Frictional behaviour of segmental retaining wall units infilled with recycled concrete aggregate

The use of segmental retaining wall units as the facing column for mechanically stabilized earth (MSE) retaining walls has increased noticeably all over the world. Hollow and solid, both types of modular block units are used in dry-stacked facing columns. Nowadays, Hollow concrete units are being implicated frequently because of its cost- ffectiveness and other technical advantages. The cavities of hollow concrete units are filled with natural (fresh) aggregates for better shear resistance. The use of fresh aggregates as in-fillers in retaining wall constructions is expensive and unsustainable (annihilation of natural resources). This study mainly focuses on frictional behavior of newly designed and manufactured precast "I" blocks infilled with fresh and recycled aggregates. A series of tests were performed using a specially designed & fabricated direct shear apparatus to assess the frictional behavior of infilled blocks under different normal loading conditions. The tests were executed based on the exiting ASTM and National Concrete Masonry Association (NCMA) test protocols. Test results were outlined in the form of shear stress displacement relationship to compare the effect of recycled aggregate against the fresh aggregate. Shear capacity envelopes were also plotted using Mohr-Coulomb failure criteria to find out the angle of friction for each case. Test results revealed that the angle of friction of the blocks infilled with the recycled aggregate is almost equal to those with the fresh aggregate

Prize-Collecting Steiner Networks via Iterative Rounding

Abstract. In this paper we design an iterative rounding approach for the classic prize-collecting Steiner forest problem and more generally the prize-collecting survivable Steiner network design problem. We show as an structural result that in each iteration of our algorithm there is an LP variable in a basic feasible solution which is at least one-third-integral resulting a 3-approximation algorithm for this problem. In addition, we show this factor 3 in our structural result is indeed tight for prize-collecting Steiner forest and thus prize-collecting survivable Steiner network design. This especially answers negatively the previous belief that one might be able to obtain an approximation factor better than 3 for these problems using a natural iterative rounding approach. Our structural result is extending the celebrated iterative rounding approach of Jain [13] by using several new ideas some from more complicated linear algebra. The approach of this paper can be also applied to get a constant factor (bicriteria-)approximation algorithm for degree constrained prize-collecting network design problems. We emphasize that though in theory we can prove existence of only an LP variable of at least one-third-integral, in practice very often in each iteration there exists a variable of integral or almost integral which results in a much better approximation factor than provable factor 3 in this paper (see patent application [11]). This is indeed the advantage of our algorithm in this paper over previous approximation algorithms for prize-collecting Steiner forest with the same or slightly better provable approximation factors.

Global age-sex-specific fertility, mortality, healthy life expectancy (HALE), and population estimates in 204 countries and territories, 1950–2019: a comprehensive demographic analysis for the Global Burden of Disease Study 2019

