大气氧化致诱黏性土土性异变现象及其机理

关注了常温、常压、常态的大气环境下黏性土土性发生缓慢异变现象。以湛江黏土为研究对象,在大气氧化影响下,土色由青灰色、绿灰色变为淡黄棕、黄棕色；颗粒团聚程度增强,塑性、膨胀性、收缩性、灵敏性、结构屈服强度皆有所降低。大气氧化对土性改造使其力学性质有所强化,但因结构强度的减损对其力学稳定性的影响是长期的,且潜在危害较大。通过建立结构概化模型讨论了大气氧化致诱黏性土土性异变机理,大气环境诱发氧化还原环境变化,水-土-大气间的化学反应与运动影响颗粒间作用力改变,导致结构单元体联结形式更改进而重塑微观结构形态,控制土体的稳定性状态。氧化反应促使土中铁离子的化合价升高,在浓度梯度与土颗粒表面吸附能的作用下发生迁移并伴随着胶体态氧化铁的老化反应向晶质态发展,由#x0201c;混铁#x0201d;变为#x0201c;包铁#x0201d;为主的存在形式,微观结构变为低塑性的、物理接触的、弱结构强度的散凝结构。该研究可为因环境变化引起的地质灾害、工程灾害的预防、控制和治理提供了一定的理论支持。

Effect of atmospheric oxidation on variation of physical-mechanical properties of clay and its mechanism

The slow variability of the physical-mechanical properties of clay in atmospheric environment with normal temperature, pressure and concentration is studied. By taking the Zhanjiang clay as the research object, the soil color of atmospheric environment changes from blue-gray, green-gray into yellowish brown, brown under impact, and the degree of particle agglomeration is enhanced. Further, the plasticity and expansibility, shrinkage, sensitivity, structural yield pressure are all reduced. Owing to the atmospheric oxidation, the mechanical properties of the clay is strengthened, but its long-term mechanical stability is depressed and the damage is potential since the structural strength is weakened. A generalized structural model for the variability of clay by atmospheric oxidation is established and discussed. The results show that the variation of atmospheric environment leads to change of redox environment, the chemical reaction among water-soil and atmosphere is carried out and moved, and the connection ways of micro-fabric unit are changed. Furthermore, the microstructure is transformed and the stability of mechanical system is affected. Oxidation reaction prompts the valence of the iron ions in the soil to increase, and they migrate along with the aging reaction of colloidal iron oxide to the crystalline state under the concentration gradient and the adsorption energy of soil particle surface. Iron oxide exists in the form of the mixed iron replaced by the coated iron one, and the microstructure becomes flocculation structure with low plasticity, physical contact and weak structural strength. This study may provide a theoretical support for the prevention and control of geological and engineering disasters owing to environmental change.