营口软土特性真三轴试验及本构模型参数研究

发布时间：2018-02-03 11:39

本文关键词： 营口软土物理力学特性真三轴试验各向异性特征　出处：《辽宁工程技术大学》2014年硕士论文　论文类型：学位论文

【摘要】：受地质构造、应力历史、颗粒成分等因素影响,软土具有显著的区域性,不同地区的软土物理力学性质差异较大。营口地区软土是辽宁滨海地区三角洲冲积平原形成的一种典型的粉质粘土,随着地铁、隧道、基坑等工程中软土变形与强度问题越来越突出,迫切需要对营口地区软土的物理力学特性和土体变形及强度进行深入研究,增强对营口地区软土的认识,为实际工程提供一定的理论参考和借鉴。文章通过搜集工程地质资料,采用室内试验与理论分析相结合的方法,开展了营口软土力学特性的试验研究,具体成果如下：1)对比分析了营口地区与上海、天津等地区软土的物理力学特性,发现营口地区软土的孔隙比、液塑限指数、饱和度等普遍偏低；统计结果表明,营口地区软土的粘聚力比上海、天津地区的软土偏小,而内摩擦角比天津地区软土偏大,但略小于上海地区的软土；无侧限抗压强度试验测得土体的灵敏度在2-4之间,表明营口地区软土属于中灵敏度土；对含水量、密度等物理参数进行线性回归拟合,并得到了该区域的线性回归方程；采用塑性图分析表明营口地区软土为中、高塑性粘土。2)开展了营口地区软土的真三轴试验研究,分析了营口软土各向异性的特征以及其变形和强度,结果表明：当载荷分别沿大主应力方向、中主应力方向和小主应力方向单向加载时,大主应变ε1、中主应变ε2、小主应变ε3呈现不同的变化趋势；保持σ3不变时,土体的应力应变曲线随b值的增加其变化趋势变陡,变化幅度也随之增大；随着中主应力比b增大,土体的粘聚力和内摩擦角变化趋势相反,前者呈先下降后上升的趋势,后者呈先上升后出现略微下降的趋势；在围压一定的条件下,随着含水率越大,土体强度逐渐降低,从含水率为15%至25%的土体最大强度差值幅度接近35%；并通过试验结果得到了试样的在不同含水率下p-q平面上的临界状态线,都可以用直线进行较好的拟合；此外根据土体破坏时的三维应力状态得到了在π平面上的屈服曲线,其在π平面上的屈服轨迹比较接近松岗-中井屈服准则(SMP)。3)采用归一化的方法对真三轴的试验结果进行了定量化分析,得到了营口地区软土的应力应变归一化方程,拟合结果能很好预测和评价对不同围压下软土的应力应变关系；针对邓肯-张模型不能考虑土体各向异性的不足,基于真三轴试验结果对邓肯-张本构模型的参数提出修正,其可以充分考虑土体各向异性的特点,并通过真三轴试验结果验证了该模型的可靠性和实用性。
[Abstract]:Affected by geological structure, stress history, particle composition and other factors, soft soil has a significant regional. The soft soil in Yingkou area is a typical silty clay formed in the delta alluvial plain of coastal area of Liaoning Province, along with the subway and tunnel. The problem of deformation and strength of soft soil is more and more prominent in foundation pit and so on. It is urgent to study the physical and mechanical properties of soft soil and the deformation and strength of soil in Yingkou area to enhance the understanding of soft soil in Yingkou area. Through collecting engineering geological data and adopting the method of combination of laboratory test and theoretical analysis, the paper carried out the experimental research on the mechanical properties of Yingkou soft soil. The concrete results are as follows: (1) the physical and mechanical properties of soft soil in Yingkou area are compared with those in Shanghai and Tianjin. It is found that the porosity ratio, liquid-plastic limit index and saturation of soft soil in Yingkou area are generally low. The results show that the cohesion of soft soil in Yingkou area is smaller than that in Shanghai, and the angle of internal friction is larger than that in Tianjin area, but slightly smaller than that in Shanghai area. The sensitivity of soil measured by unconfined compressive strength test is between 2-4, indicating that the soft soil in Yingkou area belongs to medium sensitive soil. The physical parameters such as water content and density were fitted by linear regression, and the linear regression equation of the region was obtained. The plastic diagram analysis shows that the soft soil in Yingkou area is medium and high plastic clay. 2) the true triaxial test of the soft soil in Yingkou area is carried out, and the anisotropy characteristics, deformation and strength of the soft soil in Yingkou area are analyzed. The results show that the main strain 蔚 _ 1, the medium principal strain 蔚 _ 2 and the small principal strain 蔚 _ 3 show different trends when the load is loaded in the direction of large principal stress, middle principal stress and small principal stress respectively. When 蟽 _ 3 is kept constant, the stress-strain curve of soil becomes steeper with the increase of b value, and the range of variation also increases. With the increase of the mid-principal stress ratio b, the cohesive force and the angle of internal friction of the soil have the opposite trend, the former shows the tendency of decreasing first and then rising, the latter shows a tendency of rising first and then slightly decreasing. Under certain confining pressure, with the increase of water content, the soil strength decreases gradually, and the maximum strength difference range from 15% to 25% is close to 35. The critical state line on p-q plane with different moisture content is obtained by the test results, which can be fitted well by straight line. In addition, according to the three-dimensional stress state of soil failure, the yield curve on 蟺 plane is obtained. The yield trajectory on 蟺 plane is close to the yield criterion SMP.3) the true triaxial test results are quantitatively analyzed by the normalized method. The stress-strain normalization equation of soft soil in Yingkou area is obtained. The fitting results can well predict and evaluate the stress-strain relationship of soft soil under different confining pressures. In view of the deficiency that Duncan-Zhang model can not consider soil anisotropy, the parameters of Duncan-Zhang Ben model are modified based on true triaxial test results, which can fully consider the characteristics of soil anisotropy. The reliability and practicability of the model are verified by the true triaxial test results.
【学位授予单位】：辽宁工程技术大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU447

【参考文献】