Novel adaptation of Marston's stress solution for inclined backfilled stope

In underground mining, it is crucial to consider the arching phenomenon, especially for inclined backfilled trenches and mine stopes. That phenomenon decreases the vertical stress of the fill material, so, the in-site stress has already redistributed itself to the hanging- and foot-walls when the stope was excavated. In such cases, the mobilized resistance due to friction between the granular backfill material and the inclined walls can substantially reduce the pressure at the bottom of the stope, which could have a major impact on the stability of the backfill medium and consequently also on economic aspects. Most of researchers used numerical analysis or Lab. tests to predict both of vertical and lateral stresses in inclined stopes. However, there is a need to investigate analytical solution to describe the behaviour of those stresses in inclined stopes. Based on Marston’s formula, this research provides a new approach to predicting vertical stresses at any depth in inclined backfilled stopes. The proposed approach introduces a new parameter, η, to account for the contribution of backfill arching. This parameter specifies the ratio of normal stresses on the hanging wall and foot wall of the inclined backfilled stope. This differs from previous approaches, which assumed that the normal stress on the inclined backfilled stope's hanging wall and foot wall was equal. To validate the proposed approach, results obtained are compared with numerical, analytical, and experimental results from previous research. It is found that if the proposed parameter, η, is modified to 0.2 for the lateral earth pressure coefficient at rest with an angle of inclination of 60° to 80°, good agreement with experimental data is achieved

The effect of long-term consolidation on foundations underpinned by micropiles in soft clay

So far insufficient research has been done on the long-term behavior of micropiles embedded in a clay medium, even though this has a significant influence on the expected total settlement. This paper considers a square foundation placed on a clay bed and tested under vertical loads until the clay reached its bearing capacity. Subsequently, the plate was underpinned with four micropiles, and the load test was repeated. These test data were used to validate the coupled hydraulic-mechanical three-dimensional finite difference model presented in this paper. In the numerical modelling, four different load transfer scenarios were considered to simulate different approaches to adding floors to an existing building. Consolidation periods of zero months, six months, and five years between the application of the load due to the existing building, and the application of loads due to additional storeys were considered. The six-month period represents a short-term, and the five-year period a long-term scenario. Following the first consolidation period and the application of loads representing additional storeys, a second consolidation period was implemented, such that the combined length of the two consolidation periods was five years. In this study, the results showed that the installation of micropiles immediately after the completion of existing floors is most successful in controlling the settlement of additional floors later on

Systematic review and network meta-analysis with individual participant data on cord management at preterm birth (iCOMP): study protocol

Introduction Timing of cord clamping and other cord management strategies may improve outcomes at preterm birth. However, it is unclear whether benefits apply to all preterm subgroups. Previous and current trials compare various policies, including time-based or physiology-based deferred cord clamping, and cord milking. Individual participant data (IPD) enable exploration of different strategies within subgroups. Network meta-analysis (NMA) enables comparison and ranking of all available interventions using a combination of direct and indirect comparisons. Objectives (1) To evaluate the effectiveness of cord management strategies for preterm infants on neonatal mortality and morbidity overall and for different participant characteristics using IPD meta-analysis. (2) To evaluate and rank the effect of different cord management strategies for preterm births on mortality and other key outcomes using NMA. Methods and analysis Systematic searches of Medline, Embase, clinical trial registries, and other sources for all ongoing and completed randomised controlled trials comparing cord management strategies at preterm birth (before 37 weeks’ gestation) have been completed up to 13 February 2019, but will be updated regularly to include additional trials. IPD will be sought for all trials; aggregate summary data will be included where IPD are unavailable. First, deferred clamping and cord milking will be compared with immediate clamping in pairwise IPD meta-analyses. The primary outcome will be death prior to hospital discharge. Effect differences will be explored for prespecified participant subgroups. Second, all identified cord management strategies will be compared and ranked in an IPD NMA for the primary outcome and the key secondary outcomes. Treatment effect differences by participant characteristics will be identified. Inconsistency and heterogeneity will be explored. Ethics and dissemination Ethics approval for this project has been granted by the University of Sydney Human Research Ethics Committee (2018/886). Results will be relevant to clinicians, guideline developers and policy-makers, and will be disseminated via publications, presentations and media releases

Systematic review and network meta-analysis with individual participant data on cord management at preterm birth (iCOMP): study protocol

