popular car wash facility in the Swindon area.

Working closely with the main contractor, our careful pre-planning enabled us to install a 40m deep water well in challenging geological conditions, requiring 25m of retrievable casing to be used, all without affecting the site’s redevelopment programme.

On-going site contamination issues dictated that the borehole construction had to be professionally approved and tested before use. But the results of the post-development pump testing confirmed the well would supply a clean water yield in excess of the client’s requirements.

The savings in water supply costs for our client equates to a significant increase in their future profits. What difference would a free supply of 20,000 litres of water a day make to your business?

Contact: Angus Gale Tel: 01296 739471