This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less impor...This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less importance in controlling the maximum response to impulsive loadings because the maximum response is reached in a very short time,before the damping forces can dissipate a significant portion of the energy input into the system.The development of two sine series solutions,relating to different types of impulsive loadings,one involving a single concentrated force and the other a distributed line load,are presented.This study revealed that when a simply supported Euler-Bernoulli beam,resting on a Winkler soil model,is subject to an impact load,the resulting vertical displacements,bending moments and shear forces produced along the span of the beam are considerably affected.In particular,the quantification of this effect is best observed,relative to the corresponding static solution,via an amplification factor.The computed impact amplification factors,for the sub-grade moduli used in this study,were in magnitude greater than 2,thus confirming the multiple-degree-of-freedom nature of the problem.展开更多
The durability of reinforced concrete structures is greatly influenced by the corrosion of the reinforcement. In addition to air pollution related to the repair of corroded structures, chloride ions are the main facto...The durability of reinforced concrete structures is greatly influenced by the corrosion of the reinforcement. In addition to air pollution related to the repair of corroded structures, chloride ions are the main factors of corrosion of reinforced concrete structures. This study aims to valorize a clay inhibitor against reinforcement corrosion in reinforced concrete. This clay (Attapulgite) was incorporated into reinforced concretes at different percentages of substitution of calcined attapulgite (0%, 5% and 10%) to cement in the formulation. The corrosion inhibitory power of attapulgite is evaluated in reinforced concretes subjected to the action of chloride ions at different intervals in the NaCl solution (1 day, 21 days and 45 days) by electrochemical methods (zero current chronopotentiometry, polarization curves and electrochemical impedance spectroscopy). This study showed that in the presence of chloride ions, the composition based on 10% attapulgite has an appreciable inhibitory effect with an average inhibitory efficiency of 82%.展开更多
Most reinforced concrete structures in seaside locations suffer from corrosion damage to the reinforcement, limiting their durability and necessitating costly repairs. To improve their performance and durability, we h...Most reinforced concrete structures in seaside locations suffer from corrosion damage to the reinforcement, limiting their durability and necessitating costly repairs. To improve their performance and durability, we have investigated in this paper Aloe vera extracts as a green corrosion inhibitor for reinforcing steel in NaCl environments. Using electrochemical methods (zero-intensity chronopotentiometry, Tafel lines and electrochemical impedance spectroscopy), this experimental work investigated the effect of these Aloe vera (AV) extracts on corrosion inhibition of concrete reinforcing bar (HA, diameter 12mm) immersed in a 0.5M NaCl solution. The results show that Aloe vera extracts have an average corrosion-inhibiting efficacy of around 86% at an optimum concentration of 20%.展开更多
Despite its low resistance to humidity, adobe remains the most widely used material for housing construction, particularly in developing countries. The present study aims to assess different modes of use of fermented ...Despite its low resistance to humidity, adobe remains the most widely used material for housing construction, particularly in developing countries. The present study aims to assess different modes of use of fermented RH and to evaluate their influence on the behavior of raw earth for application in plaster. The influences of two types of RH are evaluated: granular rice husk (RHg) and powdered RH (RHp). The clay mainly consists of clay (40%), silt (22%), and sand (38.4%), with a small proportion of gravel (0.24%). Its liquidity limit is 40% and the plasticity index is 26.5%. The mixtures were designed using earth and each of the two rice husks at the volumetric content of 10%, 15% and 20% of the total volume mixed with water 36.5%, 38.5% and 40.3% and fermented for three weeks. Each fermented mixture was added to the soil to form the paste, and 40 × 40 × 160 mm<sup>3</sup> test speciments were made for characterization. The results generally show an improvement in the physico-mechanical properties and water resistance of the mortars containing fermented RH, with an optimal content between 10% and 15%. The powdered RH improved the performance of the mortar better than granular RH.展开更多
In the Sahelian zone in Africa, groundwater is the main source of drinking water for domestic, industrial, and agricultural uses. The groundwater of the Samba Dia sandy aquifer was assessed for understanding processes...In the Sahelian zone in Africa, groundwater is the main source of drinking water for domestic, industrial, and agricultural uses. The groundwater of the Samba Dia sandy aquifer was assessed for understanding processes controlling the hydrogeochemistry and its drinking and irrigation suitability, on the basis of various water quality parameters. For the present study, thirty-three groundwater samples were collected in wells of the study area during the dry season in March 2021 and subjected to analysis for chemical characteristics (major ions), pH, electrical conductivity (EC), and total dissolved solids (TDS). Gibbs plot depicts that the process of ionic exchange is mainly due to the dissolution of water-rock interaction. The Piper diagram indicates a largely dominant sodium chloride facies with 70% of the groundwater samples followed by calcium chloride facies (18%) than calcium bicarbonate facies (12%). Analytical results of hydrogeochemical parameters of groundwater samples reveal that the majority of samples are within the World Health Organization safety range for drinking water. TDS and electrical conductivity (EC) values of groundwater indicate that 70% and 61% are safe for drinking water, respectively. Sodium percentage (% Na), Sodium Adsorption Ratio (SAR) values, and Ca/Mg ratio were calculated and compared with the standard guideline values recommended by the World Health Organization and agricultural water standards. This study shows that the groundwater in the area is mostly chemically suitable for drinking and irrigation, although some wells at the edge of the area exhibit signs of progressive salinization and traces of pollution.展开更多