Timing of cord clamping and other cord management strategies may improve outcomes at preterm birth. However, it is unclear whether benefits apply to all preterm subgroups. Previous and current trials compare various policies, including time-based or physiology-based deferred cord clamping, and cord milking. Individual participant data (IPD) enable exploration of different strategies within subgroups. Network meta-analysis (NMA) enables comparison and ranking of all available interventions using a combination of direct and indirect comparisons. (1) To evaluate the effectiveness of cord management strategies for preterm infants on neonatal mortality and morbidity overall and for different participant characteristics using IPD meta-analysis. (2) To evaluate and rank the effect of different cord management strategies for preterm births on mortality and other key outcomes using NMA. Systematic searches of Medline, Embase, clinical trial registries, and other sources for all ongoing and completed randomised controlled trials comparing cord management strategies at preterm birth (before 37 weeks' gestation) have been completed up to 13 February 2019, but will be updated regularly to include additional trials. IPD will be sought for all trials; aggregate summary data will be included where IPD are unavailable. First, deferred clamping and cord milking will be compared with immediate clamping in pairwise IPD meta-analyses. The primary outcome will be death prior to hospital discharge. Effect differences will be explored for prespecified participant subgroups. Second, all identified cord management strategies will be compared and ranked in an IPD NMA for the primary outcome and the key secondary outcomes. Treatment effect differences by participant characteristics will be identified. Inconsistency and heterogeneity will be explored. Ethics approval for this project has been granted by the University of Sydney Human Research Ethics Committee (2018/886). Results will be relevant to clinicians, guideline developers and policy-makers, and will be disseminated via publications, presentations and media releases. Australian New Zealand Clinical Trials Registry (ANZCTR) (ACTRN12619001305112) and International Prospective Register of Systematic Reviews (PROSPERO, CRD42019136640)

Numerical analysis of lateral earth pressure coefficient in inclined mine stopes

Investigating analytical solutions to determine stresses for mine stopes with inclined walls is essential for the design of stopes in the mining industry, contributing to the prevention of serious accidents. Two variables in the analytical formula used for computing the vertical stresses in mine stopes with inclined walls play a vital role in the design. The two variables are the coefficient of lateral earth pressure, Kα, and the ratio η. Here, Kα is the ratio of the normal earth pressure on the inclined wall at some level to the vertical stress at the same point and η is the ratio of the normal lateral earth pressure on the hanging wall to the normal lateral earth pressure on the footwall. The difficulty of using the analytical formula is to choose the correct values of both parameters. Hence, calibrating the formula involves selecting appropriate values of Kα and η in order to predict the actual results of the vertical stress, and consequently provide the designer with appropriate values that can be used in the design of mine stopes with inclined walls. Accordingly, in this study, the coefficient of lateral earth pressure in inclined mine stopes is numerically evaluated for various backfill friction angles; 30°, 35° and 40° with and without reference to the surrounding rock. The ratio η is also investigated at different depths ranging from 25 to 275 m. Moreover, Kα was formulated as a function of the ratio of the height to the breadth for different angles of the inclined stope, i.e., 60°, 70° and 80°. The considered cases in this analysis differ considerably from the commonly considered case in previous research, which completely overlooks the wall inclination effect. Furthermore, the considered cases better represent the actual in-situ conditions because they model the interaction between the sidewalls and the backfilling in the stope. The results have shown that the use of η = 0.6–0.8 and Kα ≤ Ka for the different angles of inclination in the analytical formula resulted in vertical stress being compatible with the numerical analysis results. Article highlights: Different researchers considered several aspects of mine stopes; however, none of them considered the effect of the stope wall inclination explicitly. Choosing appropriate values of the coefficient of lateral earth pressure, K, and the ratio of the normal lateral earth pressure on the hanging wall to the normal lateral pressure on the footwall, η, is crucial to predict the actual vertical stress. In this paper the ratio η is investigated at different depths ranging from 25 to 275 m. Moreover, K was formulated as a function of the ratio of the height to the breadth for different angles of the inclined stope

Grading of Intraventricular Hemorrhage and Neurodevelopment in Preterm <29 Weeks’ GA in Canada

