Highway Slope Manual

62
Filling operations for a highway project may have to be carried out simultaneously at a
number of places at long distances apart. In these circumstances, careful planning should be
made to ensure that adequate experienced site staff are available for supervising the placement
and compaction of fill and drainage and filter materials, and for conducting any necessary
compaction control supervision, arranging the sampling and testing, interpretation of test
results and keeping traceable records.
During excavation for the construction of a road, overspill of soil and rock spoil onto
the slopes below may occur. These materials can easily be obscured by existing natural
vegetation or vegetation that subsequently grows on them. Depending on their locations and
geometry, they may pose a hazard if they slide or liquefy in the event of heavy rain. Care
should be taken to avoid such overspill or to ensure that such materials are removed at the
earliest practicable time once they are identified.
Adequate temporary surface water drainage and slope surface protection should be
provided for excavations or fill embankments, especially where large areas are opened up for
the road construction in the wet season and there is a significant catchment channelling
rainwater into the area (see Sections 9.3 and 9.4.5 of the Geotechnical Manual for Slopes
(GCO, 1984)). Where the road crosses existing drainage/stream courses, temporary
diversion of the surface water will be necessary during construction. The effect of the
temporary flow on slope stability and existing drainage should be assessed.
An examination of the performance of the permanent surface water (slope and road)
drainage provisions should be carried out during construction, taking into account the actual
site and weather conditions encountered. Where necessary, improvement should be made in
consultation with the designer, who should make a careful inspection to finalise the details.
Activities that could present a public safety hazard and the sensitive receivers should
be identified. Where rock excavation or removal of spoil is to be carried out near an existing
road and the potential consequence of falling debris is significant, adequate protective
measures and/or any necessary road closure or traffic diversion should be implemented prior
to the work. A survey of the condition of the nearby slopes and likely affected facilities
should be conducted, with photographs and/or video taken of any visible signs of distress and
structural defects, before the work commences. Where it is judged that the potential volume
of falling rock cannot be adequately contained by the protective works, the contractor should
be requested to modify his proposed working methods before the work can proceed.
Contingency measures should be put in place to clear any fallen debris and repair the
protective works quickly to allow the road to re-open within an acceptable period of time. In
some situations, rockfall preventive works may have to be implemented in addition to
protective measures. Where blasting is involved, the existing slopes alongside the road
which may be affected by the blasting operation should be inspected prior to and after each
blast and their stability conditions reviewed and certified by a geotechnical engineer prior to
making arrangements for re-opening the road (eung, 1998). Further guidance on rock
removal from slopes along roads is given in Section 7.3 below.
Monitoring installations for evaluation of construction effects on sensitive receivers
(e.g. movement and vibration monitoring points) and for verification of design assumptions
(e.g. piezometers) should be protected. These should be repaired/replaced where necessary
if damaged by construction activities.
For major road projects, the Design and Build form of contract is sometimes used.
For such contracts, the contractor should be required to engage an adequate number of