粒度组成对红黏土干缩裂隙影响

为了探讨粒度组成对红黏土干缩裂隙发育的影响,从而给红黏土地区的工程建设及减灾防灾提供理论依据。通过室内干燥试验,研究了粒度组成对昆明呈贡红黏土饱和泥浆样的水分蒸发、干缩裂隙的形成和演化、表面干缩裂隙结构形态的影响。结果表明:(1)蒸发曲线分为4个阶段,常速率阶段是最重要阶段;(2)常速率阶段历时随粒径减小而增长,随粒径分布范围变大而减短;(3)蒸发速率与粒径、粒径分布范围的关系不明显;(4)干缩裂隙形成与演化过程分为5个阶段,受粒度组成影响最显著的是裂隙形成阶段;(5)粒度组成影响裂隙形成阶段历时、不同等级裂隙先后衍生关系、开裂曲线的分段性、裂隙网络结构和土块分布;(6)天然粒组样的干缩裂隙产生向上卷曲现象;(7)粒径分布范围越大,分布非均匀性越强,表面裂隙率越大,而粒径的影响不明显;(8)表面裂隙的分形维数随粒径减小而减小。综上,粒径分布范围和分布非均匀性显著影响红黏土的水分蒸发过程,干缩裂隙的形成和演化,表面干缩裂隙结构形态。     

Effects of Fiber Additives on the Desiccation Crack Behavior of the Compacted Akaboku Soil as A Material for Landfill Cover Barrier

In the daily and final landfill cover barrier system, the hydraulic properties of compacted soil liners and the strength of soil can be adversely affected by desiccation cracking, resulting in the loss of effectiveness and integrity of the containment system as a barrier. Recently, there is an interest of using fiber additive to overcome the desiccation cracking problem. In this study, the desiccation crack test was conducted to investigate the effect of fiber additive on suppressing desiccation cracks in compacted Akaboku soils. Polypropylene (C₃H₆) fiber was used as an additive material for soil sample. The percentages of fiber used were varied as 0.0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.2% (by dry weight of samples). The soil specimens were compacted under the conditions of maximum dry density and optimum water content. The surficial cracking area was measured to determine the crack intensity factor (CIF) of the soil samples. The desiccation crack test results indicated that the percentage of volume change of the compacted soil specimen decreased with addition of fiber. The change in the soil surface area decreased with increasing in the fiber content (FC), and consequently, the volumetric shrinkage strain decreased. The CIF for the soil without fiber (FC?=?0.0%) were significantly higher than the soil with fiber additive. The CIF of soil at FC?=?0.0% decreased from 2.75% to 0.6% for the soil at FC?=?0.2%. It was also found that the maximum crack depth reaches almost 50% of the thickness of the soil without fiber additive. This study suggests the potential application of the fiber additives to soils as an available method to suppress desiccation cracks encountered in landfill cover barriers.     

土壤干缩开裂三维模型构建及其参数敏感性分析

为揭示农田土壤干缩裂隙沿深度方向的发展规律及形成机理,该研究改进了Vogel提出的Hookean弹簧模型,通过构建由节点组成的三棱柱状网格结构,并考虑重力的影响,建立了可以模拟裂隙深度的三维农田土壤干缩开裂模型,分析了纵向弹性系数（与土壤沿深度的弹性有关）对模拟裂隙深度的影响,通过Minkowski密度（即面积密度、长度密度和欧拉数密度）量化分析裂隙形态。结果表明：试验与模拟裂隙图像的面积、长度、欧拉数密度及裂隙深度频率的决定系数在0.849～0.959之间,一致性指标在0.965～0.988之间,偏差在0.103～0.189之间,均方根误差在0.005～0.083之间,说明改进后的三维模型达到率定要求,该三维物理模型可以模拟出裂隙沿深度的拓展情况,模拟的表层裂隙形态特征符合自然裂隙的发育规律。敏感性分析中,纵向弹性系数越小,裂隙沿深度方向发育的趋势越明显,深裂缝（土深5～10 cm）的占比越大。研究可为模拟农田土壤裂隙沿纵向的发育和形成提供算法参考。     

