The simulation of large-strain geotechnical laboratory tests with conventional Lagrangian finite element method(FEM)techniques is often problematic due to excessive mesh distortion.The multiple reversal direct shear(M...The simulation of large-strain geotechnical laboratory tests with conventional Lagrangian finite element method(FEM)techniques is often problematic due to excessive mesh distortion.The multiple reversal direct shear(MRDS)test can be used to measure the residual shear strength of soils in a laboratory setting.However,modelling and simulation generally require advanced numerical methods to accommodate the large shear strains concentrated in the shear plane.In reality,when the standard direct shear(DS)apparatus is used,the MRDS method is prone to two major sources of measurement error:load cap tilting and specimen loss.These sources of error make it difficult or even impossible to correctly determine the residual shear strength.This paper presents a modified DS apparatus and multi-reversal multi-stage test method,simulated using the coupled Eulerian-Lagrangian(CEL)method in a finite element environment.The method was successful in evaluating equipment and preventing both load cap tilting and specimen loss,while modelling large-deformation behaviour that is not readily simulated with the conventional FEM or arbitrary Lagrangian-Eulerian(ALE)analysis.Thereafter,a modified DS apparatus was created for the purpose of analysing mixtures of organic materials found in an Australian clay.The results obtained from the modified DS CEL model in combination with laboratory tests show a great improvement in the measured residual shear strength profiles compared to those from the standard apparatus.The modified DS setup ensures that accurate material residual shear strengths are calculated,a factor that is vital to ensure appropriate soil behaviour is simulated for numerical analyses of large-scale geotechnical projects.展开更多
Major advances in computational power,as well as community modelling workflows and an improvement in data availability,has revolutionized Earth sciences over the last decade.Geological data has been synthesized into f...Major advances in computational power,as well as community modelling workflows and an improvement in data availability,has revolutionized Earth sciences over the last decade.Geological data has been synthesized into flexible and open access plate tectonic and paleogeographic reconstructions using the open-source and cross-platform GPlates(www.gplates.org)software since 2008(Muller et al.,2018;Muller et al.,2008).展开更多
Coupling Bayes’Theorem with a two-dimensional(2D)groundwater solute advection-diffusion transport equation allows an inverse model to be established to identify a set of contamination source parameters including sour...Coupling Bayes’Theorem with a two-dimensional(2D)groundwater solute advection-diffusion transport equation allows an inverse model to be established to identify a set of contamination source parameters including source intensity(M),release location(0 X,0 Y)and release time(0 T),based on monitoring well data.To address the issues of insufficient monitoring wells or weak correlation between monitoring data and model parameters,a monitoring well design optimization approach was developed based on the Bayesian formula and information entropy.To demonstrate how the model works,an exemplar problem with an instantaneous release of a contaminant in a confined groundwater aquifer was employed.The information entropy of the model parameters posterior distribution was used as a criterion to evaluate the monitoring data quantity index.The optimal monitoring well position and monitoring frequency were solved by the two-step Monte Carlo method and differential evolution algorithm given a known well monitoring locations and monitoring events.Based on the optimized monitoring well position and sampling frequency,the contamination source was identified by an improved Metropolis algorithm using the Latin hypercube sampling approach.The case study results show that the following parameters were obtained:1)the optimal monitoring well position(D)is at(445,200);and 2)the optimal monitoring frequency(Δt)is 7,providing that the monitoring events is set as 5 times.Employing the optimized monitoring well position and frequency,the mean errors of inverse modeling results in source parameters(M,X0,Y0,T0)were 9.20%,0.25%,0.0061%,and 0.33%,respectively.The optimized monitoring well position and sampling frequency canIt was also learnt that the improved Metropolis-Hastings algorithm(a Markov chain Monte Carlo method)can make the inverse modeling result independent of the initial sampling points and achieves an overall optimization,which significantly improved the accuracy and numerical stability of the inverse modeling results.展开更多