The stability analysis of passive bolt-reinforced rock slopes under seismic loads is investigated within the framework of the kinematic approach of limit analysis theory.A pseudo-static method is adopted to account fo...The stability analysis of passive bolt-reinforced rock slopes under seismic loads is investigated within the framework of the kinematic approach of limit analysis theory.A pseudo-static method is adopted to account for the inertial forces induced in the rock mass by seismic events.The strength properties of the rock material are described by a modified Hoek-Brown strength criterion,whereas the passive bolts are modeled as bar-like inclusions that exhibit only resistance to tensile-compressive forces.Taking advantage of the ability to compute closed-form expressions for the support functions associated with the modified Hoek-Brown strength criterion,a rotational failure mechanism is implemented to derive rigorous lower bound estimates for the amount of reinforcement strength to prevent slope failure.The approach is then applied to investigating the effects of relevant geometry,strength and loading parameters in light of a preliminary parametric study.The accuracy of the approach is assessed by comparison of the lower bound estimates with finite element limit analysis solutions,thus emphasizing the ability of the approach to properly predict the stability conditions and to capture the essential features of deformation localization pattern.Finally,the extension of the approach to account for slipping at the interface between reinforcements and surrounding rock mass is outlined.展开更多
This paper uses the four-variable refined plate theory (RPT) for the free vibration analysis of functionally graded material (FGM) sandwich rectangular plates. Unlike other theories, there are only four unknown fu...This paper uses the four-variable refined plate theory (RPT) for the free vibration analysis of functionally graded material (FGM) sandwich rectangular plates. Unlike other theories, there are only four unknown functions involved, as compared to five in other shear deformation theories. The theory presented is variationally consistent and strongly similar to the classical plate theory in many aspects. It does not require the shear correction factor, and gives rise to the transverse shear stress variation so that the transverse shear stresses vary parabolically across the thickness to satisfy free surface conditions for the shear stress. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM facesheet and the homogeneous core and the sandwich with the homogeneous facesheet and the FGM core. The equation of motion for the FGM sandwich plates is obtained based on Hamilton's principle. The closed form solutions are obtained by using the Navier technique. The fundamental frequencies are found by solving the eigenvalue problems. The validity of the theory is shown by comparing the present results with those of the classical, the first-order, and the other higher-order theories. The proposed theory is accurate and simple in solving the free vibration behavior of the FGM sandwich plates.展开更多
Seepage-induced fines migration under rainfall infiltration is a main cause leading to shallow failures in loose colluvial slopes. To describe the full process of fines migration within unsaturated soils during rainfa...Seepage-induced fines migration under rainfall infiltration is a main cause leading to shallow failures in loose colluvial slopes. To describe the full process of fines migration within unsaturated soils during rainfall infiltration and the associated hydromechanical behaviors, a seepage-erosion-deformation coupled formulation is proposed in this paper. The governing equations proposed are implemented into a finite element code and used to investigate the influences of skeleton deformation on the rainfall infiltration process through unsaturated soil columns.The numerical results were presented in detail for a better understanding of the rainfall-induced fines migration process within unsaturated soils. Further,the obtained results are integrated into an infinite slope model for slope stability analysis. The results show that, the skeleton deformation will affect the rainfall infiltration rate and hence the timing of slope failures; meanwhile their influences are more evident if the fines deposition process is taken into account.Moreover, the slope stability could be reduced gradually due to the soil strength loss along with loss of fine particles. Therefore, particular attentions should be paid to analyzing the stability of soil slopes susceptible to internal erosion.展开更多
The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brittleness using artificial neural networks(ANN). Herein hard rock brittleness is defined using Yagiz'method. A pre...The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brittleness using artificial neural networks(ANN). Herein hard rock brittleness is defined using Yagiz'method. A predictive model is developed using a comprehensive database compiled from 30 years' worth of rock tests at the Earth Mechanics Institute(EMI), Colorado School of Mines. The model is sensitive to density, elastic properties, and P- and S-wave velocities. The results show that the model is a better predictor of rock brittleness than conventional destructive strength-test based models and multiple regression techniques. While the findings have direct implications on intact rock, the methodology can be extrapolated to rock mass problems in both tunneling and underground mining where rock brittleness is an important control.展开更多
