After finishing
the pilot bore, reaming and pipe installation step begin depend on pipe size,
the hole is reamed in two or more steps to enlarge the hole to accept the pipe
(usually 1.5 times of pipe diameter). Then pipe is attached to drill string
with a pulling head as a cap and a swivel and pulled back to entry pit. Reamer
should be selected and designed base on soil type to bring the best result. For
small installation, a vacuum truck can be used to vacuum and dispose the mud and
cuttings but for a large installation, fluid can be recycled by special units
such as combination of centrifuge pumps, tanks with baffles, shaker screens and
desanding and desilting hydro-cyclones .

The major
challenge that faces HDD is a change in the soil profile. These changes can
result in difficulty in controlling the drill rod direction, drilling fluid
loss in soil voids and inability to advance to the exit point. Certain soil
types such as dense clay tills, gravels, soils containing cobbles and boulders
and highly compacted gravel and sand layers (ASTT, 2009b) can be challenging.

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