考虑毛细与吸附作用的黏土干缩开裂过程离散元模拟

DEM simulation of desiccation cracking in clay considering capillarity and adsorption

黏土干缩开裂过程中土颗粒间的作用非常复杂,导致难以从颗粒层面对干缩裂缝的形成机理开展定量研究。基于非饱和土中的吸应力曲线,明确区分黏土中的毛细与吸附作用,在此基础上建立考虑黏土颗粒间吸引力随含水率变化的离散元接触模型,开展黏土干缩开裂的数值模拟,并与室内试验结果进行对比。结果表明,数值模拟得到的裂缝形态、裂缝发育历程、土样应变均与室内试验较为吻合,验证了离散元接触模型的可靠性。对模拟结果的进一步分析发现:①在黏土干缩开裂过程中,毛细与吸附作用共同发挥效果。随着含水率的降低,吸附作用的影响逐渐超过毛细作用。在吸附作用占优阶段,模拟土样的土颗粒沿裂缝分布方向的平均位移为最终位移值的73%。②土颗粒间总接触数量随含水率的降低先减少后增加。③在毛细/吸附作用占优阶段,土颗粒间的物理接触力会迅速增加并引起应力集中,土颗粒间接触因此集中断开进而形成裂缝。

The interaction between clay particles during the process of desiccation cracking is highly complex,making it challenging to conduct quantitative researches on the formation mechanism of cracks at the particle level.The capillarity and adsorption in clay is distinguished based on the suction stress characteristic curve(SSCC)in unsaturated soils.A contact model of discrete element method(DEM)that accounts for the change of attraction between clay particles with water content is then established,and the numerical simulation of desiccation cracking in clay is carried out.The simulated results are compared with those of laboratory tests,and the findings indicate that the crack morphology,crack development history and strain of the soil sample obtained by the DEM simulation are in good agreement with the laboratory results,verifying the reliability of the DEM model.Further analysis of the simulated results reveals that:(1)The capillarity and adsorption both play a role in the desiccation cracking process of clay.With the decrease of water content,the effects of adsorption gradually exceed those of capillarity.At the dominant stage of adsorption,the average displacement of simulated soil particles along the crack distribution direction accounts for 73%of its final value.(2)The total contact number between soil particles initially decreases and then increases as water content decreases.(3)The physical contact force between soil particles will increase rapidly at the dominant stage of capillarity/adsorption,resulting in stress concentration,and the contact between soil particles will be centralized and cracks will be formed.The proposed DEM contact model is of significant physical implications and can offer valuable insights into the underlying mechanisms of desiccation cracking in clay at the particle level.