In this paper, we suggest to study the behavior of a mat foundation on subsoil from the plate theory taking into account the soil-structure interaction. The objective is to highlight the soil-structure interaction par...In this paper, we suggest to study the behavior of a mat foundation on subsoil from the plate theory taking into account the soil-structure interaction. The objective is to highlight the soil-structure interaction particularly the influence of the rigidities of the soil and the concrete on the subgrade reaction (k) and the displacements of the mat foundation subjected to vertical loads. From plate theory and the soil-structure interaction, the general equation is reached. This equation depends more on the subgrade properties than the concrete foundation properties. Consequently, the behavior of the mat foundation is more influenced by soil properties than the concrete.展开更多
Geological disasters such as slope failure and landslides can cause loss of life and property.Therefore,reproducing their evolution process is of great importance for risk assessment and mitigation.The recently develo...Geological disasters such as slope failure and landslides can cause loss of life and property.Therefore,reproducing their evolution process is of great importance for risk assessment and mitigation.The recently developed SIMSAND critical state sand model combined with the smoothed particle hydrodynamics(SPH)method is adopted in this work to study slope failure under large deformations.To illustrate the efficiency and accuracy of the SIMSAND-SPH approach,a series of slope collapse studies using the discrete element method(DEM)considering various particle shapes(i.e.spherical,tetrahedral and elongated)is adopted as benchmarks.The parameters of the SIMSAND model are calibrated using DEM triaxial tests.In comparison to the DEM simulations,the runout distance and final slope height are well characterized with the SIMSAND-SPH approach with less computational cost.All comparisons show that the SIMSAND-SPH approach is highly efficient and accurate,which can be an alternative numerical tool to simulate real scale granular flow.展开更多
To elucidate what controls the magnitude of longitudinal growth stress in tension wood, anatomical measurements of gelatinous fibres were carried out on poplar tension wood (Populus I4551). Sections were cut from embe...To elucidate what controls the magnitude of longitudinal growth stress in tension wood, anatomical measurements of gelatinous fibres were carried out on poplar tension wood (Populus I4551). Sections were cut from embedded blocks to avoid a border artefact described earlier. Results showed that: 1) no gelatinous fibres were observed under a growth strain level from 0.06% to 0.08%; 2) almost all of the non-conductive tissues contained gelatinous fibres above a growth strain level from 0.15% to 0.19%; 3) the amount of fibres, the amount of fibres with gelatinous layer, per unit of tissue area, and the thickness of the gelatinous layers controlled most of the magnitude of growth stress; 4) the contribution of the S2 layer in both fibre types could also play a role in the growth stress generation.展开更多
A few constitutive models for unsaturated soils have already been proposed,however,many classic models such as the Barcelona basic model can simulate neither complex volumetric soil behaviour(without forgetting its s...A few constitutive models for unsaturated soils have already been proposed,however,many classic models such as the Barcelona basic model can simulate neither complex volumetric soil behaviour(without forgetting its supreme merit of being the first consistently and rigorously formulated model) nor post-peak softening,and most advanced models generally comprise a large number of parameters making them more difficult to be applied to practical situations.In this paper,we present a new model for unsaturated soils based on an existing model developed originally for saturated soils.It comprises a minimum number of constitutive parameters.The extension to unsaturated state is achieved by following a general methodology previously developed in our laboratory.The capacities of this simple model are tested.With only 13 parameters,it can reproduce the basic behaviour of unsaturated soils such as rebound or collapse upon wetting,depending on the stress levels.It can also reproduce post-peak softening and transition from contractant to dilatant volumetric behaviour during undrained shear.Overall,the first tentative of validation gives a good correlation between simulations and experimental data,and shows encouraging signs for future developments.展开更多
Oil Palm Shell (OPS) concrete can be used in different fields of construction. To determine more accurately the fields of application, it is important to know and understand the behaviour of OPS concrete over<span ...Oil Palm Shell (OPS) concrete can be used in different fields of construction. To determine more accurately the fields of application, it is important to know and understand the behaviour of OPS concrete over<span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> the</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> long term and when it is in aggressive environments. This paper presents the results of studies conducted on the durability of OPS concrete. Water absorption capacity, electrical resistivity and apparent diffusion of chloride ions have been measured on different concrete samples. In addition, the behaviour of OPS concretes to carbonation was studied in an environment rich in carbon dioxide. Results show that OPS concrete ha</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> an absorptivity of 0.97 kg/m</span><sup><span style="font-family:Verdana;">2</span></sup></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">·</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">h</span><sup><span style="font-family:Verdana;">1/2</span></sup><span style="font-family:Verdana;">, an electrical resistivity of 64.37 Ω</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">·</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">m and an apparent diffusion coefficient of chloride ions of 3.84</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> × </span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">10</span><sup><span style="font-family:Verdana;">-12</span></sup><span style="font-family:Verdana;"> m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">/s after 90 days. All these results of OPS concrete are very close to those of concrete with normal aggregate and other lightweight concrete</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> which mean OPS concretes have globally good properties with regard to durability</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.</span></span></span>展开更多
