Evaluation of Liquefaction-Induced Lateral Spread

Transcription

1 INDIAN GEOTECHNICAL SOCIETY CHENNAI CHAPTER Evaluation of Liquefaction-Induced Lateral Spread S. Senthamilkumar 1 ABSTRACT: The earthquake shaking, during the past major earthquakes, triggered the liquefaction of various types of soils such as saturated sand, sand with silt, silt with sand, clayey soil and damaged several structures due to the ground deformations induced by liquefaction. The existing models, for the determination of liquefaction-induced lateral spread, proposed by various researchers have not estimated actual displacements in many cases. Any new method incorporating the SPT and CPT data in the vicinity of the liquefiable soil deposit near the ground surface will produce good results. Data of liquefaction-induced lateral spreads from 564 case histories of 14 earthquakes for sloping ground and free face with or without sloping ground condition are collected. In this research, a new procedure is developed to estimate liquefaction-induced lateral spreads from the case history data using multi-nonlinear regression analysis. KEYWORDS: Earthquake. Liquefaction, Model studies, SPT and CPT, Multi-nonlinear regression analysis Introduction The earthquake shaking, during the past major earthquakes, triggered the liquefaction of various types of soils such as saturated sand, sand with silt, silt with sand, clayey soil and damaged several structures due to the ground deformations induced by liquefaction. The 1964 Alaska and 1964 Niigata Earthquakes brought to limelight the phenomenon of earthquake-induced liquefaction of soils and its related ground failures. The liquefaction induced ground failure includes flow slides, lateral spreads, ground settlement, ground oscillations and sand boils. Specifically lateral spreads are the pervasive types of liquefaction induced ground failure on sloping ground, free face with or without sloping ground (Zhang et al 2004). In this research, efforts have been taken to collect more published data such as lateral displacements, standard penetration test (SPT) and cone penetration test (CPT) results, earthquake details, topographical features etc., from the past earthquake case histories. The existing models, for the determination of liquefactioninduced lateral spread, proposed by various researchers (Hamada et al 1986, Towhata et al 1992, Tokida et al 1993, Bartlett and Youd 1995, Rauch and Martin 2000, Bardet et al 2002, Youd et al 2002 and Zhang et al 2004) have not estimated actual displacements in many cases (Cetin et al 2002, Cetin et al 2004 and Bray et al 2004). Any new method incorporating the SPT and CPT data in the vicinity of the liquefiable soil deposit near the ground surface will produce good results. Hence, data of liquefaction-induced lateral spreads from 564 case histories of 14 earthquakes for sloping ground and free face with or without sloping ground condition are collected. In this research, a new procedure is developed to estimate liquefaction-induced lateral spreads from the case history data using multi-nonlinear regression analysis. The cyclic stress ratio (CSR), the seismic demand to induce liquefaction on a soil layer, is estimated from simplified procedure proposed by Seed and Idriss (1971) which was later modified by Idriss and Boulanger (2006). Liquefaction potential has been evaluated for the soil deposits using corrected penetration values, PGA. Liquefaction potential index (LPI) is also evaluated. The LPI has been empirically correlated with liquefaction effects, thereby providing an estimation of the severity of liquefaction-induced failures at a specific location for the vulnerable depth of 20 m, while the simplified procedure estimates the liquefaction potential only for a soil element. Using the topographical features and estimated LPI for the case history borehole data, new lateral spread models have been developed with the help of XLSTAT 2007, which is nonlinear multivariable regression analysis software. Liquefaction Potential Index (LPI) Liquefaction potential index (LPI) was developed as one such method to integrate liquefaction potential over a depth and provides an estimate of liquefactionrelated surface damage for a boring location (Iwasaki et al 1982). Many researchers have used the LPI for mapping liquefaction hazard (Lee et al 2004, Juang et al 2005, Holzer et al 2006, Rix and Romero-Hudock 2006 and Lenz and Baise 2007). The liquefaction potential index LPI is defined as 20 LPI = F(z)w(z)dz 0 where F( z) = 1 FS for FS 1 (2) F( z) = 0 for FS >1 (3) ( ) w z = z (4) w(z) is the depth weighting factor and FS is the factor of safety against liquefaction. The proposed liquefaction damage thresholds are: LPI = 0 stands for very low liquefaction risk; LPI 15 stands for low liquefaction risk; 5< LPI 15 stands for high liquefaction risk; and LPI > 15 stands for very high liquefaction risk. (1) 1 PhD Scholar, National Institute of Technology, Tiruchirappalli

