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Reinforced Vegetation Numerical Evaluation of Slopes

Final Report Summary - REVENUES (Reinforced Vegetation Numerical Evaluation of Slopes)

The interaction of plants and soil and its effects on the stability of slopes is of great complexity and can be best analyzed by an integrated approach, taking both hydrological and mechanical considerations into account. Due to the soil’s multi-scale and multiphase nature (solid, fluid and air), the complex interaction among these phases in combination with the hydraulic boundary conditions introduced by the plant’s root system cannot be appropriately described by simple approaches.
The proposed research focuses on the advanced development and implementation of a comprehensive numerical tool to evaluate and calculate the qualitative and quantitative impact of plants on the stability of slopes, based on a combined approach of the influence of root reinforcement and the interaction with precipitation and evapotranspiration, on the factor of safety of slopes, its theoretical validation and its experimental verification. The ultimate scientific goal of this project is to elaborate a consistent physical model with robust numerical scheme to provide reliable predictions of the stabilizing effect of the plant-root system on slopes.
The general objective of the proposed project is to realize a complete numerical environment to transfer theoretical and experimental know-how in hydrogeological slope analysis into a validated tool that can be used in routine engineering practice. The project aims to address the need of tomorrow’s engineer’s studies based on a multidisciplinary hydrogeological and mechanical approach by combining sophisticated numerical analysis and a solid theoretical and empirical background.
The project “REVENUES”, an interdisciplinary network of research organisations and industrial partners, will achieve this goal by focusing on a set of scientific challenges aimed at the following objectives:
• Specify a constitutive model capable of capturing both the hydrological and mechanical behaviour of the soil-root system, including major influence factors such as water content, density and root tensile strength;
• Develop a theoretical model for the integrated simulation of both unsaturated slope failure and roots reinforcement action to quantify a potential failure;
• Establish a database of validation tests consisting of model tests in a geotechnical centrifuge with well-defined initial and boundary conditions;
• Perform laboratory element tests and establish database for model calibration;
• Perform and document instrumented field tests of real scale ecologically reinforced slopes under additional artificially induced precipitation carried out by the industrial partners;
• Examine climate effects on plant-soil water interaction;
• Integrate a software code into a software package, simulating the hydrological and mechanical effects of plants on slope stability;
• Define and disseminate best practice through simulations with numerical techniques of real benchmark events in practice;
• Publish best practice guides on numerical modelling and probabilistic analyses.
The major works performed and results achieved under this project:
The project was started officially on 1st January 2013. Project web site ( was operational from 1st March 2013. The kick-off meeting was organised on 7th - 8th March 2013 in Vienna. A review of the project work schedule for different work packages was presented, discussed and a common TOK plan was finalised in the meeting.
The 1st Consortium Meeting was held on 18th April 2013 in Vienna. During this meeting, recruitment of ER and schedule of secondments were finalised. An ER was recruited by BOKU for 24 months starting from 1st June 2013 and another ER was recruited by WSL for 18 months who started the assignment on 1st March 2014. The second Consortium Meeting was organised on 23rd of August 2013 in Munich. This meeting fixed some secondments and finalised the mode of payment and discussed about the coming workshop event in September 2013. A mid-term review meeting was organised on 22th -23rd October 2014 in Vienna. Thereafter, secondments of researchers were continued and work on different WPs also continued and finally about 90% of major tasks have been completed successfully by the end of the project. A final symposium was organised in Vienna on 20-21 October 2016 and the final project meeting was held on 21 October 2016. The total physical progress of the project is about 90% and the financial progress is 93%. All reports and deliverables have been prepared and submitted to the authorities in time and shared among partners.
The major achievements on different work-packages by the end of the project (till 31st December 2016) are summarized below.
WP1: Material behaviour of unsaturated soils and geo-reinforcements

The main goal of WP1 is to develop advanced constitutive models together with high quality test data for calibration and validation. Under this WP, preliminary soil data and data related to geo-reinforcements (vegetation) were acquired from different sources including partner institute’s databases and used in the numerical modelling for calibration and validation. The developed numerical code has been tested using the real site data and information. The report on reference soils with geotechnical properties, report on reference vegetation with strength properties, database of laboratory tests on reference soils (Deliverables: D.2 D.3 & D.4) have been prepared and shared among partners.
WP2: Numerical modelling of rainfall induced unsaturated slope failure and geo-reinforcements

The focus of WP2 is to develop a reliable numerical tool for the simulation of hydrologically-driven slope failures by continuum approaches taking into account the reinforcement action of vegetation. For this purpose, the thermodynamically based model has been applied in the formulation of a constitutive equation and its numerical implicit scheme of integration. In this model phase transitions are characterized by a discontinuity in chemical potential and a jump in the entropy value. This physical characteristic has been solved using the Laplace transform in the resolution of the differential equations system. The model has been implemented in the software ABAQUS and Comes Geo and it has been applied in the evaluation of the effects of vegetation in the slope stability. Roots have been modelled with a damage model that accounts for the pull-out and roots breakage. Reports on constitutive model for unsaturated soils and for geo-reinforcements (D.5 & D.6) report on numerical modelling (D.7 & D.8) and report on unified modelling of rainfall induced landslides and geo-reinforcement (D.12) have been prepared and shared among partners.
WP3: Model tests, case studies and best practice

Under this work package, the best practice in modelling and documenting the effects of plants on slope stability and Factor of Safety (FoS) have been worked out and some of them is already published. Case studies of some best practices in slope protection works are carried out and report has been prepared and shared among partners. BOKU has performed centrifuge model slope stability tests on saturated soil samples. A waterproofed container has been developed for centrifuge testing. The reconstitution technique for the model soil has been evaluated and optimized. A large number of centrifuge tests have been performed to evaluate the critical slope height for varying slope conditions. Failure of model slopes is induced by a continuous increase of the gravity-induced stress field. Soil parameters such as dry density, water content, and slope angle have been varied to investigate their role on the slope. A report on design and performance of soil bioengineering slopes stabilisation and a report on centrifuge model test on rainfall induced slope has been prepared and shared among partners (D.9 & D.10).
WP4: Communication and Dissemination

Under this WP, a project website was set up for the REVENUES network (Deliverable: D.1) which served both internal communication and dissemination (both internal and external). The website had been maintained well and timely updates had been carried out. The research results had been disseminated both internally and externally through paper publication and meeting and workshop events. A workshop was organised in Vienna on 9th-10th September 2013 and a Symposium was organised on 20-21 October 2016 as a dissemination and networking event. Similarly, a Seminar on "Soil Stability and Natural Hazards, from Knowledge to Action" was organised on 27th May 2016 in Birmensdorf, Switzerland by WSL. The other events like lectures, excursions and interaction meetings have also been organised. Seven peer reviewed papers haven already been published in a book.
Final results and their potential impact and use
Under this project, a constitutive model capable of capturing both the hydrological and mechanical behaviour of the soil-root system has been developed. Based on this constitutive relationship, a numerical model for simulating rainfall induced slope failure by considering root reinforcement has also been prepared and applied in the stability analysis of some real site cases. The numerical codes are written in ABAQUS, Comes Geo and also in FLAC3D and PFC. The outputs of this project will be in the form of numerical model and peer reviewed journal publications.