Telescoping Sections

ERDC TN-DOER-T3

January 2001

second section and lift it when the weir is being extended. The blocks shall also act as mechanical

stops for the weir section as it is lowered to nest in the next lower section.

Telescoping Sections. There shall be two cylindrical telescoping sections below the crest sec-

tion. Each shall be large enough in diameter to permit the next upper section to slide within it, with

allowance made for the slide bearings described later. Each shall be of corrosion-resistant steel of

thickness adequate to withstand the hydrostatic pressure of a soil overburden resulting when the sed-

iment at the installation site has built up to the full extended height of the weir. Each shall have an

upper rim that serves as a seat for the wiper seal described later. Each shall have a set of bearing

blocks attached around the lower perimeter to engage the upper rim of the next lower section when

the sections are being telescoped.

Base Section. The base section shall be a fixed cylindrical section, large enough in diameter to

permit the next upper section to slide within it, with allowance made for the slide bearings described

later. It shall be of structural steel of thickness adequate to withstand the hydrostatic pressure of a

solid overburden resulting when the sediment at the installation site has built up to the full extended

height of the weir. It shall have an upper rim that serves as a seat for a wipe seal described later. A

flat plate seals its lower end. Near its lower end a pipe joint that will serve as the connection for the

discharge pipe shall intersect the cylindrical wall. The pipe joint outside diameter shall be not less

than 24 in. The height of the base section shall be large enough to allow the telescoping sections to

nest within it without significantly blocking the flow through the discharge pipe.

Slide Bearings. The inner wall of each weir section, except for the crest section, shall be fitted

with rectangular strips of a low-friction material that act as both spacers to maintain concentricity

between adjacent sections and as slide bearings to minimize the frictional resistance to the telescop-

ing motion of the weir. These slide bearings shall be positioned adjacent to the bearing blocks de-

scribed earlier in such a way to prevent the rotation of one section with respect to another.

Seals. A flexible seal, such as a lip seal, shall be installed at the joint between each weir section to

prevent the intrusion of sediment into the weir discharge effluent. The seal shall be sufficiently stiff

to maintain its shape and effectiveness while the weir sections are being raised through the overlying

mud strata.

Weir Foundation. The weir foundation shall be a grid formed of structural beams in a pattern suit-

able to support the weir base section and to provide attachment to the concrete pad supported by pil-

ing in the bottom of the placement site. The foundation shall be 96 in. square, with a circular area of

diameter 94 in. in the center being reserved for the weir structure. The remaining area is available for

attachment to the pilings or other preparation for installation into the bed of the placement site.

Framework. The framework shall be a tower of structural beams, attached at its lower end to the

foundation and topped by a platform on which are mounted the controls and the motor and gear

mechanism that raise and lower the weir. The width and height of the framework shall be sufficient

to straddle the weir without obstructing flow over the weir crest.

Bracing on one side of the framework shall be removable to allow insertion of the weir tele-

scoping sections.