Investigating the performance of drainage stack of high rise buildings in Hong Kong

The design and proper operation on the above-ground drainage systems can be challenging in a densely populated city like Hong Kong. Discharge loading imposed to a single vertical stack can be large enough that those systems without a proper design, installation or maintenance would suffer problems such as backflow of foul water, contaminated foul air, or even soil waste to the sanitary fitments at lower floors. Any of these nuisances can be regarded as failure because the soil and waste water cannot be properly disposed away from a building. The risk of such a failure would be higher in densely occupied tall buildings. SARS outbreak in 2003 revealed that the consequence of failing to properly manage the drainage system can be as serious as a fatal disaster. The contaminated aerosols, with water droplets with the microorganisms are fatal to human like the SARS virus since it will flow back to the living environment. This research aims at proposing advanced design and monitoring practices upon the drainage system and its components, to minimize the risk of failure and nuisances occurrence. A brief review on several types of failure will be gone through. Besides, a simulation model has been established to predict the air pressure in drainage system. The result will be compared with those from real 1:1 test-rig experiments. This assists the development of innovative inventions of system components such as 8S twin drainage stack which is designed to self-balance air pressure generated by falling water discharge in drainage stack. It ensures better protection of water seal in traps. Smart trap is available to enlarge retention time of water seal due to evaporation. Regarding the management of existing installed drainage system, a protocol has been proposed to troubleshoot the nuisances. It includes remote-control air pressure monitoring and statistical analysis with the development of probability density functions to decide future remedial engineering measures. All of these are integrated as a risk management model aimed to reduce the risk of occurrence of the nuisances