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(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.
(ii) R.S.J. 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.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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