(1)
Location.
(a)
Routing -- General.
1. Conduit systems should be located so as to
be subject to the least disturbance 410 practical. Conduit systems extending
parallel to other subsurface structures should not be located directly over or
under other subsurface structures., If this is not practical, the rules on
"Clearances" (see 220 CMR 126.32(1)(g)) should be followed.
2. Conduit alignment should be such that
there are no protrusions which would be harmful to the cable.
3. When bends are required, the minimum
radius shall be sufficiently large to prevent damage to cable being installed
in the conduit.
(b)
Routing -- Natural Hazards. Routes through unstable
soils such as mud, shifting soil, etc., or through highly corrosive soils,
should be avoided. If construction is required in these soils, the conduit
should be constructed in such a manner as to minimize movement and/or
corrosion.
(c)
Routing
-- Highways and Streets. When conduit must be installed
longitudinally under the roadway, it should be installed in the shoulder or
within the limits of one lane of traffic if practical.,
(d)
Routing -- Bridges and
Tunnels. The conduit system shall be located so as to minimize the
possibility of damage by traffic. It should be located to provide safe access
for inspection or maintenance of both the structure and the conduit
system.
(e)
Routing --
Crossing Railroad Tracks.
1. The
top of a conduit system should be located not less than 36 inches below the top
of the rails of a street railway or 60 inches below the top of the rails of a
railroad. Where unusual conditions exist or where proposed construction would
interfere with existing installations, a greater depth than specified above may
be required.
Exception: Where this is impractical,
or for further other reasons, this clearance may be reduced by agreement
between the parties concerned and the Department. In no case, however, shall
the top of the conduit or any conduit protection extend higher than the bottom
of the ballast section which is subject to working or cleaning.
2. All crossing under railroads,
manholes, handholes, and vaults should not, where practical, be located in the
road bed.
(f)
Routing -- Submarine Crossings. Submarine crossings
should be routed and/or installed so they will be protected from erosion by
tidal action or currents. They should not be located where ships normally
anchor.
(g)
Clearances
from Other Underground Installations.
1.
General. The
clearance between a conduit system and other underground structures paralleling
it should be as large as necessary to permit maintenance of the system without
damage to the paralleling structures. A conduit which crosses over another
subsurface structure shall have a minimum clearance sufficient to prevent
damage to either structure. These clearances should be determined by the
parties involved.
Exceptions: When conduit crosses a
manhole, vault or subway tunnel roof, it may be supported directly on the roof
with the concurrence of all parties involved.
2.
Separations Between Supply and
Communication Conduit Systems. Conduit systems to be occupied by
communication conductors shall be separated from conduit systems for supply
conductors by: three inches of concrete, or four inches of masonry, or 12
inches of well-tamped earth.
Exception: Lesser separations may be
used where the parties concerned concur.
3.
Sewers. Sanitary and
Storm. If conditions require a conduit to be installed parallel to
and directly over a sanitary or storm sewer, it may be done provided both
parties are in agreement as to the method. Where a conduit run crosses a sewer
it shall be designed to have suitable support on each side of the sewer to
prevent transferring any direct load onto the sewer.
4.
Water Lines.
Conduit should be installed as far as is practical from a water main in order
to protect it from being undermined if the main breaks. Conduit which crosses
over a water main shall be designed to have suitable support on each side as
required to prevent transferring any direct loads onto the main.
5.
Fuel Lines.
Conduit shall have sufficient clearance from fuel lines to permit the use of
pipe maintenance equipment. Conduit and fuel lines shall not enter the same
manhole.
6.
Steam
Lines. Conduit should be so installed as to prevent detrimental
heat transfer between the steam and conduit systems.
(2)
Excavation and
Backfill.
(a)
Trench. The bottom of the trench should be
undisturbed, tamped, or relatively smooth earth. Where the excavation is in
rock, the conduit should be laid on a protective layer of clean tamped
backfill.
(b)
Quality
of Backfill. All backfill should be free of materials that may
damage the conduit system.
Recommendation: Backfill within six
inches of the conduit should be free of solid material greater than four inches
in maximum dimension or with sharp edges likely to damage it. The balance of
backfill should be free of solid material greater than eight inches in maximum
dimension. Backfill material should be adequately compacted.
(3)
Ducts and
Joints.
(a)
General.
1. Duct
material shall be corrosion-resistant and suitable for the intended
environment.
2. Duct material
and/or the construction of the conduit shall be designed so that a cable fault
in one duct would not damage the conduit to such an extent that it would cause
damage to cables in adjacent ducts.
3. The conduit system shall be designed to
withstand external forces to which it may be subjected by the surface loadings
set forth in 220 CMR 126.32(4) except that impact loading may be reduced 1/3
for each foot of cover, so no impact loading need be considered when cover is
three feet or more.
4. The internal
finish of the duct shall be free of sharp edges or burrs which could damage
supply cable.
(b)
Installation.
1.
Restraint. Conduit, including terminations and bends,
should be suitably restrained by backfill, concrete envelope, anchors or other
means to maintain its design position under stress of installation procedures,
cable pulling operations and other conditions such as settling and hydraulic or
frost uplift.
2.
Joints. Ducts shall be joined in a manner sufficient
to prevent solid matter from entering the conduit line. Joints shall form a
sufficiently continuous smooth interior surface between joining duct sections
so that supply cable will not be damaged when pulled past the joint.
3.
Externally Coated
Pipe. When conditions are such that externally coated pipe is
required, the coating shall be corrosion-resistant and should be inspected
and/or tested to see that it is continuous and intact prior to backfill.
Precautions shall be taken to prevent damage to the coating when
backfilling.
4.
Building Walls. Conduit installed through a building
wall shall have a seal (or seals) intended to prevent the entrance of gas or
water into the building insofar as practical. The use of seals may be
supplemented by gas venting devices in order to minimize building up of
positive gas pressures in the conduit.
