Soil boring

Soil boring or drilling in the United Kingdom is typically carried out using hand held percussive window sampling, tracked mini drills or cable percussion drilling otherwise known as Shell and Auger. Other multi-functional rigs are also now available in the UK which perform a range of drilling methods.

Geoinvestigate provides a wide variety of borehole drilling services. Boreholes range from small diameter hand augers typically limited to depths < 3m; hand held percussive window sampling where a tube is driven into the ground up to 6m using a petrol, electric or hydraulic jack hammer and extracted using simple jacks or a hydraulic ram; probing or dynamic penetration testing whereby a small diameter drill string and a solid cone tip is driven into the ground up to 15m by a standard drop weight raised by chain on a small portable wheeled rig with mast.

Window sampling is a technique whereby samples of clay and sand can be recovered from small diameter boreholes using portable hand held electric, petrol or hydraulic jack hammers or tracked min drills such as the Dando Terrier 2000 or Carl Hamm’s MRZB.

The equipment is small hands portable or in the case of the tracked mini rigs maneuverable making the technique particularly useful in limited, restricted or difficult access sites for example in back gardens, building and basements.

Typically boreholes are of smaller diameter between 40mm to 100mm and do not extend below 6m depth. Window sampling is a fast and cost effective way of establishing the nature of the ground profile and identifying the presence of contamination. The samples are recovered in tubes with or without windows cut in them from which samples are taken. Windowless tubes are recent and more sophisticated advance having plastic liners which are slid out to reveal the soil sample.

Geoinvestigate operates and hires out several Dando Terrier sampling and geotechnical rigs. In accordance with the manufacturer guidance Geoinvestigate’s rigs are always manned by 2 of its well-trained operators. Though you may pay a bit more – the increase in production in metres per day and the peace of mind that comes from knowing the equipment is being  safely used is worth it.

With 2 operators the rig is capable of completing up to 8 boreholes to 5 meters a day.

Typically the rig is hired out at £650 per day with 2 operators subject to location and travelling distance excl. VAT. Geoinvestigate can provide a basic drilling and sampling service or with full logging and site attendance by an engineering geologist.

The Dando Terrier sampling and geotechnical rig has been designed specifically for sampling and testing for geotechnical and environmental analysis. Crawler-mounted for easy site access in the most arduous conditions. Simple to operate and maintain, extremely reliable and competitively priced

Compact manoeuvrable crawler-mounted design ideally suited for long wheel-base transit type vans for fast mobilisation to site and secure storage of all equipment.

2-Piece drop hammer for sampling and testing incorporated in mast assembly with hydraulic cylinder giving 7000 kgs pull-back for recovery of casing and sampling tools. The mast assembly can be detached for remote operation in restricted access locations. Hydraulic tilting undercarriage allows operation on inclined slopes up to 30 degrees from horizontal. Deck area with storage capacity for all required drilling tools.

The concrete coring head is useful when concrete and tarmac overlie the area to be sampled. Range of windowless sample tubes with plastic liners ensuring high quality samples, good presentation and ease of handling and transportation.

Cable percussion (shell and auger) still remains one of the most popular drilling method used for geotechnical site or ground investigation though in recent years it has been replaced in many jobs by hand held percussive window sampling or increasingly by window sampling carried out using tracked mini drills and rigs . The reason is simply that window sampling is cheaper, more productive, causes less disturbance and can be brought into restricted access or difficult access sites. In addition the window sampler can be transported in a van operated by 1 person and does not require a yard for storage. However the drawback of window sampling is that it is restricted to much shallower depth typically 5m to 8m though Geoinvestigate has achieved 11m on occasion.

Depending upon access limitations and favourable ground conditions boreholes up to 60m depth can be formed and even deeper though drilling time and costs tend to rise steeply as the depth increases.

Standard light-cable percussion boring uses a two tonne capacity winch driven by a diesel engine and a tripod derrick approximately 7m in height. The derrick folds down so that the rig can be towed by a four-wheel drive vehicle. If deep or wide diameter boreholes are required a larger three tonne capacity winch can be used. In areas where there is low-headroom or access limitations a modular or demountable percussive rig is used. This type of rig is either a ‘cut-down’ version of the standard towed tripod or is modular rig which is transported in sections on a trailer and the component parts are assembled at the borehole location

The borehole is formed using a ‘clay cutter’ for cohesive soils or a ‘shell’ (or bailer) for non-cohesive materials. A chiselling tool can be used to penetrate very hard ground or obstructions. The sides of the borehole are supported using steel casing which is lowered into the ground as the boring proceeds. If the exploratory hole is formed in sands or gravels, particularly within the saturated zone below the water table, the steel casing will be driven into position to support the borehole sides to allow in-situ testing to be carried out and the soil to be recovered using the shell

Water samples may also be obtained during this drilling process and because the steel casing seals the borehole from the surrounding ground, it is possible to sample water horizons at different depths with minimal risk of cross-contamination. However, it should be noted that water samples that are fully representative of the groundwater require the installation of a groundwater sampling well. Gas wells can also be installed in holes formed by this technique as well as flexible tubes and instruments to measure the vertical and/or horizontal deflection of the ground and movements of slopes and cliff tops in soil.

A heavy chisel is used to break-up obstructions such as boulders and can penetrate a short depth into weak rock. Where a core sample is required of the rock a rotary follow on pendant drill attachment can be used suspended from the tripod or the rig can be pulled back or removed altogether and rock drilling carried out using a rotary drill rig.