基于颗粒流的高含石量巨粒土填料剪切特性研究

发布时间：2018-12-18 19:01

【摘要】：西南地区基础设施建设工程的蓬勃开展形成了众多的填方工程,所用填料主要由挖方区爆破而来的碎石和土混合组成,往往具有含石量高(可达60%以上)、巨粒组土粒多(质量百分比15%以上)、石块粒径大(最大可达1m)的特点,本文称之为高含石量巨粒土填料。剪切特性作为评价填料工程性质最为重要的依据之一,相关的抗剪强度指标及剪切变形特征受到工程技术人员的高度重视。为探究高含石量巨粒土填料的剪切特性,本文依托重庆江北国际机场四期扩建工程,以蒙特卡洛方法为理论基础,利用PFC内置的FISH语言进行二次开发,构建了基于粒度成分及随机多边形石块的颗粒流填料模型,研究了尺寸效应、巨粒组土粒的粒径及含石量对填料剪切特征的影响,研究成果对山区丘陵地带的工程建设具有重要的参考价值。本文主要的研究内容及成果如下:①通过现场槽探、室内筛分与数字图像处理获得了高含石量巨粒土填料的粒度成分及表观特征;石块形态分析为构建随机多边形石块模型提供了统计依据;对采集的试样进行室内直剪试验,试验结果为后续颗粒流数值模拟提供了微观参数与宏观参数标定的关键资料。②以蒙特卡洛方法为理论基础,构建了描述石块形态的随机抽样模型;利用PFC2D内置的FISH语言进行二次开发,构建了基于粒度成分及随机多边形石块的颗粒流填料模型,实现了对填料的粒度成分及不规则多边形石块较为准确的模拟。③构建直剪试验颗粒流数值模型,模拟了填料室内直剪试验的全过程,颗粒流数值模拟结果基本反映了填料的剪切特性。通过持续监测并记录模型中裂隙的位置,获得了直剪试验过程中随着剪切位移的增加剪切面的发展历程,并分析了剪切面的形态特征。④为扩大研究尺度,重新划分了土石界限粒径,并相应改变模型最小颗粒粒径,研究了高含石量巨粒土填料的尺寸效应。结果表明,在试样级配、加载条件均保持不变的情况下,模型尺寸增大,剪应力峰值呈减小趋势,剪应力峰值对应的剪切应变有所减小,剪胀性逐渐减弱,粘聚力及内摩擦角亦呈减小趋势。这种变化在模型尺寸相对较大时趋于平缓。⑤运用等质量代换法,保持粗细料的含量不变,设计了不同巨粒组土粒分布的数值模型。数值模拟结果表明:随着模型中粒径较大的石块逐渐被粒径小、数量多的石块所取代,粘聚力逐渐降低,但内摩擦角呈增大趋势。以此指导工程实践,填筑施工中应按照相关规范控制石块的粒径,对于粒径超出规范规定的石块应对其进行分解。⑥保持加载条件及各石块粒组的相对比例不变,设计了含石量分别为10%、30%、40%、50%、60%、70%、80%、90%的数值模型。数值模拟结果表明:含石量越高,则剪应力峰值越大,模型表现出更大的刚度,剪应力-剪切应变曲线近弹性段的斜率越大,剪应力峰值对应的剪切应变越小,剪胀性逐渐增强。粘聚力及内摩擦角随不同含石量的变化曲线可分为三个部分:1)含石量10%~40%时,随着含石量增大,内摩擦角逐渐增大,粘聚力逐渐降低;2)含石量40%~70%时,随着含石量增大,粘聚力增加到一定程度后逐渐稳定,内摩擦角变化较小;3)含石量70%~90%时,粘聚力随含石量的增大显著降低,而内摩擦角明显增大。根据以上结论,含石量大于70%时,随着含石量的增大,填料的粘聚力大幅降低,加之夯实质量难以得到保证,因此在填方工程中应避免使用含石量大于70%的填料。
[Abstract]:The foundation of the infrastructure construction project in the southwest part of the Southwest has formed a large number of filling projects. The filler used mainly consists of crushed stone and soil mixed by blasting in the excavation area, and often has high stone content (up to 60%), and the large-grain group of soil particles (with a mass percentage of more than 15%). The size of the stone is large (up to 1m), which is referred to as the high-stone-containing large-particle soil filler. The shear characteristic is one of the most important bases for evaluating the properties of the filler, and the related shear strength and shear deformation characteristics are highly valued by the engineering and technical personnel. In order to study the shear characteristics of the high-stone-containing giant soil filler, this paper, based on the four-period expansion project of the Chongqing Jiangbei International Airport, based on the Monte-Carlo method, uses the FISH language built-in of the PFC to carry out secondary development. The particle flow packing model based on the particle size component and the random polygonal block is constructed, and the effect of the size effect, the particle size of the giant particle and the stone content on the shear characteristics of the filler is studied. The research results are of great reference value to the construction of the hilly land in the mountainous area. The main contents and results of this paper are as follows: The particle size composition and apparent characteristic of the high-stone-containing giant-particle soil filler are obtained through the on-site investigation, in-room screening and digital image processing, and the analysis of the stone shape provides a statistical basis for the construction of the random polygonal block model. An indoor direct shear test is carried out on the collected samples, and the experimental results provide the key data of the micro-parameter and macro-parameter calibration for subsequent particle flow numerical simulation. Based on the Monte-Carlo method, a random sampling model for describing the shape of the stone is constructed, and the particle flow packing model based on the particle size component and the random polygonal block is constructed by the secondary development of the FISH language built in the PFC2D. and the accurate simulation of the