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35 results on '"Du, Kun"'

18. A New Non-Inserted and Portable FDR Instrument for Measuring Surface Soil Water Content

Author

Li Fadong, Zhang Hao, Yunfeng Qiao, Shanbao Liu, Bo Li, Qi Li, Qiuying Zhang, and Du Kun

Subjects
Soil nutrients, Water supply for domestic and industrial purposes, adjustable high frequency oscillation, Geography, Planning and Development, frequency domain reflection, Crop growth, Soil science, soil water content, Hydraulic engineering, Aquatic Science, Biochemistry, Soil structure, non-inserted portable instrument, Soil water, Content (measure theory), Environmental science, Water cycle, TC1-978, TD201-500, Water Science and Technology
Abstract

Soil water content (SWC) is a vital parameter for understanding crop growth and the soil nutrient water cycle. Monitoring SWC without inserting sensors into the soil, which can break the soil structure, has previously been a significant challenge for scientists. In this study, we developed a non-inserted portable frequency domain reflection (NIP-FDR) instrument to monitor SWC continuously and automatically. The working technique of this instrument was based on the improved adjustable high-frequency oscillation method originating from the frequency domain reflection principle. Compared to the control SWC measurement instrument, the difference in SWC at 0–10 cm, 10–20 cm, and 20–30 cm depth was within 1%, 3%, and 15%, respectively, and the mean variation of SWC was less than 5% in the indoor measurements. In the field verification experiment conducted in the summer of 2020, the mean error of SWC measurements at a depth of 0–20 cm was 5%, while we failed to compare SWC at a depth of 20–30 cm due to low variability in the SWC measurement at this depth during the summer measurement period. This pioneer NIP-FDR was able to effectively monitor surface SWC, especially at depths of 0–20 cm.

Published
2021

28. Fracture Evaluation and Dynamic Stress Concentration of Granite Specimens Containing Elliptic Cavity under Dynamic Loading

Author

Ming Tao, Ao Ma, Yiqing Wang, Kang Peng, and Du Kun

Subjects
Control and Optimization, Materials science, 0211 other engineering and technologies, Energy Engineering and Power Technology, Magnetic dip, 02 engineering and technology, 010502 geochemistry & geophysics, impact incidence, 01 natural sciences, LS-DYNA, lcsh:Technology, Electrical and Electronic Engineering, Composite material, Engineering (miscellaneous), 021101 geological & geomatics engineering, 0105 earth and related environmental sciences, Stress concentration, Renewable Energy, Sustainability and the Environment, Axial ratio, lcsh:T, Spall, dynamic stress concentration, Dynamic loading, Fracture (geology), elliptic cavity, Energy (miscellaneous), Bar (unit)
Abstract

The Split-Hopkinson pressure bar (SHPB) was used to determine the fracture characteristics of a long bar rock specimen with an elliptical cavity under different axial ratios and dip angles. A high speed camera was applied to record the fracturing process of the granite specimen around the cavity. The experimental results showed that the fracture characteristics around the elliptical cavity were closely related to the axial ratio and dip angle. A three-dimensional numerical model was established using LS-DYNA to quantitatively analyze the dynamic stress state around the cavity. The numerical results indicate that the dip angle and axial ratio of the elliptical cavity significantly affected the dynamic stress concentration factor (DSCF), then affected the rock failure. The location of higher DSCF led to a higher possibility of spalling failure. The maximum DSCF remarkably decreased with a decreasing dip angle and increased the axial ratio. In the dynamic loading propagate process, the stress concentration distribution around the cavity formed by a compression stress wave had a certain damaging effect on the destruction of rock around the cavity, and the stress concentration generated by the tensile stress wave was the main factor of the rock fracture, which was most notable in the peak area of the stress concentration.

