降雨—蒸发循环作用下膨胀土填方边坡稳定性及机理研究

发布时间：2018-04-28 19:28

本文选题：膨胀土 + 填方边坡　；参考：《西北大学》2013年博士论文

【摘要】：本文主要以安康地区的膨胀土填方边坡为研究对象,以气候的干湿循环(降雨-蒸发)对其稳定性及变形破坏的循环作用机理为研究目的,通过现场工程地质调查、室内物理力学特性试验、现场物理模型试验、现场记录裂隙的定量描述以及热湿耦合数值分析等多种手段,全面开展膨胀土填方边坡在降雨-蒸发循环作用下各物理量的动态响应规律及边坡稳定性研究；并分别对胀缩机理、降雨以及蒸发对膨胀土的作用机理和膨胀土边坡的变形破坏机理进行探讨。主要研究内容及成果如下： (1)通过对安康地区膨胀土的工程地质调查与室内试验,分析了膨胀土的物质成分、结构特征与基本物理性质；在此基础上,探讨了不同饱和度下击实样的压缩变形性能,并分别对不同初始状态以及干湿循环作用影响下的强度特性进行了研究。结果表明：膨胀土的压缩变形性能与饱和度呈负相关关系；不同初始状态击实样的粘聚力差异极为明显；随着循环次数的增加,膨胀土的抗剪强度具有衰减性,且呈现先慢后快、最终趋于稳定的趋势。 (2)在安康膨胀土地区建立现场物理模型系统,通过气象观测、土体温湿度、土压力、吸力及边坡变形的监测,采用自行组装的数据采集系统与位移传感器,研究了膨胀土填方边坡在降雨-蒸发作用下各物理量的动态演化规律及其影响因子。结果表明：边坡的工程性状与含水量的变化息息相关；其中,降雨是影响膨胀土含水量最直接的因素,而蒸发作用属于间接影响因素,二者的耦合作用使边坡趋于变形破坏。 (3)在明确填方边坡的裂隙类型为风化裂隙的基础上,利用矢量图技术定量化描述了裂隙的演化规律,获取了裂隙的几何形态及裂隙度等一系列参数；进而分别探讨了干湿循环、含水量及大气温度等因素对裂隙发育的影响。结果表明：监测期内裂隙分布不具备定向规律,而且系统格局非常混乱,基本不存在相互平行的裂隙；裂隙在降雨时闭合,在蒸发过程中再次开裂,并互相连通逐渐发育成网状,但到一定程度后基本稳定；随着循环次数的增加,土体逐步走向完全破碎。 (4)在前人研究成果的基础上,提出降雨-蒸发作用下膨胀土的胀缩机理：降雨时,水分子进入土体并不断包裹晶层、土颗粒及其集聚体,并通过复杂的物理化学作用转化为力学作用与其相互联结,形成结合水膜,由于结合水膜的增厚,晶层、粒间距离加大,导致土体产生膨胀；反之,水膜变薄或消失时,粒间距离减小,从而使土体体积缩小。 (5)在对降雨及蒸发的物理过程有清晰了解的基础上,首先通过室内试验、现场模型试验结果的分析,提出膨胀土水土物理力学作用机理；并结合水土化学作用类型及膨胀土主要矿物成分的探讨,提出膨胀土水土化学作用机理。其次,对降雨作用的冲刷侵蚀,以及蒸发作用的土体收缩开裂的力学机制进行深入研究,推导了土颗粒冲刷启动条件、坡面宏观径流冲刷及土体开裂等一系列力学公式。最终,综合以上几个方面,对降雨-蒸发循环作用下膨胀土填方边坡的变形破坏机理做出了全面的解释。得出：蒸发是边坡变形破坏的重要前提条件,而降雨是导致变形破坏的直接原因；二者的循环作用可导致膨胀土填方边坡产生破坏。 (6)详细介绍了热湿耦合的理论模型、边界条件以及计算参数的赋值情况,并以现场试验边坡为原型建立几何模型,对其进行数值对比分析,验证了所用理论模型、边界条件的正确性。在此基础上,对考虑裂隙的边坡热湿耦合性状进行分析,结果表明：裂隙的存在使边坡对降雨-蒸发效应的响应显著,不但为雨水入渗至边坡内部提供了快速通道,使土体的渗透性能得到极大提高,而且在蒸发过程中,裂隙面与大气直接接触,同样也为水分的迁出提供了便捷。 (7)针对数值分析时需同时兼顾降雨及蒸发两种作用类型的特点,采用将裂隙的两侧视为气候作用边界的方法,使降雨-蒸发作用下边坡内部的水分变迁可通过裂隙与外界建立联系,并仍认为裂隙分割而成的土块完全符合非饱和土渗透特性。这种方法既考虑了裂隙对降雨-蒸发的影响,又符合非饱和土力学理论,适用于裂隙膨胀土填方边坡的数值分析。 (8)在以上研究和数值分析成果的基础上,对考虑裂隙以及强度衰减的边坡稳定性进行了分析。结果表明：只考虑裂隙的边坡潜在滑裂面与降雨作用下湿度场的分布密切相关,滑裂面随降雨作用逐渐趋于在浅层发生,但总体安全系数较高。考虑强度衰减后,安全系数要远小于未考虑强度衰减的,且随着干湿循环次数的增加而不断降低,最终趋于失稳。同时将膨胀土的裂隙性及强度衰减特性计入边坡稳定性分析中,所得计算结果符合人们的认知,可真实反映边坡的破坏情况。
[Abstract]:This paper mainly takes the expansive soil slope in Ankang area as the research object, and uses the dry and wet cycle of the climate (rainfall evaporation) to study the circulation mechanism of its stability and deformation damage, and through the field engineering geological survey, the indoor physical and mechanical properties test, the field physical model test, the quantitative description of the field record of the cracks and the quantitative description of the cracks. The dynamic response of various physical quantities of expansive soil slope under the action of rainfall evaporation cycle and the stability of slope under the effect of rainfall evaporation cycle are carried out comprehensively. The mechanism of expansion and shrinkage, the mechanism of rainfall and evaporation on expansive soil and the deformation and failure mechanism of expansive soil slope are discussed. The contents and results are as follows:
(1) through the engineering geological investigation and laboratory test of expansive soil in Ankang area, the material composition, structural characteristics and basic physical properties of expansive soil are analyzed. On this basis, the compressive deformation properties of the compaction samples under different saturation are discussed, and the strength characteristics under the influence of different initial state and dry and wet circulation are carried out respectively. The results show that the compressive deformation performance of expansive soil has a negative correlation with saturation, and the cohesiveness difference between different initial states is very obvious. With the increase of the cycle times, the shear strength of expansive soil is attenuated, and it is slow and fast, and eventually tends to stability.
(2) a field physical model system was established in the Ankang expansive land area. Through the monitoring of temperature and humidity, soil pressure, suction and slope deformation, the dynamic evolution law and influencing factors of the physical quantities of the expansive soil slope under the action of rainfall evaporation were studied by the meteorological observation, soil temperature and humidity, soil pressure, suction and slope deformation. The results show that the engineering properties of the slope are closely related to the change of water content, in which the rainfall is the most direct factor affecting the water content of the expansive soil, and the evaporation is an indirect influence factor. The coupling effect of the two causes the slope to be deformed and destroyed.
