[0001] The invention relates to an intercepting sewer for conveying waste water down steep
slopes.
[0002] Installation of a sewer trunk line in steeply sloping ground implies some technical
and economical problems to be handled. Most of these are arising from an essential
condition that is to limit velocity in the duct to a maximum recommended velocity
of 4-5 m/sec.
[0003] When using conventional pipes of circular cross-section, the problem is handled in
part by the provision of fall or head pits along the pipe profile and in part by increasing
the cross-sectional surface of an intercepting sewer.
[0004] The use of fall pits permits the inclination of a pipe line to be reduced, section
by section, so as to bring the intercepting sewer to the desired depth whenever this
latter would approach too much to a surface level. As is known, such an approach leads
to significant final design costs and to difficulties in achieving the work, especially
when it is to be carried out in a built-up area, since in this case in addition to
depper digging operations involving added charges, there is special works to be taken
into account in order to prevent neighbouring edifices from being damaged.
[0005] Increasing the flow sectional area will lower velocity, due to the smaller hydraulic
radius the flow is occupying in moving in the lower portion of pipe line. However,
changes are modest in extent and pipes of significantly greater diameter than strictly
necessary are to be used which obviously implies far lower filling degrees than applied
usually (normal values: about 75%).
[0006] This type of solution will also be very expensive in the end, due to higher production
costs involved (pipe and pipe-laying costs, increased digging and embankment work,
laying-bed, rebuilding, etc..) together with servicing costs for the installation
to be ma-ntained in a functional state (ordinary and special maintenance).
[0007] The object of the invention is to provide a branch sewer which is so designed that
- the flow rate and the slope being the same - it permits the flow velocity to be
reduced without having recourse to any head pits and without requiring increased pipe
diameter or other provisions which will affect economy of the work.
[0008] The above and other objects of the invention will appear to those skilled in the
art when reading the following description and claims with reference to the accompanying
drawing.
[0009] The intercepting sewer, or sewer trunk line for conveying waste water down steep
slopes, according to the invention, is essentially caharacterized in that it has projections
provided inside thereof.
[0010] More particularly, these projections are arranged circumferentially, are equidistant
and are geometrically configurated so as to give rise to a generalized turbulence
in the flow and to localized losses of head whereby any indesirable kinetik energy
can be dissipated.
[0011] Referring now to the figure of the accompanying drawing, and in order to substantialize
the advantage of the invention, it is supposed that the intercepting sewer in question
has a maximum inside diameter of 37 cm and is provided with internal protrusions having
a mean distance between the centers of 13.2 cm and a jutting-out thickness of 0.85
cm (thus, minimum diameter of intercepting-sewer at projectins, 35.3 cm and mean diameter,
36.15 cm), the intercepting sewer being laid at 10% slope.
[0012] From a study of the following table it can, for example, be noted that at flow rate
Q = 101.5 1/sec., the velocity V = 2.43 m/sec., whereas by using a conventional intercepting
sewer of constant circular section, and with the flow rate Q being the same, in order
of achieve the same velocity it would be necessary to provide a 3% slope with conventional
intercepting-sewer roughness coefficient of Strickler formula i
k 75 and 1.9% slope with i
k =95.
1. An intercepting sewer for the conveyance of waste water through steep gradients,
characterized in that it has projections provide inside thereof.
2. The intercepting sewer according to claim 1, wherein said projections are circumferential
projections.
3. The intercepting sewer according to the preceding claims, wherein said circumferential
projections are equidistant.
