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http://dx.doi.org/10.7843/kgs.2018.34.12.29

Strength Characteristics of Sedimentary Rock in Daegu-Gyungbuk Area Followed by Saturation and Crack Initiation  

Park, Sung-Sik (Dept. of Civil Eng., Kyungpook National Univ.,)
Kim, Seong-Heon (Dept. of Civil Eng., Kyungpook National Univ.,)
Bae, Do-Han (Youth Housing Planning Dept., Korea Land & Housing Corporation)
Publication Information
Journal of the Korean Geotechnical Society / v.34, no.12, 2018 , pp. 29-42 More about this Journal
Abstract
Shale and mudstone in Daegu-Gyungbuk area have low strength and resistance to weathering compared to other rocks. Therefore, it is necessary to evaluate their strength depending on the degree of saturation and crack development. In this study, shales and mudstones were collected from several construction sites in Daegu-Gyungbuk area. Their basic material properties such as porosity, SEM, chemical component, and durability were tested. A porosity (absorptivity) of mudstone was 31% (25%), which was 6 (8) times higher than that of shale. Some mudstone was easily disintegrated with water and it consisted of highly-active clay mineral such as smectite type. These rocks were prepared by small cube specimens for unconfined compression test. An unconfined compressive strength of dry rock was compared with saturated one. Microwave oven was operated step by step to stimulate void water within a saturated rock, which resulted into high temperature and micro crack initiation within rocks. A strength of microwaved rocks was compared with operation time and crack initiation. As a result, the average unconfined compressive strength of dry and saturated shale was 62 and 33 MPa, respectively. The strength of mudstone for each condition was 11 and 4 MPa. When a rock became saturated, its strength decreased by 47% and 64% for shale and mudstone at average. In addition to saturation, a rock was in the microwave for 15 secs, its strength decreased into 49% for shale and 52% for mudstone. When a microwave oven operated up to 20 sec, a rock was crushed into several pieces and its temperature was approximately 200 degrees.
Keywords
Shale; Mudstone; Strength; Saturated; Microwave oven;
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