Due to its rapid movement, preferential flow (PF) in the vadose zone allows much faster contaminant transport, which may have a significant impact on ground-water quality. PF can occur in heterogeneous vadose zones an...Due to its rapid movement, preferential flow (PF) in the vadose zone allows much faster contaminant transport, which may have a significant impact on ground-water quality. PF can occur in heterogeneous vadose zones and it strongly depends on hydric and hydraulic conditions like entering flow rates at surface. This study deals with the modeling of the establishment of PF, and related solute transfer during the infiltration phase in a strongly heterogeneous glaciofluvial deposit. This deposit is made of four contrasting lithofacies (sand, gravel, bimodal gravel and matrix-free gravel) and lies underneath an urban infiltration basin (Lyon, France). Previous studies have been carried out on this site and linked the regionalization of soil pollution with the lithological heterogeneity. But none of them clearly demonstrated how heterogeneity could impact flow and solute transfer and may explain such a regionalization. In this study, we model flow and solute transfer at the trench scale for both uniform and heterogeneous profiles in order to characterize the effect of lithological heterogeneity. In addition, such a modeling was performed for two different entering flow rates to depict the influence of condition at surface on PF. A key result is that heterogeneity clearly impacts unsaturated flow and solute transfer. Numerical modeling permitted pointing out the existence of PF paths associated with the sedimentary heterogeneity of the glaciofluvial deposit. For lower surface fluxes, the sand lens and matrix-free gravel were the sources of capillary barrier effects, leading to a funneled flow and a groundwater recharge characterized by earlier and more dispersed wetting fronts. Such a flow pattern enhances solutes transfer and reduces solute retention by soil. Thus, the effect of heterogeneity on solute transfer is significant, especially for the most reactive solutes.展开更多
The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms fr...The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kg w /kg dm to 3.12 kg w /kg dm were characterized. A novel procedure has been developed to determine the water content profiles inside samples during isothermal drying. At both temperatures, experimental results underlined that the physical properties of Spirulina are not sensitive to the geographical origin, Burkina-Faso or France. To keep Spirulina at an water activity below 0.6 in order to preserve it from micro-organisms development, sorption isotherm curves show that a sufficient requirement is to lower the water content until an upper limit of w = 0.075 db. The evolution of water transport coefficient as a function of water content highlights a monotonous exponential dependence with a transport coefficient ranging from 1.70 × 10–10 to 94 × 10–10 m2/s. The contribution of solid phase shrinkage to the transport of water is negligible for the last drying steps.展开更多
Hydric properties evolution during drying differs from one product to another and has been the subject of various studies due to its crucial importance in modeling the drying process. The variation of these parameters...Hydric properties evolution during drying differs from one product to another and has been the subject of various studies due to its crucial importance in modeling the drying process. The variation of these parameters in the solid matrix and in time during the drying of Spirulina platensis has not known an advanced understanding. The objective of this study was to evaluate the evolution of the water content profile, the mass flow, the concentration gradient and the diffusion coefficient during the drying of Spirulina platensis taking into account the shrinkage. Modeling and experimental analysis (at 50°C and HR = 6%) by the cutting method a cylinder 20 mm in diameter and 40 mm thick were carried. The water content profiles of two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kgw/kgdb and 3.12 kgw/kgdb were determined. These profiles have been adjusted by a polynomial function. Identical water behavior is observed regardless of the origin of the samples. Water distribution is heterogeneous. Mass flow and concentration gradient are greater at the edge than inside the product. The water transport coefficient, ranging from 1.70 × 10?10 to 94 × 10?10 m2/s, is determined from a linear approach.展开更多
基金l’UniversitéLaval for the financial support of his sabbatical year at Dipartimento di Bioscienze e Territorio,Universitàdegli Studi del Molise in Campobasso,Italy。
文摘This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less importance in controlling the maximum response to impulsive loadings because the maximum response is reached in a very short time,before the damping forces can dissipate a significant portion of the energy input into the system.The development of two sine series solutions,relating to different types of impulsive loadings,one involving a single concentrated force and the other a distributed line load,are presented.This study revealed that when a simply supported Euler-Bernoulli beam,resting on a Winkler soil model,is subject to an impact load,the resulting vertical displacements,bending moments and shear forces produced along the span of the beam are considerably affected.In particular,the quantification of this effect is best observed,relative to the corresponding static solution,via an amplification factor.The computed impact amplification factors,for the sub-grade moduli used in this study,were in magnitude greater than 2,thus confirming the multiple-degree-of-freedom nature of the problem.