Objective: The aim of this study was to evaluate the neurodevelopmental outcome at 18–24 months in surviving preterm infants with grades I–IV intraventricular hemorrhages (IVHs) compared to those with no IVH. Study Design: We included preterm survivors <29 weeks’ GA admitted to the Canadian Neonatal Network’s NICUs from April 2009 to September 2011 with follow-up data at 18–24 months in a retrospective cohort study. The neonates were grouped based on the severity of the IVH detected on a cranial ultrasound scan and recorded in the database: no IVH; subependymal hemorrhage or IVH without ventricular dilation (grades I–II); IVH with ventricular dilation (grade III); and persistent parenchymal echogenicity/lucency (grade IV). The primary outcomes of neurodevelopmental impairment (NDI), significant neurodevelopmental impairment (sNDI), and the effect modification by other short-term neonatal morbidities were assessed. Using multivariable regression analysis, the adjusted ORs (AOR) and 95% of the CIs were calculated. Results: 2327 infants were included. The odds of NDI were higher in infants with grades III and IV IVHs (AOR 2.58, 95% CI 1.56, 4.28 and AOR 2.61, 95% CI 1.80, 3.80, respectively) compared to those without IVH. Infants with an IVH grade ≤II had similar outcomes for NDI (AOR 1.08, 95% CI 0.86, 1.35) compared to those without an IVH, but the odds of sNDI were higher (AOR 1.58, 95% CI 1.16, 2.17). Conclusions: There were increased odds of sNDI in infants with grades I–II IVHs, and an increased risk of adverse NDI in infants with grades ≥III IVHs is corroborated with the current literature

Epidemiology of thrombosis in Canadian neonatal intensive care units

OBJECTIVE: To assess the rate, location, risk factors, management, and outcomes of neonatal thrombosis (NT). DESIGN: A retrospective study investigating infants admitted to NICUs in Canadian Neonatal Network between January 2014 and December 2016 and diagnosed with NT. Each infant with NT was matched with an infant without NT. RESULTS: Of 39,971 infants, 587 (1.5%) were diagnosed with NT: 440 (75%) venous, 112 (19%) arterial, 29 (5%) both. NT rate was 1.4% in full-term and 1.7% in preterm infants. Venous thrombi occurred most commonly in the portal vein and arterial thrombi in the cerebral artery. Conservative management and low molecular weight heparin were the most common treatment modalities. Hospital stay was longer (p \u3c 0.001) in the NT patients, but mortality was similar. CONCLUSIONS: NT was diagnosed in ~15/1000 NICU admissions and most commonly in the portal vein and cerebral arteries. Management varied based on the type and location of thrombi. Large multicenter trials are needed to address the best management strategies

A comparison of strategies for managing the umbilical cord at birth in preterm infants

Objective: to evaluate the rates of practice, and the associations between different cord management strategies at birth (delayed cord clamping [DCC], umbilical cord milking [UCM], and early cord clamping [ECC]) and mortality or major morbidity, rates of blood transfusion, and peak serum bilirubin in a large national cohort of very preterm infants. Study design: we retrospectively studied preterm infants &lt;33 weeks of gestation admitted to the Canadian Neonatal Network between January 2015 and December 2017. Patients who received ECC (&lt;30 seconds), UCM, or DCC (≥30 seconds) were compared. Multiple generalized linear/quantile logistic regression models were used. Results: of 12 749 admitted infants, 9729 were included; 4916 (50.5%) received ECC, 394 (4.1%) UCM, and 4419 (45.4%) DCC. After adjustment for potential confounders identified between groups in univariate analyses, the odds of mortality or major morbidity were higher in the ECC group when compared with UCM group (aOR, 1.18; 95% CI, 1.03-1.35). Mortality and intraventricular hemorrhage were associated with ECC as compared with DCC (aOR, 1.6 [95% CI, 1.22-2.1] and aOR, 1.29 [95% CI, 1.19-1.41], respectively). The odds of severe intraventricular hemorrhage were higher with UCM compared with DCC (aOR, 1.38; 95% CI, 1.05-1.81). Rates of blood transfusion were higher with ECC compared with UCM and DCC (aOR, 1.67 [95% CI, 1.31-2.14] and aOR, 1.68 [95% CI, 1.35-2.09], respectively), although peak serum bilirubin levels were not significantly different. Conclusions: both DCC and UCM were associated with better short-term outcomes than ECC; however, the odds of severe intraventricular hemorrhage were higher with UCM compared with DCC.</p