2 56 STUDENTS PAPER COMPETITION 2009 A new range of F(z) for the Liquefaction potential index is also proposed by Sonmez (2003), considering the SPT and CPT-based boundary curves. Iwasaki et al (1982) developed their model from the SPT-based boundary curves. Due to variations in the field procedure, the factor of safety may not be the same if it is calculated based on the SPT values and the CPT values independently, even though both SPT and CPT locations are very close. Hence, different factor of safety limits need to be applied to CPT and SPT in order to achieve the same liquefaction potential. Sonmez (2003) proposed the following limits on FS, which are suitable for both SPT and CPT. Fz ( ) = 0 forfs 1.2 (5) F( z) = 1 FS for FS <0.95 (6) ( ) FS F z x 10 e for 1.2>FS>0.95 = (7) Similarly, the classifications for liquefaction damage thresholds proposed by Sonmez (2003) are: 0 - Non-liquefiable; 0 < LPI 2 - Low; 2 < LPI 5 Moderate; 5 < LPI 15-High and LPI > 15-Very high. Liquefaction-Induced Lateral Spread Liquefaction-induced lateral spread analysis needs (Bartlett and Youd 1992): a) ground displacement amplitude data, b) Borehole data, c) ground slope and free face topographical data and d) seismic data. The ground displacement amplitude data have to be measured at liquefied site using any sophisticated methods. Borehole data should contain the penetration resistance values, fines content, particle size distribution, water table etc. Ground slope or free face topographical data is illustrated in Figure 1 to determine the details. The slope of the natural ground is defined as the ratio of horizontal distance to vertical distance in percentage. The free face ratio, in percentage, is defined as the ratio between distance from toe of the free face to point under consideration for the lateral spread determination and height of the crest from toe (height of the free face). Seismic data consists of magnitude, peak ground acceleration and epicentre distance etc. Database of Liquefaction-Induced Lateral Spread Case History The primary purpose of the collection of case history data is to propose a new model using the concept of liquefaction potential index (LPI), which combines the depth, thickness of liquefiable layer and factor of safety against liquefaction. Data are collected from the liquefaction induced lateral spread sites in the past earthquakes. Most of the data are collected from the site with CPT and SPT values that were conducted by United States Geological Survey. Data on 564 lateral spread case histories have been collected from liquefied sites by the researcher. The liquefaction induced lateral spread data are collected from 14 major earthquakes as listed in Table 1. The database consists of 442 SPT data and 122 CPT data. 50% of the data of the database is pertaining to 1964 Niigata Earthquake, which has been collected from the database developed by Bartlett and Youd (1992). The collected data have been broadly classified into three groups: > Sloping Ground condition > Free face condition > Free face with sloping ground condition The data belonging to the above groups are vigorously analyzed using multivariable non-linear regression analysis and individual models have been proposed in the present study. In the proposed models many parameters such as the liquefiable thickness, the mean grain size, fines content and distance from rupture plane are not directly included. Nevertheless, these parameters are incorporated in the calculation of factor of safety against liquefaction and liquefaction potential index. Instead of distance from rupture plane, the peak ground acceleration has been included in the liquefaction analysis. PGA is very much influenced by the local soil conditions and characteristics of soil deposits. Table 1 shows the details of the data set collected in this study. In Table 2, the minimum and maximum values of various parameters are presented. L H Toe Crust Site under consideration 1 X L = Distance from Toe of the Free Face to point at site H = Height of Free Face (Crust elevation - Toe elevation) Wff = Free Face ratio = (H/L)*100% Ssg = Slope of natural ground = (1/X)*100% Fig 1. Definitions of Free Face Ratio and Ground Slope

3 EVALUATION OF LIQUEFACTION-INDUCED LATERAL SPREAD 57 Table 1 Summary of Sites included in the Liquefaction-Induced Lateral Spread Case Histories Study Sl.No. Name of Earthquake Magnitude M No. of Data References San Simeon Earthquake Holzer et al Imperial Valley Earthquake Juran and Jumay Chi-Chi, Taiwan Earthquake Youd 2002, Chu et al Vrancea Earthquake Ishihara and Perley Kocaeli (Izmit), Turkey Earthquake Bray et al 2001, Cetin et al 2004, Bray et al Loma Prieta Earthquake Boulanger et al Alaska Earthquake Bartlett and Youd Borah Peak Earthquake Andrus and Youd Saguenay Earthquake Tuttle et al San Fernando Earthquake Youd 1973, O'Rourke et al 1990, Bartlett and Youd Imperial Valley Earthquake Bartlett and Youd Superstition Hills Earthquake Youd and Bartlett Nihonkai-Chubu Earthquake Youd 1973, O'Rourke 1990, Bartlett and Youd Niigata Earthquake Bartlett and Youd 1992 Total number of data 564 SPT Data 442 CPT Data 122 Table 2 Details of Minimum and Maximum Values of Collected Data Parameter Minimum Maximum Magnitude, M Lateral displacement, D h, cm Peak ground acceleration, a