LIQUEFACTION-COLLAPSE SINKHOLE FORMATION AND ASESSEMENT OF ITS DANGER TO BUILDINGS AND STRUCTURES 

V. P. Khomenko*, O. K. Krinochkina**

National Research Moscow State University of Civil Engineering,

 Yaroslavskoye shosse, 26, Moscow, 129337 Russia

*E-mail: khomenko_geol@mail.ru 

**E-mail: vdovinaok@mail.ru

An understudied genetic type of karst sinkhole formation is considered, which is typical for areas where karstic rocks are covered by saturated or unsaturated incoherent soils, moreover saturated ones can have an impermeable bed. It takes place only when an unfilled dissolution cavity or fissure contacts incoherent soil either directly or through a breach in the layer of cohesive impermeable soil overlying karst deposits. In this geological setting, the emergence of single (and sometimes numerous) liquefaction-collapse sinkholes on the Earth surface or under foundations can be caused by the dissolution of karst rocks, the sudden occurrence of a breach in the overlying impermeable layer, a dynamic or shock loading on saturated incoherent soils, and the development of vertical ascending water flow in it. The latter trigger is often manifested as the recovery of previously lowered groundwater level due to pumping of karstic water. In built-up areas, this can lead to destruction of buildings and structures initially by piping-collapse sinkholes and later by liquefaction-collapse sinkholes. The in-laboratory simulation modeling had shown that these sinkholes are the result of discontinuous and cyclic hydraulic-gravitational failures of soil cover. During this process the cavities in incoherent soils appear and disappear and every next appearing cavity is situated above previous disappearing cavity. The process begins at the contact between incoherent soil and dissolution cavity or communicating with it breach in impermeable layer which consists of cohesive soil and covers soluble rock. The failures of incoherent soil spread up to karst water piezometric level inside the widening from below to top cone-like area. Collapse sink formation can complete it. This process can be stopped only by a sufficiently thick layer of cohesive soil, if it exists in soil cover. The conception of triggers and mechanisms of this process have been formed. The predictive theoretical decisions have been proposed. They allow estimating the possibility of liquefaction-collapse sinkhole formation and the size of final collapse sink, taking into consideration parameters of an endangered engineering structure.

Key words: karst, piping, liquefaction, collapse sinkhole, prediction

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