干湿效应下崩岗土体的裂隙演化及收缩变形规律

为提高崩岗土体稳定性,抑制崩壁崩塌.试验共设计6次干湿循环,利用工业相机对脱湿过程中崩岗4层土进行定时定点拍照并结合数字图像处理技术,研究干湿效应下崩岗土体的裂隙演化及收缩变形规律.结果表明:(1)脱湿过程中土体形态变化顺序为轴向收缩、径向收缩和裂隙发育;(2)表面裂隙率与液限、塑性指数、黏粒含量呈显著正相关关系,4层...     

干湿循环作用下云南红土裂缝发展研究

以干湿循环为控制条件,考虑初始干密度、增湿次数和脱湿次数等影响因素,采用室内试验和图像处理相结合的方法,研究云南红土裂缝的产生及其发展演化。控制初始干密度为1.20,1.30,1.40,1.50g/cm~3,通过增湿、脱湿的干湿循环及膨胀率等试验方法,观察红土样裂缝的变化,并应用Matlab图像处理技术提取红土样的裂缝特征参数。结果表明:干湿循环作用下,初始干密度越大,红土样越容易开裂,干密度较小时(1.20g/cm~3)土样始终不开裂,随干密度增大(1.30,1.40g/cm~3),红土样在第3次增湿中开裂,干密度达1.50g/cm~3时,红土样在第2次增湿中开裂,增湿过程对红土样裂缝发展的影响显著大于脱湿过程的影响;红土样的膨胀率随浸泡时间延长逐渐增大,干密度为1.20,1.30,1.40g/cm~3时约8min膨胀基本稳定,干密度为1.50g/cm~3时约36min膨胀趋于稳定;对应红土样的裂缝条数、长度、面积和宽度等特征参数随增湿次数、脱湿次数增大而增大;随干密度增大,红土样的裂缝条数、长度与面积增大,裂缝宽度在干密度约1.30g/cm~3处存在峰值。干湿循环作用引起云南红土开裂的关键因素在于增湿过程中红土样的不均匀膨胀,红土裂缝属于膨胀裂缝,其发展过程包括裂缝孕育期(0~2次)、裂缝形成发展期(2~6次)和裂缝稳定期(6~8次)3个阶段,这3个阶段综合作用的结果,最终影响了红土裂缝的发展演化趋势。     

The wetting and drying of a grazed and ungrazed clay soil

A 4 year field experiment clearly demonstrates the role played by desiccation cracks in the redistribution of rainfall during the autumn re-wetting of a Windsor Series clay soil. Where topsoil structure is damaged by the trampling of grazing animals, cracks are well developed and a portion of rain water is diverted down them, by-passing the topsoil. Redistribution takes place from two centres, the bottom of the cracks and the surface. But where structure is unaffected by trampling, the soil accommodates seasonal shrinkage without cracking and redistribution is by diffusion from the surface only. Summer evaporation is shown to be linearly related to Penman's potential evapotranspiration over a wide range of soil moisture deficits, and simple constants are provided to correct E_T to obtain E_A. The M.A.F.F. method of estimating evapotranspiration is shown to be too conservative and fails to identify the October maximum soil moisture deficit common in this soil.     

