Minimum trench widths are specified in BS EN 1610 to ensure that adequate space is available for the pipe to be installed safely. The minimum trench width must be adhered to for both rigid and flexible pipe systems.
The trench width chosen by the designer must allow the pipe to be safely installed using the methods anticipated. Trenches may be vertically sided or V sided and can include supports such as sheet piles. The trench must be wide enough for the pipe with sufficient space at the sides for laying of the pipe, installation of any joints and for the placing and compaction of the side fill material. Minimum values for trench width are specified in BS EN 1610 and are shown below. The CivilWeb Buried Pipe Design spreadsheet includes a design check to ensure that the trench width specified is above the minimum value as specified in BS EN 1610. These minimum trench width values can be amended where automated pipe laying systems are to be used where there will never be any people in the trench or between the pipe and the trench wall.
It must be noted that where narrow trench conditions are assumed the actual width of the trench will determine the backfill loads acting on the pipe. In this case the designer must allow sufficient space for the pipe to be installed using the methods anticipated, and if this changes onsite the designer must re-evaluate the design. Also if a trench width has been allowed for this must not be exceeded onsite without the agreement of the designer. Supervision and inspection of the pipe installation must be undertaken to ensure that the design conditions are being met onsite. Indeed it has become common in the UK to include large trench widths for small diameter pipes to avoid the need to ensure that narrow trench conditions are being met onsite.