We were called to the rescue of a local home owner recently. They had been told, by both Building Control and their builder, that they needed to make substantial improvements to their existing foundations in order to be able to add a first floor extension to their property. The existing foundations had been signed off by Building Control, a number of years previously, but were considered insufficiently deep and wide to support the additional loads of the proposed extension.
To add to the problem, the existing foundations were off-set from the line of the existing walls, but there was no indication to suggest they would be inadequate. When we asked what information Building Control had used to reach their conclusion all we got in response was ‘it’s just not what we usually see’. We thought we could (and should) do a little better than that…
Given our knowledge of the local geology, we knew the property was likely to sit directly onto the bedrock chalk, which being ‘rock’ is usually pretty strong (maybe the clue is in the name?). We carried out some low-cost field tests adjacent to the existing foundations and used these data to complete an evidence-based geotechnical design. We then worked with the project’s structural engineer to confirm that the existing foundations were more than adequate to support the new loads.
The cost of carrying out the testing and subsequent report was less than 10% of the cost of the previously proposed ‘necessary improvement works’. Not only that, they yielded a significant time saving. A win the for the client and a win for us – sometimes it’s just nice to be on the right side of common sense.
The site investigation industry has, traditionally, relied on light cable percussion (generally known as shell and auger) drilling. This is slow, messy and crude providing low quality geotechnical and environmental samples at best. Thankfully, these days it isn’t the only option available to you.
The majority of our general site investigation drilling is done using hollow stem rotary methods. These provide signficantly better quality data with minimal sample disturbance, even in the toughest of conditions. This week we were working at a site underlain by glacial and millstone grit cobbles, sand and terrace gravels in a sandy clay matrix. We drilled five boreholes to their target depth on 8m in one working day – something that might have taken a shell and auger crew a week – minimising the disruption to our client’s business which was able to remain open throughout.
When it comes to sites that have narrow or restricted access, we reckon that there is no better drill rig than our Terrier. It may be the baby of our drilling fleet, but don’t let its diminutive size fool you.
In the past year it has worked in basements, narrow side passages between houses, amid demolition debris and in a host of other conditions that would have precluded larger rigs being used.
If you add in the fact that it can work on inclines as steep as 30 degrees I think you’ll agree that our Terrier is a little gem.
This week we’ve been using the Terrier to carry out post-demolition verification sampling. We’ve been able to pick our way through the demolition rubble, getting access to the entire site to drill a pattern of boreholes to 5m depth.
For further information, or to discuss your drilling requirements, please contact Angus Gale – 01296 739433
Our Terrier drill rig, Tinky, recently celebrated its sixteenth birthday. In that time it has had 2 new head gaskets, 15 calibrations, 22 oil changes and services, 2 new tyres, 2 new tracks, 1 rebuilt mast frame, 1 new radiator , 1 new weight guard and a new fan. We know that good maintenance is the key to keeping any machine working and we like to think we’ve done our Terrier proud. It has certainly paid us back.
It may be sixteen years old but last week it still managed to dynamically sample 25m of weathered sandstone to 5m depth with SPT tests every metre plus completing an additional four dynamic probes to competent bedrock at 9.5m and installing four gas monitoring wells to 1.5m. All this in two days including a round trip mobilidsation of over 300 miles. Hats off to Tinky.
We are looking for dynamic sampling operatives. If you think you fit the bill then give Angus Gale a call on 01296 739400 or email your CV to Angus Gale.
Another post discussing the joys of working at a busy airport. This time we were asked to advise on the allowable bearing capacity for a foundation to be installed at 2m depth, without either excavating a trial pit of drilling a borehole.
We opted to carry out a series of dynamic probes, using our lightweight terrier drill rig, along the line of excavation, using the data to calculate an equivalent SPT ‘N’value and thence an allowable bearing capacity. We were able to provide our client with results in real time, ensuuring there were no delays to the construction programme.
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.
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.
……is our mini dynamic sampling rig! In fact, its photographed here having its oil checked during a day’s work at a site on the south coast.
The geotechnical survey, which comprised standard penetrations tests (SPTs), dynamic probing, CBR tests and plate bearing tests, was designed to allow the design of foundations for a leading supermarket chain’s new store.
The site had a history of industrial development so, not surprisingly, it was littered with large, buried concrete obstructions from previous structures (foundations, beams and piles). We will soon be returning to complete pile probing at each of the new pile locations to enable the augers of the piling machines to keep turning thus avoiding expensive standing time.
Hopefully it will have stopped raining by then…..and no, sadly, we didn’t find the pot of gold at the end of the rainbow.
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………
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!