Showing papers in "Computers and Geotechnics in 1999"
TL;DR: In this article, a large experimental database obtained from published literature was used in training, testing, and prediction phases of three neural network based soil models, which can accurately represent the effects of mineralogy, grain shape and size distribution, void ratio, and confining pressure.
Abstract: The stress–strain and volume change behavior of sand and gravel under drained triaxial compression test conditions was modeled using feed-back artificial neural networks. A large experimental database obtained from published literature was used in training, testing, and prediction phases of three neural network based soil models. Issues related to the number of hidden units, magnitude of strain increment during feed-back, and over-training error are discussed. These models can accurately represent the effects of mineralogy, grain shape and size distribution, void ratio, and confining pressure. The observed behavior in terms of a non-linear stress–strain relation, compressive volume change at low stress levels, and volume expansion at high stress levels are captured well by these models.
147 citations
TL;DR: In this article, a fully explicit analytical solution is presented for one-dimensional consolidation of two-layered soils with partially drained boundaries, and some diagrams are prepared and the relevant consolidation behavior of layered soils associated with partially-drained boundaries.
Abstract: In this paper, a fully explicit analytical solution is presented for one-dimensional consolidation of two-layered soils with partially drained boundaries. It can be shown that the available analytical solutions so far developed for one dimensional consolidation of soil are the special cases of the solution presented herein. According to the solution, some diagrams are prepared and the relevant consolidation behavior of layered soils associated with partially drained boundaries is discussed in detail. Furthermore, the applications of the solution are illustrated in an example problem.
70 citations
TL;DR: In this paper, an interellipsoid contact detection algorithm was developed and used for simulating the behavior of assemblies of ellipsoide-shaped particles using the well-known discrete element method (DEM).
Abstract: An inter-ellipsoid contact detection algorithm was developed and used for simulating the behaviour of assemblies of ellipsoid-shaped particles using the well-known discrete element method (DEM). The contact algorithm was implemented in the modified version of the DEM program TRUBAL originally written to simulate the behaviour of assemblies of spheres. The modified program was used to perform deviatoric and axisymmetric compression tests on a 1000 prolate spheroid assembly in periodic space. The obtained stress–strain–dilation curves conform with the experimental evidence both qualitatively and quantitatively.
64 citations
TL;DR: In this article, a finite element study has been carried out to determine the pile-soil-pile interaction behavior for closely spaced pile rows and groups under passive lateral loading from soil movement.
Abstract: A finite element study has been carried out to determine the pile–soil–pile interaction behaviour for closely spaced pile rows and groups under passive lateral loading from soil movement. A horizontal section close to the piles was studied to determine the effects of pile spacing and soil constitutive law on the load–transfer relationships of the piles. The study has revealed links between the soil stress–strain law, the soil deformation mechanism and the pile load–transfer curves. Interaction behaviour was seen to depend on the prevailing deformation mechanism which in turn was governed by the soil constitutive law. Elastic-plastic and power law soil models were applied. Interaction factors suitable for design use to account for increasing lateral pressure on piles during passive lateral loading have been produced for a range of pile spacings and power law soil exponents. Interaction between piles increased both with reduction of pile spacing and with increase of soil exponent—the less soil stiffness degradation with shear strain, the greater the interaction between piles at a given spacing. This suggests that the passive interaction factors calculated using elastic methods are likely to overestimate the effects of pile–soil–pile interaction.
63 citations
TL;DR: In this paper, the authors used finite element analysis techniques to determine the capacity of suction caisson foundations in soft clays under undrained conditions using an elasto-plastic model.
Abstract: This paper documents the use of finite element analyses techniques to determine the capacity of suction caisson foundations founded in soft clays under undrained conditions. The stress–strain response of the soft clay is simulated using an elasto-plastic model. The constitutive model employed is the classical von Mises strength criterion with linear elasticity assumed within the yield/strength surface. Both two- and three-dimensional foundation configurations are analyzed. The three-dimensionality of the failure surface of the actual caisson requires that computationally intensive three-dimensional models be used. Suggestions are given on how to improve computational efficiency by using quasi three-dimensional Fourier analyses with excellent results instead of true three-dimensional analyses. The finite element techniques employed are verified against available classical limit solutions. Results indicate that both hybrid and displacement-based finite element formulations are adequate, with the restriction that reduced-integration techniques are often required for displacement-based formulations.
