2003 Vol. 28, No. 5
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2003, 28(5): 471-482.
Abstract:
Professor CHEN Chong-xi is an eminent quantitative hydrogeologist in China. Over his distinguished academic career of 50 years, Professor CHEN has made outstanding contributions to the advancement of hydrogeology in China. This article is a brief review of his academic thoughts and achievements. Professor CHEN's research has covered many aspects of groundwater hydrology, including fundamental concepts and approaches of groundwater resource evaluation, theories of transient groundwater flow dynamics and methodology of groundwater numerical modeling. Like many scientists and scholars in China, Professor CHEN's academic ideas have been greatly influenced by literature first from former USSA and then USA. In 1970s, while most groundwater hydrologists in China overwhelmingly welcomed the new theory and concepts developed by overseas scientists and were very keen to apply them to solve local hydrogeological problems, Professor CHEN was probably one of the few who really scrutinize the theory and method very critically before using them. He challenged quite a few concepts and ideas that were widely accepted in the groundwater community but had no basis in fact. In the process of learning and challenging the traditional theories and methods, he also developed his own unique approach and style of solving groundwater problems in China.For example, the "effective radius" calculated from the Dupuit equation assuming that groundwater is in steady state was widely used to design the number and pattern of wells in a well field. He pointed out that unsteady state flow prevails in real aquifer systems and the concept of "effective radius" on the basis of steady state groundwater flow theory is incorrect for most flow systems in reality. He clarified the misunderstanding of the Dupuit equation and believed that the Dupuit equation applies only for a circular aquifer bounded by a fixed head boundary such as a circular island in the middle of the sea. His speculation was confirmed by the original publication of Dupuit which was available in China only after 1981, Professor CHEN made contributions in unsteady state flow theory as well. By studying the basic equations and the superposition theory, he relaxed the assumption of horizontal initial water level for using the Theis and Hantush equations.It was well accepted that the maximum recharge under natural hydrogeological conditions can be used to determine the sustainable groundwater resource. Professor CHEN challenged such an approach and demonstrated that sustainable groundwater development should be based on the increase in recharge or/and the decrease in discharge after the aquifer system reaches a new equilibrium under pumping condition. Unfortunately, the myth that the recharge prior to pumping is important in determining the magnitude of sustainable groundwater development still goes on in the groundwater community in the world.Professor CHEN developed some creative and effective methods of numerical modeling for some special hydrogeological problems. For numerical simulation in coastal aquifers, he presented the "equivalent boundary" theory to determine the offshore boundary of a confined aquifer with roof extending under the sea on the basis of analyzing by tidal data. He proposed the equivalent hydraulic conductivity approach to simulate the pumping test data from a pumping well in a multilayer aquifer system. By taking account the different flow regimes (laminar and turbulent flows, and the transition range), his approach can simulate the dynamic interaction between the aquifers via non-Darcian vertical flow through the wellbore. He also used the approach to study groundwater flow in a horizontal well and verified his model and approach by conducting laboratory tests in a sand tank model. He further extended this approach to handling the complex groundwater flow in karst aquifers by presenting a triple porosity model for karst aquifers consisting of pipes, fissures and a porous matrix. Recently, Professor CHEN has challenged the traditional thinking about the physical meaning of water level measured from an observation well. It has been well accepted that the water level in an observation well reflects the average hydraulic head in the aquifer profile that is occupied by the screened portion of the well. Professor CHEN has been conducting research to prove that the water level in the observation well penetrating several aquifers represents only the head of the upper aquifer, or more precisely, the uppermost point of the upper aquifer.On the basis of his modeling experience over the last half century, he strongly believes that the most important element in numerical modeling is that the model designers should make every effort to ensure that a numerical model is an accurate representation of the actual processes occurring in the real aquifer system. The best way to achieve this goal is to analyze the hydrogeological conditions with great care, conceptualize the model in a rational manner and simulate the process using an appropriate numerical technique.
