Centrifuge testing to evaluate the liquefaction response of air-injected partially saturated soils beneath shallow foundations

Earthquake-induced liquefaction of saturated soils continues to cause severe damage to structures with shallow foundations. In recent years, artificially reducing the degree of saturation and forming partially saturated zones within saturated soils has been proposed as a liquefaction mitigation technique. This study experimentally investigates the liquefaction response of air-injected partially saturated soils beneath shallow foundations. A series of centrifuge tests were conducted on the shallow foundations with different bearing pressures. The results of the tests show that the generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation. Forming spatially distributed partially saturated zones in the liquefiable soils limited the development of high excess pore pressures and liquefaction susceptibility of soils, particularly at the higher confining stresses. The reduction in the degree of saturation of soils decreased the depth of liquefied soil layer, and increased the resistance of soil to the bearing capacity failure. On the other hand, the decrease in the degree of saturation of liquefiable soils led the larger accelerations to be transmitted to the foundations through unliquefied soil zones. It is therefore concluded that use of air-injection as a liquefaction mitigation measure does reduce structural settlements, but will have the consequence of larger structural accelerations.Ministry of National Education (M.E.B.) of TurkeyThis is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10518-016-9968-

Improving the lateral capacity of monopiles in submarine clay

The European offshore wind sector has been undergoing tremendous growth, resulting in offshore wind farms having larger wind turbines that are located further away from the shore in harsh environmental conditions. To cater for the resulting higher loads, the current trend has been to continually increase the size of the monopile, which is the most popular foundation type. However, this is not viable in the long term given the current installation technology. This paper presents the results of three-dimensional finite-element analyses investigating the improvement in the lateral capacity of a large-diameter monopile in clay when used in combination with hybrid features and rock armour. Non-skirted reinforced concrete and steel footings, a skirted steel footing and steel fins were assessed under a combination of vertical, lateral and moment loads expected at an offshore wind farm location with a water depth of 30 m. The findings, based on shear and bending moment developed in the monopile and mobilised soil resistance, indicate the skirted steel footing and fins to be the most effective in enhancing monopile lateral capacity at serviceability. </jats:p

Quick Annotator: an open-source digital pathology based rapid image annotation tool.

Image-based biomarker discovery typically requires accurate segmentation of histologic structures (e.g. cell nuclei, tubules, and epithelial regions) in digital pathology whole slide images (WSIs). Unfortunately, annotating each structure of interest is laborious and often intractable even in moderately sized cohorts. Here, we present an open-source tool, Quick Annotator (QA), designed to improve annotation efficiency of histologic structures by orders of magnitude. While the user annotates regions of interest (ROIs) via an intuitive web interface, a deep learning (DL) model is concurrently optimized using these annotations and applied to the ROI. The user iteratively reviews DL results to either (1) accept accurately annotated regions or (2) correct erroneously segmented structures to improve subsequent model suggestions, before transitioning to other ROIs. We demonstrate the effectiveness of QA over comparable manual efforts via three use cases. These include annotating (1) 337,386 nuclei in 5 pancreatic WSIs, (2) 5,692 tubules in 10 colorectal WSIs, and (3) 14,187 regions of epithelium in 10 breast WSIs. Efficiency gains in terms of annotations per second of 102×, 9×, and 39× were, respectively, witnessed while retaining f-scores &gt;0.95, suggesting that QA may be a valuable tool for efficiently fully annotating WSIs employed in downstream biomarker studies

Durability of partial saturation to counteract liquefaction

Recently, artificially introducing gas/air into liquefiable soils has been presented as a method for reducing the risks from liquefaction. Although this method offers a simple and cheap solution, its use in practical applications is still very limited. This might be primarily ascribed to the concerns of practising engineers about the durability of gas/air bubbles in soils over time. This paper discusses the durability of entrapped air bubbles under various simulated field conditions that may potentially cause the dissolution, diffusion, compression and escape of air bubbles. Multiple series of 1g vertical sand column and high-g centrifuge tests were undertaken to provide insights into the problem. Air-induced partially saturated soils were prepared using an air-injection technique. The test results showed that the majority of entrapped air bubbles in soils can persist under several simulated field conditions for a sufficient period of time, indicating the long-term reliability of the mitigation accomplished.Ministry of Education, Turke

Influence of air injection on the liquefaction-induced deformation mechanisms beneath shallow foundations

