Undrained behavior

Ansal, A.M., and Erken, A. 1989. Undrained behavior of clay under cyclic shear stresses. Journal of the Geotechnical Engineering Division, ASCE, 115, No. 7, p>p. 968-983. 

A nonlinear path-dependent constitutive model for the soil mainly depends on the shear stress-shear strain relationship, which is extended to three-dimensional generic conditions and assumed to follow Masing s rule for the soil hysteresis. The soil is idealized as an assembly of a finite number of elasto-perfectly plastic elements connected in parallel as shown in Fig. 25.3 (Okhovat et al. 2009, Mohammed and Maekawa 2012 Mohammed et al. 2012a). The nonlinear behavior of the soil system in liquefaction is assumed as in undrained state, since its drainage takes much longer than the duration of an earthquake (Towhata 2008). The soil undrained behavior is shown in Fig. 25.4. 

One of the more popular of the recent procedures based on this technique is SHANSEP (stress history and normalized soil engineering properties), which was proposed by Ladd and Foott (1974). This laboratory strength-testing procedure normalizes the undrained strength (Sy) and stress-strain characteristics with respect to the consolidation stress, Results from laboratory tests have shown that for a given OCR, the normalized stress can be used to represent the behavior of other samples with different consolidation stresses when sheared in the same type of test, at the same temperature, and at the same rate of loading. 

Koutsoftas, D.C. 1981. Undrained soil shear behavior of a marine clay. In Laboratory Shear Strength of Soil. ASTM STP 740. ed. R.N. Yong, and F.C. Townsend. ASTM. Philadelphia, PA 254-276. 

Prevost, J.H. 1977. Mathematical modelling of monotonic and cyclic undrained clay behavior. International Journal of Numerical and Analytical Methods in Geotechnical Engineering, 1, No. 2, pp. 195-216. 

Anderson, K. H. (1976), Behavior of clay subjected to undrained cyclic loading, Conference on the Behavior of Offshore Structures, 76, Norwegian Geotechnical Institute, Trondheim, Norway. 

While a full scale experiment to investigate the seismic behavior of a real structure together with SSPW is hard to conduct, an analytical study with a well verified computational RC and soil model (Maekawa et al. 2003) can serve as an alternative to capture the overall efficiency of SSPW. In this study, the authors use a full three dimensional nonlinear finite element analysis of soil-structure-pore water systems. The applicability of the system was verified by shaking table experiments of top-heavy piles embedded in a liquefiable model foundation (Maki et al. 2004, 2005, Mohammed and Maekawa 2012 Mohammed et al. 2012a). Using this analytical platform, the effects of SSPW as a seismic countermeasure for the rafted pile foundation is discussed with regard to the base shear induced in the RC multistorey superstructure and its overall stability. Both cases of drained and undrained soils are considered in the analysis to clarify the potential effect of soil liquefaction. 

Because CPT soundings provide continuous records of tip and sleeve resistances (and frequently pore pressure) versus depth (Figure 7.4), they provide a continuous indicator of soil and subsurface conditions, which is useful in defining soil stratification. Numerous correlations between the CPT measurements have been developed to define soil type and soil classification. In addition, empirical correlations have been published to relate the cone tip and sleeve friction resistances to engineering behavior, including undrained shear strength of clay soils and relative density and friction of granular soils. 

If we perform undrained triaxial tests (namely, void ratio e=constant) on isotropically and normally consolidated clay at several confining pressures p, the stress-strain behavior is schematically shown in Fig. 6.2. It is observed that at the final stage of loading (namely, the failure state) the stress ratio rj = q/p becomes constant qf = q/p )f = M), which is referred to as the critical state, which means that the deformation is developed under a constant volumetric plastic strain and a constant shear stress at the critical state q = Mp. ... 

Let us consider the shearing behavior of a heavily over-consolidated clay. We start to make it swell from a point A on the normally consolidated line (NCL) to a point B shown in Fig. 6.3d, e. When we perform an undrained triaxial test, the shear stress q attains the yield point P on the Hvoslev surface (namely the maximum point for the stress ratio rj = q/p ), and moves on the Hvoslev surface to reach the point C on the CSL. On the other hand, if a drained triaxial test is performed from the point B, the shear stress q attains the peak strength Q, then the stress reaches a residual state R through a softening process. Note that in practical experiments a shearing slip surface is commonly observed, and the whole specimen cannot reach the residual state. 

The liquefied shear strength represents just one aspect of undrained soil behavior. Figure 1 illustrates the response of three saturated Toyoura sand specimens monotonically loaded in undrained triaxial compression. As will be discussed in section Critical State Framework, the response of a sand depends on its state (consolidated void ratio and effective stress). Contractive response (or, more specifically, the tendency for contractive response during undrained loading) can be described as the sand... 

Terzaghi K, Peck RB, Mesri G (1996) Soil mechanics in engineering practice, 3rd edn. Wiley, New York, 549 p Vasquez-Herrera A, Dobry R (1989) Re-evaluation of the Lower San Fernando Dam report 3, the behavior of undrained contractive sand and its effect on seismic liquefaction flow failures of earth structures. US Army Corps of Engineers contract report GL-89-2, US Army Corps of Engineers Waterways Experiment Station, Vicksburg... 

Verdugo R (1992) Characterization of sandy soil behavior under large deformation. PhD thesis. Department of Civil Engineering, University of Tokyo, Tokyo Yoshimine M, Robertson PK, Wride CE (1999) Undrained shear strength of clean sands to trigger flow liquefaction. Can Geotech J 36(5) 891-906... 

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