CEMP-E
TI 810-32
10 January 2002
floor, and top thicknesses shall be 6 inches, minimum. However, thicker sections may be required to
accommodate site specific loadings or to prevent flotation. Concrete trench floors shall be sloped at a 1
inch in 20 feet slope toward all low points to ensure proper drainage. Doweled or keyed joints and water
stops shall be provided at all construction joints and shall be detailed as shown in figure 4-6. Trench
reinforcing details will be provided and will be similar to the section shown in figure 4-7. Note that actual
concrete thicknesses and reinforcing bar sizes will be verified by the designer for each project. Trench
corners will be constructed as detailed in figure 4-8. Trench tops will be no longer than eight feet to allow
easy removal and placement.
c. Trench Top Removal Devices. The most common type of removal devices for the trench tops
will be the sling type as detailed in figure 4-9. Four lifting devices are required to lift a trench top. One set
of lifting devices will accommodate all trench tops for each contract. In some instances, sling type lifting
devices will not be convenient to use (eg. when the trench top butts up against a parallel sidewalk or when
the trench is routed through a parking area). In these instances, the designer shall require coil inserts to
be cast into the trench cover in four locations that will accommodate threaded lifting eye bolts. When not
being used, threaded plugs are inserted into the coil inserts. The lifting devices are also detailed in figure
4-9.
d. Road and Parking Lot Crossings. Road crossing requirements will be designed on a case by
case basis and must take int o account pavement materials, soils, and frost characteristics of the design
site. A typical road crossing is shown in figure 4-10. Figure 4-11 details a concrete trench to curb and
gutter system transition and figure 4-12 details a concrete trench to drain pan system transition. In all
instances, the crown of the road crossing will be matched and the thickness of the trench top will be
designed to accommodate worst case loadings. Parking lot crossings typically will have the trench top
exposed at grade as shown in figure 4-13. Exposed tops allow for easier trench top removal over
extended lengths of paved areas. If appearance of the crossing is critical, black pigments may be added
to the concrete tops at the road crossing to match the surrounding pavement. In rare instances, the
trench tops may be covered with asphalt surfacing, as detailed in figure 4-14.
e. Sidewalk Intersections. In the event the trench system intersects an existing sidewalk, the
trench system will match the sidewalk as detailed in figure 4-15.
f. Expansion Compensation. Expansion loop and bend design is the responsibility of the designer,
and is covered in chapter 3 of this manual. The expansion loop design is critical. Sufficient space needs
to be provided in the expansion loop area to ensure that no pipe or insulation interference will occur due to
pipe movement as shown in figure 4-16. This detail indicates location of supports and also shows how the
piping system will be offset to allow for expansion movement in the trench. Table 4-4 is a typical loop
schedule, which corresponds to figure 4-16. The locations of the supports in the expansion loops will be
determined from the designer's piping stress analysis and then entered in Table 4-4. All piping stresses
will be less than ASME B31.1 allowables for each application. The designer will require inspection ports
be provided in the trench tops at each bend in the trench system routing for the purpose of observing pipe
movement at the bends during system startup. The inspection port is similar to the access cover detailed
in figure 4-18, except the nominal diameter of the lid will be 12 inches.
g. Sealants. The trench will be sealed to minimize the influx of ground water. A 1/4 inch thick
neoprene pad will be used between trench tops and tops of trench walls. The pad will have a minimum width
of 2 inches. All trench joints must be sealed with elastomeric sealants, which are available as a one or two
component system. Asphaltic sealants have not performed as reliably for this application. The elastomeric
sealant should be able to resist 50 percent total joint movement. The nonsagging type must be used for
vertical joints. The self-leveling type must be used for trench top butt joints as shown in figure 4-17. Other
horizontal joints may be sealed with either type of elastomeric sealant, but the sealant used in trench
bottoms must finish flush with the floor.
4-2
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