基于非饱和土理论的改良膨胀土强度特性试验研究

发布时间：2018-07-24 15:28

【摘要】：膨胀土是一种特殊的灾害性软土,由于其不良的工程特性在全世界范围内都导致了许多工程问题或工程灾害。因此,开展对膨胀土处治方法及其处治后的强度特性研究,探讨其在非饱和状态下的强度变化规律,具有重要的理论意义和工程应用价值。本文针对广西南宁膨胀土,依托国家自然科学基金资助项目“膨胀土非线性流变特性研究”(项目编号:50978097),以及湖南省科技厅资助项目“膨胀土非线性流变特性本构模型研究”(项目编号:2010SK3047),开展了对非饱和膨胀土和非饱和石灰改良膨胀土强度特性的试验与理论研究。基于非饱和土理论,结合土-水特征曲线和三轴试验结果,建立了考虑基质吸力和径-法向应力作用的素膨胀土和石灰改良膨胀土抗剪强度模型,提出了双应力状态下非饱和土的抗剪强度确定方法。通过对试验结果的分析,探索了基质吸力和含水量对非饱和土强度的影响规律;揭示了石灰改良膨胀土的强度变化机理。研究结果可为实际工程中非饱和膨胀土的强度分析提供理论依据,也为快速确定非饱和土的抗剪强度指标提供了可靠的方法。本文所开展的主要研究工作和所取得的研究进展及创新结论如下。一、开展的主要研究工作(1)对南宁膨胀土和石灰改良膨胀土进行一系列常规室内试验,包括界限含水率试验、击实试验、膨胀性试验、标准吸湿含水率试验等,分析了石灰改良膨胀土的实际效果,用以确定试验研究中的最优掺灰比。(2)利用压力板对南宁膨胀土和石灰改良膨胀土进行了土-水特征试验,分别得到了不同压实度条件下未改良膨胀土和石灰改良膨胀土的土-水特征曲线。利用Fredlund-Xing模型,对试验数据进行了拟合,并分别对不同压实度条件下的未改良膨胀土和石灰改良膨胀土的模型参数进行了分析。(3)利用英国GDS仪器设备有限公司生产的全自动三轴仪(GDSTAS)对未改良膨胀土和非饱和土进行系列三轴试验。(4)将VanapalliFredlund抗剪强度表达式和Fredlund-Xing 土-水特征曲线模型相结合,对未改良膨胀土和改良土抗剪强度进行分析,探索了不同基质吸力和净法向应力条件下土的抗剪强度变化规律。二、取得的主要研究进展和创新结论(1)基于Fredlund-Xing模型,分别构建了适合于素膨胀土和石灰改良膨胀土的土-水特征曲线模型,并通过拟合得到了相关的模型参数。通过对模型参数的分析,发现随着石灰改良膨胀土的进气值减小,残余含水量有所增大。在相同的基质吸力变化范围内,石灰改良膨胀土的含水率变化更小。说明石灰改良膨胀土的持水能力比素膨胀土较高、水稳定性比素膨胀土较好。(2)通过三轴试验研究发现,素膨胀土和石灰改良膨胀土在不同状态下的应力-应变关系曲线不同。在饱和状态下,素膨胀土的应力-应变关系主要以应变稳定和应变硬化型为主。石灰改良膨胀的应力-应变关系主要呈现为应变软化型。石灰改良膨胀土在非饱和状态下的应力-应变关系曲线呈明显的应变软化型,且随着基质吸力的增加,土的抗剪强度峰值点提前出现,且峰值强度明显提高。改良后膨胀土的粘聚力c受基质吸力影响明显,随着基质吸力的增加而增大,而内摩擦角φ则受基质吸力的影响较小。(3)基于非饱和土理论,对素膨胀土和石灰改良膨胀土进行了强度计算和分析。通过分析,探明了不同基质吸力和不同净法向应力条件下非饱和土的抗剪强度变化规律;得到了在τ-(σ-ua)-(ua-uw)三维空间的非饱和土的强度包络面。该强度包络面可以很直观地反映基质吸力和净法向应力对非饱和土的强度的影响。(4)根据饱和土三轴固结排水剪试验结果和非饱和土强度理论,提出了基于基质吸力和含水量的非饱和土抗剪强度指标(c和φ)的计算确定方法。在此基础上,建立了非饱和土抗剪强度计算理论。(5)通过对基质吸力和抗剪强度之间的变化关系分析发现,基质吸力对于非饱和土的抗剪强度的贡献是非线性的。当基质吸力较小时,随基质吸力的增大,非饱和土的抗剪强度逐渐提高;当基质吸力达到某一值时,随基质吸力的进一步增大,非饱和土的抗剪强度逐渐降低。亦即当基质吸力达到某一“最佳值”时,非饱和土的抗剪强度达到最大值。综上所述,本文通过对素膨胀土和石灰改良膨胀土的非饱和土强度特性的试验与理论研究,探索了基质吸力和含水量对非饱和膨胀土强度的影响规律,揭示了非饱和石灰改良膨胀土的强度变化机理,建立了能更好地反映膨胀土非饱和特性的分析模型和强度计算理论。研究结果为非饱和膨胀土强度分析提供了可靠的理论方法。
[Abstract]:Expansive soil is a special kind of disastrous soft soil. Because of its bad engineering characteristics, it has caused many engineering problems or engineering disasters all over the world. Therefore, it is important to carry out the study on the treatment method of expansive soil and its strength characteristics after its treatment, and to discuss the law of strength change in unsaturated state. In this paper, based on the Nanning expansive soil in Guangxi, this paper, relying on the National Natural Science Foundation of the National Natural Science Fund to study the nonlinear rheological properties of expansive soil (project number: 50978097), and the project "Research on nonlinear rheological properties of expansive soil" (project number: 2010SK3047), which is funded by the science and Technology Department of Hunan province (project number: 2010SK3047), has carried out the unsaturated expansion. Experimental and theoretical study on the strength characteristics of expansive soil with expanded soil and unsaturated lime. Based on unsaturated soil theory, combined with soil water characteristic curve and three axis test results, the shear strength model of plain expansive soil and lime modified expansive soil considering matrix suction and diameter normal stress is established, and the unsaturated soil under double stress state is put forward. Through the analysis of the test results, the influence of the matrix suction and water content on the strength of unsaturated soil is explored, and the mechanism of the strength change of the improved expansive soil is revealed. The research results can provide theoretical basis for the strength analysis of unsaturated expansive soil in practical engineering, and also to determine the unsaturated soil rapidly. A reliable method is provided for the shear strength index. The main research work and research progress made in this paper are as follows. First, the main research work (1) carries out a series of conventional indoor tests on expansive soil and lime expansive soil in Nanning, including the limit water cut test, compaction test, expansibility test, standard. The actual effect of lime modified expansive soil was analyzed, and the optimum mixing ratio in the experimental study was determined. (2) the soil water characteristics test was carried out on the expansive soil of Nanning expansive soil and lime with pressure plate, and the soil of unmodified expansive soil and lime improved expansive soil under different compactness conditions were obtained respectively. The Fredlund-Xing