Geology Reference
In-Depth Information
to prepare maintenance manuals for slopes and to carry out
routine engineer inspections at regular intervals. New and newly
upgraded slopes are generally constructed with access ladders
andoftenwithhandra lsprovidedalongbermstoa lowsafe
inspection.
6.7 Site formation, excavation and dredging
6.7.1 Excavatability
Site excavation is usually carried out by heavy machinery, and the
main questions for the engineering geologist are what machinery
would be suitable and whether the rock would need to be blasted
rst.
Where blasting is restricted, then the contractor might need to
use some kind of chemical or hydraulic rock splitter, but the noise
levels of drilling and rock breaking might still be a problem.
Generally, the factors that will control whether or not blasting is
needed are intact rock strength and the spacing between joints
(MacGregor et al ., 1994; Pettifer & Fookes, 1994). As emphasised
elsewhere, care must be taken to differentiate between mechanical
fractures with low tensile strength and incipient fractures with
high strength as this will strongly affect the ability of machines
to rip the rock.
6.7.2 Dredging
Dredging (underwater excavation) is commonly carried out for port
works, to improve navigation on rivers and as part of other land
reclamation projects in providing
fill material (Bray et al ., 1997).
There are several types of dredger and these vary in their capacity to
deal with soil and weak rock. Where there are few natural fractures in
the weak rock, excavations can be dif
cult, even for the strongest
suction-cutter dredgers and then some pre-treatment, normally blasting,
will be required. Reviews on dredging practice in various countries,
including the USA, UK, Hong Kong and Singapore, are given in Eisma
(2006).
6.8 Ground improvement
6.8.1 Introduction
At many sites, the ground conditions are too weak or wet to allow
construction by the preferred method or even to allow access by heavy
 
 
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