Case Study on the Influence of Transpiration on the Ground Behaviour

Bioengineering including native vegetation is an ancient method of improving the stability of slopes. In modern railway engineering, this technique is re-captured for increasing the soil stiffness and shear strength of sub-grade beneath rail tracks. A mathematical model for the rate of root water uptake has been developed considering ground conditions, type of vegetation and climatic parameters. The three independent features in the root water uptake model considered in detail are soil suction, root distribution, and potential transpiration. In order to establish a rigorous analysis for estimating the actual transpiration or root water uptake, the above mentioned factors have been quantified through relevant equations to develop the model. A two dimensional finite element approach has been employed to solve the transient coupled flow and deformation equations. In order to validate the model, an array of field measurements conducted at Miram site in Victoria, Australia and the data have been compared with the numerical predictions. The predicted results calculated using the soil, plant, and atmospheric parameters contained in the numerical model, compared favourably with the field and the associated laboratory measurements, justifying the assumptions upon which the model has been developed

Parametric Study of Applied Stresses on Infiltration Modular Cells installed under Roads

Abstract Modular geocellular units are applicable for the prevention and minimisation of stormwater runoff and flooding as a sustainable and cost-effective solution of road applications for drainage. The integrated units buried are exposed to the dead loads and live loads emerging from the surrounding soil pressure, pore water pressure and surcharge. Thus, a computer program using MATLAB is developed for the assessment of the total vertical and lateral earth pressure exerting on the modules complying with the Australian Standards AS 467

Predicting the environmental suitability for onchocerciasis in Africa as an aid to elimination planning

