Assessing the accuracy of simple field based root strength measurements

Root reinforcement of slopes is a key control on landslide triggering, yet remains difficult to measure. Dozens of studies have utilised a wide range of testing methods to understand the tensile strength properties to estimate root reinforcement. We present a systematic attempt to evaluate the simple and efficient field spring scale method. This study compared different testing methods to assess the strength of Picea sitchensis roots. We tested roots in the field using a spring scale and with two different pre-treatments in the laboratory using a universal testing machine. Root strengths were assessed under different testing conditions in laboratory and field experiments using different pre-testing treatments, stress concentration at clamps, and spacer types. Tensile strengths measured in the laboratory and field, with different spacers and clamping stress concentrations were not significantly different in our testing. Roots that were incompletely rehydrated after being dried were significantly stronger than wetter roots, suggesting moisture is one of the dominant controls on root strength. Our results suggest that there is a large range of natural variability in root tensile strength. The field-based, spring scale method produces results that are indistinguishable from those of more precise universal testing machines.