Vertical porosity profile of a clay-rich marsh soil

The evolution of clay soil porosity is currently demonstrated via the shrinkage curves in a large water content domain spreading from a shrinkage limit to a liquidity limit. In fact, the parallel between in situ profiles and the shrinkage curves in such a large water content range is difficult to obtain because of the lack of earth pressure in the laboratory tests and in situ limited water contents. The vertical distribution of porosity throughout a clay-rich marsh soil profile was studied in a grassland field with samples taken from the soil surface characterized by water contents near their shrinkage limit down to 2.00 m deep saturated sediments over their liquidity limit. The depth of the plasticity limit isolates a soil in a solid state characterized by a vertical prism-like structure from a plastic to pseudo-liquid state in depth. The porosity was calculated from the measurements of the density of intact samples by double weighing and image analysis of 100 cm² polished sections. The initial structure of clay soil was maintained by impregnation based on water–acetone–resin exchange. An ultraviolet photo luminescent pigment added to the resin allowed the capture of images from which shrinkage cracks and microporosity of the clay matrix were easily separated. The distribution of porosity between the shrinkage crack mesoporosity and the clay matrix microporosity was evaluated after the mathematical decomposition of the grey level curves characteristic of each level. Vertical evolution of the porosity distribution from the soil surface in a solid state to the plastic and pseudo-liquid sediment in depth was presented on the shrinkage curve of the clay material. The measurements point out how the clay matrix microporosity and mesoporosity of shrinkage cracks are complementary and the role of the scale effect on the shrinkage curve. The analysis of images captured on an optical microscope under polarized and analyzed light and the SEM observation of freeze-dried samples demonstrated the isotropic arrangement of the clay particles in typical “honey-comb” architecture in the in situ plastic-to-liquid saturated domain. Eventually the distribution of porosity through the profile results from the evolution of the initial “honey-comb” microstructure of the sediment induced by the desiccation phenomenon. It is governed by the depth of plasticity limit of the clay material and by the depth of the water table.     

温度对崩壁红土层土壤干缩裂隙形态影响的定量研究

  目的  探究干燥温度对土壤水分的蒸发速率及其崩壁土壤干缩裂隙的发育过程的影响,为准确认识崩壁土壤裂隙的形态及其对揭示崩岗的发展过程提供理论依据。  方法  研究选取典型崩岗区崩壁的红土层土壤,模拟干缩裂隙发育过程,通过图像处理技术,定量分析裂隙表面参数,探讨温度对崩壁红土层土壤裂隙发育的影响。  结果  温度降低,土壤水分蒸发速率下降,裂隙面积和裂隙总长度增大,裂隙率提高,同时块区面积降低,块区个数以及裂隙条数、节点数显著增加,整个土体呈现出越发破碎的状态。由于裂隙条数的显著增加,低温状态下（40 ℃）裂隙的平均长度小于高温条件（80 ℃）的试样,即低温条件较高温条件土壤裂隙发育数量更多,平均长度更小;土壤裂隙的平均宽度随温度升高呈现增大的趋势;分形维数随着温度的降低呈现增大的趋势。黏粒含量显著影响土壤干缩裂隙发育的温度效应。  结论  在较低温度条件下,崩壁红土层表层土壤水分蒸发时间长,裂隙发育过程更缓慢,但发育程度高,裂隙结构更复杂。     

湖南邵阳地区高液限红黏土干缩裂隙演化过程的量化分析

红黏土对环境湿度变化非常敏感,在干燥环境中极易开裂,纵横交错的裂缝网络损害了土壤结构的完整性,很容易诱发红黏土边坡失稳和崩塌,导致农田水利设施的破坏,甚至加剧整个生态环境的水旱灾害。为探究红黏土裂隙的演化规律,该研究采用自制试验装置和三维应变测量系统开展了自然湿热条件下的红黏土泥浆样干燥试验,通过采集土体水分和土表位移、应变和裂隙的变化,定量分析脱湿过程中土体表面裂隙形态和应变场的演变特征,并进一步探讨水分变化对裂隙形态和应变场的影响。结果表明：1）土样表面干缩裂隙的演化一共经历了6个阶段,后阶段裂隙分割前阶段裂隙围成的区域,且不同阶段裂隙的交叉角接近90o;2）裂隙产生初始,裂隙尖端处拉应变约为0.5%,土表面大部分区域处于受拉状态;随着裂隙进一步发展,裂隙周边土体逐渐由拉应变状态向压应变状态转变;当所有裂隙发育完成,裂隙周边土体处于压应变状态;3）裂隙演化阶段与界限含水率有关,当泥浆土样的含水率接近液限时（67.7%）,土体表面裂隙开始发育,裂隙迅速张开和延伸;当土的含水率达到塑限时（28.3%）,裂隙发展的速率逐渐变缓;当含水率小于缩限时（18.8%）,裂隙变化已经很小,裂隙发育接近完成;4）在裂隙演化过程中,早期裂隙的发展持续时间和裂隙宽度均超过后期裂隙;土表不同位置的位移和应变均不相同,土块中心竖向收缩大于边缘竖向收缩,而土块中心位移及应变均小于土块边缘,研究可为红黏土开裂引发的工程地质灾害的预防及治理提供参考。     

