贵阳红黏土轴向加卸载变形特性及损伤机理分析

Deformation characteristics and damage mechanism of Guiyang red clay under axial cyclic loading and unloading

摘要

【目的】为研究轴向加卸载对贵阳红黏土变形特性的影响，【方法】设计了轴向不同循环应力比、不同循环次数条件下的土样加卸载试验，辅以低场核磁共振技术以及SEM电镜扫描测试，探讨循环加卸载全过程土样宏观变形和孔隙结构的演化规律，揭示土样损伤机理。【结果】研究结果表明：循环加卸载使得贵阳红黏土内部结构经历着从压密到劣化的过程，随着循环次数和应力比的增大，应力-应变曲线由应变硬化型逐渐转变为应变软化型。经过多次加卸载后，试样孔隙分布T₂谱图曲线由“山峰型”向“丘陵型”发展，孔径范围与峰值频谱呈减小趋势，大、中孔隙数量逐渐减少，小、微孔隙逐渐增多，粒团之间以面接触变为线、点接触。基于循环过程中卸载模量和塑性应变的变化定义损伤系数，随着循环次数和应力比的增加，损伤呈上升趋势，与孔隙变化规律一致。【结论】研究结果可为施工期红黏土路基压实及稳定性评价提供理论指导。

Abstract

[Objective] In order to study the effect of axial loading and unloading on the deformation properties of Guiyang red clay, [Methods] the loading and unloading tests of soil samples under different axial stress ratios and cyclic numbers were designed, supplemented by low-field nuclear magnetic resonance technology and SEM electron microscope scanning. The evolution laws of macro-deformation and inner pore structure of soil samples during the whole cycle loading-unloading process were discussed to reveal the damage mechanism of soil samples. [Results] The result show that the internal structure of Guiyang red clay underwent a process from compaction to deterioration due to cyclic loading and unloading. With the increase of cycle number and stress ratio, the stress-strain curve of Guiyang red clay gradually changed from strain hardening type to strain softening type. The T₂ spectrum curve of pore distribution was developing from “mountain peak type” to “hilly type”, and the pore size range and peak spectrum of the sample were gradually decreasing. The number of large-medium pores gradually decreased, while the number of small-micro pores gradually increased. The clay particles around the pores were mostly in the form of closely cemented mineral particles, and the surface contact between the particles was changed into the form of line and point contact. The damage coefficient was defined by the change of unloading modulus and plastic deformation, indicating that the more the number of cycles and stress ratio, the more serious the damage of the soil sample, which was consistent with the law of pore change. [Conclusion] The result can provide theoretical guidance for the compaction and stability evaluation of red clay subgrade during construction period.

关键词

贵阳红黏土 / 轴向加卸载 / 核磁共振技术 / 损伤 / 孔隙结构 / 变形

Key words

Guiyang red clay / axial loading and unloading / nuclear magnetic resonance technology / damage / pore structure / deformation

基金资助

国家自然科学基金项目(42167025)

贵州省科学技术基金项目(黔科合基础-ZK[2022]重点018)