This Technical Specification, which is a guidance document for use with a structural analysis procedure for below ground installations, covers limits applicable to glass-reinforced thermosetting plastics (GRP) pipes used for the conveyance of liquids under pressure or gravity conditions. This document does not specify a particular structural analysis procedure but gives guidance on the selection of a structural analysis procedure. It concludes that any established structural analysis procedure may be used provided it includes the assessment of short and long-term deflection and buckling resistance. Products complying to the applicable GRP product standards EN 1796 or EN 14364, which are not subject to internal pressure, are suitable as long as the analysis shows that the long-term deflection of the installed pipes is limited to 6 %, which is the basic assumption of the GRP pipe product standards. Products complying with the applicable system standards (EN 1796 or EN 14364), which are subject to internal pressure, are suitable as long as the analysis shows that the initial deflection of the installed pipes does not exceed 3 %. NOTE The approach followed when preparing a general structural analysis procedure does not depend on the nominal size(s) of the pipe(s). A suitable structural analysis procedure should normally be capable of being used for pipes operating at different temperatures provided that the corresponding temperature re-rating factors for the relevant pipe properties are applied, as specified in the referring standard(s). Nevertheless, high service temperatures may require an additional analysis of the longitudinal stresses and strains and/or a special design of the joints. Normal structural analysis procedures are intended to cover normal soil installation conditions. Pipes to be designed for installations in abnormal or unusual conditions, e.g. in quick soils or a marine sea-bed, may require special engineering.