文摘The durability of reinforced concrete structures is greatly influenced by the corrosion of the reinforcement. In addition to air pollution related to the repair of corroded structures, chloride ions are the main factors of corrosion of reinforced concrete structures. This study aims to valorize a clay inhibitor against reinforcement corrosion in reinforced concrete. This clay (Attapulgite) was incorporated into reinforced concretes at different percentages of substitution of calcined attapulgite (0%, 5% and 10%) to cement in the formulation. The corrosion inhibitory power of attapulgite is evaluated in reinforced concretes subjected to the action of chloride ions at different intervals in the NaCl solution (1 day, 21 days and 45 days) by electrochemical methods (zero current chronopotentiometry, polarization curves and electrochemical impedance spectroscopy). This study showed that in the presence of chloride ions, the composition based on 10% attapulgite has an appreciable inhibitory effect with an average inhibitory efficiency of 82%.
文摘Most reinforced concrete structures in seaside locations suffer from corrosion damage to the reinforcement, limiting their durability and necessitating costly repairs. To improve their performance and durability, we have investigated in this paper Aloe vera extracts as a green corrosion inhibitor for reinforcing steel in NaCl environments. Using electrochemical methods (zero-intensity chronopotentiometry, Tafel lines and electrochemical impedance spectroscopy), this experimental work investigated the effect of these Aloe vera (AV) extracts on corrosion inhibition of concrete reinforcing bar (HA, diameter 12mm) immersed in a 0.5M NaCl solution. The results show that Aloe vera extracts have an average corrosion-inhibiting efficacy of around 86% at an optimum concentration of 20%.
文摘Despite its low resistance to humidity, adobe remains the most widely used material for housing construction, particularly in developing countries. The present study aims to assess different modes of use of fermented RH and to evaluate their influence on the behavior of raw earth for application in plaster. The influences of two types of RH are evaluated: granular rice husk (RHg) and powdered RH (RHp). The clay mainly consists of clay (40%), silt (22%), and sand (38.4%), with a small proportion of gravel (0.24%). Its liquidity limit is 40% and the plasticity index is 26.5%. The mixtures were designed using earth and each of the two rice husks at the volumetric content of 10%, 15% and 20% of the total volume mixed with water 36.5%, 38.5% and 40.3% and fermented for three weeks. Each fermented mixture was added to the soil to form the paste, and 40 × 40 × 160 mm<sup>3</sup> test speciments were made for characterization. The results generally show an improvement in the physico-mechanical properties and water resistance of the mortars containing fermented RH, with an optimal content between 10% and 15%. The powdered RH improved the performance of the mortar better than granular RH.
基金the scholarship support from the Chinese Scholarship Councilthe financial supports from the National Natural Science Foundation of China (No. 52071207)+2 种基金the China Postdoctoral Science Foundation (Nos. 2019TQ0193, 2019M661497)the National Key Research and Development Program of China (No. 2018YFB1106302)Anhui Provincial Engineering Research Center of Aluminum Matrix Composites, China (No. 2017WAMC002)
文摘In the Sahelian zone in Africa, groundwater is the main source of drinking water for domestic, industrial, and agricultural uses. The groundwater of the Samba Dia sandy aquifer was assessed for understanding processes controlling the hydrogeochemistry and its drinking and irrigation suitability, on the basis of various water quality parameters. For the present study, thirty-three groundwater samples were collected in wells of the study area during the dry season in March 2021 and subjected to analysis for chemical characteristics (major ions), pH, electrical conductivity (EC), and total dissolved solids (TDS). Gibbs plot depicts that the process of ionic exchange is mainly due to the dissolution of water-rock interaction. The Piper diagram indicates a largely dominant sodium chloride facies with 70% of the groundwater samples followed by calcium chloride facies (18%) than calcium bicarbonate facies (12%). Analytical results of hydrogeochemical parameters of groundwater samples reveal that the majority of samples are within the World Health Organization safety range for drinking water. TDS and electrical conductivity (EC) values of groundwater indicate that 70% and 61% are safe for drinking water, respectively. Sodium percentage (% Na), Sodium Adsorption Ratio (SAR) values, and Ca/Mg ratio were calculated and compared with the standard guideline values recommended by the World Health Organization and agricultural water standards. This study shows that the groundwater in the area is mostly chemically suitable for drinking and irrigation, although some wells at the edge of the area exhibit signs of progressive salinization and traces of pollution.
