Session 7: Discussion and Replies

Missouri University of Science and Technology Scholars' Mine International Conferences on Recent Advances 1981 - First International Conference on Recent in Geotechnical Earthquake Engineering and Advances in Geotechnical Earthquake Soil Dynamics Engineering & Soil Dynamics 30 Apr 1981, 1:30 pm - 5:30 pm Session 7: Discussion and Replies Multiple Authors Follow this and additional works at: https://scholarsmine.mst.edu/icrageesd Part of the Geotechnical Engineering Commons Recommended Citation Authors, Multiple, "Session 7: Discussion and Replies" (1981). International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. 25. https://scholarsmine.mst.edu/icrageesd/01icrageesd/session07/25 This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License. This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. 1176 Discusion by Albert T.F. Chen, As a modification of Makdisi and Seed's Research Civil Engineer, simplified procedure for estimating earthquake U.S. Geological Survey, induced deformation in dams and embankments, Menlo Park, CA, on "Earthdams Shieh and Huang propose the use of a permanent and Stability of Slopes Under displacement spectrum. Treating the sliding Earthquakes". portion of the dam as a single-degree-of freedom system, the authors define the permanent displacement spectrum as the difference between the displacement responses derived from a nonlinear and a linear system. The nonlinear system assumes that the sliding Four papers will be discussed here. In the mass develops a perfect plastic behavior above order of their appearance in the proceedings of a certain yield acceleration. Either the this conference, these papers are: maximum spectral value or the spectral value 1). Analysis of Dynamically Coupled corresponding to the average maximum Percolation and Deformation Problems of acceleration of the sliding mass can be used as Saturated Sands, by Shen; the design value for permanent deformation. Z). Effective Stress Analysis of Seismically This method appears effective for evaluating Induced Stability Problems, by deformation of earthdams during a given Kavanzanjian and Chameau; earthquake, and it is capable of simulating 3). Permanent Deformation of Earth Dams under gradual decrease in the shear strength of soils Earthquakes, by Shieh and Huang; and under dynamic loading caused by pore pressure 4). Pore Pressure Analysis for an Earth Dam build-up. The authors have not shown during Earthquake, by Sonpal and Davie. adequately that linear and nonlinear All of these papers deal with various deformations can be separated in the frequency analytical techniques that are used for domain. However, the authors have shown that studying earthdams and stability of slopes for three different earthdams, the results during earthquakes, and in one way or another, based on the permanent displacement spectrum each of the papers consider effects of increase method are comparable with results from other in pore pressure during earthquake loading. methods. In a very brief presentation, Sonpal and Davie Shen presents an elegant two-dimensional show that the pore pressure distribution within dynamic analysis of an earthdam with full an embankment can be established by means of a consideration given to the generation and pseudostatic analysis with assigned seismic dissipation of pore pressure. The dynamic coefficients. The pore pressure contours so response analysis is similar to the equivalent obtained led the authors to draw certain linear analysis used in the UC Berkeley conclusions about deformation patterns of computer program QUAD-4; the effective stress earthdams during earthquakes; those conclusions model appears to be a two-dimensional version are consistent with observations. Because of of the model by Finn, Lee, and Martin; and the the briefness of the authors' presentation, it consideration of pore-pressure dissipation was is not possible to comment on the relevance of based on Biot's theory of consolidation. By this approach. However, it should be manipulating the drainage conditions, the emphasized that pseudostatic approaches author was succeeded in explaining the generally do not take into account the effect mechanics of the delayed failure during the of strength reduction caused by pore-pressure 1975 Haicheng earthquake of the upstream slope increase and are not intended for making of Shimenling earthdam in Liaoning Province. quantitative estimates of permanent That upstream slope failed 80 minutes after the deformation. passage of the main shock. Kavanzanjian and Chameau stress the importance of effective stress analysis. For one- and Those who work with two- or three-dimensional two-dimensional analysis of stability problems consolidation problems have long recognized during earthquakes, they propose a stochastic that under quasi-static loadings, the maximum formulation of the Finn, Lee, and Martin excess pore pressure need not occur at the nonlinear pore pressure generation model. onset of the loading. It appears that the same According to the authors, the advantages of the phenomenon can also take place in a dynamic stochastic approach are (1) that it allows us environment. Shen's paper points out that it to consider the effect of the order of arrival is important to look into the dissipation of of the shear stress cycles in a frequency pore pressure and the effect of drainage domain analysis, and (2) that it enables the conditions both during an earthquake and engineer to incorporate geotechnical, after. All of Shen's previous papers were seismological, and analytical uncertainties published in Chinese and are not readily into the stability assessment. In addition, available outside of China; this paper provides the stochastic approach also facilitates a good indicator of the type and the level of probabilistic evaluation of the damage research being conducted in China. potential associated with pore pressure build up for use in seismic hazard analysis. Unfortuna~ely, the work described by the authors is not completely developed. The approach they propose appears to be rational and potentially useful; the value of the method will become clearer after the the work is completed. 1177 Because post-earthquake failures have been observed in China, Japan, and the United States, it is difficult to accept the statement made by Sonpal and Davie that "The critical time will be immediately at the time of earthquake, the dam will be safe in the subsequent condition." This statement should only be interpreted as a conclusion derived from the use of that particular type of analysis. Another striking contrast between the paper by Shen and the one by Sonpal and Davie is in the complexity of the input required for the type of analysis. No fewer than 17 material constants are required for the dynamically coupled analysis proposed by Shen, whereas probably no more than four material constants are needed for the pseudo-static analysis described by Sonpal and Davie. The number of material constants required for an analysis directly affects the amount of effort (and therefore the resources) required for that analysis. The economic factor is rarely mentioned in the four papers discussed herein, but this factor must be borne in mind if methods described in these papers are to be put to use. 1178 Discussion by E.G. Prater, Reference: on "Dynamically Coupled Percolation and Deformation Zienkiewicz O.C., K.H. Leung, E. Hinton and Analysis of Earthdams" by C.T. Chang (1980) Z.J. Shen Earth Dam Analysis for Earthquakes, Conf. I.C.E. London, Design of Dams to Resist Earthquakes. The author expresses the opinion, probably with justification, that if severe failure of the slope of an earth dam occurs it will not be due to inertia forces as such, but rather to the build-up of pore pressures. In an attempt to analyse the problem he has developed an effecti ve stress model requiring 11 material constants, 5 of which describe the increments of volumetric and deviatoric residual strain. He also defines two new measures, coaction and asymmetry, related to Discussion by E.G. Prater, the crest and trough values of the principle on "Design Measures to stresses, which likewise enter into the consti Improve Performance of tutive relations. Their use is not easy to Fill Dams Under Earthquake follow. The modulus and damping values are based Loading" by K.L. Logani. on the well-known equations of Hardin and Drnevich. The general approach shows similari ties with that of Finn et al (1977). The procedure for analysis, as far as the dis discusser understands it,is as follows. Sub sequent to static (preearthquake) analysis the authors program EFESD is used in conjunction This paper describes practical means of provi with the widely used program QUAD4. The latter ding seismic resistance for embankment dams. is a dynamic analysis FE program based on Perhaps the introductory remarks of the author linear elasticity and viscous damping, requiring need to be qualified somewhat. It is probably fairly small time steps for accuracy. Normally

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