model is used to fit the experimental data, and the model parameters of the unimproved expansive soil and lime improved expansive soil under different compaction conditions are analyzed. (3) the full automatic three axis instrument (GDSTAS) produced by the British GDS instrument and Equipment Co., Ltd. has been used for the unmodified expansive soil and unsaturated soil. A series of three axis tests are carried out. (4) the shear strength expression of VanapalliFredlund and the Fredlund-Xing soil water characteristic curve model are combined to analyze the shear strength of the unimproved expansive soil and the improved soil, and the shear strength of soil under different matrix suction and net normal stress is explored. Two, the main research progress and the main research progress are obtained. The innovation conclusion (1) based on the Fredlund-Xing model, the soil water characteristic curve model suitable for the expansive soil and lime expansive soil is constructed respectively, and the related model parameters are obtained by fitting the model parameters. The water content of the improved expansive soil with lime is smaller in the range of matrix suction, indicating that the water holding capacity of the improved expansive soil is higher than that of the plain expansive soil, and the water stability is better than that of the plain expansive soil. (2) the stress strain relation curves of the expansive soil and the improved expansive soil of the plain expansive soil and lime are different by the three axis test. The stress strain relationship of the expansive soil is mainly strain stability and strain hardening. The stress strain relationship of the improved expansion of lime mainly presents strain softening. The stress strain relation curve of the lime improved expansive soil under unsaturated state is obviously softening type, and with the increase of matrix suction, soil The peak strength of the shear strength appears in advance, and the peak strength increases obviously. The cohesion c of the improved expansive soil is influenced obviously by the matrix suction, and increases with the increase of matrix suction, while the internal friction angle is less influenced by the matrix suction. (3) based on the unsaturated soil theory, the strength meter of the expansive soil and the improved expansive soil of lime are carried out. The variation of shear strength of unsaturated soils under different matrix suction and different net normal stress is analyzed. The strength envelope of unsaturated soil in the three-dimensional space of tau (sigma -ua) - (ua-uw) is obtained. The strength envelope surface can visually reflect the strength of the unsaturated soil by reflecting the matrix suction and the net normal stress. (4) according to the results of saturated soil three axis consolidation and drainage shear test and unsaturated soil strength theory, the calculation and determination method of unsaturated soil shear strength based on matrix suction and water content (C and phi) is proposed. On this basis, the calculation theory of unsaturated soil shear strength is established. (5) through the matrix suction and shear strength between the matrix and the shear strength. It is found that the contribution of the matrix suction to the shear strength of unsaturated soils is nonlinear. When the matrix suction is small, the shear strength of unsaturated soil increases with the increase of matrix suction. When the matrix suction reaches a certain value, the shear strength of unsaturated soil decreases with the increase of the matrix suction step. That is, the shear strength of unsaturated soil is maximum when the matrix suction reaches a "best value". To sum up, the influence law of matrix suction and water content on unsaturated expansive soil strength is explored through the experiment and theoretical study of the unsaturated soil strength of expansive soil and lime to improve expansive soil, and the non saturation is revealed. The analysis model and strength calculation theory which can better reflect the unsaturated characteristics of expansive soil are established and the strength change mechanism of the expansive soil improved by lime. The results provide a reliable theoretical method for the strength analysis of unsaturated expansive soil.
【学位授予单位】：中南林业科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU443

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