Climate variability,together with other drivers of global change(like population growth,land-use change,etc.),is affecting the management offloods.Traditional approaches are no longer sufficient to address the increas...Climate variability,together with other drivers of global change(like population growth,land-use change,etc.),is affecting the management offloods.Traditional approaches are no longer sufficient to address the increased pressures that areas vulnerable toflooding are facing.A paradigm shift fromflood risk reduction toflood resilience-building strategies is required.An analytical framework is developed to help quantify,compare,and visualize dynamic resilience toflooding to address some shortcomings in current resilience assessment research.The proposed methodological framework forflood resilience combines physical,economic,engineering,health,and social spatio-temporal impacts and adaptive capacities offlood-affected systems.To capture the dynamic spatio-temporal characteristics of resilience and gauge the effectiveness of potential climate change adaptation options,aflood resilience simulation tool(FRST)is developed to use the analytical framework.The FRST is applied to a case study in Metro Vancouver,British Columbia,Canada.The simulation model focuses on the impacts of climate change-influenced riverineflooding and sea-level rise.Simulation results suggest that various adaptation options,such as access to emergency funding,mobile hospital services,and managed retreat can all help to increase resilience toflooding.Results also suggest that,at a regional scale,Metro Vancouver is rather resilient to climate change-influencedflood hazards.展开更多
New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age.Radiometric dating of its plutonic and volcanichypabyssal rocks ...New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age.Radiometric dating of its plutonic and volcanichypabyssal rocks yielded middle Eocene ages.On the other hand,the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge-island arc affiliated Coto block of the ophiolite complex,together with isotopic age datings of its dikes and mafic cumulate rocks,also yielded Eocene ages.This offers the possibility that the Zambales Ophiolite Complex could have:(1)evolved from a Mesozoic arc(Acoje block)that split to form a Cenozoic back-arc basin(Coto block),(2)through faulting,structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or(3)through the interplay of slab rollback,slab break-off and,at a later time,collision with a microcontinent fragment,caused the formation of an island arc-related ophiolite block(Acoje)that migrated trench-ward resulting into the generation of a back-arc basin(Coto block)with a limited subduction signature.This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation.展开更多
The variable-density flow model-SEAWAT Version 4, was used to evaluate the hydrogeological conditions associatedwith hydraulic fracturing （fracking） the limestone oil reservoir in the Lower Cretaceous Sunniland Form...The variable-density flow model-SEAWAT Version 4, was used to evaluate the hydrogeological conditions associatedwith hydraulic fracturing （fracking） the limestone oil reservoir in the Lower Cretaceous Sunniland Formation of Southwest Florida.This research contributes to the understanding of the controls on fluid and potential contaminant migration, following high pressurehydraulic fracturing. A hydraulic fracturing treatment used recently in this formation at the Collier-Hogan 20-3H well represents thebase case simulation. Multiple stage fracturing using typical stress periods, a modelled fracture zone radius, and various injectionrates were tested to evaluate the potential for horizontal and vertical fluid migration in and from the reservoir under dynamicconditions, with TDS used as a tracer. Hypothetical scenarios including preferential vertical pathways between the SunnilandFormation and the Lower Floridan aquifer Boulder Zone were also simulated. Results indicate that injected fluids do not migratesignificantly in the lateral and vertical directions beyond the design fractured zone, unless a preferential pathway exists within closeproximity to the fractured zone. In a worst-case scenario under the simulated conditions, vertical heads are approximately 580 metersgreater than static conditions and fluids associated with hydraulic fracturing vertically migrate approximately 500 meters; therefore,the quality of the deepest sources of drinking water is not compromised. Analytical results from a monitoring well installed in theimmediate vicinity of the Collier-Hogan 20-3H well and at the base of the deepest source of drinking water support the conclusionthat impacts from hydraulic fracturing fluids have not migrated into the deepest sources of drinking water.展开更多
