Overview of the Company
Borehole Services Ltd. has over 38 years of operational and administrative experience in geotechnical and environmental testing and drilling.
Our team comprises highly experienced individuals. Nicholas Icke, our lead driller on the cable percussive rig, has over 30 years of rotary drilling experience in the UK and overseas. Joseph Kulesa, our esteemed office manager, has managed field works crews providing a wide range of geotechnical services for 38 years. He also has experience running a busy geotechnical laboratory and geotechnical / geo-environmental office for a prominent local Firm.
In the UK, the most popular drilling technique for geotechnical site or ground studies is cable percussion (shell and auger). Boreholes up to 60 meters deep can occur, depending on ground conditions and access restrictions.
Conventional light-cable percussion drilling employs a tripod derrick that is about 7 meters high and a two-ton winch powered by a diesel engine. A four-wheel drive vehicle may tow the rig by folding down the derrick. A larger three-ton winch can be employed if deep or wide diameter boreholes are needed.
A modular or demountable percussion equipment is used in spaces with limited headroom or access. This kind of apparatus is either a "downsized" variant of the typical towed tripod or is a modular rig that is trailer-transported in pieces.
For cohesive soils, a "clay cutter" is used to produce the holes; for non-cohesive materials, a "shell" (also known as a bailer) is used. To get over obstacles or extremely hard ground, use a chiselling tool.
Steel casing is lowered into the ground during the boring process to support the sides of the borehole. The casing is used to support the borehole sidewalls to enable in-situ testing and sampling if the exploratory borehole is built in sand or gravel.
Samples that have been disturbed can be taken from the shell and the clay cutter. Any cohesive layers or weak chalk may yield undisturbed samples if a hollow tube (100mm open tube sampler) is pushed into the earth. Samples of soft, typically cemented soils that have not been disturbed can occasionally be recovered using thin-walled piston samples.
Additionally, water samples can be taken, and since the steel casing closes off the borehole, there is little chance of cross-contamination when sampling water horizons at various depths. It should be mentioned, nonetheless, that a groundwater sampling well must be installed in order to obtain water samples that are entirely representative of the groundwater.
Also known as windowless sampling, is a technique that involves driving cylindrical steel tubes into the ground using a hydraulic hammer. The drilling rig is mounted on rubber tracks, so there is minimal disturbance when it operates, making it suitable for use on environmentally sensitive sites. This rig is perfect for sites with limited access, close to walls, or inside buildings, where it would be difficult to obtain samples otherwise. It can be driven through a standard domestic doorway and tracked up slopes. In areas with low-headroom or access limitations, hand-held equipment can be utilised.
A percussion action is used to achieve sampling. The drive mechanism of the rubber tracked rig is a chain-driven drop weight that strikes an anvil repeatedly, forcing the sample tubes and rods into the ground. When using the hand-held rig the samples are driven using a pneumatic hammer. Both systems can drive sample tubes into all soil types, but they are not designed for sampling or coring in hard rocks.
The sample tubes are usually 1m long and include a broad slot, or window, cut down one side. The soil is pushed into the sample tube as it is driven into the ground. Drill rods are used to drive the sample tubes to greater depths. The weight and the drop height are adjustable, enabling Standard penetration testing and dynamic probing will be performed along with soil sampling.
Upon reaching the desired depth, the sample tube and drill rods are extracted using a hydraulic jack. In cases where the ground is unstable, steel casing can be installed to prevent the borehole sides from collapsing during the extraction of the tubes. Once the sample tubes are removed from the ground, the soil core is logged and sampled through the window.
Windowless sampling may also be conducted using a conventional sample tube fitted with an inner plastic liner to facilitate the easy removal of the core from the sampler. This method allows for rapid penetration to the target depth for sampling or offers a continuous core section. The sample is retained within the plastic liner, which can then be split on-site for examination or taken to a laboratory for analysis, this sampling method minimizes the risk of soil cross-contamination during the drilling process.
The window and windowless sample tubes are chosen in a series of decreasing diameters, with available sizes ranging from 35 to 80mm, depending on the encountered ground conditions. The maximum achievable depth will vary based on soil type and any obstacles present. In certain soil types where the borehole remains unsupported, depths of up to 10m can be reached; however, typical sampling depths range from 2 to 5m.
Percussive window sampling can be conducted using a portable jack-hammer system. In this process, sample tubes are driven into the ground with a hydraulic hammer and then retrieved using a compact hydraulic jack.
This system is particularly suitable for locations with limited access where traditional window sampling rigs cannot be utilized. To address challenges such as exhaust fumes in confined spaces, extra-long hydraulic hoses can be provided to position the power pack away from the working area.
Dynamic probing consists of driving a steel cone vertically into the ground with a sliding hammer while measuring the number of blows for every 100mm of penetration. The results from dynamic probe tests can be correlated with the standard penetration test (SPT).
The dimensions and angle of the cone will vary based on the selected method. For instance, the super heavy dynamic probe (DPSH) features a cone diameter of about 50mm and a cone angle of 90 degrees.
The cone is fastened to a 1.0m long steel rod, approximately 35mm in diameter, marked at 100mm intervals. The drop height can be adjusted according to the chosen method. Typically, the super heavy method is preferred, utilizing a drop weight of 63.5kg and a drop height of around 750mm.
The cone can be either attached to the rods and retrieved after the test or designed for disposal, detaching from the rods once they are retracted at the end of the test. Typically, a torque reading of the rods is performed after every meter of penetration. An additional rod is then added, and this process continues until the probe can no longer penetrate the ground or the desired depth is reached.
The depth of penetration that can be achieved depends on the density of the material encountered. In a typical project, dynamic probes can reach depths between 5.0m and 10.0m, with around 50m of probing usually completed in a single working shift. The test was created to offer a quick and cost-effective way to evaluate the ground's penetration resistance, which can be approximately compared to equivalent SPT ‘N’ values.
With over 38 years of experience in the Geotech and Drilling industry, we have gained extensive knowledge and expertise in various aspects of the field. From Drilling and design to execution and management, we have the skills to handle any project, big or small.
Our team consists of highly skilled and experienced professionals who are dedicated to delivering quality work. We have project managers, Drilling technicians, Field technicians, and other experts who work together to ensure that every project is completed to the highest standards.
We believe in a collaborative approach to project management, where we work closely with our clients to understand their needs and goals. This allows us to provide customized solutions that are tailored to their specific requirements.
We offer a range of services, including drilling boreholes, excavating investigative hand trial pits, and conducting dynamic cone penetration testing. Additionally, we can perform soakaway testing and more. Let us assist you—contact us today to get started.