Framework to assess Newmark-type simplified methods for evaluation of earthquake-induced deformation of embankments

Abstract

The simplified procedures for evaluation of the earthquake-induced displacement in earth and rockfill dams are widely used in practice. These methods are simple, inexpensive, and substantially less time consuming as compared to the complicated stress–deformation approaches. They are especially recommended to be used as a screening tool, to identify embankments with marginal factor of safety, assuming that these methods always give conservative estimates of settlements. However, recent studies show that application of these methods may not be conservative in some cases, especially when the tuning ratio of a dam is within a certain range. In this paper, the fundamental theory behind the simplified methods is critically reviewed. A case in which the results of the simplified methods are reportedly nonconservative is investigated in detail and possible reasons are discussed. The reliability of the simplified methods is examined here based on the existing thresholds proposed in the literature and accounting for the embankment geometry and type, and for the seismic activity characterization, and a practical framework is proposed accordingly. The effectiveness of this framework is evaluated in the study of seismic behaviour of a rockfill dam where all simplified procedures failed to predict the order of deformation experienced by the dam under a recent earthquake event.

Discussion of “Framework to assess Newmark-type simplified methods for evaluation of earthquake-induced deformation of embankments”

“…Generally, we find a reasonable comparison between the computed results and observed performance in the field. However, such is not the case for Kan et al (2017) with their case study of Zipingpu Dam -the computed deformations using about 12 different Newmark-based procedures (Newmark 1965) listed in Table 3 of their paper differ significantly (i) amongst themselves and (ii) from the actual observed values. Moreover, computed deformations from 11 of the 12 procedures are significantly smaller (underprediction) than the actual deformations, and those from the one exception are significantly higher (overprediction).…”

“…There are significant differences in the seismic data used in Kan et al (2017) and the plots shown in Fig. D2: (i) the time-acceleration plot for the E-W component shown in Fig.…”

“…I have read the paper by Kan et al (2017) with interest because of the U.S. Bureau of Reclamation's and my involvement in assessing seismic stability and deformations of embankment dams located in seismically active regions of the western United States. We also check validity of our analysis methods and procedures with case studies.…”

“…Additional items included herein pertain to (a) selection of earthquake component for use in Newmarkbased analysis and (b) natural vibration characteristics of the dam. Kan et al (2017) used the east-west (E-W) component of the earthquake as recorded in Mao Town scaled to 0.55g for computing the displacements of the dam cross section, which is primarily oriented in the north-south (N-S) direction. Figure D1a shows the directional orientation of Zipingpu Dam and that of the Min River; Fig.…”

“…As such, we attached a greater credence to the PCA of 1.65g than to the PCA of 0.8g. 3 This confusion regarding which of the two components (N-S or E-W) was actually used in Kan et al (2017) is also observed in Kan and Taiebat (2016). Therein, the text indicates use of the N-S component but the Fig.…”