International Journal of Geomechanics

This paper presents the formulation of the mechanics governing the changes in stress state from groundwater pumping. A two-layer alluvium consisting of a cemented alluvium layer on top of an unconfined aquifer alluvium layer is considered. It is shown that the stress state in the aquifer alluvium consists of compression, simple shear and couple stresses. The shear stresses on the vertical planes and horizontal planes are not equal. Consequently, a Cosserat rather than the conventionally used Cauchy continuum better simulates the stresses in the aquifer alluvium. Land subsidence from groundwater level decline consists of vertical compression (consolidation), shear displacement and macrorotation. The latter occurs when conditions are favorable for the microrotation imposed by asymmetric stresses to become macrorotation. Earth fissures are formed in aquifer alluvium from groundwater pumping by simple shear on vertical planes and rotation and not by tension as commonly suggested. Earth fissures are formed in the upper cemented alluvium by simple shear strains and rotations. Highly cemented alluviums are more prone to earth fissure formation than weakly cemented alluviums. It is shown that there is a critical characteristic length of $\surd 2$ times the aquifer alluvium thickness below which earth fissures would, theoretically, not develop. The distances from the well face at which earth fissures will form depend not on the total drop in groundwater level but on the gradient of the groundwater profile. The slope of the subsidence bowl, which consists of simple shear strain and rotation, is established as an indicator for the initiation of earth fissures.

The physical processes such as advection, dispersion, and diffusion and interaction between the solution and the soil solids such as sorption, biodegradation, and retention processes have been considered in the governing equation used in the present study. Finite difference method has been adopted herein to solve the one-dimensional contaminant transport model to predict the pollutant migration through soil in waste landfill. In the finite difference technique, the velocity field is first determined within a hydrologic system, and these velocities are then used to calculate the rate of contaminant migration by solving the governing equation. A total of seven contaminants have been chosen for analysis to represent a wide variety of wastes both organic and inorganic. A computer software CONTAMINATE has been developed for solution of the contaminant transport model. Results of this study have been compared with existing analytical solution for validation of the proposed solution technique. Design charts for liners have also been developed to facilitate the designers. The liner thickness has been optimized by considering the effect of velocity of advection, dispersion coefficient, and geochemical reactions for all the contaminants of this study.

The present study aims at determining the uplift capacity of axially loaded piles in clays whose undrained cohesion increases linearly with depth. With the application of the axisymmetric static limit analysis approach, proposed recently by the writers, the variation of the nondimensional uplift factors with respect to changes in the embedment ratio $\left(H/B\right)$ has been obtained for several rates of increase of soil cohesion with depth defined in terms of a nondimensional factor $m$ for given values of soil cohesion $\left(c_0\right)$ along the ground surface and diameter $\left(B\right)$ of pile. The uplift resistance has been evaluated in the form of the uplift factors, $F_{cb}$ and $F_{ct}$ due to the components of the shaft resistance and the total resistance, respectively. For the given values of $c_0$ and $B$ , the magnitude of the uplift resistance increases continuously with an increase in the value of $m$ . Furthermore, the $F_{cb}$ values are found to remain unaffected with the variation in the shaft adhesion, whereas, the $F_{ct}$ values increase continuously with an increase in the adhesion factor of the pile shaft.

Determination of stress distribution, giving due consideration to arching mechanism within minefill stopes, is of great importance because of its influence on the ground stability, ore recovery, and cost effectiveness. Most of the past studies on the stress determination have been applied to vertical stopes, and there is a lack of research study, especially analytical work, on inclined stopes. This study provides an analytical expression for the vertical stress at any depth within the inclined backfilled stopes by incorporating an arching effect within the backfill. Comparatively, the results obtained from this study agree well with other limited analytical and numerical results reported in the literature. A parametric study is undertaken to investigate the effect of various parameters involved in the proposed analytical expression. The results obtained reveal that stope geometry, fill properties, and stope inclination are critical factors in predicting the stress distribution in mine stopes.

