AS 3725 SUPP 1-1989

Gives the background to corresponding clauses in the Standard and helpful information for design engineers and those writing specifications for the installation of concrete pipelines. Emphasis is placed on the need for achieving in the field, support conditions consistent with the assumptions on which the equations in the Standard are based. An appendix gives worked examples which illustrate the load calculations and how the calculated values are used to select an appropriate class of pipe for a particular installation.

The main purpose of the Standard is to provide an agreed basis for determining the vertical working loads on installed reinforced and unreinforced concrete pipes and to relate this to the loads applied to sample pipes in the standard load tests, so that an appropriate 'strength class' of pipe can be selected from AS 1342 or AS 1392, as applicable, which will be suitable for the particular field application. Designers should be aware that installed pipes may also be subjected to non-vertical loads of considerable magnitude (e.g. at the toe of a slope). The vertical and horizontal components of such loads should be carefully assessed and appropriate action taken to ensure that they can be resisted by the pipes and adequately transferred to the foundations.A secondary purpose of the Standard is to reduce the large variety of likely installation conditions and bedding choices to a small number of representative types. Like AS CA33-1962, the Standard is based on the work of Spangler (Reference 3) and others of the Iowa Engineering Experimental Station, in relation to trench conditions. The more recent work of the California Department of Transportation has been utilized for embankment assessments and this is reflected in higher bedding factors in the Standard compared with AS CA33-1962. Bridge design rules published by ANZRC in 1974 (Reference 1) and NAASRA in 1976 (Reference 2) and their general acceptance since then, have allowed fuller treatment of railway and highway live loads to be presented here.The most recent research in the United States and elsewhere has centred on computer-aided methods of mathematical modelling and finite-element analysis for both load and pipe stress assessments. Although this appears to be the future direction of analysis and design, there are as yet insufficient practical data available to justify incorporating the results of these assessments in a Standard of this nature.Methods of pipe laying and bedding preparation are not stipulated in the Standard because the continuing and rapid development of specialized earthmoving equipment and procedures would soon render such requirements obsolete. However in Paragraph C8, detailed procedures for haunch compaction are outlined, as experience has indicated this to be one of the most difficult aspects of circular pipe bedding. Attention is also drawn to Reference 15 which contains much useful information on the subject.Compaction percentages have been included in an attempt to be more specific with regard to bedding and backfill compaction requirements. For sidefill the compaction percentages have been given for both cohesive and cohesionless soils to emphasize that some measure of cohesiveness is acceptable in the select fill. This policy has been adopted having regard to the high cost of imported material and to the ever-increasing range of compaction equipment which makes it possible to use effectively a wider range of materials.Bedding shaped to fit the outside diameter of the pipes, which was specified in AS CA33-1962, has now been omitted as there has been a definite trend away from this in Australia.