Mark Randolph

• The University of Western Australia

The offshore wind industry continues to expand rapidly around the world in response to demand for clean energy. Research to investigate monopile performance under cyclic lateral loading needs to replicate the installation process as well as the cyclic loading regimes. This has provided the impetus for the development of model pile driving hammers f...

A number of incidents of pile tip damage and extrusion buckling have been reported within the offshore industry, generally arising during driving of relatively thin-walled tubular pile foundations through hard layers or potentially heterogeneous sediments. The issue has become of particular concern with modern trends toward larger diameter piles, w...

The potential for pile tip damage and extrusion buckling has become an increasing concern for the offshore wind industry following the trend toward the use of large diameter thin-walled pile foundations, either as monopiles or as part of a jacket structure. Extrusion buckling may be triggered by an initial pile tip fabrication imperfection or pile...

The ring penetrometer is a shallow rotational penetrometer that has been developed to characterise the mechanical behaviour of surficial marine sediments. The strain-rate dependency of soils is crucial to the design of a wide range of offshore geotechnical infrastructure founded in the upper layers of the seabed (e.g. pipelines, cables and shallow...

Many offshore geotechnical problems—such as cyclic T-bar penetration and lateral buckling of pipelines—are affected by the tendency of fine-grained soils to strain-soften due to remoulding. Careful calibration of the constitutive model parameters that control strain softening is essential for accurate simulation of these processes. This is usually...

The discovery of deep trenches adjacent to suction caissons acting as anchors for semi-taut mooring systems has led to a reassessment of geotechnical design assumptions, such as: trench formation across the full front face of the caisson down to the level of the mooring chain padeye; gap formation behind the caisson; and reduction in reverse end-be...

The number of incidents worldwide where pile tip damage has occurred during driving has accelerated following the growth of the offshore wind sector, and the expansion into areas with increased risk of embedded boulders or partially weathered soft rocks. The process involving pile–boulder–soil contact can be simulated with advanced three-dimensiona...

Full-flow penetrometer testing in fine-grained soils indicates that undrained shear strength decreases due to remoulding induced generation of excess pore pressures and increases due to strain rate effects and dissipation of excess pore pressures. This paper presents a viscoplastic strain-softening–hardening constitutive model that captures this du...

Layered soil conditions are common in marine sediments, and deduction of strength properties for thin interbedded layers is often challenging. Full-flow penetrometers such as T-bar are increasingly being used in offshore site investigations and show high potential for differentiating the shear strength transition between layers. This paper reports...

The touchdown zones of steel catenary risers and lazy wave risers are fatigue hotspots, where the risers interact continuously with the seabed due to hydrodynamic loading exerted on the host vessel. The whole-life interactions can range from small-amplitude daily motion cycles to motions that involve large-amplitude cyclic interaction with the seab...

Using recent advances in data analytics techniques and tools, this paper proposes a novel data-centric paradigm for riser fatigue analysis in which practitioners can efficiently make use of large hindcast and measured metocean datasets directly in the design process.

The performance of plate anchors in sand, relative to clay, is not well understood, particularly for the more realistic case of an inclined load. This paper investigates the effect of load inclination on horizontal plate anchors in sand through centrifuge tests and numerical finite-element simulations. The centrifuge tests were performed on rectang...

This paper examines the effect of consolidation on a shallowly embedded horizontal plate anchor in medium dense and dense sand using centrifuge tests, where the loading rate was varied over four orders of magnitude. The experimental results show a 4·8 to 5·5 times increase in anchor capacity as the consolidation condition changes from drained to un...

The volume of a submarine landslide is likely to be amplified by shear band propagation along a basal surface or spreading failure extension in the sliding layer. Although the mechanism of translational submarine landslides has been understood using the interpretation of shear band propagation, assessment of the limits of failure extension, either...

Large lateral displacement of trenched subsea pipelines may be induced by ground movement, landslides, ice gouging, etc. Pre-excavated seabed soil is usually used for backfilling as a cost-effective solution. The large difference between the shear strength of the highly remoulded backfill material and the native soil may significantly affect the pi...