Recent evidence suggests that, in some foci, elimination of onchocerciasis from Africa may be feasible with mass drug administration (MDA) of ivermectin. To achieve continental elimination of transmission, mapping surveys will need to be conducted across all implementation units (IUs) for which endemicity status is currently unknown. Using boosted regression tree models with optimised hyperparameter selection, we estimated environmental suitability for onchocerciasis at the 5 × 5-km resolution across Africa. In order to classify IUs that include locations that are environmentally suitable, we used receiver operating characteristic (ROC) analysis to identify an optimal threshold for suitability concordant with locations where onchocerciasis has been previously detected. This threshold value was then used to classify IUs (more suitable or less suitable) based on the location within the IU with the largest mean prediction. Mean estimates of environmental suitability suggest large areas across West and Central Africa, as well as focal areas of East Africa, are suitable for onchocerciasis transmission, consistent with the presence of current control and elimination of transmission efforts. The ROC analysis identified a mean environmental suitability index of 071 as a threshold to classify based on the location with the largest mean prediction within the IU. Of the IUs considered for mapping surveys, 502% exceed this threshold for suitability in at least one 5 × 5-km location. The formidable scale of data collection required to map onchocerciasis endemicity across the African continent presents an opportunity to use spatial data to identify areas likely to be suitable for onchocerciasis transmission. National onchocerciasis elimination programmes may wish to consider prioritising these IUs for mapping surveys as human resources, laboratory capacity, and programmatic schedules may constrain survey implementation, and possibly delaying MDA initiation in areas that would ultimately qualify.SUPPORTING INFORMATION : FIGURE S1. Data coverage by year. Here we visualise the volume of data used in the analysis by country and year. Larger circles indicate more data inputs. ‘NA’ indicates records for which no year was reported (eg, ‘pre-2000’). https://doi.org/10.1371/journal.pntd.0008824.s001FIGURE S2. Illustration of covariate values for year 2000. Maps were produced using ArcGIS Desktop 10.6. https://doi.org/10.1371/journal.pntd.0008824.s002FIGURE S3. Environmental suitability of onchocerciasis including locations that have received MDA for which no pre-intervention data are available. This plot shows suitability predictions from green (low = 0%) to pink (high = 100%), representing those areas where environmental conditions are most similar to prior pathogen detections. Countries in grey with hatch marks were excluded from the analysis based on a review of national endemicity status. Areas in grey only represent locations masked due to sparse population. Maps were produced using ArcGIS Desktop 10.6 and shapefiles to visualize administrative units are available at https://espen.afro.who.int/tools-resources/cartography-database. https://doi.org/10.1371/journal.pntd.0008824.s003FIGURE S4. Environmental suitability prediction uncertainty including locations that have received MDA for which no pre-intervention data are available. This plot shows uncertainty associated with environmental suitability predictions colored from blue to red (least to most uncertain). Countries in grey with hatch marks were excluded from the analysis based on a review of national endemicity status. Areas in grey only represent locations masked due to sparse population. Maps were produced using ArcGIS Desktop 10.6 and shapefiles to visualize administrative units are available at https://espen.afro.who.int/tools-resources/cartography-database. https://doi.org/10.1371/journal.pntd.0008824.s004FIGURE S5. Environmental suitability of onchocerciasis excluding morbidity data. This plot shows suitability predictions from green (low = 0%) to pink (high = 100%), representing those areas where environmental conditions are most similar to prior pathogen detections. Countries in grey with hatch marks were excluded from the analysis based on a review of national endemicity status. Areas in grey only represent locations masked due to sparse population. Maps were produced using ArcGIS Desktop 10.6 and shapefiles to visualize administrative units are available at https://espen.afro.who.int/tools-resources/cartography-database. https://doi.org/10.1371/journal.pntd.0008824.s005FIGURE S6. Environmental suitability prediction uncertainty excluding morbidity data. This plot shows uncertainty associated with environmental suitability predictions colored from blue to red (least to most uncertain). Countries in grey with hatch marks were excluded from the analysis based on a review of national endemicity status. Areas in grey only represent locations masked due to sparse population. https://doi.org/10.1371/journal.pntd.0008824.s006FIGURE S7. Covariate Effect Curves for all onchocerciasis occurrences (measures of infection prevalence and disability). On the right set of axes we show the frequency density of the occurrences taking covariate values over 20 bins of the horizontal axis. The left set of axes shows the effect of each on the model, where the mean effect is plotted on the black line and its uncertainty is represented by the upper and lower confidence interval bounds plotted in dark grey. The figures show the fit per covariate relative to the data that correspond to specific values of the covariate. https://doi.org/10.1371/journal.pntd.0008824.s007FIGURE S8. Covariate Effect Curves for all onchocerciasis occurrences (measures of infection prevalence and disability). On the right set of axes we show the frequency density of the occurrences taking covariate values over 20 bins of the horizontal axis. The left set of axes shows the effect of each on the model, where the mean effect is plotted on the black line and its uncertainty is represented by the upper and lower confidence interval bounds plotted in dark grey. https://doi.org/10.1371/journal.pntd.0008824.s008FIGURE S9. ROC analysis for threshold. Results of the area under the receiver operating characteristic (ROC) curve analysis are presented below, with false positive rate (FPR) on the x-axis and true positive rate (TPR) on the y-axis. The red dot on the curve represents the location on the curve that corresponds to a threshold that most closely agreed with the input data. For each of the 100 BRT models, we estimated the optimal threshold that maximised agreement between occurrence inputs (considered true positives) and the mean model predictions as 0·71. https://doi.org/10.1371/journal.pntd.0008824.s009TABLE S1. Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER) checklist. https://doi.org/10.1371/journal.pntd.0008824.s010TABLE S2. Total number of occurrence data classified as point and polygon inputs by diagnostic. We present the total number of occurrence points extracted from the input data sources by diagnostic type. ‘Other diagnostics’ include: DEC Patch test; Knott’s Method (Mazotti Test); 2 types of LAMP; blood smears; and urine tests. https://doi.org/10.1371/journal.pntd.0008824.s011TABLE S3. Total number of occurrence data classified as point and polygon inputs by location. https://doi.org/10.1371/journal.pntd.0008824.s012TABLE S4. Covariate information. https://doi.org/10.1371/journal.pntd.0008824.s013TEXT S1. Details outlining construction of occurrence dataset. https://doi.org/10.1371/journal.pntd.0008824.s014TEXT S2. Covariate rationale. https://doi.org/10.1371/journal.pntd.0008824.s015TEXT S3. Boosted regression tree methodology additional details. https://doi.org/10.1371/journal.pntd.0008824.s016APPENDIX S1. Country-level maps and data results. Maps were produced using ArcGIS Desktop 10.6 and shapefiles to visualize administrative units are available at https://espen.afro.who.int/tools-resources/cartography-database. https://doi.org/10.1371/journal.pntd.0008824.s017This work was primarily supported by a grant from the Bill & Melinda Gates Foundation OPP1132415 (SIH). Financial support from the Neglected Tropical Disease Modelling Consortium (https://www.ntdmodelling.org/), which is funded by the Bill & Melinda Gates Foundation (grants No. OPP1184344 and OPP1186851), and joint centre funding (grant No. MR/R015600/1) by the UK Medical Research Council (MRC) and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreement which is also part of the EDCTP2 programme supported by the European Union (MGB).The Neglected Tropical Disease Modelling Consortium which is funded by the Bill & Melinda Gates Foundation, the UK Medical Research Council (MRC) and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreement which is also part of the EDCTP2 programme supported by the European Union (MGB).http://www.plosNTDS.orgam2022Medical Microbiolog

