【作者】 杨永俊；

【导师】 骆亚生；

【作者基本信息】 西北农林科技大学 ， 岩土工程， 2009， 硕士

【摘要】 我国黄土分布广、厚度大、成因类型复杂,尽管近几年来黄土动力研究取得了一定成果,但是这些成果只是限制于某一特定的区域,由于黄土分布地区自然地理位置不同,气候特点和自然地理环境的差别,所以在黄土形成的条件上,成岩作用的程度上以及演变的过程中均有其区域特征,各地黄土的性状、结构和力学性质都有所差别。而对黄土进行不同区域研究,分析比较黄土动强度在各自不同黄土区域内的联系以及比较不同地区黄土动强度规律研究尚不多见。因此,利用振动扭剪仪正确地揭示不同地区黄土动强度特性具有重要的理论和实际意义。本文首先以“西气东输二线管道通过高烈度黄土地区研究”项目为依托,以宁夏固原黄土为研究对象,主要研究了其在动荷载作用下的动力特性。其次,以兰州、洛川、杨凌、巩义四个地区的黄土为研究对象,在前人对黄土动力学特性研究成果的基础上,一方面对兰州、洛川、杨凌、巩义四个地区的黄土强度特性进行各自分析,探寻其相互差异,同时还作出了不同含水率的兰州、巩义、洛川地区的原状黄土的τd/σ3与破坏振次N的关系曲线,对归一性进行了分析;另一方面以兰州黄土为例,利用动强度曲线做出不同振次不同含水下的摩尔应力圆,以求得该地区黄土的动强度指标的变化趋势以及其影响因素,深化黄土动力学特性的认识。文中最后分析了在三维应力空间内π平面上的黄土强度变化特征,进行一定破坏振次条件下动强度的分析。所得成果如下:动扭剪荷载条件下,固原黄土的应力应变骨干曲线呈软化型,反映了结构性变化对动变形特性的影响;固原黄土的动强度曲线与初始固结条件和黄土的结构性有密切的关系。利用岩土软件Geo-studio对黄土在循环荷载作用下的微观受力特性进行了模拟,模拟结果显示,土样中各点的剪应力随时间的变化并不是同步的,并且各点的剪应力大小也不相同,循环荷载作用下土样的破坏状态与试验结果十分相似。固结应力和含水率对试样强度均有影响,而含水率的影响更为突出。黄土动强度随固结应力的增大不是均匀增大,而是因区域不同表现出各自不同的变化趋势。由兰州、巩义、洛川三个地区的原状黄土的τd/σ3与破坏振次N的关系曲线,得出这些地区黄土均没有归一性,但随着含水率的增大归一性增强。由各地区动强度比较可以很明显的看出各地区黄土动强度特性由强到弱依次是杨凌、巩义、洛川、兰州。总趋势上呈现出由北向北南逐渐增强的态势,由西向东上逐渐增强。而随着含水率的升高,杨凌黄土的动强度急剧下降,逐渐与巩义黄土持平。不同p ~ q平面内试验所用不同地区黄土的强度包线都呈线性变化,且强度包线的截距近似趋近于零;黄土π平面上不同洛德参数的动强度位于广义米塞斯破坏面和拉德-邓肯破坏面之间变化特征。更多还原

【Abstract】 Extensive distribution、large thickness and complex causes are the features of loess , Despite of loess research in recent years has achieved some results, However, these results only limited to a particular regional,because of the different natural geographical in loess distribution, Climate characteristics and geographical differences in the its formation environment, therefore, in the terms and conditions of loess formation, diagenesis, as well as the extent of the process of evolution has its own regional characteristics,there are differences among the characters、structure and mechanical properties .Torsional Vibration shear triaxial apparatus is an advanced state of geotechnical equipment that is able to simulate complex initial stress conditions and complex cyclic shear stress. Therefore, it has the great theoretical and practical significance to correctly reveal the dynamic characteristics of soils by the adoption of advanced equipment.and it has an important theoretical and practical significance in research with Torsional Vibration shear triaxial apparatus.Therefore, at first, relying on the program“the research of west to east gas pileline two througth high earthquake intensity loess areas”,taking the loess of Guyuan in NingXia province for research object .It mainly researches the dynamic characteristics of the loess of Guyuan.. Secondy, ,taking the loess of Lanzhou、Luochuan、Yangling、Gongyi for research object,Based on the loess research results done by the predecessors on dynamic characteristics, On the one hand,it analized the dynamic strength of loss in the four reigons above,and explored the differences from each other,meanwhile the cuver of original loess betweenτd /σ3 and N in different water content were given out in order to research the normalization of loess ;On the other hand, taking the loess of Lanzhou for example, based on the dynamic strength curve of loess ,it analized the mohr’s stress circle in different vibration time and differnet water content aimde to explore thechange tendency and influencing factorsof the loess dynamic strength indexs.Finaly, Three-dimensional stress space in theπplane changes in the characteristics of the strength of loess was analyzed. Test results show as follows:The stress-strain backbone curve of loess under the cyclic torsion shear test conditions is in softening, which reflect structure change impacting on the dynamic deformation.Because of the dynamic strength of loess related with the initial consolidation stress and the structure conditions, the dynamic strength curves and cumulative energy of loess are closely related to stress paths in different static and dynamic stress conditions. It simulates the micro mechanical Characteristics of loess under cyclic load by geotechnical software Geo-studio 2007. Simulation result shows out that shear stress of each point changes with time is asynchronous; and the shear stress of each point is different from each other; the destruction state simulated of sample is simila with the test;the dynamic strength was influened by consolidation stress and water content,but the had a significant impact on the dynamic strength.And the increasing of the dynamic strength with the consolidation stress was inhomogeneous, the increasing of the dynamic strength was different accronding to the regins.Based on the the cuver of original loess betweenτd/σ3and N in Lanzhou、Luochuan、Yangling、Gongyi,it found out that the normalization of loess in these regins was not obvious,but with the increasing of water content ,the normalization become obvious gradually.And the the order of loess dynamic strength from strong to weak was Yangling、Gongyi、Luochuan、Lanzhou. The whole tendency was that the dynamic strength become stronger from north tosouth,meanwhile it become become stronger from west to east.And with increasing of water conten the dynamic strength of Yangling loess declined Sharply to the the dynamic strength of Gongyi loess;Based on the strength analysis in 3D stress space of consolidation stress pulsing cyclic shear stress, the dynamic strength curves on the different p ? q plane are linear and the intercept of line is near zero;the dynamic strength point located the place that between Mises curve and Lade-Duncan curve.更多还原