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Cleanings
Inspection scheme
Inspection procedure
Rehabilitation
Rehabilitation procedure
Renovation
Figure 7.
Figure 8.
Figure 15.
Figure 16. Figure 17.
Inspection technique
Damages
Repair
Reason for repair
Replacement
Figure 6.
industry review
April 2010 - Trenchless International
€5.50 per piece and the cleaning costs
of a SS averaging at €12.60 per piece.
The cleaning costs accrued for different
road gullies all over Germany amount to
approximately €251 million.
Inspection of road gullies
These questions dealt with inspection
procedures and inspection techniques as
well as the existent damage potential of
road gully systems.
Inspection scheme
Approximately 20 per cent of local
authorities confirmed that road gullies
and their connection sewers were
included in the sewer inspection scheme
(see Figure 7). Consequently, we can
record that only one fifth of the participating
local authorities are aware of the
significance of their road gully systems
and keep informed about their current
state on a regular basis.
The same cannot be said of the public
sewer system. According to the DWA [4],
inspections of sewers and manholes are
carried out in about 80 per cent of the
local authorities. However, the actual state
of laterals is only recorded in 9.7 per cent of
the local authorities. This can be ascribed
to the fact that laterals are privately owned
and are not usually operated by local
authorities.
Inspection procedure and technique
Figure 8 shows the inspection procedures
used on road gully systems. The majority
of the local authorities (67 per cent) check
Figure 9.
their road gully systems by visual inspections,
however this method only allows
the detection of gross damages in the
area of the road surface and in the
upper part of the corpus, and an explicit
statement concerning the leak tightness
of the road gully (SB) and the waterless
corpus above the sludge space (SS)
cannot be made.
Connection sewers are inspected both
via road gullies and public sewers (see
Figure 9). The TV-satellite camera is
mainly used out of sewers (86 per cent).
In 14 per cent of cases, the inspection of
connection sewers is carried out by reflection
out of the sewer.
Leak tightness testing
Only ten per cent of the local authorities
carry out leak tightness testing at road
gullies after road construction. The lack of
leak tightness testing has been attributed
to a lack of experience, and a lack of special
guidelines, rules and standards.
Types of damages of road gullies
As shown in Figure 10, the most common
form of road gully damage is positional
Figure 10.
Documentation
Figure 11.
Figure 12. Figure 13. Figure 14.
deviations of the top (30 per cent) and
congestions (26 per cent). Broken frames
are the next most common type of damage
(15 per cent), followed by leakages in
the wall area (14 per cent), and leakages
in the bottom area (7 per cent).
Documentation
Only 35 per cent of local authorities
document the actual state of road gullies
(see Figure 11).
This result means that the majority (65
per cent) of the local authorities do not
have records of the state of road gullies,
which are important for future planning.
Number of defective road gullies
Figures 12 and 13 show the distribution
of defective road gullies SB and SS.
Of the 68 per cent of the local authorities
who responded in full to this question,
13 per cent make an average damage
potential for SB and 17 per cent for SS.
The statistical spread of the number of
damages is very wide-ranging there,
ranging from less than 1 per cent to
55 per cent. This data is not based on
results of inspections that were carried
Figure 18. Figure 19. Figure 20.
out, but on a subjective assessment by
network operators. Provided that only data
of network operators is taken into account,
it shows damage potential of between 40
per cent and 55 per cent.
Rehabilitation of road gully systems
Questions in the final section of the survey
dealt with rehabilitation procedures,
techniques, practised rehabilitation strategies
and accruing costs.
Reason for launching
rehabilitation action
The main reasons for launching rehabilitation
action of road gullies were
positional deviations of the top (43 per cent)
and broken frames (19 per cent) (see
Figure 14). This may relate to the fact that
positional deviations on the road surface
are recorded within the scope of sewer
rehabilitation and maintenance and that
they require urgent remedial action due to
the risk of endangering traffic.
The main reasons for launching rehabilitation
action of sewers are ingrown
roots (20 per cent) and congestions
(17 per cent), as well as pipe fractures and
collapses (19 per cent) (see Figure 15).
Rehabilitation procedures of road
gullies and connection sewers
The rehabilitation of road gullies was
carried out by repair (48 per cent) and
replacement (52 per cent) (see Figure 16).
In the course of rehabilitation action of
connection sewers, renovation (13 per cent)
took place in addition to repair (44 per
cent) and replacement (43 per cent) (see
Figure 17).
Repair of road gully systems
The predominant reasons for repair
measures of road gullies were positional
deviations/settlement of the top (33 per
cent), followed by broken frames and
leakages due to rust (24 per cent), and
bursting joints (14 per cent). Ingrown
roots, congestions, and other damages
played a minor part with a percentage of
less than 10 per cent (see Figure 18).
The most frequent reasons for launching
repair measures of connection sewers
were pipe fractures (21 per cent), ingrown
roots (19 per cent), and the formation of
shatter cracks (16 per cent). Altogether,
these constitute a share of more than
50 per cent (see Figure 19).
Replacement of road gully systems
The most common reasons for launching
replacement action of road gully
systems are road renewals or road
reconstructions (39 per cent), sewer
replacement (32 per cent), and severe
damages to road gullies (29 per cent), for
example cracks or positional deviations
(see Figure 20).
Concerning replacement measures of
road gullies, there is a clear trend in favour
of the SB type (66 per cent). The SS type
is employed only half as often.
Number and costs
The number of repairs and replacements
of road gullies launched strongly
depends both on the size of the
local authority and the number of the
installed road gullies. On average, 182
road gullies are repaired and 105 road
gullies are renewed annually per local
authority.
The survey showed that the costs of
replacement are more than twice as
high for road gullies than for repair. The
replacement of a road gully represents the
most cost-intensive recovery procedure
with a maximum of €1,500 and an average
of €1,000. In comparison, the repair of a
road gully is cheaper and amounts to an
average of about €450.
Summary
Based on the results of the survey,
15.2 million road gully systems exist in
Germany, with an average of 15 per cent
of these showing defects. This translates
to 2.2 million defective road gullies across
Germany. Based on the rehabilitation
costs for SB and SS road gullies, it would
cost €1.63 billion to repair the 2.2 million
defective road gullies.
The results of the survey confirm that
the maintenance of road gully systems in
drain and sewer networks is a necessity,
otherwise the already known technical,
ecological and economical defects of
sewer systems will shift their damage
consequences to gully systems.
This article is an edited version of UNITRACC's Survey on the Condition of Road Gully Systems in Germany
(Part 2). For more information, acknowledgements and references please see the original. All graphics are
sourced from S & P Consult.
Did you miss Part 1? Visit www.trenchlessinternational.com and enter ‘road gully’ in the search field.
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