干湿循环作用下红黏土胀缩性与裂隙性的耦合互馈效应研究

There are potential engineering hazards under atmosphere environment for laterite soil, which has main engineering characteristics, such as swell-shrink, fissurity and hyperdispersion. Usually it can be applied after being treated and evaluated though special processing. The strength and deformation of laterite soil under the coaction of moisture and temperature will be investigated and the coupling effect of swell-shrink and crack on laterite soil will be analyzed in this research. It will be done to laterite soil from GuiZhou province on the basis of unsaturated soil mechanics theory through unsaturated soil indoor test and field monitoring. The wetting and drying cycle condition can be obtained by making the soil samples air drying and saturating repeatedly, in which the saturation and matric suction of them are controlled. The distribution of crack is got by CT. Thus the soil shear strength formula which behaves as attenuation of strength and deformation is built. Much important multi-parameters including soil moisture, soil temperature, deformation of the superficial and deep layer, run-off of the superficial layer, are monitored in field tests. At the same time, the crack condition in the laterite soil is obtained by ground penetrating radar. Then the evaporation capacity, which is propitious to field environmental condition, is induced and the response of soil is analyzed. The mechanism of coupling effect of swell-shrink and crack on the laterite soil, which affects the mechanics characteristics of soil, is discussed on the basis of the results of indoor and field tests and the moisture-heat equation of Philip & de Vries model.

红黏土因其胀缩性、裂隙性和地层分布不均等工程特性而存在很大的工程隐患，常要求给予单独研究和评价处理。项目以贵州黔东南红黏土为研究对象，以非饱和土力学理论为基础，以室内非饱和土力学试验和现场原位监测为手段，开展水分和温度共同作用下红黏土强度和变形特征的研究，剖析胀缩性与裂隙性耦合互馈机制。研究通过控制试样饱和度和基质吸力使试样反复风干和饱和的方法模拟干湿循环条件，利用CT扫描技术掌握试样裂隙分布情况，分析红黏土试样干湿循环下强度和变形发展规律，建立可反映衰减性的抗剪强度和变形指标；通过现场原位监测空气温度与湿度、土体含水量、土温、浅层与深部位移和表层降雨径流量，利用探地雷达获得土体中裂隙的发生和发展情况，归纳出适合当地气候的潜在蒸发量和红黏土力学响应；以室内外研究成果和Philip & de Vries湿热耦合模型为基础，深入剖析胀缩性与裂隙性耦合互馈效应及其对红黏土力学性状的影响。

红黏土因胀缩性、裂隙性和地层分布不均等工程特性而存在很大的工程隐患，常要求给予单独研究和评价处理。项目以贵州黔东南红黏土为研究对象，以非饱和土力学理论为基础，以室内非饱和土力学性能试验，如胀缩性试验，土水特征曲线试验和强度试验，以及室内模型试验为手段，开展水分、温度和湿度共同作用下红黏土强度和变形特征的研究，剖析红黏土胀缩性、裂隙性等工程特性的形成机理、影响因素及耦合互馈机制。研究中水分、温度和湿度对红黏土的共同作用是通过对试样施以反复干湿循环得以实现的。在此基础上，通过压汞试验分析和归纳了试样孔隙结构随干湿循环次数的变化情况，得出了红黏土具有双孔隙结构，且干湿循环使得小孔径数量增多的结论。通过红黏土土水特征之干湿循环效应的研究，表明干湿循环使得SWCC的滞回性减弱，即干湿循环作用对于红黏土持水能力具有重要影响，尤其是在3次循环内，在第4,5次循环后红黏土脱湿曲线基本稳定。在收缩试验和SWCC试验的基础上，对考虑体变的红黏土SWCC模型（FX3）进行了探讨，研究表明脱湿阶段红黏土具有明显的收缩性，考虑体变的FX3模型能与实测曲线吻合的更好。对干湿循环作用下红黏土的胀缩和裂隙特征的研究表明，干湿循环作用使红黏土的体缩率不断增大，但受到初始含水率的影响，存在高含水率红黏土的体缩率增长弱于低含水率的现象，这说明干湿循环过程对于土体内部聚集体与孔隙水间相互作用的影响是明显且重要的。干湿循环对红黏土强度的作用总体上是使其降低的，但对黏聚力的影响明显强于对内摩擦角的影响。研究中对红黏土湿化性状的干湿效应进行了分析，随着干湿循环次数的增加，试样的湿化崩解程度也呈递增趋势，但初始含水率在最优含水率附近的试样受干湿循环的影响较小。