Geological and geotechnical investigation on in situ stress regime around the Yangsan Fault Zone in Korea

Abstract

For the purpose of designing and analyzing the stability of the B-tunnel which is a part of the Korea Train Express (KTX) Kyungbu Line and is planned to pass through the existing Kyungbu Expressway as well as the Yangsan Fault zone, the in-situ stress regime on this site has been measured by hydraulic fracturing tests to compare with the geological survey results. The Yangsan Fault is one of the major faults in Korea. Apart from a fold that shows the ductile deformation behavior, a fault shows a characteristic of the brittle deformation behavior and it is very important to perform a drastic survey on the fault to get the information on shape, dimension, mechanical properties, and so forth. Considering the impossibility of any borehole tests in fault zone, the authors used the two boreholes which are excavated in a base rock at both sides of the Yangsan fault. The hydraulic fracturing test results are proven to be in accord with the geological survey results. In other words, the geological site investigation let us know that the direction of fault movement is NS to NNE, and the geotechnical results by hydraulic fracturing tests show that the direction of the maximum horizontal principal stress is 6 to about 24 degrees from the true north. In-situ stress measurements on and around the fault zone are known to be uncommon all over the world, and this study is the first case in Korea. In view of this, the authors insist that this result will be helpful to analyze the stability of the B-tunnel, and can be applied to other similar cases in tunnel construction field. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.