Yufeng Gao

Bio: Yufeng Gao is an academic researcher from Hohai University. The author has contributed to research in topics: Slope stability analysis & Slope stability. The author has an hindex of 28, co-authored 179 publications receiving 2618 citations. Previous affiliations of Yufeng Gao include Oregon State University.

Effects of Topographic Amplification Induced by a U‐Shaped Canyon on Seismic Waves

Abstract: The series solution of wave functions for 2D scattering and diffraction of plane SH (shear horizontal) waves induced by a U‐shaped canyon is proposed herein to account for the topographic effect of such a canyon. The wave function expansion method has been frequently employed to study the topographic effect because it can reveal the physics of the wave scattering and can test the accuracy of other methods. Through a new domain decomposition strategy, the half‐space having a U‐shaped canyon is divided into three subregions. Hence, we defined three cylindrical coordinate systems. In each coordinate system, the wave field satisfying the Helmholtz equation was represented by means of the separation of variables method, in terms of the series of both Bessel functions and Hankel functions with unknown complex coefficients. Then three wave fields are all represented in the same coordinate system using the Graf addition theorem. The unknown coefficients are solved by satisfying the continuity conditions of the auxiliary boundary and the traction‐free boundary conditions on the bottom of the canyon. To show the effects of symmetrical and nonsymmetrical U‐shaped canyons on the surface ground motion, a parametric analysis is carried out in the frequency domain. Surface and subsurface transient responses in the time domain demonstrate the phenomenon of wave propagating and scattering. It is found that a zone of amplification can obviously take place at the bottom of a U‐shaped canyon with nearly vertical walls.

An extended limit analysis of three-dimensional slope stability

Abstract: A three-dimensional rotational failure mechanism for earth slope is extended from toe failure to include face failure and base failure. An efficient optimisation method is simultaneously employed to find the least upper bounds to the critical height in order to avoid missing the global minimum. Compared with the results from analysis based on toe failure alone, best estimates of the critical height and the critical failure mechanism are obtained. The calculated results are given in the form of graphs and tables for a wide range of parameters. The critical failure surfaces are also investigated to assess the influences of geometrical constraint and soil property on failure mechanism.

Effect of 2D spatial variability on slope reliability: A simplified FORM analysis

Abstract: To meet the high demand for reliability based design of slopes, we present in this paper a simplified HLRF (Hasofer–Lind–Rackwitz–Fiessler) iterative algorithm for first-order reliability method (FORM). It is simply formulated in x -space and requires neither transformation of correlated random variables nor optimization tools. The solution can be easily improved by iteratively adjusting the step length. The algorithm is particularly useful to practicing engineers for geotechnical reliability analysis where standalone (deterministic) numerical packages are used. Based on the proposed algorithm and through direct perturbation analysis of random variables, we conducted a case study of earth slope reliability with complete consideration of soil uncertainty and spatial variability.

Gradual unlocking of plate boundary controlled initiation of the 2014 Iquique earthquake

Abstract: A long foreshock series unlocked the South American plate boundary until eventually initiating the M 8.1 Iquique, Chile, earthquake. Two groups publishing in this issue of Nature analyse the seismic context of the Iquique earthquake that occurred off the coast of northern Chile on 1 April 2014 in a seismic zone that had been quiescent since a significant event in 1877. Gavin Hayes et al. identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region, and conclude that the 2014 Iquique event was not the earthquake that had been anticipated. Given that significant sections of the northern Chile subduction zone have not ruptured in almost 150 years, they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 Iquique sequence. Bernd Schurr et al. show that the April 2014 earthquake broke a central fraction of the 'northern Chile seismic gap', the last major segment of the South American plate boundary that had yet to rupture in the past century. From July 2013 up to the April earthquake they identify three seismic clusters along this part of the plate boundary, each lasting a few weeks, with earthquakes of increasing peak magnitudes. They conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure. On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks. The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events, providing unprecedented resolution of the build-up to the main event and its rupture evolution. Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap, the last major segment of the South American plate boundary that had not ruptured in the past century1,2. Since July 2013 three seismic clusters, each lasting a few weeks, hit this part of the plate boundary with earthquakes of increasing peak magnitudes. Starting with the second cluster, geodetic observations show surface displacements that can be associated with slip on the plate interface. These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion. Leading up to this earthquake, the b value of the foreshocks gradually decreased during the years before the earthquake, reversing its trend a few days before the Iquique earthquake. The mainshock finally nucleated at the northern end of the foreshock area, which skirted a locked patch, and ruptured mainly downdip towards higher locking. Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch. We conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure, distinguishing the Iquique earthquake from most great earthquakes. Finally, only one-third of the gap was broken and the remaining locked segments now pose a significant, increased seismic hazard with the potential to host an earthquake with a magnitude of >8.5.

P-ultimate for undrained analysis of laterally loaded piles. discussion and closure

Abstract: A discussion of a paper with the aforementioned title by Murff and Hamilton, published in this journal (Volume 119, Number 1, January 1993), is presented The discussion focuses on laterally loaded piles in layered soils Maugeri, Castelli, and Motta assert that the authors' method overpredicts the ultimate lateral resistance on the pile Discussion is followed by closure from the authors

Elastoplastic Constitutive Model for Rockfill Materials Considering Particle Breakage

Abstract: Particle breakage has a great influence on stress-strain behaviors of rockfill materials. A new relative breakage was proposed for rockfill materials. A critical state line incorporating particle breakage was termed as a breakage critical state line (BCSL). It was found that the BCSL position of rockfill materials pertained to the relative breakage. An elastoplastic model considering state dependence and particle breakage was proposed for rockfill materials. The effect of particle breakage was incorporated into the proposed state parameter, dilatancy stress ratio, stress dilatancy relation, bounding stress ratio, and plastic modulus in the proposed model. The model considering particle breakage can well predict the stress-strain and particle-breakage behaviors of rockfill materials at various confining pressures.

Efficient reliability analysis of earth dam slope stability using extreme gradient boosting method

Abstract: Reliability analysis approach provides a rational means to quantitatively evaluate the safety of geotechnical structures from a probabilistic perspective. However, it suffers from a known criticism of extensive computational requirements and poor efficiency, which hinders its application in the reliability analysis of earth dam slope stability. Until now, the effects of spatially variable soil properties on the earth dam slope reliability remain unclear. This calls for a novel method to perform reliability analysis of earth dam slope stability accounting for the spatial variability of soil properties. This paper develops an efficient extreme gradient boosting (XGBoost)-based reliability analysis approach for evaluating the earth dam slope failure probability. With the aid of the proposed approach, the failure probability of earth dam slope can be evaluated rationally and efficiently. The proposed approach is illustrated using a practical case adapted from Ashigong earth dam. Results show that the XGBoost-based reliability analysis approach is able to predict the earth dam slope failure probability with reasonable accuracy and efficiency. The coefficient of variations and scale of fluctuations of soil properties affect the earth dam slope failure probability significantly. Moreover, the earth dam slope failure probability is highly dependent on the selection of auto-correlation function (ACF), and the widely used single exponential ACF tends to provide an unconservative estimate in this study.