Missouri University of Science and Technology Scholars' Mine International Conferences on Recent Advances 2010 - Fifth International Conference on Recent in Geotechnical Earthquake Engineering and Advances in Geotechnical Earthquake Soil Dynamics Engineering and Soil Dynamics 27 May 2010, 8:45 am - 9:15 am Criterions, Prediction and Prevention of Loess Liquefaction Lanmin Wang Lanzhou Institute of Seismology, China Earthquake Administration, China Zhongxia Yuan Lanzhou Institute of Seismology, China Earthquake Administration, China Haimei Sun Lanzhou Institute of Seismology, China Earthquake Administration, China Jin Deng Lanzhou Institute of Seismology, China Earthquake Administration, China Follow this and additional works at: https://scholarsmine.mst.edu/icrageesd Part of the Geotechnical Engineering Commons Recommended Citation Wang, Lanmin; Yuan, Zhongxia; Sun, Haimei; and Deng, Jin, "Criterions, Prediction and Prevention of Loess Liquefaction" (2010). 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CRITERIONS, PREDICTION AND PREVENTION OF LOESS LIQUEFACTION Lanmin Wang Zhongxia Yuan, Haimei Sun, Jin Deng Lanzhou Institute of Seismology, Lanzhou Institute of Seismology, China Earthquake Administration China Earthquake Administration Lanzhou, Gansu-China 730000 Lanzhou, Gansu-China 730000 ABSTRACT Although loess liquefaction is not very common during earthquakes in Northwest of China, it is disastrous if it happens. Both study and valid evidence from Haiyuan 8.5 Earthquake in 1920 and Tajikistan 5.9 Earthquake in 1989 have proved that loess liquefaction could be very disastrous under certain conditions. In this paper, the criterions of loess liquefaction are discussed to show that unlike typical liquefaction of sand, loess which falls into the category of both silt clay and clayey silt has unique characteristics during liquefaction test. To predict liquefaction of loess, a simple method based on laboratory test and field evidences using GIS is proposed. The prediction results and corresponding measure have been adopted in Seismic Design Code for Buildings in Lanzhou Urban Area. Finally, recent approach of treatment of loess with chemicals methods is developed, which may have some application implication as an simple and feasible treatment method against liquefaction of loess. INTRODUCTION Loess is widely distributed in Northwest of China, where along the hillside. Even 50 years later, the flow trace of the Loess Plateau, with 400,000 square kilometers, is the largest loess can still be identified in the field. In 1990, based on field plateau of loess in the world. The plateau is covered by thick investigation, an overall assessment of loess liquefaction were loess layer, which is from tens meters to more than 500 meters. given by Bai et al. (Bai, 1990), since then there comes a great Lanzhou, Gansu area, with completely developed loess layer interest for loess liquefaction study. Wang Lanmin performed and large deposit thickness, has been named as “the thickest dynamic triaxial test of loess liquefaction and made inversion loess sedimentation area in the world” and represents the analyses of the three cases, which shows that the PGAs typical geological characteristics of the loess layer in China. triggering loess liquefaction during the Haiyuan earthquake, New Madrid earthquake and Tajik earthquake are respectively For a long period, liquefaction of silt soils including loess is around 380gal, 240gals and 150gals. not recognized even if there were some study and it is often controversial. This attitude changed during 1990’s. Loess Liquefaction of loess is unique in many ways. First of all, it is liquefaction is not very common but surely observed during a flow type of liquefaction. That is, under the effect of cyclic earthquakes in Northwest of China and other part of the world loading, the pore water pressure in loess rises, effective stress like Tajikistan and central states of Untied States (Ishihara, is down and large amount of residual strain develops, finally, 1990; Hwang and Wang, 2000). During Haiyuan 8.5 loess loses its strength and became mud flow. The amount of Earthquake in 1920, Tajikistan 5.9 Earthquake in 1989 and residual strain as it is shown in dynamic test could easily be much earlier, the New Madrid earthquake in 1811-1812, there more than 10%, which is really huge. The loess sample after were loess liquefaction which caused landslides of nearly liquefaction test is very soft and cannot stand on itself without horizontal layers and other types of geotechnical hazard. leaving for desiccation of certain amount of time. The shape of Villages were buried and hundreds of lives lost for the cases of sample, which is a normal cylinder before liquefaction test, China