淡水诱因干湿循环下超氯盐渍土强度演变

INFLUENCE OF FRESH WATER ON THE STRENGTH OF PERCHLORINATED SALINE SOIL UNDER DRY-WET CYCLES

青藏高原盐湖地区超氯盐渍土地基在气候环境引起的干湿循环作用下力学及变形特性复杂多变,威胁上部结构安全使用。为模拟土体从施工到服役过程的强度演变过程,以青藏高原北部的察尔汗盐湖地区自然超氯盐渍土为研究对象,通过控制不同压实度制作3种土体试样并展开干湿循环试验,每次烘干后增加纯水至预期含水率模拟淡水入侵影响,在达到预定干湿次数后进行无侧限抗压强度试验和直剪试验,结合不同循环工况下盐渍土微观结构的改变,分析和揭示超氯盐渍土强度演变规律及机理。结果表明,经过5个干湿循环后,无侧限抗压强度达到峰值,分别提高128.3%(k=85%)、138.9%(k=90%)和231.9%(k=95%),同时,黏聚力c也达到峰值,分别提高200.0%,215.7%,197.2%。当试样经历6~12个干湿循环后,其强度先降低后趋于稳定;微观结构观测表明,土体颗粒间联结作用随循环次数增加先增强后减弱,与土体强度变化规律一致。研究表明,淡水影响下超氯盐渍土强度随干湿循环先增强后降低,其演变规律主要由盐结晶微观结构变化引起,实际工程中应在施工结束后重视超盐渍土地表的合理排水。

Mechanical and deformation properties of perchlorinated soil are complicated under dry-wet cycles caused by the climatic environment,which threatens the safety of superstructures.In order to simulate the strength evolution process of soil from construction to service,natural perchlorinated saline soil in Qarhan Salt Lake region was selected and three compactness of soil samples with compaction were prepared to do wetting-drying test.Distilled water was added after each drying cycle to simulate the raining process.Unconfined compressive strength and shear strength were determined during dry-wet cycles.Microstructural changes during dry-wet cycles were observed to reveal the changing mechanism of soil mechanical properties.Experiments show that the unconfined compressive strength of soil samples is increased by 128.3%,138.9%,and 231.9%,and reaches the peak values at the 5 dry-wet cycles.Meanwhile,the cohesion c is also increased by 200.0%,215.7%,and 197.2%.When the soil samples undergo 6~12 dry-wet cycles,the strength of the soil samples first decreases and then tends to be basically stable.Microstructural observation indicates that the amount of bond materials among particles nearly shows the same change tendency with soil strength.Results indicate that the strength of perchlorinated soil increases at the early stage and then decreases with the increase of dry-wet cycles,which is mainly caused by the changes in microstructures.More attention should be paid to the drainage of rainwater on the ground surface of perchlorinated soil after the construction process.