基于表层含水量控制的膨胀土植绿陡坡研究

The more gradual slope seems more stable. But expansive soil is a highly water-sensitive special soil. Widely exists in nature of expansive soil gentle slope continued to slide and very stable plant slope of expansive soil. According to bionics idea, firstly, natural expansive soil slope with plant conducts a two-year in-situ observation. Fixed slope geometry and soil parameters, the influences of complex climate conditions on the shallow water content are further discussed. The observation results will provide the contrast basis for the later model test, numerical calculation and theoretical analysis. By indoor test, the influence law of saturation degree on the physical and mechanical parameters of soil is discussed and the relationship between water content of expansive soil cracking and plastic limit is proposed. The use of plant root and stem to maintain moisture and reduce transpiration, supplemented by drip irrigation technology, ensure the plant slope surface does not appear fracture, thus the surface at a very low state of expansive soil permeability, so expansive soil surface becomes impermeable membrane. Using model tests and numerical analysis, under the typical weather conditions, the influences of the stability of the slope, slope length, plant and soil parameters on expansive soil slope with plant are discussed, and design method for expansive soil slope with pant based on shallow water content of control is proposed. This study will develop the expansive soil practical theory, also conforms to the ideas of the city sponge; Steep slope is relatively gentle slope, can reduce the amount of fill and covers an area of, also have important economic and social value.

边坡似乎越缓越稳，但膨胀土是一种水敏性强的特殊土，自然界也存在持续滑动的膨胀土缓坡和稳定的膨胀土植绿陡坡。根据仿生学原理，首先对天然膨胀土植绿陡坡开展为期两年的原位观测，探讨复杂气候条件对膨胀土表层含水量影响的规律，为后期模型试验、数值计算和理论分析提供比照依据；采用室内试验，探讨饱和度对膨胀土物理力学参数影响的规律，建立膨胀土开裂含水量与塑限的关系，提出膨胀土表层含水量控制指标；利用植物根系和茎叶保持水分和减少蒸腾，并辅以滴灌技术，确保膨胀土植绿陡坡表层不出现裂隙，从而其渗透性处于极低状态，这样表层膨胀土就可作为防渗膜；采用模型试验和数值分析，探讨典型气候条件下坡度、坡长和土体参数等对膨胀土边坡稳定性的影响，提出基于表层含水量控制的膨胀土植绿陡坡设计方法。本研究将发展膨胀土实用化理论，亦符合海绵城市的思想；陡坡相对缓坡，可减少填方量和占地，亦具有重要的经济和社会价值。

膨胀土是在自然地质过程中形成的富含亲水性矿物的粘土，其吸水膨胀、失水收缩，分布范围广、工程危害大。膨胀土边坡一旦失稳，会影响公路、铁路的正常运营，甚至威胁到人民的生命财产安全。当前很少有人从控水保湿角度对膨胀土边坡进行防护，本课题在前期研究基础上提出基于表层含水量控制的膨胀土边坡实用轻量化防护方法，根据已有研究成果总结出膨胀土边坡的失稳机理,通过控制边坡表层土体的水分变化来限制土体强度弱化及裂缝开展。围绕膨胀土在水分影响下的物理力学特性，开展了不同初始湿度及不同吸湿量的膨胀土物理力学室内试验；在膨胀土边坡的裂隙及湿度影响因素方面，开展了室内开裂含水量及模型边坡径渗流试验；在边坡表层的防渗保湿技术方面，进行了滴灌及客土层覆盖保湿数值模拟及现场试验。结果表明，膨胀土的强度参数随含水量增大而减小，但其初始含水量过低时，土体吸水膨胀软化更严重，对边坡稳定更为不利，采用植绿、陡坡、客土层覆盖等措施能较好得保持膨胀土边坡土体含水量处在相对稳定的范围之内。本研究设计出基于表层含水量控制的膨胀土边坡防护方法，取得了较好的应用和推广，也创造了一定的经济价值和社会效益。