1000 Hydraulics Chapter - Ministry of Transportation

BC MoT
SUPPLEMENT TO TAC GEOMETRIC DESIGN GUIDE
MoT Section 1040 TAC Section Not Applicable
1040.04 CULVERT INSTALLATION
Some miscellaneous notes:
• Culvert Installation shall generally conform to the
current MoT Standard Specifications for Highway
Construction, Section 303.
• Designate re-corrugated culvert ends with annular
couplers for helical CSP culverts where the
installation will be on a gradient greater than 15%.
• Annular couplers shall be indicated on the drawings,
the additional materials list, and the H741 and H742
forms.
Foundation Excavation/Base Preparation
Foundation excavations for culverts less than 3000 mm
diameter are shown in Figure 1040.G. Special
conditions apply to SPCSP.
For information on base preparation, refer to:
♦ The current MoT Standard Specifications for
Highway Construction, Section 303.
Backfill/Bedding
For information on backfill or bedding, refer to:
♦ The current MoTH Standard Specifications for
Highway Construction, Section 303.
Camber
In situations involving weak foundation soils or high fills,
camber should be considered to account for anticipated
settlement.
For information on camber, refer to:
♦ CSPI Handbook of Steel Drainage and Highway
Construction Products (2002), p. 309.
♦ RTAC Drainage Manual Volume 2 (1982), p. 4.14.
Headwalls and Wingwalls
A culvert with mitered ends may require headwalls to
provide reinforcement by securing the metal edges at the
inlet and outlet against earth pressures and hydraulic
forces. Headwalls may also be used to counter-weigh
hydrostatic uplift and prevent end scour.
Wingwalls should be considered for culverts which
require end extensions, improved inlet capacity or are in
areas with debris or severe scour problems. The purpose
of wingwalls is to retain and protect the embankment, and
provide a transition between the culvert and the channel.
Normally they will consist of flared vertical wingwalls, a
full or partial apron and a cutoff wall.
For information on end structures, refer to:
♦ RTAC Drainage Manual Volume 2 (1987), p. 4.104.
Cutoff Walls
The inlets of CMP, PVC and HDPE culverts are
susceptible to hydrostatic lift and may collapse due to this
effect. To prevent undermining and uplift, concrete cut
off walls shall be constructed at the ends of culverts equal
to or greater than 900 mm diameter or span.
For information on typical cutoff walls, refer to:
♦ CSPI Handbook of Steel Drainage and Highway
Construction Products (2002),Fig. 6.27, p.300.
Safety
For culverts larger than 2000 mm and located within the
clear zone, the culvert ends can be made safe by the use
of suitable grates, but only if the grates do not become a
hazard by causing upstream flooding. Culverts in urban
environments require grates to prevent human entry.
Grates are generally not permitted on culverts which
provide fish passage.
Grates are also installed to prevent debris from entering
the culvert. For culverts providing fish passage, debris
racks rather than grates, should be installed.
At locations where culverts ends cannot be located
outside the clear zone and where grates would be
impractical or unsafe, roadside barrier protection should
be provided.
For information on safety measures, refer to:
♦ RTAC Drainage Manual Volume 2 (1987), p. 4.15.
Multiple Installations
For multiple pipe installations, one inlet should be lower
than the others so that at low to medium flows the water
is concentrated in one pipe. This is conducive to fish
passage and discourages silting up of the installation.
For multiple pipes and installations refer to:
♦ CSPI Steel Drainage and Highway Construction
Products (2002), p. 181, p. 336.
Page 1040-10 June, 2007