56 citations
TL;DR: In this article, a 3D finite element model (FEM) has been developed for the deformation analysis of nailed soil structures, considering the soil nonlinearity, the soil-nail interaction and the staged construction.
Abstract: In recent years, soil nailing has been widely used to stabilize excavated steep slopes. Its design is often controlled by the allowable deformation level especially when buildings and/or other underground facilities exit near the excavation. In this paper a three-dimensional (3-D) finite element model (FEM) has been developed for the deformation analysis of nailed soil structures. In this model, the soil nonlinearity, the soil–nail interaction and the staged construction are all considered. Parametric studies are carried out to investigate some influence factors on the deformation behavior. An engineering case is also analyzed and the predicted soil movements at various stages of excavation are compared with field measurements. Good agreement between the prediction and the measurements proves the reliability of the model.
47 citations
TL;DR: In this article, an identification process for determination of material parameters in a constitutive relationship, describing time dependency of air permeability of shotcrete tunnel lining, was described, and a numerical model has been developed to predict the air losses from tunnel face and perimeter walls in compressed air tunnelling.
Abstract: This paper describes an identification process for determination of material parameters in a constitutive relationship, describing time dependency of air permeability of shotcrete tunnel lining. A numerical model has been developed to predict the air losses from tunnel face and perimeter walls in compressed air tunnelling. Field data from a Tunnel in Germany has been used to verify and calibrate the numerical model. A relationship has been established to describe the variation of the air permeability of shotcrete tunnel lining with time and the technique of parameter identification has been used to determine the parameters of this relationship. A genetic algorithm has been used in the optimisation procedure. It has been shown that time dependency of permeability of shotcrete plays a key role in controlling the air losses in driving tunnels under compressed air with shotcrete as a temporary or permanent lining and this time dependency should be taken into account in design.
47 citations
TL;DR: In this paper, the influence of the sealing condition on the stress, displacement and pore pressure fields is studied using a number of results presented in the time domain, and it is concluded that the stress and displacement fields are highly sensitive to the flow condition imposed along the tunnel wall.
Abstract: Biot‘s general consolidation theory is used to study time-dependent stress-displacement fields induced by tunnel excavation in a poroelastic saturated soil. The tunnel is considered circular and deeply embedded so an analytical solution can be obtained in the Laplace transform domain and the results in the time domain are obtained using a numerical technique for the inverse Laplace transform. Special attention is paid on the flow boundary condition along the tunnel wall. A partially sealing boundary condition is developed in order to represent most of the real practical situations. The permeable and impermeable boundaries are only two extreme cases of the general condition developed. The influence of the sealing condition on the stress, displacement and pore pressure fields is studied using a number of results presented in the time domain. It is concluded that the stress and displacement fields are highly sensitive to the flow condition imposed along the tunnel wall.
47 citations
TL;DR: A parallel pore-scale numerical model based on SPH is described for modeling flow phenomena in porous media and aspects of SPH which complicate parallelization are emphasized.
Abstract: Smoothed particle hydrodynamics (SPH) is a versatile technique which can be applied to single and multiphase flow through porous media. The versatility of SPH is offset by its computational expense which limits the practicability of SPH for large problems involving low Reynolds number flow. A parallel pore-scale numerical model based on SPH is described for modeling flow phenomena in porous media. Aspects of SPH which complicate parallelization are emphasized. The speed of the method is demonstrated to be proportional to the number of processors for test cases where load balance was achieved. The parallel algorithm permits the application of SPH to more complicated porous media problems than previously considered. For such problems, best performance is achieved when several soil grains are simulated by each processor. Finally, future applications of the method and possible extensions are discussed.
40 citations
TL;DR: In this article, a multiphase flow model based on the two-phase flow model of Brooks and Corey is presented to express the dependence of saturation and relative permeability on the capillary pressure.
Abstract: A fully coupled numerical model has been developed which describes multiphase fluid flow through soil: namely gas, water and a nonaqueous phase liquid (NAPL) in a deforming porous media for subsurface systems. A multiphase flow model, based on the two-phase flow model of Brooks and Corey, is presented to express the dependence of saturation and relative permeability on the capillary pressure. Nonlinear saturation and relative permeability on the capillary pressure. Nonlinear saturation and relative permeability functions are incorporated into a Galerkin finite element model which is subsequently used to simulate multiphase immiscible fluid flow under saturated and unsaturated conditions in porous media. The governing partial differential equations, in terms of soil displacements and fluid pressures, which are coupled and non-linear, are solved by the finite element method. Numerical implementation of the formulation are discussed and example problems are performed to demonstrate the model and solution procedure.
