基于等时压缩曲线理论的软土一维固结特性研究

发布时间：2018-06-16 03:45

本文选题：软土 + 一维压缩　；参考：《暨南大学》2015年硕士论文

【摘要】：软土具有含水率高、孔隙比大、压缩性高、渗透性差、抗剪强度低等特性,其长期变形量一般较大。在软土地基上修筑建筑物时,变形问题和长期沉降问题是工程面临的主要难题。软土的变形与时间密切相关,这既包括超静孔隙水压力消散的固结压密过程,也包括由土体粘滞性所引起的蠕变变形,两者相互影响,共同决定着土体的长期沉降。因此,开展反映软土变形与时间相关的性状研究以及建立能够考虑时间效应的固结模型,对软土地基固结沉降过程和固结沉降量的预测是具有理论和实际意义的。本文针对汕头东部吹填软土,在掌握试样基本物理力学性质的基础上,通过室内一维压缩试验系统研究了软土在不同固结条件下的压缩特性及压缩性指标。主要研究内容及成果如下:(1)针对试样进行了K0侧限固结试验,对比分析了试样在不同初始状态、排水距离和固结时间等条件下的等时压缩曲线特性、基本变形规律和各项压缩性指标的发展规律。结果表明,不同固结因素影响下,试样的等时压缩曲线特性、基本变形规律和各项指标的发展规律是一致的,只是指标的量值会因固结影响因素改变而发生变化,说明elgp等时压缩曲线规律具有普遍适用性,能够直观地反映固结变形与时间相关的性状,但是指标的取值需要考虑固结影响因素。(2)作为对比,进行了等K柔性侧限固结试验,将试验结果与K0侧限条件下的成果进行了对比分析。结果表明,等K柔性侧限条件下,除了在正常固结阶段0~0.1min时段内产生了明显的瞬时变形外,之后的压缩变形特性及压缩性指标的发展规律与K0侧限条件下的相同。等K柔性侧限条件下允许发生一定侧向变形,导致压缩性指标发生相应变化,其压缩指数CK0侧限条件下的1.8~2.6倍,次固结系数Ca约为K0侧限条件下的2.3~2.4 倍。(3)为进一步了解软土的回弹再压缩特性,还进行了K0侧限回弹-再压缩试验,分析了回弹再压缩变形特性及各阶段应力应变关系。试验结果表明,压缩曲线具有明显的分段特性,不同固结压力回弹起点下的回弹-再压缩等效直线可视为近似平行的,再压缩超固结阶段变形以弹性变形为主,可用弹性理论计算该过程的应力应变关系;回弹再压缩之后的正常固结压缩线可视为回弹前正常固结压缩线的延续,正常固结阶段变形以粘塑性变形为主,弹性变形量很小,可采用粘塑性理论给出该过程的变形计算。(4)在上述试验及成果整理的基础上,基于等时压缩曲线理论和等效时间概念,建立了分段式的一维弹-粘塑性固结模型,并明确了参数的物理意义和确定方法。该模型还给出了结构屈服应力点的确定方法,考虑了时间效应对变形及土体结构屈服应力的影响,能够较好地描述软土的压缩变形特性,反映固结过程中准先期固结压力增加的现象。该模型也被推广到等K柔性侧限条件,使之可以考虑侧向变形对模型参数的影响。
[Abstract]:Soft soil is characterized by high moisture content, high porosity ratio, high compressibility, poor permeability and low shear strength. Deformation and long-term settlement are the main problems in building on soft foundation. The deformation of soft soil is closely related to time, which includes both consolidation and compaction process of excess pore water pressure dissipation and creep deformation caused by soil viscosity. Therefore, it is of theoretical and practical significance to study the characteristics of soft soil deformation related to time and to establish a consolidation model which can take account of time effect to predict the consolidation settlement process and consolidation settlement of soft soil foundation. Based on the basic physical and mechanical properties of the soft soil in the east of Shantou, the compression characteristics and compressibility indexes of the soft soil under different consolidation conditions were studied by one-dimensional compression test system in laboratory. The main research contents and results are as follows: (1) the K0 side limit consolidation test is carried out for the specimen, and the characteristics of isochronous compression curves under different initial state, drainage distance and consolidation time are compared and analyzed. Basic deformation law and the development law of each compressibility index. The results show that under the influence of different consolidation factors, the characteristics of isochronous compression curve, the basic deformation law and the development law of each index are consistent, but the value of the index will change with the change of consolidation factors. The results show that the law of elgp isochronous compression curve is universal and can directly reflect the properties of consolidation deformation related to time, but the value of the index needs to consider the influence factor of consolidation. The experimental results are compared with those under K _ 0 side limit. The results show that under the condition of equal K flexible lateral limit, except for the obvious instantaneous deformation during the 0~0.1min period of normal consolidation stage, the development law of compression deformation and compressibility index is the same as that under K0 lateral limit condition. A certain lateral deformation is allowed under the condition of equal K flexible lateral limit, which results in the corresponding change of compressibility index, and its compression index CK0 is 1.82.6times higher than that under the lateral limit condition. In order to further understand the springback and recompression characteristics of soft soil, K0 side limited springback and recompression tests were carried out, and the deformation characteristics of springback recompression and the stress-strain relationships in each stage were analyzed. The experimental results show that the compression curve has obvious piecewise characteristics, and the springback-recompression equivalent straight line at different springback starting points of consolidation pressure can be regarded as approximately parallel, and elastic deformation is the main deformation in the recompression overconsolidation stage. The stress-strain relationship of the process can be calculated by elastic theory, and the normal consolidation compression line after springback and recompression can be regarded as a continuation of the normal consolidation compression line before springback. The deformation in normal consolidation stage is mainly viscoplastic deformation, and the elastic deformation is very small. The deformation calculation of the process can be given by using the viscoplastic theory. (4) based on the above experiments and the arrangement of the results, based on the theory of isochronous compression curve and the concept of equivalent time, a segmented one-dimensional elastic-viscoplastic consolidation model is established. The physical meaning and determination method of the parameters are clarified. The model also gives a method to determine the yield stress point of the structure, considering the influence of time effect on the deformation and the yield stress of the soil structure, which can better describe the compressive deformation characteristics of the soft soil. It reflects the increase of quasi-preconsolidation pressure in the consolidation process. The model is also extended to the equivalent K flexible lateral limit condition, so that the influence of lateral deformation on the model parameters can be considered.
【学位授予单位】：暨南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU447;TU411

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