黄土状压实填土压缩和强度特性研究

发布时间：2018-04-26 20:49

本文选题：压实黄土 + 击实能　；参考：《太原理工大学》2014年博士论文

【摘要】：随着改革开放和现代化建设的不断推进,我国国民经济取得了长足发展,社会化进程不断加快。然而建设规模的不断扩大、城市化进程的加快与自然环境产生了不可避免的冲突,自然环境恶化、建设用地紧张的问题日益突出。开山填洼,人工造地的办法很好地解决了建设用地紧张的问题。我国西北、华北等地多数位于黄土高原地带,山多川少,特殊的地形地貌导致了在经济建设加快发展过程中大量填方工程的出现,其中不乏高填方工程。此外,我国西北、华北又广泛分布黄土。黄土工程性质特殊,具有水敏性。因此,针对黄土状填土的岩土工程问题逐渐凸显。长期以来,人们对原状黄土各种工程性质的研究已较为深入,但基于黄土状填土的强度、变形或结构方面的系统研究尚不多见。未经处理或处理不当的填土地基,往往存在不均匀沉降或过大沉降等问题,从而引发上部建(构)筑物开裂、下沉等各种工程事故。压实或强夯是目前处理填土地基最常用的手段,而填土的压实质量直接影响地基或路基的工程质量,保证填土压实质量是保证回填地基或路基工程质量的关键,也是保证上层建筑正常使用的重要环节。本文以国家自然科学基金项目“压实黄土的强度与变形影响因素及其微观结构研究(51178287)”为依托,对取自山西吕梁和太原两地的典型黄土作为填土材料的工程力学性质进行了分析研究,揭示了黄土的压实特性以及压实黄土强度、变形等变化规律受击实含水量、击实能以及浸水等因素的影响,结合微观结构分析,将内、外因素相结合对压实黄土及其受浸水影响表现的力学性质进行了合理的解释。为进一步深入认识和把握压实黄土的工程力学特性,正确评价压实黄土的性状及压实质量,有效开展黄土地区回填工程设计、施工质量控制等提供相关的物理性质指标和参数,具有一定的现实意义。主要成果整理如下： (1)压实黄土试样在不浸水时的各项强度指标均随击实含水量增加而降低,压缩变形随击实含水量增加而增大。不同含水量范围内压实黄土的强度和变形随击实能增长的变化规律不同,在最优含水量干侧压实的土体,拥有较高的强度指标和较低的压缩性。但击实的作用使得压实黄土的结构不同于原状黄土,在较小含水量击实下的土体更具亲水性,从而造成遇水软化、强度降低等现象。相对而言,在最优含水量湿侧压实的土体受浸水的影响要小。 (2)多因素影响分析结果表明初始含水量对压实黄土压缩应变的影响最大,而垂直压力对抗剪强度的影响最大；单因素分析时击实能的影响相对较小,但击实能与含水量的交互作用对于压实黄土压缩变形和抗剪强度的影响都比较大。 (3)当压力不超过400kPa时,压实黄土的εs-P关系可用双曲线模型拟合,但对于较大压力范围内压实黄土的εs-P关系采用幂函数模型拟合更符合实际。在幂函数拟合基础上,提出了采用改进的割线模量法计算填土地基沉降量公式,并结合工程实例进行了验证。 (4)相同击实能作用下,压实黄土试样的主应力差-轴向应变关系随初始含水量的增加呈现由应变软化—弱应变硬化—强应变硬化的变化趋势。可将最优含水量作为区分压实黄土试样应变软化和应变硬化的分界含水量。 (5)压实黄土的微结构类型为团粒体结构,基本单元体以团粒为主,孔隙主要包括团粒间孔隙和团粒内孔隙两种。相同击实能作用下的压实黄土其结构形式随初始含水量由小到大变化呈现由松散到密实,由无序的粒间排列到有序的粒间排列,由各向同性到各向异性的变化过程。 (6)对于黄土这种对水具有特殊敏感性的典型细粒土,压实过程中对其含水量的控制尤为重要。在保证压实度达到要求的前提下,可同时采用空气体积率作为黄土状填土压实质量控制指标。空气体积率的控制标准应结合具体压实土样的室内击实试验来制定,一般以不超过10%为佳。采用重型机械压实时,最好将黄土状填土施工时的含水量控制在最优含水量的湿侧2%以内,这样在满足相应的压实标准前提下,既可使变形和强度指标达到设计的要求,而且对于保证填土地基或路基的水稳定性更为有利。
[Abstract]:With the continuous promotion of reform and opening up and modernization, China's national economy has made great progress and accelerated the process of socialization. However, the expansion of the scale of construction, the acceleration of the process of urbanization and the natural environment inevitably conflict with the natural environment, the problem of construction land tension is becoming more and more prominent. In the northwest, North China and other places, most of China's northwest, North China and other places are located in the Loess Plateau, and there are many mountains and few mountains. The special terrain and landforms have led to the emergence of a large number of fill projects in the process of accelerating economic development, among which there are no lack of high fill project. In addition, North China and North China are widely distributed yellow. The engineering properties of loess are special and have water sensitivity. Therefore, the geotechnical problems of the Loess Fill are gradually highlighted. For a long time, the research on the engineering properties of the original loess has been deeply studied, but the research on the strength, deformation and structure based on the Loess Fill is still rare.
Untreated or untreated fill subsoil often has problems such as uneven settlement or excessive settlement, which leads to a variety of engineering accidents, such as the cracking and sinking of the upper construction (construction). Compaction or dynamic compaction is the most commonly used means to deal with the fill subgrade. The compaction quality of the fill directly affects the quality of the foundation or subgrade, and guarantees the filling. The quality of soil compaction is the key to guarantee the quality of backfilling foundation or subgrade, and it is also an important link to ensure the normal use of superstructure. Based on the National Natural Science Foundation Project "the influence factors of compaction and deformation of compacted loess and its microstructure study (51178287)", the typical yellow from Lvliang and Taiyuan, Shanxi, is a typical Yellow River. The soil, as a filling material, has been analyzed and studied. The compaction characteristics of the loess, the intensity and the deformation of the compacted loess are influenced by the factors such as the water content, the compaction energy and the soaking water. Combined with the microstructure analysis, the effects of the internal and external factors on the compacted loess and the water affected by the soaking are combined. In order to further understand and grasp the engineering mechanical properties of compacted loess, correctly evaluate the properties of the compacted loess and the quality of compaction, effectively carry out the design of backfilling engineering in the loess region and the quality control of the construction, it is of certain practical significance. Collate as follows:
