交通荷载下宁夏滨河粉细砂路基变形机理研究

To adapt to the rapid development of economy and tourism in the surrounding area of the Yellow River, it has been built Riverside Avenue at the top of the standard flood protection embankment. The subgrade is made up of silty fine sand with a little silty soil. On both sides of the subgrade are the Yellow River and farmland, and the subgrade has been saturated. The engineering practice shows that the Riverside Avenue has significantly arose non-uniform settlement under the traffic load. Although the mechanism of settlement is more complex. However, this is likely that the drainage conditions of the subgrade with mixed silty soil are poor in closed semi-infinite space, the pore water pressure increases rapidly for this subgrade under the traffic load, which results in the decrease of the effective stress between the soil particles. In order to find out the nature of the subgrade settlement and propose the feasible treatment plan should be studied from the following three aspects: The specific method is first carried out investigation of subgrade, experimental study for engineering property of subgrade soil and embedded the number of a variety of sensors, in order to measure the data under various loading modes in-site. Followed by simplification of stress path in the laboratory, the main features of the stress path is the size and the direction for the traffic load in the subgrade should be cyclic changes, the main features of the stress path should be simplified to cardioid in two-dimensional space, the dynamic hollow cylinder apparatus(HCA-d) can obtain strength properties and pore water pressure of the saturated silty fine sand under the condition of principle stress rotation, this is a feasible method, further study the possibility of saturated silty fine sand liquefaction under the continue rotation of principal stress axis, And finally the elasto-plastic constitutive model of subgrade settlement is established to further study the deformation of subgrade under complex traffic load. It can provide effective solutions for the treatment and design of silty fine sand to be used for subgrade.

宁夏沿黄经济带在防洪堤坝顶部修建了以粉细砂填筑路基的滨河公路，该公路已在长期交通荷载下产生了由孔隙水压力上升引起的明显非均匀性沉降。为此，本项目首先对路基的工程特性进行勘察和试验，在路基中埋设孔隙水压力、压力和位移传感器。其次对实际路基中的应力路径进行必要的简化，利用空心圆柱仪和动三轴研究应力主轴循环旋转下饱和路基的孔隙水压力和液化的可能性。最后建立路基沉降的弹塑性本构模型，为研究各种交通荷载下堤坝路基的治理和设计提供经济有效的方案。

宁夏黄河沿岸地区集中了全区43%的土地、57%的人口、80%的城镇、90%的城镇人口，创造了宁夏90%以上的GDP。投资近50亿元的滨河大道，极大的改善了两岸的交通、产业和城市格局。滨河大道直接修建在防洪堤坝的顶部，路基土体主要是粉土或粉细砂。很多路段处在黄河和农田之间，路基含水量普遍较高，自通行以来路面整体龟裂严重。.项目的研究意义是弄清路基在交通荷载下变形的机理，重要的研究结果表明：滨河大道路基土的粒径大于75um和小于5um 的分别占全重的 14.0%和7.1%；液限和塑性分别为27.58%和20.13%，塑性指数为7.45，是典型的粉土，工程性质较差。土壤中阴离子以氯离子为主导，硫酸根离子次之，阳离子中钠离子占主导，镁离子和钙离子较次之，主要以离子化合物NaCl为代表，含盐量为 2.93%，是典型的中氯盐渍土。在三轴固结不排水实验中发现：应变在2%以内孔隙水压力快速增长。当围压较小时，盐分胶结封闭的空间开始充水，盐渍土的孔隙水压力很快发展为负孔隙水压力。随着围压的增加，颗粒间变得更加紧密，孔隙水压力没有出现低围压那样的负孔隙水压力。盐渍土较洗盐土的强度高出1.3~1.67倍，孔隙水压力几乎一致小于洗盐土。固结排水实验中发现在相同围压下排水强度一致高于不排水强度，盐渍土较洗盐土的强度高出1.0~1.26倍，当围压逐渐增大时，盐渍土体积变形逐渐由剪涨变化为剪缩。交通荷载下对盐渍土和洗盐土的滞回特性、应力应变关系和孔隙水压力增长进行了对比研究。动载条件下盐渍土的孔隙水压力增长比洗盐土快很多，主要的原因动载加载速度快，易溶盐和中溶盐来不及溶解，孔隙水压力随着剪应变快速增长。根据路基土的静力和动力特性，建立了一个能反映主应力轴旋转的非共轴弹塑性模型，能合理预测路基土的力学特性。对滨河路基的治理和再设计提出了一个在路堤中增加砾石减少孔隙水压力产生的研究报告。