Buried Rigid Pipes PDF

Preface

In wntmg a book of this nature that will have reasonably general application the authors are confronted at the outset with the problem that although theory remains much the same everywhere, constructional practices that affect the design of pipelines are prone to vary, being influenced by such factors as local traditions, climate and geology. Also, although official regulations and recommendations within the UK are now fairly uniform, such requirements vary from country to country, and indeed can vary considerably within a single country. Also the extent to which the design engineer is free to make his own decisions and choice varies. Relative labour costs, availability of sophisticated plant and equipment and standards of workmanship exert powerful influences.

Inevitably the book is directed in the first instance to practice within the UK, but where occasions arise throughout the text attention is drawn to variations that may arise elsewhere. In making comparisons between different practices it is of importance to consider the overall design. For instance in some countries it is customary to design for loadings that are average rather than maxima and to employ a relatively high overall design factor of safety to take care of contingencies, whereas in others, such as the UK, the reverse is the case.

Ideally design and construction should be interdependent, but not infrequently it is customary for the construction work to be placed outside the direct control of the design engineer. With such a division of responsibility it is particularly important that the design engineer should be in possession of the fullest possible information concerning site conditions, so that he may foresee problems liable to arise during the carrying out of the work, and also that his requirements should be fully specified in the contract. In general it is preferable for the designer to have a measure of control over the site work, or at least that there should be a feedback of information from site to design office.

Since underground pipelines are not usually visible after construction, the importance of this field of engineering may not be fully appreciated by those coming fresh to the subject. In developed countries such as the UK the amount of invested capital represented by existing pipelines is large. As an indication of the implications of this a recent report by the National Water Council 1 estimated that an annual expenditure of about £260 million (at the then ruling level of prices) was needed for maintenance and renewal alone of public sewers and water mains to keep them in a satisfactory condition. This figure takes no account of private drains and other pipelines, nor of expenditure on new projects in areas under development. It is clearly incumbent on engineers responsible for new or replacement work to ensure that it shall have an adequate life at the lowest cost, taking into account expenditure on maintenance and repairs over the expected lifetime of the pipeline as well as the initial expenditure.

Design charts, tables and computers make design calculations a relatively easy matter, but it is important to keep in mind that this apparent ease should not be allowed to obscure the fact that engineering skill and experience are also necessary. A number of decisions are usually called for at different stages of the design and construction, and for these professional skil! and expertise are needed in making a correct choice between often conflicting requirements.

Although this book is specifically concerned with pipes of rigid materials, some information on 'flexible' pipes that are available and on their behaviour and use is included as being of value to the engineer in making an initial choice.

Author: OC Young, JJ Trott