Asbtract Quantifying the risk of system failure is a key input to a risk-based decision-making process for the in-service integrity management of aging steel catenary risers (SCRs), which are prone to fatigue failure within the touchdown zone (TDZ). However, in practice the computational cost of assessing the probability of failure (POF) for SCRs i...

Most offshore wind turbines (OWTs) are supported by large-diameter monopiles, installed by impact driving. OWTs are dynamically sensitive structures, with a narrow design range for the eigenfrequency. Fatigue and serviceability limit states can be critical in design, so the foundation stiffness plays an important role. The pile installation process...

Subsea pipelines buried in the seabed may undergo large lateral displacement under environmental, operational, and accidental loads at different interaction rates and hence different drainage conditions. The undrained shear strength is commonly used in practice to assess the pipe-soil interaction assuming a sufficiently high displacement rate. This...

Single (or mono) suction buckets have been put forward by others as possible offshore wind turbine (OWT) foundations. This paper presents a series of centrifuge model tests conducted in dense sand to investigate their monotonic response for a range of drainage conditions. The results from the centrifuge tests suggest that the mono-bucket rotational...

Offshore pipelines are important infrastructure for transporting oil and gas. They are subjected to cycles of high temperature and pressure variation during operation and shutdown periods, and are therefore susceptible to the stability problem of axial walking due to the asymmetry between the expansion and contraction. Axial walking can cause damag...

Monopiles are widely used as the foundation to support offshore wind turbines (OWTs). The response of monopile-supported OWTs is strongly affected by the natural frequency of the system relative to the load spectrum, and in turn, the natural frequency is governed by the initial stiffness of the foundation. Both fatigue limit state (FLS) and service...

Monopiles under in-service conditions are subjected to lateral forces and resultant bending moments from the offshore environment. The subsequent lateral response following installation is significantly influenced by the initial soil state postinstallation, which is influenced by the pile installation process, as demonstrated in previous numerical...

In recent years, the interaction between submarine slide runout and offshore pipelines has received extensive attention, based on the need to protect pipelines crossing regions susceptible to submarine slides. The interaction force between the slide material and a pipeline may be resolved into horizontal and vertical components, but with most atten...

p>This technical note presents simplified parametric solutions for the axial response of surface-laid submarine pipelines subjected to axial drag from debris flows. In assessing the response of pipelines impacted by debris flow emanating from a submarine landslide, both normal and axial responses must be considered. Previous work has indicated that...

Suction buckets are expected to be increasingly used as foundations for offshore wind turbine (OWT) projects as they move to deeper water and monopiles become impractically large. Since OWTs are relatively light and operational loads include high overturning moments, potential exists for individual foundations to experience periods of net tension w...

Deriving a design approach for spudcan penetration directly from cone penetrometer data relies heavily on the contrasting soil failure mechanisms that evolve around the objects during continuous penetration. This paper describes centrifuge modelling of penetration of a half-cone and a half-spudcan in four layered profiles comprising silica sand-kao...

Offshore pipelines are usually buried in a trench and covered by pre-excavated materials for physical protection. Large lateral displacement of trenched pipelines may be induced by mechanisms such as ground movement and ice gouging. The different soil properties between the backfilling material and the native ground may significantly influence the...

Seabed in regions, such as the Gulf of Guinea and North West Shelf of Australia, may exhibit a crust layer where the undrained shear strength can be an order of magnitude higher than that of the immediately underlying sediment. This can complicate design of steel catenary risers, where fatigue depends on the cyclic vertical stiffness of the pipe-so...

In-service integrity management (IM) of steel lazy wave risers (SLWRs) can benefit significantly from quantitative assessment of the overall risk of system failure as it can provide an effective tool for decision making. SLWRs are prone to fatigue failure within their touchdown zone (TDZ). This failure mode needs to be evaluated rigorously in riser...

This paper investigates the uplift capacity of horizontal plate anchors in sand through finite element analyses and centrifuge experiments. The finite element simulations adopt a sophisticated bounding surface plasticity model that accounts for stress- and density-dependent behaviour, as well as loading- and fabric-related anisotropic effects in sa...

