考虑物质结构和制样差异的黄土强度问题研究

发布时间：2018-01-06 15:38

本文关键词：考虑物质结构和制样差异的黄土强度问题研究　出处：《西安建筑科技大学》2014年博士论文　论文类型：学位论文

【摘要】：黄土物质成分和结构存在明显的地域性差异，不同地域黄土的强度明显不同，对此目前尚缺乏系统研究，尚难以把握黄土强度的地域性差异大小。另外，在黄土压实工程和室内试验研究中，经常出现将不同含水量土体压实到相同干密度的情况，此制样差异得到的土体在相同含水量条件下存在多大强度差异亦属未知问题。基于此，论文以兰州土样和西安土样为比较对象，考虑物质结构和制样差异对黄土强度问题开展研究工作。对兰州土样、西安土样进行了物质组成差异研究。得出，兰州土样是以粗粉粒为骨架颗粒呈支架接触的粘质粉土，西安土样是以细粉粒为骨架颗粒呈基底式胶结的粉质粘土，西安土样粘土矿物含量较兰州土样粘土矿物含量高，其比重、液塑限均较大。利用三轴剪切试验，得到了增湿条件下，兰州原状黄土极限强度与含水量、围压的计算公式。通过研究兰州、西安两种黄土原状样和重塑样的剪切特性，对比分析了不同物质组成黄土的抗剪强度和结构强度特性。西安原状土样的粘聚力是兰州原状土样粘聚力的两倍，其内摩擦角比兰州原状土样的内摩擦角小但差值不大。在相同围压下，西安土样的结构强度远远大于兰州土样的结构强度。在低围压时，西安土样的结构强度峰值是兰州土样结构强度峰值的4倍；在高围压时，西安土样的结构强度峰值是兰州土样结构强度峰值的2倍。随着围压的增大，兰州土样结构强度增长较西安土样结构强度增长的速度快。基于压力板试验，比较分析了不同物质组成、不同制样结构黄土的土水特征曲线。结果表明，相同制样结构西安土样的吸力大于兰州土样的吸力。相同含水量下，当制样含水量较小时，相同制样结构西安土样的吸力比兰州土样的吸力大15%；当制样含水量较大时，相同制样结构西安土样的吸力比兰州土样的吸力大30%。在常见制样含水量范围，制样含水量越小的同密度兰州土样，在相同含水量下其吸力越大；制样含水量越小的同密度西安土样，在相同含水量下其吸力越小。在物质组成相同情况下，土样含水量越小，制样差异引起的基质吸力差值越大。当土样含水量较小时，制样差异引起的基质吸力差异超过15%。进一步考虑制样差异对黄土的强度特性进行了常规三轴试验研究，探明不同制样结构土样的抗剪强度参数随制样含水量的增大呈先增大后减小的趋势，随干密度的增大而增大。干密度较小时，制样含水量的变化所引起的抗剪强度参数的变化较大，干密度较大时，制样含水量的变化引起的抗剪强度参数的变化较小。相同干密度下，当制样含水量较大时，制样差异引起的抗剪强度参数的变化较大。相同制样结构西安土样的粘聚力大于兰州土样的粘聚力，其内摩擦角比兰州土样的内摩擦角小但差值不大。基于真三轴试验和常规三轴试验结果的对比分析，探讨了试验尺寸及端部效应对试验结果的影响。在相同试验条件下，利用真三轴试验所测得的土样抗剪强度参数值均大于常规三轴试验所测得的抗剪强度参数值。当制样含水量较小时，两种试验方法所得抗剪强度参数差值较小，随着制样含水量的增大，，抗剪强度参数差值逐渐增大。真三轴试验条件下，不同制样结构兰州黄土、西安黄土的抗剪强度参数均随中主应力比的增大而增大。当制样含水量较小时，b值对土样抗剪强度参数的影响较大，当制样含水量较大时， b值对土样抗剪强度参数的影响较小。在相同b值下，随着制样含水量的增大，土样粘聚力的减小幅度大于内摩擦角的减小幅度。
[Abstract]:There is obvious difference among loess material composition and structure of different regions, the strength of loess is obviously different, this is still a lack of systematic research, it is difficult to grasp the regional differences of loess strength. In addition, in the Loess Compaction Engineering and indoor experiment study, often appear to be different water content of soil compaction to the same dry density. There is much difference, is also the problem of unknown strength of soil sample difference in the same moisture condition. Based on this, the thesis takes Lanzhou soil and Xi'an soil as the comparison object, considering the material structure and the differences in sample preparation to carry out research work on the strength of loess.
The Lanzhou Xi'an soil samples, soil samples were obtained. The differences of material composition, Lanzhou soil is clayey silt with coarse powder as the skeleton particles with bracket contact, Xi'an soil is in fine silt as the skeleton particles are the basal cement silty clay minerals like clay content than Xi'an soil Lanzhou soil clay mineral content is high, the proportion of liquid plastic limit are larger.
The three axle shear test, get wet conditions, and water content of Lanzhou loess ultimate strength calculation formula of confining pressure. Through the study of Lanzhou, Xi'an two kinds of shear properties of undisturbed and remolded loess, comparative analysis of the shear strength and the shear strength characteristics of loess structure composed of different substances. Xi'an undisturbed the cohesion of Lanzhou is two times the undisturbed soil cohesion and the internal friction angle of Lanzhou than the undisturbed soil sample internal friction angle is small but the difference is not large. Under the same confining pressure, the structural strength of Xi'an soil is far greater than the structural strength of Lanzhou soil. Under low confining pressure, the peak intensity structure of Xi'an the soil sample is 4 times that of Lanzhou soil structure strength peak; under high confining pressure, the peak strength of soil structure in Xi'an is 2 times the Lanzhou soil structure strength peak. With the increase of confining pressure, Lanzhou soil structural strength growth than the Xi'an soil structure is strong The rate of growth is fast.