INTRODUCTION Winter snow and ice can have a significant impact on our mobility,whether on foot or by car.Alongside plowing,arguably the greatest tool in combating snow and ice is salt.The most commonly used salt for w...INTRODUCTION Winter snow and ice can have a significant impact on our mobility,whether on foot or by car.Alongside plowing,arguably the greatest tool in combating snow and ice is salt.The most commonly used salt for winter maintenance is Sodium Chloride(NaCl),the same salt used in food and water softeners,is applied to roads,sidewalks,and parking lots as it is an effective deicer when temperatures are between 0℃ and-12℃.Studies have shown that deicing with salt reduces accidents by 88%and injuries by 85%(Salt Institute 2017).The effectiveness of road salt,as well as its relative affordability,means that as much as four million tonnes may be applied annually in Canada for deicing(Environment Canada 2012).However,while salt is relatively inexpensive to purchase,there are a number of external costs that are becoming increasingly apparent.These include corrosion of vehicles and infrastructure like concrete,bridges,and water mains;damage and staining to the interior and exterior of buildings;impacts to roadside vegetation and soils;and the contamination of fresh water.In fact,the environmental impacts are such that it prompted Environment Canada to propose that winter salt be considered a toxic substance primarily due to the quantity that is applied annually(Environment Canada 2001).The Lake Simcoe watershed,approximately 3,400km2 in size,is situated just 20km north of Toronto,Ontario,with the southern portion of the watershed being considered part of the Greater Toronto Area(GTA),the most populous metropolitan area in Canada.As part of the GTA,the Lake Simcoe watershed has experienced and continues to experience considerable growth,and with this growth comes an increase in the amount of impervious surfaces requiring winter salting.Indeed,chloride has been showing a strong increasing trend in the urban creeks and in Lake Simcoe itself over the last 30 years.Even rural creeks are showing an increasing trend,albeit not as severe,nor are the concentrations of chloride reaching the same levels(LSRCA 2015).The highest chloride level recorded in a Lake Simcoe tributary was 6,120mg/l in the winter of 2013.Chloride guidelines for the protection of aquatic ecosystems utilize a guideline of 120mg/L for chronic exposure and 640mg/L for acute exposure(CCME 2011).While the high value recorded in the Lake Simcoe tributary greatly exceeds these guidelines,it is still drastically lower than values being recorded in larger,intensively urbanized catchments such as Cooksville Creek in Mississauga,Ontario,which sees concentrations in excess of 20,000 mg/L,the concentration of sea water,nearly every winter(Credit Valley Conservation personal comm).Similarly,in July of 2011 a small population of Atlantic blue crabs,a marine species,was found surviving in Mimico Creek in Toronto(Toronto Star:May 26,2012).That a marine species was able to survive in this fresh water creek in summer demonstrates that the impacts of winter salt are not just limited to winter but are impacting shallow groundwater and thus summer baseflow,maintaining high chloride concentrations year round.The same is being seen in some urban creeks in the Lake Simcoe watershed,with summer baseflow concentrations exceeding the chronic guideline and trending upwards(LSRCA unpublished).While not yet as extreme as rivers in the more densely urbanized parts of the GTA,these examples foreshadow what is in store for Lake Simcoe rivers if current winter salt practices continue along with the projected urban growth.During the winter of 2012 an estimated 99,300 tonnes of salt was applied in the Lake Simcoe watershed,an amount that equals nearly 250kg of salt per capita,or~3 times the average person’s body weight in salt.This estimate was generated through a survey of local road agencies along with the total area of commercial/institutional parking lots within the watershed.The exercise served to highlight a knowledge gap around application practices and rates in commercial/institutional parking lots.The majority of road agencies were found to record annual volumes,application dates and rates whereas literature values range from 10-40%of the salt applied in a catchment come from commercial/institutional parking lots(Perera et al,2009;Trowbridge et al,2010;Lake Simcoe Region Conservation Authority,2015),and a survey of winter maintenance contractors cite an average value of approximately 58g/m2/application(Fu et al,2013)(Figure 1).展开更多
