Creep Behavior of Intact Loess Followed Unloading Paths

Zhenxiao Li,Jiading Wang,Dengfei Zhang

doi:10.3389/feart.2021.744864

Abstract

Several high-fill projects are carried out on the Loess Plateau, China, accompanying the progressive failure of slopes due to excavation. The compelling need requires a deep understanding of variation in the creeping behaviors of intact loess exposed to unloading. A series of creep tests of intact loess were performed under two separated unloading paths: decrease in confining pressure at constant deviator stress and decrease in confining pressure at axial stress. The results demonstrated that axial deformation followed the first unloading path always appears as compression while the three forms of axial deformation followed the second path, depending on the applied axial stress level. At a low unloading stress level, the elongation of axial deformation was observed. At a relatively unloading stress level, the axial deformation of the soil experienced the first elongation and then compression. At a high unloading stress level, the axial deformation appeared as compression, and finally, failure occurred with the increase of the unloading stress level. The failure approach index was introduced to use as the criterion for the loess to transform from stable to accelerated creeping. Finally, a modified Burgers model was proposed to characterize the creeping behavior of intact loess followed unloading paths. There was a good comparison between the calculated and measured data of the soil that establishes the rationality and validity of the proposed model.

Highlights

In recent years, with the rapid economic development, many engineering construction activities have been carried out in the Loess Plateau area, accompanied by a large number of loess slopes subjected to excavation and high-fill projects
The reason for the above phenomenon is that, at the initial stage of unloading the confining pressure, the soil can be considered to be in an elastic deformation stage, which corresponds to the first deformation form mentioned above; as the level of unloading stress increases, tiny cracks appear inside the soil, and the deformation of the soil gradually changes from elastic deformation to plastic deformation, which corresponds to the second form of deformation; with the further increase of the unloading stress level, the internal micro-cracks of the soil are penetrated, and the deformation of the soil is mainly plastic deformation, which corresponds to the third form of deformation
The transition stress state points of the first deformation form and the second deformation form can be used to distinguish the elastic deformation from the plastic deformation

Summary

Introduction

With the rapid economic development, many engineering construction activities have been carried out in the Loess Plateau area, accompanied by a large number of loess slopes subjected to excavation and high-fill projects. When soils are subjected to long-term loading, creep deformation increases over time, posing a safety hazard to the actual project. The study of creep deformation of loess has tremendous significance for the construction of loess projects. With the rapid development of economic construction, it is necessary to broaden its development space, and the project of gully control and land construction has been carried out in Yan’an New Area, China. It is beneficial to alleviate the shortage of land reserve resources in the urban area and is conducive to protecting the revolutionary sites in the Unloading Creep Behavior of Loess old urban area, promoting the development of the tourism industry, stimulating the healthy and sustainable growth of the economy, and improving the living environment

Objectives

Methods

Results

Discussion

Conclusion