冻融循环下罗布泊盐渍土的累积变形特性研究

ACCUMULATIVE DEFORMATION CHARACTERISTICS OF SALINE SOILS IN LOP NUR UNDER FREEZE-THAW CYCLES

土体的累积变形特征对于地下结构设计与路基长期动力稳定性能保持具有关键作用。在盐渍土地区由于冻融循环作用影响,盐渍土中赋存的易溶盐溶液与结晶盐颗粒,随着温差变化与水分迁移产生的结晶-溶解、积盐-脱盐过程,可引起土体颗粒结构与物理性质变化,从而影响盐渍土动力学性质。为研究铁路动荷载作用下新疆罗布泊地区盐渍土的累积变形特性,在室内冻融循环试验的基础上开展不同应力水平的动三轴试验,提出盐渍土塑性行为判定准则,得到盐渍土累积塑性应变预测模型及模型参数。结果表明:盐渍土的累积塑性应变随冻融循环的次数增加和动应力幅值的增大而增大,在模拟铁路振动荷载条件下,研究区盐渍土的累积塑性应变行为主要为塑性安定型和塑性蠕变型,其累积塑性应变速率εp与循环振次N之间呈幂函数关系。在此基础上,建立了考虑冻融循环次数和动应力的盐渍土累积塑性应变预测模型。研究成果可为盐渍土路基在冻融循环和循环动荷载下的沉降预测和动力稳定性评估提供参考。

The accumulative deformation characteristics of soils are crucial for designing subgrade structures and maintaining the long-term dynamic stability of the subgrade.Due to the effects of freeze-thaw cycles in saline soil regions,liquid soluble salt solutions and solid crystalline salt particles undergo crystallization-dissolution and salt accumulation-desalination.These processes not only cause changes in soil structure and physical properties but also influence the dynamic properties of saline soil.Based on freeze-thaw cycle tests,dynamic triaxial tests with different dynamic stress levels were conducted to study the accumulative deformation characteristics of saline soils in the Lop Nur region under the dynamic load of railway.Criteria for plastic behavior and a prediction model of accumulated plastic strain were established.The results show that accumulative deformation increases with both the number of freeze-thaw cycles and the increase in dynamic stress level.Under the simulated dynamic load of railway,the accumulative deformation behavior of saline soil in the study area is mainly characterized by plastic shakedown and plastic creep phases.The relationship between the accumulated plastic strain rate of saline soil and the number of loading cycles can be well described by a power function.Based on this,an accumulated plastic strain model considering freeze-thaw cycles and dynamic stress is proposed.These research results can provide references for settlement prediction and dynamic stability evaluation of saline soil subgrades under freeze-thaw effects and cyclic dynamic loads.