Published
2019

32. Evaluation of Excavation-Damaged Zone around Underground Tunnels by Theoretical Calculation and Field Test Methods

Author

Kang Peng, Cao Mingyu, Sun Pengwei, Du Kun, Zhixian Hong, and Ming Tao

Subjects
on-site measurement, Control and Optimization, in situ stress, 0211 other engineering and technologies, Underground mining (hard rock), Energy Engineering and Power Technology, excavation-damaged zone, closed-form solution, 02 engineering and technology, lcsh:Technology, Seismic wave, Stress (mechanics), Brittleness, Cohesion (geology), Geotechnical engineering, Geological Strength Index, Electrical and Electronic Engineering, Rock mass classification, Engineering (miscellaneous), 021102 mining & metallurgy, 021101 geological & geomatics engineering, lcsh:T, Renewable Energy, Sustainability and the Environment, Stress field, Geology, Energy (miscellaneous)
Abstract

Excavation-damaged zones (EDZs) induced in underground mining and civil engineering potentially threaten tunnel safety and stability, and increase construction and support costs. In this paper, an investigation of the excavation damaged zone (EDZ) around roadways in Fankou lead-zinc mine in Guangzhou, China is performed by applying a seismic velocity method accompanied by SET-PLT-01 nonmetallic ultrasonic detector. Meanwhile, the in situ stress in the mining area was measured based on the stress relief method with the Swedish high-precision LUT system. The results indicate that the stress field is dominated by the maximum horizontal tectonic stress, and the extents of the EDZ on the roof-floor region are greater than that on the sidewall. In addition, both of the in situ stresses and EDZs show an increasing trend with an increase of depth. Analytical solutions of EDZ around circular openings in the brittle rock mass subjected to non-hydrostatic stress fields are presented in terms of the Mohr−Coulomb and generalized Hoek−Brown criteria, and validated by several cases mentioned above. The extents of EDZ solved by closed-form solutions were found to be in a great agreement with those obtained in the field. Finally, a series of parametric studies are conducted to investigate the effects of cohesion (c), friction angle (φ), geological strength index (GSI), mi, uniaxial compressive strength (σc), and disturbance factor (D) on EDZ. It is shown that the effects of c, φ, GSI, and σc are significant; however, more attention should be paid to consider the dynamic disturbances induced by mechanical drilling, blasting, and seismic waves in tunnel excavations or operations.

Published
2019
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35. Damage evolution of RC beams under simultaneous reinforcement corrosion and sustained load

Author

Shen, Jiansheng, Gao, Xi, Li, Bo, Du, Kun, Jin, Ruoyu, Chen, Wei, Xu, Yidong, Shen, Jiansheng, Gao, Xi, Li, Bo, Du, Kun, Jin, Ruoyu, Chen, Wei, and Xu, Yidong

Abstract

To accurately obtain the performance of concrete structures in coastal regions, it is necessary to correctly understand the damage evolution law of reinforced concrete (RC) members under real working conditions. In this paper, four RC beams, subjected to different levels of corrosion and sustained load, are first tested. Reinforcement corrosion coupled with sustained load increases the number and width of cracks at the soffit of beams but decreases their loading capacities. Crack width of the corroded beam under 50% of designed load is two times of that under 30% of designed load. Residual loading capacities of the corroded beams subjected to 30% and 50% of designed load are 87.5% and 81.8% of the control beam. A finite element model is developed for the corroded RC beams. Due to less confinement, concrete below and at the sides of reinforcements is subjected to a higher stress, compared to concrete above the reinforcements. Corrosion expansion of reinforcements is successfully modelled by a temperature-filed method, as it properly simulates the damage evolution of the corroded RC beams. As a result, concrete cracking, caused by the reinforcement corrosion, is well captured. Coupling reinforcement corrosion with sustained load significantly increases the damage level in RC beams, particularly for those subjected to a high sustained load. The whole damage evolution process of concrete cracking due to corrosion expansion under the coupling effect of sustained loading and environment can be simulated, thus providing a reference for the durability evaluation, life prediction, and numerical simulation of concrete structure

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