【作者】 刘斌；

【导师】 韦秉旭； 廖爱平；

【作者基本信息】 长沙理工大学 ， 工程硕士（专业学位）， 2015， 硕士

【摘要】 膨胀土是一种水敏性材料,矿物成分主要由强亲水性粘土矿物成分(蒙脱石和伊利石)组成。膨胀土受自然气候条件的影响比较敏感,在干湿交替频繁的气候环境中,膨胀土材料结构内部在基质吸力反复加卸载作用下会形成较多的细观裂隙,随着应力循环次数的增加,细观裂隙逐渐发育,并在膨胀土结构内部形成错综复杂的裂隙网络,最终导致土体结构松散,力学性能发生劣化。干湿循环作用下膨胀土细观结构的变化是导致其宏观力学性能劣化的根本原因,是膨胀土边坡失稳破坏的关键所在。因此,有必要开展干湿循环作用下的膨胀土细观结构特征变化研究。基于此,本文利用CT技术对不同初始控制含水率下经历干湿循环作用后的南阳膨胀土进行CT扫描,并结合计算机图像处理技术,定量化分析膨胀土试样的内部细观裂隙,研究了裂隙网络的几何结构和形态特征随循环次数的变化规律;利用聚类分析和逐步回归法,从定量描述膨胀土裂隙的指标中筛选出了表征其裂隙发育程度的基本指标;最终基于CT数定义损伤变量,建立了干湿循环作用下膨胀土体细观结构特征与低应力抗剪强度指标之间的关系。本文主要研究结论如下:1.第1-4次干湿循环对膨胀土细观结构变化影响较大,内部微裂隙发育明显,第7-8次干湿循环对细观结构影响甚微。在控制干密度相同的情况下,较高的的初始控制含水率可以有效的抑制土体的开裂。2.裂隙的节点个数、块区个数、裂隙平均长度和裂隙率是描述其形态结构和几何特征的基本指标,可以用来描述裂隙的发育程度。裂隙条数和总长度受节点个数控制,区块个数反映了区块面积的变化情况,平均长度反映了内部细观裂隙的连通性,裂隙率则在总体上反映了土体的体积变化情况。3.经干湿循环作用后膨胀土的强度衰减主要表现为粘聚力大幅度降低,而内摩擦角则无明显变化。4.随着干湿循环次数的增加,膨胀土的各向异性越来越明显,主要表现为CT数方差逐渐增大。膨胀土的损伤变量也随循环次数的增加逐渐增加,其细观结构损伤演化是一种非线性累积过程;膨胀土粘聚力与CT损伤变量具有良好的指数衰减关系。更多还原

【Abstract】 Expansive soil is a kind of water sensitive material,mineral composition is mainly composed of strong hydrophilic clay minerals(montmorillonite and illite).Expansive soil is sensitive to the natural climate conditions.In the climate of dry and wet alternation,the internal structure of expansive soil can form a large number of micro fractures in the matrix suction.The variation of the meso structure of expansive soil under the action of wet and dry cycles is the root cause of the deterioration of the macro mechanical properties and the key to the failure of the expansive soil slope.Therefore,it is necessary to study the mechanical properties of expansive soil under the action of wet and dry cycles and the changes of its microstructure characteristics.Based on this,the CT scanning of Nanyang expansive soil,which is based on CT technology,is used to quantitatively analyze the characteristics of expansive soil,and then,by means of cluster analysis and stepwise regression analysis,the relationship between the characteristics of expansive soil and low stress shear strength is established by using cluster analysis and stepwise regression method.The main conclusions of this paper are as follows:1.The influence of 1st-4th times of drying-wetting cycles on the structure of expansive soil is bigger,the development of internal fracture was obviously.The influence of 7th-8th times of drying-wetting cycles on the structure is little.Under the same control dry density,the initial control water content can effectively inhibit the cracking of soil.2.The intersections of cracks,number of blocks,the average length and crack rate was basic index to describe the structure and geometric feature,can be used to describe the degree of crack development.Number of crack segments and total length was controlled by the intersections of cracks.Number of blocks reflect block area change rules.The average length reflects Internal crack connectivity.Crack rate can be used to explain the volume change of the soil in general fall.3.After the drying-wetting cycles,the strength attenuation of expansive soil is mainly decrease of cohesion,and the variation of internal friction angle is not significantly.4.With the increase of drying-wetting cycles times,the anisotropy of expansive soils is becoming more and more obvious,and the main performance of the CT is gradually increasing.With the increase of drying-wetting cycles times,the damage variable increases gradually,and the evolution of meso-structure damage is a non-linear accumulating process.CT damage variable and cohesion of expansive soil has a good index decay relationship.更多还原