Background: Accurate and up-to-date assessment of demographic metrics is crucial for understanding a wide range of social, economic, and public health issues that affect populations worldwide. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 produced updated and comprehensive demographic assessments of the key indicators of fertility, mortality, migration, and population for 204 countries and territories and selected subnational locations from 1950 to 2019. Methods: 8078 country-years of vital registration and sample registration data, 938 surveys, 349 censuses, and 238 other sources were identified and used to estimate age-specific fertility. Spatiotemporal Gaussian process regression (ST-GPR) was used to generate age-specific fertility rates for 5-year age groups between ages 15 and 49 years. With extensions to age groups 10–14 and 50–54 years, the total fertility rate (TFR) was then aggregated using the estimated age-specific fertility between ages 10 and 54 years. 7417 sources were used for under-5 mortality estimation and 7355 for adult mortality. ST-GPR was used to synthesise data sources after correction for known biases. Adult mortality was measured as the probability of death between ages 15 and 60 years based on vital registration, sample registration, and sibling histories, and was also estimated using ST-GPR. HIV-free life tables were then estimated using estimates of under-5 and adult mortality rates using a relational model life table system created for GBD, which closely tracks observed age-specific mortality rates from complete vital registration when available. Independent estimates of HIV-specific mortality generated by an epidemiological analysis of HIV prevalence surveys and antenatal clinic serosurveillance and other sources were incorporated into the estimates in countries with large epidemics. Annual and single-year age estimates of net migration and population for each country and territory were generated using a Bayesian hierarchical cohort component model that analysed estimated age-specific fertility and mortality rates along with 1250 censuses and 747 population registry years. We classified location-years into seven categories on the basis of the natural rate of increase in population (calculated by subtracting the crude death rate from the crude birth rate) and the net migration rate. We computed healthy life expectancy (HALE) using years lived with disability (YLDs) per capita, life tables, and standard demographic methods. Uncertainty was propagated throughout the demographic estimation process, including fertility, mortality, and population, with 1000 draw-level estimates produced for each metric. Findings: The global TFR decreased from 2•72 (95% uncertainty interval [UI] 2•66–2•79) in 2000 to 2•31 (2•17–2•46) in 2019. Global annual livebirths increased from 134•5 million (131•5–137•8) in 2000 to a peak of 139•6 million (133•0–146•9) in 2016. Global livebirths then declined to 135•3 million (127•2–144•1) in 2019. Of the 204 countries and territories included in this study, in 2019, 102 had a TFR lower than 2•1, which is considered a good approximation of replacement-level fertility. All countries in sub-Saharan Africa had TFRs above replacement level in 2019 and accounted for 27•1% (95% UI 26•4–27•8) of global livebirths. Global life expectancy at birth increased from 67•2 years (95% UI 66•8–67•6) in 2000 to 73•5 years (72•8–74•3) in 2019. The total number of deaths increased from 50•7 million (49•5–51•9) in 2000 to 56•5 million (53•7–59•2) in 2019. Under-5 deaths declined from 9•6 million (9•1–10•3) in 2000 to 5•0 million (4•3–6•0) in 2019. Global population increased by 25•7%, from 6•2 billion (6•0–6•3) in 2000 to 7•7 billion (7•5–8•0) in 2019. In 2019, 34 countries had negative natural rates of increase; in 17 of these, the population declined because immigration was not sufficient to counteract the negative rate of decline. Globally, HALE increased from 58•6 years (56•1–60•8) in 2000 to 63•5 years (60•8–66•1) in 2019. HALE increased in 202 of 204 countries and territories between 2000 and 2019. Interpretation: Over the past 20 years, fertility rates have been dropping steadily and life expectancy has been increasing, with few exceptions. Much of this change follows historical patterns linking social and economic determinants, such as those captured by the GBD Socio-demographic Index, with demographic outcomes. More recently, several countries have experienced a combination of low fertility and stagnating improvement in mortality rates, pushing more populations into the late stages of the demographic transition. Tracking demographic change and the emergence of new patterns will be essential for global health monitoring. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens

Global burden of 87 risk factors in 204 countries and territories, 1990�2019: a systematic analysis for the Global Burden of Disease Study 2019