(3) on the basis of the crack type of the fill slope, the vectorgraph technique is used to quantitatively describe the evolution law of the fissure, obtain a series of parameters such as the geometric shape and crack degree of the fissure, and then discuss the effects of dry and wet cycle, water content and atmospheric temperature on the fracture development. In the monitoring period, the distribution of the cracks does not have the orientation law, and the system pattern is very chaotic, and there is no parallel cracks. The cracks are closed in the rainfall and are cracked again during the evaporation process, and they are connected gradually into a network, but it is basically stable after a certain degree. With the increase of the cycle times, the soil gradually goes to complete. Fracture.
(4) on the basis of previous research results, the expansion and contraction mechanism of expansive soil under rainfall evaporation is proposed. When rainfall, water molecules enter the soil and continuously wrap the crystal layer, soil particles and their clusters, and interconnect with the mechanical action through complex physical and chemical effects, forming a combined water film, because of the thickening of the water film and the crystal layer. As the distance between grains increases, the soil expands; otherwise, when the water film thins or disappears, the distance between grains decreases, thus reducing the volume of the soil.
(5) on the basis of the clear understanding of the physical process of rainfall and evaporation, first through the laboratory test and the analysis of the results of the field model test, we put forward the mechanism of soil and water physical and soil mechanics of expansive soil, and put forward the mechanism of soil and water chemical action of expansive soil combined with the types of soil and water chemical action and the main mineral composition of expansive soil. Secondly, the mechanism of soil and water chemical action of expansive soil is put forward. The erosion erosion of rainfall and the mechanical mechanism of soil shrinkage cracking caused by evaporation are deeply studied. A series of mechanics formulas are derived, such as the starting condition of the soil particle scour, the macroscopic runoff scour of the slope and the soil cracking. Finally, the deformation of the expansive soil fill slope under the action of rainfall evaporation cycle is broken. A comprehensive explanation of the bad mechanism is made. It is concluded that evaporation is an important prerequisite for the deformation and failure of the slope, and the rainfall is the direct cause of the deformation and failure, and the cyclic action of the two can cause the failure of the expansive soil fill slope.
(6) the theoretical model of heat and humidity coupling, the boundary condition and the calculation of the calculation parameters are introduced in detail, and the geometric model is built on the site test slope as the prototype. The numerical comparison and analysis are carried out to verify the theoretical model and the correctness of the boundary conditions. On this basis, the thermal and wet coupling properties of the slope are analyzed. The results show that the existence of the crack leads to the significant response of the slope to the rainfall evaporation effect, which not only provides a fast channel for the infiltration of rainwater into the slope, but also greatly improves the permeability of the soil. In the process of evaporation, the fracture surface is directly exposed to the atmosphere, and it also provides convenience for the migration of water.
(7) according to the characteristics of the two types of action of rainfall and evaporation at the same time, the two sides of the fracture are considered as the boundary of the climatic action, so that the water change in the slope inside the slope can be connected to the outside by the fissure, and the soil block divided by the split gap is still fully conformed to the infiltration of the unsaturated soil. The method not only takes account of the influence of cracks on rainfall evaporation, but also accords with the theory of unsaturated soil mechanics, and is suitable for numerical analysis of the expansive soil fill slope.
(8) on the basis of the above and numerical analysis results, the slope stability considering the crack and the intensity attenuation is analyzed. The results show that the potential sliding surface with only the crack is closely related to the distribution of the humidity field under the rainfall action, and the sliding surface tends to occur in the shallow layer with the rainfall, but the overall safety coefficient is more than that. When the strength attenuation is considered, the safety factor is far less than that of unconsidered strength attenuation, and it decreases with the increase of dry and wet cycles, and eventually tends to instability. At the same time, the fracture and strength attenuation characteristics of expansive soil are included in the slope stability analysis. The calculated results conform to people's cognition, which can truly reflect the failure of the slope. Situation.

【学位授予单位】：西北大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU443;TU43

【参考文献】