This paper assesses methods to predict the saturated hydraulic conductivity, k, of clean sand and gravel. Currently, in engineering, the most widely used predictive methods are those of Hazen and t...

Predicting the saturated hydraulic conductivity of sand and gravel using effective diameter and void ratio

The science of pipe corrosion: A review of the literature on the corrosion of ferrous metals in soils

This paper examines and assesses predictive methods for the saturated hydraulic conductivity of soils. The soil definition is that of engineering. It is not that of soil science and agriculture, which corresponds to “top soil” in engineering. Most predictive methods were calibrated using laboratory permeability tests performed on either disturbed or intact specimens for which the test conditions were either measured or supposed to be known. The quality of predictive equations depends highly on the test quality. Without examining all the quality issues, the paper explains the 14 most important mistakes for tests in rigid-wall or flexible-wall permeameters. Then, it briefly presents 45 predictive methods, and in detail, those with some potential, such as the Kozeny-Carman equation. Afterwards, the data of hundreds of excellent quality tests, with none of the 14 mistakes, are used to assess the predictive methods with a potential. The relative performance of those methods is evaluated and presented in graphs. Three methods are found to work fairly well for non-plastic soils, two for plastic soils without fissures, and one for compacted plastic soils used for liners and covers. The paper discusses the effects of temperature and intrinsic anisotropy within the specimen, but not larger scale anisotropy within aquifers and aquitards.

Predicting the saturated hydraulic conductivity of soils: a review

Introduction.- Mathematical Models of Flow in Porous Media.- Numerical Solution of Flow Equations.- Computation of Inter-Nodal Permeabilities for Richards Equation.- Upscaling from Darcy Scale to Field Scale.- Flow in Binary Media with Heterogenous Hydraulic Diffusivity.- Flow in Binary Media with Heterogenous Air-Entry Pressure.

Modelling Water Flow in Unsaturated Porous Media: Accounting for Nonlinear Permeability and Material Heterogeneity

This paper presents a case history of the leakage behavior during dewatering tests in the gravel strata of an excavation pit of a metro station in Hangzhou, China. The groundwater system at the tes...

Characteristics of groundwater seepage with cut-off wall in gravel aquifer. I: Field observations

Numerical models are useful tools to evaluate problems and design remedial measures relative to groundwater seepage. They provide information for decision-making and guidance for collecting new dat...

A user's approach to assess numerical codes for saturated and unsaturated seepage conditions

Two types of variable-head permeability tests in driven flush-joint casings, the end-of-casing test and the lateral injection test (Lefranc test), were performed in two sand tanks. Hydraulic conditions in the sand tanks included a constant vertical hydraulic gradient that was null, positive, or negative. The gradients were monitored by lateral piezometers, which confirmed that the large-scale hydraulic conductivity (k) value of the sand layer remained constant throughout the test program. Any interpretation method for these variable-head tests implicitly requires an assumed piezometric level (APL) for analysis. According to a common practice, the elevation of the ponded water surface above the sand deposit was taken as the APL to plot the test results as the logarithm of the difference in total head versus time. After each casing installation, permeability tests were performed for the three gradient conditions. When the vertical gradient was null in the tank, the test data provided straight lines as assumed in theory. When the gradient was positive or negative, the test data provided curved graphs that may be interpreted as giving k values that vary with time. The velocity graph method, however, provided the same constant k value for the three gradient conditions. It also detected the error in the APL and provided in all cases a local piezometric level (PL) equal to that given by lateral piezometer monitoring. Thus, the velocity graph method, a graphical representation of the conservation equation, eliminated the potential for misanalysis of variable-head tests. The experimental k values, as determined by the two types of tests, usually ranged between 0.5 and 2 times the larger-scale values determined independently by the monitored flow rates and gradients in the sand tanks. The variability in experimental k values was partly due to the local variations of void ratio and effective diameter of the sand, and partly due to the influence of casing installation. Numerical simulations of the tests confirmed the validity of the velocity graph method for providing k and the local piezometric level for a test.

Variable-head field permeability tests in driven flush-joint casings: Physical and numerical modeling

Variable-head (slug) tests in a confined aquifer can be interpreted using different methods that either consider or neglect the influence of the instantaneous deformation of an elastic solid matrix...

Slug tests in a confined aquifer: experimental results in a large soil tank and numerical modeling

When a fully penetrating well pumps an ideal unconfined aquifer at steady state, the water table usually does not join the water level in the well. There is a seepage face inside the well, which is a key element in evaluating the well performance. This problem is analyzed using the finite-element method, solving the complete equations for saturated and unsaturated flow. The seepage face position is found to be almost independent of the unsaturated zone properties. The numerical results are used to test the validity of several analytic approximations. Equations are proposed to predict the seepage face position at the pumping well for any well drawdown, and the water table position at any distance from the pumping well for any in-well drawdown. Practical hints are provided for installing monitoring wells and evaluating well efficiency.

Seepage face height, water table position, and well efficiency at steady state.

An unconfined aquifer was instrumented with monitoring wells over a surface area of about 100 m × 100 m. The aquifer is a sand deposit overlying a thick nonfissured layer of Champlain Sea clay. The paper presents the results of a pumping test at a constant flow rate. None of the curves of drawdown versus time presented the S shape of current theories; however, all drawdowns indicated that the aquifer was homogeneous. The values for the specific yield were too low and varied with distance and time instead of being constant. The theories for steady and unsteady states provided different values for the saturated hydraulic conductivity. To understand the field behavior that differs from theoretical predictions, the pumping test conditions were modeled numerically using a finite element method. The transmissivity was derived from the Dupuit equation, and different curves for capillary retention and unsaturated permeability were examined. The numerical drawdowns agree with the experimental drawdowns. Several nu...

Unusual drawdown curves for a pumping test in an unconfined aquifer at Lachenaie, Quebec: field data and numerical modeling

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