Synopsis.
This Paper outlines the gradual development of vented causeways on sand foundations on the Grand Trunk Road across Indian rivers which are not snow-fed; such rivers have their sources in, and flow through, the old geological formation south of the Indo-Gangetic plain, the sand of their beds being of a coarse and heavy variety. Descriptions are given of the Sone, the Leelajan, and the Butane causeways.
The latest designs of causeway, introduced in Bihar by the Author, and exemplified in the construction of the Subarnarekha and Torpa causeways, are described.
The theoretical aspects of the designs are then discussed, with special reference to their stability against scour under foundation, safe bearing-pressure distribution, scour on the downstream side, and horizontal pressure due to moving water; formulae used in calculations are also noted.
Costs of the two recently constructed works are given.
The causeways are submerged on only a few occasions annually for brief periods and are, in effect, submersible bridges.
In conclusion, it is suggested that this type of design be adopted for rapid construction when the plant and equipment required for high-level bridges with deep pier foundations are not available and where uninterrupted traffic is not essential.