Parameters of rock failure criteria are estimated using an optimization procedure based on appropriate objective function. In the development of objective function, it is assumed that the independent variables are free from errors. But, as measurement error is attributed to equipment and random testing effects, all the measuring variables may have some error. In such cases, a statistical approach known as error-in-variables (EIVs) method has been proposed in literature. In EIV, the parameter vectors and reconciled values of the measured variables are estimated. The parameter estimation of such problem is associated with increase in dimensions of the optimization problems, and due to chosen nonlinear models, the resulting optimization problem is generally nonconvex. In the present study, the EIV approach has been applied for estimation of rock strength parameter for multiaxial rock failure criteria using evolutionary optimization algorithms. The rock strength parameters and the mean square error values so obtained have been compared with that obtained from least square and reweighted least-square methods.

Due to the inherent geological complexity and characterization difficulties in rock formations, the evaluation of geomechanical parameters is very complex, mostly in the initial project stages and in small-scale geotechnical works, where information is scarce for the definition of an accurate geotechnical model. However, in large geotechnical projects, a great amount of data are produced and used to establish near-homogeneous geotechnical zones. If properly analyzed, these data can provide valuable information that can be used in situations where knowledge of the rock mass is limited. Yet, this implies the organization of geotechnical data in formats for proper analysis using advanced tools which is not normally done. Data-mining techniques have been successfully used in many fields but scarcely in geotechnics. They seem to be adequate as an advanced technique for analyzing large and complex databases that can be built with geotechnical information within the framework of an overall process of knowledge discovery in databases (KDD). In this work, a first approach of a KDD process applied in the context of rock mechanics is presented. The main goal was to find new models to evaluate strength and deformability parameters. In this process, a large database of geotechnical data was assembled concerning an important underground structure built in a predominantly granite rock formation. These innovative methodologies and tools were used to analyze and extract new and useful knowledge. The procedure allowed developing new, simple, and reliable models to predict geomechanical parameters, namely friction angle, cohesion, and deformability modulus using different sets of input data that can be used in different situations of information availability.

This note outlines the theoretical development of a new subgrade model with inherent spring coupling called the modified Kerr-Reissner (MK-R) model. The MK-R model is a novel hybrid that synergistically combines the advantages of mechanical and simplified-continuum subgrade models with the specific objective of producing a model that is straightforward to implement in routine practice.

An analytical solution of the fully coupled system of equations governing the axisymmetric quasistatic deformation of a poroelastic medium with anisotropic permeability and compressible fluid and solid constituents is obtained by employing the Laplace-Hankel integral transforms. This solution is used to study the consolidation of a poroelastic clay layer with free permeable surface resting on a rough-rigid impermeable base. The problem of axisymmetric normal loading is discussed in detail. Numerical computations are performed for normal disk loading. The effects of the anisotropy in permeability and the compressibility of the fluid and solid constituents on the consolidation process are studied. The compressibility of the pore fluid increases the initial settlement but has no effect on the final settlement. For a thin layer, the surface settlement increases steadily from its undrained value, attains a maximum, and decreases steadily to the drained value. This kind of behavior is not observed for a thick layer or a uniform half-space.

The interface boundary relations are derived in this study for the numerical analysis of one-dimensional consolidation in multilayered clay profiles. The finite difference solutions are formulated based on Mikasa’s consolidation equation with infinitesimal strains and constant consolidation parameters under the same fundamental assumptions and limitations of the classic Terzaghi equation. Numerical examples are presented for multilayer clay profiles under single and double drainage conditions that validate the predicted excess pore pressures, strains, settlements, and rates of consolidation using interface boundary relations in terms of infinitesimal strains that are equivalent to those expressed in terms of excess pore pressures.

This note intends to approach the mechanical characterization of rock joints, emphasizing the application of pull tests, which are an economic and simple type of shear experiments. Explanation is given on the drawbacks resulting from the classical testing procedures which do not control the sample’s middle plane position, leading to normal scale effects (represented by negative exponential regressions), where small sample results are misleading in terms of safety. In effect, pull tests allow a very easy measurement of several joint properties, such as the so-called joint roughness coefficient, the slope of joint roughness, the roughness anisotropy, and joint strengths under low normal stresses. Some rules for their standardization are suggested by pointing out the systematic leveling of the middle joint sample plane, thus rehabilitating the interest on small samples, because of the inverse scale effects on strength that are obtained, represented by positive exponential regressions.