Geotechnical Site Investigation

By: Gillian Hogarth | 0 Comment

Geotechnical Site Investigation and Soil Sampling

In recent times Compact Lightweight Drilling and Sampling Machines have become very popular.

Several companies manufacture excellent compact soil sampling machines including:

Dando Terrier http://www.dando.co.uk/geotechnical-site-investigation

Archway Competitor http://www.archway engineering.com/products/competitor_index.html

Premier Plant http://www.premierplantengineering.co.uk/

Equipment for this method of ground penetration and sampling can be rapidly deployed on a trailer behind a 4×4 vehicle or inside of a panel van.
The generally rubber tracked machines can move quickly around a site causing minimal surface damage while obtaining good quality representative samples of strata beneath the site usually to depths of around 10mtr although in favourable conditions this depth can be substantially increased.

Geotechnical Exploration Services carries out this work using machines fitted with a drop hammer that can rapidly be replaced with a rotary drillhead enabling penetration into bedrock including coring to 50mtr.

A range of cutting and sampling tools has been designed for use with this type of shallow ground investigation.

Concrete Coring Barrels

On many sites it is necessary to cut through concrete or tarmac and other man made materials in order to gain access to the ground that is to be investigated. A concrete cutting/coring barrel is used for this and consists of a tube with a diamond impregnated shoe easily capable of cutting the hardest of materials including reinforced concrete. The top of the tube is fitted with a water swivel for injection of water to cool the bit and clear drill cuttings.

Window & Windowless Sampling Tubes

Window sampling tubes are usually 1mtr – 2mtr long. They have a cutting shoe on the leading edge and slots or windows up the side which give direct access to the sample. They are driven into the ground by a drop weight or hydraulic hammer. Casing is advanced during sampling when needed to stabilise collapsing strata.

Other similar types of sampling tubes have no windows (windowless) but have removable clear plastic liners which can be sealed to maintain integrity and then cut open along their length in the laboratory where they are logged, analysed and samples are tested giving excellent representative information on the site being investigated.

Other geotechnical information can be gathered during this type of ground investigation.

Standard Penetration Tests (SPT) to BS1377B

A test to estimate the degree of compactness of soil in place by counting the number of blows required to drive a standard sampling spoon 1′ (0.3 meter) using a 140 pound (64 kilogram) weight falling 30″ (0.8 meter).

Dynamic Probing (BS 1377 Part 9)

This test is done to determine the penetration resistance of soil and consists of dropping a hammer onto an anvil over a distance of 300mm and at a rate of between 20 and 60 blows per minute. The anvil is directly connected via rigid rods to the probe which is resting on the strata at the base of a hole. Blows are counted and recorded for every 100mm of penetration.

U100 Sampling
This is a sampling method whereby a sampling tube is driven into the ground (usually clay type material). Samples are retained in the tube by fingers at the base which grip when the tube is lifted from the base of the hole. There are several systems od U100 samplers – U100 Standard System, U100 Plastic Liner System & U100 Thin Wall System.

BOREHOLES ARE OUR BUSINESS

Dave Gowans

Managing Director

Drilcorp Ltd