Freeze-thaw cycles caused by climate change can change the structure and strength of the soil. In seasonally frozen soil areas, the use of improved loess as a filling material must consider the effects of freeze-thaw cycles. With the increasingly severe global environmental problems, the search for suitable new environmental protection improvement materials has become one of the hotspots in soil performance improvement research. The purpose of this paper is to use lignin fiber to improve the engineering performance and freeze-thaw resistance of loess and to reduce the negative impact of engineering construction on the environment of the loess area. Based on a series of triaxial shear tests, the effects of freeze-thaw cycles on the stress-strain relationship, shear strength, and Mohr-Coulomb’s strength parameters of loess reinforced with lignin fiber were analyzed. Combined with the volume change and microstructure characteristics of fiber-reinforced loess before and after the freeze-thaw cycles, the reasons for the effects of the freeze-thaw cycles on the shear strength characteristics of fiber-reinforced loess are discussed. The research results showed that after 15 freeze-thaw cycles, the shear strength of loess reinforced with 1% fiber increased by 0.15%, 2.05%, and 1.35% at 80, 140, and 200 kPa, respectively. The shear strength of the reinforced loess with other fiber contents decreases to different degrees, and the maximum reduction ratio can reach 9.54%. Freeze-thaw cycles changed the variation of shear strength and strength parameters with fiber content. When the fiber content is less than 1%, the shear strength, cohesion, and friction angle of fiber-reinforced loess increase the fastest after freeze-thaw cycles. When the fiber content is 1%, the overall destruction effect of freeze-thaw cycles on fiber-reinforced loess is inhibited, and the soil has the best freeze-thaw resistance.
Abstract Weighted optimization framework (WOF) achieves variable dimensionality reduction by grouping variables and optimizing weights, playing an important role in large-scale multi-objective optimization problems. However, because of possible problems such as duplicate weight vectors in the selection process and loss of population diversity, the algorithm is susceptible to local optimization. Therefore, this paper develops an algorithm framework called multi-population multi-stage adaptive weighted optimization (MPSOF) to improve the performance of WOF in two aspects. First, the method of using multi-population is employed to address the issue of insufficient algorithmic diversity, while simultaneously reducing the likelihood of converging towards local optima. Secondly, a processing stage is incorporated into MPSOF, where a certain number of individuals are adaptively selected for updating based on the weight information and evolutionary status of different subpopulations, targeting different types of weights. This approach alleviates the impact of repetitive weights on the diversity of newly generated individuals, avoids the drawback of easily converging to local optima when using a single type of weight for updating, and effectively balances the diversity and convergence of subpopulations. Experiments of three types designed on several typical function sets demonstrate that MPSOF exceeds the comparison algorithms in the three metrics for Inverse Generation Distance, Hypervolume and Spacing.
Abstract With the increasing demand for filling engineering construction in the Loess Plateau, the engineering problems related to saturated loess caused by rainfall and irrigation are also increasingly prominent. This work studied the shear characteristics of saturated compacted loess by experiments, and qualitatively and quantitatively explained the meso-mechanism of the effect of compaction degree on the shear characteristics combined with the meso-pore characteristic parameters. The study shows that the stress–strain curve of saturated loess under 80 and 85% compaction degree is strain softening, it is strain weak softening under 90% compaction degree, and strain hardening under 95% compaction degree. The failure strength and pore water pressure have a good fitting linear relationship with compaction degree, and the fitting correlation coefficients are more than 0.97. Under 95% compaction degree, the pore water pressure increases with the development of axial strain, then decreases after the peak, and may appear negative. With the increase in compaction degree, the micro and small pore content of the saturated loess soil increases, the medium, large and super large pore content decreases, the proportion of pore area decreases, the pore shape becomes uniform and smooth, the complexity of pore shape decreases, the pore arrangement tends to be regular and neat, and the directionality increases. The research results can provide references for engineering design, construction, and numerical calculation of filling engineering in loess area.
Air pollution and pulmonary tuberculosis (PTB) are still serious worldwide problems, especially in areas of developing countries. Whether there is an association between high ambient air pollutant concentrations and PTB has not been fully explored.Bayesian spatial-temporal models were constructed to analyse the association between ambient air pollutants (particulate matter with aerodynamic diameters of ≤10 μm (PM10), sulfur dioxide (SO2) and nitrogen dioxide (NO2)) and PTB incidence, adjusting for socioeconomic covariates. We collected data on pulmonary TB, ambient air pollution (PM10, SO2 and NO2) concentrations and socioeconomic covariates from 17 prefectures in the central Chinese province of Hubei between Jan 1, 2006, and Dec 31, 2015.For every annual 10 μg/m3 increase in SO2, the relative risk (RR) of PTB incidence was 1.046 (95% credible interval [CI], 1.038-1.054) in the study area. Moreover, we found positive associations with each annual 10 μg/m3 increase in ambient air pollutants (PM10, SO2 and NO2) in females but only with SO2 in males. A significant association for each 10 μg/m3 increase in SO2 was observed in all the age groups, with a significant association for PM10 only in children under 14 years of age. A significant response relationship was also observed at a 0-1 month moving average lag for each 10 μg/m3 increase in SO2.High ambient air pollution concentrations in areas of developing countries might increase the risk of regional PTB incidence, especially for women and young people. Precautions and protective measures and efforts to reduce ambient air pollutant concentrations should be strengthened in developing countries.
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