At Substruck, most trial holes completed form part of an investigation into possible subsidence. In most instances they are opened by hand, however in relatively deeper excavations and where space allows, we use micro diggers.
In subsidence investigation works, shallow trial holes are used to:
- Establish the depth, profile and construction of the existing foundation.
- Visually inspect the structure of the ground beneath the foundation, take samples or complete simple field tests of the soil into which it penetrates.
- Establish the presence of any water.
The depth, profile and construction of the foundation will determine if the foundation is of adequate design and construction. Furthermore, should remedial works be required, it is an important factor in determining the most appropriate approach. For example, the foundation may not be constructed at enough depth to allow for a piled raft solution or may not have any projection to allow for ground improvement.
The nature of the soil at formation level can also be inspected. The traditional method of determining the local resistance is by means of probing the ground with a crowbar. If a more scientific approach is required, dynamic probing can be completed to determine the relative resistance of the soils at formation level around the building.
A trial hole should be located as close as possible to a suspected leaking drain in order to demonstrate the insured peril to the insurance company. This may be based on evidence from a previous hydrostatic drain test or CCTV survey (See Drainage Investigation and Subsidence Investigation). A further trial hole can be excavated in other areas of the building to demonstrate the relative damage to the soil. This is known as a ‘control’ in the industry.