| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 85 === It has been confirmed that the self-cleansing velocity
required for sewers is a function of pipe diameter, pipe
roughness, and sediment characteristics, such as size
distribution, specific gravity, and concentration. The
constant self-cleansing velocity of present R.O.C. sewer
design criteria seem to be unsuitable for all sizes of pipes.
According to available foreign and native data, we set up the
typical values and varying ranges of the parameters stated above
and then analyze their influence on Camp*s, Yao*s, University
of NewCastle, and CIRIA equations. A comparison between new and
old design criteria is also presented in this thesis.
Furthermore, the Q-S-D design charts are plotted with typical
parameter values for application. Considering sediment
characteristics and engineering feasibility, this research
suggests that all sediments in sanitary sewers should be
transported in suspension and sufficient erosion ability
should be provided to avoid deposition of cohesive
material. Parts of sediments might be transported in bed-
load state for storm sewers, thereby reducing the design
velocity to an acceptable degree.
To show the difference between new and old design methodology,
a case study on some design results of a sanitary branch system
in Taipei city is discussed. We find that the new
requirements are more economic in small pipes with low
hydraulic capacities.
Present R.O.C. sewer self-cleansing criteria would cause
overdesign in small sanitary sewers and underdesign in large
ones. In storm sewers, the present criteria are generally
insufficient for all pipe sizes. Hence, it is necessary to
establish new sewer design criteria.
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