水环境下泥岩细观损伤机理及改性研究

Damage elements, such as micro-pore and micro-crack, exist in mudstone under the action of water. The degree of damage can be reduced by chemical modification of mudstone. In this project, the meso-damage-mechanisms of mudstones under different water action are studied by the method combining experimental research, theoretical research, comprehensive analysis with site inspection. The composition of mudstones with different rate of water is researched by XRD. Different kinds of polysiloxane silicon materials are chosen to modify the properties of mudstone to improve its harmful properties. The composition and microstructure of unmodified and modified mudstone are studied by SEM and EDX analyses. The process of crack for mudstone in saturation-dry cycle is focused on real time by laser scanning confocal microscope. The process of crack of unmodified and modified mudstones, which are load by compression and tension, is observed synchronously by non-contact optical scanning system, the stress-strain curves of mudstone under different water action are analyzed. By Digital Image Processing Technique, the change laws of damage elements of unmodified and modified mudstones under water action are researched quantitatively. The meso-damage-mechanisms of unmodified and modified mudstones are studied. Based on fractal theory, the relations between the fractal dimension of crack and the rate of water and strength of mudstone are researched. Relation between damage variable and the rate of water is set up. Damage constitutive equations are established by strain equivalence hypothesis.

水环境作用下，泥岩内部产生微孔隙、微裂纹等细观损伤基元，通过化学改性能够有效降低损伤程度。项目采用现场考察、实验研究、理论分析和综合分析相结合的方法，研究不同含水率及饱水-风干循环作用下改性前、后泥岩的细观损伤机理。利用XRD研究不同含水率泥岩成分的变化规律；选择不同聚硅氧烷类有机硅材料对泥岩改性，利用SEM和EDX研究改性前、后泥岩成分和微观结构的变化；利用激光共聚焦显微镜，实时观测饱水-风干循环过程中裂纹的演化过程；利用非接触光学扫描系统，同步观测改性前、后泥岩在加载过程中微裂纹的演化过程，分析不同水环境下泥岩的应力-应变全程曲线；通过数字图像分析处理技术，定量分析水环境下改性前、后泥岩损伤基元变化规律；揭示改性前、后泥岩的细观损伤机理；利用分形理论，研究裂纹的分形维数与含水率和力学强度之间的关系；建立损伤变量与含水率之间的关系，根据应变等效假设，建立改性前、后泥岩的损伤本构方程。

水环境作用下，泥岩内部产生微孔隙、微裂纹等细观损伤基元，通过化学改性能够有效降低损伤程度。项目采用现场考察、实验研究、理论分析和综合分析相结合的方法，研究不同含水率及饱水-风干循环作用下改性前、后泥岩的细观损伤机理。项目取得以下研究成果：(1)泥岩的崩解主要受饱水过程中产生的次生孔隙和泥岩表面受到的拉应力影响，总次生孔隙主要由水化学作用产生的次生孔隙和水的冲刷、运移物理作用产生的次生孔隙构成，饱水过程中泥岩受到不均匀应力，拉应力大于抗拉强度时孔隙相互扩展形成裂隙，裂隙的相互贯穿引起试样崩解。(2)随遇水-风干次数的增加，泥岩表面的裂纹数目、宽度逐渐增加。伊利石粘粒遇水后水分子进入粘粒晶胞之间，引起晶格膨胀。粘粒表面吸附的水膜导致粘粒间距增加。泥岩遇水过程中在水的物理、化学作用下内部产生大量次生孔隙并且体积膨胀。风干过程中泥岩表层风干速度大于内部风干速度，表层局部粘粒富集区域体积收缩产生裂纹，随着遇水-风干循环次数的增加泥岩内部裂纹的数量和尺寸逐渐增加，当裂纹贯穿试样时试样断裂。(3)有机改性时岩粒表面形成一层非极性憎水膜，但泥岩的抗剪强度提高幅度较小；无机改性时泥岩内部孔隙被三维网状凝胶结构填充，力学强度明显提高，但耐崩解性提高幅度较小；双重改性综合了有机改性和无机改性的优点，力学强度和耐崩解性显著提高。(4)拉应力较小时，泥岩内部形成局部变形区；随着拉应力的逐渐增加，局部变形区的面积逐渐增加，相邻的局部变形区相互合并，形成更大的局部变形区；局部变形区演化成应变局部化带；最终应变局部化带发展成宏观裂纹，试件发生破坏。水泥改性泥岩时，泥岩中聚集体间孔隙大部分被填充，抗拉强度提高。水泥改性泥岩后，随着水泥含量的增加，局部变形区演化成应变局部化带的位置逐渐向峰值载荷移动。水泥提高了泥岩的胶结程度，拉应力超过抗拉强度时，弹性能短时间内释放出来，使宏观裂纹迅速扩展。