Quantification of impact forces from submarine landslides is vital to the safe design of mudmats and other subsea structures that are laid out in the hazard area. In this paper, the dynamic process of the submarine landslides running across a partially-embedded mudmat is analysed using a novel numerical method, the material point method (MPM). The...

There are several different anchoring systems that have been developed for deep water applications, where seabeds mostly comprise relatively low strength sediments. The optimum system will depend on the nature of the required mooring, whether temporary or permanent, the form of mooring system, whether catenary or semi-taut, and the magnitude of the...

There have been a number of incidents worldwide where pile tip damage has occurred during pile driving, generally requiring costly remedial actions. The number of such occurrences has increased recently, consistent with the trend of increasing diameter tubular piles, which are increasingly thin-walled relative to the diameter, used to support offsh...

There have been a number of incidents worldwide where pile tip damage has occurred during pile driving, generally requiring costly remedial actions. The number of such occurrences has increased recently, consistent with the trend of increasing diameter tubular piles, which are increasingly thin-walled relative to the diameter, used to support offsh...

The paper examines the merit of a bounding surface plasticity model at both element and system level. The governing equations are based essentially on the parent bounding surface plasticity model reported by Dafalias and Manzari in 2004 with some simple yet practical changes to enable realistic predictions for monotonic loading along different load...

Field observations of semi-taut mooring systems have shown severe trench development in front of suction caissons. Trenches extend back from where the chain emerges from the seabed under ambient mooring loads to relatively close to the caisson, and with depths approaching the padeye depth. To help understand the process, a Coupled Eulerian-Lagrangi...

Reliable characterization of surficial marine sediments is essential to ensure the safe and economical design of subsea infrastructure for offshore energy facilities (e.g., seabed cables, pipelines, and shallow foundations). Conventional in-situ testing methods (e.g., cone penetrometer test or T-bar) require careful interpretation to account for th...

Lateral buckling analysis of on-bottom submarine pipelines is of particular interest in the offshore industry due to the complexities involved in the analysis, and the potential design efficiencies that can be unlocked. Classical buckling theories by previous researchers and recent joint industry projects provide a basis for estimation of the criti...

Soil–water interaction is a pivotal process in many underwater geohazards such as underwater landslides where soil sediments gradually evolve into turbidity currents after interactions with ambient water. Due to the large deformations, multiphase interactions and phase changes this involves, investigations from numerical modelling of the transition...

This study investigated the change in monotonic and cyclic capacity of a plate anchor across different degrees of consolidation in dense sand. To quantify the effect of consolidation on anchor capacity, a framework is introduced and validated using centrifuge model anchor test data. The centrifuge tests considered a rectangular plate loaded at vary...

Full paper at https://rdcu.be/b3yzZ Gigantic submarine landslides pose a significant threat to offshore infrastructures and may be initiated by an inconspicuous weakened zone, followed by catastrophic shear band propagation under the effect of strain softening. Much attention has been paid over the last two decades to unidirectional (parallel to t...

Carbonate sediments are prevalent in many major offshore oil and gas basins, as well as a growing number of regions assigned to offshore wind development. Identified as difficult from an engineering perspective, the failure to properly characterize and design for these sediments has adversely influenced several projects. This paper provides a brief...

This paper describes a centrifuge study using a range of penetrometer tests (T-bar, piezocone and free-fall piezocone) to explore strength changes in a reconstituted, normally consolidated, natural calcareous silt. Various penetrometer test procedures were applied to measure the penetration resistances including monotonic, cyclic and twitch-type mo...

Understanding the soil resistance along an embedded anchor chain is imperative for efficient and economic design of an overall mooring system as it determines the magnitude and direction of the load at the padeye of the anchor. The tensioning process of an embedded chain for catenary moorings was modeled using a coupled Eulerian–Lagrangian (CEL) fi...

