The main reason for a budget over runs on construction sites is due to inadequate understanding of the ground conditions. There are many unforeseen hazards in the ground that can only be identified by an appropriate ground investigation. A relatively small amount of investment at the outset of a project can provide large savings in the long term.
As part of the Phase II site investigation we also provide information on the ground conditions on the site, which will be required for foundation design.
We utilise a range of intrusive and non-intrusive techniques to undertake ground investigations. These include trial pitting, cable percussion boreholes, dynamic sampling, dynamic probing, plate load tests, cone penetration testing and geophysics.
We design our site investigations in line with the requirements of the “Guidelines for the Investigation by Drilling of Landfills and Contaminated Land”, published by the ICE Site Investigation Steering Group.
All staff undertaking ground investigations are engineers with appropriate qualifications and experience in geological/civil engineering disciplines, and hold current CSCS cards. All works are generally carried out in accordance with Eurocode 7 and the appropriate British standards.
All drilling rigs are operated by qualified drillers with NVQ’s in Land Drilling, CSCS certification and are first aid trained.
Drilling and Boring
We offer a full range of drilling options, from dynamic sampling and cable percussion boring in drift soils to rotary (open hole and cored) in bedrock (solid geology). Where required monitoring installations can be placed in the boreholes (gas/water monitoring wells to piezometers).
Cable Percussion Boring
Cable percussive drilling is the oldest and simplest form of drilling where advancement of the borehole is by hammering (percussion) a tool into the formation by cutting a hole or by bailing out the material. It is the most common form of drilling in the UK.
The type of rig is usually an “A” frame type, which arrives on site pulled by a four-wheel drive vehicle. Some cable percussion rigs are fitted to lorry bases and these may offer rotary drilling as well. This system of drilling is very common for geotechnical investigations but is widely used on environmental projects as well. This technique is used mainly for boring into and sampling superficial deposits rather than bedrock. The boring equipment is simple in design and comprises a cable passing from a winch, over a pulley at the top of the rig’s mast to the boring tools. The tools are lifted and dropped successively and, as they advance and the borehole is deepened, more cable is fed from the winch drum.
The boring tools are robust steel tubes with a solid weight fitted above them, around 1500 mm long and of diameters ranging from 140 mm to 300 mm. They are designed to sample the ground in that, as the open end hits the formation on the down stroke; material is forced inside and retrieved when the tool is withdrawn at the surface. Water is sometimes added to the borehole to assist in this. Different boring tools are available to suit different types of ground conditions. A shell (a round cylinder with a flap valve) is used in non-cohesive materials while a claycutter (with windows in its sides) is used in cohesive materials. When the ground contains layers of cobbles or boulders that inhibit the boring tools, a chisel can be used instead to break through and then boring resumes below.
As this technique is used mainly in soft ground conditions, the borehole may need to be lined with “casing” that is advanced at the same rate as the boring tools to maintain stability and minimise the entry of unwanted groundwater into the deepening borehole. In some circumstances, it may be necessary to use several different strings of casing and the more formations that are requiring sealing-off, the larger the diameter of casing that will be needed to start the borehole. Casings of 250 mm, 200 mm and 150 mm are conventional and it is the 150 mm diameter casing that is most commonly used. The technique may be used 