TM 5-820-3/AFM 88-5, Chap. 3
it is desirable that the openings be made as large as
intercepted such as near hangar doors. The design
traffic and safety requirements will permit.
and construction details of the box drain will
j. For rigid concrete pavements, grates may be
depend on local conditions in accordance with hy-
protected by expansion joints around the inlet
draulic and structural requirements. However, cer-
frames. Construction joints, which match or are
tain general details to be followed are illustrated by
equal to the normal spacing of joints, may be re-
the typical section through a box drain in a paved
quired around the drainage structure. The slab
area shown in figure 3-4. The walls of the box drain
around the drainage structure should include steel
will extend to the surface of the pavement. The
reinforcements to control cracking outwardly from
pavement will have a free thickened edge at the
each corner of the inlet.
drain. An approved expansion-joint filler covering
the entire surface of the thickened edge of the
pavement will be installed at all joints between the
3-4. Box drains.
pavement and box drain. A -inch-thick filler is
a. Where box drains are used within paved areas
usually sufficient, but thicker fillers may be
to remove surface drainage, no special inlet
required. Grating for box drains can be built of
structures are required and a continuous-type
steel, cast iron, or reinforced concrete with
grating, generally covering the entire drain, is used
adequate strength to withstand anticipated load-
to permit entrance of water directly into the drain.
ings. Where two or more box drains are adjacent,
Box drains are generally more costly than
they will be interconnected to provide equalization
conventional inlets. Accordingly, their use will be
of flow and optimum hydraulic capacity.
restricted to unusual drainage and grade situations
where flow over pavement surface must be
3-5
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