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Water Tightness in Joints of Drainage Channels and Box Culverts

This document discusses the need for water tightness in the joints of drainage channels and box culverts. It explains that water tightness is usually required to maintain water flow and is achieved through the use of water stops. While some think weep holes negate the need for water tightness, the document outlines two key reasons water tightness is still important: to prevent soil loss from high water tables or washout, and to prevent structural failure from dowel bar corrosion over the structure's lifetime. Maintaining water tightness eliminates issues from corrosion and ensures the structural integrity of drainage joints.

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64 views1 page

Water Tightness in Joints of Drainage Channels and Box Culverts

This document discusses the need for water tightness in the joints of drainage channels and box culverts. It explains that water tightness is usually required to maintain water flow and is achieved through the use of water stops. While some think weep holes negate the need for water tightness, the document outlines two key reasons water tightness is still important: to prevent soil loss from high water tables or washout, and to prevent structural failure from dowel bar corrosion over the structure's lifetime. Maintaining water tightness eliminates issues from corrosion and ensures the structural integrity of drainage joints.

Uploaded by

mora287
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Water tightness in joints of drainage channels and box culverts

By Vincent T H Chu

The question of the need for water tightness in the joints of drainage channels is often raised by
graduate engineers. In particular, many graduate engineers and assistant engineers have asked
me about the need to provide a water stop in the joints of drainage channels. This article serves to
clarify the issue and eliminate their uncertainty when confronted with this issue again during their
day-to-day design work.

In designing the joints for box culverts and drainage channels, water tightness is usually required to
maintain water flow in the channel and is normally achieved by the installation of a water stop
across the joints of the drainage structure. The plain, dumb-bell type water stop is used for joint
locations where small movements are anticipated. Therefore, this type of water stop is desirable for
construction joints. On the other hand, the center-bulb type water stop is suitable for expansion
joints or locations where lateral and shear movements occur due to settlement or deflection.

It is a common engineering practice to design weep holes along the walls of drainage channels and
box culverts to relieve the water pressure so that its effect can be ignored during the design of
channel walls and box culverts. Given the presence of weep holes, it would appear that the water
tightness achieved by installing water stops across the joints is meaningless because water flowing
in the channel can escape through the weep holes on the walls of the drainage structures.

If the purpose of maintaining water tightness in the joints of drainage structures is to reduce the
amount of water loss through joints, the above argument would be correct. However, the main
reason for achieving water tightness across the joints in drainage structures is not directly related to
the amount of water lost in drainage channels and box culverts.

Water tightness in the joints of drainage channels and box culverts is considered desirable under
the following two scenarios:
(i) Where there is a high water table in the vicinity of the box culverts/channels, water stops should
be installed across the joints. The high groundwater level and rainwater seepage through the
embankment may cause water to pass through the joints and into the adjacent soil. The loss of soil
may lead to failure of the structure when it is subject to severe loads.

(ii) Where the box culvert/channels are designed in such a way that water flowing through the joints
washes out the bedding materials, joint water tightness has to be fulfilled. Otherwise there may be a
structural failure as in the scenario mentioned above, when the box culvert/channel is subject to
heavy loads.

Apart from the concern that foundation materials may be washed away, water tightness in the joints
of drainage channels and box culverts is considered beneficial because it eliminates the potential
problem associated with the corrosion of dowel bars across the joints. In essence, dowel bars serve
to maintain the alignment of the structure when the structure experiences contraction and
expansion throughout its design life; as well as to transfer shear forces across the joints.

If the dowel bars malfunction due to corrosion, the joints would be subject to additional stresses
which may lead to the structure's failure. Where a drainage channel/box culvert is expected to be
continually in contact with seawater, which contains various corrosive agents, water tightness in
joints is recommended, to avoid corrosion in the dowel bars. In cold countries salt is sometimes
applied on roads above box culverts or at channel crossings to prevent freezing and thawing. The
leaching of road salts into the joints may cause corrosion of the joint reinforcement.

About the author: Vincent T H CHU is a civil engineer with a government works departme

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