Preliminary observations on the design and construction of a four-lane highway through expansive clay in Cyprus

Abstract

Summary A case history is presented describing some aspects of the design process and the early stages of construction of a four-lane highway across an outcrop of expansive clay in southern Cyprus. The clay, of the Moni Formation, affects 7.5 km of the total 85 km of the new road alignment between Nicosia and Limassol. A special construction treatment was devised to deal with anticipated swell-pressures from the clay beneath the pavement construction. The original concepts were reviewed and revised after the contractor took over the site. During the first half of the contract period, following new investigations, the standard cross sections were changed and the treatment was extended. A minimum surcharge of 2 m of construction (filling plus pavement layers) was provided throughout the 7.5 km of cut and fill to balance the swell-pressures. Intercepting drains were also provided to prevent ground water entering the clay sub-grade layers. This minimum ground loading was adopted after a study of potential swell and from calculations made using measured soil classification values and a theoretical relationship devised elsewhere. Cuttings in the clay were originally designed at 1:2 (vertical: horizontal) but a major slope failure shortly after excavation led to a flattening of this particular face and gave an indication that existing factors of safety on slope stability were low. There are old landslips on the natural slopes across which the highway runs. An instruction was given to the contractor to locate all waste tips away from these slopes to prevent re-mobilization of slipping.