A survey using the electrical resistivity and test pit methods is carried out in the Douala subbasin in order to investigate the sub-surface layering and evaluate the thickness of each layer through the variation of t...A survey using the electrical resistivity and test pit methods is carried out in the Douala subbasin in order to investigate the sub-surface layering and evaluate the thickness of each layer through the variation of the resistivity with the depth. Applying the Schumberger array, a total of 48 vertical electrical sounding is conducted along 8 profiles directed W-E and using traditional method, 25 test pits with depth between 15 and 19 meters are done. Qualitative interpretation is carried out through the resistivity and test pit maps. The test pit maps reveal the presence of the following layers: The first layer of thickness varies from 0.2 to 2.0 m (average of 1.9 m). The thickness of the second layer varies between 0.2 and 4.0 m with an average of 2.8 m. The thickness of the third layer is between 2.0 and 4.0 m with an average of 3.8 m. That of the fourth and fifth layers ranges respectively between 4.0 and 6.0 m (average of 5.4 m) and between 2.0 and 6.0 m with an average of 4.4 m. Isoresistivities maps from resistivities computed for different AB/2 values (1.5;4.4;13.5;19;27.5;58 m) are generally characterized by the apparent resistivities which define many domains in function of the AB/2 values. The superficial layer is characterized by electric resistivity values ranging from 720 to 2073 Ωm for AB/2 = 1.5 m and probably represents pedologic materials. For other values of AB/2, resistivity varies from 253 to 32,381 Ωm (AB/2 = 4.4 m), 0.1 to 1838 (AB/2 = 13.2 m) with an average of 341 Ωm, 0.3 to 1608 Ωm (AB/2 = 19 m) with an average of 279 Ωm, 6.4 to 1427 Ωm (AB/2 = 27.5 m) with an average 291 Ωm, and 19.7 to 3555 Ωm (AB/2 = 58 m) with an average of 850 Ωm. These different values of resistivity represent the sedimentary materials.展开更多
The management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important f...The management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important factors affecting the disposal phase. Economic and environmental requirements must be followed in order to achieve the best reclamation results, keeping into account site constraints such as slope stability, hauling and dumping issues, and interactions with groundwater. This paper deals with the above mentioned issues, illustrating a rational approach applied on the case of a large limestone quarry where the thickness of the overburden is relevant and the spoil material has to be dumped in a flooded pit. The proposed multidisciplinary approach led to the selection of most suitable methods for excavation, transportation and disposal. The selection was based on a detailed laboratory and site characterisation that defined favorable and adverse factors to be considered during the preliminary study of a large quarrying project.展开更多
In terms of controlling groundwater in deep foundation pit projects, the usual methods include increasing the curtain depth, reducing the amount of pumped groundwater, and implementing integrated control, in order to ...In terms of controlling groundwater in deep foundation pit projects, the usual methods include increasing the curtain depth, reducing the amount of pumped groundwater, and implementing integrated control, in order to reduce the drawdown and land subsidence outside pits. In dewatering design for confined water, factors including drawdown requirements, the thickness of aquifers, the depth of dewatering wells and the depth of cutoff curtains have to be considered comprehensively and numerical simulations are generally conducted for calculation and analysis. Longyang Road Station on Shanghai Metro Line 18 is taken as the case study subject in this paper, a groundwater seepage model is developed according to the on-site engineering geological conditions and hydrogeological conditions, the excavation depth of the foundation pit as well as the design depth of the enclosure, hydrogeological parameters are determined via the pumping test, and the foundation pit dewatering is simulated by means of the three-dimensional finite difference method, which produces numerical results that consistent with real monitoring data as to the groundwater table. Besides, the drawdown and the land subsidence both inside and outside the pit caused by foundation pit dewatering are calculated and analyzed for various curtain depths. This study reveals that the drawdown and the land subsidence change faster near the curtain with the increase in the curtain depth, and the gradient of drawdown and land subsidence changes dwindles beyond certain depths. In this project, the curtain depth of 47/49 m is adopted, and a drawdown-land subsidence verification test is completed given hanging curtains before the excavation. The result turns out that the real measurements basically match the calculation results from the numerical simulation, and by increasing the depth of curtains, the land subsidence resulting from dewatering is effectively controlled.展开更多
