Deterioration of the Internal Structure of Loess under Dry-Wet Cycles

Wanjun Ye,Xu Duan,Chenyang Cui,Yang Bai

doi:10.1155/2020/8881423

Wanjun Ye, Xu Duan + Show 2 more

Open Access

https://doi.org/10.1155/2020/8881423

Copy DOI

Abstract

To understand the structural damage evolution process of loess under the action of dry-wet cycles, a triaxial test of a dry-wet cycle was performed by considering three influencing factors: initial moisture content, amplitude of the dry-wet cycle, and number of dry-wet cycles. The stress-strain curves of undisturbed loess samples at different cycling times vary under different compacted loess cycles. Under the same axial strain, the stress value of the undisturbed loess is higher than that of the loess sample after a dry-wet cycle, indicating that such cycle can reduce the strength of loess. As the number and amplitude of dry-wet cycles increase, the shear strength of the loess sample and the value of cohesion (c) of the strength index gradually decrease, and the amplitude gradually decreases. With an increase in the number and amplitude of dry-wet cycles, the change in the internal friction angle of the strength index is inevident, indicating that the effect of dry-wet cycles on the internal friction angle of loess is insignificant. Computed tomography (CT) scan experiments were also conducted to obtain the evolution of loess cracks before and after a dry-wet cycle. Studies have shown that as the number and amplitude of dry-wet cycles increase, the mean (ME) value of CT decreases, the standard deviation (SD) value increases, and the ME value is obtained during the initial stage of a dry-wet cycle. Meanwhile, the decreasing trend of ME and the increasing trend of SD values are most evident during the period of a dry-wet cycle. In conclusion, dry-wet cycles promote the development of cracks.

Highlights

In Northwest China, loess is distributed continuously and widely, with thick strata
The structural degradation of loess is analyzed through the physical action of water, i.e., dry-wet cycles. e effects of this cycle on the structural and strength degradation of loess are investigated. e following conclusions are obtained from the micro and meso tests using hightechnology techniques
(1) Using fractal theory and MATLAB to calculate fractal dimension, the evolution of the surface cracks of the soil sample is observed from a macro perspective

Summary

Introduction

In Northwest China, loess is distributed continuously and widely, with thick strata. Loess in this region is typical Quaternary loose sediment with the best development and the most complete strata [1, 2]. Given the rapid economic development in Northwest China, the construction of various cities and the expansion of railways, highways, and water conservation projects have resulted in varying degrees of damage to the loess area Geological disasters, such as collapse and landslides, frequently occur and affect the progress of construction projects or the safe use of engineering buildings. Other scholars, including Zhang Fangzhi, Zhao Yanlin, Zheng Jun, and Gong Biwei, analyzed the change laws of the physical and mechanical characteristics of expansive soil under the action of dry-wet cycles from different angles and obtained certain results [9,10,11,12]. Zhang [14] studied the strength and deformation of the gravel soil slopes in the ree Gorges Reservoir area under dry-wet cycle conditions. From the micro and meso perspectives, CT images and numerical analyses were utilized to perform the meso-structure inspection of crack development and structural degradation inside a loess structure under the action of a dry-wet cycle. e damage evolution law of loess under the action of a dry-wet cycle from the macro and meso perspectives was comprehensively analyzed. e findings can provide a reference for analyzing the damage and degradation of loess during dry-wet cycles and predicting a loess slope disaster

Test Process

Analysis of Test Results

Effect of Dry-Wet Cycles on the Strength of Loess

Findings

Conclusion