基金Projects(51908069, 51908073, 51838001, 51878070) supported by the National Natural Science Foundation of ChinaProject(2019SK2171) supported by the Key Research and Development Program of Hunan Province, China+3 种基金Project(2019IC04) supported by the Double First-Class Scientific Research International Cooperation Expansion Project of Changsha University of Science & Technology,ChinaProject(kfj190605) supported by the Open Fund of Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province (Changsha University of Science & Technology), ChinaProject(kq1905043) supported by the Training Program for Excellent Young Innovators of Changsha, ChinaProject(SJCX202017) supported by the Practical Innovation Program for Graduates of Changsha University of Science & Technology, China。
基金financial support from Ecole des Ponts et Chaussées-ParisTech(France)the French Institute of Tunisia (French Embassy-Tunisia)Laboratoire de Génie Civil (ENIT) through project SSHN2015-ENPC/ENIT
文摘The stability analysis of passive bolt-reinforced rock slopes under seismic loads is investigated within the framework of the kinematic approach of limit analysis theory.A pseudo-static method is adopted to account for the inertial forces induced in the rock mass by seismic events.The strength properties of the rock material are described by a modified Hoek-Brown strength criterion,whereas the passive bolts are modeled as bar-like inclusions that exhibit only resistance to tensile-compressive forces.Taking advantage of the ability to compute closed-form expressions for the support functions associated with the modified Hoek-Brown strength criterion,a rotational failure mechanism is implemented to derive rigorous lower bound estimates for the amount of reinforcement strength to prevent slope failure.The approach is then applied to investigating the effects of relevant geometry,strength and loading parameters in light of a preliminary parametric study.The accuracy of the approach is assessed by comparison of the lower bound estimates with finite element limit analysis solutions,thus emphasizing the ability of the approach to properly predict the stability conditions and to capture the essential features of deformation localization pattern.Finally,the extension of the approach to account for slipping at the interface between reinforcements and surrounding rock mass is outlined.
文摘This paper uses the four-variable refined plate theory (RPT) for the free vibration analysis of functionally graded material (FGM) sandwich rectangular plates. Unlike other theories, there are only four unknown functions involved, as compared to five in other shear deformation theories. The theory presented is variationally consistent and strongly similar to the classical plate theory in many aspects. It does not require the shear correction factor, and gives rise to the transverse shear stress variation so that the transverse shear stresses vary parabolically across the thickness to satisfy free surface conditions for the shear stress. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM facesheet and the homogeneous core and the sandwich with the homogeneous facesheet and the FGM core. The equation of motion for the FGM sandwich plates is obtained based on Hamilton's principle. The closed form solutions are obtained by using the Navier technique. The fundamental frequencies are found by solving the eigenvalue problems. The validity of the theory is shown by comparing the present results with those of the classical, the first-order, and the other higher-order theories. The proposed theory is accurate and simple in solving the free vibration behavior of the FGM sandwich plates.
基金support from the Hundred YoungTalents Program of IMHE(SDSQB-2016-01)NSFC(Grant Nos.41702331,41771021,41472293)+4 种基金NSFC-ICIMOD(Grant No.41661144041)"Light of the West"of CAS(Y7R2070070)Youth fund of IMHE(Y7K2050050)the Key Research&Development Program and the Scientific Support Program of the Science&Technology Department of Sichuan Province(Grant No.2017SZ0041Grant No.2016SZ0067)
文摘Seepage-induced fines migration under rainfall infiltration is a main cause leading to shallow failures in loose colluvial slopes. To describe the full process of fines migration within unsaturated soils during rainfall infiltration and the associated hydromechanical behaviors, a seepage-erosion-deformation coupled formulation is proposed in this paper. The governing equations proposed are implemented into a finite element code and used to investigate the influences of skeleton deformation on the rainfall infiltration process through unsaturated soil columns.The numerical results were presented in detail for a better understanding of the rainfall-induced fines migration process within unsaturated soils. Further,the obtained results are integrated into an infinite slope model for slope stability analysis. The results show that, the skeleton deformation will affect the rainfall infiltration rate and hence the timing of slope failures; meanwhile their influences are more evident if the fines deposition process is taken into account.Moreover, the slope stability could be reduced gradually due to the soil strength loss along with loss of fine particles. Therefore, particular attentions should be paid to analyzing the stability of soil slopes susceptible to internal erosion.
