R.S. Merifield

Effect of Surface Heave on Response of Partially Embedded Pipelines on Clay

The as-laid embedment of an on-bottom pipeline strongly influences the resulting thermal insulation, and the resistance to subsequent axial and lateral movement of the pipeline. Reliable assessment of these parameters is essential for the design of offshore pipelines. Static vertical penetration of a pipe into a soft clay seabed—which can be modeled as an undrained process—causes heave of soil on each side of the pipeline. The heaved soil contributes to the vertical penetration resistance and the horizontal capacity. This paper describes a series of large deformation finite-element analyses of pipe penetration, supported by a simple analytical assessment of the heave process. The conventional bearing capacity approach to the analysis of pipe penetration is reviewed, and modifications for the effects of soil weight and heave are presented. It is shown that in soft soil conditions—which are typical for deep water—the soil self-weight contributes a significant portion of the vertical penetration resistance a...

Undrained stability of footings on slopes

Solutions for the ultimate bearing capacity of footings on purely cohesive slopes are obtained by applying finite element upper and lower bound methods. In a footing-on-slope system, the ultimate bearing capacity of the footing may be governed by either foundation failure or global slope failure. The combination of these two factors makes the problem difficult to solve using traditional methods. The importance of a dimensionless strength ratio in determining the footing capacity is broadly discussed, and design charts are presented for a wide range of parameters. In addition, the effect of footing roughness and surface surcharge are briefly quantified.

Ultimate Uplift Capacity of Multiplate Helical Type Anchors in Clay

In recent years, the use of helical anchors has expanded beyond their traditional use in the electrical power industry. The advantages of rapid installation and immediate loading capability have resulted in their being used in more traditional civil engineering infrastructure applications. Unfortunately, our current understanding of these anchors is unsatisfactory, and the underlying theoretical framework adopted by engineers has proven to be largely inappropriate and inadequate. A better understanding of helical anchor behavior will lead to increased confidence in design, a wider acceptance as a foundation alternative, and more economic and safer designs. The primary aim of this research is to use numerical modeling techniques to better understand multiplate circular anchor foundation behavior in clay soils. A practical design framework for multiplate anchor foundations will be established to replace existing semiempirical design methods that are inadequate and have been found to be excessively under- or...

Two-and three-dimensional bearing-capacity solutions for footings on two-layered clays

In this paper, finite element analysis is used to predict the undrained bearing capacity of strip, square and circular footings resting on layered clays. The soil profile consists of two clay layers with different thicknesses and properties. The results are compared with previous solutions for strip footings on layered clays. The bearing-capacity behaviour is discussed and the bearing-capacity factors are given for various cases involving a range of layer thicknesses and properties of the two clay soil layers.

Trench Stability under Bentonite Pressure in Purely Cohesive Clay

AbstractTrench stability is a conventional geotechnical problem; however, current evaluations are often based entirely on empiricism. This paper uses numerical finite-element upper and lower bound limit analysis to produce stability charts for two-dimensional and three-dimensional homogeneous and inhomogeneous undrained diaphragm wall trenches. Using the limit theorems cannot only provide a simple and useful way of analyzing the stability of the trench, but also avoid the shortcomings and arbitrary assumptions underpinning the limit equilibrium method. By considering the effects from the bentonite slurry pressures, the collapse load in this study has been bracketed to within ±8.5% or better by the numerical upper and lower bound limit analyses. The chart solutions can be used to predict either the critical depth or the safety factor of the trench and provide a convenient tool for preliminary designs by practicing engineers.

Slope stability charts for two-layered purely cohesive soils based on finite-element limit analysis methods

AbstractStability charts for soil slopes, first produced in the first half of the twentieth century, continue to be used extensively as design tools, and draw the attention of many investigators. This paper uses finite-element upper and lower bound limit analysis to assess the short-term stability of slopes in which the slope material and subgrade foundation material have two distinctly different undrained strengths. The stability charts are proposed, and the exact theoretical solutions are bracketed to within 4.2% or better. In addition, results from the limit-equilibrium method (LEM) have been used for comparison. Differences of up to 20% were found between the numerical limit analysis and LEM solutions. It also shown that the LEM sometimes leads to errors, although it is widely used in practice for slope stability assessments.

The Ultimate Uplift Capacity of Multi-Plate Anchors in Undrained Clay

Soil anchors are commonly used as foundation systems for structures requiring uplift resistance such as transmission towers, or for structures requiring lateral resistance, such as sheet pile walls. Anchors commonly have more than one plate or bearing element and therefore there is a complex interaction between adjacent plates due to overlapping stress zones. This interaction will affect the failure mode and ultimate capacity. However, no thorough numerical analyses have been performed to determine the ultimate pullout loads of multi—plate anchors. The primary aim of this research paper is to use numerical modeling techniques to better understand plane strain multi-plate anchor foundation behavior in clay soils.

Slope stability analysis for cohesive materials filled on purely cohesive undrained clay

Stability charts for soil slopes were first produced by Taylor in 1937 and they continue to be used extensively as design tools and draw the attention of many investigators. From a review of literature, it was found that there is no convenient solution has been provided for cohesive materials filled on purely cohesive undrained clay. A recent study revealed that the embankment slope which has two-layered clays failed in an undrained state which shows the importance of this study. In order to obtain the solutions for this type of fill slope. A number of numerical method are employed, namely the finite element upper and lower bound limit analysis methods and limit equilibrium method. The numerical upper and lower bound limit analysis method can bracket true solutions within a small range (6%). The solutions of limit equilibrium analysis are used for comparison purpose.