BITUMEN IN COASTAL ENGINEERING

Abstract

Artificial coast protection is required where coasts are subjected to erosion. Where the country is low it will be necessary to build sea-walls where natural protection by dunes is not adequate or is completely lacking. In both cases it may also be necessary to protect the country from further advance of the sea by the construction of groynes and breakwaters where lateral currents cause displacement of granular shore material. From the study of the history of coast lines and the development of their protection it is apparent .that apart from the necessity of construction the governing factors of the constructions are safety and economy, or as the British "Departmental Committee on Coastal Flooding" states in its Terms of Reference, it has "to consider what margin of safety for sea defences would be reasonable and practicable having regard on the one hand to the estimated risks involved and on the other to the cost of protective measures". New methods of approach and execution of technical problems such as improved methods of observations and measurements, the use of laboratory experiments, availability of modern equipment and new materials open a wide scope for more economic construction. On the other hand, however, development in this field has been comparatively slow because the consequences of failures oblige the responsible engineer only to alter the traditional design step by step in accordance with progress made in the scientific analysis of the destructive forces of waves and of the properties of the new building materials. The need for investigation is sometimes accentuated by a disaster such as was recently caused by the storm surge of January/February 1953 when on the East Coast of England the observed height of the water-level reached a record of 6 ft. or more than the predicted height according to the astronomical conditions for a continuous period of 15 hours as against 5 hours for former surges. In Holland a water level of 75 cm« above the highest ever recorded level was reached on some sea-walls, causing overtopping of waves. Reports by the "Delta Commissie" in Holland and the "Waverley Committee" in England as well as Papers read on the North Sea Floods for The Institution of Civil Engineers, London, and the Koninklijk Instituut van Ingenieurs, The Hague, deal with the subject adequately. In dealing with coast defence schemes it should be borne in mind that for low lying countries designs should not only be limited to artificial works for direct protection of beacheis, sea walls and dunes. Consideration should also be given to works for reducing areas liable to flooding by overtopping of or breaches in sea-walls or by damage to dunes. In such instances a "second line defence" can be usefully suggested with cross banks to divide the areas in bays or compartments. If these cross banks carry access roads,connecting the inland centres with the sea defence works, they will certainly facilitate communications before and during storms and operations for restoring conditions after storms. In all these works bitumen can be applied to advantage for the protection of beaches, sea walls, dunes and banks as well as for road construction and maintenance works. The use of bitumen in coastal engineering is, of course, also based on practice and theory gained from other civil engineering fields, such as road construction and the building industry. The properties of bitumen and bituminous compounds have first been gradually developed to their present standards in these fields and this knowledge has facilitated the scientific and practical approach of the application of bitumen in sea defence works. In this paper the problem is only described from a practical point of view. After dealing with various aspects of the design of coastal works pertaining to the use of bitumen, a short review is given of the most important types, methods of application and properties of bituminous constructions and finally a number of representative examples of each of the types of application is given.