Numerical investigation of the effects of tunnelling on existing tunnels

Construction of the Crossrail tunnels just beneath the existing Central line tunnels at the northern side of Hyde Park provided the impetus for this paper. A basic three-dimensional (3D) finite-element (FE) model was developed to study a general case of a new tunnel (NT) crossing perpendicularly below an existing tunnel (ET). A series of 3D FE analyses was carried out and the results presented in this paper reveal some of the interaction effects. Changes in hoop forces, bending moments and lining deformations of the ET due to excavation of the NT are discussed. Conclusions are drawn about how the relative position of the excavation face of the NT in relation to the ET's axis affects the latter's behaviour. Cross-sectional and longitudinal deformations of the ET are discussed, leading to recommendations for field monitoring of similar interaction cases. Two parametric studies were also carried out to quantify the effects of the magnitude of the earth pressure balance machine face pressure and the longitudinal stiffness of the ET on the predicted behaviour of the ET due to construction of the NT

The use of kinematic hardening models for predicting tunnelling-induced ground movements in London Clay

The use of a kinematic hardening soil model for predicting short- and long-term ground movements due to tunnelling in London Clay is investigated. The model is calibrated against oedometer and triaxial tests on intact samples from different units of the London Clay. The calibrated model is then used in finite-element analysis to simulate the field response at St James's Park during excavation of the Jubilee Line Extension tunnels. The finite-element predictions compare well with the available field monitoring data. The importance of using consistent initial conditions for this complex boundary value problem in conjunction with the model parameters selected is highlighted. The stiffness response of different regions of the finite-element mesh indicates that the rate at which the stiffness degrades and the stiffness response further away from the tunnel boundary affect the short-term predictions significantly. The long-term predictions confirm that the compression characteristics of the soil control the magnitude of the consolidation settlements and its permeability the shape of the long-term settlement profiles

Predicting tunnelling-induced ground movements and interpreting field measurements using numerical analysis: Crossrail case study at Hyde Park

Ground response to the construction of the Crossrail tunnels in London Clay beneath Hyde Park has been modelled numerically using advanced finite-element analyses. The soil model used for modelling the London Clay was a kinematic hardening soil model (named M2-SKH). This model, when used for the St James's Park greenfield site, provided excellent predictions of tunnelling-induced ground movements. Comparison of the results from the analysis of the Hyde Park greenfield site with associated field monitoring data also suggests excellent predictions, even though in this case the tunnels were: of larger diameter; deeper in the London Clay; and constructed with earth-pressure-balance machines. The influence of lining permeability was found to influence significantly short- and longer-term predictions. Interpretation of the predicted surface and subsurface vertical and horizontal displacements due to the construction of the Crossrail tunnels exemplifies how numerical analysis can assist in explaining and identifying potential ambiguities in field measurements

Investigating the effect of tunnelling on existing tunnels

A major research project investigating the effect of tunnelling on existing tunnels has been completed at Imperial College London. This subject is always of great concern during the planning and execution of underground tunnelling works in the urban environment. Many cities already have extensive existing tunnel networks and so it is necessary to construct new tunnels at a level beneath them. The associated deformations that take place during tunnelling have to be carefully assessed and their impact on the existing tunnels estimated. Of particular concern is the serviceability of tunnels used for underground trains where the kinematic envelope must not be impinged upon. The new Crossrail transport line under construction in London passes beneath numerous tunnels including a number of those forming part of the London Underground networ

Myonecrosis secondary to Clostridium Septicum in a patient with Occult Colon Malignancy: a case report

© 2008 Gibson et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Inverse Relationship between Adherence to the Mediterranean Diet and Serum Cystatin C Levels

OBJECTIVE: The aim of the present study was to examine serum cystatin C levels in association with the Mediterranean diet in a healthy Greek population. METHODS: Cystatin C together with basic clinical chemistry tests was measured in a total of 490 adults (46±16 years, 40% of males), who underwent an annual health check. Demographic, anthropometric and lifestyle characteristics were recorded, while adherence to the Mediterranean diet was evaluated through the MedDietScore (0-55). RESULTS: The mean level of serum cystatin C was 0.84 mg/L, while men had increased serum cystatin C levels compared to women (0.86 mg/L vs. 0.83 mg/L, respectively, 0.017). After adjusting for age, gender, body mass index, smoking status, hypertension, diabetes, hypercholesterolemia, estimated glomerular filtration rate (eGFR), albumin and ferritin levels, each unit increase in MedDietScore led to 0.002 mg/dL drop off in cystatin C serum levels. CONCLUSIONS: We have demonstrated an inverse relationship between the MedDietScore and serum cystatin C levels. Our finding that increases in MedDietScore are associated with decreases in serum cystatin C levels could imply that adherence to the Mediterranean diet may reduce the cardiovascular risk, as assessed by cystatin C, a prognostic marker of the cardiometabolic risk. This notion could have a great impact on public health

Surgical Outcomes in Syndromic Tetralogy of Fallot: A Systematic Review and Evidence Quality Assessment

Tetralogy of Fallot (ToF) is one of the most common cyanotic congenital heart defects. We sought to summarize all available data regarding the epidemiology and perioperative outcomes of syndromic ToF patients. A PRISMA-compliant systematic literature review of PubMed and Cochrane Library was performed. Twelve original studies were included. The incidence of syndromic ToF was 15.3% (n = 549/3597). The most prevalent genetic syndromes were 22q11.2 deletion (47.8%; 95% CI 43.4–52.2) and trisomy 21 (41.9%; 95% CI 37.7–46.3). Complete surgical repair was performed in 75.2% of the patients (n = 161/214; 95% CI 69.0–80.1) and staged repair in 24.8% (n = 53/214; 95 CI 19.4–30.9). Relief of RVOT obstruction was performed with transannular patch in 64.7% (n = 79/122; 95% CI 55.9–72.7) of the patients, pulmonary valve-sparing technique in 17.2% (n = 21/122; 95% CI 11.5–24.9), and RV-PA conduit in 18.0% (n = 22/122; 95% CI 12.1–25.9). Pleural effusions were the most common postoperative complications (n = 28/549; 5.1%; 95% CI 3.5–7.3). Reoperations were performed in 4.4% (n = 24/549; 95% CI 2.9–6.4) of the patients. All-cause mortality rate was 9.8% (n = 51/521; 95% CI 7.5–12.7). Genetic syndromes are seen in approximately 15% of ToF patients. Long-term survival exceeds 90%, suggesting that surgical management should be dictated by anatomy regardless of genetics