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A simple approach to slope stability analysis of naturally occurring, mild nonlinear slopes is proposed through extension of shear band propagation (SBP) theory. An initial weak zone appears in the steepest part of the slope where the combined action of gravity and seismic loads overcomes the degraded peak shear resistance of the soil. If the length of this steepest part is larger than the critical length, the shear band will propagate into the quasi-stable parts of the slope, where the gravitational and seismically induced shear stresses are smaller than the peak but larger than the residual shear strength of the soil. Growth of a shear band is strongly dependent on the shape of the slope, seismic parameters and the strength of soil and less dependent on the slope inclination and the sensitivity of clay. For the slope surface with faster changing inclination, the criterion is more sensitive to the changes of the parameters. Accounting for the actual nonlinear slope geometry eliminates the main challenge of the SBP approach-determination of the length of the initial weak zone, because the slope geometry can be readily obtained from submarine site investigations. It also helps to identify conditions for the early arrest of the shear band, before failure in the sliding layer or a change in loading or excess pore water pressures occurs. The difference in the size of a landslide predicted by limiting equilibrium and SBP approaches can reach orders of magnitude, potentially providing an explanation for the immense dimensions of many observed submarine landslides that may be caused by local factors acting over a limited portion of the slope.

Reliable robotic perception and planning are critical to performing autonomous actions in uncertain, unstructured environments. In field robotic systems, automation is achieved by interpreting exteroceptive sensor information to infer something about the world. This is then mapped to provide a consistent spatial context, so that actions can be planned around the predicted future interaction of the robot and the world. The whole system is as reliable as the weakest link in this chain. In this paper, the term mapping is used broadly to describe the transformation of range-based exteroceptive sensor data (such as LIDAR or stereo vision) to a fixed navigation frame, so that it can be used to form an internal representation of the environment. The coordinate transformation from the sensor frame to the navigation frame is analyzed to produce a spatial error model that captures the dominant geometric and temporal sources of mapping error. This allows the mapping accuracy to be calculated at run time. A generic extrinsic calibration method for exteroceptive range-based sensors is then presented to determine the sensor location and orientation. This allows systematic errors in individual sensors to be minimized, and when multiple sensors are used, it minimizes the systematic contradiction between them to enable reliable multisensor data fusion. The mathematical derivations at the core of this model are not particularly novel or complicated, but the rigorous analysis and application to field robotics seems to be largely absent from the literature to date. The techniques in this paper are simple to implement, and they offer a significant improvement to the accuracy, precision, and integrity of mapped information. Consequently, they should be employed whenever maps are formed from range-based exteroceptive sensor data. C 2009 Wiley Periodicals, Inc.

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The paper proposes a mechanism of submarine spreading failures, which combines retrogressive shear band propagation (SBP) with a series of active block failures in the ‘stable’ zone of the slope, where the gravitational shear stress is smaller than the residual shear strength. Gradual downhill removal of the failed material causes a decrease in the supporting earth pressure, leading to the progressive uphill propagation of the shear band (termed here ‘retrogressive’ SBP) and uniquely determining its length, which can be linked to the dimensions of the spreading failure block mechanisms. Two conjugate energy balance based criteria have been formulated for the spreading failure, in terms of either the critical depth of the sliding surface or the critical drop of the failed seabed level. Both criteria have been validated against the observed phenomena (presence and absence of the evidence of spreading failure for different landslide depths and a step in the sliding surface) in palaeo-landslide examples from the Caspian Sea. The proposed framework provides closed-form criteria, which could be incorporated into a geographical information system based deterministic and probabilistic stability analysis framework for assessment of spreading failure risks in submerged slopes across offshore developments.

