In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations amo...In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations among free load swelling rate, non-load time, the proportion of mixed sand and initial dry density. Experimen- tal studies have shown that： Free load swelling deformation is mainly divided into three stages of rapid expan- sion, slow expansion and final stability; when the initial dry density is constant, free load swelling rate of the weathered sand modified soil will reduce rapidly before they slow down with the increase of sand proportion, and weathered sand modified soil free load swelling rate is not sensitive to the large amount of sand mixed; in the same mixed sand ratio, weathered sand modified soil free load swelling rate increases rapidly with the in- crease of initial dry density, there is a good linear correlation between them. To take appropriate control of the initial dry density during the expansive soil subgrade construction helps to reduce its swelling deformation and ensures the stability of the embankment.展开更多
In this study, extender and bender element tests were conducted investigating the small-strain Poisson’s ratio of variable sands, with a focus on the effect of stress anisotropy in order to quantify the sensitivity o...In this study, extender and bender element tests were conducted investigating the small-strain Poisson’s ratio of variable sands, with a focus on the effect of stress anisotropy in order to quantify the sensitivity of Poisson’s ratio to the applied deviatoric stress. Four different uniform sands were tested, including a biogenic sand, a crushed rock and two natural sands, covering a wide range of particle shapes. From these sands, eleven samples were prepared in the laboratory and were tested under variable stress paths,maintaining a constant mean effective pressure while increasing the deviatoric compressive load. Under the application of these given stress paths, the data analysis indicated that the sensitivity of Poisson’s ratio to the stress ratio was more pronounced for sands with irregularly shaped particles in comparison to sands with fairly rounded and spherical grains. For sands with very irregularly shaped particles, the increase of Poisson’s ratio from the isotropic to the anisotropic stress state reached 50%, while this increase for natural sands with fairly rounded particles was in the order of 20%.展开更多
Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the norm...Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the normal operation of railway lines. This study is to obtain the influencing rules of freeze-thaw on the dynamic properties （dynamic strain, confining pressure and compactness） of silty sand. Based on an amount of inner tests, the dynamic modulus and damping ratio properties of silty soil subjected to repeated freeze-thaw cycles were deeply researched and analyzed. The results are as follows： At the same dynamic strain, the relationship of dynamic stress and freeze-thaw cycles presents negative cor- relation, and the relationship of dynamic stress, confining pressure and compactness present positive correlation. The dynamic modulus double decreases while the damping ratio double increases with incremental increase in dynamic strain. The dynamic modulus sharply decreases while the damping ratio increases with incremental increase in freeze-thaw cycles, and then the changes level off after six freeze-thaw cycles. The dynamic modulus increases while the damping ratio decreases as the confining pressure and compactness increase at the same strain level.展开更多
The dynamic shear modulus (DSM) is the most basic soil parameter in earthquake or other dynamic loading conditions and can be obtained through testing in the field or in the laboratory. The effect of consolidation rat...The dynamic shear modulus (DSM) is the most basic soil parameter in earthquake or other dynamic loading conditions and can be obtained through testing in the field or in the laboratory. The effect of consolidation ratios on the maximum DSM for two types of sand is investigated by using resonant column tests. And, an increment formula to obtain the maximum DSM for cases of consolidation ratio κc>1 is presented. The results indicate that the maximum DSM rises rapidly when κc is near 1 and then slows down, which means that the power function of the consolidation ratio increment κc-1 can be used to describe the variation of the maximum DSM due to κc>1. The results also indicate that the increase in the maximum DSM due to κc>1 is significantly larger than that predicted by Hardin and Black's formula.展开更多
Copper metallurgical slags are solid wastes resulting from the copper extraction process through pyrometallurgy. These granulated materials, dumped in the center of the city of Lubumbashi, contain certain “trace meta...Copper metallurgical slags are solid wastes resulting from the copper extraction process through pyrometallurgy. These granulated materials, dumped in the center of the city of Lubumbashi, contain certain “trace metal elements (ETM)” and/or “heavy metals” and are subjected to aerial leaching during the dry season, causing air pollution, and to leaching by rainwater, which leads to the contamination of the surrounding soil and surface water. The objective of this work was to use these slags, poor in recoverable elements (Cu, Co, Zn, Ge, and Ga), as fine aggregates for partial replacement of sand in concrete. The slags studied are of the ferrosilicate type belonging to the SiO2-FeO-CaO (MgO-Al2O3) system. They are completely vitreous, and their grain size distribution ranges from 0 to 3 mm. For this study, crushed sand with a granulometric distribution similar to that of the slags was chosen. The Bolomey method was used to optimize the sand content of the concrete as well as to calculate the optimum amount of water for concrete production. Once optimized, the sand was replaced with slag at respective rates of 0%, 25%, 50%, 75%, and 100% by weight. The compressive strengths of the hardened concretes based on these slags were measured at 1, 3, 7, 14, and 28 days of curing with a W/C (Water/Cement) ratio of 0.6. Slump tests of the fresh concrete were conducted to characterize the influence of sand replacement by slag on the concrete’s workability. The durability of the concrete with the optimized slag content was studied in corrosive solutions of HCl (5% wt), H2SO4 (3% wt), and Na2SO4 (1% wt). The results show the possibility of replacing crushed sand with slag up to a maximum rate of 50% by weight. The use of copper slag as sand decreases the cement’s water demand and therefore increases the value of the concrete’s mechanical strength. It was found that the optimum W/C ratio that allows for acceptable workability of the slag-based concrete is around 0.49. The durability study of the slag-based concretes in various corrosive solutions showed better performance of the slag-based concrete in the presence of H2SO4 and Na2SO4 solutions. Using the slag as a fine aggregate densifies the concrete structure, improves its workability by decreasing its W/C ratio, and increases its mechanical strengths while improving its resistance to corrosive environments.展开更多
In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of thi...In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive tests’results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm<sup>2</sup> for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m<sup>3</sup> of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.展开更多
The influence of core sand properties on flow dynamics was investigated synchronously with various core sands, transparent core-box and high-speed camera. To confirm whether the core shooting process has significant t...The influence of core sand properties on flow dynamics was investigated synchronously with various core sands, transparent core-box and high-speed camera. To confirm whether the core shooting process has significant turbulence, the flow pattern of sand particles in the shooting head and core box was reproduced with colored core sands. By incorporating the kinetic theory of granular flow(KTGF), kinetic-frictional constitutive correlation and turbulence model, a two-fluid model(TFM) was established to study the flow dynamics of the core shooting process. Two-fluid model(TFM) simulations were then performed and a areasonable agreement was achieved between the simulation and experimental results. Based on the experimental and simulation results, the effects of turbulence, sand density, sand diameter and binder ratio were analyzed in terms of filling process, sand volume fraction(αs) and sand velocity(Vs).展开更多
文摘In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations among free load swelling rate, non-load time, the proportion of mixed sand and initial dry density. Experimen- tal studies have shown that： Free load swelling deformation is mainly divided into three stages of rapid expan- sion, slow expansion and final stability; when the initial dry density is constant, free load swelling rate of the weathered sand modified soil will reduce rapidly before they slow down with the increase of sand proportion, and weathered sand modified soil free load swelling rate is not sensitive to the large amount of sand mixed; in the same mixed sand ratio, weathered sand modified soil free load swelling rate increases rapidly with the in- crease of initial dry density, there is a good linear correlation between them. To take appropriate control of the initial dry density during the expansive soil subgrade construction helps to reduce its swelling deformation and ensures the stability of the embankment.
基金the financial support by the grant from the Research Grant Council of the Hong Kong Special Administrative Region(HKSAR)China Project No.9041880(City U112813)the start-up grant of the College of Science and Engineering,City University of Hong Kong(Code:7200533-ACE)
文摘In this study, extender and bender element tests were conducted investigating the small-strain Poisson’s ratio of variable sands, with a focus on the effect of stress anisotropy in order to quantify the sensitivity of Poisson’s ratio to the applied deviatoric stress. Four different uniform sands were tested, including a biogenic sand, a crushed rock and two natural sands, covering a wide range of particle shapes. From these sands, eleven samples were prepared in the laboratory and were tested under variable stress paths,maintaining a constant mean effective pressure while increasing the deviatoric compressive load. Under the application of these given stress paths, the data analysis indicated that the sensitivity of Poisson’s ratio to the stress ratio was more pronounced for sands with irregularly shaped particles in comparison to sands with fairly rounded and spherical grains. For sands with very irregularly shaped particles, the increase of Poisson’s ratio from the isotropic to the anisotropic stress state reached 50%, while this increase for natural sands with fairly rounded particles was in the order of 20%.