Effects of cropping and puddling practices on the cracking patterns in paddy fields

Shrinkage cracks in clayey paddy fields are major pathways for the drainage of excess water through tile drainage. In this study, the factors that affect the cracking pattern were investigated in a paddy field where paddy-rice was planted in rows. The factors examined included 1) the existence of transpiration, 2) row spacing, and 3) the puddling intensity. The experiment was designed according to the Taguchi method of experimental design. Shrinkage cracks were induced by drying the field after the release of the ponding water in mid-summer. The cracking patterns between the rows were recorded on transparent sheets, and their geometry was quantified using the crack direction index (CDI), which represents the direction of cracks relative to the rows of rice, as well as the equivalent width (EW) and compactness (CP) which represent the average width of the cracks and the complexity of the cracking patterns, respectively. Variations in the degree of desiccation affected the cracking patterns; these effects were taken into account in the analyses. ANOVA was performed on the variables CDI, EW, and CP, and the following conclusions were drawn: 1) transpiration from the crops planted in rows induces significant straight cracks along the rows; 2) row spacing exerts a significant effect on the EW of cracks, for example, when the spacing doubled from 30 cm (the conventional spacing in Japan), the cleavage became more concentrated and the cracks became wider; 3) repeated puddling also induces wider straight cracks along the rows and makes the cracking patterns simpler.     

土壤表面干缩裂隙形态定量分析及其数值模拟

为揭示农田土壤表面干缩裂隙发展规律以及形成机理,该文对农田土壤裂隙演化试验图像进行二值化、去除噪点、提取裂隙边缘等处理,应用闵科夫斯基函数定量分析裂隙形态变化,并基于胡克定律模拟由于水分蒸发而引起的土壤收缩开裂过程。结果表明:闵科夫斯基函数可以有效地描述裂隙形态;形态学分析结果显示裂隙的闵科夫斯基面积、长度、欧拉数密度函数具有不同的变化规律;应用数值方法模拟由于水分蒸发而引起土壤收缩开裂的二维裂隙,试验图像裂隙面积、长度、欧拉数密度基本分布在100组模拟图像裂隙密度均值与标准差之间,裂隙试验图像与模拟图像面积、长度、欧拉数密度决定系数在0.893~0.928之间,均方根误差在0.002~0.039之间,偏差在0.064~0.144之间,一致性指标大于0.888,表明模拟结果较好。应用数值方法模拟土壤表面裂隙,有助于研究农田土壤裂隙的形成机理以及土壤裂隙随时间变化过程中动态演化规律。     