35 citations
TL;DR: In this paper, a rotational mechanism of slope failure, caused by horizontal shaking, is considered, and irreversible displacements can be represented as the product of a coefficient characteristic of a given collapse mechanism and a double time integral of an earthquake acceleration record.
Abstract: Earthquake events in recent years have brought about renewed interest in analyses of slopes subjected to seismic loads. These loads have been accounted for traditionally by using quasi-static loads. Such analyses do not provide any information about permanent displacements, and they neglect the history of seismic shaking. The analysis presented in this note is based on the rigid block displacement technique. A rotational mechanism of slope failure, caused by horizontal shaking, is considered. Yield accelerations are calculated for uniform slopes, and irreversible displacements are calculated for different earthquake records. The displacements can be represented as the product of a coefficient characteristic of a given collapse mechanism and a double time integral of an earthquake acceleration record. Charts are produced to make the application of the results effortless.
TL;DR: In this paper, a fully coupled heat and mass transfer numerical model is presented to describe the migration of a contaminant gas through an engineered clay liner of a sanitary landfill site.
Abstract: This paper presents a fully coupled heat and mass transfer numerical model describing the migration of a contaminant gas through an engineered clay liner of a sanitary landfill site. The governing system of non-linear partial differential equations are derived from a mechanistic approach where the mass and energy conservation laws are defined for a particular phase into which Darcy’s law and Fick’s law are substituted. The model treats the migration of liquid water, heat, air and contaminant gas separately with independent system variables of capillary potential, temperature, pore air pressure and molar concentration of the contaminant gas. A numerical solution is presented, which is compared against the classical advection–diffusion equation, to highlight the effect of a temperature gradient on the contaminant gas concentration.
TL;DR: In this article, a two dimensional axisymmetric finite element based model for analysis of a soil-pile system in expansive soils is developed, where the pile is assumed to behave as linearly elastic while the soil is modelled as nonlinear elastic material.
Abstract: A two dimensional axisymmetric finite element based model for analysis of a soil–pile system in expansive soils is developed. The pile is assumed to behave as linearly elastic while the soil is modelled as nonlinear elastic material. Swelling and shrinkage of the soil are related to change in soil suction. The predictions of the model are compared to the results of field experiments from two expansive soil sites in Sudan, Wad Madani and Elfao. The predictions of the numerical model are in good agreement with field results. Parametric studies are performed using the model. The study shows that increase in pile length decreases the upward vertical movement of the pile. As the axial load increases, both the upward vertical movement and the tensile stress decreases and eventually the pile may be subjected only to downward movement and compressive stresses. Tensile stresses for loaded piles occur throughout most portions of the pile within the active zone with the maximum stress developing near the mid height of the pile.
TL;DR: In this paper, two parameter identification procedures for linear viscoelastic materials are presented, one using the incremental constitutive relation for linear elastic materials, and the other using the elastic-visco-elastic correspondence principle.
Abstract: Two parameter identification procedures for linear viscoelastic materials are presented. One is the method using the incremental constitutive relation for linear viscoelastic materials, and the other is the method using the elastic–viscoelastic correspondence principle. Part of back analysis in both methods is formulated based on the boundary control concept (Ichikawa Y, Ohkami T. A parameter identification procedure as a dual boundary control problem for linear elastic materials. Soils and Foundations 1992;32(2):35–44). Two numerical examples are presented to compare the efficiency of both methods.
TL;DR: In this paper, the effects of randomness of initial damage in a rock mass and the critical tensile strain of the rock material on its dynamic responses and damage under explosive loads are addressed.
