Evaluation of foam conditioning effect on groundwater inflow at tunnel cutting face

This paper presents an analytical evaluation on the influence of foam conditioning on groundwater inflow at shield tunnel cutting face by the force-equilibrium principle. Three key variables are highlighted, namely, the maximum foam infiltration distance, the critical infiltration distance, and the hydraulic conductivity of foam-conditioned soil or rock fissure. To capture the variation of water level induced by foam injection, a dynamic water-level equation is considered in the force-equilibrium principle. The proposed analytical equations are employed to analyze a water inflow case during shield tunneling in a weathered mylonite fault. The results indicate that the hydraulic conductivity of foam-conditioned mylonite and the infiltration distance decrease with an increase of shear stress of foam fluid. A three-dimensional finite element model is employed to validate the analytical solutions. The comparison between the observed and calculated results confirms that the proposed method can predict groundwater inflow in foam-conditioned soils.     

Analytical theory for one‐dimensional consolidation of clayey soils exhibiting rheological characteristics under time‐dependent loading

This paper presents analytical solutions to the one‐dimensional consolidation problem taking into consideration the rheological properties of clayey soil under variable loadings. A four‐element rheological model is introduced, and different loading types are involved, i.e. constant loading, one‐step loading, triangular loading, rectangular loading, and isosceles–trapezoidal cyclic loading. The differential equations governing consolidation are solved by the Laplace transform. Based on the solutions obtained, the influences of the rheological parameters and loading conditions on the consolidation process are investigated. It has been shown that the consolidation behavior is mainly governed by four dimensionless parameters, a₁, a₂, b, and T_v0. Load shape has a great influence on the rate of consolidation. A decrease either in the modulus of the spring in the Kelvin body or in the viscosity coefficient of independent dashpot will slow down the rate of consolidation. An increase in the viscosity coefficient of the dashpot in the Kelvin body will make the rate of consolidation increase at an early stage but decrease at a later stage. For isosceles–trapezoidal cyclic loading, the consolidation rate in each cycle reaches a maximum at the end of the constant loading phase and the minimum at the end of this cycle. Copyright © 2008 John Wiley & Sons, Ltd.     

Numerical modeling of groundwater inflow from a confined aquifer into Sangan open pit mine,northeast Iran

Numerical models are useful in the evaluation of the interaction between groundwater systems and mining activities. They can be successfully used to predict the quantity of inflow into open pits and to design an appropriate dewatering system. In this paper, a two-dimensional axi-symmetric finite element model called SEEP/W has been used to predict the groundwater inflow into Sangan open pit mine (anomaly north C). The Sangan iron mine is located at 280 km south-east of Mashhad, Iran, in arid and warm climate conditions wherein precipitation is generally limited. The water inflow to the pit is mainly from a confined aquifer, mainly by horizontal flow in the upper layers and vertical flow at the pit bottom. The results of the numerical model of the ground water inflow are presented and compared with those obtained from Theis, Cooper-Jacob and Jacob-Lohman analytical solutions. Ground water inflow monitoring was also carried out in a trial excavation at the Sangan mine in order to calibrate the model. The model was then used to predict groundwater inflow into Sangan open pit mine during its advancement. This model provides valuable information for designing an appropriate dewatering system.     

半无限含水层中带衬砌隧洞渗流解析研究

现有关于半无限含水层中隧洞渗流的解析解不能考虑衬砌部分排水的特性。假定土体和衬砌均为饱和均匀连续介质,采用土体与衬砌分算;利用复变函数解决孔口问题基本方法,对土体采用共形映射坐标变换,将土体中的渗流方程转换为与衬砌部分类似的二维Laplace方程圆环域的Dirichlet问题;通过Fourier解法,根据边界条件并利用流量连续条件,求得半无限空间中带衬砌隧洞渗流量和衬砌周边水头解析解答。分析了径深比、土体与衬砌渗透系数相对值、内壁水压力等因素对渗流量和衬砌周边水头的影响,并与数值算例进行了比较。结果表明,对浅埋隧洞该解析解仍具有较好的精度,是简便、实用的计算方法。     

Semi‐analytical solution to one‐dimensional consolidation for unsaturated soils with semi‐permeable drainage boundary under time‐dependent loading

This paper presents semi‐analytical solutions to Fredlund and Hasan's one‐dimensional consolidation of unsaturated soils with semi‐permeable drainage boundary under time‐dependent loadings. Two variables are introduced to transform two coupled governing equations of pore‐water and pore‐air pressures into an equivalent set of partial differential equations, which are easily solved by the Laplace transform. The pore‐water pressure, pore‐air pressure and settlement are obtained in the Laplace domain. Crump's method is adopted to perform the inverse Laplace transform in order to obtain semi‐analytical solutions in time domain. It is shown that the present solutions are more general and have a good agreement with the existing solutions from literatures. Furthermore, the current solutions can also be degenerated into conventional solutions to one‐dimensional consolidation of unsaturated soils with homogeneous boundaries. Finally, several numerical examples are provided to illustrate consolidation behavior of unsaturated soils under four types of time‐dependent loadings, including instantaneous loading, ramp loading, exponential loading and sinusoidal loading. Parametric studies are illustrated by variations of pore‐air pressure, pore‐water pressure and settlement at different values of the ratio of air–water permeability coefficient, depth and loading parameters. Copyright © 2017 John Wiley & Sons, Ltd.     

