Some New Approaches to Assessment of Collapse Risks in Covered Karsts

In a mantled karst terrain engineering practices can vary often requiring innovative approaches that are significantly different from traditional ones. Three situations are considered as an example. The problems were as follows: (1) Pre-construction assessment of sinkhole development probability for a residential area located in the vicinity of Moscow with insufficient karstological data. (2) Pre-construction karst risk assessment for an industrial site in Dzerzhinsk, Nizhny Novgorod region. (3) Quantitative classification of karstified terrains for the purposes of selection of waste disposal area for industrial and household wastes. The researchers dealing with problem number 1 had limited data on previously recorded sinkholes but sufficient information on previous overburden studies in the region. Assessment of collapse risks was performed with due attention to the specificities of the karstified terrain relief, karst location depths and the properties of the overburden rock. Among the methods used there was assessment by experts (rating scales), entropy and a round cylinder model of karst sinkholes. In the second case related to designing of an industrial structure there were no difficulties with basic data on registered sinkholes and hence a traditional method could be used. But the customer's demand was to assess the karst risk for both the entire industrial site and some separate constructions in order to plan adequate karst monitoring and protection measures of a long- and short-term period. The assessment method proposed was to obtain the risk level as a ratio between probable construction collapse risk and the allowable risk. Risk levels were assessed at different stages: after engineering protection of the building had been performed and after regular maintenance procedures. Problem number 3 considered a method of classifying karstic terrain according to the level of geological environment contamination for the purposes of selection of a site for waste disposal (household/industrial wastes). The classification is based on a probable level of the environmental contamination resulting from sinkhole development.