COMPARATIVE ASSESSMENT OF OPERATING CONDITIONS OF TUBULAR DROP MANHOLES OF SEWERAGE SYSTEMS

Abstract

The evaluation of standard pipes of drop sewerage manholes is carried out on the basis of the literature data analysis. A new design of the drop manhole with height-variable cross-sectional area is proposed on this basis. A series of experimental studies was conducted on a specially mounted setup to study and compare the characteristics and operating conditions of standard structures and structures of the proposed design. The models of drop standpipes were made of plexiglass, which allowed to visualize the structure of fluid flows in both cases. It is established that three modes of motion can take place in drop standpipes, depending on the passed flow rate: pressureless, transitional and pressure. Pressureless mode of motion should be considered as calculated for permanent cross-sectional drop. Much attention has been paid to measuring the magnitude of dynamic loads from the falling flow to the manhole bottom in the research. Non-uniformity coefficient of the dynamic load from the flow stream impact also was determined. It was defined that its value depends on the flow rate passed by the standpipe and can reach values of 3 or more for drops, that are made of a constant cross-sectional standpipe. The non-uniformity coefficient of the dynamic load for such drop should be taken equal to 1.5. The non-uniformity coefficient does not exceed 1.5 for arbitrary flow rates for variable cross-sectional standpipes.