Calcareous sediments are prominent throughout the low-latitudinal offshore environment and have been known to be problematic for offshore foundation systems. These fascinating soils consist largely of the skeletal remains of single-celled marine organisms (plankton and zooplankton) and can be as geologically complex as their onshore siliceous counter parts. To enable an adequate understanding of their characteristics, in particular, their intra-granular micro-structure, it is important that geotechnical engineers do not forget about the multifaceted biological origins of these calcareous sediments and the different geological processes that created them. In this paper, the 3D models of soils grains generated from micro-computed tomography scans, scanning electeron microscope images, and optical microscope images of two calcareous sediments from two different depositional environments are presented and their geotechnical implications discussed. One is a coastal bioclastic sediment from Perth, Western Australia that is geologically similar to carbonate sediments typically used in micro-mechanics and particle crushing studies in the literature. The other is a hemipelagic sediment from a region of the North West Shelf of Australia that has historically been geotechnically problematic for engineers. The results show there is a marked difference between coastal bioclastic and hemipelagic sediments in terms of geological context and the associated particle micro-structures. This brings into question whether a coastal bioclastic calcareous sediment is a good micro-mechanical substitute for a hemipelagic one.

Many offshore structures currently in use are supported by piles with large length-to-diameter aspect ratios, because it is well known that such foundations can hold large forces and moments. In environments where long piles are not suitable, structures will use foundations with very low aspect ratios such as skirts and mats. Capacity of long piles has been studied for decades and is well documented, whilst more recent tests have also addressed the behaviour of skirts, mats, and other low-aspect ratio foundations. The vertical and lateral capacity of mid-size foundations, with aspect ratios between one and five, has generally been thought too low for the requirements of most offshore structures. However, in recent years, structures of increasingly different shapes and sizes have been used in offshore environments, such as water-based renewable energy sources or marginal oil and gas platforms. In many of these cases, the usage of a low aspect ratio foundation could significantly reduce installation and transportation costs. Limited studies have been performed on such foundations, and most of the existing work uses only analytical and numerical solutions. Geotechnical centrifuge tests and corresponding numerical analyses were started at Texas A&M University and were continued at the University of Cambridge on the lateral capacity of piles with an aspect ratio of two in normally consolidated clay. Piles were loaded under both pure rotation and a mix of rotation and translation. This work is relevant to offshore structures requiring foundations that are strong but easily installed and cost-efficient, specifically structures secured with piles that experience point loads either through or above the water. It is also of interest for structures in difficult environments, such as areas too shallow or sedimentary for long piles or too fragile for skirts and mats.

and the wonderful experiences the City of Philadelphia has to offer. From the early days of modern geotechnical engineering, sharing field experiences of the performance of geostructures-dams, foundations, tunnels, landfills-in the form of case histories has driven the advancement of knowledge for the geo-profession. Starting in 1984, Professor Shamsher Prakash formalized this tradition and organized the First International Conference on Case Histories in Geotechnical Engineering. This conference brought together more than 190 engineers from 30 countries to share their experiences, learn from each other, and advance the profession. By 2013, the 7th conference in this series drew nearly 320 engineers from 40 countries spanning the globe, culminating in symposia to honor Ralph B. Peck and Clyde Baker. But the essence of the conference had not changed: to advance our profession through shared engineering judgment. Geo-Congress 2019 continues this tradition and features experiences and observations from hundreds of geoengineering projects. The conference includes a wide range of informative technical and panel sessions, short courses, and workshops. Join us in celebration of our geo-accomplishments!

In the ever expanding quest to understand the nature and behavior of soil, translucent and even transparent media have been developed to serve as soil simulates. These artificial soils can be used in experimental models to make visual measurement of phenomena such as geosystem kinematics, soil mass movement, soil particle motion, and pore fluid flow that would be nearly impossible to obtain in natural opaque soils without expensive equipment or boundary effects. One successful type of translucent clay simulate is lithium sodium magnesium silicate (LNM silicate, commonly referred by the trade name Laponite®); however, it's low density/high void ratio results in higher than typical permeability, low undrained shear strength, and extremely long consolidation times. Until now, translucent soil simulates of only 4.5% by mass LNM silicate to total mass have been possible. This paper provides a method for creating mixtures of translucent LNM silicate gel/glass as high as 15% by mass with the additions of an emulsifier, sodium pyrophosphate decahydrate (SPP), which impedes gelation so additional silicate powder can be added. Further, digital image processing techniques are used to present a relationship between LNM silicate, SPP, and translucency and an analysis of the modified simulate's permeability and consolidation properties, with comparisons to natural clays, is also included.