A novel analytical solution for constant‐head test in a patchy aquifer

A mathematical model describing the hydraulic head distribution for a constant‐head test performed in a well situated at the centre of a patchy aquifer is presented. The analytical solution for the mathematical model is derived by the Laplace transforms and the Bromwich integral method. The solution for the hydraulic head has been shown to satisfy the governing equations, related boundary conditions, and continuity requirements for the hydraulic head and flow rate at the interface of the patch and outer regions. An efficient numerical approach is proposed to evaluate the solution, which has an integral covering an integration range from zero to infinity and an integrand consisting the product and square of the Bessel functions. This solution can be used to produce the curves of dimensionless hydraulic head against dimensionless time for investigating the effect of the contrast of formation properties on the dimensionless hydraulic head distribution. Define the ratio of outer‐region transmissivity to patch‐region transmissivity as α. The dimensionless hydraulic head for α=0.1 case is about 2.72 times to that for α=10 case at dimensionless large time (e.g. τ?10⁶) when the dimensionless distance (ρ) equals 10. The results indicate that the hydraulic head distribution highly depends on the hydraulic properties of two‐zone formations. Copyright © 2006 John Wiley & Sons, Ltd.     

A semi‐analytical approach for modelling heat transfer during salt‐cavern leaching process

The use of gas‐storage caverns in salt formations is a growing industry that continues to gain momentum because it allows gas to be injected and withdrawn at high rates compared with other underground gas‐storage systems such as porous rock systems. In order to predict cavern production performances, cavern thermodynamics behaviour must be studied by higher accuracy approaches. This behaviour is extremely related to the temperature distribution in the surrounding formations. During the leaching process, the thermal equilibrium of the rock salt surrounding the cavern is extensively disrupted. The purpose of this paper is to study the heat transfer problem during the leaching process and to develop a thermal model that can be easily used in field applications. The results of this work will be the input data for the prediction of the gas temperature and pressure during cavern gas‐storage operation phase. Moreover, the developed model can find its use in the design of salt caverns since it can be coupled with geometrical modelling of salt dissolution codes. Copyright © 2008 John Wiley & Sons, Ltd.     

Time‐dependent modelling for soils and its application in tunnelling

Monitoring of the progressive convergence of a tunnel shows that deformations occurring in the soil surrounding a tunnel exhibit a strong evolution with time. This time‐dependent behaviour can be linked to three essential factors: the distance from the point of interest to the working face over time, the distance of unsupported tunnel to the working face and the viscous properties of the soil. The objective of this paper is to propose a constitutive model of the time‐dependent behaviour of soil which has been developed within the framework of elastoplasticity–viscoplasticity and critical state soil mechanics. The consideration of viscoplastic characteristic sets the current model apart from the CJS (Cambou, Jafari and Sidoroff) model as the basic elastoplastic model, and introduces an additional viscous mechanism. The evolution of the viscous yield surface is governed by a particular hardening called ‘viscous hardening’ with a bounding surface. The proposed constitutive model has been applied in the analysis of tunnelling. Two kinds of numerical calculations have been used in the analysis, axisymmetric analysis and plane strain analysis. Monitoring of the progressive convergence of a tunnel conducted in the railway tunnel of Tartaiguille (France), has been used to describe the calculation procedure proposed and the capability of the model. The finite difference software, fast Lagrangian analysis of continua (FLAC), has been used for the numerical simulation of the problems. The comparison of results shows that the observed deformations could have been reasonably predicted by using the constitutive model and calculation strategy proposed. Copyright © 2004 John Wiley & Sons, Ltd.     

Sedimentation and time‐of‐transition techniques for measuring grain‐size distributions in lagoonal flats: comparability of results

A comparative study was performed of three instruments used to measure the grain‐size distribution of thirty sediment samples from shallow lagoonal flats: the hydrometer, the Sedigraph 5100 and the CIS‐1. The hydrometer and Sedigraph are based on sedimentation whereas the CIS‐1 uses the time of transition. The percentage of the samples accounted for by the <8 μm fraction was not affected by the technique used, but this was not the case with the clay fraction (<2 μm). Due to its relative independence from the analytical method applied, the <8 μm fraction can be used in ternary diagram classifications. This fraction also has an environmental significance in coastal lagoons in terms of hydrodynamics, organic enrichment and macrozoobenthos assemblages. The linear relationships obtained in this study may provide useful operational indications for similar studies.