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Sewers and drains: common and deep trenchesCommon trenchIt is common for foul water and storm water sewers to be laid at different levels in a common trench.Before setting-out, check that the invert level of upper sewer will allow connections to the lower sewer. To set out thesewers: prepare and issue a Site Information Sheet to the foreman/ganger erect upper and lower profiles as shown and paint uphill face of the sight rails (see end papers for colourcode) ensure that trench sheeting will not obstruct boning on lower sight rail construct the traveller that will be used in conjunction with the upper and lower sight rail with one crosspiece.Deep trenchIn a deep sewer trench with battered sides, if the usual profiles cannot be set within 3 m of the centre-line, andaccurate boning is not possible, the following is recommended: set up pairs of profiles parallel to and on both sides of the trench at about 8 m intervals as shown in thediagram bone in traveller across the trench to give appropriate excavation level, leaving the ground a little high set up new profiles perpendicular to the trench line and within the trench for final trimming to level set up temporary datum level within the trench to set pipes to level.In a deep supported trench, it is difficult to obtain accurate levels when the traveller is more than 5 m high, therefore: excavate roughly to depth using normal profiles set up profiles in trench and trim to final level.Note: Beware disturbance of profiles in trench if trench sheets or sheet piles are being driven progressively. Checkafter each round of driving.CIRIA C70963