Chang'an University

About: Chang'an University is a education organization based out in Xi'an, China. It is known for research contribution in the topics: Asphalt & Groundwater. The organization has 18415 authors who have published 15102 publications receiving 125436 citations. The organization is also known as: Cháng'ān Dàxué & Changan University.

Assessment of fluoride contamination and distribution: a case study from a rural part of Andhra Pradesh, India

Abstract: In total, 123 groundwater samples were collected to evaluate the suitability for drinking purpose in a rural part of Andhra Pradesh, India. The groundwater is alkaline in nature and pH varying from 7.18 to 9.32 with a mean value of 8.36. The hydrogeochemical analysis reveals that the fluoride concentration varies from 0.4 to 5.8 mg/L with a mean of 1.98 mg/L. Higher fluoride concentration is found in west-central parts of Markapur region. The villagers have been exposed to the intake of high fluoride-bearing groundwater for the prolonged period and suffering from the deadly disease fluorosis. However, with respect to groundwater chemistry, the fluoride concentration is high in Na+–HCO3−-type groundwater and low in Ca2+–HCO3−-type groundwater in the Markapur region. Data plotted in Gibbs diagram show that all groundwater samples fall under rock weathering dominance group with a trend toward the evaporation dominance category. Therefore, rock–water interaction is the primary cause of elevated fluoride in the groundwater of the study region. Furthermore, a significant positive correlation exists between F− and pH, HCO 3 - as well as negative correlation exists between F- and Ca2+ and NO3−, which supports that the alkaline nature of water is the main cause for dissolving fluoride-bearing minerals.

Centrifuge modelling of twin-tunnelling induced ground movements in loess strata

Abstract: A great concern for the safety of large cross-section tunnels, which are being or to be built in the loess strata of China, is attracted. Generally, loess is a multi-phase porous medium and develops complex stress and strain variation while executing a tunnel project. Another problem is that the soil surrounding both tunnel arches is subjected to a complex loading due to the double excavation. To obtain an in-depth knowledge of the mechanism of tunnel deformation induced by the twin-tunnelling, we conducted comprehensive centrifuge tests, which can simulate and reproduce strictly the action process of twin-tunnelling. Through the model tests, the response of twin-tunnelling on loess stratum deformation was obtained. The investigations showed that with the increase of tunnel spacing, the stratum deformation distribution near the vault changes from a single-peak V shape to a double-peak W shape. Additionally, the height of the stratum pressure arch effect increases significantly. The settlement of the preceding tunnel is slightly larger than that of the latter tunnel, and the twin-tunnelling effect gradually decreases with the increase of tunnel spacing. Through comparative analysis of the different combinations of tunnel spacing and tunnel interval, the interaction between two tunnels with different spacing and interval during tunnelling was investigated, further optimizing the reasonable tunnel spacing and construction steps, as well as providing reference for tunnel route selection in the loess strata.

Investigation of diffusion of rejuvenator in aged asphalt

Abstract: Recycling asphalt pavement creates a cycle of reusing materials that optimize the use of natural resources. For optimal rejuvenation of the aged binder, the diffusion rate of the rejuvenator should be considered. However, the diffusion mechanism between the rejuvenator and aged asphalt is still far from understood. In this study, two experimental methods were conducted to research the diffusion of rejuvenator in aged asphalt. The two asphalt binders were identical in terms of asphalt A7 (60/80 pen) and asphalt A11 (100/120 pen) and two rejuvenators were identical in terms of RA (containing 90% alkyl aromatic oil and 10% saturate oil), and RS (containing 10% alkyl aromatic oil and 90% saturate oil). Experimental results indicated that two experimental methods are also an effective means to research the diffusion of rejuvenator in asphalt in spite of a slight difference. The effect of temperature on the diffusion coefficient is large and the effect of layer thickness of the rejuvenator on diffusion coefficient is obviously not. The rejuvenator RA has a high diffusion rate in asphalt over a wide range of temperatures. In addition, the diffusion coefficient of rejuvenator in asphalt A11 is larger than that in asphalt A7. The test data suggested that the use of rejuvenator with high diffusion is a viable option for recycling old asphalt mixture.

Multi-Objective Optimization of Traffic Signal Timing for Oversaturated Intersection

Abstract: For the purpose of improving the efficiency of traffic signal control for isolate intersection under oversaturated conditions, a multi-objective optimization algorithm for traffic signal control is proposed. Throughput maximum and average queue ratio minimum are selected as the optimization objectives of the traffic signal control under oversaturated condition. A simulation environment using VISSIM SCAPI was utilized to evaluate the convergence and the optimization results under various settings and traffic conditions. It is written by C