Failures in Limestones in Humid Subtropics

Limestones and similar carbonate rocks comprise about 10% of the world's surface rocks. Solution of porous limestones creates networks of small cavities from less than an inch to several feet wide and weakened rock similar to petrified swiss cheese. Solution along cracks and bedding planes produces criss-crossing slots and chambers feet to tens of feet across. The rock-soil associations are subject to sudden rock cavity collapse, ravelling of soil into cavities followed by sudden soil surface subsidence, and to consolidation of the weakened porous rock in a humid tropical and subtropical environment. Lateral expansion due to residual stresses produces horizontal foundation movements. Construction of shallow foundations is complicated by ravelling cavities in the soil and pitting and slotting of the bedrock. Pile and caisson construction is confounded by rock slots and pits as well as by local punching of the weakened rock.