Professor CHEN Chong-xi is an eminent quantitative hydrogeologist in China. Over his distinguished academic career of 50 years, Professor CHEN has made outstanding contributions to the advancement of hydrogeology in China. This article is a brief review of his academic thoughts and achievements. Professor CHEN's research has covered many aspects of groundwater hydrology, including fundamental concepts and approaches of groundwater resource evaluation, theories of transient groundwater flow dynamics and methodology of groundwater numerical modeling. Like many scientists and scholars in China, Professor CHEN's academic ideas have been greatly influenced by literature first from former USSA and then USA. In 1970s, while most groundwater hydrologists in China overwhelmingly welcomed the new theory and concepts developed by overseas scientists and were very keen to apply them to solve local hydrogeological problems, Professor CHEN was probably one of the few who really scrutinize the theory and method very critically before using them. He challenged quite a few concepts and ideas that were widely accepted in the groundwater community but had no basis in fact. In the process of learning and challenging the traditional theories and methods, he also developed his own unique approach and style of solving groundwater problems in China.For example, the "effective radius" calculated from the Dupuit equation assuming that groundwater is in steady state was widely used to design the number and pattern of wells in a well field. He pointed out that unsteady state flow prevails in real aquifer systems and the concept of "effective radius" on the basis of steady state groundwater flow theory is incorrect for most flow systems in reality. He clarified the misunderstanding of the Dupuit equation and believed that the Dupuit equation applies only for a circular aquifer bounded by a fixed head boundary such as a circular island in the middle of the sea. His speculation was confirmed by the original publication of Dupuit which was available in China only after 1981, Professor CHEN made contributions in unsteady state flow theory as well. By studying the basic equations and the superposition theory, he relaxed the assumption of horizontal initial water level for using the Theis and Hantush equations.It was well accepted that the maximum recharge under natural hydrogeological conditions can be used to determine the sustainable groundwater resource. Professor CHEN challenged such an approach and demonstrated that sustainable groundwater development should be based on the increase in recharge or/and the decrease in discharge after the aquifer system reaches a new equilibrium under pumping condition. Unfortunately, the myth that the recharge prior to pumping is important in determining the magnitude of sustainable groundwater development still goes on in the groundwater community in the world.Professor CHEN developed some creative and effective methods of numerical modeling for some special hydrogeological problems. For numerical simulation in coastal aquifers, he presented the "equivalent boundary" theory to determine the offshore boundary of a confined aquifer with roof extending under the sea on the basis of analyzing by tidal data. He proposed the equivalent hydraulic conductivity approach to simulate the pumping test data from a pumping well in a multilayer aquifer system. By taking account the different flow regimes (laminar and turbulent flows, and the transition range), his approach can simulate the dynamic interaction between the aquifers via non-Darcian vertical flow through the wellbore. He also used the approach to study groundwater flow in a horizontal well and verified his model and approach by conducting laboratory tests in a sand tank model. He further extended this approach to handling the complex groundwater flow in karst aquifers by presenting a triple porosity model for karst aquifers consisting of pipes, fissures and a porous matrix. Recently, Professor CHEN has challenged the traditional thinking about the physical meaning of water level measured from an observation well. It has been well accepted that the water level in an observation well reflects the average hydraulic head in the aquifer profile that is occupied by the screened portion of the well. Professor CHEN has been conducting research to prove that the water level in the observation well penetrating several aquifers represents only the head of the upper aquifer, or more precisely, the uppermost point of the upper aquifer.On the basis of his modeling experience over the last half century, he strongly believes that the most important element in numerical modeling is that the model designers should make every effort to ensure that a numerical model is an accurate representation of the actual processes occurring in the real aquifer system. The best way to achieve this goal is to analyze the hydrogeological conditions with great care, conceptualize the model in a rational manner and simulate the process using an appropriate numerical technique.
2003, 28(5): 483-491.
Abstract:
The paper questions the traditional method for the calculation of the water level in the conventional observation wells for three-dimensional groundwater flow, and proposes that the Hantush -Бочевер equation, a pure mathematical method, is lacking in the basis of physics. The analysis of the formation mechanism of water level in the observation wells shows that the flux is zero only at the mouth of three-dimensional groundwater observation well, but the interior of the well contains actually "discharge" and "recharge" from the aquifers; that the water level in one homogeneous aquifer may have the same essential features as the multilayer well has; that the water level in the multilayer well is not mixed, and that the distribution of the head and flow in the multilayer well conforms to its own mechanism. Generally speaking, the observation well in the three-dimensional groundwater flow may not be described with the line sinks and line sources, nor can it be assumed that the flow in the observation well is determined by the laminar flow (linear flow) that has been proposed in recent years. However, the "seepage-pipe coupling model" and "equivalent hydraulic conductivity" (EHC) presented by the author in 1993 can be used to simulate very conveniently and effectively the three-dimensional groundwater flow. For the further illustration, the Hantush-Бочевер equation can only be approximately used in the conditions where the diameter of observation well is more than 0.2 m and that the distance between the well and the observation well is more than 10-20 m.