max, g Slope of ground, S sg, % Free face ratio, W ff, % Liquefaction Potential Index, LPI Case No. of Data Sloping ground condition, S sg 311 Free face condition, W ff 199 Free face with sloping ground condition, S sg+w ff 54 Evaluation of Lateral Spread Free Face with Sloping Ground For the free face with sloping ground condition a new approach has been developed for prediction of liquefaction-induced lateral spread during earthquake. For the condition of free face with sloping ground 54 numbers of boreholes and topographical data have been collected. Using multivariable nonlinear regression analysis in the XLSTAT 2007 Equation (8) has been developed for the free face with sloping ground conditions as a power function. A regression coefficient of 0.74 is obtained for this model. D +1 h = LPI W ff S sg (8) where, D h is lateral displacement in cm, LPI is liquefaction index, S sg is the slope of the ground in percentage and W ff is the free face ratio.

4 58 STUDENTS PAPER COMPETITION 2009 Sloping Ground 400 An approach has been presented for prediction of liquefaction-induced lateral spread during earthquake for the sloping ground condition. The 311 data, which were collected from sloping ground condition, are included in the process of nonlinear regression analysis and Equation (9) has been developed. Actual Dh, cm R 2 = ( 0.24( S )) sg+ 0.1 S sg LPI D e e 9.844e = h (9) Figure 2 shows the prediction capabilities of the proposed model as scatter plot of measured versus predicted displacements. It is shown that the models are capable of predicting with a medium accuracy. Free Face Equation (10) has been developed from the 199 data points, which were collected for the free face condition. The variation of actual displacement with the predicted displacement is shown in Figure 3 as scatter plot. D +1 = W LPI (10) h ff Actual (Dh+1), cm Predicted D h, cm Fig. 2 Scatter Plot for the Actual and Predicted Lateral Spread for Sloping Ground Condition R 2 = 1 In Equations (9) and (10), D h, LPI, W ff and S sg are having same descriptions and units as in Equation (8). The accuracy of the calculated displacement using the proposed approach is generally accepted if more than 80% of the calculated lateral displacements are between 50% and 200% of measured lateral displacement values for the field case studies in geotechnical engineering. From the scatter plots, it is concluded that the above requirement is satisfied in all the cases. Hence, the accuracy of the proposed approach may be reasonable and acceptable for low to medium risk projects. In addition, for any approach, few values of predicted results fall outside the range of the measured results, it should be taken with caution and allowance should be made for the uncertainty. It should be noted that a perfect correlation between the soil and earthquake parameters and the lateral spreading is probably impossible due to the errors in the actual data sets and the complex and heterogeneous nature of soil deposits. As well, these models are generated from massive amount of data. In addition, for design purposes, the proposed models are simple to use for the assessment of liquefaction-induced lateral spread. Conclusion A new approach has been proposed based on the liquefaction potential index (LPI), to estimate the liquefaction-induced lateral spread for the free face with sloping ground condition has been developed using multivariable nonlinear regression analysis. It is concluded that more than 80% of the calculated lateral displacements are between 50% and 200% of measured lateral displacement. Hence, the accuracy of the proposed approach may be reasonable and acceptable for low to medium risk projects. The measured lateral displacements of the case histories ranges from few centimeters to 10.16m and therefore the relevant models can be used for displacements within this range. Hence, an earthquake magnitude in the range of 5.9 to 9.2 is applicable for the above range. The peak ground acceleration, as discussed earlier, influences the liquefaction-induced deformations. It is obtained with the values between 0.13g and 0.67g, which cover wide range. Thus this approach may be applied for the above range of peak ground acceleration. The slope of ground and free face ratio are varying from 0 to 17.38% and 0 to 55.68% respectively. Thus, this approach covers large ranges. It may be applied for the values lying in the above ranges. References Predicted (Dh+1), cm Fig. 3 Scatter Plot for the Actual and Predicted Lateral Spread free Face Condition Andrus R.D. and Youd T.L. (1987) Subsurface Investigation of a Liquefaction Induced Lateral Spread, Thousand Springs Valley, Idaho: U.S. Army Corps of Engineers Miscellaneous Paper GL-87-8, p Bardet J.P., Tobita T., Mace N. and Hu J. (2002) Regional Modelling of liquefaction Induced Ground Deformation, Journal of Earthquake Spectra, Vol. 18, pp Bartlett S.F. and Youd T.L. (1992) Empirical Analysis of Horizontal Ground Displacement Generated by Liquefaction-Induced Lateral Spread, Technical Report No. NCEER , National Center for Earthquake Engineering Research, Buffalo, New York.

