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RISS 인기검색어
- 검색키워드
- 저자 : Yoshiaki Kikuchi (검색결과 3 건)
- 무료
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- 유료
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Evaluation of Area- and Volume-based Gradations of Sand-Crushed Stone Mixture by 2D Images
Janaka J. Kumara,Kimitoshi Hayano,Yoshiaki Kikuchi 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.3
Ballast fouling is a challenging issue in ballasted railway tracks due to frequent maintenance works. At present, sieve analysis is conducted to obtain the gradation curve of fresh and fouled ballasts at laboratories. The investigation time is quite long since it requires a sampling. The information obtained from sieve analysis are not sufficient to propose appropriate maintenance plans since it does not produce shape characteristics of the particles properly. In this research, area- and volume-based gradation curves of fresh and fouled ballasts, simulated by laboratory-scale particles, were studied using an image analysis method. A simple method was proposed to obtain the volume-based gradation curve by 2D images. This method can be practised as an in-situ test method since it needs only a camera and a computer. The results suggest that the grain size should be defined appropriately according to the shape assigned for the particles. It was also found that area-based gradation curve produced by an ellipse shape for the crushed stone particles match sieve analysis closer than circle and rectangle shapes. The results also indicate that area-based gradation match sieve analysis closer than number- and volume-based gradations for the crushed stone particles. It was also found that the volume-based gradation curves evaluated by parallel and diagonal passing overestimate and underestimate respectively its grain size compared to sieve analysis. The gradation curve evaluated by an equivalent passing with a grain size correction factor match the sieve analysis for crushed stone, sand and sand-crushed stone samples. The image analysis results also indicate that the crushed stone particles are more angular than sand particles, which is important in numerical analysis to simulate fresh and fouled ballasts.
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Deformation Behaviour of Gap-graded Fouled Ballast Evaluated by a 3D Discrete Element Method
Janaka J. Kumara,Kimitoshi Hayano,Yoshiaki Kikuchi 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.6
The ballast fouling has been identified as a challenging issue in ballasted railway tracks due to huge maintenance costs. In this research, the deformation characteristics of gap-graded fouled ballast were studied from laboratory experiments and a Discrete Element Method (DEM). The fouled ballasts were prepared with different values of a fouling index, FIp. After the packing behaviour of fouled ballasts was studied by density tests, the stress-strain behaviour of them was studied from triaxial compression tests under both dense and loose states. It was found that the void ratio decreases with FIp up to 50%, then it increases with FIp. The results also indicate that the strain-hardening behaviour of ballast is weakened when fouled by FIp ≥ 30%. The DEM simulation by clump particles produce a similar stress-strain behaviour as the laboratory specimens than their spherical counterparts. The results also reveal that the dilation behaviour of ballast is deteriorated significantly when fouled by FIp > 50%. The peak frictional angle indicates that the strength properties of ballast are deteriorated significantly when fouled by FIp ≥ 30%. Therefore, we recommend that fouled ballast should be treated by a maintenance application when ballast is fouled by FIp > 30%.
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Effects of pile geometry on bearing capacity of open-ended piles driven into sands
Kumara, Janaka J.,Kurashina, Takashi,Kikuchi, Yoshiaki Techno-Press 2016 Geomechanics & engineering Vol.11 No.3
Bearing capacity of open-ended piles depends largely on inner frictional resistance, which is influenced by the degree of soil plugging. While a fully-plugged open-ended pile produces a bearing capacity similar to a closed-ended pile, fully coring (or unplugged) pile produces a much smaller bearing capacity. In general, open-ended piles are driven under partially-plugged mode. The formation of soil plug may depend on many factors, including wall thickness at the pile tip (or inner pile diameter), sleeve height of the thickened wall at the pile tip and relative density. In this paper, we studied the effects of wall thickness at the pile base and sleeve height of the thickened wall at the pile tip on bearing capacity using laboratory model tests. The tests were conducted on a medium dense sandy ground. The model piles with different tip thicknesses and sleeve heights of thickened wall at the pile tip were tested. The results were also discussed using the incremental filling ratio and plug length ratio, which are generally used to describe the degree of soil plugging. The results showed that the bearing capacity increases with tip thickness. The bearing capacity of piles of smaller sleeve length (e.g., ${\leq}1D$; D is pile outer diameter) was found to be dependent on the sleeve length, while it is independent on the sleeve length of greater than a 1D length. We also found that the soil plug height is dependent on wall thickness at the pile base. The results on the incremental filling ratio revealed that the thinner walled piles produce higher degree of soil plugging at greater penetration depths. The results also revealed that the soil plug height is dependent on sleeve length of up to 2D length and independent beyond a 2D length. The piles of a smaller sleeve length (e.g., ${\leq}1D$) produce higher degree of soil plugging at shallow penetration depths while the piles of a larger sleeve length (e.g., ${\geq}2D$) produce higher degree of soil plugging at greater penetration depths.
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