Abstract: This paper addresses the effects of randomness of initial damage in a rock mass and the critical tensile strain of the rock material on its dynamic responses and damage under explosive loads. A fuzzy definition is proposed to describe the fuzzy nature of failure phenomenon in a rock mass. The initial damage of the rock mass is estimated using the longitudinal and transverse elastic wave velocities. By using statistical analysis, the initial damage of the rock mass is found having the Beta distribution. The statistical estimation of a damage state and properties of randomly damaged rock mass are evaluated by the Rosenbluth's point estimate method. In numerical calculation, an isotropic continuum damage model with the initial damage and the cumulative damage dependent on an equivalent tensile strain is suggested to model the rock mass behavior under blast loads. A Beta distribution is proposed to represent the probabilistic distribution of the damage variable of the rock mass under explosive loads. Several types of membership functions are suggested to represent the fuzziness of material failure. Based on the fuzzy–random probabilistic theory, a model including both the effects of randomness and fuzziness is proposed for the failure analysis of rock mass under explosive loads. The suggested models are coded and linked with an available computer program AUTODYN2D through its user's subroutine capacity. The fuzzy failure probability and dynamic responses of the rock mass are calculated. Numerical results are compared with those obtained from independent field tests.
TL;DR: In this paper, the moment-carrying capacity of short pier foundations in loose and dense cohesionless soil is investigated, where the results of non-linear three-dimensional finite element analyses are compared with data from centrifuge tests modelling the behaviour of 1 m diameter prototype piers.
Abstract: This study is concerned with the moment-carrying capacity of short pier foundations in loose and dense cohesionless soil. The results of non-linear three-dimensional finite element analyses are compared with data from centrifuge tests modelling the behaviour of 1 m diameter prototype piers. The numerical predictions are shown to be very sensitive to the value of coefficient of earth pressure at rest, and most closely match obserbations when coefficient of earth pressure at rest = 0.6 is assumed. The results of parametric studies of square prototype piers in loose and dense cohesionless soils are then presented. Empirical equation are derived between moment-carrying capacity and pier geometry, for limiting pier rotations of 1 degree and 2 degrees, and very close fits are demonstrated between the values given by these equations and the original computed values. (A)
TL;DR: Comparison of single instruction multiple data stream (SIMD) and multiple-instruction multiple-data stream (MIMD) operation showed MIMD processing to provide the best overall parallelization.
Abstract: Reconfiguration of a discrete element code for parallel operation provided the opportunity to compare processing speeds on various hardware platforms. The program employed in this comparison, NURBM3DP, is a three dimensional, distinct element code employed to calculate dynamic response of a cavern in a jointed rock mass. On a 16 processor IBM SP2, it is capable of calculating dynamic response with 1000's of explicit time steps of jointed rock masses with up to 2,000,000 blocks. Comparison of single instruction multiple data stream (SIMD) and multiple-instruction multiple-data stream (MIMD) operation showed MIMD processing to provide the best overall parallelization. The full report of the comparisons of operation on different hardware with different data streaming configurations can be found at the research section of the Northwestern University Computational Mechanics site: http://www.tam.nwu.edu/compmech.html. In addition, a color movie of dynamic response of a million block model of a cavern responding to dynamic excitation can be seen at: http://geotech.civen.okstate.edu/ejge/ppr9801/index.htm.
Abstract: This paper presents analytical solutions and associated computational methods for the stresses and displacement field in elastic geo-materials induced by external loading concentrated at a point. The geo-materials can have their elastic properties exhibiting arbitrary variations in depth and keeping constant in lateral directions. Numerical results indicate that there is no problem in the evaluation of the point load solutions with high accuracy and efficiency, and that the material non-homogeneity has a significant effect on the elastic field due to external loading.
TL;DR: In this paper, analytical solutions are presented for hammer impact using a model which uses lumped masses for the ram and anvil, a spring for the anvil cushion, and another spring for a cap cushion on the top of a pile.
Abstract: The drivability study of piling requires modelling of the hammer impact to calculate the input force wave at the pile head. This force wave can be computed numerically or by using simple analytical solutions. In this paper, analytical solutions are presented for hammer impact using a model which uses lumped masses for the ram and anvil, a spring for the anvil cushion, and another spring for the cap cushion on the top of a pile. The pile is modelled as a dashpot. The solutions account for the separation of the anvil mass from the pile cap cushion as well as the separation of the ram mass from the anvil cushion. The developed solutions are used to perform a parametric study to illustrate the influence of the pile cushion on the maximum force transmitted to the pile head.
TL;DR: In this article, the authors derived equations that govern the dynamic behavior of the machine foundations and consider the inhomogeneity of the elastic foundation, particularly for Gibson type soil, by using variational principles.
