a critical review of pore pressure predictive models

Proceedings of Indian Geotechnical Conference IGC-20 14 December 18-20, 2014, Kakinada, India 1636 A CRITICAL REVIEW OF PORE PRESSURE PREDICTIVE MODELS Rajesh Prasad Shukla, Research Scholar, IIT Roorkee, [email protected]. Ravi Sankar Jakka, Assistant Professor, IIT Roorkee, [email protected] et.in. ABSTRACT: The response of soil and structure under dynamic loading predominantly depends on the magnitude and rate of built up excess pore pressure. Excess pore pressure affects the behaviour, settlement and strength of soil. Liquefaction also depends on developed excess pore pressure during earthquake. It is very important to determine accurate value of pore pressure to analyse soil behaviour under dynamic loading. This paper presents a critical review of all predictive models of pore pressure including, equivalent Cycle Method by Seed et al. (1975), Analytical Model by Ishibashi et al. (1977) and modified equivalent Cycle Method by Liyanapathirana & Poulos (2002). Equivalent cycle method is simpler method but suitable only for sand and cannot be used efficiently in case of clay, silt and silty clay samples. Ishibash i et al. (1977) method predicts pore pressure more accurate ly compared to Liyanapathira na & Poulos (2002) an d Seed et al. (1975) methods, but requires mo re data for pore pressu re prediction. Effect of fines on liquefaction potential is a matter of debate and researc hers are still not sure about effect of fine due to absent of an efficient pore pressure prediction mode ls for fine grain soil. INTRODUCTION Dynamic and impulsive loading cause development of excess pore pressure and which leads to degradation of strength, additional settlement and deformation of soil. Excessive increase in excess pore pressure can leads to liquefaction [1]. The response of saturated soil and structure under dynamic loading predominantly depends on the magnitude of development of excess pore pressure. It is very important to determine accurate value of pore pressure to analyze soil behaviour accurately under dynamic loading. In last five decades, various attempts have been made to model the excess pore water pressure through various techniques to solve the stability problem, foundation problems and specially to determine the liquefaction potential of a soil. Pore pressure modeling can be done by either using uncoupled total stress analysis or a fully coupled effective stress analysis. A model can be non-linear or equivalent linear model [2]. Coupled analysis is more realistic and accurate as it considers all parameters simultaneously in each and every step. Whereas in case of uncoupled analysis modeling is done by without consideration of soil-water interaction [3]. The equivalent linear model is simplest model and considerer only few parameters [1, 4, 5]. Most of data used in studies were developed from either either stress controlled or strain controlled cyclic load test. Equivalent linear modeling replaces the non-linear properties of soil system by a linear system in such a way that the effect of transformation from nonlinear to linear will be minimal [6]. There are various factors that affect the magnitude and rate of generation of excess pore water pressure such as type of soil, state of soil, and characteristic of loading as well. Development of excess pore pressure in dense sand is similar to lose sand under cyclic loading but there is difference in the rate of development of pore pressure. In dense sand, the rat e of development of pore pressure is moderate compare to lose sand and in case of loose sand shear strain amplitude increases suddenly [7]. Earlier, before Kocaeli earthquake, it was a common to assume that fine gained soil will not get liquefy and most of studied were neglected the consideration of fine grained soil for liquefaction and pore pressure prediction modeling. In clay-silt mixture, clay imparts plasticity to the soil and it causes to decrease in hydraulic conductivity of soil. Decrease in plasticity leads to increase in chances of hi gh pore pressure development. Plasticity als o increases the resistance to liquefaction. Now it is a great question between scientists and researchers that whether fine grained plastic soil leads to increase

a critical review of pore pressure predictive models

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