【作者】 韩春鹏；

【导师】 贾艳敏； 何东坡；

【作者基本信息】 东北林业大学 ， 林区交通工程， 2011， 博士

【摘要】 石灰是道路工程中常用的工程材料之一,石灰掺加在路基填土中,可以起到减水、增强、加固的效果,有效的提高了土体的强度及抗冻性等性能,并且由于其经济性好、施工方便,在我国得到了较广泛的应用。我国冻土面积占全国总面积的三分之二,且北方冬季气候寒冷,道路结构必然要受到冻融作用,而目前对于石灰处治路基土在冻融循环作用下的力学性能变化还没有清晰的认识,其强度衰减规律并没有定量的研究。本文针对石灰处治土的研究现状,对不同掺量下的石灰处治土进行了室内试验,分析土体在冻融循环作用下模量、强度等指标的变化规律,并与素土相应指标进行了对比；同时结合黑龙江省鸡西至讷河公路的石灰处治土路基,进行了路基温度场的测试,并以室内试验结果为基础,进行有限元分析,分析在实测温度场下路基的应力分布及变形特征,其主要研究内容和研究成果如下：(1)对于不同掺量下石灰处治土的基本物理指标进行了室内试验,随着掺灰剂量的增加,石灰处治土的液限变化不大,但塑限不断增大,塑性指数随之逐渐减小。土体的弹性模量及无侧限抗压强度随石灰掺量的增大而增大,土体的粘聚力及内摩擦角也随之逐渐增大。(2)基于DS18B20温度传感器和单片机,针对寒区公路路基温度场监测的实际要求,设计了路基温度场监测系统,并实现了连续监测和数据的自动采集、存储。通过路基温度场测试,发现路基冻融过程跨度达8个月,在整个冻融循环期内,与气温相比,路基深处温度的变化有大约50天左右的延迟效应,路面下路基与土路肩下路基温度变化具有明显差异,且均大于天然地基,说明道路修筑改变了原地基的温度场。从路基横断面来看,无论是冻结期还是融化期,路基冻结区域均呈现不均匀分布,在融化初期内,路基内部出现冰冻夹层,随着时间推移,温度上升,冰冻夹层逐渐变薄,直至缩小成未化冻土核,大约在6月末土体全部融化。测试路段路基含水率全年范围内保持相对较平稳状态,且呈现出在融化期内较高,而在冰冻期内较低的状态。(3)石灰的掺加在一定程度上能抑制土体的冻胀现象。经试验测定,在相同的含水率下,石灰掺量越大,土体冻胀率越小,土体起始冻胀的温度区间为-2℃～-4℃,当温度降至-10℃时冻胀基本结束,-2℃～-8℃为冻胀现象明显的温度区间；冻胀量与土体的密实程度和饱和度有一定关系；含水率越大,冻胀率越大,掺灰剂量越大,起始含水率越高。(4)土体的无侧限抗压强度随着掺灰剂量的增加而增加,随冻融循环次数的增加而降低,且各级掺灰剂量下土体的压实度越大,经过冻融后土体的强度衰减率越小。掺灰剂量越大,土体的粘聚力和内摩擦角越大,冻融次数越多,土体的粘聚力越小,内摩擦角越大；土体的回弹模量也随着掺灰剂量的增大而不断增大,并随冻融循环的次数增加而不断降低；土体的强度在第一次冻融作用下衰减幅度较大,随着冻融作用次数的增多,强度衰减幅度逐渐减小,当冻融循环次数达到6次时趋于稳定。对于不同循环温度下土体的各指标进行了试验,-9℃～-3℃是土体水分相变的过渡温区,土体随着循环温度低温下限的降低,各指标衰减幅度慢慢增大,当低温区间达到-9℃时,土体的各项指标均与-15℃～15℃冻融循环相差不多,含水率越大的土体,其强度衰减越大。不同循环温度区间土体各项指标随循环次数的变化规律与前述基本一致;对于不同冻结温度下冻土的力学性能指标进行试验发现,冻结温度越低,土体的粘聚力越大,内摩擦角越小,回弹模量越大。同时探讨了石灰增强土体与冻融循环作用下石灰处治土强度衰减的机理。(5)运用有限元理论结合abaqus软件对石灰处治土在冻融过程中的应力和变形规律进行了分析,通过模拟分析发现,在冻融循环周期内,路基出现先冻胀后融沉的现象,且.路肩处的竖向变形均小于道路中心线处。随着冻融循环次数的增多,路基中心处的沉降量逐渐增大；路基在经过10次冻融循环后其沉降量随掺灰剂量的增加而减小,但路中心与路肩处不均匀沉降有增大趋势,道路中心线下路基土应力最大,在行车荷载的作用下有破坏的可能,而未掺灰土体由于冻融作用强度降低将产生破坏。更多还原

