厦门地区非饱和残积土土水特征及强度性状研究

发布时间：2018-10-20 07:00

【摘要】：残积土层约占厦门岛土地面积的三分之二,是工程建设岩土层的重要组成部分。在自然或人为地改变环境条件下,残积土常经受脱湿、增湿及干湿交替作用。此时,残积土会呈现出与其在饱和状态迥异的体积、强度、渗透和固结等性状。非饱和土的强度在土坡稳定、地基承载力及侧向土压力等分析计算中起着重要作用。而土水特征曲线(简称SWCC)是基质吸力与含水量或饱和度的关系曲线,它可帮助我们了解含水量对非饱和土强度的影响。因此,研究非饱和残积土的土水特征曲线及抗剪强度具有重要的工程意义和应用前景。本文针对厦门地区常见的残积砂质粘性土和残积粘土,进行了不同干密度、含水量、竖向应力和干湿循环作用下SWCC测定、无侧限抗压强度和直接剪切的试验研究,建立了SWCC模型、无侧限抗压强度及剪切强度模型。主要研究内容如下： 1.采用滤纸法测定基质吸力,分析了干密度、含水量、竖向应力及干湿循环作用等因素对残积砂质粘性土和残积粘土的脱湿曲线、吸湿曲线及滞回环的影响。试验结果表明,砂质粘性土的SWCC与粘土的SWCC相比,前者的脱湿速率较大,进气值较低,持水能力较弱。砂质粘性土的SWCC对干密度和竖向应力的变化较敏感,而粘土SWCC对含水量的变化较敏感；3次干湿循环中,第1次干湿循环对两类残积土SWCC的影响较大。 2.选择了6个SWCC模型,剔除残余饱和度参数,建立修正SWCC模型。设置了考虑参数个数的模型权值,根据已测残积土的SWCC试验数据,综合考虑拟合精度及模型参数个数,评估各修正SWCC模型的优劣。计算结果表明修正Gardner模型是最适合于厦门地区的残积砂质粘性土和粘土的SWCC模型。推导了修正的SWCC模型特征值计算公式,它们可取代作图法,从而较准确地计算出空气进气值、曲线拐点的斜率、残余基质吸力及残余饱和度等参数。 3.设计了残积砂质粘性土和粘土的无侧限抗压强度试验,得到了考虑初始干密度和含水量下砂质粘性土的无侧限抗压强度经验模型和不同初始含水量下粘土的无侧限抗压强度经验模型。另外,测定了不同干湿幅度、路径及次数下两类残积土的无侧限抗压强度,得到了干湿幅度、次数和路径对两类残积土的无侧限抗压强度的影响规律。 4.采用普通的直剪仪进行非饱和残积土的剪切强度试验,并用滤纸法测定各不同含水量状态下的基质吸力,研究剪切强度及强度指标随初始含水量的变化规律,建立不同初始含水量下残积砂质粘性土和粘土的剪切强度模型,能够较好地预测残积土的抗剪强度及强度指标。同时,开展了干湿循环作用对残积土的试验研究,得到了不同干湿循环幅度、路径及次数下两类残积土的剪切强度和强度指标的变化规律,为今后干湿循环作用下残积土强度模型的研究奠定基础。
[Abstract]:The residual soil layer accounts for 2/3 of the land area of Xiamen Island and is an important part of the engineering construction of geotechnical strata. Under natural or artificial environmental conditions, residual soils are often subjected to dehumidification, humidification, and alternate drying and wetting. At this time, the residual soil will show different volume, strength, permeability and consolidation from its saturation state. The strength of unsaturated soil plays an important role in the analysis and calculation of slope stability, foundation bearing capacity and lateral earth pressure. The soil-water characteristic curve (SWCC) is the relationship between the matrix suction and water content or saturation, which can help us understand the influence of water content on the strength of unsaturated soil. Therefore, the study of soil water characteristic curve and shear strength of unsaturated residual soil has important engineering significance and application prospect. In this paper, SWCC measurement, unconfined compressive strength and direct shear of residual sandy clay and residual clay, under different dry density, water content, vertical stress and dry-wet cycle, are studied in Xiamen area. SWCC model, unconfined compressive strength and shear strength model are established. The main contents are as follows: 1. The effects of dry density, moisture content, vertical stress and dry wet cycle on the dehumidification curve, hygroscopic curve and hysteresis loop of residual sandy clay and residual clay were analyzed by filter paper method. The experimental results show that the SWCC of sandy clay is higher than that of clay SWCC, the former has higher moisture removal rate, lower inlet air value and weaker water holding capacity. The SWCC of sandy clay is more sensitive to the change of dry density and vertical stress, while the clay SWCC is more sensitive to the change of water content, and the first dry and wet cycle has a great effect on the SWCC of the two types of residual soils in three dry and wet cycles. 2. Six SWCC models were selected and the residual saturation parameters were eliminated. The modified SWCC model was established. The weight value of the model considering the number of parameters is set. According to the SWCC test data of the measured residual soil, the fitting accuracy and the number of model parameters are considered synthetically to evaluate the merits and demerits of each modified SWCC model. The results show that the modified Gardner model is the most suitable SWCC model for residual sandy clay and clay in Xiamen area. The modified formulas for calculating the eigenvalues of SWCC model are derived, which can replace the drawing method, so that the parameters such as air intake value, slope of curve inflection point, residual matrix suction and residual saturation can be calculated more accurately. The unconfined compressive strength tests of residual sandy clay and clay are designed. The empirical model of unconfined compressive strength of sandy clay under initial dry density and water content and the empirical model of unconfined compressive strength of clay with different initial water content are obtained. In addition, the unconfined compressive strength of the two types of residual soils under different dry-wet ranges, paths and times were measured, and the influence of dry and wet amplitude, times and paths on the unconfined compressive strength of the two types of residual soils was obtained. 4. The shear strength of unsaturated residual soil was tested with a direct shear apparatus, and the matrix suction under different water content was measured by filter paper method. The variation of shear strength and strength index with initial water content was studied. The shear strength model of residual sandy clay and clay under different initial water content can be used to predict the shear strength and strength index of residual sandy clay. At the same time, the experimental study of dry and wet cycling on residual soil was carried out, and the change rules of shear strength and strength index of two kinds of residual soil under different dry-wet cycle amplitude, path and times were obtained. It will lay a foundation for the study of strength model of residual soil under dry and wet cycle in the future.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU41;TU44

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