Simulation of Vegetative Induced Deformation in an Unsaturated Soil (original) (raw)

Parametric evaluation of tree root water-uptake effect on ground movement

International Journal of Physical Sciences, 2011

A model is a tool that simulates the reality through simplification by ignoring what is not important. Therefore, assumptions are usually involved, prompting the need for parametric analysis for identification of the responsive parameters with respect to the numerical simulation results. A negative pore-water pressure was estimated through two-dimensional governing equation for unsaturated soil in an axi-symmetrical form due radial nature tree roots water-uptake. The results of the root wateruptake analysis are then used as an input for the prediction of ground displacements in a stressdeformation analysis. The proposed method was studied and tested against data collected on a case history involving a mature Lime tree on Boulder clay at Stacey Hall, Wolverton, England and mechanical properties of Boulder Clay. The results of the analysis showed that the predicted ground displacement is sensitive to all the parameters tested. Initial time step sizes analysis showed that the results differs not more than ±5% indicating there are no problems with convergence. These results suggest that accurate measurements of these parameters would be necessary for the study of ground displacement due root water-uptake.

Trees, soil moisture and foundation movements

Computers and Geotechnics, 2009

Trees growing close to buildings in urban landscapes may change the soil moisture around foundations, producing shrinkage and swelling. This paper presents a numerical solver to estimate the movements resulting from these volumetric strains. This tool will be of assistance in both designing the footings of new buildings and in the analysis of damage associated with buildings that have already been constructed. The conceptual model used is based on current knowledge of the hydro-mechanical behaviour of unsaturated soils. Its numerical implementation is simple, making it easy for users to make changes as they see fit. The program has been verified, validated, and applied in a real stabilization problem.

Numerical and experimental modeling of geomechanical behavior of partially saturated soils

International Journal of Geo-Engineering

The Barcelona Basic Model (BBM) has been implemented in a finite difference-based computer program to simulate the behavior of unsaturated soils subjected to wetting. The BBM implementation was verified using analytical solutions, and the proposed model has been used to simulate the response of a compacted embankment under complete saturation and suction induced conditions. Numerical analyses indicate that considerable amount of total and differential settlements could develop at the top surface of the embankment. BBM is executed into FLAC2D extending a defined module for modified Cam Clay (MCC) and has been set up an analytical solution for suction-dependent stress and strain. Evaluating the effect of anisotropy and nonlinear apparent tensile strength in unsaturated soils, a modification to BBM formulation has been proposed and optimized by developing numerical analyses to reduce the size of elastic region of loading collapse (LC) curve. Then, an experimental study in the literatur...

Bioengineering ground improvement considering root water uptake model

Ecological Engineering, 2010

Bioengineering features of native vegetation are currently being evolved to enhance soil stiffness, slope stabilisation and erosion control. The effects of tree roots on soil moisture content and ground settlement are discussed in this paper. Matric suction induced by tree roots is a key factor, governing the properties of unsaturated soils, directly imparting stability to slopes and resistance for yielding behaviour. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters has been developed. This study highlights the interrelated parameters contributing to the development of a conceptual evapo-transpiration and root moisture uptake equilibrium model that is then incorporated in a comprehensive numerical finite element model. The developed model considers fully coupled-flow-deformation behaviour of soil. Field measurements obtained by the Authors from a site in Victoria, South of Australia, are used to validate the model. In this study, the active tree root distribution has been predicted by measuring soil organic content distribution. The predicted results show acceptable agreement with the field data in spite of the assumptions made for simplifying the effects of soil heterogeneity and anisotropy. The results prove that the proposed root water uptake model can reliably predict the region of the maximum matric suction away from the tree axis.

