Gewählte Doctoral Thesis:
Samira Ladjal
(2013):
Scale effect of cavity expansion in soil with application to plant root growth.
Doctoral Thesis  Institut für Geotechnik (IGT),
BOKUUniversität für Bodenkultur,
pp 117.
UB BOKU
obvsg
FullText
Data Source: ZID Abstracts
 Abstract:
 A procedure for analyzing the expansion of spherical cavities in cohesivefrictional and in cohesionless materials is described. The aim is to provide a theoretical Framework based on a constitutive law with highorder strain gradient, which takes the microstructure of soil into consideration. It is demonstrated that the Penetration pressure required to expend a cavity in soil depends on the ratio between the cavity size and the mean grain diameter of the soil particles. The need for these highorder
formulations originates from the inability of the classical plasticity Framework to account for the underlying microstructure and to explain the observed size effects. According to the classical theory of cavity expansion, the expansion pressure remains independent of the cavity size since the governing equations is written in a dimensionless form, predicting for all the geometrically similar cavities the same limit pressure. To validate the theory, laboratory experiments with 2, 5 and 10
mm penetrometer diameters are performed on loose and dense sand. Comparison between experimental results and calculations yields a good agreement for the penetration cone resistance with coecients of determination of 0.97 and 0.85 for loose and dense sand respectively .
The above theoretical models have some interesting implications for the growth of root in soil with high impedance. The seminal roots of most plants thicken when growing into soil with higher mechanical impedance. This study provides a further explanation to root thickening, an increase in root diameter may give rise to reduced penetration pressure. This implies that enhanced penetration can be obtained by root thickening even when the turgor pressure remains unchanged.

Betreuer:
Wu Wei

1. Berater:
Wang Yongqi

2. Berater:
Bergmeister Konrad