A moving wheel load induces a principal stress rotation (PSR) in pavement foundation geomaterials including subgrade/subbase soils. Simulating such a stress condition is not possible with stress path tests conducted with conventional cyclic triaxial (CT) equipment. More complex stress paths such as a heart-shaped stress path are required to determine the deformation characteristics of these under a PSR. A heart-shaped stress path can be simulated on a soil specimen in cyclic hollow cylinder (CHC) tests via user-defined waveforms for its stress components (axial stress, and torsional shear stress). In this study, a series of CT and CHC tests were performed to analyze the impact of a PSR on strain behaviors of medium-dense sand-clay mixtures. The specimens contained 0%, 5%, 10%, and 20% clay by weight and were prepared at an initial relative density of 50%. All specimens were anisotropically consolidated under K₀≈0.5. It was determined that all CT specimens underestimated the strain performances (both axial strain and shear strain) of the sand-clay mixtures. On the other hand, a heart-shaped stress path was simulated successfully in CHC tests and thus, all specimens yielded more accurate strain results. At low clay content (≤10%), the impact of a PSR on strain performances of the sand-clay mixtures was observed to be less (axial strain (ε_z) < 0.12%, and shear strain (γ_zθ) < 0.8% after number of load cycles (N) = 5000) due to the low stress ratios (CVSR = 0.15 and η = 1/3). On the other hand, despite the low stress ratios, a PSR caused a rapid increase in axial strain and shear strain (ε_z = 5%, and γ_zθ > 0.8%) of the specimen containing 20% clay, which resulted in the failure of the specimen at N = 478. Results of this study clearly indicated that the effect of a PSR should be taken into consideration while evaluating the strain characteristics of the sand-clay mixtures that contain clay particularly at high contents (≥20%) under traffic loads.

移动的车轮载荷会在包括路基/底基层土壤在内的路面基础土工材料中引起主应力旋转 (PSR)。使用传统的循环三轴 (CT) 设备进行应力路径测试是不可能模拟这种应力条件的。需要更复杂的应力路径，如心形应力路径，以确定这些在 PSR 下的变形特性。在循环空心圆柱体 (CHC) 测试中，可以通过用户定义的应力分量（轴向应力和扭转剪切应力）波形在土样上模拟心形应力路径。在这项研究中，进行了一系列 CT 和 CHC 测试来分析 PSR 对中密度砂粘土混合物应变行为的影响。试样含有 0%、5%、10%、和按重量计 20% 的粘土，并以 50% 的初始相对密度制备。所有试样均在以下条件下各向异性固结K ₀ ≈0.5。确定所有 CT 试样都低估了砂粘土混合物的应变性能（轴向应变和剪切应变）。另一方面，在 CHC 测试中成功模拟了心形应力路径，因此所有试样都产生了更准确的应变结果。在低粘土含量（≤10%）下，观察到 PSR 对砂粘土混合物应变性能的影响较小（轴向应变 ( ε _z ) < 0.12%，剪切应变 ( γ _zθ ) < 0.8%）负载循环（数后ñ）= 5000）由于低应力比（CVSR  = 0.15和η = 1/3）。另一方面，尽管应力比较低，但 PSR 导致 含有 20% 粘土的试样的轴向应变和剪切应变（ε _z  = 5%，γ _zθ > 0.8%）迅速增加，导致失效N  = 478处的试样。本研究的结果清楚地表明，在评估包含粘土的砂粘土混合物的应变特性时，应考虑 PSR 的影响，特别是在交通条件下，粘土含量较高（≥20%）负载。