The paper questions the traditional method for the calculation of the water level in the conventional observation wells for three-dimensional groundwater flow, and proposes that the Hantush -Бочевер equation, a pure mathematical method, is lacking in the basis of physics. The analysis of the formation mechanism of water level in the observation wells shows that the flux is zero only at the mouth of three-dimensional groundwater observation well, but the interior of the well contains actually "discharge" and "recharge" from the aquifers; that the water level in one homogeneous aquifer may have the same essential features as the multilayer well has; that the water level in the multilayer well is not mixed, and that the distribution of the head and flow in the multilayer well conforms to its own mechanism. Generally speaking, the observation well in the three-dimensional groundwater flow may not be described with the line sinks and line sources, nor can it be assumed that the flow in the observation well is determined by the laminar flow (linear flow) that has been proposed in recent years. However, the "seepage-pipe coupling model" and "equivalent hydraulic conductivity" (EHC) presented by the author in 1993 can be used to simulate very conveniently and effectively the three-dimensional groundwater flow. For the further illustration, the Hantush-Бочевер equation can only be approximately used in the conditions where the diameter of observation well is more than 0.2 m and that the distance between the well and the observation well is more than 10-20 m.
2003, 28(5): 492-496.
Abstract:
A modified algorithm of finite cell method (FCM) is presented for simulating complex physical, biological and chemical transport in porous media. It not only has the same advantages as the original finite cell method, but also can keep local mass conservation in more finer meshes, so we may get the locations of cells as well as the final results with high accuracy. Two numerical examples show the comparison between the solutions of modified FCM and original FCM and analytical solutions.
A modified algorithm of finite cell method (FCM) is presented for simulating complex physical, biological and chemical transport in porous media. It not only has the same advantages as the original finite cell method, but also can keep local mass conservation in more finer meshes, so we may get the locations of cells as well as the final results with high accuracy. Two numerical examples show the comparison between the solutions of modified FCM and original FCM and analytical solutions.
2003, 28(5): 497-504.
Abstract:
The amount of water seeping into the waste emplacement underground openings is an important issue for the long-term performance of any underground waste repository. Seepage controls the corrosion rates of waste packages, the waste mobilization rates and transport rates of contaminant leaving the underground openings. Predicting the seepage rate is difficult under any circumstances, and is particularly complicated for repository sites located in unsaturated, heterogeneous media. In this study, a 3-D numerical model is used to study unsaturated flow and seepage through a heterogeneous medium into the underground openings with strongly variable parameters and boundary conditions. The model has been compared with homogeneous model. The seepage rate into the underground openings increases with an increase in percolation flux introduced into the system. Four parameters, (1) fracture continuum permeability, (2) Van Genuchten parameter α, (3) spatial correlation length and (4) standard deviation σ, are chosen to measure permeability-field heterogeneity. Based on a stochastically realized permeability distribution, the authors scale the mean permeability to study its effect on seepage into underground openings. For a chosen percolation flux, the seepage rate into the underground openings was reduced as the Van Genuchten parameter α decreased. Simulation results show that the seepage into the underground openings is sensitive to the mean permeability, with seepage rate decreasing as the mean permeability increased. Simulation results indicate that the seepage is also very sensitive to the correlation length and standard deviation of the heterogeneous field. Either a high correlation value or a high standard deviation σ value increases seepage into the underground openings for a substantially heterogeneous continuum.
The amount of water seeping into the waste emplacement underground openings is an important issue for the long-term performance of any underground waste repository. Seepage controls the corrosion rates of waste packages, the waste mobilization rates and transport rates of contaminant leaving the underground openings. Predicting the seepage rate is difficult under any circumstances, and is particularly complicated for repository sites located in unsaturated, heterogeneous media. In this study, a 3-D numerical model is used to study unsaturated flow and seepage through a heterogeneous medium into the underground openings with strongly variable parameters and boundary conditions. The model has been compared with homogeneous model. The seepage rate into the underground openings increases with an increase in percolation flux introduced into the system. Four parameters, (1) fracture continuum permeability, (2) Van Genuchten parameter α, (3) spatial correlation length and (4) standard deviation σ, are chosen to measure permeability-field heterogeneity. Based on a stochastically realized permeability distribution, the authors scale the mean permeability to study its effect on seepage into underground openings. For a chosen percolation flux, the seepage rate into the underground openings was reduced as the Van Genuchten parameter α decreased. Simulation results show that the seepage into the underground openings is sensitive to the mean permeability, with seepage rate decreasing as the mean permeability increased. Simulation results indicate that the seepage is also very sensitive to the correlation length and standard deviation of the heterogeneous field. Either a high correlation value or a high standard deviation σ value increases seepage into the underground openings for a substantially heterogeneous continuum.
2003, 28(5): 505-510.