基金funded by the National Key Basic Research Development Plan of China (Grant No. 2012CB026104)the National Natural Science Foundation (NSFC) of China (Grant Nos.51208320 and 51171281)
文摘Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the normal operation of railway lines. This study is to obtain the influencing rules of freeze-thaw on the dynamic properties （dynamic strain, confining pressure and compactness） of silty sand. Based on an amount of inner tests, the dynamic modulus and damping ratio properties of silty soil subjected to repeated freeze-thaw cycles were deeply researched and analyzed. The results are as follows： At the same dynamic strain, the relationship of dynamic stress and freeze-thaw cycles presents negative cor- relation, and the relationship of dynamic stress, confining pressure and compactness present positive correlation. The dynamic modulus double decreases while the damping ratio double increases with incremental increase in dynamic strain. The dynamic modulus sharply decreases while the damping ratio increases with incremental increase in freeze-thaw cycles, and then the changes level off after six freeze-thaw cycles. The dynamic modulus increases while the damping ratio decreases as the confining pressure and compactness increase at the same strain level.
基金The Science and Technology Ministration of China and the Earthquake Science Foundation of China (Grand No. 102033)
文摘The dynamic shear modulus (DSM) is the most basic soil parameter in earthquake or other dynamic loading conditions and can be obtained through testing in the field or in the laboratory. The effect of consolidation ratios on the maximum DSM for two types of sand is investigated by using resonant column tests. And, an increment formula to obtain the maximum DSM for cases of consolidation ratio κc>1 is presented. The results indicate that the maximum DSM rises rapidly when κc is near 1 and then slows down, which means that the power function of the consolidation ratio increment κc-1 can be used to describe the variation of the maximum DSM due to κc>1. The results also indicate that the increase in the maximum DSM due to κc>1 is significantly larger than that predicted by Hardin and Black's formula.
文摘Copper metallurgical slags are solid wastes resulting from the copper extraction process through pyrometallurgy. These granulated materials, dumped in the center of the city of Lubumbashi, contain certain “trace metal elements (ETM)” and/or “heavy metals” and are subjected to aerial leaching during the dry season, causing air pollution, and to leaching by rainwater, which leads to the contamination of the surrounding soil and surface water. The objective of this work was to use these slags, poor in recoverable elements (Cu, Co, Zn, Ge, and Ga), as fine aggregates for partial replacement of sand in concrete. The slags studied are of the ferrosilicate type belonging to the SiO2-FeO-CaO (MgO-Al2O3) system. They are completely vitreous, and their grain size distribution ranges from 0 to 3 mm. For this study, crushed sand with a granulometric distribution similar to that of the slags was chosen. The Bolomey method was used to optimize the sand content of the concrete as well as to calculate the optimum amount of water for concrete production. Once optimized, the sand was replaced with slag at respective rates of 0%, 25%, 50%, 75%, and 100% by weight. The compressive strengths of the hardened concretes based on these slags were measured at 1, 3, 7, 14, and 28 days of curing with a W/C (Water/Cement) ratio of 0.6. Slump tests of the fresh concrete were conducted to characterize the influence of sand replacement by slag on the concrete’s workability. The durability of the concrete with the optimized slag content was studied in corrosive solutions of HCl (5% wt), H2SO4 (3% wt), and Na2SO4 (1% wt). The results show the possibility of replacing crushed sand with slag up to a maximum rate of 50% by weight. The use of copper slag as sand decreases the cement’s water demand and therefore increases the value of the concrete’s mechanical strength. It was found that the optimum W/C ratio that allows for acceptable workability of the slag-based concrete is around 0.49. The durability study of the slag-based concretes in various corrosive solutions showed better performance of the slag-based concrete in the presence of H2SO4 and Na2SO4 solutions. Using the slag as a fine aggregate densifies the concrete structure, improves its workability by decreasing its W/C ratio, and increases its mechanical strengths while improving its resistance to corrosive environments.
文摘In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive tests’results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm<sup>2</sup> for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m<sup>3</sup> of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.
基金supported by the National Science Foundation of China(Grant Number 51575304)the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant Number 2012ZX04012011)
文摘The influence of core sand properties on flow dynamics was investigated synchronously with various core sands, transparent core-box and high-speed camera. To confirm whether the core shooting process has significant turbulence, the flow pattern of sand particles in the shooting head and core box was reproduced with colored core sands. By incorporating the kinetic theory of granular flow(KTGF), kinetic-frictional constitutive correlation and turbulence model, a two-fluid model(TFM) was established to study the flow dynamics of the core shooting process. Two-fluid model(TFM) simulations were then performed and a areasonable agreement was achieved between the simulation and experimental results. Based on the experimental and simulation results, the effects of turbulence, sand density, sand diameter and binder ratio were analyzed in terms of filling process, sand volume fraction(αs) and sand velocity(Vs).
