【作者】 王艳；

【导师】 刘伟平； 谭光伟；

【作者基本信息】 南昌大学 ， 工程硕士（专业学位）， 2022， 硕士

【摘要】 我国赣南花岗岩残积土地区受高温、暴雨、干旱等极端气候的影响,诱导大量裂缝的发育,裂缝是加剧土体的出现崩岗侵蚀的先导,引发严重的水土流失。因此干缩裂缝与崩岗侵蚀密切相关,同时也是控制崩岗侵蚀的重要因子。花岗岩残积土是赣南崩岗侵蚀区域的代表性土体,然而目前对于花岗岩残积土的裂缝扩展相关研究较少,尤其针对不等颗粒粒径和多因素共同耦合对裂缝扩展的影响,还需要进一步分析。本文将花岗岩残积土作为主要研究对象,考虑两种不同颗粒粒径,通过室内干缩裂缝试验和正交试验,分别研究单因素作用和多因素共同作用对土体裂缝的影响,同时开展了相关微观机理分析,主要得出以下结论:(1)基于控制变量法,对两种不等颗粒粒径土体进行室内干缩裂缝试验,分别研究厚度、界面摩擦以及含砂量三种单因素对土体裂缝扩展的影响。从而获得了三种单因素分别作用下,土体的含水率、裂隙率、土体裂缝最终形态和裂缝的定量统计,以及土体干缩过程中的微观现象。同一初始土层厚度,颗粒粒径越小,裂隙的发育程度越高,表面破碎程度越大;当界面摩擦为一恒定值时,小颗粒粒径最终形成的裂隙率均大于大颗粒粒径形成的裂隙率;在同一含砂量的作用下,大颗粒粒径试样最终形成的裂缝区块数量较少,单一区块的面积较大,试样表面形成的裂缝宽度大小不一致。(2)基于正交实验法,采用室内干缩裂缝试验,研究厚度、界面摩擦以及含砂量三种因素共同作用下对土体裂缝扩展的影响,结果表明:在三种因素中厚度起决定性作用。本文将花岗岩残积土进行烘干和筛分得到2～1mm、0.5～0.25mm以及0.25～0mm三个粒组土。为研究不等颗粒粒径的发展机理,将2～1mm粒组和0.5～0.25mm粒组混合,以下简称2mm+0.5mm试样;将2～1mm粒组和0.25～0mm粒组混合,以下简称2mm+0.25mm试样。对于2mm+0.5mm的试样含砂量的影响处于第二位,而对于2mm+0.25mm的试样界面摩擦的影响处于第二位。2mm+0.5mm和2mm+0.25mm各试样的最终裂隙率曲线、裂缝面积曲线以及总长度曲线的变化趋势相似。(3)以土体裂缝扩展为研究背景,研究土体干缩过程中处于吸附状态下的不等颗粒粒径之间基质吸力与体积含水率的理论曲线。结果表明:不同间距和土颗粒之间的体积含水率与基质吸力均呈反比例关系;随着土颗粒之间间距的增加,同一基质吸力条件下,体积含水率也逐渐增加。大颗粒粒径土体对应的体积含水率大于小颗粒粒径土体对应的体积含水率。理论值求解的土水特征曲线与压力板试验法求解出的土水特征曲线基本一致。(4)所有试样的裂缝断面均出现羽化结构。裂缝扩展方向与羽化结构扩展方向一致;同一裂缝两侧的羽化结构方向相同。试验模具底面有界面摩擦时,多数裂缝在底部成核向上发展,而表面裂缝出现气泡、杂点时,裂缝会在优先在气泡处成核向下发展;试验模具底面无界面摩擦时,裂缝从土体表面出现并向下延伸,此外裂缝会优先在土体表面的杂点、气泡等缺陷处产生;一级裂缝、二级裂缝和三级裂缝的断面缺口不会影响一级裂缝的羽化结构;非自发性生成的裂缝,不会形成羽化结构。更多还原

【Abstract】 Under the influence of extreme climate,such as high temperature,heavy rain and drought,a large number of cracks are induced,which promotes the serious soil erosion in the southern Jiangxi region of China.Therefore,the dry shrinkage fracture is closely related to the collapse erosion and is also an important factor to control the collapse erosion.Granite residual soil is the representative soil in southern Jiangxi,which has obvious collapsing erosion characteristics.However,there are limited studies on fracture propagation of granite residual soil at present,especially the influence of different particle sizes and coupling multiple factors,which needs further analysis.In this paper,granite residual soil is taken as the main research object and two different particle sizes are considered.Through indoor dry shrinkage crack test and orthogonal test,the influence of single factor and multiple factors on soil cracks is studied respectively.The main research contents are as follows:(1)Based on the control variable method,the indoor dry shrinkage crack test is carried out to study the effects of three single factors,namely thickness,interfacial friction and sand content,on the crack propagation of soils with two different particle sizes.Thus,the quantitative statistics of water content,fracture rate,final morphology and fracture of soil under the action of three single factors are obtained,as well as the microscopic phenomenon of soil shrinkage process is analyzed.(2)Based on orthogonal experiment method,indoor dry shrinkage crack test is used to study the influence of thickness,interface friction and sand content on the propagation of soil cracks.The results show that thickness plays a decisive role in the three factors.In this paper,granite residual soil is dried and sieved to obtain three granular soils of 2～1mm,0.5～0.25 mm and 0.25～0mm.In order to study the development mechanism of unequal particle size,2～1mm particle group and0.5～0.25 mm particle group are mixed,hereinafter referred to as 2mm+0.5mm sample.The 0.5～0.25 mm granule group and 0.25～0mm granule group are mixed,hereinafter referred to as 2mm+0.25 mm sample.The influence on sand content of 2mm+0.5mm sample is in the second place,and the influence on interface friction of 2mm+0.25 mm sample is in the second place.The final fracture rate curve,fracture area curve and total length curve of 2mm+0.5mm and 2mm+0.25 mm specimens have similar trends.(3)The theoretical curves of matric suction and volumetric water content of soils with different particle sizes in adsorption state during dry shrinkage of soil are studied under the background of soil crack propagation.The results show that the volumetric water content between soil particles and matric suction are inversely proportional with different distance.With the increase of the distance between soil particles,the volume water content increases gradually under the same suction.The volumetric water content of soil with large particle size is larger than that of soil with small particle size.The soil-water characteristic curves obtained from theoretical values are basically consistent with those obtained by pressure plate test method.(4)The fracture sections of all samples showed plumose structures.The direction of crack propagation is consistent with that of plumose structures.The plumose structures on both sides of the same crack have the same direction.When the bottom of the test mold has interface friction,most cracks nucleate upward at the bottom.While bubbles and impurities appear on the surface cracks,cracks will nucleate downward at the bubbles preferentially.When there is no interfacial friction at the bottom of the test mold,cracks appear from the soil surface and extend downward.In addition,cracks preferentially occur at the defects of the soil surface such as impurities and bubbles.The section gap of primary,secondary and tertiary fractures does not affect the emergence structure of primary fractures.The non-spontaneous cracks will not form the emergence structure.更多还原