Rooting for sustainable performance

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

More frequent intense rainfall events, associated with climate change, increase the likelihood of shallow slope failures that lead to costly disruption of road and rail journeys, with risk to life and property. There have been recent slope failures adjacent to transport corridors in the UK, sometimes disrupting important road and rail routes for days. Vegetation has a stabilising effect on slopes: Plant root systems interlock with the soil, increasing its stiffness and strength. Uptake of water by root systems dries the soil profile, again increasing soil stiffness and strength. However, engineers need to be able to predict the combined root reinforcement and soil drying effects on slope stability, so that vegetation management can be used proactively to decrease the probability of slope failure. Vegetation has numerous benefits over conventional hard-engineering solutions, in terms of burying carbon in the soil, enhancing biodiversity, and improving the aesthetic quality of the environment for society.

This project will develop and test a quantitative coupled hydro-mechanical model for the in-service and ultimate-failure performance of slopes planted with vegetation. Rooted-soil represents an innovative sustainable construction material, with distinct mechanical and hydrological properties, that can be used in geotechnical systems. The model will be applicable to both slopes covered with natural vegetation and slopes where vegetation and soil have been chosen and managed according to engineering principles. The validated model will provide a clear framework for assessment and remediation of slopes with potential for reducing economic and carbon costs.

The model will be developed within a multi-scale continuum modelling framework. It will build on knowledge of the elemental components of the system, working from individual soil-root interaction, to continuum soil-root system, and to complete slope, incorporating spatial variability of materials. Modelling will be informed by X-ray CT imaging of the 3-D deformation of rooted soil undergoing shear, using the micro-VIS facility at the University of Southampton, and by field data from slopes containing established vegetation. Predictions of slope performance will be validated against scaled-slopes in the Dundee geotechnical centrifuge under different rainfall regimes. The geotechnical centrifuge enables the testing and monitoring of small-scale slopes containing roots at realistic stresses, which can be manipulated until the slopes ultimately fail.

Template guidelines will be produced for a manual of combinations of plant species, soils and management schemes for optimum performance of designed soil-plant systems suited to emerging climatic conditions. Example data will also be included to allow cost-benefit analyses when designing for slope improvement using vegetation. The potential to translate research findings into related areas will be investigated (e.g. river banks, sand dunes, flood embankments, agricultural and amenity systems). We will engage with an important group of Project Partners, representing key industrial sectors and infrastructure owners, to facilitate the rapid adoption of research findings.
 
Description A novel apparatus has been developed that enables rooted soil to be sheared within a large X-ray CT scanner. This has enabled three-dimensional visualisation (particularly of strains and displacements) within the root-soil composite during shear, and has enabled us to get a much better understanding of fundamental mechanisms by which the roots and soil interact to provide a much larger (compared with fallow soil) shearing resistance/strength. The experimental results have enabled us to understand the advantages and limitations of different models for plant-root reinforcement proposed within the scientific literature. We have also developed a novel numerical code that combines unsaturated soil behaviour, a suitable soil constitutive (failure) model, plant evapotranspiration and atmosphere interactions, and a plant root reinforcement model (created by partner institution Dundee University, based on shear box tests above). This model is being used to investigate how plant roots can be incorporated into engineering slope stability calculations in a more accurate and reliable way, to give improved guidance on the use of plants in enhancing slope stability.
Exploitation Route The findings from the numerical modelling work have the potential to impact the way in which plant root reinforcement is incorporated into the design of engineered and natural slopes, with the idea that the vegetation can be 'designed' to enhance slope stability in addition to the usual ecological and environmental functions. It is intended that improved design approaches can be incorporated into appropriate industry guidance on managing slopes and earthworks. This would be used infrastructure earthwork owners and their managing agents (for earthworks on the highway, railway and canal networks), and in forestry systems on natural slopes prone to instability. There are also links to agricultural systems, where there is interest in the way in which the roots of crops reinforce the soil against erosion.

The numerical models and shear box apparatus/method developed, can be used for allied academic research into the impacts of root reinforcement on soils, for slope stability, forestry and agriculture. There are clear opportunities to take knowledge and modelling approaches developed relating to plant root reinforcement into wider academic research into the long-term deterioration of engineered slopes and earthworks being considered by the major EPSRC programme grant ACHILLES, in which the PI and one Co-I on this grant are also involved.
Sectors Agriculture, Food and Drink,Construction,Environment,Transport

 
Description The findings and models developed in the grant were applied as part of an Institutional EPSRC Impact Acceleration Account award run with High Speed 2 (HS2), looking at trying to achieve more effective engineering design for vegetated slopes that would enable reduced land-take.
First Year Of Impact 2020
Sector Construction,Transport
Impact Types Economic