干湿循环过程中壤质黏土干缩裂缝的开闭规律

为研究干湿循环过程中农田土壤干缩裂缝的开闭规律,在室内试验的基础上,结合数字图像处理技术对壤质黏土干湿循环过程中土壤干缩裂缝网络几何形态特征进行了定量分析。结果表明:干燥过程中土壤含水率随试验时间的变化经历3个阶段。增湿过程中,含水率达到45%时裂缝完全闭合;裂缝面积率、长度密度、面积周长比与连通性指数分别在含水率增加到30%、32%、30%、35%时开始迅速减小。裂缝开裂与闭合是2个不可逆的过程。土壤水分在田间持水率和凋萎系数时裂缝几何参数统计表明,大多数裂缝面积在0~30 mm2之间,长度在0~40 mm之间。从田间持水率干燥到凋萎系数的过程中,裂缝面积与长度的频数分布均显著变化,从凋萎系数增湿到田间持水率的过程中,频数分布几乎没有变化。土壤含水率为凋萎系数时,干燥过程与增湿过程面积、长度的频数分布差异较小,而为田间持水率时差异明显。该成果有助于土壤干缩裂缝开闭机理及裂缝优先流的研究,为基于裂缝网络的精量灌溉制度的制定提供理论基础。     

Shrinkage Characteristics of Lime Concretion Black Soil as Affected by Biochar Amendment

Studies have reported that biochar is a sustainable amendment that improves the chemical and physical properties of soil.In this study,an incubation experiment was conducted to investigate the effects of different application rates of biochar on the cracking pattern and shrinkage characteristics of lime concretion black soil after three wetting and drying cycles.Biochar derived from the corn straw and peanut shell mixture was applied to the soil at rates of 0,50,100,and 150 g kg~(-1)dry weight,representing the treatments T_(0),T_(50),T_(100),and T_(150),respectively.During the wetting and drying cycles,the cracking pattern and shrinkage characteristics of the unamended and amended soil samples were recorded.Application of biochar significantly increased soil organic carbon content in the samples.During soil desiccation,biochar significantly reduced the rate of water loss.Cracks propagated slowly and stopped due to the relatively higher water content in the soil applied with biochar.The cracking area density(ρ_c),equivalent width,fractal dimension,and cracking connectivity index decreased during the drying process with increasing application rate of biochar.Theρ_(c )value of the T_(50),T_(100),and T_(150) treatments decreased by 33.6%,52.1%,and 56.9%,respectively,after three wetting and drying cycles,whereas the T_(0) treatment exhibited a marginal change.The coefficient of linear extensibility,an index used to describe onedimentional shrinkage,of the unamended soil sample(T_(0))was approximately 0.23.Application of 100 and 150 g kg~(-1)biochar to the soil significantly reduced the shrinkage capacity by 41.45%and 45.54%,respectively.The slope of the shrinkage characteristics curve,which indicates the ralationship between soil void ratio and moisture ratio,decreased with increase in the application rate of biochar.Furthermore,compared with the T_(0) treatment,the proportional shrinkage zone of the shrinkage characteristic curve of the T_(50),T_(100),and T_(150) treatments decreased by 5.8%,13.1%,and 12.1%,respectively.Differences were not observed in the moisture ratio at the maximum curvature of the shrinkage characteristic curve among the treatments.The results indicate that biochar can alter the cracking pattern and shrinkage characteristics of lime concretion black soil.However,the effects of biochar on the shrinkage of lime concretion black soil are dependent on the number of wetting and drying cycles.     

Modelling cracking stages of saturated soils as they dry and shrink

Cracks that form when clay soils shrink on drying eventually form a network that determines transport properties. I propose and validate a model for (i) analysing the initial cracking stages of shrinking saturated soils, (ii) estimating the minimum dimension of quasi‐brittle cracks capable of developing in such conditions, and (iii) determining relations between the minimum crack dimension and other characteristic dimensions of the soil structure. Shrinkage cracks in soils can be classified on the concept of the minimum quasi‐brittle crack capable of developing at shrinkage. I use the model of developing a shrinkage crack in a semi‐infinite brittle medium with constant relevant properties, desiccating in conditions of shock drying. The model is generalized to the cracking of a saturated clay soil with a limited maximum crack depth. The available data justify the use of constant elastic, strength, diffusivity, and shrinkage properties of clay soil. The critical point of crack development is the existence of the minimum crack capable of developing in the particular conditions. The dimension of the crack is related to the soil properties. The crack goes through stages of delay, jump, stable growth with approximately constant velocity, and then quick decline until it stops. I show that the minimum crack dimension is related to the mean dimension of soil particles, the thickness of an upper intensive‐cracking layer, and the mean spacing of primary cracks at the soil surface.     

