KR-97(0-46 (KIGAM Research Report) Geological Hazards Investigation - Relative Slope - stability Map - Korea Institute of Geology, Mining & Materials DISCLAIMER Portions of this document may be illegible electronic image products. Images are produced from the best available original document. KR - 97(C) ~ 46 8 f^L$iSW(KIGAM Research Report) Geological Hazards Investigation - Relative Slope - stability Map - Korea Institute of Geology, Mining & Materials -//SIB- w^,* ^€^,* -s-nm,* ^^^,* Geological Hazards Investigatigtion —Relative Slope-stability Map— Dae-Suk Han,* Won-Young Kim,* Il-Hyon Yu,* Kyeong-Su Kim,* Sa-Ro Lee,* Young-Sup Choi** ABSTRACT The Republic of Korea is a mountainous country; the mountains occupy about three quarters of her land area, an increasing urban development being taken place along the mountainsides. For the reason, planners as well as developers and others must realize that some of the urban areas may be threaten by geologic hazards such as landslides and accelerated soil and rock creeps. For the purpose of environmental land-use planning, a mapping project on relative slope-stability was established in 1996, comprising 2-year-investigation for each of the several areas between 4,000km' and 6,000km" throughout the Republic of Korea. The selected area for the first project encompasses about 5,900km" including the topographic maps of Pusan, Kimhae, Miryang, Yangsan, Pangojin, Tonggok, Onyang, Ulsan, YQngch'On, KySngju, Pulguksa, and Kamp'o, all at a scale of 1=50,000. Investigated in % # f-r- (Environmental Geology division) (Geology division) - i 1996 was the area covering the first seven of the topographic maps mentioned above, while the area of the rest was done in 1997. Many disturbed and undisturbed soil samples, which were collected from the ares of the landslides and unstable slopes, were tested for their physical properties and shear strength. They were classified as GC, SP, SC, SM, SP-SM, SC-SM, CL, ML, and MH according to the Unified Soil Classification System, their liquid limit and plasticity index ranging from 25.3% to as high as 81.3% and from 4.1% to 41.5%, respectively. The internal friction angle of the undisturbed soils varied from 3° to 42.5°, while their cohesion ranged from 2 to 40 kPa. X-ray analysis revealed that many of the soils contained a certain amount of montmorillonite. Based on the available information as well as both field and laboratory investigation, it was found out that the most common types of slope failures in the study area were both debris and mud flows induced by the heavy rainfalls during the period of rainy season; the flows mostly occurred in the colluvial deposits at the middle and foot of mountains. Thus the deposits generally appear to be the most unstable slope forming materials in the study area. Produced for the study area were six different maps consisting of slope classification map, soil classification map, lineament density map, landslide distribution map, zonal map of rainfall, and geology map, most of them being stored as data base. Using the first four maps and GIS, two sheets of relative slope-stability maps were constructed, each at a scale of 1:100,000; the maps can be utilized for regional land-use planning. - n 1. 4 4....................................................................................................................................... 1 2. *1 ! ....................................................................................................................................... 3 3. *1 1....................................................................................................................................... 6 3-1. 7B 1................................................................................................................................6 3-2. *11711.5. ....................................................................:...................................................... 9 3-3. 4 1 .............................................................................................................................. 11 3-4. *114#.......................................................................................................................... 13 3- 5. *119-2: .......................................................................................................................... 23 4. 44#4(Slope movements) ..................................................................................................25 4- 1. 4 4..............................................................................................................................25 4-2. 4 5..............................................................................................................................39 4- 3. -FHl-S^h.......................................................................................................................... 41 5. 4^149 ..................................................................................................................................46 5- 1. S44 1-511 41...............................................................................................48 5-2. *1-11:11 chart............................................................................................................ 54 5-3. 11-41 41 ................................................................................................................. 55 5-4. Flow! ■§•#.......................................................................................................56 5- 5. !*M 4 4414!............ 57 6. ntMEMM*, 94 4 4^1 H............................................................................................... 99 6- 1. ell 014 nil o]>, 94 ..........................................................................................................99 6-2. 4*115. ............................................................................................................................ 101 7. 4! 411 445................................................................................................................110 8. 4 4....................................................................................................................................112 #2.44.....................................................................................................................................114 m LIST OF FIGURES Figure 1. Map showing the study area................................................................................... 2 Figure 2. Hillshaded map of the study area........................................................................... 5 Figure 3. Simplified geology map and the index of 1:50,000 geologic sheet........................7 Figure 4. Geological map of the study area............................................................................8 Figure 5. Stratigraphic classification of the Gyeongsang BasinCafter Choi, et al., 1981). •••••.....................................................................................................................10 Figure 6. Mechanism for the downhill movement of material on a slope caused by soil creep(after E. Bryant, 1991). .....................................................................25 Figure 7. Diagram showing creep and its effects(after Sharpe, 1983). ..............................26 Figure 8. Trunks of trees curved by creeping colluvium, 2nd Moonhyondong, Pusan. Photo taken September, 1996. ............................................................................... 27 Figure 9. Masses of rock moved downslope primarily by falling or bouncing through the airCafter T. H. Nelsen, 1979). .......................................................... 28 Figure 10. Example of soil fall : a soil block(see the arrow mark) failed from the colluvium cliff artificially cut at the foot of the Imho mountain, Kimhae. Photo aken April, 1996. ............................................................................28 Figure 11. Example of rock fall : huge rock masses failed from the volcanic rock cliff, Taejongde, Pusan. Photo taken September, 1996. ........................... 29 Figure 12. Toppling failures : (a) Single; (b) Multiful; (c) Debris topple! 1) Weak sub-stratum; 2) Stream erosion! 3) Beach; 4) Sand," 5) Tension crack; 6) Clayey gravel; 7) Intact tilKafter G. P. Giani, 1992). ........................ 30 Figure 13. Flexural toppling (after Goodman and Bray, 1976). .............................................31 Figure 14. Block toppling (after Goodman and Bay, 1976). ...................................................31 Figure 15. Block flexural toppling(after Goodman and Bray, 1976). ...................................32 Figure 16. Main types of rotational slides(after D. Vames, 1978): (a) Single! (b) Multiple; (c) Successive; 1) Slope instability; 2) Base in stability; 3) Rocky surcharge! 4) Clay; 5) Bed-rock. .........................................32 - iv - Figure 17. Principal types of translational slides: 1) Sheet slides: 2) Slab slides; 3) Rcok slides (a-d: 2-D phenomena; e-h: 3-D phenomena; 4) Debris slides; 5) Sudden spreading failuresCafter Hutchinson, 1988: Kovari and Fritz, 1984). ...................................................................................33 Figure 18. Soil slump at Dukamri, Juchonmyon, Kimhae. Photo taken April, 1996. ........35 Figure 19. Successive slumps at Dusami, Taedongmyon, Kimhae, 1978. (Courtesy of the Forest Dept, of Kyongsangmando). ......................................... 35 Figure 20. Wedge failure