Modelling of influence of matric suction induced by native vegetation on sub-soil improvement

Bioengineering including native vegetation is an ancient method of improving the stability of slopes. In modern railway engineering, this technique is re-captured for increasing the soil stiffness and shear strength of sub-grade beneath rail tracks. Currently this practice has become increasingly popular in Australia for stabilising railway corridors built over expansive clays and compressive soft soils. The tree roots provide three stabilising functions: (a) reinforcement of the soil, (b) dissipation of excess pore pressures and (c) establishing sufficient matric suction to increase the shear strength. The main focus of this research is to investigate the effects of vegetation on soil matric suction, ground settlement and lateral movement (radial consolidation). A mathematical model for the rate of root water uptake has been developed based on the root growth rate and considering ground conditions, type of vegetation and climatic parameters.The three independent features in the root water uptake model considered in detail are soil suction, root distribution, and potential transpiration. In order to establish a rigorous analysis for estimating the actual transpiration or root water uptake, the above mentioned factors have been quantified through relevant equations to develop the proposed root water uptake model. A two dimensional finite element approach based on ABAQUS has been employed to solve the transient coupled flow and deformation equations. The proposed root water uptake model has been implemented in the coupled analysis by introducing a sink term as a subroutine in the finite element analysis. The finite element mesh can be constructed using partially/fully saturated soil elements, representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the general effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the matric suction profile adjacent to the tree has been numerically analysed. To validate the model, an array of field measurements conducted at Miram site in Victoria, Australia and the data have been compared with the numerical predictions. The predicted results calculated using the soil, plant, and atmospheric parameters contained in the numerical model, compared favourably with the field and the associated laboratory measurements, justifying the assumptions upon which the model has been developed. The numerical analysis encompassing the developed root water uptake model can reasonably predict the region of maximum matric suction (away from the tree trunk axis), which has been consistent with the field measurements. Moreover, field measurements taken from the previously published literature have been compared with the 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 influence of different parameters on the maximum rate of root water uptake is investigated through parametric and sensitivity analyses. In addition, the rate of selected parameters such as potential transpiration and its distribution, suction at wilting point, the coefficient of permeability and the distribution of root length density have been studied in detail. The findings of this study confirm that four key parameters, including permeability, wilting point suction, density and distribution of the root length, and the rate of potential transpiration should be estimated or measured accurately in order to predict the behaviour of clayey soils near tree roots. The action of a single tree on improving the soil behaviour has been compared to a vertical drain with applied suction (vacuum pressure). It is seen that root water uptake and associated matric suction is analogous to a prefabricated vertical drain with vacuum preloading, and the lateral inward displacements simulate the radial consolidation process of prefabricated vertical drains. If a pattern of trees can be grown systematically along rail corridors, this may offer a cheaper and more environmentally attractive solution to vertical drains in the long-term. The results of this study provide a valuable and a relatively accurate mean to estimate the influences of vegetation on ground. The numerical model developed herein offers practicing geotechnical engineers an effective tool for designing structures on vadose zones containing vegetation. It is desirable to consider the influence zone of tree roots and the improved soil properties in modern geotechnical designs, benefiting from native vegetation

Effects of salinity and sand content on liquid limit and hydraulic conductivity

Soil conditions of construction sites have become worse than ever due to the overpopulation in the metropolitan areas throughout the world. Likewise, the prevention of environmental risks due to individual activities is one of the most important subjects in the geo-environmental problems. Saline soils may induce several problems in geotechnical engineering projects such as infrastructure embankments, road construction and clay liners. Effect of the various concentrations of sodium chloride (NaCl) on several different soils including bentonite, kaolinite and fine sand mixtures has been evaluated. In addition, influence of salinity and the period of submergence on the hydraulic conductivity of soil samples collected from a certain area of east coast of India was investigated. The results show that the liquid limit of the mixtures generally decreases with an increase in the salt concentration. Liquid limit decreased significantly with an increase in NaCl concentration up to a certain level. However, a further increase in the concentration does not induce any significant decrease in liquid limit. Furthermore, the soil hydraulic conductivity increase with the salt concentration and with increase in the period of submergence, the hydraulic conductivity of the soil increases asymptotically

