Evaluation of Sensitive Parameters in the Design of Deeper Manhole

Abstract

Manholes are critical sections in the design of underground construction. Concrete manholes have become mainstream in the recent decades due to its durability and are widely used for cleaning sewer lines. Therefore, the manuscript focused to study the influential parameters such as depth of manhole, grade of concrete and thickness of wall in the design of concrete manholes using Staad Pro, finite element software and a total of 240 simulations were performed on the manhole of 15 different depths (2.4 to 30 m), four different grade of concretes (M25-M40) and four different thickness of walls (125–200 mm). Also, two different diameters (1.5 and 1.8 m) of manhole were taken in the simulation as per the existing design code. The most critical loading conditions that exert pressure on the manhole outer surface from different directions were identified from the simulations and the results were presented in terms of displacement, moments and stresses. The validation on 1.5 and 1.8 m top slanting portions was performed as it is most vulnerable to overturning due to comparatively lesser self- weight by applying stability check against overturning. The predicted results in terms of safety factor against overturning found about 1.7 whereas recommended as 1.4 as per IS code. It is concluded that the deflection found to increases with increase in depth. It was also concluded that the deflection found to decreases with increase in grade of concrete, however it was observed that the moment and stress remained same for all the grades of concrete.