particle size component and the irregular polygonal block of the filler is realized. The numerical model of the particle flow of the direct shear test is constructed, and the whole process of the direct shear test in the packing chamber is simulated, and the numerical simulation results of the particle flow basically reflect the shearing characteristics of the filler. By continuously monitoring and recording the position of the fracture in the model, the development of the shear plane with the shear displacement in the course of the direct shear test is obtained, and the morphological characteristics of the shear plane are also analyzed. In order to enlarge the research scale, the particle size of the soil-rock boundary is re-divided, and the minimum particle size of the model is changed accordingly, and the size effect of the high-stone-containing giant-particle soil filler is studied. The results show that, under the condition that the sample stage and the loading condition are all the same, the size of the model is increased, the peak value of the shear stress is reduced, the shear strain corresponding to the peak value of the shear stress is reduced, the shear expansion is gradually reduced, and the viscosity and the internal friction angle are also reduced. this change tends to be gentle as the size of the model is relatively large. The numerical model of soil particle distribution in different macro-particle groups was designed by using the mass substitution method and other mass substitution method to keep the content of the coarse and fine material unchanged. The results of the numerical simulation show that, with the larger diameter of the stone in the model, the particle size is small, the number of stones is replaced, and the cohesive force is gradually reduced, but the internal friction angle is increasing. In order to guide the practice of the project, the particle size of the stone shall be controlled in accordance with the relevant specifications in the filling construction, and the stone shall be decomposed for the stone with the particle size exceeding the specification. In order to maintain the loading condition and the relative proportion of each block group, the numerical model with the stone content of 10%, 30%, 40%, 50%, 60%, 70%, 80% and 90%, respectively, was designed. The results of the numerical simulation show that the higher the stone content, the higher the shear stress peak, the higher the shear stress-shear strain curve near the elastic section, the smaller the shear strain corresponding to the shear stress peak, and the shear expansion. the viscosity and the internal friction angle can be divided into three parts along with the change curve of the different rock-containing quantity: 1) when the stone-containing amount is 10-40%, the internal friction angle is gradually increased with the increase of the stone-containing amount, and the viscous-accumulation force is gradually reduced; and 2) when the stone-containing amount is 40-70%, the stone-containing amount is increased, When the cohesive force is increased to a certain extent, the internal friction angle is small; 3) When the stone content is 70-90%, the adhesion force is significantly reduced with the increase of the stone content, and the internal friction angle is obviously increased. According to the above conclusion, when the stone content is more than 70%, with the increase of the stone content, the adhesion and accumulation force of the filler is greatly reduced, and the compaction quality is difficult to be guaranteed, so that the filler with the stone content of more than 70% shall be avoided in the filling project.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU751.4;TU432

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