Özgür Aktürk

Stability Charts for the Collapse of Residual Soil in Karst

Collapse of the residual soil over bedrock cavities often occurs during construction in karst terrain, particularly when the thickness of the residuum is reduced during excavation. Even if an estimate of the strength of the residual soil is known, uncertainty with respect to the size/geometry of the subterranean voids makes a detailed analysis difficult, and straightforward methods to check the stability are needed. In this study, numerical analyses were performed to develop a stability chart expressed in terms of a dimensionless stability number and the geometry of a potential void in the residual soil. The stability charts include the effect of friction angle, and are also developed to allow the investigation of the effect of the inverted strength profile typically observed in karst terrain. Such stability numbers may be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters.

Simulation of Graded Rock Fill for Sinkhole Repair in Particle Flow Model

The use of graded rock fill is a cost-effective means of sinkhole repair, providing a stable platform for infrastructure while allowing controlled flow of surface water into the sinkhole throat. Typically, the sinkhole is excavated and large diameter (0.25 to 0.5 m) shot rock aggregate is dumped down the excavated throat of the sinkhole. This paper discusses the two-dimensional modeling of the placement of shot rock using the Discrete Element Method, where the aggregate placement is assumed to be similar to granular materials flowing through a hopper. The stability is investigated for a range of rock particle and sinkhole throat radii. It is demonstrated that for a given throat radius, there exists a range of particles sizes that could be either stable or unstable depending upon how the particles arrange during the dumping procedure. The gradual transition from unstable to stable behavior is best described by a logistic regression.

Undrained Stability of Residual Soil in Karst

Human activity on the karst landscape can result in subsidence or collapse, particularly when the thickness of the residual soil layer is reduced due to excavation. When collapse occurs beneath or adjacent to structures or highways, it may result in extensive damage. The stability of the residual soils that overlie solution cavities in limestone is often a concern during the construction, and a simple means to evaluate the stability of these residual soils may be valuable. In this study, the undrained stability of residual soil in karst terrain was investigated by the Finite Element Method (FEM). The results are summarized in a design chart in terms of dimensionless stability numbers and the geometry of a potential soil void above a cavity in the underlying limestone. The use of the stability chart for short-term stability is demonstrated by an example. Such stability numbers can be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters.