Marine Geotechnics

The paper makes a brief review of the state-of-the-art in marine geotechnics. The design problems for different offshore foundation types, from traditional piled and gravity base foundations to the new lightweight skirted foundation concepts, are described. Geotechnical breakthroughs have enabled new and daring constructions offshore and opened the way to cost-effective solutions. At the same time, the requirements and conditions imposed by the offshore industry also greatly contributed to an improved understanding of the behavior of soils under new loading conditions. The paper looks into the development of enhanced site investigations and soil characterization, model testing, improved design methods and new foundation solutions. The challenges facing the geotechnical engineering profession when moving into deeper waters and the steps needed to meet these challenges are outlined

Risk analysis for landslides and snow avalanches. Example applications for snow avalanches

Prediction of snow avalanche occurrence and its run-out distance inherently involves many uncertainties. The main reason for the large uncertainties is that the mechanical behaviour of snow is extremely complicated, and other external factors that affect the problem, such the climate, wind direction, amount of snowfall, loading rate, etc. are all more-or-less random processes. The aim of the work described in this report is to demonstrate potential applications of probabilistic analysis to problems related to snow avalanches. Two problems are looked into. The first problem is evaluating the probability of a slab avalanche. A mechanical model based on traditional geotechnical approach to slope stability was adopted. To account for the uncertainties in the input parameters, the stability model was coupled to reliability analysis software. In addition to the failure probability, the probabilistic analyses provide the most likely combination of parameters at failure and the sensitivity factors that quantify the contribution of each random variable to the total uncertainty. The second problem considered is related to the development of hazard maps for snow avalanche. Current practice is to use a statistical model for run-out distance in areas where topography and climate are favourable for avalanche activity. The procedure may be conservative because it basically assumes that in the area of interest, avalanche activity occurs every year. The actual annual probability of snow avalanche occurrenceat a given area is ignored because it is difficult to estimate this probability from physical models. A procedure is outlined in the report to use historical observations and Bayesian updating to estimate the annual probability of snow avalanche occurrence. The procedureis demonstrated through an example application.Norges Forskningsråd (NFR

Risk and Reliability in Geotechnical Engineering

Statistics, reliability analyses and risk estimates can be very useful decision-making tools in geotechnical problems. Yet the methods are little used in practice. The offshore and mining industry are at the forefront for the use of these approaches, having encouraged their use and sponsored research that has enabled the methods to be well-documented and of proven usefulness in the study of alternatives for design and decision-making in face of uncertainties. The paper presents a few case studies in different areas of geotechnical engineering and discusses the results that would have been obtained without the use of the risk approach. Special emphasis is given to dams and offshore structures, both piled and shallow foundations. The authors take a look at the reasons why the methods are not used to a greater extent in practice and make recommendations as to when and how one should uses such methods

On Tsunami Risk Assessment for the West Coast of Thailand

The catastrophic Indian Ocean tsunami of 26 December 2004 raised a number of questions for scientists and politicians on how to deal with the tsunami risk in coastal regions. This paper discusses the challenges in tsunami risk evaluation and presents the results of a tsunami risk mitigation study for the west coast of Thailand. It is argued that a scenario-based approach is particularly well suited for evaluation of the risk posed by tsunamis. The approach consists of considering scenarios of plausible extreme, tsunami-generating events, computing the tsunami inundation levels caused by these events, estimating the possible range of casualties for the computed inundation levels, and estimating the upper and lower bounds on the annual probability of occurrence of the scenarios. Other challenges related to perceived risk vs. real risk, acceptable/tolerable risk levels, and the use of the results in the decision making process are also put into perspectives

Effects of Hysteretic Shape on Dynamic Response

The parameters determined in laboratory tests for use in dynamic analyses are usually the secant modulus and the area of the hysteresis loop. The accuracy of this approach was studied for highly non-linear behavior through analytical solutions and numerical simulations of a single degree of freedom system. Only the effect of the shape of the hysteresis loop was studied, i.e. the stiffness and the area of the loop were kept constant independent of amplitude. The study shows that irregular hysteresis may cause a significant increase in the response of the system in higher frequencies compared to what would be expected from visco-elastic and standard non-linear models. The area of the hysteresis loop provides a good measure of the damping also for high degrees of non-linearity

Earthquake Disaster Risk Reduction in Iran: Lessons and ‘‘Lessons Learned’’ from Three Large EarthquakeDisasters—Tabas 1978, Rudbar 1990, and Bam 2003

This article addresses three large earthquake disasters in Iran: Tabas in 1978, Rudbar in 1990, and Bam in 2003. Lessons and "Lessons Learned" from these three earthquake disasters were investigated together with their contributions over time towards earthquake disaster risk reduction in Iran. Many lessons from 1978 Tabas, 1990 Rudbar, and 2003 Bam did not become "Lessons Learned" and they were identified again within the dramatic context of other earthquake disasters in various places of Iran. Both lessons and "Lessons Learned" from Tabas, Rudbar, Bam, and other earthquake disasters in Iran require a sustainable long-term framework-an earthquake culture.This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://​creativecommons.​org/​licenses/​by/​4.​0/​), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were mad

On probability analysis in snow avalanche hazard zoning

The reduced societal acceptance of living in regions exposed to snow avalanches, and the increased economic consequences when houses are located within a hazard zone, highlight the uncertainty concerning avalanche run-out prediction. The limitations of today’s zoning procedures are especially pronounced in potential avalanche terrain where there are few observations of snow avalanches, where old buildings are present in the potential run-out zone, and where the local climate does not favour severe snow accumulation. This paper combines a mechanical probabilistic model for avalanche release with a statistical/topographical model for avalanche run-out distance to obtain the unconditional probability of extreme run-out distance. For the mechanical model, a first-order reliability method (FORM) and Monte Carlo simulations are compared. The interpretation of the statistical/topographical model either as an extreme value model or as a single value model is discussed. Furthermore, both a classical approach where the probability of an avalanche occurring is a constant, and a Bayesian approach with stochastic probability, are compared. Finally, example applications in hazard zoning are presented, with emphasis on how the influence of historical observations, local climate, etc., on run-out distance can be quantified in statistical terms and how a specified certainty level can be found from constructing confidence intervals for, for example, the most likely largest run-out distance during various time intervals

GBS Platform Evaluation Using Field Instrumentation

A case history of the foundation behaviour of an offshore gravity base structure (GBS) is presented. The platform rests on an overconsolidated fissured clay, bounded, top and bottom, by pervious sand layers. Sixteen piezometers have been placed within this 30 m layer. Based on one-dimensional consolidation theory, independent analyses using both settlement and pore pressure measurements indicated a high degree of consolidation had occurred much sooner than was estimated in the initial design phase. These analyses indicated that laboratory oedometer tests underpredicted the coefficient of consolidation by one to two orders of magnitude. Updated settlements and stability analyses yielded 50% of the initially anticipated settlement and a 20% increase in the available safety factor. In addition, the certainty that the theory relating pore pressure to settlements was appropriate, led to confidence in the piezometer performance, and in turn the procedure used to install them