文摘The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brittleness using artificial neural networks(ANN). Herein hard rock brittleness is defined using Yagiz'method. A predictive model is developed using a comprehensive database compiled from 30 years' worth of rock tests at the Earth Mechanics Institute(EMI), Colorado School of Mines. The model is sensitive to density, elastic properties, and P- and S-wave velocities. The results show that the model is a better predictor of rock brittleness than conventional destructive strength-test based models and multiple regression techniques. While the findings have direct implications on intact rock, the methodology can be extrapolated to rock mass problems in both tunneling and underground mining where rock brittleness is an important control.
基金Projects(51908069, 51908073, 51838001, 51878070) supported by the National Natural Science Foundation of ChinaProject(2019SK2171) supported by the Key Research and Development Program of Hunan Province, China+2 种基金Project(kfj190605) supported by the Open Fund of Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province (Changsha University of Science & Technology),ChinaProject(2019IC04) supported by the Double First-Class Scientific Research International Cooperation Expansion Project of Changsha University of Science & Technology, ChinaProject(kq1905043) supported by the Training Program for Excellent Young Innovators of Changsha, China。
文摘In this paper, we suggest to study the behavior of a mat foundation on subsoil from the plate theory taking into account the soil-structure interaction. The objective is to highlight the soil-structure interaction particularly the influence of the rigidities of the soil and the concrete on the subgrade reaction (k) and the displacements of the mat foundation subjected to vertical loads. From plate theory and the soil-structure interaction, the general equation is reached. This equation depends more on the subgrade properties than the concrete foundation properties. Consequently, the behavior of the mat foundation is more influenced by soil properties than the concrete.
基金supported by Shenzhen(China)Science and Technology Innovation Committee(Grant Nos.JSGG20180504170449754)supported by Center for Computational Science and Engineering at Southern University of Science and Technology,Shenzhen,China。
文摘Geological disasters such as slope failure and landslides can cause loss of life and property.Therefore,reproducing their evolution process is of great importance for risk assessment and mitigation.The recently developed SIMSAND critical state sand model combined with the smoothed particle hydrodynamics(SPH)method is adopted in this work to study slope failure under large deformations.To illustrate the efficiency and accuracy of the SIMSAND-SPH approach,a series of slope collapse studies using the discrete element method(DEM)considering various particle shapes(i.e.spherical,tetrahedral and elongated)is adopted as benchmarks.The parameters of the SIMSAND model are calibrated using DEM triaxial tests.In comparison to the DEM simulations,the runout distance and final slope height are well characterized with the SIMSAND-SPH approach with less computational cost.All comparisons show that the SIMSAND-SPH approach is highly efficient and accurate,which can be an alternative numerical tool to simulate real scale granular flow.
文摘To elucidate what controls the magnitude of longitudinal growth stress in tension wood, anatomical measurements of gelatinous fibres were carried out on poplar tension wood (Populus I4551). Sections were cut from embedded blocks to avoid a border artefact described earlier. Results showed that: 1) no gelatinous fibres were observed under a growth strain level from 0.06% to 0.08%; 2) almost all of the non-conductive tissues contained gelatinous fibres above a growth strain level from 0.15% to 0.19%; 3) the amount of fibres, the amount of fibres with gelatinous layer, per unit of tissue area, and the thickness of the gelatinous layers controlled most of the magnitude of growth stress; 4) the contribution of the S2 layer in both fibre types could also play a role in the growth stress generation.
文摘A few constitutive models for unsaturated soils have already been proposed,however,many classic models such as the Barcelona basic model can simulate neither complex volumetric soil behaviour(without forgetting its supreme merit of being the first consistently and rigorously formulated model) nor post-peak softening,and most advanced models generally comprise a large number of parameters making them more difficult to be applied to practical situations.In this paper,we present a new model for unsaturated soils based on an existing model developed originally for saturated soils.It comprises a minimum number of constitutive parameters.The extension to unsaturated state is achieved by following a general methodology previously developed in our laboratory.The capacities of this simple model are tested.With only 13 parameters,it can reproduce the basic behaviour of unsaturated soils such as rebound or collapse upon wetting,depending on the stress levels.It can also reproduce post-peak softening and transition from contractant to dilatant volumetric behaviour during undrained shear.Overall,the first tentative of validation gives a good correlation between simulations and experimental data,and shows encouraging signs for future developments.
