A Study on Sewer Self-Cleansing Design

• Main Authors: Liao, Bor-Yann, 廖浡延
• Other Authors: Lo Shang-Lian
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/19694549749031084625

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.