文摘The simulation of large-strain geotechnical laboratory tests with conventional Lagrangian finite element method(FEM)techniques is often problematic due to excessive mesh distortion.The multiple reversal direct shear(MRDS)test can be used to measure the residual shear strength of soils in a laboratory setting.However,modelling and simulation generally require advanced numerical methods to accommodate the large shear strains concentrated in the shear plane.In reality,when the standard direct shear(DS)apparatus is used,the MRDS method is prone to two major sources of measurement error:load cap tilting and specimen loss.These sources of error make it difficult or even impossible to correctly determine the residual shear strength.This paper presents a modified DS apparatus and multi-reversal multi-stage test method,simulated using the coupled Eulerian-Lagrangian(CEL)method in a finite element environment.The method was successful in evaluating equipment and preventing both load cap tilting and specimen loss,while modelling large-deformation behaviour that is not readily simulated with the conventional FEM or arbitrary Lagrangian-Eulerian(ALE)analysis.Thereafter,a modified DS apparatus was created for the purpose of analysing mixtures of organic materials found in an Australian clay.The results obtained from the modified DS CEL model in combination with laboratory tests show a great improvement in the measured residual shear strength profiles compared to those from the standard apparatus.The modified DS setup ensures that accurate material residual shear strengths are calculated,a factor that is vital to ensure appropriate soil behaviour is simulated for numerical analyses of large-scale geotechnical projects.
基金supported by the Australian Research Council(Grant No.IH130200012)Alfred P Sloan Foundation(Grant Nos.G-2017-9997 and G-2018-11296)through the Deep Carbon Observatory.
文摘Major advances in computational power,as well as community modelling workflows and an improvement in data availability,has revolutionized Earth sciences over the last decade.Geological data has been synthesized into flexible and open access plate tectonic and paleogeographic reconstructions using the open-source and cross-platform GPlates(www.gplates.org)software since 2008(Muller et al.,2018;Muller et al.,2008).
基金This work was supported by Major Science and Technology Program for Water Pollution Control and Treatment(No.2015ZX07406005)Also thanks to the National Natural Science Foundation of China(No.41430643 and No.51774270)the National Key Research&Development Plan(No.2016YFC0501109).
文摘Coupling Bayes’Theorem with a two-dimensional(2D)groundwater solute advection-diffusion transport equation allows an inverse model to be established to identify a set of contamination source parameters including source intensity(M),release location(0 X,0 Y)and release time(0 T),based on monitoring well data.To address the issues of insufficient monitoring wells or weak correlation between monitoring data and model parameters,a monitoring well design optimization approach was developed based on the Bayesian formula and information entropy.To demonstrate how the model works,an exemplar problem with an instantaneous release of a contaminant in a confined groundwater aquifer was employed.The information entropy of the model parameters posterior distribution was used as a criterion to evaluate the monitoring data quantity index.The optimal monitoring well position and monitoring frequency were solved by the two-step Monte Carlo method and differential evolution algorithm given a known well monitoring locations and monitoring events.Based on the optimized monitoring well position and sampling frequency,the contamination source was identified by an improved Metropolis algorithm using the Latin hypercube sampling approach.The case study results show that the following parameters were obtained:1)the optimal monitoring well position(D)is at(445,200);and 2)the optimal monitoring frequency(Δt)is 7,providing that the monitoring events is set as 5 times.Employing the optimized monitoring well position and frequency,the mean errors of inverse modeling results in source parameters(M,X0,Y0,T0)were 9.20%,0.25%,0.0061%,and 0.33%,respectively.The optimized monitoring well position and sampling frequency canIt was also learnt that the improved Metropolis-Hastings algorithm(a Markov chain Monte Carlo method)can make the inverse modeling result independent of the initial sampling points and achieves an overall optimization,which significantly improved the accuracy and numerical stability of the inverse modeling results.
