Segmental hollow stem augers can be installed in 200 mm and 300 mm diameters to great depths depending on ground conditions. However, this technique is limited where boulders are present as it is installed as a rotary bore only.
SFA micropiles are constructed by augering down to the required depth, which will offer suitable bearing capacity. At this point, a sacrificial bung is displaced at the bottom of the augers and the augers are filled with grout. The augers are then withdrawn whilst maintaining a head of pressure of grout through the augers. In cohesive soils, the augurs may be withdrawn without grouting.
Although we rarely use this system due to low production rates and the increasing cost of labour, this system is very applicable where micropiles are required to carry lateral loads such as secant or contiguous walls in restricted access or low headroom areas.
Normal design loads using 200 mm and 300 mm augers range from 50Kn to 300Kn in compression. As this is generally an overburden technique, tension capabilities are relatively low to those in compression.
Normally, 100% of micropiles are integrity tested and 10% subject to dynamic load testing. We can also offer static load tests if required, however, many consultants consider the dynamic tests sufficient due to the associated costs.
Our rig can operate in restricted access and low headroom areas and is powered by a separate diesel power pack so fumes are not a concern. The system is also dust-free due to the rotary nature of installation.
Advantages:
- Works in tension and compression,
- Minimal vibration,
- Low head room,
- Limited access,
- No dust,
- Low cost of materials.
Disadvantages:
- Low productivity,
- Increased manual handling,
- Cannot penetrate boulders or bedrock,
- Low tension capabilities, particularly in low overburden.