Abstract:
While it is well known that the groundwater level in coastal areas fluctuates frequently due to tidal seawater, it is not so well-recognized that air pressure in the subsurface soil near the coast may also fluctuate in response to sea tides. If the soil is well capped by less permeable materials such as concrete or asphalt, which is common in the extensively urbanized coastal areas in Hong Kong, significant high pressure may be produced by the watertable fluctuation and causes geotechnical problems such as surface heave. Therefore, understanding air flow induced by tidal fluctuation is of not only theoretical significance but also engineering implications. In this paper, a case study is conducted to explore the air pressure fluctuations observed below the asphalt pavement in a coastal reclamation area of Hong Kong. An isothermal, two-dimensional, cross-sectional model was built to describe the water-air two-phase flow in the unsaturated zone of the area. TOUGH2 simulator was used to obtain the numerical solutions. Sensitivity analysis was carried out to investigate the effects of model parameters on the air pressure fluctuations. After the boundary conditions and the model parameters were derived from the hydrogeological background in the area, the simulation reproduced the observed air pressure below the asphalt pavement with a satisfactorily small error.
While it is well known that the groundwater level in coastal areas fluctuates frequently due to tidal seawater, it is not so well-recognized that air pressure in the subsurface soil near the coast may also fluctuate in response to sea tides. If the soil is well capped by less permeable materials such as concrete or asphalt, which is common in the extensively urbanized coastal areas in Hong Kong, significant high pressure may be produced by the watertable fluctuation and causes geotechnical problems such as surface heave. Therefore, understanding air flow induced by tidal fluctuation is of not only theoretical significance but also engineering implications. In this paper, a case study is conducted to explore the air pressure fluctuations observed below the asphalt pavement in a coastal reclamation area of Hong Kong. An isothermal, two-dimensional, cross-sectional model was built to describe the water-air two-phase flow in the unsaturated zone of the area. TOUGH2 simulator was used to obtain the numerical solutions. Sensitivity analysis was carried out to investigate the effects of model parameters on the air pressure fluctuations. After the boundary conditions and the model parameters were derived from the hydrogeological background in the area, the simulation reproduced the observed air pressure below the asphalt pavement with a satisfactorily small error.
2003, 28(5): 511-516.
Abstract:
This article briefly introduces recent researches on horizontal wells in water resources and environmental engineering. This paper focuses on the location of semi-analytical solutions of groundwater flow to horizontal wells under different aquifer conditions such as confined, leaky confined, unconfined aquifers and aquifers under streams. The type curves and the derivative type curves of drawdowns are analyzed. Such semi-analytical solutions are useful for the interpretation of drawdowns characteristics after intermediate pumping time. This article also studies the hydraulics of a horizontal well at a large pumping rate, which is commonly used for dewatering and water supply. The authors have to consider the hydraulic head loss within the wellbore and to incorporate the Darcian flow and the pipe-flow into an integrated flow system. This article discusses vapor extraction in the unsaturated zone using horizontal wells and provides simplified analytical solutions to describe vapor pressure distribution and vapor flux across the ground surface (if the ground is open). It also reports the capture zone and capture time calculations under different aquifer conditions.
This article briefly introduces recent researches on horizontal wells in water resources and environmental engineering. This paper focuses on the location of semi-analytical solutions of groundwater flow to horizontal wells under different aquifer conditions such as confined, leaky confined, unconfined aquifers and aquifers under streams. The type curves and the derivative type curves of drawdowns are analyzed. Such semi-analytical solutions are useful for the interpretation of drawdowns characteristics after intermediate pumping time. This article also studies the hydraulics of a horizontal well at a large pumping rate, which is commonly used for dewatering and water supply. The authors have to consider the hydraulic head loss within the wellbore and to incorporate the Darcian flow and the pipe-flow into an integrated flow system. This article discusses vapor extraction in the unsaturated zone using horizontal wells and provides simplified analytical solutions to describe vapor pressure distribution and vapor flux across the ground surface (if the ground is open). It also reports the capture zone and capture time calculations under different aquifer conditions.
2003, 28(5): 517-521.
Abstract:
NaOH water solution is chosen as an original reactant by changing the parameters such as activation temperature, thickness of NaOH water solution and synthesis time. In addition, the fly ash can be heated up and directly crystallized, on the condition of hydrothermal alkaline activation, by using microwave. As a result, three kinds of zeolites are synthesized: laumontite, chabazite and NaP1 zeolites. The ratio of translating fly ash into zeolites is 15%-40%. The research shows the following three results: (1) zeolites can be synthesized for about 15 min, and the best ratio of translating fly ash into zeolites can be achieved for about 30 min. (2) In order to pretest the formation of crystalline nucleus and the growth of crystallize, the ratio of solution and fly ash should be more than 2.5. (3) The heating time should be controlled for about 30 min with the ratio of solution and fly ash 2.5.
