What Does Intrusive Investigation Mean?
An intrusive investigation is the physical part of geotechnical investigation and involves in-situ testing of soil and sampling of the soil and groundwater using trial pits and boreholes. It is designed on the basis of findings obtained from reconnaissance and desk study.
Intrusive investigation is only one stage of geotechnical site investigation, the others being:
- Data and map study (or desk study.)
- Laboratory testing.
An intrusive investigation is also known as an intrusive site investigation or in-depth investigation.
Trenchlesspedia Explains Intrusive Investigation
For intrusive site investigation, drill rigs are used to access the soil at the desired depth. Different techniques such as trial pits, boreholes and probing are used.
A trial pit is a shallow intrusive investigation method. Trial pits can indicate lateral and vertical variation in the ground condition that is not detectible by other methods. Other shallow methods include digging observation pits and trenches as well as inspection pits.
Boreholes penetrate to deeper strata than trial pits while causing less disturbance. They can penetrate any type of strata, and the most commonly used methods for drilling boreholes are percussion boring and rotary drilling.
Probing uses a steel rod about 25mm in diameter that is driven into the ground to probe or sound. The resistance to driving the rod, and the particles that stick to the rod when it is pulled out, indicate the properties of the soil. There are two types of probing: dynamic and static.
The encountered ground conditions are recorded, then undisturbed and disturbed soil samples are taken from the desired depth and inspected.