Sei Sun Hong, Korea Institute of Geoscience and Mineral Resources (Republic of Korea)
Jin Young Lee, Korea Institute of Geoscience and Mineral Resources (Republic of Korea)
Hyun Soo Yun, Korea Institute of Geoscience and Mineral Resources (Republic of Korea)
Ju Yong Kim, Korea Institute of Geoscience and Mineral Resources (Republic of Korea)
Bedrock quality studies for the preparation of digital maps have been carried out since 2003 in Korea. The purpose of bedrock quality mapping is to provide information about the characteristics of natural geological environments for planning land use, assessment of the best use of different rock types, and site characterization of suitable exploitation area.
Bedrock quality map is a type of geological map which provide a generalized representations of slope gradient, weathering depth of basement rocks, discontinuity patterns of joints and veins, depth to unconsolidation material and technical properties of crushed rock materials. This thematic map is planned to cover the Daeah sheet(1:25,000) near the Jeonju city because of extensive infra-structural activities. The compilation of the bedrock quality map is based on the field examination of the main geological rock units. A total of 400 localities were studied, and from 22 sites, approximately 40kg of crushed rock materials from each sites were collected for physical quality analyses. Crushed rock materials were mainly taken from quarries and blasted road-cuts. The list of mechanical property analysis includes density, water absorption, point load test, bulk density, solid content, impact value, LA value, size analyses and amount of material finer than 0.08mm sieve.
In the Daeah area, the depth to unconsolidated materials ranges to 1 m in average. Weathering degree was divided into four groups, i.e., fresh rock(FR), slightly weathered rock(SWR), moderated weathered rock(MWR) and highly weathered rock(HWR). FR and SWR are distributed in southwest and northeast area. Most of outcrops investigated are composed of FR(21%), SWR(49%) and subordinated MWR(26%), HWR(4%). Weathering depth was grouped into three parts, i.e., below 1m, 1¢¦5m, above 5m. The outcrops having weathering depth below 1m are about 60%, about 30% in 1¢¦5m depth, and about 10% in above 5m. Among different rock types, the granites with coarse grains have deeper weathering depth than fine- grained rocks such as schist, acidic tuff, and rhyolitic rocks.
When physical properties of different rock types in the Daeah area are compared, absorption ratios are very similar falling within the narrow range of 0.5% while absolute dry density show considerable changes.