5 EVALUATION OF LIQUEFACTION-INDUCED LATERAL SPREAD 59 Bartlett S.F. and Youd T.L. (1995) Empirical Prediction of Liquefaction-Induced Lateral Spread, Journal of Geotechnical Engineering, Vol. 121, No. 4, pp Boulanger R.W., Idriss I.M. and Mejia L.H. (1995) Investigation and Evaluation of Liquefaction Related Ground Displacements at Moss Landing During the 1989 Loma Prieta Earthquake, Report No. UCD/CGM-95/02, Center for Geotechnical Modeling, Department of Civil and Environmental Engineering, University of California, Davis. Bray J.D., Sancio R.B., Youd L.F., Christensen C., Cetin O.K., Onalp A., Durgunoglu T., Stewart J.P., Seed R.B., Baturay M.B., Karadayilar T. and Oge C. (2001) Documenting Incidents of Ground Failure Resulting from the August 17, 1999 Kocaeli, Turkey Earthquake, Pacific Earthquake Engineering Research Center website: Bray J.D., Sancio R.B., Youd L.F., Christensen C., Cetin O.K., Onalp A., Durgunoglu T., Stewart J.P., Seed R.B., Baturay M.B., Karadayilar T., Oge C. and Ertan Bol (2004) Subsurface Characterization at Ground Failure Sites in Adapazari, Turkey, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 130, No. 7, pp Cetin K.O., Youd T.L., Seed R.B., Bray J.D., Sancio R., Lettis W., Yilmaz M.T., and Durgunoglu H.T. (2002) Liquefaction-Induced Ground Deformations at Hotel Sapanca during Kocaeli (Izmit), Turkey earthquake, Soil Dynamics and Earthquake Engineering, Vol. 22, No. 9-12, pp Cetin K.O., Youd T.L., Seed R.B., Bray J.D., Stewart J.P., Durgunoglu H.T., Lettis W. and Tolga Yilmaz M. (2004) Liquefaction Induced Lateral Spreading At Izmit Bay During The Kocaeli (Izmit) - Turkey Earthquake, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 130, No. 12, pp Chu D.B., Stewart J.P., Youd T.L. and Chu B.L. (2006) Liquefaction-Induced Lateral Spreading in Near-Fault Regions during the 1999 Chi-Chi, Taiwan Earthquake, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 132 No.12 pp Hamada M., Yasuda S., Isoyama R. and Emoto K. (1986) Study on Liquefaction-Induced Permanent Ground Displacements, Association for the Development of Earthquake Prediction, Japan. Holzer T.L., Bennett M.J., Noce T.E., Padovani A.C. and Tinsley III J.C. (2006) Liquefaction Hazard Mapping with LPI in the Greater Oakland, California area, Earthquake Spectra, Vol. 22, No. 3, pp Holzer T.L., Noce T.E., Bennett M.J., Di Alessandro C., Boatwright J., Tinsley J.C., III Sell R.W. and Rosenberg L.I. (2004) Liquefaction-Induced Lateral Spreading at Oceano, California, during the 2003 San Simeon earthquake, U.S. Geological Survey Open-file Report (Accesed on ). Idriss I.M. and Boulanger R.W. (2006) Semi-Empirical Procedure for Evaluating Liquefaction Potential during Earthquake, Soil Dynamics and Earthquake Engineering, Vol. 26, No. 2-4, pp Ishihara K. and Perlea V. (1984) Liquefaction-Associated Ground Damage during the Vrancea Earthquake of March 4, 1977, Soils and Foundations, Journal of the Japanese Society of Soil Mechanics and Foundation Engineering, Vol. 24, No. 1, pp Iwasaki T., Tokida K., Tatsuoka F., Watanabe S., Yasuda S. and Sato H. (1982) Microzonation for Soil Liquefaction Potential using Simplified Methods, Proceedings of the 3rd International Conference on Microzonation, Vol. 3, pp Juran I. and Tumay M.T. (1989) Soil