基金Social Sciences and Humanities Research Council of CanadaNatural Sciences and Engineering Research Council of Canada+1 种基金Canadian Institute of Health ResearchIDRC。
文摘Climate variability,together with other drivers of global change(like population growth,land-use change,etc.),is affecting the management offloods.Traditional approaches are no longer sufficient to address the increased pressures that areas vulnerable toflooding are facing.A paradigm shift fromflood risk reduction toflood resilience-building strategies is required.An analytical framework is developed to help quantify,compare,and visualize dynamic resilience toflooding to address some shortcomings in current resilience assessment research.The proposed methodological framework forflood resilience combines physical,economic,engineering,health,and social spatio-temporal impacts and adaptive capacities offlood-affected systems.To capture the dynamic spatio-temporal characteristics of resilience and gauge the effectiveness of potential climate change adaptation options,aflood resilience simulation tool(FRST)is developed to use the analytical framework.The FRST is applied to a case study in Metro Vancouver,British Columbia,Canada.The simulation model focuses on the impacts of climate change-influenced riverineflooding and sea-level rise.Simulation results suggest that various adaptation options,such as access to emergency funding,mobile hospital services,and managed retreat can all help to increase resilience toflooding.Results also suggest that,at a regional scale,Metro Vancouver is rather resilient to climate change-influencedflood hazards.
基金support from the University of the PhilippinesNational Institute of Geological Sciencesfinancial support from the Department of Science and Technology through the years
文摘New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age.Radiometric dating of its plutonic and volcanichypabyssal rocks yielded middle Eocene ages.On the other hand,the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge-island arc affiliated Coto block of the ophiolite complex,together with isotopic age datings of its dikes and mafic cumulate rocks,also yielded Eocene ages.This offers the possibility that the Zambales Ophiolite Complex could have:(1)evolved from a Mesozoic arc(Acoje block)that split to form a Cenozoic back-arc basin(Coto block),(2)through faulting,structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or(3)through the interplay of slab rollback,slab break-off and,at a later time,collision with a microcontinent fragment,caused the formation of an island arc-related ophiolite block(Acoje)that migrated trench-ward resulting into the generation of a back-arc basin(Coto block)with a limited subduction signature.This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation.
文摘The variable-density flow model-SEAWAT Version 4, was used to evaluate the hydrogeological conditions associatedwith hydraulic fracturing （fracking） the limestone oil reservoir in the Lower Cretaceous Sunniland Formation of Southwest Florida.This research contributes to the understanding of the controls on fluid and potential contaminant migration, following high pressurehydraulic fracturing. A hydraulic fracturing treatment used recently in this formation at the Collier-Hogan 20-3H well represents thebase case simulation. Multiple stage fracturing using typical stress periods, a modelled fracture zone radius, and various injectionrates were tested to evaluate the potential for horizontal and vertical fluid migration in and from the reservoir under dynamicconditions, with TDS used as a tracer. Hypothetical scenarios including preferential vertical pathways between the SunnilandFormation and the Lower Floridan aquifer Boulder Zone were also simulated. Results indicate that injected fluids do not migratesignificantly in the lateral and vertical directions beyond the design fractured zone, unless a preferential pathway exists within closeproximity to the fractured zone. In a worst-case scenario under the simulated conditions, vertical heads are approximately 580 metersgreater than static conditions and fluids associated with hydraulic fracturing vertically migrate approximately 500 meters; therefore,the quality of the deepest sources of drinking water is not compromised. Analytical results from a monitoring well installed in theimmediate vicinity of the Collier-Hogan 20-3H well and at the base of the deepest source of drinking water support the conclusionthat impacts from hydraulic fracturing fluids have not migrated into the deepest sources of drinking water.