Abstract: Real modulus of elasticity of the soil usually increases with the depth of the soil due to the increase in overburden pressure. Therefore, incorporation of the effect of the soil inhomogeneity in the formulation to obtain the response of the machine foundations is an important and a necessary step. In this paper, equations that govern the dynamic behavior of the machine foundations and consider the inhomogeneity of the elastic foundation, particularly for Gibson type soil are derived by using variational principles. The coupled equations of the motion of the physical system are solved by applying iterative procedure, and the computer code developed for the numerical model can be run even on the small computers.
TL;DR: In this article, a finite-difference method of solution for gas-bubble flow in natural rock fractures was developed, where two-phase fluid mechanics were used for the formulation of the equations that govern the problem, and the velocity and pressure distribution of the two phases was pursued inside the fracture.
Abstract: A novel numerical procedure has been developed, and is being investigated to model gas-bubble flow in natural rock fractures. Experimental observations and numerical computations are combined in the process of developing a finite-difference method of solution for the problem. Two-phase fluid mechanics are used for the formulation of the equations that govern the problem, and the velocity and pressure distribution of the two phases is pursued inside the fracture. A simplified analytical solution has also been developed for the purpose of comparing it to the numerical scheme.
TL;DR: In this paper, the Extended Bayesian Method (EBM) was adopted for the feedback analysis and the finite element analysis, which was implemented to predict the ground response to an actual tunnel site in Pusan, Korea.
Abstract: Effort was made in this paper to formulate a parameter estimation technology by systematically combining the field measurements and the prior information of underground structure. The Extended Bayesian Method (EBM) was adopted for the feedback analysis and the finite element analysis, which was implemented to predict the ground response. Determined in the present study were various geotechnical parameters including the elastic modulus (E), the initial horizontal stress coefficient at rest (Ko), the cohesion (c) and the internal friction angle (φ). The validity of the feedback system proposed herein was demonstrated through an elasto-plastic example problem. The proposed method was applied to an actual tunnel site in Pusan, Korea and has shown to be highly effective in actual field problems.
TL;DR: In this paper, two infinite elements, harmonic and transient, are presented for the solution of the transient and harmonic response of unbounded media problems, respectively, for linear elastic and visco-elastic foundations.
Abstract: Using the governing diAerential equations of wave propagation problems and making use of the Galerkin weighted residual method, discretized formulations in the Laplace transform domain for the transient behaviour of unbounded domain problems have been presented for linear elastic and visco-elastic foundations. In this paper, two infinite elements, harmonic and transient, are presented. These elements are capable of considering three diAerent wave types simultaneously. Examples considered in this study indicate that present formulations have suAcient computational accuracy for the solution of the transient and harmonic response of unbounded media problems. # 1999 Elsevier Science Ltd. All rights reserved.
TL;DR: In this article, a viscoplastic constitutive model of rock is proposed for which both yield stress and viscosity undergo variation during the deformation process, and the model is initially formulated for a uniaxial stress state; its extension for a general stress state is also provided.
Abstract: A viscoplastic constitutive model of rock is proposed for which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension for a general stress state is also provided. Model parameters are determined from compression tests at different values of strain rate, and its application to simulate results of such tests is given. The examples of stress redistribution in a coal seam due to progressing longwall exploitation are presented by applying the developed degradation model. The model provides good simulation of material response in both stable and post-critical stages.
TL;DR: In this paper, a stochastic method and its computer implementation to evaluate the earth structure settlements that occur under static loading is presented, where the settlements are calculated with a commercial finite difference program called Dynard, which considers a non-linear elasto-plastic soil model based on the shear and bulk moduli and the undrained strength of the soil.
Abstract: A stochastic method and its computer implementation to evaluate the earth structure settlements that occur under static loading is presented in this paper. The settlements are calculated with a commercial finite difference program called Dynard, which considers a non-linear elasto-plastic soil model based on the shear and bulk moduli and the undrained strength of the soil. The Monte Carlo simulation technique and the Rosenblueth's point estimate methods are considered in the proposed approach. To illustrate the suitability and accuracy of the proposed procedure, the settlements arising on an earth dam model under gravity loads are calculated. The results are compared and validated with the settlements obtained with a boundary element method program codified by the authors.
TL;DR: In this paper, two theoretically consistent methods are proposed and examined for the analysis of triaxial tests, and the effect of these three methods on strain-dependent material parameters is analyzed using key geotechnical parameters and an advanced constitutive model.