NaOH water solution is chosen as an original reactant by changing the parameters such as activation temperature, thickness of NaOH water solution and synthesis time. In addition, the fly ash can be heated up and directly crystallized, on the condition of hydrothermal alkaline activation, by using microwave. As a result, three kinds of zeolites are synthesized: laumontite, chabazite and NaP1 zeolites. The ratio of translating fly ash into zeolites is 15%-40%. The research shows the following three results: (1) zeolites can be synthesized for about 15 min, and the best ratio of translating fly ash into zeolites can be achieved for about 30 min. (2) In order to pretest the formation of crystalline nucleus and the growth of crystallize, the ratio of solution and fly ash should be more than 2.5. (3) The heating time should be controlled for about 30 min with the ratio of solution and fly ash 2.5.
2003, 28(5): 522-526.
Abstract:
This paper presents and investigates an inverse method to simulate three-dimensional discrete fracture network of rock masses. The guiding principle of this method is to optimize the model to produce the same results as those from the filed observations, including the number and size of fractures, which is actualized through fitting the simulated fractures to the mapped fractures on outcrops and bore-holes. An illustrated example is presented to demonstrate the method.
This paper presents and investigates an inverse method to simulate three-dimensional discrete fracture network of rock masses. The guiding principle of this method is to optimize the model to produce the same results as those from the filed observations, including the number and size of fractures, which is actualized through fitting the simulated fractures to the mapped fractures on outcrops and bore-holes. An illustrated example is presented to demonstrate the method.
2003, 28(5): 527-532.
Abstract:
A large number of exploration and monitoring data in this paper show that a comprehensive groundwater system in the regimes characteristics of the interlayers between saturation and unsaturation is simulated using 3-D numerical model. The change in groundwater level is also predicted when surface water is delivered under four different scenarios. Subsequently, optimal scenarios of the surface water diversion are proposed, and the reasonable water output is 750 million m3/yr ranging from the upper-middle reaches of Heihe River to Ejina basin, in which the output water through Langxinshan hydrology is no less than 550 million m3/yr. It is expected that this study has great implications in the utilization and exploitation of groundwater resources, in the protection of ecosystem, as well as in the development in Ejina basin.
A large number of exploration and monitoring data in this paper show that a comprehensive groundwater system in the regimes characteristics of the interlayers between saturation and unsaturation is simulated using 3-D numerical model. The change in groundwater level is also predicted when surface water is delivered under four different scenarios. Subsequently, optimal scenarios of the surface water diversion are proposed, and the reasonable water output is 750 million m3/yr ranging from the upper-middle reaches of Heihe River to Ejina basin, in which the output water through Langxinshan hydrology is no less than 550 million m3/yr. It is expected that this study has great implications in the utilization and exploitation of groundwater resources, in the protection of ecosystem, as well as in the development in Ejina basin.
2003, 28(5): 533-536.
Abstract:
With the example of Shengou flume in Dongchuan of Yunnan Province, the dynamic process and space appearance of debris flow deposit were studied in the case of the debris flow disasters every 20 years (5% frequency)and every 100 years(1% frequency), using numerical simulation method. The debris flow deposit thickness and speed characteristics on the space are analyzed in different times.
With the example of Shengou flume in Dongchuan of Yunnan Province, the dynamic process and space appearance of debris flow deposit were studied in the case of the debris flow disasters every 20 years (5% frequency)and every 100 years(1% frequency), using numerical simulation method. The debris flow deposit thickness and speed characteristics on the space are analyzed in different times.
2003, 28(5): 537-544.
Abstract:
Based on the hydraulic performance of horizontal well, the authors produced a grant sand tank model, by which they took horizontal well pumping testson the different flux, measured the value of the head and flux obtained from time to time, and studied its hydraulic performance. The hydraulic test of the sand tank model showed that(1)several kinds of flow regimes are presented in the horizontal well pipe during the horizontal well pumping, such as transient region of laminar flow, hydraulic smooth region, transient region of turbulent flow and hydraulic roughness region.(2)The head loss of horizontal well pipe, which is neither neglected nor linear, is closely related to the flow regime, so thatitis not perfect to describe a horizontal well-bore with the linear or square sink. The reflectance theory is used to establish the analytical model. On the linear sink basis, when only flow of laminar(Re < 2 320)or flow of laminar and transient regions of laminar flow(Re < 4 000)are presented in the horizontal well pipe, the analytical solution is approaching the test data. However, when flow of laminar, flow of laminar and transient regions of laminar flow, hydraulic smooth region, and transient region of turbulent flow or hydraulic roughness region(Re < 4 000)occur, the analytical solution is not applicable. Then a new combined mathematical model of flow should be used in an aquifer-horizontal well system to obtain a solution.