 
Description Assessment, Costing and enHancement of long lIfe, Long Linear assEtS (ACHILLES)
Amount £4,872,904 (GBP)
Funding ID EP/R034575/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 07/2018 
End 12/2022
 
Description EPSRC Centre for Doctoral Training in Sustainable Infrastructure Systems
Amount £100,000 (GBP)
Funding ID EP/L01582X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2015 
End 09/2019
 
Description Impact Acceleration Account - University of Southampton 2017 - specfic impcat proposal related to slope engineering
Amount £2,933,116 (GBP)
Funding ID EP/R511766/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2019 
End 03/2020
 
Description Network Rail CP6 R&D Programme Project - Investigation of geometry problems at transitions onto and off underbridges due to soil moisture deficit effects
Amount £50,000 (GBP)
Organisation Network Rail Ltd 
Sector Private
Country United Kingdom
Start 09/2020 
End 09/2021
 
Description UKCRIC Pump Priming Panel July 2017
Amount £1,013,092 (GBP)
Funding ID EP/R013535/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2018 
End 12/2019
 
Title A large direct shearbox for shearing rooted soil in the X-Ray CT scanner 
Description Development and construction of a working shear apparatus that can shear large plant-rooted samples of soil within an X-Ray CT scanner. This enables visualisation of how the plant roots and soil interact during the soil shearing process. It is a technically challenging and novel apparatus. 
Type Of Material Improvements to research infrastructure 
Year Produced 2018 
Provided To Others? No  
Impact It has enabled a complete three-dimensional visualisation of how plant roots interact with a soil during the shearing process. This will lead to a much better understanding of how plant roots stabilise the soil, and prevent soil slope erosion and landslide problems. 
 
Title A numerical model that incorperates the key physical processes for understanding plant root effects on engineered slopes 
Description A new complex numerical (finite difference) model that incorporates: unsaturated water flow, soil mechanics and a constitutive model of soil failure, a plant-soil-atmosphere model, and a root mechanics/soil reinforcement model. 
Type Of Material Improvements to research infrastructure 
Year Produced 2019 
Provided To Others? No  
Impact The model is being used to investigate plant root reinforcement effects in engineered slopes. It is being written up as a journal paper. 
 
Title Data for: Mechanisms of root-reinforcement in soils: an experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation 
Description Collection of data files used in the paper titled: Mechanisms of root-reinforcement in soils: an experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation. Additional dataset which covers the noise study CT scans and digital volume correlation noise studies can be found in DOI: 10.5281/zenodo.3361832 Data contains the following: X-ray CT data for the interrupted direct shear tests of a soil sample containing a Willow plant. The first file is the specimen scanned unloaded, followed by seven incremental shear load steps to 20 mm shear displacement. Files are 8-bit unsigned and 1800x1800x1600px. Voxel resolution is 0.04642 mm. 20180430_HUTCH_1839_DJB_willow_C_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_A_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_B_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_C_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_D_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_E_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_F_8-bit_1800x1800x1600.raw 20180430_HUTCH_1839_DJB_willow_C_Load_G_8-bit_1800x1800x1600.raw Direct shear vs. displacement data is presented in an Excel spreadsheet: All_load_data_with_reducing_area.xlsx Normal and shear strain DVC data which has been averaged and plotted against specimen depth is presented in an Excel spreadsheet: Average_slice_vs_depth_data_all_samples_all_loads3.xlsx CT scan metadata giving information to the scan settings, voxel resolution, etc. is contained in a .zip file which consists of .xtekct and .XML files generated from the Nikon CT scanner. CT_Scan_Metadata.zip Drawings and Solidworks CAD files of the direct shear test rig are contained within the .zip file. There are a number of parts to the assembly. The file SSSB1003-5.SLDASM contains the complete assembly of the direct shear rig and will help identify the part names. The folder CAD_Drawings contains pdf documents of the part drawings. Direct_Shear_Drawings_Solidworks_Files.zip Tabulated DVC data taken at 32x32x32px subset size is contained inside a .zip file. These consist of tab separated .dat files from unloaded (data_1.dat) through incremental load steps Load A, Load B... Load G, (data_2.dat, data_3.dat... data_8.dat). The structure of the .dat file contains columns of data with each column number corresponding to the following: (1) x, (2) y (3) z, (4) vx, (5) vy, (6) vz, (7) exx, (8) eyy, (9) ezz, (10) exy, (11) exz, (12) eyz, (13) volumetric strain, (14) is valid. Columns 1-3 are subset positions in mm, 4-6 are displacements in mm, 7-9 are normal strains, 10-12 are shear strains, 13 is volumetric strain and 14 is a binary value indicating if the subset is valid. DVC_Load_Data_Willow_C.zip Tabulated DVC data applied to the load step CT data at 32, 48, 64, 96, 128 pixels is presented in the .zip files containing .dat tab separated files. The structure of the .dat files is described in the previous bullet point. These files were used to construct the noise study applied to incrementally loaded CT data by sampling regions away from the shear zone where the strain signals are close to zero. DVC_Noise_Study_Data_Load_Steps_Willow_C.zip Processed noise study data which compares the effects of DVC subset size is presented in the .xlsx file. This file contains both the controlled noise experiment data (stationary, magnification and rigid body motion) and noise study data applied to incrementally loaded data using sampled regions away from the shear zone where the strain signals are close to zero. Willow_C_Processed_Noise_study2.xlsx Tabulated data which compares the local x displacement vs depth profile from DVC and direct measurement of root position is contained in the following Excel spreadsheet file: X_Displacement_Root_and_DVC_Comparison_Willow C.xlsx 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact The dataset has been used by others to test CT image algorithms. 
URL https://zenodo.org/record/3352268
 
