Numerical modelling of stiff clay cut slopes with nonlocal strain regularisation

The aim of this project is to investigate the stability of cut slopes in stiff clay. The findings are subsequently applied to model stabilisation with piles, used to remediate failure of existing slopes and stabilise potentially unstable slopes created by widening transport corridors. Stiff clay is a strain softening material, meaning that soil strength reduces as the material is strained, for example in the formation of a slip surface. In an excavated slope this can lead to a progressive, brittle slope failure. Simulation of strain softening behaviour is therefore an important aspect to model. The interaction of piles and stiff clay cut slopes is investigated using the Imperial College Geotechnics section’s finite element program ICFEP. In designing a suitable layout of the finite element mesh, preliminary analyses found the two existing local strain softening models to be very dependent on the size and arrangement of elements. To mitigate this shortcoming, a nonlocal strain softening model was implemented in ICFEP. This model controls the development of strain by relating the surrounding strains to the calculation of strain at that point, using a weighting function. Three variations of the nonlocal formulation are evaluated in terms of their mesh dependence. A parametric study with simple shear and biaxial compression analyses evaluated the new parameters required by the nonlocal strain softening model. The nonlocal results demonstrated very low mesh dependence and a clear improvement on the local strain softening models. In order to examine the mesh dependence of the new model in a boundary value problem compared to the local strain softening approach, excavated slope analyses without piles were first performed. The slope was modelled in plane strain with coupled consolidation. These analyses also investigated other factors such as the impact of adopting a small strain stiffness material model on the development of the failure mechanism and the impact of the spatial variation of permeability on the time to failure. The final set of analyses constructed vertical stabilisation piles in the excavated slope, represented as either solid elements or one dimensional beam elements. The development of various failure mechanisms for stiff clay cuttings was found to be dependent on pile location, pile diameter and pile length. This project provides an insight into the constitutive model and boundary conditions required to study stabilisation piles in a stiff clay cutting. The nonlocal model performed very well to reduce mesh dependence, confirming the biaxial compression results. However, the use of coupled consolidation was found to cause further mesh dependence of the results.Open Acces

Inactivation of murine norovirus on a range of copper alloy surfaces is accompanied by loss of capsid integrity

Norovirus is one of the most common causes of acute viral gastroenteritis. The virus is spread via the fecal-oral route, most commonly from infected food and water, but several outbreaks have originated from contamination of surfaces with infectious virus. In this study, a close surrogate of human norovirus causing gastrointestinal disease in mice, murine norovirus type 1 (MNV-1), retained infectivity for more than 2 weeks following contact with a range of surface materials, including Teflon (polytetrafluoroethylene [PTFE]), polyvinyl chloride (PVC), ceramic tiles, glass, silicone rubber, and stainless steel. Persistence was slightly prolonged on ceramic surfaces. A previous study in our laboratory observed that dry copper and copper alloy surfaces rapidly inactivated MNV-1 and destroyed the viral genome. In this new study, we have observed that a relatively small change in the percentage of copper, between 70 and 80% in copper nickels and 60 and 70% in brasses, had a significant influence on the ability of the alloy to inactivate norovirus. Nickel alone did not affect virus, but zinc did have some antiviral effect, which was synergistic with copper and resulted in an increased efficacy of brasses with lower percentages of copper. Electron microscopy of purified MNV-1 that had been exposed to copper and stainless steel surfaces suggested that a massive breakdown of the viral capsid had occurred on copper. In addition, MNV-1 that had been exposed to copper and treated with RNase demonstrated a reduction in viral gene copy number. This suggests that capsid integrity is compromised upon contact with copper, allowing copper ion access to the viral genome

A study into urban roadworks with shuttle-lane operation

In urban areas where roadworks are required, single lane shuttle operation is applied, especially where there is limited road space. There are operational problems relating to the site such as site geometry, visibility, length of roadworks zone, position of signs with other traffic control devices and signal timing. Other problems are mainly related to drivers’ behaviour and their compliance with traffic controls on site. The reduced road width caused by the works will interrupt the free flow of traffic and it can also add to the risks to road users. In addition, shuttle operation may introduce long queues and increase delays especially during peak periods. There is a need to identify those parameters and behaviours which might influence traffic performance in terms of safety and capacity. An investigation of four roadworks sites in urban roadworks within the Greater Manchester area was undertaken for this purpose. Parameters included in the examination were position of the STOP sign, signal timing, weather conditions, time headway, vehicle speed and percentages of heavy goods vehicles (HGV) in the traffic stream. Statistical analysis and comparisons between sites were conducted. Other factors related to the operation of the shuttle-lane were provided based on site observations

