Water, Sewage & Effluent November December 2018 | Page 23

Figure 2: Cost of pipe bursting (trenchless) vs open-cut excavation for water
mains, 100mm diameter 6 .
Table 2: Comparative cost of pipe bursting and open-cut excavation for sewers 7
PIPE DIAMETER
CLASS
MATERIAL
P.O.S
RESERVE
ROAD
Nom OD ID * * *
mm mm mm R/m R/m R/m
Open-cut 160 160 151 34 uPVC 482 609 846
Pipe Bursting 160 160 150 4 HDPE
Cost Saving
368 400 458
24% 34% 46%
METHOD
2.3 Rand value
Within the Gauteng region, for every
R1-million spent on pipe replacement
using 160mm-diameter class 16
HDPE water pipe (inclusive of fittings
and reinstatement), approximately
1 000m can be replaced using open-
cut methods in comparison to pipe-
bursting,
where
approximately
1 300m can be replaced. Both
methods
employ
approximately
60 people on an ongoing basis
for the duration of the project.
Thus, the number of employment
opportunities created by trenchless
and open-cut methods are similar,
but the increased efficiency yields
approximately 30% more pipe in the
ground due to time and cost savings.
Figure 2 shows the ratio of pipe
bursting as the base cost when
compared to open-cut excavation
with shoring and excluding shoring.
In some instances, the cost of
conventional open-cut excavation
with shoring is almost 2.7 times more
expensive than the pipe bursting
alternative. A similar comparison was
done for sewer pipeline installations
as given in Table 2, which excludes
preliminary and general costs.
By summarising and scoring the
various decision-making objectives
for both a pipe bursting and open-cut
option, Table 3 was compiled.
The basic analysis given in these
tables clearly reveals that pipe
bursting is a better option than the
conventional open-cut excavation
approach whether for water or sewer
mains. In fact, the replacement of
•
direct and indirect jobs as well
as commercial opportunities for
new entrants into the construction
sector (SMMEs).
•
Thus, any type of trenchless
application is already more
efficient than the conventional
open-cut excavation approach.
In present day South Africa, the
need for service delivery is now
more urgent than ever before.
Entire areas require complete
pipeline replacement. For a
conventional open-cut excavation
project, the logistics required, in
conjunction with the interruption
created during the installation
process, makes the roll-out of
large-scale projects impractical.
With
trenchless
methods,
interruption to local road users,
inhabitants, businesses and the
environment are significantly
reduced. Large-scale projects are
ideal for trenchless applications.
The trenchless industry is a
relatively small component of
the civil engineering sector. The
implementation of trenchless
construction methods creates
a significant opportunity for
this sector to grow and result in
•
When
undertaking
any
conventional excavation work,
contractors will utilise the most
efficient means possible i.e.
mechanical excavation and not
manual labour. Labour-intensive
excavation is only feasible for
very shallow trenches in unpaved
areas as is the case for optic fibre
ducting installations along the
road verges in urbanised areas.
For any excavations deeper
than 1m (which includes most
infrastructure pipelines), several
safety measures such as lateral
support or trench shoring is
mandatory in accordance to
the country’s health and safety
regulations to safeguard the
workers against trench collapses.
The use of shoring increases the
overall cost of the installation and
reduces productivity due to the
constant installation and removal
of the shoring. Accordingly, the
objective is to reduce the length of
open excavation thereby reducing
the amount of shoring required.
innovations
•
*60m manhole to manhole length at 1.5m depth, including excavation, and reinstatements
Excludes P&Gs, lateral connections, MH benching repairs. Rates being exclusive of VAT
Source: Avenant, Martin & East
Source: S Efrat, Trenchless Technologies CC
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www.waterafrica.co.za
Water Sewage & Effluent November/December 2018
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P.O.S: Public open space, parks, open areas or undeveloped land. Reserve: Road reserve, unpaved sidewalks and
paved driveways. Road: Road surface, tarred