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RISS 인기검색어
- 검색키워드
- 저자 : Kimitoshi Hayano (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
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Importance of particle shape on stress-strain behaviour of crushed stone-sand mixtures
Kumara, Janaka J.,Hayano, Kimitoshi Techno-Press 2016 Geomechanics & engineering Vol.10 No.4
In ballasted railway tracks, ballast fouling due to finer material intrusion has been identified as a challenging issue in track maintenance works. In this research, deformation characteristics of crushed stone-sand mixtures, simulating fresh and fouled ballasts were studied from laboratory and a 3-D discrete element method (DEM) triaxial compression tests. The DEM simulation was performed using a recently developed DEM approach, named, Yet Another Dynamic Engine (YADE). First, void ratio characteristics of crushed stone-sand mixtures were studied. Then, triaxial compression tests were conducted on specimens with 80 and 50% of relative densities simulating dense and loose states respectively. Initial DEM simulations were conducted using sphere particles. As stress-strain behaviour of crushed stone-sand mixtures evaluated by sphere particles were different from laboratory specimens, in next DEM simulations, the particles were modeled by a clump particle. The clump shape was selected using shape indexes of the actual particles evaluated by an image analysis. It was observed that the packing behaviour of laboratory crushed stone-sand mixtures were matched well with the DEM simulation with clump particles. The results also showed that the strength properties of crushed stone deteriorate when they are mixed by 30% or more of sand, specially under dense state. The results also showed that clump particles give closer stress-strain behaviour to laboratory specimens than sphere particles.
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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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