مقاله انگلیسی رایگان در مورد تخمین پتانسیل روانگرایی خاک توسط الگوریتم GMDH – اسپرینگر 2017

Liquefaction is the phenomena when there is loss of strength in saturated and cohesionless soils because of increased pore water pressures and hence reduced effective stresses due to dynamic loading. After the disastrous damage observed during the Niigata and Alaska 1964 earthquakes, the liquefaction phenomenon has become the scope of many studies in the field of geotechnical earthquake engineering (e.g., Lee and Fitton 1969; Seed and Idriss 1971; Seed et al. 1975; Dabiri et al. 2011). Several methods are developed to assess the liquefaction potential in the field. The available methods for evaluation of liquefaction are classified into three main groups (Green 2001; Alavi and Gandomi 2012): stress-based methods, strain-based methods and energy-based methods. The most widely used method for evaluating liquefaction is the stress-based approach. This method was proposed by Seed and Idriss (1971) and Whitman (1971). Stress-based method is mainly empirical and is based on laboratory and field data. In this approach to correlate real earthquake motion to laboratory harmonic loading condition, the equivalent shear stress level, the number of cycles and the equivalent earthquake duration should be defined such that differences are always available between the results of researches (Ishihara and Yasuda 1975; Seed et al. 1975; National Research Council 1985; NCEER 1997). Although this approach has been continually modified as a result of newer studies and the increase in the number of liquefaction case histories (e.g., NCEER 1997; Youd et al. 2001), this deficiency still persists. Dobry et al. (1982) proposed the strain-based method as an alternative to the empirical stress-based procedure. This method was derived from the mechanics of two interacting idealized sand grains and then generalized for natural soil deposits (Green 2001; Baziar and Jafarian 2007). The strain-based method has been less common than the stress-based method because of the fact that the strain approach only predicts the initiation of pore pressure buildup, which is required for liquefaction occurrence, but does not imply that liquefaction will happen. Energy-based assessment of liquefaction potential considers effects of strain and stress concurrently, unlike the stress- or strain-based procedures (Liang 1995; Baziar et al. 2011). In the energy-based method, the amount of strain energy required to trigger liquefaction in sandy soils is obtained from laboratory testing or field data. Figure 1 represents a schematic of shear stress–strain curve (hysteresis loop) from a cyclic triaxial test. The area inside the hysteresis loop represents the dissipated energy per unit volume of the soil mass. The summation of energy is computed until the onset of liquefaction phenomena. For prediction of liquefaction triggering, this strain energy is compared with the strain energy divulged by dynamic loading such as earthquake to the sand layer during the seismic design event (Jafarian et al. 2011).