- Email: [email protected]
Geological and geotechnical investigation on in situ stress regime around the Yangsan Fault Zone in Korea
Tunnelling and Underground Space Technology incorporating Trenchless Technology Research
Tunnelling and Underground Space Technology 21 (2006) 243
www.elsevier.com/locate/tust
Geological and geotechnical investigation on in situ stress regime around the Yangsan Fault Zone in Korea S.O. Choi, B.J. Lee, H.S. Shin Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea
For the purpose of designing and analyzing the stability of the B-tunnel, which is a part of the Korea Train Express (KTX) Gyeongbu Line and plans to pass through the existing Gyeongbu 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 the fault zone, authors used two boreholes, which were excavated in a base rock at both sides of the Yangsan Fault. Results from hydraulic fracturing tests for two boreholes show an obvious difference in magnitude and direction of principal stresses in rock mass. The difference in geological origin for andesitic rocks and sedimentary rocks would be one reason for this, and the direction of fault running would be another. Geological survey has been resulted to that the andesitic rocks are dominant in the western part of the Yangsan fault and the sedimentary rocks are prevalent in the eastern part. And the directions of fault running are NS in the andesitic rocks and NNE in the sedimentary rocks. This phenomenon explains very well that the directions of the maximum horizontal principal stress are 24° clockwise from the true north in the andesitic rock mass and 6° in sedimentary rocks, respectively. The Yangsan Fault is known to be a strike-slip fault in the geological sense. Authors expect that it will be proven mechanically with the additional hydraulic fracturing tests in a great depth. Depth (m)
Sv (MPa)
Sh (MPa)
SH (MPa)
K
SH Dir. (°)
Kh
KH
Mean
Average
TB-35-4 (in andesitic rocks) 26 0.697 28 0.750 34 0.911 46 1.233 48 1.286 64 1.715 66 1.769
1.431 1.643 1.353 – – 2.398 2.951
2.239 2.760 2.167 – – 3.999 4.699
2.05 2.19 1.49 – – 1.40 1.67
3.21 3.68 2.38 – – 2.33 2.66
30 ± 5 25 ± 5 25 ± 5 – – 20 ± 5 20 ± 5
24 ± 5
TB-37-6 (in sedimentary rocks) 20 0.536 23 0.616 30 0.804 34 0.911 38 1.018 41 1.099 45 1.206
2.264 2.100 2.389 2.526 2.246 2.639 2.668
3.157 2.218 3.006 3.247 2.518 3.471 3.897
4.22 3.41 2.97 2.77 2.21 2.40 2.21
5.89 3.60 3.74 3.56 2.47 3.16 3.23
0±5 10 ± 5 10 ± 5 5±5 5±5 5±5 –
6±5
Keywords: Hydraulic fracturing test; The Yangsan Fault; In situ stress regime
doi:10.1016/j.tust.2005.12.021
Tunnelling and Underground Space Technology 21 (2006) 243
www.elsevier.com/locate/tust
Geological and geotechnical investigation on in situ stress regime around the Yangsan Fault Zone in Korea S.O. Choi, B.J. Lee, H.S. Shin Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea
For the purpose of designing and analyzing the stability of the B-tunnel, which is a part of the Korea Train Express (KTX) Gyeongbu Line and plans to pass through the existing Gyeongbu 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 the fault zone, authors used two boreholes, which were excavated in a base rock at both sides of the Yangsan Fault. Results from hydraulic fracturing tests for two boreholes show an obvious difference in magnitude and direction of principal stresses in rock mass. The difference in geological origin for andesitic rocks and sedimentary rocks would be one reason for this, and the direction of fault running would be another. Geological survey has been resulted to that the andesitic rocks are dominant in the western part of the Yangsan fault and the sedimentary rocks are prevalent in the eastern part. And the directions of fault running are NS in the andesitic rocks and NNE in the sedimentary rocks. This phenomenon explains very well that the directions of the maximum horizontal principal stress are 24° clockwise from the true north in the andesitic rock mass and 6° in sedimentary rocks, respectively. The Yangsan Fault is known to be a strike-slip fault in the geological sense. Authors expect that it will be proven mechanically with the additional hydraulic fracturing tests in a great depth. Depth (m)
Sv (MPa)
Sh (MPa)
SH (MPa)
K
SH Dir. (°)
Kh
KH
Mean
Average
TB-35-4 (in andesitic rocks) 26 0.697 28 0.750 34 0.911 46 1.233 48 1.286 64 1.715 66 1.769
1.431 1.643 1.353 – – 2.398 2.951
2.239 2.760 2.167 – – 3.999 4.699
2.05 2.19 1.49 – – 1.40 1.67
3.21 3.68 2.38 – – 2.33 2.66
30 ± 5 25 ± 5 25 ± 5 – – 20 ± 5 20 ± 5
24 ± 5
TB-37-6 (in sedimentary rocks) 20 0.536 23 0.616 30 0.804 34 0.911 38 1.018 41 1.099 45 1.206
2.264 2.100 2.389 2.526 2.246 2.639 2.668
3.157 2.218 3.006 3.247 2.518 3.471 3.897
4.22 3.41 2.97 2.77 2.21 2.40 2.21
5.89 3.60 3.74 3.56 2.47 3.16 3.23
0±5 10 ± 5 10 ± 5 5±5 5±5 5±5 –
6±5
Keywords: Hydraulic fracturing test; The Yangsan Fault; In situ stress regime
doi:10.1016/j.tust.2005.12.021