Better benches design enables to optimizes the risks of instabilities, to guarantee maximum of the ore recovery with minimum waste stripping. This requires detailed data on their geometric properties and the mechanica...Better benches design enables to optimizes the risks of instabilities, to guarantee maximum of the ore recovery with minimum waste stripping. This requires detailed data on their geometric properties and the mechanical properties of the materials (soil and rock), thus defining the appropriate means for investigation, modeling and numerical calculations. The objective of this article is to study the geotechnical behavior of slopes and edges of a mining pit under the influence of variations in the geometric parameters of the bench and mechanical parameters of the ground in the case of open-pit mines. To do this, we used the stability calculation software well adapted to landslide problems, called RocScience (Slide module version 6.020). Four geometric models were tested in order to assess the slopes and the mining pit edges stability, in order to choose the best model for the application of the different parameter’s variation. The stability calculations showed the influence of variations in the geometric parameters of the benches and the mechanical parameters of the soil on the factor of safety. The results of variations in favor of a decrease in the bench height, slope angle and an increase in the bench width show an increase in the factor of safety and vice versa. With the first three models, under static conditions all the factors of safety are greater than or equal to 1.4, which shows a state of satisfactory long-term stability, whereas under Pseudo-static conditions, the factors of safety are all less than 1, which means that collapse is inevitable with these models. It can be seen that with a fourth model whose geometric characteristics, the factors of safety obtained are greater than 1.5 in static conditions and 1 in Pseudo-static conditions, which shows of the slopes and pit edges long-term stability. As for the variations in mechanical parameters, the factor of safety increases with the increase of the mechanical parameters in static and Pseudo-static conditions. The sandstone layer showed inevitable instabilities with values of the internal friction angle below 40˚ and internal cohesion below 65 KPa. Instabilities are observed in the limestone layer with internal friction angle values below 35˚ and internal cohesion below 120 KPa. The pegmatite showed a state of guaranteed stability in an interval of the internal friction angle ranging from 30˚ to 35˚ and internal cohesion ranging from 250 to 300 KPa outside which instabilities inevitably occur. The variation of the parameters showed a very low effect on the last two layers due to the high values of the different parameters.展开更多
This study aims to delineate the spatial distribution of nitrate and fluoride in groundwater and to estimate the non-carcinogenic risks using the human health risk assessment model recommended by the United States Env...This study aims to delineate the spatial distribution of nitrate and fluoride in groundwater and to estimate the non-carcinogenic risks using the human health risk assessment model recommended by the United States Environmental Protection Agency (USEPA). Forty-two samples were collected from wells and boreholes and analyzed for nitrate, fluoride and other water quality parameters. Results of the study indicate that fluoride and nitrate concentrations vary respectively from 0.13 to 9.41 mg·L−1 and from 0.13 to 432.24 mg·L−1 with respective median values of 2.65 and 13.85. About 69% of groundwater samples exceed the allowable limit (1.5 mg·L−1) of fluoride for drinking water. Spatial distribution of fluoride shows high concentrations in certain localities with values ranging from 6.74 mg·L−1 to 9.41 mg·L−1. The spatial distribution of nitrate indicates that the majority of water samples (87.18%) have nitrate concentrations lower than the World Health Organization (WHO) standard guideline value of 50 mg·L−1. Assessment of non-carcinogenic risks associated with intake of polluted groundwater in local populations indicates that 82.05% and 87.18% of groundwater samples have a THI > 1 in adults and children, respectively. However, the highest THI value (15.87) was recorded for children suggesting that children face greater non-carcinogenic risks than adults. The results of this study can be used as a support by the policymakers and practitioners to develop appropriate policies for effective and sustainable groundwater management and to monitor human health implications.展开更多
This work’s aim is to participate in local materials (raw or fiber improved), which can be used in sustainable and accessible buildings to every Senegalese. To do this, studied materials are respectively collected fr...This work’s aim is to participate in local materials (raw or fiber improved), which can be used in sustainable and accessible buildings to every Senegalese. To do this, studied materials are respectively collected from a laterite clay pit in Ndouloumadjie Dembe (Matam, Northern Senegal) and another from a termite mound in Tattaguine (Fatick, Central Senegal). These samples are first subjected to Geotechnical identification tests. Mud bricks are then made with raw or sifted millet involucre improved to 1%, 2%, and 3% at 5 mm sieve samples. These briquettes are subjected to compression tests and thermal evaluations. Lagrange and Newton methods of numeric modelling are used to test the whole mixture points between 1% and 3% millet involucre for a better correlation between mechanical and thermal parameters. The results show that in Matam, as well as in Tattaguine, these muds, raw or improved, are of good thermomechanical quality when they are used in bricks making. And the thermomechanical coupling quality reaches a maximum situated at 2.125% for Ndouloumadjie and 2.05% for Tattaguine. These briquettes’ building quality depends on the mud content used in iron, aluminum, silica and clay. Thus, same natural materials can be used in the establishment of habitats according to their geotechnical, chemical, mechanical and thermal characteristics.展开更多
