Identification and quantitative analysis of sinkhole contributing factors in Florida's Karst

Abstract

Sinkholes are one of the major geohazards in karst areas, causing loss of life and significant economic loss as well. Sinkhole forming mechanism varies depending on the geological environment, and Florida's sinkholes are formed through the process of interaction between groundwater flow and cover soils. The significance of this paper is (1) to identify key sinkhole contributing factors and (2) to quantify the impact of those factors on sinkhole formation. Particularly, this study accounted for geomechanical factors that contribute to sinkhole raveling (due to erosion) and mechanical stability of overburden soils. Identification of key sinkhole contributing factors will allow developing a probabilistic sinkhole prediction model. The study area was focused on East Central Florida, where cover-collapse sinkholes often occur. Uniform-distribution transformation was employed for the quantitative analysis on each factor, and then case studies with specific examples are then presented to validate the results of the quantitative analysis. In conclusion, the identified key factors are hydraulic head difference, soil permeability, thicknesses of aquifer systems, and proximity to karst features (e.g., existing sinkhole). The critical permeability (k(crit)) showing a rapid increase of sinkhole occurrence is about 20 cm/h. Thickness and characteristics of cover soils seem a controlling factor of sinkhole types, and the overburden thickness around 40 to 45 m tends to form the collapse type. A multivariate regression analysis indicates that the thickness of the surficial aquifer system is the most significant factor, and then the head difference and the proximity to karst features follow in order.