Earthquake-induced liquefaction of soils frequently causes serious damage to structures with shallow foundations. Reducing the degree of saturation of liquefiable soils by air injection is offered as a cost-effective and reliable method of mitigating liquefaction hazards. Nevertheless, very little experimental research is available on the performance of this method. Particularly, the way that air injection influences the deformation mechanisms beneath shallow foundations is not well defined. Gaining a deeper insight into soil displacements during and after air injection can pave the way for developing effective guidelines for the use of this particular technique. For this purpose, a series of dynamic centrifuge tests are presented in this paper. The prevailing deformation mechanisms are identified in a novel way using displacement vector fields. The results indicate that air injection alters the deformation mechanisms that develop underneath and in the ground surrounding a shallow foundation, substantially reducing the average settlements.The first author wishes to acknowledge the financial assistance provided during the course of this study by the Ministry of National Education (M.E.B.) of Turkey

Successful transition from fed-batch to continuous manufacturing within a mAb process development cycle

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Physical modelling of air injection to remediate liquefaction

Seismic liquefaction of loosely packed, saturated soils poses a significant threat to the built environment. Recently, air injection into liquefiable soil deposits has been introduced as an innovative and cost-effective liquefaction mitigation technique. However, few effective guidelines are available to the engineers for its application and performance. The way that air should be injected appropriately, most particularly, in the presence of structures, is not clearly defined. The distribution of retained air bubbles within the saturated soil medium and its effect on the seismic response also need further investigation. In an effort to offer insights into this problem, an experimental programme consisting of a series of centrifuge and 1g shaking table tests was undertaken. The results have shown that the use of higher air injection pressure provides a much wider and a more uniform air-entrapped zone, but increases the risk of soil deformations developed under the foundations. The distance from the air injector and preferential flow pathways influence the distribution of the retained air bubbles and seismic response of the soil models. Moreover, it was shown in a novel way that the air injection technique is not very effective at low confining stresses to reduce liquefaction-induced deformations beneath shallow foundations. The first author extends his thanks to the Ministry of National Education (MEB) of Turkey for their financial support

Twenty-one years of heave monitoring in London Clay at Horseferry Road Basement

An 11 m-deep basement structure in London SW1 was left vacant from 1968 to 1989. The basement heaved significantly during this period due to the lack of a superstructure, providing a unique opportunity to study the development of long-term heave in London Clay. May (1975) presented the monitoring results from 1968-73 and excerpts of site data collected after 1973 have also been circulating informally in the industry since the 1990s. However, the full set of monitoring data remains hitherto unpublished. This paper was initially drafted in the early 1990s when three of the authors (Nicholson, Chapman, and Solera) were working together with Arup. The paper somehow never got published as people and circumstances changed. More recently, the first author (Chan) started postgraduate research on heave and pressure beneath slabs in excavations in over-consolidated clays, using the heave monitoring data from the draft paper to complement centrifuge test results. For this reason, it was decided that the draft paper should be revised and published for the benefit of the wider industry. This paper provides a comprehensive case history of the site, publishing further heave data to June 1989, giving a total of 21 years of heave monitoring. Further site investigation data and calculations are included for comparison. The data show that the presence of a basement did not significantly reduce the shear strength of the clay beneath it. The coefficient of consolidation of the clay was 38 – 52 m²/year and long-term heave was still ongoing 21 years after the end of excavation.EPSRC grant reference number EP/L016095/

Centrifuge Modelling of Earthquake Effects in Uniform Deposits of Saturated Sand

Centrifuge models representing level uniform saturated deposits of relatively loose and dense sand were tested at Cambridge University\u27s Schofield Centre to clarify the behaviour of these deposits under earthquake loading. The excess pore pressure, vertical propagation of the accelerations and ground surface settlements resulting from a model earthquake are presented and discussed. The results show that, for similar dynamic loading, the models undergo large shear stiffness degradation resulting from significant pore pressure build up, this taking place at a slower rate in the dense sand. As a result of the cyclic loading, the models suffer settlements, occurring mostly during the event, that are noticeably smaller in the dense model. The upwards propagation of the accelerations through the model depends on the relative density of the sand and changes during the seismic event, following degradation of sand mechanical properties. Large short-duration acceleration spikes are observed near the surface of the dense model, corresponding to large amplification of input acceleration. The results presented and discussed contribute to the understanding of the basic mechanisms of earthquake-induced liquefaction and the use of densification as a measure to mitigate its effects