(1) the strength index of compacted loess decreases with the increase of compaction water content, and the compression deformation increases with the increase of compaction water content. The intensity and deformation of compacted loess in different water content range vary with the increase of compaction energy, and the soil which is compacted at the optimal water content has a higher strength. But the compaction effect makes the compacted loess structure different from the original loess, and the soil under the smaller water content is more hydrophilic, thus resulting in the softening of the water and the decrease of the strength. In contrast, the soil under the optimum moisture content and wet side is less affected by the water immersion.
(2) the results of multi factor analysis show that the initial water content has the greatest influence on compacted loess compression strain, while the vertical pressure has the greatest impact on the shear strength; the impact of the compaction energy is relatively small when the single factor analysis is analyzed, but the influence of the interaction of compaction and water content on the compression deformation and shear strength of the compacted yellow soil is relatively large.
(3) when the pressure is not more than 400kPa, the epsilon s-P relationship of the compacted loess can be fitted with a hyperbolic model, but the fitting of the power function model for the s-P relationship of the compacted loess in the larger pressure range is more practical. On the basis of the power function fitting, a formula for calculating the settlement of the soil foundation with an improved secant model quantity method is proposed and combined with the work. The process example is verified.
(4) under the action of the same compaction, the relationship between the main stress difference and the axial strain of the compacted loess samples with the increase of initial water content shows the changing trend of strain softening, weak strain hardening and strong strain hardening, and the optimal water content can be used as the dividing water content of strain softening and strain hardening in compacted loess samples.
(5) the microstructural type of compacted loess is a pellet structure, and the basic unit body is mainly pellet, and the pores mainly include two kinds of intergranular pores and inner pores in the pellet. The structure form of compacted loess under the same compaction energy is changed from loose to dense with the initial water content from small to large, from disordered intergranular to ordered intergranular. Arrangement, from isotropic to anisotropic.
(6) for the typical fine-grained soil with special sensitivity to the water, the control of water content is particularly important in the compaction process. The air volume rate can be used as the quality control index of the Loess fill compaction at the same time, and the control standard of the air gas accumulation should be combined with the concrete compacted soil sample. Indoor compaction tests are made, generally not more than 10%. When heavy mechanical compaction is used, the water content in the Loess Fill Construction is best controlled within 2% of the wet side of the optimum water content. Under the condition of the corresponding compaction standard, the deformation and strength index can be reached to the design requirements, and the filling foundation is guaranteed. Or the water stability of the subgrade is more favorable.

【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU444

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