Test speed and other factors affecting the measurements of tree root properties used in soil reinforcement models

Measured values of the mechanical properties of tree roots are found to be affected by a number of factors. Shear properties of tree roots are found t o be partly influenced by size of the testing equipment. level of soil comp action. deformation of the root material and estimated width of the shear z one in the soil etc. Among others. tensile root properties are found to be affected by factors such as season, age, root types or species, root prepar ation before experiment, clamping procedure of the root, and rate of elonga tion used. The aims of this paper were (1) finding an appropriate clamping procedure for root measurements: and (2) studying the effect of elongation rate on stress-strain relationships of beech (Fagus sylvatica L.) roots. It was found that problems associated with root clamping (i.e., in root exper iments) such as breakage of the root sample close to the jaws of the clampi ng devices and slippage may be eliminated by introducing wooden blocks of a ppropriate hardness within the jaws of the clamps and exerting a suitable c lamping force, respectively. An appropriate wood hardness and suitable clam ping force were found by conducting a number of initial trial experiments. Tensile experiments conducted with beech roots pairs showed that elongation rate does influence the stress-strain relationships of roots. In general, stress values of beech roots were found to increase between 8 and 20% for a n increase in the rate of elongation from 10 to 400 mm/min. Similar finding s have been reported in textile fibres. (C) 2001 Elsevier Science B.V. All rights reserved.