吸力控制干湿循环作用下非饱和膨胀土的表面裂隙和微观结构形态演化规律及其定量描述

Unsaturated expansive soils exist in many regions of China, and it is sensitive to the climate change. Expansive soils have swelling-shrinking, cracking and overconsolidation characteristics due to wetting and drying, and it is different from other unsaturated soils. Geological or engineering disaster often occurs due to drying and wetting cycles in the area of expansive soils. The macroscopic manifestations of physical and mechanical properties are the performance of internal microscopic structure of the soil. In a certain extent, the macroscopic properties of soil are affected by the changes in the soil microstructure. To study the evolutions of the cracking and microstructure of unsaturated expansive soils under the suction-controlled drying-wetting cycles is a fundamental issue for understanding and predicting various kinds of the disaster and proposing the control measure. On the basis of the existing research results of unsaturated expansive soils, a series of experimental study on the surface cracking and microstructure characteristics of expansive soils under the suction-controlled drying-wetting cycles is planned by using the suction-controllable pressure plate, measurable tensiometer, and the vapor equilibrium method, together with the test platform of particle image velocimetry, scanning electron microscopy and mercury intrusion porosimetry, and taking one kind of typical expansive soil in China as a testing material, and the description methods of the evolutions of the surface cracking and microstructure of unsaturated expansive soils are proposed by using the suction as basic variable in the plan. The study aims to reveal the evolutions of the cracking and microstructure of unsaturated expansive soils under the suction-controlled drying-wetting cycles and its quantitative relationship with suction. This project can provide some useful research results for geotechnical engineering problem with unsaturated expansive soils.

我国多地存在着对气候变化敏感的非饱和膨胀土，膨胀土具有胀缩性、裂隙性和超固结性等，经常因干湿循环引起地质或工程灾害。土体在宏观上表现的物理力学性状均是其内部微细结构的具体表现，其宏观性质在一定程度上受微观结构的影响。因此定量研究干湿循环作用下非饱和膨胀土的裂隙和微观结构形态演化规律是理解和预测膨胀土各种灾害和提出防治措施的基础。本项目计划在已有研究成果基础上，以国内典型膨胀土为试验材料，用吸力可控制或量测的压力板、张力计及蒸汽平衡法，同时联合粒子图像测试技术试验平台、扫描电镜仪和压汞仪，在吸力控制干湿循环作用下对非饱和膨胀性土表面裂隙和微观结构形态特征等进行一系列试验研究，并以吸力为基本变量提出描述非饱和膨胀性土表面裂隙和微观结构形态演化规律的方法。研究旨在揭示吸力控制干湿循环作用下非饱和膨胀土的裂隙和微观结构形态演化规律及其定量关系。本项目可为膨胀土相关的岩土工程问题提供有用的研究成果。

土体在宏观上表现的物理力学性状均是其内部微细结构的具体表现，因此定量研究干湿循环作用下非饱和膨胀土的裂隙和微观结构形态演化规律是理解和预测膨胀土各种灾害和提出防治措施的基础。本项目经过3年持续不断的深入研究，取得了如下成果：.（1）揭示了吸力控制干湿循环作用下非饱和膨胀土裂隙演化规律及主要影响因素，并提出了相应的定量描述方法；基于粒子图像测速技术(PIV)，揭示了非饱和膨胀土径向劈裂及其裂隙演化规律。.（2）揭示了吸力控制干湿循环作用下非饱和膨胀土的微观结构形态演化规律及其影响因素，并提出了定量描述的公式；提出了由微观结构特征预测土水特征曲线的方法；提出了预测干湿循环作用多次后土水特征曲线和强度的预测模型；揭示了不同温度条件下膨润土的变形特性及其微观机理；揭示了非饱和膨润土径向劈裂宏观表现及其微观演化规律。.（3）基于PIV技术揭示了非饱和土在沉桩过程中桩周土体变形场的变化规律；获得了考虑土体三维强度特性的不排水圆柱孔收缩相似解解析及演变规律。.（4）国内外学术交流方面，在基金资助下参加了2017年第二届全国非饱和土与特殊土力学及工程学术研讨会，2018年第七届全国岩土工程青年学者论坛，2019年第十三届全国土力学及岩土工程学术大会等，分别作了关于本课题研究成果的学术报告。.(5)发表学术论文15篇，其中SCI收录6篇，EI收录7篇，核心2篇，获授权发明专利7项。以项目研究为依托，毕业硕士研究生3名，获得2018年河南省教育厅科技成果壹等奖1项，排名3，获河南省科技进步奖壹等奖1项，排名12。 研究成果已在南水北调总干渠穿越禹州采空区工程、前坪水库高边坡工程等工程中成功运用，取得了显著的经济、社会和环境效益。