Visible Care: Nan Goldin and Andres Serrano’s Post-mortem Photography

This thesis investigates artistic post-mortem photography in the context of shifting social relationship with death in the 1980s and 1990s. Analyzing Nan Goldin’s Cookie in Her Casket and Andres Serrano’s The Morgue, I argue that artists engaging in postmortem photography demonstrate care for the deceased. Further, that demonstrable care in photographing the dead responds to a crisis of the late 1980s and early 1990s in America. At the time, death returned to social and political discourse with the visibility of AIDS and cancer and the euthanasia debates, spurring on photographic engagement with the corpse. Nan Goldin’s 1989 post-mortem portrait of her friend, Cookie in Her Casket, was first presented within The Cookie Portfolio. The memorial portfolio traced the friendship between Cookie and Goldin over fourteen years. The work relies on a personal narrative, framing the works within a familial gaze. I argue that Goldin creates the sense of family to encourage empathy in the viewer for Cookie’s loss. Further, Goldin’s generic and beautified post-mortem image of Cookie is a way of offering Cookie respect and dignity in death. Andres Serrano’s 1992 The Morgue is a series of large-scale cropped, and detailed photographs capturing indiscriminate bodies from within an unidentified morgue. I assert that Serrano intentionally presents these corpses as objects, outside of life. His stark lighting, emphasis on texture and the rich colours of Cibachrome print beautify and lavish aesthetic care on the corpse-objects. I propose a reading of The Morgue through Serrano’s deliberate use of beauty to transform the corpses into icons, and read the entire series as a visualisation of the sublime within the abject. Goldin and Serrano have fundamentally different approaches to post-mortem photography. Goldin’s work follows an artistic and historical tradition of memorial portraits taken of the deceased by friends or family; whereas Serrano follows from a forensic framework appropriated by artists who photograph within a morgue. Previous discourse separated memorial and forensic post-mortem photography in order to better appreciate the historical trajectory of each field. In the context of a time where death was moving from near invisibility into the mainstream, comparing Goldin and Serrano offers insight into the changes in America’s visual relationship with death

Stabilisation of excavated slopes in strain softening materials with piles

The use of a row of discrete vertical piles is an established method, successfully used to remediate failure of existing slopes and to stabilise potentially unstable slopes created by widening transport corridors. This paper challenges the assumptions made in current design procedures for these piles, which treat the pile only as an additional force or moment and simplify soil–pile interaction. Two-dimensional plane-strain finite-element analyses were performed to simulate the excavation of a slope in a stiff clay and the interaction of vertical piles within the slope. A non-local strain-softening model was employed for the stiff clay to reduce the mesh dependency of the solution. An extensive parametric study was performed to systematically examine the impact of pile position, dimensions (length and diameter) and time of pile construction on the stability of a cutting in London Clay, which was chosen as a representative strain-softening material. A variety of different failure mechanisms were identified, depending on pile location, dimensions and time of construction. The variability of the pile and slope interaction that was modelled suggests that an oversimplification during design could miss the critical failure mechanism or provide a conservative stabilisation solution. Given the prevalence of stiff clay slopes in the UK, increased capacity requirements of transport infrastructure and the age of slopes in this material, an informed and more realistic design of stabilisation piles will become increasingly necessary

On the use of nonlocal regularisation in slope stability problems

This study examines the use of nonlocal regularisation in a coupled consolidation problem of an excavated slope in a strain softening material. The nonlocal model reduces significantly the mesh dependency of cut slope analyses for a range of mesh layouts and element sizes in comparison to the conventional local approach. The nonlocal analyses are not entirely mesh independent, but the predicted response is much more consistent compared to the one predicted by local analyses. Additional Factor of Safety analyses show that for drained conditions the nonlocal regularisation eliminates the mesh dependence shown by the conventional local model

Real-Time PCR Detection of Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella pneumophila in Respiratory Specimens Using the ARIES® System

Background: Mycoplasma pneumoniae (Mpn), Chlamydia pneumoniae (Cpn), and Legionella pneumophila (Lpn) can cause both epidemic and endemic occurrences of acute respiratory disease and are responsible for up to 22% of cases of community acquired pneumonia. Due to the limited availability of FDA-approved molecular diagnostic assays, we developed and evaluated a multiplexed Real-time PCR assay for the detection of these agents in two respiratory specimen types on the Luminex ARIES® instrument. The instrument provides for nucleic acid extraction plus PCR amplification and target detection in the same cassette. The ARIES® instrument generates a cycle threshold value and a confirmatory melt curve value for each reaction, including results for an internal sample processing control. The limit of detection for Mpn, Cpn and Lpn, was 100 CFU/mL, 1000 CFU/mL and 100 CFU/mL, respectively. In addition, accuracy, precision, specificity and stability studies were conducted to validate the assay for diagnostic use. Between November 2016 and June 2017, a total of 836 patient specimens were processed in our reference laboratory, with six positive Mpn and two positive Lpn. No specimens were positive for Cpn during this time period. The availability of a robust multiplex PCR assay greatly enhances the ability to rapidly diagnose infections caused by these three agents causing atypical pneumonia

Preliminary Evaluation of an lytA PCR Assay for Detection of Streptococcus pneumoniae in Urine Specimens from Hospitalized Patients with Community-Acquired Pneumonia

Community acquired pneumonia (CAP) due to Streptococcus pneumoniae still occurs in at risk populations, despite the availability of effective vaccines. Laboratory confirmation of S. pneumoniae remains challenging in cases of CAP despite advances in blood culture techniques and the availability of nucleic acid amplification tests such as PCR-based methods. Urine specimens are an attractive sample type because they are non-invasive compared to bronchial washes or whole blood specimens for patients with CAP. While urine specimens have been used successfully in antigen detection assays, they have not been extensively evaluated for PCR-based assays. In this preliminary study, we evaluated the potential for a real-time PCR assay targeting the S. pneumoniae autolysin gene (lytA) to detect in archived urine samples from patients with CAP. Results indicate that the real time lytA PCR assay on the Luminex ARIES® system shows promise as a screening tool for patients with CAP based on comparison to urine antigen detection assay results