Historically, there have been many devastating events in which offshore pipelines were displaced over a large distance or fractured under the impact of submarine slide hazards, which has stimulated detailed assessment of the interaction forces between a sliding soil mass and submarine pipelines. In particular, the impact force from the sliding mate...

Large diameter steel catenary risers (SCRs) are considered a cost efficient export riser solution for gas field developments at deep-water sites. However, SCRs are prone to fatigue damage at their interface with the seabed (the touchdown zone, TDZ) and hence accurate estimation of their fatigue life is crucial. The major source of TDZ fatigue damag...

Offshore landslides are major geohazards in deep water, posing significant threat to offshore infrastructure, marine animal habitats, and coastal urban centres. Even small offshore landslides can cause disastrous consequences to offshore installations e.g. pipelines for oil and gas transport and cables for transoceanic data traffic. Catastrophic of...

This paper attempts to explain how a normally consolidated lakebed sediment can have an undrained strength ratio of approximately unity, when the lithic component of the sediment is less than 3% by volume. The structured clay framework, coupled with sensitivity measurements of the sediment, show that the structure retains a very high strength in a...

Site investigation data have shown that a crust layer may occur at the surface of many seabeds, with the crust exhibiting undrained strengths up to an order of magnitude higher than that of underlying normally consolidated sediments. This may affect the fatigue life assessment of steel catenary riser (SCR) as a result of riser-soil interaction. The...

p>With the increase in demand and supply gap in the oil and gas industry, new developments of oil and gasinfrastructure are moving into deeper water. This requires design and construction of long high temperature and high pressure pipelines from deep sea to shore. These pipelines are subjected to cyclic expansion during operating cycles. Accumulate...

The shaft friction of displacement piles in sand depends on the change in the horizontal stresses on the pile shaft during installation. Recent research has revealed that the sectional shape of a pile has a strong influence on the horizontal stresses, leading to great difference of the pile shaft friction. Based on these findings, an optimization i...

This paper investigates the effectiveness of the effective area method (EAM) for assessing the undrained load-carrying capacity of rectangular foundations under combined vertical (V), horizontal (H) and moment loading (M) by comparing with finite-element method (FEM) results. Predicted ultimate limit states under combined loading from the two metho...

The risk posed by seabed instability is of increasing significance as offshore activities including oil and gas developments continue to expand in this century. Many studies have considered runout of debris flows resulting from submarine landslides and potential impact on offshore infrastructure. However, initiation of slab failure resulting from s...

The parkable piezoprobe is a site investigation tool for measuring the coefficient of consolidation, in situ offshore, at shallow embedment depths. The device applies a similar bearing pressure to subsea infrastructure so it reaches a comparable self-weight penetration when ‘parked’ at the seabed, representative of an unburied pipeline. Instrumenta...

This paper investigates the effect of riser-soil interaction model selection on the assessment of steel catenary riser (SCR) fatigue life for realistic environmental conditions at a deep-water Australian North west shelf (NWS) site. Using a fatigue wave scatter diagram consisting of the 100 metocean conditions at the site (combining irregular seas,...

p class="para" style="margin: 0px 0px 10px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-stretch: inherit; font-size: 13px; line-height: 19.5px; font-family: Helvetica, Arial, Verdana, sans-serif; vertical-align: baseline; color: rgb(51, 51, 51); text-align: justify;">The embedded portion of a mooring line plays an important role...

New analytical models have recently been presented for evaluating the peak bearing capacity of circular footings penetrating sand-over-clay and the subsequent capacity once embedded in the underlying clay. However, in lieu of any analytical model, current methods of analysis use an inaccurate linear interpolation for the bearing capacity between th...

Subsea developments require the design of large numbers of shallow skirted foundations to support structures such as manifolds, pipeline and umbilical terminations and in-line tees. Safe and economic design relies on the accurate assessment of foundation capacity against thousands of load-combinations. Performing these design calculations is a sign...

A simplified framework is presented in which an existing artificial neural network (ANN) based tool for critical stress range prediction is used in order to rapidly assess the fatigue life of a steel catenary riser (SCR). The simplified approach considers the first-order motions of the hosting floater (heave, pitch and roll motions) and irregular s...