Stratification Using the Dual-Pore-Pressure Piezocone Test, Transportation Research Record 1235, National Academy Press, pp Juang C.H., Yuan H., Li D.K., Yang S.H. and Christopher R.A. (2005) Estimating Severity of Liquefaction-Induced Damage near Foundation Journal Soil Dynamics and Earthquake Engineering, Vol. 25, pp Lee D.H., Ku C.S. and Yuan H. (2004) A study of the Liquefaction Risk Potential at Yuanlin, Taiwan, Engineering Geology, Vol. 71, No. 1-2, pp Lenz J.A. and Baise L.G. (2007) Spatial Variability of Liquefaction Potential in Regional Mapping Using CPT and SPT Data, Soil Dynamics and Earthquake Engineering, Vol. 27, pp O Rourke T.D., Stewart H.E., Blackburn F.T. and Dickerman T.S. (1990) Geotechnical and Lifeline Aspects of the October 17, 1989 Loma Prieta Earthquake in San Francisco, Technical Report NCEER , National Center for Earthquake Engineering Research, Buffalo, New York. Rauch A.F. and Martin J.R. (2000) EPOLLS Model for Predicting Average Displacements on Lateral Spreads, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 126, No. 4, pp Rix G.J. and Romero-Hudock S. (2006) Liquefaction Potential Mapping in Memphis and Shelby County, Tennessee,Earthquake Spectra, oad/ MEM/memphis_lpi.pdf. Seed H.B. and Idriss I.M. (1971) Simplified Procedure for Evaluating Soil Liquefaction Potential, Journal of Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. 9, pp Sonmez H. (2003) Modification of The Liquefaction Potential Index and Liquefaction Susceptibility Mapping for a Liquefaction-Prone Area (Inegol, Turkey), Environmental Geology, ASCE, Vol. 44, No. 7, pp Tokida K., Matsumoto H., Azuma T. and Towhata I. (1993) Simplified Procedure to Estimate Lateral Ground Flow by Soil Liquefaction, In: Cakmak A.S., Brebbia C.A.,Editors.Proceedings of the Fifth International Conference on Soil Dynamics and Earthquake Engineering, New York: Elsevier Applied Science, Vol. 6, pp Towhata I., Sasaki T., Tokida K.I., Matsumoto H., Tamari

6 60 STUDENTS PAPER COMPETITION 2009 Y. and Yamada K. (1992) Prediction of Permanent Displacement of Liquefied Ground By Means of Energy Principle, Soils and Foundations, Vol. 32, No. 3, pp Tuttle M., Tim Law K., Seeber L. and Jacob K. (1990) Liquefaction and Ground Failure Induced by the 1988 Sagnenay, Quebec, earthquake, Canadian Geotechnical Journal, Vol. 27, pp Youd T.L. (1973) Ground movements in Van Norman Lake Vicinity during San Fernando, California, Earthquake, U.S. Dept. of Commerce, Natl. Oceanog, and Atmospheric Adm, Vol. 3, pp Youd T.L. (2002), Youd, Hansen, and Bartlett Database for Induced Lateral Spreads, data.html (Accessed on ). Youd T.L. and Bartlett S.F. (1988) US Case Histories of Liquefaction-Induced Ground Displacement 1 st Japan- United States Workshop on Liquefaction, Large Ground Deformation and Their Effects on Lifeline Facilities, Tokyo, pp Youd T.L., Hansen C.M. and Bartlett S.F. (2002) Revised Multilinear Regression Equations for Prediction of Lateral Spread Displacement Journal of Geotechnical and Geoenvironmental Engineering, Vol. 128, No. 12, pp Zhang G., Robertson P.K, and Brachman R.W.I. (2004), Estimating Liquefaction-Induced Lateral Displacements Using the Standard Penetration Test or Cone Penetration Test, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 130, No. 8, pp