黄土土体节理裂隙在切坡卸荷作用下扩展机理研究

发布时间：2018-06-13 01:12

本文选题：黄土崩塌 + 切坡　；参考：《西安科技大学》2015年硕士论文

【摘要】：黄土崩塌作为黄土地区地质灾害的一种形式,其危害性极大。大量实践表明,人为地对边坡进行切坡卸荷是导致黄土崩塌的主要原因之一。随着经济的发展,居民的增加和城市的不断扩大,为了扩大建筑用地,切坡施工将大大增加,潜在的崩塌灾害也将随之增加。针对研究切坡卸荷引起黄土崩塌的机理及切坡卸荷实践工程的需要,以切坡卸荷诱发黄土土体节理裂隙扩展机理为研究主旨做了较全面的研究。首先对洛川塬边Q3原状黄土的基本物理力学性质进行分析;然后利用GDS非饱和土三轴仪模拟不同卸荷条件下黄土土体的卸荷应力路径,并借助CT扫描仪、电镜扫描仪观察卸荷前后土样内部细观、微观结构的变化,探讨黄土体节理裂隙扩展的影响因素及扩展机理;最后结合FLAC3D对垂直裂隙扩展过程的数值模结果,总结切坡卸荷作用下节理裂隙扩展机理,为切坡卸荷实践工程提出指导性意见。通过对以上试验结果分析,得到以下结论:(1)卸荷应力路径下黄土体的强度要比常规三轴压缩强度小得多,且应力-应变曲线随着含水率、初始卸荷围压的增大逐渐由软化型过渡到硬化型,卸荷的过程中土样出现剪胀。(2)不同卸荷条件下土样的变形破坏特征不同,总体上可为劈裂破坏、滑移破坏和塑性破坏三种破坏模式。(3)卸荷后土样断面不同区域的CT数大部分出现增大的趋势,卸荷量、卸荷速率、含水率、初始围压越大,CT数增幅越大;中心的方差大部分减小,大区和全区的方差值大部分增大。(4)卸荷条件对黄土节理裂隙的扩展具有一定程度的影响,只有达到一定的卸荷量时土样才会出现裂隙,卸荷速率较小、含水率较大、初始卸荷围压较大时,土样容易出现粗大的裂隙,反之,微裂隙较发育。(5)卸荷裂隙的产生是内外因素共同作用的结果,内部因素有颗粒集配、矿物质含量、结构特征等,外部因素主要是切坡卸荷和水。
[Abstract]:As a form of geological disaster in loess area, loess collapse is very harmful. A great deal of practice shows that cutting slope unloading is one of the main causes of loess collapse. With the development of economy, the increase of residents and the expansion of cities, in order to expand the construction land, slope cutting construction will be greatly increased, and the potential collapse disaster will also increase. In order to study the mechanism of loess collapse caused by sloping unloading and the need of practical engineering of sloping unloading, the mechanism of fracture expansion of loess soil induced by sloping unloading is studied comprehensively. The basic physical and mechanical properties of Q3 undisturbed loess in Luochuan tableland are analyzed firstly, then the unloading stress path of loess soil under different unloading conditions is simulated by GDS unsaturated soil triaxial instrument, and the unloading stress path of loess soil is simulated by CT scanner. The microstructure of soil samples before and after unloading was observed by electron microscope scanner, and the influencing factors and mechanism of fracture propagation of loess body were discussed. Finally, the numerical model results of FLAC3D for vertical fracture propagation were combined. The mechanism of joint crack expansion under the action of sloping unloading is summarized, and some guiding suggestions are put forward for the practical engineering of sloping unloading. Through the analysis of the above test results, the following conclusion is drawn: the strength of loess body under unloading stress path is much smaller than that of conventional triaxial compression, and the stress-strain curve is with moisture content. The increase of initial unloading confining pressure gradually changes from softening type to hardening type. During unloading, the soil sample appears shear dilatation. (2) the deformation and failure characteristics of the soil sample under different unloading conditions are different, which can be divided into fracturing failure, as a whole, the deformation and failure characteristics of the soil sample under different unloading conditions are different. After unloading, the CT number of different areas of soil sample section showed an increasing trend. The larger the unloading amount, unloading rate, water content and initial confining pressure, the larger the increase of CT number. The variance of the center is mostly reduced, and the square difference between the large area and the whole area is mostly increased. The unloading condition has a certain degree of influence on the expansion of the loess joint fracture. Only when the unloading amount reaches a certain amount, the soil sample will appear a crack, and the unloading rate will be smaller. When the water content is high and the initial unloading confining pressure is high, the coarse cracks are easy to appear in the soil samples, whereas, the micro-cracks are relatively developed. The generation of unloading fractures is the result of the interaction of internal and external factors, and the internal factors include particle aggregate, mineral content, and so on. Structural characteristics, external factors are mainly cut slope unloading and water.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU444

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