(i) The groove is used to facilitate the maintenance of manholes and sewer/drain pipes.
Shutoff boards are erected on the grooves during maintenance operation so that water flow coming from upstream is terminated in the manhole and backwater from downstream is also blocked.
In addition, the groove also facilitates water flow diversion for routine maintenance operation.
is a small-scale size of universal beams and is used for resisting the high stresses incurred by heavy traffic loads acting directly on the upper narrow projected section of manholes.
(iii) Double seal terminal manhole covers are used for sealing off gases emitted inside sewer/drains and prevent them from releasing out of the manhole.
(iv) U-trap with rodding arms is also used for sealing off unpleasant gas smell by the trapped u-shaped water columns.
Rodding arm is normally closed with rubber rings during normal operation.
However, during maintenance operation, the rubber ring is removed and rodding can be carried out through the rodding arm.