文摘A survey using the electrical resistivity and test pit methods is carried out in the Douala subbasin in order to investigate the sub-surface layering and evaluate the thickness of each layer through the variation of the resistivity with the depth. Applying the Schumberger array, a total of 48 vertical electrical sounding is conducted along 8 profiles directed W-E and using traditional method, 25 test pits with depth between 15 and 19 meters are done. Qualitative interpretation is carried out through the resistivity and test pit maps. The test pit maps reveal the presence of the following layers: The first layer of thickness varies from 0.2 to 2.0 m (average of 1.9 m). The thickness of the second layer varies between 0.2 and 4.0 m with an average of 2.8 m. The thickness of the third layer is between 2.0 and 4.0 m with an average of 3.8 m. That of the fourth and fifth layers ranges respectively between 4.0 and 6.0 m (average of 5.4 m) and between 2.0 and 6.0 m with an average of 4.4 m. Isoresistivities maps from resistivities computed for different AB/2 values (1.5;4.4;13.5;19;27.5;58 m) are generally characterized by the apparent resistivities which define many domains in function of the AB/2 values. The superficial layer is characterized by electric resistivity values ranging from 720 to 2073 Ωm for AB/2 = 1.5 m and probably represents pedologic materials. For other values of AB/2, resistivity varies from 253 to 32,381 Ωm (AB/2 = 4.4 m), 0.1 to 1838 (AB/2 = 13.2 m) with an average of 341 Ωm, 0.3 to 1608 Ωm (AB/2 = 19 m) with an average of 279 Ωm, 6.4 to 1427 Ωm (AB/2 = 27.5 m) with an average 291 Ωm, and 19.7 to 3555 Ωm (AB/2 = 58 m) with an average of 850 Ωm. These different values of resistivity represent the sedimentary materials.
文摘The management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important factors affecting the disposal phase. Economic and environmental requirements must be followed in order to achieve the best reclamation results, keeping into account site constraints such as slope stability, hauling and dumping issues, and interactions with groundwater. This paper deals with the above mentioned issues, illustrating a rational approach applied on the case of a large limestone quarry where the thickness of the overburden is relevant and the spoil material has to be dumped in a flooded pit. The proposed multidisciplinary approach led to the selection of most suitable methods for excavation, transportation and disposal. The selection was based on a detailed laboratory and site characterisation that defined favorable and adverse factors to be considered during the preliminary study of a large quarrying project.
基金supported by the Researches on the Control of Confined Water Drawdown and Subsidence in Foundation Pit Projects (Project No. JS-KY16R009-1)this project is funded by Shanghai Metro Line 18 Development Co., Ltd.
文摘In terms of controlling groundwater in deep foundation pit projects, the usual methods include increasing the curtain depth, reducing the amount of pumped groundwater, and implementing integrated control, in order to reduce the drawdown and land subsidence outside pits. In dewatering design for confined water, factors including drawdown requirements, the thickness of aquifers, the depth of dewatering wells and the depth of cutoff curtains have to be considered comprehensively and numerical simulations are generally conducted for calculation and analysis. Longyang Road Station on Shanghai Metro Line 18 is taken as the case study subject in this paper, a groundwater seepage model is developed according to the on-site engineering geological conditions and hydrogeological conditions, the excavation depth of the foundation pit as well as the design depth of the enclosure, hydrogeological parameters are determined via the pumping test, and the foundation pit dewatering is simulated by means of the three-dimensional finite difference method, which produces numerical results that consistent with real monitoring data as to the groundwater table. Besides, the drawdown and the land subsidence both inside and outside the pit caused by foundation pit dewatering are calculated and analyzed for various curtain depths. This study reveals that the drawdown and the land subsidence change faster near the curtain with the increase in the curtain depth, and the gradient of drawdown and land subsidence changes dwindles beyond certain depths. In this project, the curtain depth of 47/49 m is adopted, and a drawdown-land subsidence verification test is completed given hanging curtains before the excavation. The result turns out that the real measurements basically match the calculation results from the numerical simulation, and by increasing the depth of curtains, the land subsidence resulting from dewatering is effectively controlled.