gco component of centrifugal acceleration for a known reference gravity vector, gõ, on the vertical reference plane, R ge magnitude of Earth's gravity vector, gẽ α angle between a centrifuge gravity vector, g, and the centrifuge radial coordinate, r αo angle between a reference gravity vector, gõ, and the centrifuge radial coordinate, r β angle between a centrifuge gravity vector, g, and the local vertical coordinate, z βo angle between the local vertical coordinate axis, z, and the centrifuge radial coordinate, r ξ angle between the local vertical coordinate axis, z, and the centrifuge radial coordinate, r gx component of centrifuge gravity, g, in model local horizontal coordinate, x gz component of centrifuge gravity, g, in model local vertical coordinate, z M Mass of centrifuge basket αb Angle of centrifuge basket relative to centrifuge radial coordinate, r Lb Distance between basket hinge and the basket mass, M Rb Distance between centrifuge axis, Y, and basket hinged Distance between the basket centreline and the basket mass, M L Angle between the centreline of the basket and the project line, L, between the basket hinge and the basket mass, M Δαb Angle between the centreline of the basket and the project line, L, between the basket hinge and the basket mass, M α2D

Geotechnical centrifuge tests were conducted to examine the behavior of low aspect ratio piles and caissons in clayey soils subjected to high moment loading. Model piles with aspect ratio of two were tested in the 150g-ton centrifuge at Rensselaer Polytechnic Institute. Results include moment-inclination and force-displacement response for different loading conditions. Numerical studies were also performed consisting of three dimensional finite element simulations in order to predict capacities. The comparisons are performed in terms of the total resistance that is exerted by the soil on the caisson. This paper focuses on presenting the ultimate bearing capacity factors including both experimental and numerical results. In addition, results are compared to a series of studies available in the literature, which include upper bound solutions and experimental results.

Microelectromechanical systems (MEMS) sensors have become a common part of everyday life and can be found in a number of consumer electronics. Specifically, MEMS accelerometers have become widespread because of their low cost, due to mass production techniques, and ability to sense constant acceleration. This ability allows devices, such as cellular phones, to measure their rotation relative to Earth's gravity. These properties also make MEMS accelerometers an option for measuring the rotation of geo-structures, such as foundations, in the field or in scale model geotechnical centrifuge tests. MEMS accelerometers appear to be especially beneficial for measuring orientation in centrifuge experiments because they are not limited by the design constraints of traditional tilt sensors: a single constant acceleration vector (Earth's gravity). This paper presents the theory behind using single-axis MEMS accelerometers to measure the orientation of an object on a plane of reactive centrifugal acceleration and Earth's gravity within a geotechnical centrifuge. The paper specifically addresses cross-axis sensitivity which can significantly impact measurements and is typically excluded from simpler theories.

Microelectromechanical systems (MEMS) accelerometers are becoming more prevalent in geotechnical engineering and geotechnical centrifuge modelling. In centrifuge experiments these sensors have shown great promise, but still exhibit limitations. This paper proposes a new methodology for the use of single-axis, low-g, high accuracy MEMS accelerometers to measure orientation of on object on the vertical rotational plane of centrifugal acceleration and Earth's gravity in a geotechnical centrifuge. The method specifically compensates for measured cross-axis acceleration by a MEMS accelerometer when in a high-g environment. This is done by determining the apparent internal misalignment of the MEMS sensing unit, relative to its packaging, from a high-g cross-axis calibration. The misalignment can then be used to correct the measured orientation of sensor relative to a centrifuge gravity vector. When compared to simplified approaches measurements of absolute orientation are improved by 0.98º and the standard deviation of measurements between multiple sensors is reduced by 0.73º. Overall, this new methodology significantly improves the accuracy of orientation measurements by a MEMS accelerometers in the geotechnical centrifuge, opening the door to use these inexpensive sensors in more experiments.