Background: Rigorous analysis of levels and trends in exposure to leading risk factors and quantification of their effect on human health are important to identify where public health is making progress and in which cases current efforts are inadequate. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 provides a standardised and comprehensive assessment of the magnitude of risk factor exposure, relative risk, and attributable burden of disease. Methods: GBD 2019 estimated attributable mortality, years of life lost (YLLs), years of life lived with disability (YLDs), and disability-adjusted life-years (DALYs) for 87 risk factors and combinations of risk factors, at the global level, regionally, and for 204 countries and territories. GBD uses a hierarchical list of risk factors so that specific risk factors (eg, sodium intake), and related aggregates (eg, diet quality), are both evaluated. This method has six analytical steps. (1) We included 560 risk�outcome pairs that met criteria for convincing or probable evidence on the basis of research studies. 12 risk�outcome pairs included in GBD 2017 no longer met inclusion criteria and 47 risk�outcome pairs for risks already included in GBD 2017 were added based on new evidence. (2) Relative risks were estimated as a function of exposure based on published systematic reviews, 81 systematic reviews done for GBD 2019, and meta-regression. (3) Levels of exposure in each age-sex-location-year included in the study were estimated based on all available data sources using spatiotemporal Gaussian process regression, DisMod-MR 2.1, a Bayesian meta-regression method, or alternative methods. (4) We determined, from published trials or cohort studies, the level of exposure associated with minimum risk, called the theoretical minimum risk exposure level. (5) Attributable deaths, YLLs, YLDs, and DALYs were computed by multiplying population attributable fractions (PAFs) by the relevant outcome quantity for each age-sex-location-year. (6) PAFs and attributable burden for combinations of risk factors were estimated taking into account mediation of different risk factors through other risk factors. Across all six analytical steps, 30 652 distinct data sources were used in the analysis. Uncertainty in each step of the analysis was propagated into the final estimates of attributable burden. Exposure levels for dichotomous, polytomous, and continuous risk factors were summarised with use of the summary exposure value to facilitate comparisons over time, across location, and across risks. Because the entire time series from 1990 to 2019 has been re-estimated with use of consistent data and methods, these results supersede previously published GBD estimates of attributable burden. Findings: The largest declines in risk exposure from 2010 to 2019 were among a set of risks that are strongly linked to social and economic development, including household air pollution; unsafe water, sanitation, and handwashing; and child growth failure. Global declines also occurred for tobacco smoking and lead exposure. The largest increases in risk exposure were for ambient particulate matter pollution, drug use, high fasting plasma glucose, and high body-mass index. In 2019, the leading Level 2 risk factor globally for attributable deaths was high systolic blood pressure, which accounted for 10·8 million (95 uncertainty interval UI 9·51�12·1) deaths (19·2% 16·9�21·3 of all deaths in 2019), followed by tobacco (smoked, second-hand, and chewing), which accounted for 8·71 million (8·12�9·31) deaths (15·4% 14·6�16·2 of all deaths in 2019). The leading Level 2 risk factor for attributable DALYs globally in 2019 was child and maternal malnutrition, which largely affects health in the youngest age groups and accounted for 295 million (253�350) DALYs (11·6% 10·3�13·1 of all global DALYs that year). The risk factor burden varied considerably in 2019 between age groups and locations. Among children aged 0�9 years, the three leading detailed risk factors for attributable DALYs were all related to malnutrition. Iron deficiency was the leading risk factor for those aged 10�24 years, alcohol use for those aged 25�49 years, and high systolic blood pressure for those aged 50�74 years and 75 years and older. Interpretation: Overall, the record for reducing exposure to harmful risks over the past three decades is poor. Success with reducing smoking and lead exposure through regulatory policy might point the way for a stronger role for public policy on other risks in addition to continued efforts to provide information on risk factor harm to the general public. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens

Improvement in physical properties for ground treated with rapid impact compaction

Ground improvement has been used on many construction sites to densify granular material, in other word to improve soil properties and reduce potential settlement. This paper evaluates the efficiency of rapid impact compaction (RIC), which is an improvement on the process of deep dynamic compaction, in improving soil properties and controlling soil settlement. In this technique ground improvement is achieved by impacting the ground with a 7 ton weight, 35 times/min, and drop height of 0.8 m at 2.5 m c/c square grid spacing. Evaluation of improvement in soil properties was based on field data by comparing pre-treatment and post-treatment cone penetrometer test (CPT) soundings. An interpretation of soil properties from CPT was made using interpretation software to assess the degree of improvement achieved. Load test was conducted to estimate soil settlement. It was found that the RIC succeeded in improving soil properties like relative density from 45 to 70, increase the friction angle of soil by an average of 3° and reducing soil settlement criteria by 50

Reinforcement in concrete piles embedded in sand

In this study, the necessity of reinforcement in concrete pile (bored or driven) is assessed. The soil was assumed to be unsaturated and homogeneous sandy soil. Throughout the study, a finite element computer program was used and the pile was modeled as a beam-on-elastic foundation. The soil is represented by discrete spring. The stiffness of each spring is considered to be linearly variable with depth. The moment loading, lateral loading, pile length, pile diameter, in addition to the angle of internal friction and soil density were taken as parameter to study their effect on the extent of reinforcement along the pile shaft. It is concluded that for piles embedded in sand, a length of reinforcement not less than 40 of pile length for bored piles and 20 for driven piles is needed

