【作者】 谈云志；

【导师】 孔令伟；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 工程力学， 2009， 博士

【摘要】 红粘土在我国是一种分布十分广泛的特殊粘土,具有失水开裂、遇水泥化的典型水敏性特征,其中在湖南和广西地区覆盖面很广。大量交通基础设施建设难以回避使用红粘土作为路基填料,但因其天然含水量较高致使填筑阶段很难达到重型压实标准,同时又因其典型的水敏性可能引起运营阶段路基的性能弱化。因此,需要深入研究路基填筑阶段的压实度控制指标与外部营力对其长期性能的作用机制。论文以厦门至成都高速公路湖南郴州段的红粘土为研究对象,以环境因素作用下红粘土路基的变形特征与防护方法为研究目的,通过室内试验研究了不同压实度红粘土的持水性能、毛细上升、湿热耦合迁移及湿化变形等特征,借助郴州地区连续两年的气象数据,模拟在地下水和大气的共同作用下路基内部红粘土水分迁移与路基变形的耦合过程,主要研究内容及结论如下:(1)针对不同压实度的红粘土,系统开展了其渗透、固结、收缩、剪切等试验研究。在分析上述特性指标随压实度变化规律的基础上,以红粘土特征指标随压实度变化的敏感程度作为路基压实度能否降低的判别依据,指出将各指标随压实度变化曲线上的拐点特征值作为适当降低压实度的临界参考值,为确定红粘土路基填筑压实度控制指标提供了依据。(2)利用压力板仪研究了四种压实度试样的持水性能,发现与其它粘土的土水特征曲线相比有很大的不同,压实红粘土的土水特征曲线在吸力增大的过程中出现了类似于进气值前和残余含水量后的水平阶段。水平阶段的性状与试样的干密度有很大的关系,干密度越小水平阶段持续越长。通过液氮冷冻干燥和压汞相结合的方法测试了四种压实度试样的孔隙分布特征。发现孔隙孔径分布曲线存在两个峰值,不同干密度试样对应的小孔径及其孔隙分布密度差别不大,但对应的大孔径及其分布差别迥然。根据不同压实度试样的孔隙分布特征解释了对应压实度试样的持水。(3)为模拟地下水作用下路基底部土体的毛细效应,自制了毛细上升试验装置。在常地下水位边界条件下,获得了三种不同压实度土体的含水量随高度的分布规律,并利用Bruce推导的方法计算了等温水分扩散系数。(4)为了解大气温度作用下路基内部土体的水分迁移规律,自行设计加工了一套湿热耦合试验装置。研究了绝湿边界条件下三种压实度和三种初始含水量试样的水分传输特征,发现水分的绝对迁移量与土体初始含水量有关,初始含水量过高和过低都不能产生大量的水分迁移,而存在一个“最优含水量”迁移点,这为潮湿地区红粘土偏湿碾压提供了一定的理论支持。最后,采用任奋芝推导的公式计算了热湿扩散系数。(5)在三轴仪的基础上改装了一套可供湿化变形试验的仪器,并对传统的单线和双线试验法进行了修正。模拟了不同压实度试样在水分湿化作用下的变形特征,提出了丧失基质吸力与湿化变形的本构关系。(6)以Philip&de Vries湿热耦合模型为基础,考虑了湿化变形对体积含水量的影响,实现了温度、水分、变形三场之间的耦合,利用有限元计算方法模拟了环境因素作用下路基的温度、水分、变形场的演化规律,并针对性地提出了路基病害的防治方法。更多还原

【Abstract】 Laterite soil is a kind of special clay,which is widely distributed in most parts of our country,,especially in Hunan and Guangxi provinces.It features water sensitivity of losing-water shrink cracks and softening by absorbing water.With the undertaking of a large number of communication infrastructure construction,the use of Laterite soil as roadbed filling is becoming an inevitable project problem.However,it’s difficult to achieve the heavy compaction standard in construction stage as a result of the high nature moistuer content;meanwhile,it may cause the performance attenuation during using period due to the water sensitivity.Therefore,the compaction control index at the subgrade filling stage as well as the long-term stability of the subgrade under the effects of environment factors have been studied in this paper.In this paper,Laterite soil adjacent to some stake of the highway in Chenzhou, Hunan section from Xiamen to Chengdu was used to investigate the deformation characteristics and protection methods of the Laterite soil subgrade under the influence of environment factors.Properties like water-holding capacity,capillary rise, coupled heat-moisture transfer and wetting deformation of samples under different compactness were studied through a series of laboratory tests.In addition,by using meteorological data of two consecutive years in Chenzhou,coupled process of moisture transfer and subgrade deformation was stimulated under the impacts of groundwater and the atmosphere.Specific work done in this paper is as follows:(1) Samples under different compactness were subjected to a series of conventional laboratory tests,such as permeability,consolidation,contraction,shear test and etc.Based on these test results,relationships between mechanical indexes obtained from the above tests versus compactness have been analyzed in this paper. And the sensitivity of the index changes with respect to compactness changes is referred to as the distinguish basis for the decreasing of subgrade compactness—values with a little lower than that of the inflection points of these curves are seen as the critical reference values of the decreasing of subgrade compactness,which provides a reference method for the control of compactness of roadbed filling of the Laterite soil.(2) Pressure plate extractor was used to study the soil-water characteristic curves(SWCC) of specimens under four different compactness and the obtained SWCC were distinctly different from those of the other clays.In the SWCC,there has appeared plateau stage in the process of suction increasing.What’s more,the length of the plateau stage is intimately related to the dry density of samples—the lower the dry density is,the longer the length of the plateau stage is.Through the combination of test methods of freeze at liquid nitrogen and mercury injection,pore size distributions of samples under four different compactness have been measured.It was found that there are two peaks in the distribution curves and that small pore sizes and the corresponding distribution density are not sensitive to dry density of soils whereas big pore sizes and the corresponding distribution density are interrelated with dry density of soils.Based on this study,the water holding capacity of specimens under different compactness is also explained with it.(3) A capillary rise apparatus was self-made to stimulate the capillary-effect of subsoils under the impact of groundwater.Under constant groundwater table boundary condition,water content distributions along the heights of capillary rise of samples under three different compactness are presented in this paper.And the isothermal moisture diffusion coefficient was also obtained by Bruce method.(4) To investigate the mechanism of moisture transfer of the subsoils under the influence of atmospheric temperature,a coupled heat-moisture apparatus has been self-designed and processed.Under adiabatic boundary condition,water transport characteristics were studied for specimens of three different water contents and compactness.It can be found that the absolute moisture transport of soils are related to their initial water contents.Lots of moisture transport will appear once the optimum water content is reached,which provides a theoretical basis for the practice of the Laterite soil rolling under a wetter condition.In the end,heat and moisture diffusion coefficient was obtained by REN-Fenzhi method.(5) A new moistening deformation apparatus were made based on the theory of triaxial apparatus and the traditional single line and double line testing methods were modified.By using the moistening deformation apparatus,the deformation characteristics of specimens of different compactness were stimulated under the effects of water humidification,and a constitutive model of matric suction and wetting deformation were thus proposed.(6) Based on the Philip&de Vries heat-moisture coupling model and taking into account the impacts of wetting deformation on the volumetric water content of soils, the evolution law of temperature,moisture,and deformation fields of subgrade under the influence environmental factors were stimulated by using finite element calculation method and the corresponding protection methods of roadbed diseases were proposed on this basis.更多还原