5.
Bridges. Conduit
installed in bridges shall include the capability to allow for expansion and
contraction of the bridge.
Conduits passing through a bridge abutment should be installed
so as to avoid or resist any shear due to soil settlement;
Conduit of Conductive material installed on bridges shall be
effectively grounded.
6.
In Vicinity of Manholes. Conduit shall be installed on
compacted soil, or otherwise supported when entering a manhole to prevent shear
stress on the conduit at the point of manhole entrance.
(4)
Manholes,
Handholes, Vaults.
(a)
Strength. Manholes, handholes and vaults shall be
designed to sustain all expected loads which may be imposed upon the structure.
The horizontal and/or vertical design loads shall consist of dead load, live
load, equipment load, impact, load due to water table, frost and any other load
expected to be imposed upon and/or occur adjacent to the structure. The
structure shall sustain the combination of vertical and lateral loading that
produces the maximum shear and bending moments in the structure.
1. In roadway areas, the live load shall
consist of the weight of a moving tractor -- semi trailer truck illustrated in
220 CMR 126.32 Figure 1. The vehicle wheel load shall be considered applied to
an area as indicated in 220 CMR 126.32 Figure 2. In the case of multilane
pavements, the structure shall sustain the combination of loadings which
results in vertical and lateral structure loadings which produce the maximum
shear and bending moments in the structure.
Note: Loads imposed by equipment used
in road construction may exceed loads to which the completed road may be
subjected.
2. In designing
structures not subject to vehicular loading, the minimum live load shall be 300
pounds per square foot.
3. Live
loads shall be increased by 30% for impact.
4. When hydraulic, frost or other uplift will
be encountered, the structure shall be of sufficient weight or so restrained as
to withstand this force: The weight of equipment installed in the structure is
not to be considered as part of the structure weight.
5. Where pulling iron facilities are
furnished, they should be installed with a factor of safety of two based on the
expected load to be applied to the pulling iron.
Click to view
imageV = Variable spacing -- 14 feet to 30 feet. Spacing to be used
is that which results in vertical and lateral structure loading which produces
the maximum shears and bending moments in the structure.
Click to view
image
(b)
Dimensions.
Manholes shall meet the following requirements:
A clear working space sufficient for performing the necessary
work shall be maintained. The horizontal dimensions of the clear working space
shall be not less than three feet. The vertical dimensions shall be not less
than six feet except in manholes where the opening is within one foot,
horizontally, of the adjacent interior side wall of the manhole.
Exception 1: Where one boundary of the
working space is an unoccupied wall and the opposite boundary consists of
cables only, the horizontal working space between these boundaries may be
reduced to 30 inches.
Exception 2: In manholes containing
only communications cables and/or equipment, one of the horizontal dimensions
of the working space may be reduced to not less than two feet, provided the
other horizontal dimension is increased so that the sum of the two is at least
six feet.
(c)
Manhole Access Openings.
1. Round access openings in a manhole
containing supply cables shall be not less than 26 inches in diameter. Round
access openings in any manhole containing communication cables only or manholes
containing supply cables having a fixed ladder which does not obstruct the
opening, shall be not less than 24 inches in diameter. Rectangular access
openings should have dimensions not less than 26 inches by 22 inches.
2. Openings shall be free of protrusions
which will injure personnel or prevent quick egress.
(d)
Covers.
1. Manholes and handholes, when not being
worked in, shall be securely closed by covers of sufficient weight or proper
design so they cannot be easily removed without tools.
2. Covers should be suitably designed or
restrained so that they cannot fall into manholes or protrude into manholes
sufficiently far to contact cable or equipment.
3. Strength of covers and their supporting
structure shall be at least sufficient to sustain the applicable loads of 220
CMR 126.32(4)(a).
(e)
Access.
1. Vault or
manhole openings shall be located so that safe access can be provided. When in
the highway, they should be located outside of the paved roadway when
practical. They should be located outside the area of street intersections and
crosswalks whenever practical to reduce the traffic hazards to the men working
at these locations.
2. Personnel
access openings in vaults or manholes should be located so that they are not
directly over the cable or equipment. Where these openings interfere with
curbs, etc., they may be located over the cable if one of the following is
provided:
A conspicuous warning sign,
A protective barrier over the cable,
A fixed ladder.
In vaults, other types of openings may be located over
equipment to facilitate work on this equipment.
(f)
Access Doors.
1. Where accessible to the public, access
doors to utility tunnels and vaults shall be locked unless qualified persons
are in attendance to prevent entry by others.
2. Such doors shall be designed so that a
person on the inside may exit when the door is locked from the outside.
Exception:
220 CMR 126.00 does not
apply where the only means of locking is by padlock and the latching system is
so arranged that the padlock can be closed on the latching system to prevent
unauthorized locking from the outside.
(g)
Ladder
Requirements. Fixed ladders shall be painted or otherwise treated
to resist corrosion when location demands.
(h)
Drainage. Where
drainage is into sewers, suitable traps or other means should be provided to
prevent entrance of sewer gas into manholes, vaults or tunnels.
(i)
Ventilation.
Adequate ventilation to open air shall be provided for manholes, vaults and
tunnels, having an opening into enclosed areas used by the public. Where such
enclosures house transformers, switches, regulators, etc., the ventilating
system shall be cleaned at necessary intervals.
Exception: This does not apply to
enclosed areas under water or in other locations where it is impractical to
comply.
(j)
Mechanical Protection. Supply cables and equipment
should be installed or guarded in such a manner as to avoid damage by objects
falling or being pushed through the grating.
(k)
Identification.
Manhole and handhole covers should have an identifying mark which will indicate
ownership or type of utility.
