Presentation on theme: "Application of CPT data for evaluation of ground liquefaction in Chi-Chi Earthquake, Taiwan D.H. Lee 1, C.S. Ku 2, C.S. Chen 1, C.H. Juang 3 &J.H. Wu 3."— Presentation transcript:
Application of CPT data for evaluation of ground liquefaction in Chi-Chi Earthquake, Taiwan D.H. Lee 1, C.S. Ku 2, C.S. Chen 1, C.H. Juang 3 &J.H. Wu 3 1 National Cheng Kung University, Taiwan 2 I-Shou University, Taiwan 3 Clemson University, USA
Acknowledgment This study was sponsored by the National Science Council of Taiwan (Grant No. ： NSC 91-2211-E-214-006)
Evaluation of ground liquefaction in the Chi- Chi, Taiwan earthquake using CPT data u CPT equipment and test procedure u CPT data of the liquefied areas u Soil resistance change of the liquefied area u Post earthquake assessment of liquefaction u CPT-based liquefaction curve u Summary and Conclusion
CPT equipment and procedure u CPT is a relatively rapid and reliable in-situ test that can provide an almost continuous soil profile. u Cone :apex angle=60 o, base area=10cm 2, friction sleeve area = 150cm 2. u Penetration rate is about 20 ±5 mm/sec, readings are taken at every 50mm.
CPT sounding Raw data ： Cone resistance (q c ), Local friction (f s ), Porewater pressure (P w )
CPT data of the liquefied area The liquefaction manifestations in Yuanlin, Nantou, Wufeng and Changhua coastal industrial park are more apparent and more extent. 275 CPT soundings were collected from these liquefied sites. Most of the CPT explorations in land were conducted by MAA for TNCREE. In the newly reclaimed area, CPT sounding were conducted by the writers.
Geotechnical Characteristic of the liquefied area According to these SCPT soundings at the liquefied area, the continuous sandy soil (SP, SP-SM, SM) with low cone resistance and slow Vs were observed, it could be the most susceptible liquefaction layer.
Soil resistance change of the liquefied area u It is a interesting that the alteration of the soil characteristics with time at the liquefied site after an earthquake. u The CPT are employed at the same location but in different time (November, 1999, July, 2000, and May, 2002), and the results were used to check the soil resistance change of the liquefied area.
Soil resistance change of the liquefied area The CPT profiles of LW- C1, wherein the sand boil occurred, the changes of q c data were relatively small. The CPT profiles of LW- C2, non-liquefied evidence observed therein, the q c, f s and porewater pressure are no obvious difference between the two stages soundings.
Post earthquake assessment of liquefaction Simplified methods Vs-based method SPT-based method CPT- based method Olsen (1981~1997) Robertson (1983~1998) Juang (1999~2003): probabilistic methods
Assessment of liquefaction potential at LW-C1 (liquefied) A thick layer with high probability of liquefaction can be observed.
Assessment of liquefaction potential at LW-C2 (non-liquefied) Most of the soil are with small to medium probability of liquefaction
CPT-based liquefaction curve ※ Liquefaction or non-liquefaction The sounding could be judged as the occurrence of liquefaction when the liquefaction phenomena such as sand boils, ground subsidence, lateral spread and building settlement are observed on the ground. ※ The liquefaction related phenomena only indicate that the liquefactions occur in the place but not the precise location or depth.
Evaluation Criteria The liquefied soil could be disturbed to a loose state and has lower cone resistance value. The resistance of the non-liquefaction soil have insignificant changes and are almost the same as their original values. The sandy soil with normal high cone resistance values could be considered as non-liquefaction.
This soil is defined as non-liquefied layer because of it high cone resistance value. ?
Summary and Conclusion A thick continuous loose sandy soil with low resistance and slow shear wave velocity were measured, and this layer could be the most susceptible to liquefaction. From the liquefied and not liquefied CPT soundings of the different periods after the Chi-Chi earthquake, the soil resistances in the liquefied zone almost don’t change.
Summary and Conclusion (cont.) A site with liquefaction experiences in an earthquake will not necessarily reduce its liquefaction potential in the future seismic events. According to the proposed judgment criteria of liquefaction or non-liquefaction in this study, 46 liquefaction cases and 88 non-liquefaction cases could be derived from the 43 CPT soundings in the liquefied areas during Chi-Chi earthquake.