基于流变学法研究容重和含水率对土壤结构力学稳定性的影响

土壤结构力学稳定性不仅与土壤质量和肥力密切相关，而且还与农业器具设计和农业水土工程建设紧密联系。该研究以黄土高原广泛分布的塿土和黄绵土为研究对象，采用振幅扫描试验模拟振荡荷载过程，研究土壤容重和含水率对土壤结构力学稳定性的影响。结果表明：1）随土壤容重的增加，土粒间接触点增多，使得剪切强度参数：线性黏弹区的剪切应力、屈服点的剪切应力、最大剪切应力及屈服点的储能模量均增加，土壤结构强度增强；其在较大剪切应变下的弹性和总的弹性（屈服点的剪切应变和积分z）先增大后降低，表明土壤颗粒存在一个最稳定的排列组合方式。同时，剪切强度参数对土壤容重的响应更为敏感。2）随含水率的增加，土壤颗粒间黏聚力和摩擦力降低，剪切强度参数：线性黏弹区的剪切应力、屈服点的剪切应力、最大剪切应力及屈服点的储能模量均降低，土壤结构强度降低；当剪切应变在线性黏弹区时，弹性随含水率的增加而增加，而较大的剪切应变下的弹性和总的弹性随含水率增加均降低。3）对比2种土壤，因塿土的黏粒、有机质、阳离子交换量、比表面积等较高，增加了土粒间的胶结强度，使得塿土的弹性和剪切强度较高，而黄绵土结构更具脆性。该研究结果表明基于流变仪中的振幅扫描测试所获取的流变学参数能够定量表征土壤细观结构力学稳定性，为进一步深入认识土壤微观力学特性提供了丰富的评价参数。

Effects of soil bulk density and water content on the mechanical stability of soil structure using rheological method

Mechanical stability of soil structure determined the scour resistance, erodibility, collapsibility, slope stability, and foundation stability of the soil, even the large-scale agricultural instruments, as well as irrigation and water conservancy projects. Alternatively, rheology has widely been one part of soil physical characterization under deformation. The rheological parameters can be utilized to clarify the highly complex soil process, including the most significant soil aggregation factors, such as soil bulk density and water content. In this study, the widely distributed Lou soil and loessal soil on the Loess Plateau were selected as the research objects. An amplitude scanning test was selected to simulate the oscillation load process. An investigation was made on the effect of soil bulk density and water content on the mechanical stability of soil structure under the oscillation load. The results show that: 1) The soil density increased the contact point between soil particles, leading to the increasing cohesion and friction between particles. The shear strength parameters were all increased, including the shear stress at the linear viscoelastic region, the shear stress at yield point, the maximum shear stress, and the storage modulus at the yield point, as the increase of soil bulk density, indicating the increase in the stability of soil structure. In terms of viscoelastic parameters, the shear strain at the linear viscoelasticity region and the maximum shear stress decreased, whereas, the shear strain at yield points and integral zone increased first and then decreased, with the increase of soil bulk density. Soil particles were under the most stable way of organization and combination (1.3 g/cm3). Shear strength parameters with the change of soil bulk density were more sensitive than viscoelastic parameters. 2) As the increase of soil water content, the shear strength parameters presented the decreasing trends, including the shear stress at the linear viscoelastic region, the shear stress at yield point, the maximum shear stress, and the storage modulus at the yield point, indicating the decreased stability of soil structure. In viscoelastic parameters, the shear strain at the linear viscoelasticity region increased with the increase of water content, but the shear strain at yield point and integral zone decreased. It indicated that the cohesion and friction between soil particles decreased, with the increase of soil water content. The higher water content of soil particles decreased the relative sliding resistance between particles, leading to the deterioration of soil structural stability. 3) The elasticity and shear strength of Lou soil was higher than that of Loessal soil. This was mainly because Lou soil contained a higher content of clay, organic matter, cation exchange capacity, and specific surface area than those of Loessal soil, indicating the improved cementation strength between soil particles. Consequently, the rheological parameters from the amplitude scanning test in the rheometer can be used to quantitatively characterize the mechanical stability of soil structure, providing for rich evaluation parameters to further understand the micromechanical properties of soil. The finding can provide a shred of strong scientific evidence for agricultural water and soil engineering design, as well as the prevention and control of landslide and geological disasters in the Loess Plateau.