Pipeline Trench Preparation

The following table provides guidance on the depth of cover that is required for gas distribution systems:

The bottom of the trench should be trimmed to enable the pipeline to be bedded evenly and consistently, throughout its length, at the correct cover.Sharp stones should be excluded from the base of the trench and, where laying across rock or ground of irregular consistency, the trench should be excavated to 75mm below the required depth, to enable the pipe to be laid on a suitably compacted material (e.g. sand).

Prior to any excavation for trenches, a location device should be used. As most premises are supplied with a variety of services, it is safest to assume that pipes and cables will be in the vicinity. It should be remembered that conventional pipe and cable locators do not detect plastic pipes or other non-metallic services unless tracer wires or signal transmitters are present.

Mains and Service Pipework

Under no circumstances should an LPG distribution main or service be installed beneath a foundation or in an unventilated void.

A minimum clearance of 250mm should also be maintained from all other services (e.g. electricity cables. pipes etc.). Further guidance for services beneath paved footways is given in the diagram to the right.

Click image to enlarge.

Excavated Material

Excavated material is normally placed along the side of the trench. Care must be taken so that the weight of excavated material does not cause the collapse of the trench side. To provide adequate working space and to avoid debris falling into the trench, a space between 600 and 1200mm should be left between the trench and excavated material.

If the excavated material is to be used for the backfill it should be protected against adverse wet weather conditions or excessive drying out. Consideration should be given to covering the excavated material in order to maintain the moisture content.

Backfilling of Pipeline Trenches

The trench may be part backfilled between pipe joints, leaving all joints and connections exposed, prior to pressure testing. Before doing so, please check with the Calor Project Manager as pipe marker tape will have to be laid prior to any backfill commencing.

The backfill material must be clean, moist and free from sharp stones to prevent damage to the pipeline. Some soils can be riddled to remove sharp stones and produce a fine backfill material. If this is not possible, it will be necessary to import a suitable material. This fine material should be compacted firmly around the pipe to give a compacted thickness of 75mm.

The gas pipe marker tape should be placed at a depth of not less than 200mm above the gas pipe.

The following information is for general guidance. Your Calor Project Manager will provide more site specific advice together with the necessary technical specifications.