文摘INTRODUCTION Winter snow and ice can have a significant impact on our mobility,whether on foot or by car.Alongside plowing,arguably the greatest tool in combating snow and ice is salt.The most commonly used salt for winter maintenance is Sodium Chloride(NaCl),the same salt used in food and water softeners,is applied to roads,sidewalks,and parking lots as it is an effective deicer when temperatures are between 0℃ and-12℃.Studies have shown that deicing with salt reduces accidents by 88%and injuries by 85%(Salt Institute 2017).The effectiveness of road salt,as well as its relative affordability,means that as much as four million tonnes may be applied annually in Canada for deicing(Environment Canada 2012).However,while salt is relatively inexpensive to purchase,there are a number of external costs that are becoming increasingly apparent.These include corrosion of vehicles and infrastructure like concrete,bridges,and water mains;damage and staining to the interior and exterior of buildings;impacts to roadside vegetation and soils;and the contamination of fresh water.In fact,the environmental impacts are such that it prompted Environment Canada to propose that winter salt be considered a toxic substance primarily due to the quantity that is applied annually(Environment Canada 2001).The Lake Simcoe watershed,approximately 3,400km2 in size,is situated just 20km north of Toronto,Ontario,with the southern portion of the watershed being considered part of the Greater Toronto Area(GTA),the most populous metropolitan area in Canada.As part of the GTA,the Lake Simcoe watershed has experienced and continues to experience considerable growth,and with this growth comes an increase in the amount of impervious surfaces requiring winter salting.Indeed,chloride has been showing a strong increasing trend in the urban creeks and in Lake Simcoe itself over the last 30 years.Even rural creeks are showing an increasing trend,albeit not as severe,nor are the concentrations of chloride reaching the same levels(LSRCA 2015).The highest chloride level recorded in a Lake Simcoe tributary was 6,120mg/l in the winter of 2013.Chloride guidelines for the protection of aquatic ecosystems utilize a guideline of 120mg/L for chronic exposure and 640mg/L for acute exposure(CCME 2011).While the high value recorded in the Lake Simcoe tributary greatly exceeds these guidelines,it is still drastically lower than values being recorded in larger,intensively urbanized catchments such as Cooksville Creek in Mississauga,Ontario,which sees concentrations in excess of 20,000 mg/L,the concentration of sea water,nearly every winter(Credit Valley Conservation personal comm).Similarly,in July of 2011 a small population of Atlantic blue crabs,a marine species,was found surviving in Mimico Creek in Toronto(Toronto Star:May 26,2012).That a marine species was able to survive in this fresh water creek in summer demonstrates that the impacts of winter salt are not just limited to winter but are impacting shallow groundwater and thus summer baseflow,maintaining high chloride concentrations year round.The same is being seen in some urban creeks in the Lake Simcoe watershed,with summer baseflow concentrations exceeding the chronic guideline and trending upwards(LSRCA unpublished).While not yet as extreme as rivers in the more densely urbanized parts of the GTA,these examples foreshadow what is in store for Lake Simcoe rivers if current winter salt practices continue along with the projected urban growth.During the winter of 2012 an estimated 99,300 tonnes of salt was applied in the Lake Simcoe watershed,an amount that equals nearly 250kg of salt per capita,or~3 times the average person’s body weight in salt.This estimate was generated through a survey of local road agencies along with the total area of commercial/institutional parking lots within the watershed.The exercise served to highlight a knowledge gap around application practices and rates in commercial/institutional parking lots.The majority of road agencies were found to record annual volumes,application dates and rates whereas literature values range from 10-40%of the salt applied in a catchment come from commercial/institutional parking lots(Perera et al,2009;Trowbridge et al,2010;Lake Simcoe Region Conservation Authority,2015),and a survey of winter maintenance contractors cite an average value of approximately 58g/m2/application(Fu et al,2013)(Figure 1).