The pressure plate test based on the comparative analysis of different material composition, soil water characteristic curve of different loess like structure. The results showed that the same sample suction structure in Xi'an soil is greater than that of Lanzhou. The same suction of soil water content, the water content is smaller when the sample preparation, sample preparation of the same suction structure in Xi'an soil the soil suction is larger than Lanzhou 15%; when the sample with higher water content, suction the same sample preparation structure in Xi'an soil than Lanzhou soil suction 30%. in common sample moisture content range, with the density of Lanzhou soil sample preparation water content is small, in the same water content under the suction more with the same density; Xi'an soil sample water content is small, in the same water content under the suction is smaller. The components under the same conditions, the soil moisture content is small and the difference caused by differences in sample preparation of matric suction increases. When the soil moisture is lower, due to differences in sample preparation base The difference of mass suction exceeds 15%.
Further considering the strength characteristics of sample preparation differences on loess were conventional three axis test, the shear strength parameters of sample preparation with the increase of water content decreased to investigate different sample preparation structure of soil samples, and increases with the increase of dry density. The dry density is small, the change of water content of sample preparation the shear strength parameters change greatly, the dry density is high, small changes in the shear strength parameters caused by the change of water content in the sample preparation. The same dry density, water content is larger when the sample preparation, sample preparation caused by differences in shear strength parameters changed greatly. The same sample structure in Xi'an the cohesion of the soil samples is larger than Lanzhou, the cohesion of the soil samples, the internal friction angle than Lanzhou soil internal friction angle is small but the difference is not large.
Comparative analysis of the three axle test and the conventional three axis based on the experimental results, effects of the test size and the end effect on the test results. Under the same experimental conditions, using the three axle test measured soil shear strength parameters were greater than the conventional three axis test of shear strength parameter the sample preparation. When the water content is smaller, smaller difference of shear strength parameters of the two kinds of test methods, as the moisture content increases, the shear strength parameter difference increases gradually. The three axle test under the condition of different sample preparation structure of Lanzhou loess, Xi'an loess shear strength parameters with the main the stress ratio increases. When the sample water content is small, the b value influence on the shear strength of the soil is larger, when the sample with higher water content, the b value has little influence on the shear strength of the soil. In the same b value, with the increase of water content in sample preparation The decrease of cohesive force of soil sample is greater than that of internal friction angle.

【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU444

【参考文献】