Parametric modeling of root length density and root water uptake in unsaturated soil

Turkish Journal of Agriculture and Forestry, 2010

The problem of water movement through the root zone has attracted increasing interest during the last few decades. In this research, the spatial and temporal pattern of root water uptake in wetted soil was studied in the root zone of a 6-year-old apple tree. An important part of the root water uptake model is root length density, which was measured by sampling soil cores in one quarter of the root zone. The exponential model better described the observed apple root distribution. The measured data were compared against the outputs of the root density distribution model. A normalized root length density was used to simulate root water uptake and determine the effect of root distribution on the water content pattern. A 2-dimensional (2D) model of root water uptake was established, which includes root density distribution function, potential transpiration, and the soil water stress-modified factor. Root water uptake distribution was measured with an array of time domain reflectometry (T...

A Method for Simulation of Upward Root Growth Pressure in Compacted Sand

Arboriculture and Urban Forestry, 2011

In order to model the impacts of tree root growth under pavement as a layered design, the behavior of the components need to be defined or assumed. Since the behavior of materials and the design of pavement sections work on the presumption of loading from the pavement surface downward, it is reasonable to check engineering behavior assumptions with a testing method for controlled loading upward from a growing perennial root. A root simulation was developed to inflate with water to known input pressure. Sand displacement in response to increasing input pressure was tracked over several sand density-moisture level pairings. Load cells tracked the translation of sand displacement to load at a simulated pavement surface to develop data plots of a line-load spreading wider with increasing distance between root and pavement. The results from the laboratory experiments were compared to the results from numerical simulations using finite elements to develop better understanding of the mechanisms of load generation due to the root growth. Sand was modeled as a Mohr-Coulomb type material for that purpose. The numerical results are qualitatively in agreement with the experimental results.

Numerical analysis of matric suction effects of tree roots

Proceedings of the ICE - Geotechnical Engineering, 2006

The use of native vegetation in the coastal regions of Australia has become increasingly popular for stabilising railway corridors built over expansive clays and compressive soft soils. The tree roots provide three stabilising functions: (a) they reinforce the soil; (b) they dissipate excess pore pressures; and (c) they establish sufficient matric suction to increase the shear strength. The matric suction generated within the tree root zone propagates radially into the soil matrix, as a function of the moisture content change. Considering soil conditions, the type of vegetation and atmospheric conditions, a mathematical model for the rate of root water uptake is developed. A conical shape is considered to represent the geometry of the tree root zone. Based on this model for the rate of root water uptake, the pore water pressure distribution and the movement of the ground adjacent to the tree are numerically analysed. Field measurements taken from the previously published literature are compared with the authors' numerical predictions. It is found that, given the approximation of the assumed model parameters, the agreement between the predicted results and field data is still promising. The study indicates that native vegetation improves the shear strength of the soil by increasing the matric suction, and also curtails soil movements.

Simulation of soil water dynamics in structured heavy soils with respect to root water uptake

Biologia, 2006

In agricultural lands has the soil moisture uptake from the root system a significant effect on the water regime of the soil profile. In texturally heavy soils, where preferential pathways are present, infiltrated precipitation and irrigation water with diluted fertilizers quickly penetrate to a significant depth and often reach an under-root zone or even the groundwater level. Such a scenario is likely to happen during long summer periods without rain followed by heavy precipitation events, when a part of the water may flow through desiccated cracks. Since 2001 the effects of drip irrigation and nitrogen fertilization of potatoes (Solanum tuberosum L., cultivar Agria) have been monitored within the frame of a research project at the experimental site Valecov (Czech Republic). Based upon the measured data an attempt has been made to simulate the water regime of the soil profile at a selected experimental plot, considering the impact of preferential flow and root water uptake. The dual-permeability simulation model S 1D Dual was used for the simulation. The soil hydraulic parameters were inversely determined using Levenberg-Marquardt method. Measured and simulated pressure heads were utilized in the optimization criterion. The scaling approach was applied to simplify the description of the spatial variability of the soil profile. The results of simulations demonstrate that during particular rainfall events the water reaches significant depths of the soil profile via preferential pathways. The effect of the root zone is dominant during dry periods, when capillary water uptake from the layers below roots becomes important. This should be taken in account into the optimization of the drip irrigation and nitrogen fertilization schedule.