干湿交替下膨胀土裂隙演化与强度衰减规律试验研究

为揭示干湿循环效应下膨胀土胀缩裂隙的演化特征及土体结构强度的劣化规律,对合肥弱膨胀土试样开展不同循环幅度下的干湿循环试验,利用图像处理技术从试样表面裂隙图像中提取出裂隙参数,并进行低应力下的抗剪强度试验。试验结果表明:1)裂隙开展分为裂隙酝酿期、裂隙快速传播期和裂隙平稳发展期3个阶段,裂隙指标的增长主要集中在裂隙快速传播期,且循环幅度的增大会使土体的开裂程度加剧;2)在干湿循环作用下,膨胀土的内摩擦角变化幅度小于2.2°,其受干湿循环次数的影响很小,土体的强度衰减主要源于粘聚力的大幅降低。膨胀土的粘聚力呈现出先快后缓的衰减趋势,其中前4次干湿循环期间粘聚力的衰减率达到50.97%～66.92%,且衰减率也与干湿循环幅度的大小密切相关;3)通过灰色关联度分析发现,粘聚力的衰减与裂隙面积率、裂隙总长度、裂隙平均宽度的变化趋势具有明显的关联性,其中裂隙面积率的关联度最大,其与粘聚力衰减率间的关联度为0.785～0.832,相应的权重达到0.461～0.472,且裂隙面积率与粘聚力衰减率间具有较好的线性关系,而裂隙平均宽度的关联度最小,其与粘聚力衰减率间的关联度为0.392～0.414,对应的权重仅为0.228～0.240。研究成果可为进一步揭示剧烈温湿变化诱发的膨胀土边坡灾变机理提供重要依据。     

农田土壤表面干缩裂缝的随机分布统计特征

该文对不同耕地类型土壤表面干缩裂缝的发展规律进行了室内试验研究,通过计算机图像处理,研究裂缝形态的统计规律。结果表明:裂缝面积密度和长度密度都是随着含水率的减少而增大,达到最大值后保持稳定。水田和旱田试样的连通性指数随着含水率的减小而增大,分别在质量含水率为20%和12%左右达到最大值并且稳定,最大值分别为0.935和0.598,反映了不同耕地类型下土壤干缩裂缝网络的形成过程和连通性的实际情况。裂缝面积和长度的概率密度和累积概率符合正态分布,裂缝面积和长度的概率密度实测值与概率密度函数的拟合决定系数分别大于0.94和0.91;裂缝面积和长度的累积概率实测值与分布函数的拟合决定系数分别大于0.90和0.94。可以用正态分布描述土壤表面裂缝的形态,有助于研究土壤干缩裂缝的形成机理以及不同裂缝形态对土壤优先流的影响。     

华北平原农田裂缝对硝态氮淋溶的影响

土壤干缩开裂是常见的自然现象。目前关于土壤干缩开裂的研究主要集中于裂缝的最终形态特征,并且以室内试验为主。本研究通过室外大田试验,结合动态计算机图像分析及水氮运移模拟软件WHCNS,研究土壤干缩开裂的动力学过程、特征及其对农田水氮运移的影响。利用原位熔化石蜡浇筑得到了裂缝三维结构形态,借助三维激光扫描仪量化裂缝的几何特征,发现每平米裂缝平均长度为4.58m,裂缝上表面平均宽度为5.72 mm,平均深度为9.06 cm。基于三维扫描仪提取得到的裂缝几何参数,通过WHCNS仿真模拟,发现相较于无裂隙情况,裂隙的存在分别增加了传统施肥和优化施肥情况下97.40%和256.43%的硝态氮淋失量;与优化施肥模式相比,传统施肥模式更容易造成硝态氮的淋失风险。在模拟灌溉模式对硝态氮淋洗情况的影响时,其差异不明显;强降雨的设置同样增加了硝态氮的淋失风险,导致硝态氮的年均淋洗量增加83.61%。裂缝的存在严重影响农田作物对肥料的吸收和利用,通过优化施肥量、更改灌溉模式以及避免强降雨前施肥都可以减少肥料的损失。     