The aim of this work is to identify a substitute for imported standardized sand for determining the strength class of cements using local sands. To this end, three (03) local sands (Manga, Kaya and Dori) were characte...The aim of this work is to identify a substitute for imported standardized sand for determining the strength class of cements using local sands. To this end, three (03) local sands (Manga, Kaya and Dori) were characterized and then used to formulate sand mixtures fitting into the granular spindle of standardized sand noted SM1, SM2 and SM3. SM1 is composed of 80% Manga sand plus 20% Dori sand. SM2 is a mixture of 80% of the refusal and 20% of the passing through the 0.25 mm sieve of the Manga sand. SM3 is composed of 77% Manga sand 0.25 mm sieve refusals plus 23% Kaya sand. These sands were used to characterize a CEM II/B-M (P-L) 42.5 R cement by comparing it with the results of a standardized sand noted SS. Characterization of the local sand showed them to be less dense and more absorbent than the standardized sand. Mortars made with SM1, SM2 and SM3 thus have lower workability and bulk densities in the fresh and hardened states than the SS-based mortar, with higher porosities accessible to water after 28 days of curing. Mechanical characterization of the cement gave lower compressive strength values with local sands at 2 and 28 days cure. At 2 days cure, local sands gave 17.42 MPa, 14.68 MPa and 17.13 MPa respectively for SM1, SM2 and SM3, compared with 21.12 MPa for standard sand. At 28 days, mortars based on SM1 and SM3 sands give higher strength values than the 42.5 MPa required by standard NF EN 197-1, with 44.21 MPa and 43.17 MPa respectively, compared with 49.84 MPa for standardized sand. On this basis, correction factors have been proposed for the use of local sands in cement characterization. They nevertheless require repeatability studies before validation.展开更多
This study presents various approaches to calculating the bearing capacity of spread footings applied to the rock mass of the western corniche at the tip of the Dakar peninsula. The bearing capacity was estimated usin...This study presents various approaches to calculating the bearing capacity of spread footings applied to the rock mass of the western corniche at the tip of the Dakar peninsula. The bearing capacity was estimated using empirical, analytical and numerical approaches based on the parameters of the rock mass and the foundation. Laboratory tests were carried out on basanite, as well as on the other facies detected. The results of these studies give a range of allowable bearing capacity values varying between 1.92 and 11.39 MPa for the empirical methods and from 7.13 to 25.50 MPa for the analytical methods. A wide dispersion of results was observed according to the different approaches. This dispersion of results is explained by the use of different rock parameters depending on the method used. The allowable bearing capacity results obtained with varying approaches of calculation remain admissible to support the loads. On the other hand, the foundation calculations show acceptable settlement of the order of a millimeter for all the layers, especially in the thin clay layers resting on the bedrock at shallow depths, where the rigidity of the rock reduces settlement.展开更多
文摘Better benches design enables to optimizes the risks of instabilities, to guarantee maximum of the ore recovery with minimum waste stripping. This requires detailed data on their geometric properties and the mechanical properties of the materials (soil and rock), thus defining the appropriate means for investigation, modeling and numerical calculations. The objective of this article is to study the geotechnical behavior of slopes and edges of a mining pit under the influence of variations in the geometric parameters of the bench and mechanical parameters of the ground in the case of open-pit mines. To do this, we used the stability calculation software well adapted to landslide problems, called RocScience (Slide module version 6.020). Four geometric models were tested in order to assess the slopes and the mining pit edges stability, in order to choose the best model for the application of the different parameter’s variation. The stability calculations showed the influence of variations in the geometric parameters of the benches and the mechanical parameters of the soil on the factor of safety. The results of variations in favor of a decrease in the bench height, slope angle and an increase in the bench width show an increase in the factor of safety and vice versa. With the first three models, under static conditions all the factors of safety are greater than or equal to 1.4, which shows a state of satisfactory long-term stability, whereas under Pseudo-static conditions, the factors of safety are all less than 1, which means that collapse is inevitable with these models. It can be seen that with a fourth model whose geometric characteristics, the factors of safety obtained are greater than 1.5 in static conditions and 1 in Pseudo-static conditions, which shows of the slopes and pit edges long-term stability. As for the variations in mechanical parameters, the factor of safety increases with the increase of the mechanical parameters in static and Pseudo-static conditions. The sandstone layer showed inevitable instabilities with values of the internal friction angle below 40˚ and internal cohesion below 65 KPa. Instabilities are observed in the limestone layer with internal friction angle values below 35˚ and internal cohesion below 120 KPa. The pegmatite showed a state of guaranteed stability in an interval of the internal friction angle ranging from 30˚ to 35˚ and internal cohesion ranging from 250 to 300 KPa outside which instabilities inevitably occur. The variation of the parameters showed a very low effect on the last two layers due to the high values of the different parameters.