文摘Oil Palm Shell (OPS) concrete can be used in different fields of construction. To determine more accurately the fields of application, it is important to know and understand the behaviour of OPS concrete over<span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> the</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> long term and when it is in aggressive environments. This paper presents the results of studies conducted on the durability of OPS concrete. Water absorption capacity, electrical resistivity and apparent diffusion of chloride ions have been measured on different concrete samples. In addition, the behaviour of OPS concretes to carbonation was studied in an environment rich in carbon dioxide. Results show that OPS concrete ha</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">s</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> an absorptivity of 0.97 kg/m</span><sup><span style="font-family:Verdana;">2</span></sup></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">·</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">h</span><sup><span style="font-family:Verdana;">1/2</span></sup><span style="font-family:Verdana;">, an electrical resistivity of 64.37 Ω</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">·</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">m and an apparent diffusion coefficient of chloride ions of 3.84</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> × </span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">10</span><sup><span style="font-family:Verdana;">-12</span></sup><span style="font-family:Verdana;"> m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">/s after 90 days. All these results of OPS concrete are very close to those of concrete with normal aggregate and other lightweight concrete</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"> which mean OPS concretes have globally good properties with regard to durability</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.</span></span></span>
文摘Due to its rapid movement, preferential flow (PF) in the vadose zone allows much faster contaminant transport, which may have a significant impact on ground-water quality. PF can occur in heterogeneous vadose zones and it strongly depends on hydric and hydraulic conditions like entering flow rates at surface. This study deals with the modeling of the establishment of PF, and related solute transfer during the infiltration phase in a strongly heterogeneous glaciofluvial deposit. This deposit is made of four contrasting lithofacies (sand, gravel, bimodal gravel and matrix-free gravel) and lies underneath an urban infiltration basin (Lyon, France). Previous studies have been carried out on this site and linked the regionalization of soil pollution with the lithological heterogeneity. But none of them clearly demonstrated how heterogeneity could impact flow and solute transfer and may explain such a regionalization. In this study, we model flow and solute transfer at the trench scale for both uniform and heterogeneous profiles in order to characterize the effect of lithological heterogeneity. In addition, such a modeling was performed for two different entering flow rates to depict the influence of condition at surface on PF. A key result is that heterogeneity clearly impacts unsaturated flow and solute transfer. Numerical modeling permitted pointing out the existence of PF paths associated with the sedimentary heterogeneity of the glaciofluvial deposit. For lower surface fluxes, the sand lens and matrix-free gravel were the sources of capillary barrier effects, leading to a funneled flow and a groundwater recharge characterized by earlier and more dispersed wetting fronts. Such a flow pattern enhances solutes transfer and reduces solute retention by soil. Thus, the effect of heterogeneity on solute transfer is significant, especially for the most reactive solutes.
文摘The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kg w /kg dm to 3.12 kg w /kg dm were characterized. A novel procedure has been developed to determine the water content profiles inside samples during isothermal drying. At both temperatures, experimental results underlined that the physical properties of Spirulina are not sensitive to the geographical origin, Burkina-Faso or France. To keep Spirulina at an water activity below 0.6 in order to preserve it from micro-organisms development, sorption isotherm curves show that a sufficient requirement is to lower the water content until an upper limit of w = 0.075 db. The evolution of water transport coefficient as a function of water content highlights a monotonous exponential dependence with a transport coefficient ranging from 1.70 × 10–10 to 94 × 10–10 m2/s. The contribution of solid phase shrinkage to the transport of water is negligible for the last drying steps.
文摘Hydric properties evolution during drying differs from one product to another and has been the subject of various studies due to its crucial importance in modeling the drying process. The variation of these parameters in the solid matrix and in time during the drying of Spirulina platensis has not known an advanced understanding. The objective of this study was to evaluate the evolution of the water content profile, the mass flow, the concentration gradient and the diffusion coefficient during the drying of Spirulina platensis taking into account the shrinkage. Modeling and experimental analysis (at 50°C and HR = 6%) by the cutting method a cylinder 20 mm in diameter and 40 mm thick were carried. The water content profiles of two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kgw/kgdb and 3.12 kgw/kgdb were determined. These profiles have been adjusted by a polynomial function. Identical water behavior is observed regardless of the origin of the samples. Water distribution is heterogeneous. Mass flow and concentration gradient are greater at the edge than inside the product. The water transport coefficient, ranging from 1.70 × 10?10 to 94 × 10?10 m2/s, is determined from a linear approach.