Complex variable solution of elastic tunneling problems

The ground loss problem occurs when a cylindrical tunnel is constructed in a soil with the radius of the tunnel being somewhat smaller than the radius of the cavity. The method used in this paper is Muskhelishvilli's complex variable method considering conformal mapping of the elastic region onto a circular ring. The problem of an elastic half plane with a circular cavity was investigated, regarding the case that along the boundary of the cavity, the surface tractions were prescribed. The computer program (ground loss) was used. The program worked interactively, on the basis of values of Poisson's ratio and the ratio of the radius of the cavity to its depth (r/h). It was investigated whether certain problems of stresses and deformations caused by deformation of a tunnel in an elastic half plane could be solved by the complex variable method. For this purpose, two elementary boundary value problems were considered in detail. These include the problem of a half plane with a circular cavity loaded by a uniform radial stress, and the problem in which a uniform radial displacement is imposed on the cavity boundary (this is usually called the ground loss problem). It was concluded that the displacement of the bottom of the tunnel was always smaller than the value, u(o) (the displacement of the cavity). For large values of r/h, the displacement may even be negative, that is, downward. The displacement of the bottom was always equal to the average displacement of the tunnel plus a constant value Mo which is the imposed radial displacement

Frictional performance of infilled I-blocks with geosynthetic inclusions

Geosynthetic reinforced segmental retaining walls (GR-SRWs) are in a period of development and have achieved popularity all over the world. Inclusion of geosynthetic layer at the interface has great influence on interface frictional performance of segmental retaining wall units. In this investigation, three (3) types of geosynthetic reinforcements were chosen and used to find out their influences on the interface shear capacity of newly designed and locally produced precast I-blocks. A series of direct shear tests were conducted using a specially designed and fabricated direct shear apparatus to assess the frictional characteristics of the blocks with geosynthetic inclusions. The results presented in this paper report that flexible geosynthetic reinforcements perform well than stiff geosynthetics although decrease the interface shear capacity than no inclusion condition. The presence of geosynthetic layers also minimizes the localized stress concentrations at the interface

Distribution of earth pressure behind retaining walls considering different approaches

In this paper, the earth pressure distribution generated behind a retaining wall is estimated by the finite element method and compared with that obtained from classical earth pressure theories. In this analysis, the behavior of the soil is assumed to be elasto-plastic with Mohr-Coulomb failure criterion. The concrete retaining wall is represented by linear elastic model. The thin layer interface element proposed by Desai et al. (1984) is used to represent the interface between the wall and the surrounding soil. A two-dimensional plane-strain finite element computer program CRISP is utilized after some modification. The results show that the distribution of earth pressure depends on the mode of wall movement (whether translation, rotation or both), and the active earth pressure obtained from the finite element analysis is close to Coulomb's solution in case of bottom wall rotation. Whereas, in case of top wall rotation, the obtained earth pressure is greater than that of Coulomb solution. This is mainly because Coulomb equation is originally based on wall rotating about its base (failure mechanism)

Wave data for shallow and deep water sedimentary basins of Malaysia

The recent years have seen significant development of offshore structures in Malaysian region for oil and gas exploration. Analyzing and studying the behavior of offshore marine structures subjected to environment conditions native to Malaysian seas offshore of Terengganu and Sarawak requires that the sea wave characteristics be properly probed. In addition, the knowledge of wave characteristics is essential for planning, design and construction of new ports coastal protection constructions, harbors and navigational channels. It correspondingly contributes to fisheries activities, navigation, marine habitat management and coastal development and planning. As this kind of research is still young for the case of Malaysian oil and gas exploration cum production activity, research methods are introduced and implemented in the study to catch on the wave characteristics in deep water be existent at offshore Terengganu and Sarawak. These essentially include obtaining reliable sea wave data for the purpose of offshore engineering design, studying the wave height distributions to predict the probability of occurrences of different sea states. Subsequently, the wave data's for the water depths of the Terengganu and Sarawak basin, which is 200 m (shallow) and 2000 m (ultra-deep) respectively are developed. The sea wave data have been predicted for 100 years occurrence probabilities and 1000 years return periods