Optimal upgrade of sewers

Summary

Choosing the optimal structures and parameters of new and upgraded wastewater disposal systems has been a determining factor in designing their prospective development schemes. This task is suggested to be fulfilled on the basis of preliminary designed redundant schemes that are formed by overlapping pre-engineered options of wastewater system development. On the basis of the redundant scheme a transportation network scheme is designed to determine the maximum flow at minimum costs. For this purpose the flow-through capacity limits of the existing sewers are assigned on the basis of self-cleansing velocities (lower limits) and impermissibility of gravity sewer operation under pressure (upper limits). The cost of the flow units is determined for every network section on the basis of the capital and operation cost data. From the optimization results the route and parameters of the new network sections, options of the existing sewers upgrade (open cut or trenchless relaying, parallel pipeline construction) are determined. The suggested method can be useful when designing prospective development schemes of wastewater systems, and can be used by wastewater services providers for developing investment programs.

Key words

water disposal system , optimization method , maximum flow at minimum cost , flow unit , cost function , linear approximation

Improvement of the integrity and seismic resistance of gravity sewers

Summary

The problems of improving the integrity and seismic resistance of wastewater disposal systems have been urgent and must be solved in the process of designing prospective plans of territorial and urban development as well as investment programs of public utilities. The procedure of wastewater system structure optimization based on developing redundant layout and searching the maximum flow of the minimum weight function (minimum cost, maximum integrity and seismic resistance) is suggested. Redundant layout is developed by overlapping the predesigned sewer routes. The integrity is evaluated by the quantitative index – raw sewage amount that is generated for the certain time period as a result of an accident and pipeline rehabilitation time. Seismic resistance is taken into consideration by increasing failure rate depending on the earthquake intensity and orientation of the seismic impact. The suggested procedure takes into account seismic impacts by increasing the length of the designed sections of the redundant sewer layout. It is shown that construction of subsidiary and loop sewers improves significantly the integrity and seismic resistance of sewers.

Key words

water disposal system , seismic forces , optimization method , redundant layout , quantitative index of integrity , seismic resistance