The paper describes the evolution of a new deep water in-situ testing system that is designed to measure the seabed soil-pipe interaction forces in the vertical, axial and lateral directions in very soft clay encountered in the deep water environment. The forces and displacements on the pipe are measured using an instrumented 8-inch diameter section of polypropylene-coated steel pipe mounted within a deployment frame. In addition to the measurement of forces in three dimensions, changes in pore water pressure are measured at discrete points along the underside of the pipe section. The system is suitable for deployment from geotechnical and construction support vessels with a 20 tonne A-frame. The paper describes the development of the equipment from the initial specification through field trials to readiness for deepwater deployment. It also discusses how the data from in-situ measurements will complement and enhance the results from existing methods. For unburied high temperature, high pressure pipeline systems, correctly predicting axial " walking?? and controlling lateral buckling is extremely sensitive to the selection of the pipe-soil interaction parameters. Very soft clay soils in deep water are difficult to sample and characterise especially within the first half metre of the seabed where most deepwater pipelines interact with the soil. Several authors have developed analytical models to characterise pipe-soil interaction, but there remains a large degree of uncertainty in the soil behaviour. These models have been developed using numerical methods and model tests on soils reconstituted in the laboratory and in the centrifuge. These techniques by their nature do not properly account for in-situ conditions, particularly the soil structure which is destroyed during sampling and reconsolidation prior to laboratory tests. The paper describes how in-situ measurements could fill this knowledge gap and discusses the relative merits and limitations of each technique. Results from the equipment are load-displacement curves in the three directions, coupled with pore-water pressure measurements, enabling the effective stress state around the pipe to be understood. The data also provide information on the rate of consolidation of the soil under the installed weight of the pipe and the build-up of and interaction with soil berms created as the pipe displaces laterally. Comparisons are made between the in-situ test results, numerical models and 1g and centrifuge model tests to demonstrate how these measurements can be used to complement existing techniques. Subtle changes in the pipe-soil interaction parameters can make several tens of million dollars difference to subsea hardware CAPEX and OPEX. There have been some well-publicised failures of such flowlines and equally probably many over-designed systems. This subject is one case of soil-structure interaction where it is not possible to use a marginally conservative estimate of interface resistance and apply it to each mode of pipeline movement - i.e. what is conservative in the axial sense may not be conservative in the lateral sense. The authors believe that in-situ measurements will reduce this uncertainty and improve the reliability of unburied deep water pipelines. Introduction The assessment of pipe-soil interaction of High Pressure High Temperature (HPHT) and other deepwater pipeline systems in deep water is a highly complex subject. One of the fundamental issues with the problem is the low contact effective stresses (<10kPa) between the unburied pipe and soil. It is a poorly understood subject area within soil mechanics as most civil engineering applications concern stress levels considerably higher. This is compounded by the uncertainties on pipeline embedment due to the dynamic effects during pipeline installation, the variability in loading rate during start-up and shut-down and the interaction between lateral and axial pipeline movement.

This paper introduces two objective functions for computing the expected cost in the Stochastic Collection and Replenishment (SCAR) scenario. In the SCAR scenario, multiple user agents have a limited supply of a resource that they either use or collect, depending on the scenario. To enable persistent autonomy, dedicated replenishment agents travel to the user agents and replenish or collect their supply of the resource, thus allowing them to operate indefinitely in the field. Of the two objective functions, one uses a Monte Carlo method, while the other uses a significantly faster analytical method. Approximations to multiplication, division and inversion of Gaussian distributed variables are used to facilitate propagation of probability distributions in the analytical method when Gaussian distributed parameters are used. The analytical objective function is shown to have greater than 99% comparison accuracy when compared with the Monte Carlo objective function while achieving speed gains of several orders of magnitude.

This paper outlines recent research into axial pipe-soil interaction from the geotechnical elements of the SAFEBUCK Joint Industry Project. The operational axial pipe-soil friction strongly influences the initiation and cyclic development of lateral buckles, and also controls the magnitude of pipeline end expansions as well as rates of axial walking. Results from model tests performed at the University of Cambridge are presented in this paper, and provide new insights into the axial pipe-soil response on fine-grained clayey soils. A simple test arrangement was used to pull an 8 m long plastic pipe axially over a bed of soft natural clay collected from a deepwater location offshore West Africa. Many axial sweeps were performed, spanning a wide range of velocities (0.001 mm/s - 5 mm/s) and a wide range of intervening pause periods (up to several days). Both of these variables had a strong influence on the axial pipe-soil resistance - or ‘friction’. The peak values of equivalent friction factor were as high as 1.5 and the residual values were generally in the range 0.2 - 0.5, but fell to below 0.1 in some cases. Higher peak values are associated with longer waiting periods between axial sweeps. The lowest residual values are associated with the fastest rates of shearing. This wide range of axial resistance was observed in a single test using the same pipe resting on the same soil, which is disconcerting from a design perspective. To identify the origin of this variability, an interpretation based on the generation and dissipation of excess pore pressure is explored. This provides a reasonable explanation for the results, but some unexpected aspects of the behavior remain. The results show the important influence of pore pressure effects, consolidation, and the level of drainage during sliding. They also highlight the complexity of axial pipe-soil interaction. For these experimental results, conventional design calculations do not provide adequate predictions of the observed behavior except for during very slow drained movements. The undrained behavior is not captured by conventional design calculations, which provides a cautionary warning to designers. In particular, in the slow-draining natural clay used in this experiment, very low equivalent axial friction factors - as low as F/W' is ~ 0.1 - can be sustained for a long period of movement. The SMARTPIPE® is a recently-developed tool for performing pipe-soil interaction tests in situ offshore, using an instrumented model pipe mounted on a seabed frame. Selected results from a SMARTPIPE® cyclic axial pipe test performed at a deep water location are also presented and discussed. The results support the proposed interpretation based on the generation and dissipation of excess pore pressure. Some differences exist between the in situ and model test data but they can be explained by the smaller magnitude of axial velocity tested, the higher coefficient of consolidation of the in-situ soil and the absence of pause periods between sweeps. Minimal data from experiments on axial pipe-soil interaction is in the public domain, so the results provided here represent a significant contribution to the available knowledge. This research is continuing within the SAFEBUCK JIP, via additional model testing using a new facility that is described in this paper. The aim is to establish new and more robust design guidance for pipe-soil interaction, to support the reliable and efficient design of seabed pipelines.