文摘This study aims to delineate the spatial distribution of nitrate and fluoride in groundwater and to estimate the non-carcinogenic risks using the human health risk assessment model recommended by the United States Environmental Protection Agency (USEPA). Forty-two samples were collected from wells and boreholes and analyzed for nitrate, fluoride and other water quality parameters. Results of the study indicate that fluoride and nitrate concentrations vary respectively from 0.13 to 9.41 mg·L−1 and from 0.13 to 432.24 mg·L−1 with respective median values of 2.65 and 13.85. About 69% of groundwater samples exceed the allowable limit (1.5 mg·L−1) of fluoride for drinking water. Spatial distribution of fluoride shows high concentrations in certain localities with values ranging from 6.74 mg·L−1 to 9.41 mg·L−1. The spatial distribution of nitrate indicates that the majority of water samples (87.18%) have nitrate concentrations lower than the World Health Organization (WHO) standard guideline value of 50 mg·L−1. Assessment of non-carcinogenic risks associated with intake of polluted groundwater in local populations indicates that 82.05% and 87.18% of groundwater samples have a THI > 1 in adults and children, respectively. However, the highest THI value (15.87) was recorded for children suggesting that children face greater non-carcinogenic risks than adults. The results of this study can be used as a support by the policymakers and practitioners to develop appropriate policies for effective and sustainable groundwater management and to monitor human health implications.
文摘This work’s aim is to participate in local materials (raw or fiber improved), which can be used in sustainable and accessible buildings to every Senegalese. To do this, studied materials are respectively collected from a laterite clay pit in Ndouloumadjie Dembe (Matam, Northern Senegal) and another from a termite mound in Tattaguine (Fatick, Central Senegal). These samples are first subjected to Geotechnical identification tests. Mud bricks are then made with raw or sifted millet involucre improved to 1%, 2%, and 3% at 5 mm sieve samples. These briquettes are subjected to compression tests and thermal evaluations. Lagrange and Newton methods of numeric modelling are used to test the whole mixture points between 1% and 3% millet involucre for a better correlation between mechanical and thermal parameters. The results show that in Matam, as well as in Tattaguine, these muds, raw or improved, are of good thermomechanical quality when they are used in bricks making. And the thermomechanical coupling quality reaches a maximum situated at 2.125% for Ndouloumadjie and 2.05% for Tattaguine. These briquettes’ building quality depends on the mud content used in iron, aluminum, silica and clay. Thus, same natural materials can be used in the establishment of habitats according to their geotechnical, chemical, mechanical and thermal characteristics.
文摘The aim of this work is to identify a substitute for imported standardized sand for determining the strength class of cements using local sands. To this end, three (03) local sands (Manga, Kaya and Dori) were characterized and then used to formulate sand mixtures fitting into the granular spindle of standardized sand noted SM1, SM2 and SM3. SM1 is composed of 80% Manga sand plus 20% Dori sand. SM2 is a mixture of 80% of the refusal and 20% of the passing through the 0.25 mm sieve of the Manga sand. SM3 is composed of 77% Manga sand 0.25 mm sieve refusals plus 23% Kaya sand. These sands were used to characterize a CEM II/B-M (P-L) 42.5 R cement by comparing it with the results of a standardized sand noted SS. Characterization of the local sand showed them to be less dense and more absorbent than the standardized sand. Mortars made with SM1, SM2 and SM3 thus have lower workability and bulk densities in the fresh and hardened states than the SS-based mortar, with higher porosities accessible to water after 28 days of curing. Mechanical characterization of the cement gave lower compressive strength values with local sands at 2 and 28 days cure. At 2 days cure, local sands gave 17.42 MPa, 14.68 MPa and 17.13 MPa respectively for SM1, SM2 and SM3, compared with 21.12 MPa for standard sand. At 28 days, mortars based on SM1 and SM3 sands give higher strength values than the 42.5 MPa required by standard NF EN 197-1, with 44.21 MPa and 43.17 MPa respectively, compared with 49.84 MPa for standardized sand. On this basis, correction factors have been proposed for the use of local sands in cement characterization. They nevertheless require repeatability studies before validation.
文摘This study presents various approaches to calculating the bearing capacity of spread footings applied to the rock mass of the western corniche at the tip of the Dakar peninsula. The bearing capacity was estimated using empirical, analytical and numerical approaches based on the parameters of the rock mass and the foundation. Laboratory tests were carried out on basanite, as well as on the other facies detected. The results of these studies give a range of allowable bearing capacity values varying between 1.92 and 11.39 MPa for the empirical methods and from 7.13 to 25.50 MPa for the analytical methods. A wide dispersion of results was observed according to the different approaches. This dispersion of results is explained by the use of different rock parameters depending on the method used. The allowable bearing capacity results obtained with varying approaches of calculation remain admissible to support the loads. On the other hand, the foundation calculations show acceptable settlement of the order of a millimeter for all the layers, especially in the thin clay layers resting on the bedrock at shallow depths, where the rigidity of the rock reduces settlement.
