International Journal of Geomechanics

A numerical model, called CC1, is presented for one-dimensional large strain consolidation in a geotechnical centrifuge. The model includes all the capabilities of a previous large strain consolidation code, CS2, written for surcharge loading under normal gravity conditions. In addition, CC1 accounts for variation of acceleration factor $N$ over the depth of a centrifuge test specimen. The development of CC1 is first presented, followed by a comparison of simulated time–settlement curves with experimental measurements for Singapore marine clay and a parametric study illustrating the effects of nonuniform $N$ distribution on centrifuge consolidation behavior. Simulations indicate that the effect of spatially varying $N$ is most strongly controlled by the ratio of specimen height to centrifuge arm length and that the error associated with the assumption of constant $N$ is relatively small if this ratio is 0.2 or less. Finally, CC1 is used to calculate the optimal location within a centrifuge specimen of Singapore marine clay at which to match the desired $N$ value and the error that results if $N$ is matched at the initial midheight of the specimen.

The paper presents a computational assessment of the influence of damage on the behavior of a rigid rock socket embedded in a fluid-saturated poroelastic solid. The iterative computational scheme takes into consideration the irreversible alteration in the fluid transport characteristics that takes place as a result of damage and the stress dependency of the isotropic damage process. Numerical results illustrate the influence of the stress-state-dependent damage process on transient consolidation response of the rock socket head displacement.

A constitutive model based on the disturbed state concept (DSC) is proposed for stress-deformation and liquefaction response of interfaces in dynamic soil-structure interaction problems. The model parameters are determined by using comprehensive test data for Ottawa sand–concrete (medium roughness) interfaces by using the cyclic multidegree of freedom device. The model is validated by comparing the finite element predictions with the test data used for the determination of parameters and independent test not used for finding the parameters. A procedure based on the critical disturbance for the identification of liquefaction in the interfaces is proposed. It is found that the liquefaction in the interface can occur earlier than that in the surrounding sand. The DSC model can provide a realistic characterization of the interface behavior and can be used in analysis and design of dynamic soil-structure interaction problems.

The paper presents a theoretical and experimental approach for the modeling of moisture loss during the drying of cementitiously stabilized pavement materials containing varying contents of fine-grained soil. The process of moisture loss was characterized by the isotropic nonlinear diffusion theory. Laboratory tests were undertaken using general purpose Portland cement and two binders comprising industrial waste products. Measurement of material characteristics included the coefficient of moisture diffusivity and the humidity isotherm. Locally available basaltic crushed rocks and clay were respectively used as the host pavement material and fine-grained soil. Independent laboratory tests were undertaken to validate the adopted theoretical approach, which showed close agreement between the experimental and predicted results. The laboratory results indicated that moisture loss decreased with the inclusion of clay soil within the mix. As the drying progressed, the rate of moisture loss became slower, which can be explained by the reduction in the coefficient of moisture diffusivity with the decrease of moisture content.

Drilled shaft groups are often designed to resist lateral loads for transportation structures. The shaft group capacity usually corresponds to a load being applied at the shaft cap level. However, in abutment wall applications, the lateral load is, in fact, applied well above the cap elevation. Thus, the load is transferred to the cap with an additional moment, causing the cap to deflect and rotate more than if this added moment were absent. As a result, the lateral capacity for a given allowable deflection of the group should be reduced because of this effect. Design engineers usually select or approve the allowable deflection at the top of the abutment wall. However, deflection at the cap level is needed to design the group capacity. The main objective of this paper is to report the results from a series of finite-element analyses on abutment wall cap configurations to study the effect of moment on the capacity of the shaft group under lateral load. A scaling factor is defined as the ratio between the group capacity for load applied at a given height above the cap and the group capacity for load applied at the bottom of the cap, and it was found to be dependent on the wall height, the spacing between shafts, and the cap deflection level, and more or less independent of the soil type, the cap thickness, and the shaft diameter. The ratio between the deflection at the top of the abutment wall and the deflection at the cap was found to be dependent on the wall stiffness (wall thickness to wall height ratio).

The grading entropy of a soil $\left(S\right)$ is derived in terms of the more general concept of statistical entropy. It consists of two terms: the base entropy $\left(S_0\right)$ , arising from the difference in the width of the statistical cells in the conventional grading curve, and the entropy increment $\left(\Delta S\right)$ . The goal of the research was to study which grading entropy plays the role of the “true” entropy in a thermodynamic sense (i.e., undergoes an increase during the crushing process being considered as an irreversible thermodynamic process): the entropy increment $\left(\Delta S\right)$ or the sum of the base entropy and the entropy increment $\left(S\right)$ . The soil samples were subjected to successive crushing treatments; the grading curve and the grading entropy were determined after each treatment. It was found that only the entropy increment $\left(\Delta S\right)$ increased monotonically with an increasing number of crushing treatments. Therefore, the ultimate state can be expected to be characterized by maximum entropy increment $\left(\Delta S\right)$ and, by such grading curve where the relative frequencies of the fractions are equal.

This study investigates the relationship between the sediment resisting force and embedment depth for horizontal cylinders in a vertical trench. Plane-strain calculations of collapse loads are performed for a series of trench depths. Collapse load predictions are based on finite element predictions validated by upper and lower bound solutions from classical plasticity theory. This study extends work by previous investigators by considering variable soil shear strength profiles and embedment depths exceeding one cylinder radius. Curve fits are applied to the finite element predictions to develop simplified equations relating collapse load to trench depth. The predictions are relevant to a number of applications, including pipeline penetration, waste disposal, and mine detection.

A finite element model has been developed to simulate two-phase, (i.e., oil and gas) flow and solid deformation in a dual-porosity medium. The model accounts for coupling between solid deformations and fluid flow in both the primary medium (representing the matrix pores and solid) and the secondary medium (used to represent fractures in the present study). The model is verified against relevant analytical solutions and then applied to the problem of an inclined wellbore under generalized plane strain conditions, subjected to a three-dimensional in situ state of stress in a fractured formation saturated with oil and gas. A parametric study has been carried out to demonstrate the effect of dual-porosity parameters, phase saturations, and interaction between the two media. The implementation of double effective stress laws in the present study is a significant deviation from some classical dual-porosity models and helps to incorporate the effect of deformation of the secondary medium (representing the fractures).

A literature review is presented that identifies a number of areas where procedures for the engineering design of bored installations in soil using horizontal directional drilling (HDD) can be improved through a more realistic consideration of drilling fluid drag effects and skin friction coefficients. The current HDD practice of calculating annular frictional pressure loss caused by drilling fluid drag based on the assumption of concentric annular flow of a Bingham plastic fluid is demonstrated to be overly conservative. Consequently, critical design parameters, such as depth of cover, which affects crossing length, and drilling equipment size, which is selected based on anticipated pulling load, cannot be optimized. This can result in overly conservative design and unnecessary construction costs. Parameter values currently employed in HDD pulling load prediction are challenged suggesting that the viscous shear of drilling fluid is significantly less than typically quoted and that the friction coefficients often employed are not representative of all skin friction effects in HDD. A new real-time monitoring cell for large-scale HDD is described that can be used to optimize installations and to assess and update current prediction models.

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.