International Journal of Geomechanics

Active pressure for axisymmetric problem under general conditions is formulated and solved by an iterative finite difference solution of the characteristic equations in the present paper. A general lateral stress coefficient is used instead of the Haar-von Karman hypothesis and numerical modeling has also confirmed that Harr-von Karman hypothesis is a reasonable assumption for the present problem if sufficient wall movement is allowed. The shape of the failure zone and variation of active pressure with depth and wall friction are investigated. Some interesting results on the active pressures arising from the arch action are found. Principle of superposition of the effect of soil weight, surcharge, and cohesive strength is discussed. Finally, the results in the present study are applied to bore pile construction and it is demonstrated that no casing for construction is required under some conditions.

The response of dowel jointed concrete pavements to the combined effect of nonlinear thermal gradient and moving axle load is examined using three-dimensional finite-element (3DFE) modeling. The 3DFE-computed response to moving axle load was field validated versus measured concrete slab response to a fully loaded moving dump truck. The 3DFE-predicted slab curling due to nonlinear thermal gradient through the slab thickness was validated versus: (1) corner-dowel bar bending as measured using instrumented dowel embedded in an instrumented rigid pavement section in West Virginia; and (2) Westergaard’s closed-form solution. The effects of slab thickness, slab length, axle loading position, and axle type on slab stresses are examined. It is shown that while a negative temperature gradient reduces the intensity of traffic-induced stresses, positive temperature gradient increases it several fold. Formulas are developed for the computation of the peak principal stresses due to the combined effect of tandem axle load and nonlinear thermal gradient.

Particle migration within porous networks often results in permeability reductions due to clogging. In many field applications, fluids and entrained particles travel radially toward producing wells. The nonhomogeneous velocity field associated with radial flow produces particle-level force variations that in turn lead to spatially dependent pore-scale mechanisms and unique clogging phenomena. The fluid-driven migration and entrapment of particles in radial flow is studied experimentally in custom-built pervious monolayers that allow for direct visualization of clogging processes. Experimental results demonstrate that in particular hydrodynamic conditions, particle clogging evolves in the form of a self-stabilizing clogging ring that localizes at a characteristic radial distance that depends on the initial producing flow rate. Gradual clogging by surface deposition of particles is observed in less severe hydrodynamic conditions. The particle migration and clogging processes observed are analyzed by considering particle-level force balance through dimensionless parameters.

Soil disturbance caused by the installation of prefabricated vertical drains (PVDs) has a large impact on the rate of consolidation. It is essential in design to quantify this effect. In this paper, we investigate the consolidation rate of soils with PVDs installed in a triangular pattern using two-dimensional finite-element analysis with full consideration of disturbance effects. This is done by accounting for the transition zone that exists between the highly disturbed smear zone and the undisturbed zone. The hydraulic conductivity in the transition zone is assumed to increase linearly from a low value in the smear zone to the original in situ value in the undisturbed zone. The actual band shape of the PVD and hexagonal zone of influence around it are used in the analysis. In addition to soil disturbance effects, the influence on consolidation rate of the size of the smear and the transition zones, the PVD spacing, and the mandrel size and shape is also investigated. Guidelines are given for using an equivalent system, where the transition zone is replaced by an expanded smear zone producing the same effect. This equivalent-system approach allows use of existing analytical solutions that consider only the smear zone in analysis and design.

In the finite-element analysis of soil-structure interaction problems, shell elements are important to model structural components such as tunnel linings or sheet pile walls. In this paper the development, implementation, and testing of a curved quadrilateral isoparametric shear deformable shell element are presented. An overriding concern in the analysis of soil-structure interaction problems is the $C^0$ compatibility of the shell elements with the solid elements used to model the soil. Many recent publications on shell elements deal with the elements in a purely structural context and therefore do not require the $C^0$ compatibility with solid elements. The development of the shell element presented here forms an extension of a new approach to curved Mindlin and axisymmetric shell elements introduced by Day and Potts in 1990. There are no generally accepted benchmarking marking problems for the use of shell elements in three-dimensional geotechnical engineering problems. Consequently, the performance of the shell element is first assessed by analyzing standard structural benchmarking problems. It is found that the new element performs well compared to other elements used in a purely structural context. Further, it is demonstrated that the same element that is used to analyze curved shells can be used to analyze flat plates without the requirement of a different formulation. Finally, the performance of the new shell element is compared with a closed form solution in the analysis of a deep tunnel.

The ultimate bearing capacity of two interfering strip footings was determined by using the method of stress characteristics. The analysis was performed by choosing two different possible failure mechanisms. The variation of the efficiency factor $\left({\xi }_{\gamma }\right)$ was computed with respect to change in the clear spacing $\left(s\right)$ between the two footings. For a given $s∕B$ , the value of ${\xi }_{\gamma }$ predicted on the basis of Mechanism 1 was always found to be smaller than those on the basis of Mechanism 2. For Mechanism 1, the maximum value of ${\xi }_{\gamma }$ , which becomes always equal to 2.0, always occurs at $s∕B=0$ . On the other hand, the Mechanism 2 provides maximum value of ${\xi }_{\gamma }$ even greater than 2.0, especially with $\varphi >20°$ , corresponding to $s∕B=s_{\mathrm{cr}}∕B$ . It was noted that the results from Mechanism 2 compare more closely with the theory of Stuart in 1962 and with the recent upper bound limit analysis solution of the writers.

We present results of a parametric study on shearband formation in geomaterials, examining the influence of material dilatancy on shearband properties. The study is based on a new higher order continuum theory, called gradient elastoplasticity, developed to model localization of deformation. We present results for two problems with different initial stress fields: The biaxial test and the hollow cylinder test. We show that nonassociativity promotes bifurcation at lower deformation, leading to localized deformation and more abrupt final failure. Both the inclination and thickness of the calculated shearbands decrease with increasing nonassociativity. Gradient elastoplasticity is capable of reproducing the experimentally observed localized failure modes, including details such as reorientation of shearband close to a free boundary.

Two new diagnostic curve methods, which do not require the implicit or explicit determination of initial or final dial gauge readings for primary settlement, are proposed for the identification of the consolidation coefficient. Besides the estimate of the consolidation coefficient, these methods also yield an estimate of the range of primary settlement. In these methods, the diagnostically plotted points are matched to the diagnostic curves with a parallel shift of axes to yield the estimates of the consolidation coefficient and range of primary settlement. The new methods do not require dial gauge readings up to 100% of primary consolidation and can also be used even when very scarce data are available. Using the proposed methods, a nonideal condition can also be identified.