高应力下西安含水层砂土蠕变特性的试验研究

Experimental research on creep characteristics of aquifer sand sediments in Xi′an under high stress

针对西安市地面沉降研究,运用自行研制的高压固结仪,选取了西安市含水层具有代表性的中细砂样,模拟承压含水层的深部的应力环境和水位变化,进行了高应力状态下的一维蠕变试验研究。试验结果表明:西安中细砂的蠕变特征除了受有效应力大小影响外,还与砂土所受应力历史有关。在承压水位下降的情况下,西安中细砂的压缩变形具有显著的蠕变特征;而在承压水位上升情况下,中细砂发生膨胀过程蠕变不明显。根据试验前后激光粒度分析曲线和电镜扫描对比,砂土的蠕变除了和土颗粒间的滑移错动有关外,还和砂土颗粒的破裂有关。在总结试验规律和变形机理的基础上,提出了适合于西安市中细砂蠕变特性的广义Kelvin模型。模型识别得到的广义Kelvin模型的5个参数并不是常数,而是随着应力水平的不同呈现出一定的规律变化性。

For a better understanding of the mechanism of land subsidence in Xi′an,a high-stress consolidation system was designed,and several tests on the medium-to fine-grained sand sediments were conducted under different stresses.The variations of overlaying pressure and water table of confined aquifer were simulated using the system,and one-dimensional creep deformation tests were conducted under high stress.The results showed that(1)the creep characteristics of aquifer sand is not only affected by the magnitude of effective stress but also the stress history;(2)when the confined water level decreases,the compressive deformation of sand samples shows obvious creep characteristics;(3)when the confined water level increases,the sand samples begin to expand but the creep characteristics are insignificant;and(4)according to the comparison of laser granularity analysis curve and scanning electron microscope before and after the tests,the creep deformation of aquifer sand is not only related to the slip dislocation but also the fracture of sand sediments.The generalized Kelvin model was proposed to characterize the creep deformation of aquifer sand in Xi′an based on the summary of experiments and deformation mechanism.The five rheological parameters in the generalized Kelvin odel were not constant but varied with the effective stress.