Geotechnical Drilling

What a Geotechnical Investigation Tells You

The first step in onsite construction is site analysis. You need to know what is there, not just on the surface but metres below, so the structure stands the test of time. Sample locations are chosen with your quality control professionals to build a picture of the subsurface material throughout the site.

A properly executed investigation identifies unsafe rock, establishes soil conditions and determines the integrity of the site. Where that work is skipped or rushed, the consequences show up later as uneven settling, cracked walls and plumbing that moves, and in serious cases as a foundation that has to be rebuilt entirely.

Investigation is equally important on existing structures. Subsurface material can degrade or erode over time, so where a building is showing damage or movement, a comprehensive subsurface analysis is what makes the repair sound for the long term rather than temporary.

Sampling and In Situ Testing

Different ground and different design questions call for different methods, and we carry the range so the programme is not limited by the rig on site.

Solid flight augering from 90 to 300 mm and hollow flight augering cover most soil profiles and let samples be taken at depth through the core of the auger. Push tube sampling using Macrocore and dual tube systems recovers a continuous column of material where the profile itself matters.

For in situ strength, we run automatic standard penetration tests and super heavy dynamic probing, and take U75 and U63 undisturbed tube samples where the laboratory needs material in its natural condition. Packer testing measures the permeability of the ground in place, which matters wherever water movement is part of the design question.

Coring, Rock and Angle Drilling

Where the investigation reaches rock, conventional diamond coring in NMLC and PMLC sizes and wireline diamond coring in NQ, HQ and PQ recover intact core for logging. Rotary air blast and down hole hammer give us penetration through harder formations, and mud drilling supports the hole where the walls will not stand on their own.

Tubex advance casing lets us case as we drill through unstable ground, so the hole stays open and the samples stay representative. Angle drilling covers investigations that cannot be taken vertically, and concrete coring from 60 to 500 mm handles slabs and structures that sit over the area to be investigated.

Instrumentation and Monitoring

An investigation does not always end when the rig leaves. We install inclinometers for measuring ground movement over time, and monitoring wells where groundwater levels or quality need to be tracked across a period rather than captured once. Where the scope extends into contamination assessment, our environmental drilling crews cover soil, groundwater and soil vapour sampling.

Non Destructive Drilling Support

Geotechnical work frequently happens on live sites, in car parks, against existing buildings and above underground services. Our drilling is supported by dedicated Non Destructive Drilling crews who can concrete core and air or water vacuum excavate boreholes in advance of the drill crews.

On many sites this combined approach is the more efficient way to complete an incident free investigation on time and on budget, because it removes the guesswork about what sits in the first few metres before a rig is ever set up over the hole.

Rigs and Site Access

BG Drilling operates a fleet of 20 drill rigs, from hand portable equipment through to truck mounted and tracked units. Tougher ground calls for a bigger machine, and constrained sites call for the opposite, so having the range means we can match the rig to the site rather than asking the site to accommodate the rig.

For confined locations we run 9 dedicated tight access rigs with a small footprint and low impact, which keeps investigations viable inside buildings, in basements, in rear yards and on constrained blocks. Where the work forms part of a wider civil package, we also provide construction and civil drilling including road pavement investigations and test pits.

Talk to BG Drilling about your next geotechnical site investigation. Tell us the site constraints, the depths and the testing your engineer has specified, and we will tell you which rig and methods suit. Get in touch.