沙漠绿洲区路基盐分积聚机理与路基性能的劣化效应研究-以阿拉善额济纳地区为例

Alxa Ejina area is located in the arid and semi-arid climate zones, the characteristic of climate is large temperature variation, dry with little rain,the difference of the temperature between day and night is high, evaporation is strong. Because of the influence of special climatic environmental factors in desert oasis area and the pavement coverage effects, free water evaporation was prevented which makes redistribution of humidity and at the same time makes migration accumulationin of salt in the interior of subgrade, leading to the deterioration of subgrade performance and the decrease of highway life. The subject establish coupling migration model of water(gas), temperature and salt in unsaturated soil of subgrade and reveal accumulation mechanism of salt in desert oasis area through in-situ test that is real-time monitoring of humidity field,temperature field and salt field and indoor test combined wiht soil discipline theory. Based on it, subject ananlyzes the variation of resilient modulus of salt subgrade soil with the effect of periodic dry-wet and freeze-thaw circulation function and the soil-water characteristic curve,establish prediction model which can represent modulus of resilience of salt subgrade soil legitimately,summarize evolution law of deterioration of subgrade performance. Compound barrier technology which can conside time effect on the results of salt resistance will be developed to prevent secondary salinization of subgrade and it will be verified by field comparison test. The subjct will offer theoretical guarantee and practical basis for improvment of working performance of subgrade in desert area.

阿拉善额济纳地区处干旱半干旱气候区，高温高寒，干燥少雨，昼夜温差大，蒸发强烈。在特殊气候环境因素作用下，沙漠绿洲区路基内部的水分迁移受路面覆盖效应的影响，明显异于裸露状态下的水分迁移规律，湿度重新分布，水分携带的盐分迁移积聚，进而导致路基性能劣化，影响使用寿命。本课题拟通过实时监测路基湿度场、温度场、盐分场的原位试验与室内模型试验研究，结合土壤学科理论，建立路基非饱和土水（气）、热、盐耦合运移模型，揭示沙漠绿洲区路基盐分的积聚机理；在此基础上分析含盐路基土回弹模量受周期性干湿、冻融循环作用的变化规律及土水特征曲线，结合试验数据，基于非饱和土理论，构建合理表征含盐路基土回弹模量的预估模型，总结路基性能劣化演变规律；研发防止路基发生次生盐渍化的可考虑阻盐效果时间效应的阻隔技术，并通过野外对比试验对其有效性进行验证，为改善沙漠区路基工作性能提供理论保障与实践依据。

阿拉善额济纳地区多条运营公路发生盐渍化病害，围绕此病害，展开路面覆盖与赋存气候环境影响下的病害成因调查、风积沙路基水、热、盐运移规律、风积沙路基土性能与的、土水特征曲线与隔断层处治措施的研究。病害路段基层、路基不同深度试样及路基坡面试样的化学成分分析表明，阿拉善额济纳地区沙漠气候环境与路面覆盖影响，路基内盐分迁移积聚，使路基与基层发生硫酸盐盐渍化，硫酸钠盐在温度降低时结晶形成10H2O硫酸钠，体积发生膨胀，是额济纳地区已建公路产生横向凸隆起病害的重要原因；风积沙路基在最佳含水率条件下压实成型初期，重力势是水盐迁移的主要动力，路基内初始均匀分布的水盐场在重力势作用下完成了重新分布，形成了路基内部初期的水分势与盐分梯度场，为后期路基土内盐分积聚发生盐渍化奠定了基础；风积沙路基内部的水盐迁移是由汽、液两态交互作用的结果，路基顶面浅层受温度影响剧烈区以水汽迁移方式为主；在影响薄弱区风积沙内无法形成有效的毛细水上升孔道，水分主要以薄膜水的形式进行迁移；基于沙漠区风积沙路基内水分的存在形式，对Richards水平衡方程进行修正，并在对流-弥散方程基础上建立了土壤溶质运移两区模型（TRM）考虑非均质土壤孔隙中存在的不动水体在溶质运移过程中所起的作用，更加真实反映一维热传导土壤水盐迁移的分布特征；风积沙路基盐渍化试验成果表明一般认为风积沙土层具有阻融盐分作用的观点是忽略了盐渍化时间效应，根据数值模拟与试验结果，建立了考虑路基内部初始含水率和初始含盐率并可预测路基发生盐渍化（以含盐率为0.3%为盐渍化界线）所用时间的回归方程；利用风积沙隔断层防止沙漠区防路基盐渍化的方法并不可取，风积沙中水汽和薄膜水的存大形式盐分的迁移提供了渠道和载体， 为了隔断路基下垫面地基的盐分向路基内部的迁入，宜在地基表层铺设阻止形成水汽与薄膜水携带盐分迁移条件的碎石隔断层，而不是毛细水隔断层。