Distortion of soil from shear stresses during field traffic may be even more damaging to soil functions than compression related to isotropic stresses. A torsional shear test was applied to undisturbed topsoil samples drained to either of six matric potentials (range -30 to -300 hPa) and tested at either of six normal loads, NL (range 30–180 kPa)(Series A). Soil clay and organic matter (SOM) content ranged 0.038−0.157 and 0.021−0.033 kg kg⁻¹, respectively. Bulk density (BD) varied from 1.19 to 1.71 g cm^-3. The preload suction stress, PSS, was calculated as the product of soil pore water saturation and the water suction in hPa. PSS ranged from 17 to 234 hPa. Data from two independent data sets with contrasting soil texture (Series B: loess soil) or management (Series C: long term fertilization) but tested with the same methodology were included for validation of prediction equations established from Series A soils. Multiple regression revealed that soil cohesion taken as the intercept term in a linear regression of shear strength, τ, and applied NL correlated positively to PSS, BD and SOM, while the internal friction estimated as the slope in regression was poorly explained by soil properties. A model combining NL in tests with PSS, clay, BD and SOM accounted for more than 90 % of the variation in τ and is suggested as a pedotransfer function (ptf) for prediction of τ for given soil and loading conditions. The model predicted well τ measured in Series B and C soils. Also subsoil τ measured for similarly textured samples was reasonably predicted by the suggested ptf. In accordance with theory, PSS seems to be a key driver of soil mechanical strength. More measurements of soil shear strength and further studies of the effect of PSS are encouraged.

与各向同性应力相关的压缩相比，在野外运输过程中土壤因剪应力而变形可能对土壤功能的损害更大。扭剪试验应用于排水至六个基质电位（范围为-30至-300 hPa）中的未扰动表土样品，并在六个正常载荷NL（范围为30–180 kPa）中进行测试（A系列）。土壤黏土和有机质（SOM）含量分别为0.038-0.157和0.021-0.033 kg kg ^-1。堆积密度（BD）从1.19到1.71 g cm ^-3。将预负荷吸力PSS计算为土壤孔隙水饱和度与吸水力（以hPa为单位）的乘积。PSS范围从17到234 hPa。来自两个具有对比土壤质地（B系列：黄土）或管理（C系列：长期施肥）但使用相同方法测试的独立数据集的数据用于验证从A系列土壤建立的预测方程式。多元回归分析表明，土壤内聚力作为抗剪强度τ线性回归中的截距项，施加的NL与PSS，BD和SOM正相关，而内部摩擦估计为回归坡度时，土壤特性很难解释。将测试中的NL与PSS，黏土，BD和SOM占τ变化的90％以上，建议作为给定土壤和负荷条件下τ预测的pedotransfer函数（ptf）。该模型预测了在B系列和C系列土壤中测得的τ井。建议的ptf还可以合理地预测针对相似纹理的样品测得的地下土壤τ。根据理论，PSS似乎是土壤机械强度的关键驱动力。鼓励更多地测量土壤抗剪强度，并进一步研究PSS的效果。