全吸力范围生物炭−黏土混合土的土−水特性

土−水特征曲线在研究非饱和土的水力与力学特性中发挥着重要的作用。生物炭具有多孔结构、高比表面积和强吸附的特性。将生物炭改性土应用于垃圾填埋场上覆盖层，因受自然环境因素的影响会使其水力特性发生改变。为了研究全吸力范围内生物炭掺量对生物炭−黏土混合土保水特性的影响，利用蒸汽平衡法（吸力范围 3～368 MPa）、滤纸法（吸力范围 0 ～40 MPa）和压力板法（吸力范围 0～1.5 MPa）控制土样的吸力，测定吸力平衡后土样的含水率和饱和度，得到全吸力范围内生物炭−黏土混合土的土−水特征曲线。试验结果表明：（1）3种吸力测试方法很好地表达了生物炭−黏土混合土全吸力范围内的土−水特征曲线。（2）生物炭能够影响黏土的保水性，但在一定的吸力范围内，生物炭−黏土混合土的保水性还与孔隙结构和孔隙中水的形态相关。（3）通过压力板法测得，试样的进气值随着生物炭掺量的增加而减小。当吸力值小于进气值时，曲线出现水平段，土样始终处于饱和状态，生物炭掺量越大，试样的保水性越好。（4）由生物炭−黏土混合土微观孔隙结构以及生物炭在黏土中的分布形态来解释生物炭改性黏土的保水能力随生物炭掺量的变化关系。

Soil-water characteristic of biochar-clay mixture in the full suction range

Soil-water characteristic curve (SWCC) plays an important role in defining the hydro-mechanical behavior of unsaturated soils. Biochar has the properties of porous structure, high specific surface area and high adsorption. The hydraulic characteristics of biochar-amended soil may change due to the influence of natural environmental factors when applied as the cover layer of landfills. In order to study the effect of biochar content on the water retention behavior of biochar-clay mixture in full suction range, the suction of samples was controlled by vapor equilibrium technique (suction range 3–368 MPa), filter paper method (suction range 0–40 MPa) and pressure plate method (suction range 0–1.5 MPa), and the water content and saturation degree of samples after suction equilibrium were determined. The soil-water characteristic curve of biochar-clay mixtures was obtained in the full suction range. The results showed that: (1) The soil-water characteristic curve in the full suction range of biochar-clay mixtures was effectively expressed by the three suction testing methods. (2) Biochar can affect the water retention behavior of clay, but within a certain range of suction, the water retention behavior of biochar-clay mixtures was also related to the pore structure and the morphology of water in the pores. (3) As measured by the pressure plate method, the air intake value of samples decreased as the biochar content increased. When the suction value was less than the air intake value, a horizontal section appeared in the curve, and the samples were always in the saturated state. The greater the content of biochar, the better the water retention of the sample. (4) The relationship between the water retention capacity of biochar-amended clay and biochar content was explained by the microscopic structure of the biochar-clay mixture and the distribution form of biochar in clay.