The mathematical model of an equilibrium fan-structure in the interface between two elastic blocks, simulating the shear rupture head in a hard rock under high confining pressure, is constructed. The stress–strain state far from the fan-structure is analyzed with the help of a solution of the problem on edge dislocation. The fan length is estimated...

This article summarizes design methods for pile foundations subjected to axial and lateral loading. It addresses the main factors that need to be considered in a basis of design, focusing on driven steel pipe piles, which are almost universally used in offshore practice. The response of less frequently used piles grouted into stronger sediments, su...

Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques. In this paper, the runout of slides on rigid bases is explored using the material point method with focus on the geotechnical aspects of the morphologies. In MPM, the sliding material and bases are discre...

In this paper a novel modelling procedure is proposed to estimate whole-life settlements of tolerably mobile sliding foundations. A new kinematic hardening-critical state-state parameter constitutive model, the Memory Surface Hardening model, is implemented in a one-dimensional analysis to predict accumulated vertical settlements under drained late...

Increasing numbers of subsea structures related to wells and pipelines are being placed on the seabed as part of typical subsea or tie-back developments. Given the proliferation of these structures and the marginal cost of offshore developments, controlling installation and fabrication costs for subsea structures can be key to project viability. Sk...

Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques. In this paper, the runout of slides on rigid bases is explored using the material point method (MPM) with focus on the geotechnical aspects of the morphologies. In MPM, the sliding material and bases are...

The paper reviews recent advances in the understanding of pipe-soil interaction, and provides a updated knowledge on best practices for on-bottom pipeline design. Since the late 1990s, major programs of research work have been undertaken to develop appropriate models for pipe-soil interaction for seabed pipelines in challenging environments and ope...

The paper provides a review of the state of knowledge regarding the impact of soil response in the touchdown point region on Steel Catenary Riser (SCR) fatigue. For almost 20 years the impact of soil-pipe interaction on SCR fatigue has received considerable attention within the offshore geotechnical community. Over this course of time field measure...

This paper presents a toolbox for optimizing geotechnical design of subsea foundations. The geotechnical design challenge of subsea shallow foundations is to withstand greater dead and operational loads on soft seabeds without increasing the footprint size or weight. The motivation is to reduce costs associated with installation – for example elimi...

As oil and gas developments move into deeper waters, potential exposure to geohazards becomes an important project risk driver. Landslide deposits and features observed on the seabed in the vicinity of potential future development indicate processes that were active in the geological past and can be expected to continue in the future. Rapid yet spa...

Pile foundations for offshore structures can be installed in different ways, with this article focusing on two main pile types: (i) driven; and (ii) drilled and grouted. An overview of simplified mechanics-based concepts for issues affecting analysis of pile installation is provided. For driven piles, the concepts considered include soil resistance...

Quantification of the risk posed by submarine landslides is an essential part of the design process for offshore oil and gas developments and also for prediction and mitigation of potentially devastating tsunamis. A number of studies have been conducted to quantify the initiation of catastrophic failure in planar slopes triggered by undercutting at...

Seabed strength may be determined rapidly using free-fall penetrometers as the tool is simply released from above the sea-floor and penetrates under gravity into the seabed. The speed and ease of deployment relative to conventional ‘push-in’ penetrometers is attractive, with the trade-off of more complex interpretation. This paper considers two app...

Tolerable mobility of subsea foundations and pipelines supporting offshore oil and gas developments has recently become an accepted design concept. It enables a smaller foundation footprint and so is a potential cost-saving alternative to conventionally engineered ‘fixed’ seabed foundations. Dominant sources of loading on subsea infrastructure aris...

A new type of displacement pile, the X-section cast-in-place concrete (XCC) pile, has been developed recently in China. Extensive field and laboratory experiments are being undertaken in order to evaluate the soil displacements during pile installation. The paper describes laboratory arrangements and results of transparent soil model tests aimed at...

