Determination of Passive Failure Surface Geometry for Cohesionless Backfills

Abstract

Correct determination of the passive failure surface geometry is necessary for the design of retaining structures. The conventional theories assume linear passive failure surfaces even though it is known that the actual failure surfaces are non-linear. Many researchers claimed the appropriateness of a hybrid curved-linear method. This approach estimates the curved section by a log-spiral function, which then connects to the backfill surface with the conventional linear assumption. The main drawback here is that the geometric properties of the hybrid mathematical function is not directly related to the mechanical properties of soils. Thus, this study attempts to provide a mechanical description for the assumed geometrical parameters. For this purpose, a series of 1 g small scale retaining wall model tests, simulating passive failure, are conducted on two different backfill soils. The relative density is varied in the model tests and the resultant peak friction angles of the backfills are calculated as functions of failure stress state and relative density using a well-known empirical equation. Transparent sidewalls allow for visualization of the failure surface evolution, which is obtained by capturing images and analysing then through Particle Image Velocimetry (PIV) technique. Subsequently, the quantified slip zones are fitted with the hybrid curved-linear approach. The relationships between the peak friction angle and the geometrical characteristics of the best-fit log-spiral and linear functions are investigated. Obtained results are used to propose a set of equations that allow the estimation of non-linear passive failure surfaces as function of peak friction angle.

Characterizing Sediment Flux of Deforming Glacier Beds

“…There is no single agreed upon criterion to determine the thickness of a shear band, t sb , in a granular material (Alshibli & Sture, 1999; Rattez et al., 2020; Rechenmacher & Finno, 2004; Soltanbeigi et al., 2020; Zhu et al., 2016). Shear bands are characterized by a loss of homogeneity in the deformation field that concentrates excessive shear strain and dilatancy in a thin band.…”

“…We adopt an approach developed by Soltanbeigi et al. (2020), who suggest that the boundaries of a shear band can be approximated as the inflection points on a cross‐sectional strain profile of the shear band (Figure 4). Our workflow can be summarized as follows: First, we calculate the spatial derivatives of the velocity vectors derived for each image pair in the time series using the central difference for interior data points and a single‐sided difference method for gradients at the boundaries.…”

“…Median shear strain rate profiles are calculated from the time series, normalized by their maximum value, and then plotted against depth to form a cross‐sectional shear strain rate intensity profile. The criteria for estimating shear band width in this parameter space (i.e., “method II” in Soltanbeigi et al., 2020) can be summarized succinctly as: (a) fitting tangents to the two tails of the profile where the rate of strain change is approximately constant, (b) fitting tangents to the linear regions of the curve between the tails and the peak, (c) locating the points of intersection for both sets of tangent lines, and then (d) measuring the distance between these two points of intersection on either side of the shear band—this value is presumed to be t sb . An advantage of this method with respect to our data is that it does not rely on the assumption of a Gaussian distribution of shear strain, since distributions were bimodal at certain stages of the experiments (Figure 4b).…”

Analysis of Active Earth Pressure Behind Rigid Retaining Walls Considering Curved Slip Surface

“…Many experimental studies [28,29] show a curved failure surface developing in the backfill behind rigid walls. As Spangler and Handy [30] indicated, the shape of emerging failure surface can be defined as a parabolic curve.…”

Numerical analysis of failure mechanism observed in backfills supported by masonry walls

“…Failure surface geometry behind the wall was examined experimentally (Leśniewska & Mróz 2000, Tejchman 2004, Leśniewska et al 2012, Altunbas et al 2017) by many researchers. Most of these researches are focused on the mechanical properties of the backfill, backfill density (Nuebel 2002), grain shape and diameter (Leśniewska et al 2012, Soltanbeigi et al 2018) dilatancy angle (Altunbas et al 2017, Soltanbeigi et al 2020. According to the results of these studies, the geometry of the potential failure surface in the non-limit states plays an important role for the soil response and it is not linear.…”