Journal of MMIJ (Nov 2018)
Analyzing the Impacts of Rainfall on Rock Slope Behavior in Une Mine and Evaluating the Effec-Tiveness of Countermeasure Methods
Abstract
Forward and downward displacements were measured in a section of a limestone slope in the Une mine, Ryoko Lime Industry Co. Ltd. Although the causes of rock slope behaviors at Une site have not been clarified, but rainfall unambiguously impacts on the rock slope. Une mine has taken countermeasures that are generally considered to be effective to stabilize the rock slope without delay. In this study, displacements were monitored using a crack gage installed over the fracture plane in an observation crosscut excavated in the rock slope on 1,010 mL. And it is found, the measured fracture displacements can be classified into two types:“ Type 1 displacement” not directly related to rainfall and“ Type 2 displacement” due to rainfall. All the displacements observed on the monitoring points located on the rock slope and by the crack gages installed other than 1,010 mL were analyzed and found to be composed of the Type 1 and Type 2 displacements. The areas with a large impact of rainfall were identified and the geological/geotechnical characteristics of the areas were investigated to prepare new countermeasures. In order to evaluate the effects of the countermeasures, the author formulated a statistical equation predicting the rock slope displacements from the rainfall history before applying any countermeasures for stabilization. It is confirmed the statistical equation gives a fairly fine agreement between actual and predicted displacements before commencing the countermeasures reducing the rainfall impacts. In addition, the statistical equation also makes possible the quantitative evaluation of the effects of the countermeasures, namely difference between predicted displacement without any countermeasures and observed displacement after activating the countermeasures. As a result, the statistical equation will be used for planning comprehensive and strategic stabilization projects in future for the Une rock slope.
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