The tensile strength of loess is important for the tension-related crack and failure in the Loess regions. While the previous work on the tensile strength of loess mainly focuses on the test method and its variation with different internal and external factors, the micro-mechanical characteristics of the tensile experiments are seldom studied. Taking the unconfined penetrated test (UP test) as example, the tensile strengths and internal stress distributions of undisturbed loess samples under the loading plate-sample ratios (d/D) ranging from 0.05 to 0.95 are numerically investigated using discrete element method. The internal stress distribution, failure pattern of sample and variation of internal crack are clearly reflected by the discrete element modelling. The DEM simulation results also show that: 1) the d/D in the range of 0.15 to 0.35 is recommended for measuring the tensile strength of undisturbed loess; 2) the tensile strength of undisturbed loess increases with d/D recommended above ;3) the failure of sample is mainly controlled by the tensile stress when the d/D is equal or lower than a critical d/D 0.50, while that is mainly controlled by the compressive stress when the d/D is larger than a critical d/D 0.50. This study shows the capability of discrete element method to simulate the UP test, thereby providing us a relatively reliable way to investigate the tensile strength of loess numerically and to explore the internal stress and crack distribution of soil sample.

黄土的抗张强度对于黄土地区与张力有关的裂缝和破坏很重要。尽管以前关于黄土抗张强度的研究主要集中在黄土的试验方法及其随内部和外部因素的变化，但很少研究抗张试验的微观力学特性。以无侧限渗透试验（UP试验）为例，采用离散元法数值研究了在荷载板样比（d / D）为0.05〜0.95的条件下，原状黄土的抗拉强度和内应力分布。离散元素建模清楚地反映了内部应力分布，样品的破坏模式和内部裂纹的变化。DEM仿真结果还表明：1）d / D在0.15到0的范围内。建议使用35来测量原状黄土的抗张强度；2）未扰动黄土的抗拉强度随上述d / D的增加而增加; 3）当d / D等于或低于临界d / D 0.50时，样品的破坏主要由拉伸应力控制，而主要是当d / D大于临界d / D 0.50时，受压应力控制。这项研究表明了离散元法模拟UP试验的能力，从而为我们提供了一种相对可靠的方法，可以对黄土的抗张强度进行数值研究，并探索土壤样品的内部应力和裂缝分布。3）当d / D等于或低于临界d / D 0.50时，样品的破坏主要由拉伸应力控制，而当d / D大于临界d时，样品的破坏主要由压缩应力控制。 / D 0.50。这项研究表明了离散元法模拟UP试验的能力，从而为我们提供了一种相对可靠的方法，可以对黄土的抗张强度进行数值研究，并探索土壤样品的内部应力和裂缝分布。3）当d / D等于或低于临界d / D 0.50时，样品的破坏主要由拉伸应力控制，而当d / D大于临界d时，样品的破坏主要由压缩应力控制。 / D 0.50。这项研究显示了离散元法模拟UP试验的能力，从而为我们提供了一种相对可靠的方法，可以通过数值方法研究黄土的抗张强度，并探索土壤样品的内部应力和裂缝分布。