Seismic Earth Pressures on Retaining Structures and Basement Walls in Cohesionless Soils

Abstract

Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep excavation walls in earthquakes are rare even if the structures were not designed for the actual intensity of the earthquake loading. Failures of retaining structures are most commonly confined to waterfront structures retaining saturated backfill with liquefaction being the critical factor in the failures. Failures of other types of retaining structures are relatively rare and usually involve a more complex set of conditions, such as sloping ground either above or below the retaining structure, or both. While some failures have been observed, there is no evidence of a systemic problem with traditional static retaining wall design even under quite severe loading conditions. No significant damage or failures of retaining structures occurred in the recent earthquakes such as Wenchuan earthquake in China (2008) and, or the large subduction zone earthquakes in Chile (2010) and Japan (2011). Therefore, this experimental and analytical study was undertaken to develop a better understanding of the distribution and magnitude of seismic earth pressures on cantilever retaining structures.The experimental component of the study consists of two sets of dynamic centrifuge model experiments. In the first experiment two model structures representing basement type setting were used, while in the second test a U-shaped channel with cantilever sides and a simple cantilever wall were studied. All of these structures were chosen to be representative of typical designs. Dry medium-dense sand with relative density on the order of from 75% to 80% was used as backfill. Results obtained from the centrifuge experiments were subsequently used to develop and calibrate a two-dimensional, nonlinear, finite difference model built on the FLAC platform.The centrifuge data consistently shows that for the height of structures considered herein, i.e. in the range of 20-30 ft, the maximum dynamic earth pressure increases with depth and can be reasonably approximated by a triangular distribution This suggests that the point of application of the resultant force of the dynamic earth pressure increment is approximately 1/3H 2 above the base of the wall as opposed to 0.5-0.6 H recommended by most current design procedures. In general, the magnitude of the observed seismic earth pressures depends on the magnitude and intensity of shaking, the density of the backfill soil, and the type of the retaining structures. The computed values of seismic earth pressure coefficient ( K ae ) back calculated from the centrifuge data at the time of maximum dynamic wall moment suggest that for free standing cantilever retaining structures seismic earth pressures can be neglected at accelerations below 0.4 g. While similar conclusions and recommendations were made by , their approach assumed that a wall designed to a reasonable static factor of safety should be able to resist seismic loads up 0.3 g. In the present study, experimental da...

Seismic Earth Pressures on Deep Stiff Walls

“…Figure 5 is a summary of data obtained from the centrifuge experiment and numerical simulation, as well as results from previous centrifuge work by Mikola & Sitar (2013) and Candia & Sitar (2013) Therefore, to maintain consistency with the predictive methods it seems appropriate to use an average acceleration measured over the depth of the assumed failure wedge. In our study the acceleration value is computed by taking the average of all accelerations measured throughout the depth of the basement structure in the free field at every instance in time, then computing the peak value of the new acceleration record.…”

The Generalized Coefficients of Earth Pressure: A Unified Approach

“…However, the question is not to find a solution that is more conservative, but a solution that effectively reflects reality; and this because the cost of an overconservative design can be just as much of a problem as the cost of a future failure [40]. Over the last decades, a great number of experimental, numerical, and analytical studies led to a consensus that the M-O method yields conservative earth pressure values and excessively conservative values for Peak Ground Accelerations (PGA) in excess of 0.4 g (e.g., [40][41][42][43][44][45][46][47][48][49][50][51][52][53]). Generally, these studies refer to the active state, although some of them refer to the M-O-K solution for the passive state [47,54].…”

Geotechnical Aspects of the 2015 Mw 8.3 Illapel Megathrust Earthquake Sequence in Chile

“…The exposed backfill material was a mixture of very angular rock fragments (average size of 15 cm) and coarse beach sand. The measured peak horizontal and vertical accelerations at the nearest station are 0.25 g and 0.18 g respectively, peak ground velocity of 19 cm/s (located 1.9 km south of the site) and significant duration of 59 s; this level of acceleration is generally not sufficient to mobilize the shear strength of the retained material (Geraili Mikola et al 2016), and thus, the likely cause of failure is the combined effect of hydrodynamic forces induced by the repeated tsunami waves and the ground shaking. Similar patterns of damage to quay walls and breakwaters were observed in the Chile earthquake of 2010 (Bray and Frost 2010), and the Japan earthquakes of 1993 (Burcharth et al 2001) and 2011 (Meneses and Arduino 2011).…”