基于VG-PENG收缩特征曲线与收缩各向异性的裂隙率估算模型

为量化农田裂隙发育程度,考虑脱湿过程中土壤孔隙在基质域、沉降域和裂隙域间转化,该研究提出基于土壤收缩特征和收缩各向异性的裂隙体积比率(裂隙率)关于含水率的预测模型。该模型包括3个子模型:改进VG型式的基质域收缩特征VG-PENG模型,描述收缩各向异性的几何因子Logistic模型,基于上述VG-PENG收缩特征模型和几何因子模型的裂隙率预测模型。通过土壤收缩试验和裂隙演化监测试验,采用图像处理技术提取裂隙数据,评价了该模型的优度及适用性。结果表明,VG-PENG收缩模型具有较好的连续性和明确的物理意义,可精确描述土壤收缩特征(R~20.98);该研究引入Logistic曲线描述土壤收缩几何因子,揭示了收缩过程中土壤横向开裂和纵向沉降的各向异性机理,提出了脱湿初期纵向沉降(几何因子趋近1)、中期主沉降-副开裂(几何因子处于1～3之间)、后期趋于稳定3个阶段,Logistic模型可精确描述收缩几何因子随含水率变化;基于VG-PENG收缩模型和Logistic几何因子模型,构建了裂隙率关于含水率的演化模型,该模型呈"S"型曲线,取决于土壤收缩属性及其各向异性特征,裂隙率模拟值和实测值吻合较好,呈显著水平(R~20.90,P0.001)。该研究裂隙率预测模型修正了土壤收缩各向异性在裂隙率估算中造成的误差,并突破性地将VG-PENG收缩特征曲线进一步推演并应用于裂隙率模拟,可方便、快捷地通过土壤收缩数据预测农田裂隙率随含水率演化规律,为膨缩土裂隙流研究提供理论依据和参数基础。     

膨胀土胀缩裂隙演化及其扰动规律分析

为定量研究膨胀土胀缩裂隙的演化特征及其对土体的扰动规律,从而探究其引发工程和生态环境灾害的机理。论文对合肥膨胀土进行干湿循环-CT(computed tomography)扫描试验,从获取的CT图中提取灰度值以及灰度共生矩阵特征值:角二阶矩(angular second moment,ASM)和对比度(contrast,CON),研究在干湿循环作用下裂隙图像的灰度值及其纹理的变化规律;并通过三轴剪切试验研究了在干湿循环作用下膨胀土的强度特征。结果表明:1)图像灰度值随裂隙的发育状态而变化;初始阶段灰度值沿试样轴向分布比较离散,但在后期逐渐均匀,离散系数在3次干湿循环后达到最大值,比干湿循环前增加了106%,随后逐渐减小;2)ASM随干湿循环次数的增加而减小,并且在0°和90°方向上的值比在45°和135°方向上的值大9%;CON随干湿循环次数的增加而减小,并且在0和90°方向上的值比在45°和135°方向上的值小52%,其对纹理的方向差异性更加敏感;3)胀缩裂隙对原状膨胀土的结构性会造成破坏,强度劣化显著;在5次干湿循环后,2种土强度分别降低62%和46%,并且原状膨胀土与重塑膨胀土强度的差值也由347.3 kPa降至21.3 kPa;4)由ASM和CON定义的扰动函数与由土体原生联结结构强度定义的扰动函数,扰动过程中函数变化曲线吻合度高,故基于灰度共生矩阵特征值的扰动函数能很好地描述胀缩裂隙扰动下的膨胀土强度特性。