Why is construction of rails and roads difficult in areas of sinkholes
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Answer:
Lowland terrains of soil-mantled cavernous karst provide some of the worst conditions possible for civil engineering and construction. The soil cover may not offer a sound foundation medium because it can fail slowly or rapidly by suffosion into the underlying karst, with consequent development of destructive subsidence sinkholes. Foundations carried to bedrock avoid this sinkhole problem, but encounter the twin difficulties of extremely irregular rockhead profiles and the possibilities of open caves that may collapse within the bedrock. An engineering classification of karst ground conditions (Waltham and Fookes, 2003) offers a general view of what sort of difficulties may be anticipated or encountered within a particular karst terrain (Chapter 10). Rockhead in juvenile karst is generally sound except for isolated fissures or shallow caves: in youthful karst, rockhead only gives rise to minor problems due to its irregularities that usually can be dealt with by the use of piles or rafts; in both karst classes, small sinkholes can be spanned by rafts or piles with reinforced ground-beams. Pinnacled rockhead in complex and extreme karst may mean that piles are required to found buildings or structures in competent rock; caves commonly extend to 10 m or so in width, and therefore necessitate adequate probing below pile tips and may need filling with mass concrete.