Based on the hydraulic performance of horizontal well, the authors produced a grant sand tank model, by which they took horizontal well pumping testson the different flux, measured the value of the head and flux obtained from time to time, and studied its hydraulic performance. The hydraulic test of the sand tank model showed that(1)several kinds of flow regimes are presented in the horizontal well pipe during the horizontal well pumping, such as transient region of laminar flow, hydraulic smooth region, transient region of turbulent flow and hydraulic roughness region.(2)The head loss of horizontal well pipe, which is neither neglected nor linear, is closely related to the flow regime, so thatitis not perfect to describe a horizontal well-bore with the linear or square sink. The reflectance theory is used to establish the analytical model. On the linear sink basis, when only flow of laminar(Re < 2 320)or flow of laminar and transient regions of laminar flow(Re < 4 000)are presented in the horizontal well pipe, the analytical solution is approaching the test data. However, when flow of laminar, flow of laminar and transient regions of laminar flow, hydraulic smooth region, and transient region of turbulent flow or hydraulic roughness region(Re < 4 000)occur, the analytical solution is not applicable. Then a new combined mathematical model of flow should be used in an aquifer-horizontal well system to obtain a solution.
2003, 28(5): 545-550.
Abstract:
The non-steady radial flow surrounding a pumping well in a fully confined or leaky confined aquifer will induce the bending of confining unit, and then the radial flow patterns are affected by the bending effect through reducing of total stress.However, in conventional theory of groundwater flow, this interaction was omitted. In this study, the elastic plate theory was introduced to establish the analytical models of coupling of radial flow in a confined aquifer and bending of the confining unit, and meanwhile both of non-leaky and leaky conditions were considered as well as the compressibility of skeleton and water. It was indicated by the analytical solutions of the new theory that Theis equation underestimated the drawdown for fully confined aquifers. For leaky confined aquifers, the drawdown simulated by Hantush-Jacob equation was less than that evaluated by the new theory which considered the bending effect of confining unit. The relative errors would be remarkable in the beginning of pumping and/or near the pumping well.
The non-steady radial flow surrounding a pumping well in a fully confined or leaky confined aquifer will induce the bending of confining unit, and then the radial flow patterns are affected by the bending effect through reducing of total stress.However, in conventional theory of groundwater flow, this interaction was omitted. In this study, the elastic plate theory was introduced to establish the analytical models of coupling of radial flow in a confined aquifer and bending of the confining unit, and meanwhile both of non-leaky and leaky conditions were considered as well as the compressibility of skeleton and water. It was indicated by the analytical solutions of the new theory that Theis equation underestimated the drawdown for fully confined aquifers. For leaky confined aquifers, the drawdown simulated by Hantush-Jacob equation was less than that evaluated by the new theory which considered the bending effect of confining unit. The relative errors would be remarkable in the beginning of pumping and/or near the pumping well.
2003, 28(5): 551-556.
Abstract:
Based on systematology and the recognition to underground environment and root mass, the paper submits the conception of plant species stable layer in underground habitat and survival regions for the first time. Then from different aspects, the paper determines the depth range of plant species stable layer in underground habitat for perennial plant in middle-lower drainage of Heihe River, and the depth range is between 40 and 100 cm.By the connection of growth statusof representative species and the water and soil codition of plant species stable layer in underground habitat, the paper adumbrates survival regions of various species and acquires some recognition from the figure of survival regions of species as well as the superposed figure of all survival regions.
Based on systematology and the recognition to underground environment and root mass, the paper submits the conception of plant species stable layer in underground habitat and survival regions for the first time. Then from different aspects, the paper determines the depth range of plant species stable layer in underground habitat for perennial plant in middle-lower drainage of Heihe River, and the depth range is between 40 and 100 cm.By the connection of growth statusof representative species and the water and soil codition of plant species stable layer in underground habitat, the paper adumbrates survival regions of various species and acquires some recognition from the figure of survival regions of species as well as the superposed figure of all survival regions.
2003, 28(5): 557-562.