Rectangular mudmat foundations are frequently used for supporting subsea structures for offshore oil and gas developments. The self-weight of the subsea structure and mudmat often mobilise a relatively small proportion of the vertical bearing capacity and horizontal–torsional sliding generally represents the governing load case. However, the effect...

Steel Catenary Risers (SCRs) provide a technically feasible and commercially efficient solution for the offshore field developments in deep waters. Fatigue design of SCRs in the touchdown zone (TDZ) is among the most complicated engineering challenges in riser design. The cyclic interaction of the riser with seabed leads to a number of complex nonl...

This paper presents key outcomes of a 3-year Joint Industry Project funded by 6 Operators on the impact of submarine slides on pipelines. This JIP developed new techniques to simulate slide runout, and assess the resulting loading and deformation of seabed pipelines. The work was distilled into guidance for practical application, which has found ad...

Quantitative assessment of the risk of submarine landslides is an essential part of the design process for offshore oil and gas developments in deep water, beyond the continental shelf. Landslides may be triggered by a reduction in shear strength of subsea sediments over a given zone, caused for example by seismic activity. Simple criteria are then...

This paper focuses on elastic stiffness parameters for axial, horizontal, and vertical motions of a pipeline relative to the seabed, with the aim of expressing these parameters in terms of fundamental elastic properties of the soil. Limited information exists in the literature on the axial elastic response of on-bottom pipelines, particularly for n...

Using large monopod bucket foundations as an alternative to monopiles for offshore wind turbines offers the potential for large cost savings compared to typical piled foundations. In this paper, numerical simulations are carried out to assess the risk of structural buckling during installation of large-diameter bucket foundations. Since shell struc...

The piezoball, a ball penetrometer featuring pore pressure measurements, is a relatively new device that is potentially superior to the more commonly used piezocone for profiling fine-grained soils. This is due to lower uncertainty in how to derive soil strength from the net penetration resistance and the option of measuring consolidation character...

The typical depth–frequency distribution of earthquake hypocentres (DFDE) demonstrates that, below an upper cutoff, the earthquake frequency increases with depth up to a maximum value and then decreases and ceases at a lower cutoff. Such regular behaviour of earthquakes implies the existence of some fundamental mechanisms responsible for the distri...

Mark Randolph and Susan Gourvenec, professors at the University of Western Australia's Centre for Offshore Foundation Systems, share their views about deepwater geotechnical challenges, such as complex carbonates found off the coast of Australia, and new developments for effectively exploiting deepwater. They believe that unlike areas such as the G...

Piezoballs, which are full-flow ball penetrometers incorporating pore pressure measurements, are an attractive soft soil characterisation tool as they allow measurement of the intact and remoulded strength and the consolidation coefficient in a single test. The merit of full-flow penetrometers as a reliable tool that is superior to the cone in quan...

Full-flow penetrometers such as the cylindrical T-bar and spherical ball are now being used widely in soft seabed sediments due to their advantages of larger projected area and minimal correction for overburden pressure. A ball penetrometer fitted with one or more pore pressure transducers (piezoball) is of special interest as it can provide inform...

Helical anchors are used widely onshore and have recently been mooted as an innovative foundation method for lightweight offshore structures. From structural considerations, as the load requirement for each plate on a helical anchor increases, it becomes necessary to increase the diameter ratio of the central shaft to the plate, and even to replace...

Catastrophic landslides pose significant threats to life and property, and in the case of submarine landslides damage to offshore infrastructure. Although widely discussed, the triggering mechanisms and propagation criteria for catastrophic failure remain open issues. This study investigates a particular case of shear band initiation history: creat...

Current site investigation practice for offshore pipeline design relies on soil parameters gathered from boreholes or in situ test soundings to depths of 1–2 m below the mudline. At these depths, the fine-grained seabed is very soft and possesses low undrained strength, which can be difficult to measure. This paper describes a centrifuge test progr...

The paper presents analytical solutions for the evolution of excess pore pressures in the vicinity of a shear band in a rate-dependent, strain-softening permeable soil, with the aim to explore, both qualitatively and quantitatively, the potential variation of failure shear stress in the shear band. The solutions encompass both dissipation of a pre-...