【Abstract】 Lime is one of common materials used in road engineering. It plays the role of reducing water content, strengthening and consolidating, and improves strength and freezing resistance of soil, when lime is added into subgrade soil. This is applied on a large scale in China, because of its economy and convenience.In China, the area of frozen soil is over 2/3 of all the area and the weather in north is cold in winter, so the road must be thawed and freozen. At present, it is not fully known about change of mechanical property of lime modified soil with freezing and thawing. There is no quantificational study about strength attenuation of soil with freezing and thawing. Aim at current situation of lime modified soil, indoor test about different ratio of lime modified soil was carried out, index of modulus and resilience of soil with freezing and thawing was analyzed, compared with natural soil. With the result of indoor test, the subgrade temperature field was measured on the highway from Jixi to Nehe in Heilongjiang province, the stress distribution and deformation characteristic is analysed based on subgrade temperature field by finite element analysis. The principal contents and results of the study are as follows:(1) The basic physics index of lime modified soil on different ratio of lime to soil was tested indoor. The more ratio of lime to soil was, the more plastic limit was, the less plasticity index was, but liqiut limit changed a little. the more ratio of lime to soil was, the more resilience modulus and unconfined compression were, the more shear strength index, friction angle and cohesion were all.(2) Base on DS18B20 temperature sensor and singlechip, aim at practical requirement of measure of subgrade temperature field, the measure system was designed, in order to continuously observe, automatically collect and save data. The process of subgrade freezing and thawing lasted 8 mouth by measure of subgrade temperature field. During the time, the change of temperature under subgrade delayed for about 50 days, compared with air temperature. The changing range of soil temperature was significantly different between under pavement and under road shoulder. However, both were higher than the soil temperature under natural foundation. It indicated that the original temperature field of natural foundation was changed by subgrade.Judging from the subgrade cross-section, asymmetrical distribution existed in the period of freezing and thawing. In subgrade frozen area, in the preliminary period of thawing, the frozen interlayer appeared in subgrade. The frozen interlayer was gradually getting thin with increasing of temperature, and disappeared at the end of June. The water content of subgrade was high in the period of thawing and low in the period of freezing. but it remained a relatively stability in all a year.(3) Lime can limit frost heave of soil on a certain extent. The result indicated the more ratio of lime to soil was, the less ratio of frost heave was, at same moisture content. Initiative range of temperature of lime modified soil’s frost heave was from -2℃to -4℃Frost heave almost ended at-10℃, and was obvious from -2℃to -8℃. Frost heave was relevant with soil compaction and saturation.. The frost heave increased with degree of moisture. The more ratio of lime to soil was, the more initial moisture of frost heave was.(4) Unconfined compression increased with ratio of lime to soil, while decreased with times of freezing and thawing. The same result was found for resilience modulus. At every ratio of lime to soil, the more degree of compaction was, the less ratio of soil strength attenuation was. The more ratio of lime to soil is,the more soil cohesion and friction angle are. Soil cohesion is rise and friction angle is descend with the time of freezing and thawing rise. At the first time of freezing and thawing, strength attenuation was the biggest. Then the more times of freezing and thawing were, the less strength attenuation was. Strength attenuation went to stable, at 6th times of freezing and thawing.Every index of soil was tested under all kind of tempreture of freezing and thawing, which indicating -9℃--3℃was regarded as the transitional temperature range of moisture phase transition. The low the floor temperature of freezing and thawing is, the more all kinds of index attenuation. when the temperature arrived at -9℃,all kinds of index of soil was similar to that of normal soil.The ratio of strength attenuation increased with water content. During the range of temperature of freezing and thawing, regularity of every index changing with times of freezing and thawing was the same as the upper stated. for the mechanical property index of frozen soil under different temperature of freezing and thawing, the lower freeze temperature was, the more soil cohension and resilience modulus was, the less soil friction angle was. It discussed the mechanism of lime strengthen soil and lime modified soil strength attenuation by freezing and thawing.(5) Regularity of the stress distribution and deformation of lime modified soil subgrade in freezing and thawing were analyzed by finite element theory and Abaqus software. It indicated frost heave before thawing sink and portrait deformation is less in subgrade shoulder than that in center line of road in freezing and thawing by simulative analysis. the more times of freezing and thawing were, the more amount of precipitation of subgrade was. The less amount of precipitation of subgrade was, the more ratio of lime to soil was, after 10 times of freezing and thawing. But asymmetrical precipitation in center line of road and subgrade shoulder has increasing trend. The stress was the biggest in center line of road. Road might split under load of vehicles. Road might fracture because of low sthength of soil without lime.更多还原