不同层次花岗岩残积土抗剪强度影响因素研究

发布时间：2018-03-26 04:11

本文选题：花岗岩残积土　切入点：崩岗　出处：《华中农业大学》2015年硕士论文

【摘要】：花岗岩残积土广泛分布于中国南方,形成于花岗岩残积土上的崩岗、滑坡是南方水土流失的重要类型。花岗岩残积土具有显著的不均匀性及各向异性、软化性、崩解性,是一种结构特殊的土壤。采取湖北省通城县发育典型、分层明显(表土层、红土层、砂土层、碎屑层)的花岗岩残积土,进行三轴固结不排水实验和直剪快剪实验,结合不同土层花岗岩残积土的基本性质,研究发现:1、不同土层应力应变关系均呈应变硬化型,表现为塑性破坏,对于同一种土,4种围压下,应力-应变曲线间距均比较明显;红土层和砂土层在应变初期,偏应力变化受围压影响较小,与应变水平关系密切;在同等围压条件下,表土层破坏所需的偏应力较小,而碎屑层所破坏的偏应力较大。毛管孔隙度在一定程度上影响了土体的孔隙压力,破坏比Rf变异系数与毛管持水量极其显著相关,毛管孔隙度的变化是影响土体破坏比Rf发生变异的原因,即孔隙的突变影响土体破坏比在一定程度上发生变化。2、花岗岩残积土的软化性非常显著,4层土内摩擦角均和黏聚力均出现先增大后减小的趋势,黏聚力峰值出现在的平均含水率8.11%,内摩擦角峰值出现在的平均含水率11.76%,在含水率在10%左右时,花岗岩残积土可能获得最大的抗剪强度值,当超过一定含水率后,随着花岗岩残积土含水量的增加,其强度显著降低。表现为黏聚力迅速消散,内摩擦角锐减,内摩擦角的大幅降低可能是强度降低的主因。花岗岩残积土的孔隙发育,过多的水分起到了分散土粒的作用,降低了颗粒间的接触作用。3、在处于含水率(平均为23.98%)无显著差异的条件下(p0.5),碎屑层土体的黏聚力为显著低于其它三层,表土层、红土层、砂土层之间的黏聚力差异不显著。黏聚力在表土层和碎屑层的变异较小,在红土层和砂土层的变异较大。4层土的内摩擦角变异均较小,表土层的内摩擦角最小,数值分布较为集中,与相邻的红土层之间并无显著性差异。红土层的内摩擦角处于中间水平,表现为只与碎屑层有显著性差异,这可能是由于砂土层的颗粒分布、密度、胶结作用物、空隙条件等均处于适中水平的原因。砂土层内摩擦角与红土层的差异并不显著,碎屑层的内摩擦角最大,与其它三层差异性显著。4、黏聚力随土层深度变深,先增加,再减小,峰值深度在2m左右,随土层深度变深,黏聚力的变异性也表现为先变大,再减小。内摩擦角随土层深度变深,而出现平缓增加的趋势,黏聚力的变异性则表现为先变大,再减小。内摩擦角的增大对抗剪强度的增大贡献量明显大于黏聚力的消散对抗剪强度的减小量。5、影响花岗岩残积土抗剪强度指标的主要因素为水分含量以及砂粒含量。在同种土层或不同土层处于外界条件或结构类似的情况下时,影响其抗剪性能发生变异的可能是饱和导水率、最大容重变化量以及土壤干密度。同时考虑水分和砂粒含量的抗剪强度发展趋势为,在一定含水率范围内,抗剪强度随含水率的降低、砂粒含量的增多而增大,黏聚力总体随含水率降低而升高,随砂粒含量的增大而减小,内摩擦角总体随含水率降低而升高,随砂粒含量的增多而增大。影响抗剪强度指标趋势面发生震荡的原因很可能是孔隙气水压力的突变,土壤胶结物对花岗岩残积土的抗剪强度影响可能被高估。
[Abstract]:Granite residual soil is widely distributed in the South China, formed in the granite residual soil on the slope collapse, landslide is an important type of soil erosion in the south. The granite residual soil has inhomogeneity and anisotropy, significant softening, disintegration, is a kind of special soil structure. Taking Hubei Province Tongcheng County typical development, clear layers (surface layer, clay layer, sand layer, debris layer) of the granite residual soil, three axis consolidated undrained test and quick direct shear experiment, study basic properties, combined with different layers of granite residual soil: 1 different soil stress-strain relationship were strain hardening type, show plastic failure, for the same kind of soil, 4 kinds of confining pressure, the stress-strain curve of pitch are more obvious; the clay and sand layer in the initial strain, the deviatoric stress changes influenced by the confining pressure is smaller, and the strain level is closely related; under the same confining pressure Small, partial surface damage should force required, while the detritus layer damaged by partial stress is larger. The effect of capillary porosity pore pressure of the soil to a certain extent, failure ratio Rf coefficient of variation and capillary water capacity is a significant correlation between the changes of capillary porosity, is the impact of soil damage than Rf mutation causes that is, the pore mutations affecting soil failure ratio changes.2 to some extent, the granite residual soil softening is very significant, the 4 layer soil internal friction angle and cohesion were first increased and then decreased, the cohesion peak in the average moisture content of 8.11%, 11.76% average water friction angle the peak in the rate of water content in around 10%, the granite residual soil shear strength may be obtained with the maximum value, when more than a certain water content, with the increase of granite residual soil water content, the strength is remarkably reduced. The cohesion quickly dissipated, the internal friction angle decreased, significantly reduce the internal friction angle of the strength reduction may be the main reason. The granite residual soil porosity, too much water to disperse soil particles, reduce the contact interaction between.3 particles and in water content (average 23.98%) no significant different conditions (p0.5), cohesion clastic soil layer for significantly lower than the other three layer, surface layer, clay layer, sand layer between the cohesion of the difference was not significant. The cohesion in the topsoil and the debris layer variation of friction angle variation are smaller in clay and sand layer and the variation of.4 soil layer in the surface layer of the internal friction angle of the minimum value, the distribution is more concentrated, there is no significant difference between the clay layer and the adjacent layer of clay. The internal friction angle in the middle level, only showed significant difference and detrital layer, this may be due to sand layer The particle size distribution, density, cementation, void condition etc in the cause of moderate level. The internal friction angle and the difference of sand clay layer is not significant, the internal friction angle of the largest debris layer, and the other three layers.4 significant difference, cohesion with soil depth increases, increased first and then decreased. That peak at about 2m depth, with soil depth increases and variability of cohesion as well as to get bigger, and then decreased. The internal friction angle with the soil depth becomes deeper, and the emergence of slowly increasing trend, the variability of the cohesion was larger, and a small amount of.5 reduction of internal friction decreases. Angle increases the shear strength increases with volume was significantly higher than the dissipation against cohesion shear strength. The main factors affecting the granite residual soil shear strength index for water content and sand content. In the same soil or soil in different external conditions or structure in a similar situation When the possible influence the shear performance variation is saturated hydraulic conductivity, bulk density and maximum dry density of soil. Considering the shear strength of the development trend of water and sand content, water content in a certain range, the anti shear strength decreased with increasing water content, increasing sand content increasing. The overall cohesion with the water content increased, and decreased with increasing sand content, the internal friction angle with the overall moisture content decreased, and increases with the increase of sand content. The influence of shear strength index concussion reason trend is likely to occur mutation pore gas water pressure, the shear strength may be affected overestimation of soil cement on the granite residual soil.

【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S157

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