Evaluation of temperature and freeze–thaw effects on excess pore pressure generation of fine-grained soils Kenan Hazirbaba a,n , Yu Zhang b , J. Leroy Hulsey b a Department of Civil Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b Department of Civil and Environmental Engineering, University of Alaska Fairbanks, AK, United States article info Article history: Received 1 April 2010 Received in revised form 8 September 2010 Accepted 13 September 2010 abstract The November 3, 2002 Denali-Alaska earthquake (M w ¼7.9) caused significant liquefaction associated damage to various infrastructure built on fine-grained soils. The seismic response, liquefaction potential, and excess pore pressure generation of soils in cold regions, especially those of fine-grained nature, have not been studied thoroughly and therefore are not well-understood. This paper presents results from an extensive laboratory study on the characteristics of excess pore pressure generation and liquefaction potential of fine-grained soils. Laboratory-constituted soils specimens were tested in four categories: (1) tests on specimens subjected to no thermal conditioning or freeze–thaw cycles; (2) tests on specimens conditioned at 24, 5, 1, 0.5, and 0.2 1C; (3) tests on specimens subjected to 1–4 freeze–thaw cycles; and (4) tests on specimens conditioned at near-freezing temperatures of 0.5 and 0.2 1C through different freeze–thaw paths. Strain-controlled, undrained, cyclic triaxial tests were performed at shear strain levels of 0.005–0.8%. Specimens conditioned at different temperatures were found to generate significantly different pore pressures with cyclic loading. The excess pore pressure generation at near or slightly below freezing was found to change dramatically. A transitional change in the dynamic soil behavior, attributed to unfrozen- or frozen-dominant pore water, was discovered. The threshold shear strain was also found to be influenced by the temperature. Subjecting the soil specimens to 1, 2 and 4 freeze–thaw cycles caused a reduction in excess pore pressure generation and slight change in the threshold shear strain. The temperature conditioning path to reach the target temperature was found to be important on the development of excess pore pressure at near and slightly below-freezing temperatures. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Saturated fine-grained, non-plastic to low-plasticity soil deposits are commonly encountered in the seismically active Arctic region. Moderate to strong shaking of such deposits can lead to significant excess pore water pressure generation and ultimately to liquefaction if the pore water is completely unfrozen. If the pore water is fully frozen, no pore pressure is generated. As the ground temperature nears the freezing point (i.e., 0 1C), the state of the pore water becomes partially frozen. The response of the ground to earthquake loading in this case is completely different from either the fully frozen or the unfrozen case. The stiffness of the ground typically increases with decreasing temperature [34]; however this increase in stiffness may not translate into decreasing liquefaction potential. This is because formation of ice layers within the ground can lead to a decrease in permeability. Together with earthquake loading, this may become a significant contributing factor to liquefaction of the ground at near-freezing temperature. During the November 3, 2002, Denali earthquake (M w ¼ 7.9), significant liquefaction damage was observed at near-freezing ground temperatures [23,37]. In addition to liquefaction damage, as much as 75 cm horizontal and 45 cm vertical deformations were measured during the Denali earthquake (AK DOT Report [1]). The main objectives of the present research were: (i) to characterize the excess pore water pressure generation, which is responsible for the occurrence of liquefaction, of fine- grained soils of cold regions and investigate the effect of ground temperature on the generation of excess pore pressure, and (ii) to investigate the effect of freeze–thaw cycles (i.e., seasonal variation of ground temperature) on excess pore pressure generation. Through a systematic experimental program, which is outlined in detail in [40], responses of laboratory-reconstituted soil specimens were studied. The soil specimens were subjected to strain-controlled, undrained, cyclic triaxial testing, and the excess pore water pressure generation was measured directly at different levels of strain and for various temperature conditions. 2. Review of previous studies The liquefaction potential of fine-grained soils has been extensively investigated by a number of researchers (Chang Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/soildyn Soil Dynamics and Earthquake Engineering 0267-7261/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.soildyn.2010.09.006 n Corresponding author. E-mail address: k.hazirbaba@gmail.com (K. Hazirbaba). Soil Dynamics and Earthquake Engineering 31 (2011) 372–384