Abstract:
Cover-collapse is one of frequent geological hazards in karst zone. Predicting the probability of cover-collapse occurrence is a requisite task for territorial planning, resource exploiting and hazard harnessing. Regional quantitative prediction of cover-collapse probability has become very intricate problem for the following reasons: (1)interactions between many influencing factors; (2)a sophisticated developing process; (3) difficulty associated with the value acquisition of factors. Some recent prediction models can not display the nonlinear characteristicsof collapse development pattern, nor can they eliminate the impact of empiricism during the course of weights allocation. Three major characteristics of artifical neural network(ANN)technology, i.e. self-learning, self-adapting and nonlinear mapping, indicate a powerful application potential in collapse prediction field. This paper reports the methodology of developing an ANN model to predict cover-collapse occurrence probability. An approach was established to measure the relative probability of the collapse corresponding to certain factor combinations, and some impact factors were specified. Consequently, the structure of ANN prediction model was created.292 stochastic collapse samples from the sample aggregate, of which the size was 312, were used to train the ANN model. The testing results of the 20 remaining samples show that this model has a good precision. Evaluation grids division and their value acquisition of every factor were accomplished with the aid of GIS software tools. The unstable probability of each grid was calculated through the trained ANN model, which enables us to delineate the different stable zones in the study area.
Cover-collapse is one of frequent geological hazards in karst zone. Predicting the probability of cover-collapse occurrence is a requisite task for territorial planning, resource exploiting and hazard harnessing. Regional quantitative prediction of cover-collapse probability has become very intricate problem for the following reasons: (1)interactions between many influencing factors; (2)a sophisticated developing process; (3) difficulty associated with the value acquisition of factors. Some recent prediction models can not display the nonlinear characteristicsof collapse development pattern, nor can they eliminate the impact of empiricism during the course of weights allocation. Three major characteristics of artifical neural network(ANN)technology, i.e. self-learning, self-adapting and nonlinear mapping, indicate a powerful application potential in collapse prediction field. This paper reports the methodology of developing an ANN model to predict cover-collapse occurrence probability. An approach was established to measure the relative probability of the collapse corresponding to certain factor combinations, and some impact factors were specified. Consequently, the structure of ANN prediction model was created.292 stochastic collapse samples from the sample aggregate, of which the size was 312, were used to train the ANN model. The testing results of the 20 remaining samples show that this model has a good precision. Evaluation grids division and their value acquisition of every factor were accomplished with the aid of GIS software tools. The unstable probability of each grid was calculated through the trained ANN model, which enables us to delineate the different stable zones in the study area.
2003, 28(5): 563-567.
Abstract:
On the basis of the investigation into the oil contamination of soil-water-plant systems in the Shenyang-Fushun irrigation field, surface soils and bottom soils were sampled along 3 representative profiles and their major physical and chemical properties were analyzed. Kinetic curves and isotherms of aqueous oil adsorption on soils were measured and influence of organic matter, clay particle and salt contents on the adsorption was evaluated. The research results show that the equilibrium period of the adsorption is 20-24 hours, and all the adsorption isotherms are straight. In addition, it was found that the soils release some oil when the aqueous oil concentrations are lower than certain values.
On the basis of the investigation into the oil contamination of soil-water-plant systems in the Shenyang-Fushun irrigation field, surface soils and bottom soils were sampled along 3 representative profiles and their major physical and chemical properties were analyzed. Kinetic curves and isotherms of aqueous oil adsorption on soils were measured and influence of organic matter, clay particle and salt contents on the adsorption was evaluated. The research results show that the equilibrium period of the adsorption is 20-24 hours, and all the adsorption isotherms are straight. In addition, it was found that the soils release some oil when the aqueous oil concentrations are lower than certain values.
2003, 28(5): 568-574.
Abstract:
In the first part of this paper, the falling head permeability tests were conducted on bentonite-enhanced liner (BEL) specimens (sand-bentonite and clay-bentonite mixtures) to obtain the hydraulic conductivity. The results show that the hydraulic conductivity of clay-bentonite is about 6.0×10-9—3.0×10-8cm/s, and that of sand-bentonite about 1.0×10-9—3.0×10-9cm/s. Compared with the standard hydraulic conductivity used in Japan (1.0×10-6 cm/s), the hydraulic conductivity of both clay-bentonite and sand-bentonite is much lower. Then, the water retentivity and water migration tests were performed on the two liner specimens to evaluate the water retention and migration properties from saturated/unsaturated base soil. Based on the above tests, direct shear tests were conducted to obtain the internal shear strength of BEL specimens and the interface shear strength between BEL and base soil under five different water control conditions. Triaxial shear tests were also conducted on the two liner specimens to obtain the total and effective shear strength. Test results show that pore water in the underlying base soil has great potential to migrate to the BELs, resulting in a significant increase in water content of BELs, and the shear strength of both BEL internal and BEL/base interface tends to decrease with the increase of water content in BELs. Finally, the slope stability of a typical canyon solid waste landfill related to the two liners under various conditions was analyzed with the obtained shear strength parameters. Landfills at a gentle slope (with the total angle of the slope not greater than 20 degree) do not fail in both cases of sand-bentonite liner and clay-bentonite liner. Therefore, sand-bentonite and clay-bentonite mixtures are suitable for landfill bottom liners.
