Civil Engineering Reference
In-Depth Information
Temporary slope profile
1
1
In-situ r.c. capping beam
Anchor pile
Tension pile
Gravity piles
Figure 3.38
Cross section of Horsfall tunnel showing ground support with micro-piles. (Illustration
courtesy of White Young Green Environmental.)
3.6.2 Installation methods
As for larger piles, there are two main methods of installation: non-displacement
(i.e. drilling/boring cast-in-place methods) or displacement (e.g. driven) methods.
3.6.2.1 Non-displacement micro-pile installation
(i)
Drilled or bored cast-in place methods
. Such methods vary according to the type
of soils encountered. It is usual to employ a small crawler mounted rig which
has a low mast and hydraulic rotary head although the motive power for the
drilling or boring (using an auger) may also be electric or pneumatic. Micro-pile
rigs need to be versatile because of the variety of uses to which the piles may serve.
Therefore rigs need to be capable of forming boreholes in diameters ranging from
around 100 to 250mm (or even 300mm) though a variety of natural materials
in areas of confined space or limited headroom. Also however, materials such
as concrete, steel, timber or natural obstructions, may be encountered, and if
the rig itself cannot form a hole through such obstructions, especially reinforced
concrete forming an existing foundation, a diamond coring facility or a down-hole
percussive rig will be needed as an adjunct. In stiff cohesive soils, continuous flight