and Tajikistan. Investigation and records have shown turns into a bulged form at the bottom (Fig.1). This indicates that Haiyuan earthquake caused the rise of the underground that loess samples turns into a mud flow due to liquefaction. water of nearly 4-5 meters, which led to liquefaction in Late An interesting feature of microstructure of loess after Pleistocene(Q3) loess layer at depth of 14-16m. The sliding liquefaction test is the formation of many round holes, which distance reached a maximum of 1.5km of the super stratum do not observed in sample before test. The diameter of these Paper No. OSP 11 1 round holes is from 60 to 200 micron(Fig.2 ). Because of its liquefaction, the pores were damaged and the particles regular shape, it has to do with the pore water movement. We rearranged to contact more closely each other. assume that there are two reasons for the formation of such round holes: 1. during the test there are collapse of Since 1990’s liquefaction of Loess has been an hot topic and microstructure which formed a larger pore, 2. the pore water on the front of scientific exploration. Wang L.M et al (1996, movement using such holes as main channel, and thus they are 1999) carried comprehensive study on the liquefaction also subjected to pore water pressure, which is homogenous, characteristics of loess liquefaction and its mechanism. Also, the homogenous pore water pressure caused these holes to sit explosion is applied to show that loess liquefaction is have a round shape. This phenomenon also indicates that possible. Yang Zhenmao et al. (2004) studied the pore because of low permeability of loess, pore water movement is pressure increase characteristics and steady state strength. quite uneven at different parts of the sample, most of the pore Yuan Zhongxia et al. (2004) studied on mechanism and water running through the channels composed with the round discrimination criterion of loess liquefaction and regarded that holes and channels connecting or around them. loess liquefaction is a “ flow type” and has large deformation. Liao Shengxiu, Chen Juhong (2007) using hard evidence from site, showed that long duration of mechanical vibration of pile driver caused liquefaction of loess field. Wang L.M et al. (2007) applied the research results into practices through drafted “Seismic Design Code for Buildings in Lanzhou Urban Area”, which is the first local engineering specification for the discrimination and treatment of loess liquefaction. The loess liquefaction is fall into the category of liquefaction of silt-clay mixtures as the term used by American scientists. Prakash et al. (1998) proved that PI and initial void ratio are two relatively independent parameters, which decide whether the loess could liquefies or not. And the age and structure decide the pattern of pore pressure increase during liquefaction. The development of pore pressure and strain Fig.1 Loess samples after liquefaction test during loess liquefaction are different from that of sand under the cyclic loading. Boulanger and Idriss (2006) divided the liquefaction behavior into “sand-like” and “clay-like”. This through new light on study of liquefaction of loess and draw a clear line on problems and type of silt soils that were debatable as far as liquefaction is concerned. Although liquefaction mechanism and behaviors of loess have been studied, there is also some no well established test procedures and criteria to assess liquefaction potential or treat loess ground for liquefaction. With the development of urbanization and agriculture irrigation, the area of saturated loess and loess with high water content has been enlarging. There is a very high probability to liquefy loess under the earthquake with certain intensity. So there is still urgent need to study loess liquefaction and clarify some of the filed where 600μm which it still not well accepted or recognized. Fig.2 Microstructure of loess after liquefaction (Magnification factor: 100) TEST OF LOESS LIQEFACTION There is a major difference between liquefaction of sand and that of loess. For sand liquefaction, it is the result of Most laboratory loess liquefaction tests have been done on the densification of sand structure which forced some portion of electromagnetic dynamic triaxial instrument in Lanzhou water move out from the skeleton and even rise up. But for Institute of Seismology (LIS) before 2006. The instrument has loess, because of its low permeability, water cannot move as some disadvantages, such as, lacking of back pressure for freely as it is in sand. As a result, the pore water pressure saturation, open-loop control and which makes the test process buildup applies shear stress to loess structure and causes it to rather awkward sometimes.