Title Noise study data for: Mechanisms of root-reinforcement in soils: an experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation 
Description This dataset contains noise study data used in the paper: Mechanisms of root-reinforcement in soils: an experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation. These include raw CT scans and processed digital volume correlation data. This dataset is part of another dataset which covers other aspects of the paper DOI: 10.5281/zenodo.3352268 The structure of the dataset is as follows: Noise study CT raw volumes are contained in a zip file. There are four raw files corresponding to the four noise study steps. These files are 8-bit unsigned, dimensions are 1800 x 1800 x 1400 pixels. A txt file giving more details to the data is included. CT_Raw_data_Noise_Scans.zip Metadata files generated for each scan given details of scan parameters are found in the zip file: CT_Scan_Metadata.zip Tabulated digital volume data for the noise study scans are contained in the zip file. Tabulated data for each subset size is included in subfolders. A .txt file explains the structure of the tab separated .dat files, i.e. what each column of data represents, and what CT scan each of the four .dat files relate to. DVC_Noise_Study_Data.zip 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact The dataset has been used by others for testing CT image analysis algorithms. 
URL https://zenodo.org/record/3361832
 
Description Highways England 
Organisation Department of Transport
Department Highways Agency
Country United Kingdom 
Sector Public 
PI Contribution Provision of research data, once the fieldwork is complete.
Collaborator Contribution Staff time in accessing bioengineered slope sites and help with exhuming vegetation root systems for the purposes of the research project.
Impact The collaboration will produce data on the performance of existing bioengineered slope sites, both of use to the research project and to Highways England.
Start Year 2015
 
Description Presentation to COST Action TU1202 final conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The presentation given as part of the final dissemination conference for EU COST Action TU1202 on climate impacts on infrastructure slopes.
Year(s) Of Engagement Activity 2016
 
Description Presentation to the Dundee Roots Group meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Two presentations on Rooting for Sustainable Performance research work were given to the 'Dundee Roots Group', which includes practitioners, academics, members of James Hutton Institute, and postgraduate students with an interest in plant root systems for agriculture and engineering.
Year(s) Of Engagement Activity 2016
 
Description Talk at an International Conference - IS-Glasgow 2019 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Conference talk to an audience of academics, industry practitioners, and infrastructure owners.
Year(s) Of Engagement Activity 2019
URL https://www.is-glasgow2019.org.uk/
 
Description The 4th Annual Advances in X-Ray Imaging Workshop, Dimond Light Source Ltd 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact The aim of the workshop was to bring scientists from different fields to discuss developments and applications of a variety of X-ray imaging and complementary techniques, and to build international collaborations. Others attending the conference were very keen to have a copy of x-Ray CT data sets that we have generated in the project, once these are publicly available.
Year(s) Of Engagement Activity 2019
URL https://www.diamond.ac.uk/Home/Events/2019/Advances-in-X-ray-Imaging0.html#
 
Description Workshop on slopes research and and discussion with industry panel, including some Project Partners 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact To engage relevant stakeholders with recent University research on slope stability. There are on-going discussions with High Speed 2 about a project to deliver direct impact from research to design practice.
Year(s) Of Engagement Activity 2017
 
Description Workshop with Project Partners and other intertested industry participants 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact An engagement workshop with Project Partners and other industry participants. We asked the industry participants to tell us what they thought their problems related to vegetation and slopes were, and how the research project could influence these. There was a very helpful discussion which has influenced decisions on how the academic team proceed with the research project, and industry has also provided opportunities in relation to particular bioengineered slope sites.
Year(s) Of Engagement Activity 2016