Improvement of soil stability along rail corridors through native vegetation

Field studies conducted along the railway lines in Australia have revealed the ability to implement the green corridor concept as a soil stabilization method. Native trees grown along rail corridors are capable of increasing the matric suction of the subgrade soil underneath the track substructure via root water uptake, in conjunction with the tree canopy evapo-transpiration. Moreover, these trees are capable of providing significant mechanical reinforcement through the anchoring effect provided by the root network plus the additional cohesive increment due to hair roots generating osmotic suction. Much of the previous research carried out to quantify the mechanical strength generated by tree roots has been mainly based on empiricism. In many cases, empirical relations have been developed for a given tree species grown under known soil conditions. The extrapolation of such empirical relations from one tree-soil system to another can be misleading. Furthermore, the effect of transpiration by tree canopy and its influence on the sustained suction equilibrium generated at the root zone for stabilising soft subgrade has not been considered rationally. To accommodate the above natural phenomena, a novel computational model has been developed to quantify the overall suction effect provided by the tree roots and its continual link with the rate and magnitude of canopy evapo-transpiration. Root based suction of a tree improves the shear strength; accelerates the pore water pressure dissipation and it may alter the potential failure conditions of the soil-root system from a saturated to an unsaturated domain. Therefore, it is necessary for the root based suction and the mechanical properties of the root network to be analysed within a coupled multiphase framework. Accordingly, this paper will present the requirement of an advanced shear strength model that captures and combines the root reinforcement effect with both osmotic and matric suction components generated in the soil through naturally coupled osmotic evapo-transpiration phenomenon

Mechanical Model to Analyse Multilayer Geosynthetic Reinforced Granular Layer in Column Supported Embankments

Abstract The objective of this paper is to develop a mechanical model to predict the behaviour of a multilayer geosynthetic reinforced granular fill soft soil system improved with controlled modulus columns beneath the embankment. Deformation of geosynthetics embedded granular layer due to bending and shear is considered in this study. Therefore, geosynthetic reinforced granular fill has been idealised as a reinforced Timoshenko beam while the columns and the soft soil have been idealised as a layer of linear springs with varied stiffness. Plane strain conditions are considered for the loading and reinforced foundation soil system. Tension developed in the geosynthetics, rotation and settlements of the improved soft ground are predicted using the proposed model. This study shows the effects of multilayer geosynthetics on the settlement response of the granular layer. A notable reduction of the settlement has been observed as a result of the using multilayer weaker geosynthetic reinforcement system when compare to one stronger geosynthetics layer. It is also observed that the top reinforcement layer is subjected to maximum mobilised tension at the column edge whereas bottom reinforcement layer is more effective in controlling the deflection in the middle of two columns

Liquefaction and Post-liquefaction Assessment of Lightly Cemented Sands

Post-liquefaction response of lightly cemented sands during an earthquake may alter and become similar to uncemented sands due to bonding breakage. In this study, the effect of degree of cementation on liquefaction and post-liquefaction behaviour of lightly cemented sands was studied through a series of cyclic and monotonic triaxial tests. Portland cement with high early strength and Sydney sand were used to reconstitute the lightly cemented specimens with unconfined compression strength ranging from 25 to 220 kPa. A series of multi-stage soil element tests including stress-controlled cyclic loading events with different amplitudes and post-cyclic undrained monotonic shearing tests were carried out on both uncemented and cemented specimens. Furthermore, a series of undrained monotonic shearing tests without cyclic loading history on different types of specimens were conducted to investigate the effect of cyclic loading history on the post-cyclic response of specimens. Results show that residual excess pore water pressure is correlated to the cyclic degradation of lightly cemented sands during cyclic loading. Optical microstructure images of the cemented specimens after liquefaction showed that a major proportion of cementation bonds remained unbroken which resulted in a superior post-liquefaction response with respect to initial stiffness and shear modulus in comparison to uncemented sand.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Sustainable Applications of Tyre-Derived Aggregates for Railway Transportation Infrastructure

Scrap tyres are used to produce tyre-derived aggregates (TDA), which can be used as fill material, backfill material, drainage layers, and vibration-damping material, among other uses. This study presents a comprehensive review of TDA applications in civil engineering with a specific focus on railway projects. A review of the existing literature reveals the lack of sufficient knowledge on the use of TDA in slab tracks. This article also analyses the adequacy of different constitutive models to properly simulate the performance of TDA while highlighting the importance of adopting the most suitable constitutive model. The variations in shear stresses and displacements with depth below ballasted and slab tracks in the presence and absence of TDA are discussed. It is shown that TDA effectively reduces the shear stresses for the subgrade layer of both track types. Moreover, the impact of TDA on stress transfer in the vertical and lateral track directions is assessed. The findings from the present analysis reveal that TDA helps in reducing the vertical and lateral stresses near its placement position in ballasted and slab tracks