Abstract: Constitutive models for geomaterials are frequently developed and calibrated on the basis of element tests. Prior to the analysis of element tests a suitable set of work-conjugated stress and strain measures has to be selected. The paper points out that the traditional analysis of triaxial tests is theoretically inconsistent as finite and infinite strain measures are mixed in the analysis. Therefore, two theoretically consistent methods are proposed and examined for the analysis of triaxial tests. These three methods affect strain-dependent material parameters differently. The effect is analysed using key geotechnical parameters and an advanced constitutive model.
TL;DR: An analytical procedure to obtain the response of pile-group in time domain using an adaptive direct integration method which has all the advantages of time domain scheme which is local in space and time with small computational effort.
Abstract: An analytical procedure to obtain the response of pile-group in time domain is described. The procedure makes use of large domain for discretization along with coordinate transformation using Lanczos vectors. The responses are obtained in time domain using an adaptive direct integration method. The scheme has the ability of error estimation due to temporal discretization and coordinate transformation. The procedure has been applied to three dimensional pile-group foundations. The compliance functions of the foundations have been obtained for all modes of vibration. The computational scheme has also been used to analyze the response of a machine foundation transmitting non-harmonic but periodic forces. The present method has all the advantages of time domain scheme which is local in space and time with small computational effort.
TL;DR: In this article, a mass-conservative numerical technique for solving the advection-dispersion equation for miscible contaminant transport is presented, which combines features of puff transport models from air pollution studies with features from the random walk particle method used in water resources studies, providing a deterministic time-marching algorithm which scales from one to higher dimensions simply.
Abstract: A flexible, mass-conservative numerical technique for solving the advection–dispersion equation for miscible contaminant transport is presented. The method combines features of puff transport models from air pollution studies with features from the random walk particle method used in water resources studies, providing a deterministic time-marching algorithm which is independent of the grid Peclet number and scales from one to higher dimensions simply. The concentration field is discretised into a number of particles, each of which is treated as a point release which advects and disperses over the time interval. The dispersed puff is itself discretised into a spatial distribution of particles whose masses can be pre-calculated. Concentration within the simulation domain is then calculated from the mass distribution as an average over some small volume. Comparison with analytical solutions for a one-dimensional fixed-duration concentration pulse and for two-dimensional transport in an axisymmetric flow field indicate that the algorithm performs well. For a given level of accuracy the new method has lower computation times than the random walk particle method.
TL;DR: Generic forms for the representation of correlations in the system were established as part of the development, and this generic form minimises the dangers of applying a correlation which is not applicable to the material under consideration or is beyond the range of values for which the correlation was derived.
Abstract: A knowledge-based system has been developed to provide a tool for storing and using correlations for the estimation of geotechnical properties. Generic forms for the representation of correlations in the system were established as part of the development. This generic form for the representation of correlations ensures that all relevant information is available to the user. It minimises the dangers of applying a correlation which is not applicable to the material under consideration or is beyond the range of values for which the correlation was derived. The Correlations Knowledge Base was implemented as an object base, and the slot and facet structure is outlined in the paper. A brief description of the inference mechanism and user interface is also provided. These allow the user to make use of the knowledge contained within the correlation objects to produce estimations for ground properties. The system was implemented using ProKappa software, running under X windows on a Sun Spark 2 workstation.
TL;DR: In this paper, a study of the remediation of a contaminated aquifer of uniform thickness by multi-well systems, which include both discharge wells and recharge wells, is presented, showing that an appropriately designed pump and treat system (PAT) can have a significant effect on the decontamination of a polluted aquifer and can preclude the further spreading of a contaminant plume.
Abstract: Various numerical techniques have been developed and used to design waste repositories such as landfills, in order to reduce the impact of contamination. However, even with good design, potential contamination such as groundwater contamination may still arise in the future due to unforseen circumstances or negligence. Thus there is a need to seek efficient, cost-effective and carefully designed remediation strategies for the cleanup of contaminated groundwater. This paper presents a study of the remediation of a contaminated aquifer of uniform thickness by multi-well systems, which include both discharge wells and recharge wells. These investigations show that an appropriately designed pump and treat system (PAT) can have a significant effect on the decontamination of a polluted aquifer and can preclude the further spreading of a contaminant plume. However, if the system is not designed appropriately, it may cause a further serious spreading of the contamination. This possibility is illustrated by the examples presented in the paper, which highlight the need for care in the design of remediation strategies.