In the first part of this paper, the falling head permeability tests were conducted on bentonite-enhanced liner (BEL) specimens (sand-bentonite and clay-bentonite mixtures) to obtain the hydraulic conductivity. The results show that the hydraulic conductivity of clay-bentonite is about 6.0×10-9—3.0×10-8cm/s, and that of sand-bentonite about 1.0×10-9—3.0×10-9cm/s. Compared with the standard hydraulic conductivity used in Japan (1.0×10-6 cm/s), the hydraulic conductivity of both clay-bentonite and sand-bentonite is much lower. Then, the water retentivity and water migration tests were performed on the two liner specimens to evaluate the water retention and migration properties from saturated/unsaturated base soil. Based on the above tests, direct shear tests were conducted to obtain the internal shear strength of BEL specimens and the interface shear strength between BEL and base soil under five different water control conditions. Triaxial shear tests were also conducted on the two liner specimens to obtain the total and effective shear strength. Test results show that pore water in the underlying base soil has great potential to migrate to the BELs, resulting in a significant increase in water content of BELs, and the shear strength of both BEL internal and BEL/base interface tends to decrease with the increase of water content in BELs. Finally, the slope stability of a typical canyon solid waste landfill related to the two liners under various conditions was analyzed with the obtained shear strength parameters. Landfills at a gentle slope (with the total angle of the slope not greater than 20 degree) do not fail in both cases of sand-bentonite liner and clay-bentonite liner. Therefore, sand-bentonite and clay-bentonite mixtures are suitable for landfill bottom liners.
2003, 28(5): 575-578.
Abstract:
The water gushing test in an artesian well, a simple and economical test method for confirmation of the hydrogeology parameter in the water containing layer, basically belongs to the test of constant drawdown yield. During the water gushing test in the infinite confined aquifer, the inrush of water and the random water head H in the confined aquifer decrease with the time, except the well itself, but the fall of well water sw is kept unchangeable. The calculation of the hydrogeology parameter using the linear diagrammatized method l/Q-lg t in the constant drawdown yield test of single well, helps the authors to establish the linear diagrammatized method, s/Q-lg t method, in which one well is a main hole while the other wells can be used for watching the lowering of water.
The water gushing test in an artesian well, a simple and economical test method for confirmation of the hydrogeology parameter in the water containing layer, basically belongs to the test of constant drawdown yield. During the water gushing test in the infinite confined aquifer, the inrush of water and the random water head H in the confined aquifer decrease with the time, except the well itself, but the fall of well water sw is kept unchangeable. The calculation of the hydrogeology parameter using the linear diagrammatized method l/Q-lg t in the constant drawdown yield test of single well, helps the authors to establish the linear diagrammatized method, s/Q-lg t method, in which one well is a main hole while the other wells can be used for watching the lowering of water.
2003, 28(5): 579-582.
Abstract:
The movement of landslide in reservoir is divided into two stages, which are movement on ground and movement below water level, and the forcing characteristics of both stages are analyzed in this paper. The Newton law and the basic principles of kinematics are used to solve velocity and acceleration of landslide when it moves on ground surface, and the terminal conditions of stage on ground are considered as the initial conditions of stage below water level. The resistance formula in flow field and viscous force formula are applied to solve velocity and time of landslide when it moves below water level. At last, the momentum theory is adopted to calculate surge height. This paper takes Xintan landslide in the Three Gorges reservoir as the example and takes use of vertical slice method to calculate speed on ground surface, time below water level and surge height of each slice. It comes to the conclusions that the landslide firstly accelerates, then decelerates on surface, and the relationship between time and speed below water level is arc tangent and shows that the surge height keeps a great correlation with the height of slice.
The movement of landslide in reservoir is divided into two stages, which are movement on ground and movement below water level, and the forcing characteristics of both stages are analyzed in this paper. The Newton law and the basic principles of kinematics are used to solve velocity and acceleration of landslide when it moves on ground surface, and the terminal conditions of stage on ground are considered as the initial conditions of stage below water level. The resistance formula in flow field and viscous force formula are applied to solve velocity and time of landslide when it moves below water level. At last, the momentum theory is adopted to calculate surge height. This paper takes Xintan landslide in the Three Gorges reservoir as the example and takes use of vertical slice method to calculate speed on ground surface, time below water level and surge height of each slice. It comes to the conclusions that the landslide firstly accelerates, then decelerates on surface, and the relationship between time and speed below water level is arc tangent and shows that the surge height keeps a great correlation with the height of slice.
