Three-dimensional stability of two-step slope with crack considering temperature effect on unsaturated soil

Abstract

In existing studies, most slope stability analyses concentrate on conditions with constant temperature, assuming the slope is intact, and employ the Mohr-Coulomb (M-C) failure criterion for saturated soil to characterize the strength of the backfill. However, the actual working temperature of slopes varies, and natural phenomena such as rainfall and groundwater infiltration commonly result in unsaturated soil conditions, with cracks typically present in cohesive slopes. This study introduces a novel approach for assessing the stability of unsaturated soil stepped slopes under varying temperatures, incorporating the effects of open and vertical cracks. Utilizing the kinematic approach and gravity increase method, we developed a three-dimensional (3D) rotational wedge failure mechanism to simulate slope collapse, enhancing the traditional two-dimensional analyses. We integrated temperature-dependent functions and nonlinear shear strength equations to evaluate the impact of temperature on four typical unsaturated soil types. A particle swarm optimization algorithm was employed to calculate the safety factor, ensuring our method’s accuracy by comparing it with existing studies. The results indicate that considering 3D effects yields a higher safety factor, while cracks reduce slope stability. Each unsaturated soil exhibits a distinctive temperature response curve, highlighting the importance of understanding soil types in the design phase.

1. Introduction

The stability assessment of slopes is a classic topic within the field of geotechnical engineering. In the realm of slope and excavation engineering, the stability of stepped slopes exhibits a certain degree of improvement compared to their single-level counterparts. In the past, the majority of research on slope stability has primarily focused on failure mechanisms within a two-dimensional (2D) framework [1]. However, the failure of the slope usually exhibits three-dimensional (3D) characteristics when the width of a slope is constrained, indicating the necessity of considering a 3D model in the analysis. As of now, a considerable amount of research has been dedicated to evaluating the stability of slopes under 3D failure modes. These approaches can generally be categorized into three types: (a) limit analysis methods [2−4], (b) limit equilibrium methods [5−8], and (c) numerical analysis methods [9−12]. Limit analysis method circumvents the prolonged computational time and diverse parameter settings in numerical analysis as well as the various complex stress assumptions in the limit equilibrium method, which can cleverly analyze the stability of slopes and yield the required safety factor. Over the past few decades, the limit analysis method has proven to be effective, progressively evolving into one of the most efficient and powerful tools in the assessment of slope stability.

As is widely recognized, owing to the impact of human activities, the occurrence of extreme weather events on earth has been progressively increasing in recent years, with frequent and anomalous fluctuations in atmospheric temperatures. Slope engineering is highly susceptible to the influence of temperature changes due to the majority being exposed to the external environment. Meteorological data indicate that the likelihood of future occurrences of extreme events such as droughts and high temperatures is increasing in certain regions. ZHAN et al [13] conducted an analysis of soil temperature using daily temperature data from the Nanchang Meteorological Station spanning from 1961 to 2018. They found that over the past 58 years, the annual average temperature, seasonal average temperatures, and soil temperature primarily exhibited a significant upward trend. Based on daily measurements from 1970 to 2017 in Jiangsu Province, China, SHI et al [14] found that soil temperatures at most observation stations generally exhibited a warming trend, with these trends being more pronounced during the cold seasons than the warm seasons. MAZDIYASNI and AGHAKOUCHAK [15] mentioned in their study that the occurrences of drought and heatwaves have shifted towards more frequent and simultaneously more extreme events. From these facts, it is not difficult for us to recognize that considering temperature effects is pressing for slope stability analysis.