非饱和石灰改良土持水与变形特性的温度-土颗粒尺度效应研究

Lime treatment is an economical and efficient soil stabilization method. However, under the climate cycles, , the lime-treated soils specially in field could suffer the frost heave and thawing settlement, which will induce the degradation of soil strength and its stability. Actually, the key scientific problems are the effects of temperature and aggregate size on the water retention and mechanical behavior of lime-treated unsaturated soils. In this project, both the experimental method and the theoretical approach will be applied for the systematical investigation of the water retention and mechanical behavior of lime-treated unsaturated soils systematically in view of the external factor, such as the temperature effect, and the internal factor, like the aggregate size effect, from the perspective of unsaturated soil mechanism, soil science and thermodynamics. It includes: the effect of temperature on the suction and void ratio of lime-treated unsaturated soils; the effect of temperature and degree of saturation on the mechanism of interactions between the solid phase and the pore water-gas-ice phase; the modeling that provides the prediction of the temperature effect on the water retention and mechanical behavior of lime-treated unsaturated soils with various aggregate sizes. It will also indicate the changes in the water retention and mechanical behavior of lime-treated unsaturated soils with the varying temperature in theory, and the qualitative and quantitative relation between the internal performance of solid phase/water-gas-ice phase and the macroscopic geotechnical behavior; while in field, it can make a prediction about the macroscopic hydro-mechanical behavior of lime-treated soils in the large scale of aggregates.

石灰处理是一种经济有效的土质改良方法，实际工程中经常遇到冻胀融沉、强度不稳定的难题，其对应的关键科学问题是非饱和石灰改良土持水-变形特性的温度效应与土颗粒尺度效应。本项目围绕以上关键科学问题，从非饱和土力学、土质学、热力学三个角度出发，采用试验与理论分析相结合的方法，针对外在气候因素（温度效应）和内在土体自身因素（土颗粒尺度效应），进行非饱和石灰改良土的持水-变形特性试验与模型研究。研究内容包括：温度对非饱和石灰改良土吸力与孔隙比的影响及其机理；温度和饱和度对土体内土颗粒/孔隙水-气-冰微观作用机制的变化规律；建立不同土颗粒尺度下石灰改良土持水-变形特性温度效应的预测模型。在理论上揭示不同温度作用下非饱和土石灰改良土持水-变形特性的变化规律以及土体内土颗粒与孔隙水、气、冰各相间的微观性状与宏观工程特性的定性定量关系；在实际工程中，解决现场大颗粒尺度石灰改良土宏观水力特性难以预测的问题。

现场石灰改良土的工程特性极易受到外在气候环境因素（例如干湿、冻融循环等）长期影响作用而难以准确预测，本项目针对非饱和石灰改良土开展了考虑温度影响的持水特性试验、饱和渗透特性试验和NMR试验等系统研究，重点分析了温度和石灰改良对持水特性、饱和渗透特性以及微观孔隙结构的影响及其机理，取得了一下重要结果：（1）标定了不同温度下Whatman No.42滤纸总吸力率定曲线，尤其确定了0摄氏度下该滤纸总吸力的率定方程；（2）揭示了石灰改良、养护龄期、含水量和温度对重塑土样的持水特性和变形特性的影响规律，并且土体持水性能的温度效应随温度升高而逐渐减弱，而土体体积变化系数随温度升高而减小；（3）揭示了石灰改良、养护龄期和温度对重塑土样的渗透性能的影响规律；（4）表明石灰改良和养护龄期是影响重塑土样微观孔隙结构的主要因素，而温度对孔隙结构的影响较小；（5）验证了冻结温度降低法同样适用于非饱和土样，非饱和土样的冻结特征曲线与持水曲线具有较好的一致性，另外揭示了饱和土样的冻结特征曲线以及由滤纸法测得的持水曲线的根本区别; (6)揭示了土颗粒尺寸效应对石灰改良土水力特性及其微观孔隙机构的影响规律。本项目通过结合室内试验以及理论分析，系统分析了温度效应对非饱和石灰改良土水力特性的作用规律以及内在机理，该项目所取得的成果可为不同气候变化条件下石灰改良土的设计、施工与长期养护提供理论依据。