Effects of Ballast Degradation on Permanent Deformation Behavior From Large-Scale Triaxial Tests

2014 ◽  
Author(s):  
Yu Qian ◽  
Erol Tutumluer ◽  
Youssef M. A. Hashash ◽  
Jamshid Ghaboussi
Keyword(s):  
Los Angeles ◽  
Large Scale ◽  
Fine Particles ◽  
Coal Dust ◽  
Permanent Deformation ◽  
Triaxial Tests ◽  
Los Angeles Abrasion ◽  
Aggregate Breakdown ◽  
Fouled Ballast ◽  
Repeated Load

Consisting of large sized aggregate particles with uniform size distribution, ballast is an essential component of the track substructure to facilitate load distribution and drainage. As freight tonnage accumulates with traffic, ballast will get fouled increasingly due to either aggregate breakdown and degradation or contamination by other materials such as coal dust and subgrade soil intrusion. Fouling affects shear strength and load carrying ability of ballast layer especially under wet conditions. According to Selig and Waters [1], ballast fouling is often due to aggregate degradation, which covers up to 76% of all the fouling cases. To investigate the effects of ballast aggregate breakdown and degradation on the mechanical behavior of fouled ballast, a series of Los Angeles abrasion tests were performed in this study to generate fouled ballast materials caused by particle breakage and abrasion under a well-controlled laboratory environment. The change of particle shape properties during the Los Angeles abrasion tests was quantified and studied through image analysis technology. Large-scale triaxial tests were performed on specimens of new ballast, degraded ballast coarse particle fraction (without fines), and full gradation of degraded ballast (with fines) under repeated load application using a triaxial test device recently developed at the University of Illinois specifically for ballast size aggregate materials. The large-scale triaxial results indicated that the specimen having those degraded coarse particles yielded higher permanent deformation trends from repeated load triaxial testing when compared to the specimen with the new ballast gradation. As expected, the highest permanent deformation was obtained from the degraded ballast specimen having fine particles and the Fouling Index (FI) value of approximately 40.

Moisture Effects on Degraded Ballast Shear Strength Behavior

2016 ◽  
Author(s):  
Yu Qian ◽  
Debakanta Mishra ◽  
Erol Tutumluer ◽  
Youssef M. A. Hashash ◽  
Jamshid Ghaboussi
Keyword(s):  
Shear Strength ◽  
Los Angeles ◽  
Large Scale ◽  
Coal Dust ◽  
Axial Strain ◽  
Dust Collection ◽  
Uniform Size ◽  
Classical Text ◽  
Fouled Ballast ◽  
Strength Behavior

Ballast consisting of large sized aggregate particles with uniform size distribution is an essential component of the track substructure, to facilitate load distribution and drainage. As freight tonnage accumulates with traffic, ballast will accumulate an increasing percentage of fines due to either aggregate breakdown or outside contamination such as subgrade soil intrusion and coal dust collection. According to the classical text by Selig and Waters [1], ballast degradation from traffic involves up to 76% of all fouling cases; voids will be occupied by fines from the bottom of ballast layer gradually causing ballast clogging and losing its drainage ability. When moisture is trapped within ballast, especially fouled ballast, ballast layer stability is compromised. In the recent studies at the University of Illinois, the focus has been to evaluate behavior of fouled ballast due to aggregate degradation using large scale triaxial testing. To investigate the effects of moisture on degraded ballast, fouled ballast was generated in the laboratory through controlled Los Angeles (LA) abrasion tests intended to mimic aggregate abrasion and breakdown and generate fouled ballast at compositions similar to those observed in the field due to repeated train loadings. Triaxial shear strength tests were performed on the fouled ballast at different moisture contents. Important findings of this preliminary study on characterizing wet fouled ballast are presented in this paper. Moisture was found to have a significant effect on the fouled ballast strength behavior. Adding a small amount of 3% moisture (by weight of particles smaller than 3/8 in. size or smaller than 9.5 mm) caused test specimens to indicate approximately 50% decrease in shear strength of the dry fouled ballast. Wet fouled ballast samples peaked at significantly lower maximum deviator stress values at relatively smaller axial strains and remained at these low levels as the axial strain was increased.

Repeated compressive loading of a sand

1979 ◽  
Vol 16 (4) ◽  
pp. 798-802 ◽  
Author(s):  
P. N. Gaskin ◽  
G. P. Raymond ◽  
F. Y. Addo-Abedi ◽  
J. S. Lau
Keyword(s):  
Threshold Stress ◽  
Resilient Modulus ◽  
Permanent Deformation ◽  
Compressive Loading ◽  
Triaxial Tests ◽  
Failure Strength ◽  
Stress Cycles ◽  
Repeated Load ◽  
Static Failure

Twelve repeated load drained triaxial tests to at least 105 cycles on a sand are reported. A threshold stress of about 50% of the static failure strength was found. Below the threshold stress, the permanent deformation and resilient modulus reached constant values. Above the threshold stress, the permanent deformation began to increase rapidly and the resilient modulus to decrease as the number of stress cycles increased. The importance of keeping the traffic stress in the pavement below the threshold stress is outlined.

Resilient and permanent deformation of unsaturated unbound granular materials under cyclic loading by the large-scale triaxial tests

2020 ◽  
Vol 15 (12) ◽  
pp. 3343-3356
Author(s):  
Chuan Gu ◽  
Yun Zhan ◽  
Jun Wang ◽  
Yuanqiang Cai ◽  
Zhigang Cao ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Granular Materials ◽  
Large Scale ◽  
Permanent Deformation ◽  
Triaxial Tests ◽  
Unbound Granular Materials

Repeated-load response of aggregates in relation to track quality index

1994 ◽  
Vol 31 (4) ◽  
pp. 547-554 ◽  
Author(s):  
Gerald P. Raymond ◽  
Richard J. Bathurst
Keyword(s):  
Large Scale ◽  
Railway Track ◽  
Triaxial Tests ◽  
Repeated Loading ◽  
Published Data ◽  
Load Response ◽  
Trade Offs ◽  
Aggregate Index ◽  
Repeated Load ◽  
Track Quality

Track quality rating systems are briefly introduced as a background for undertaking a study of the repeated-load response of ballast aggregates. The results from a number of different laboratory investigations are reviewed and this data interpreted in terms of track quality behaviour. The paper reviews selected results from repeated-load triaxial tests used to investigate the repeated-loading response of different granular railway ballasts at stress levels comparable with those below North America heavy freight axle loads. These results are used to establish an aggregate index to predict deformation and breakdown of ballast under repeated loading. Large-scale test programs are reviewed that relate aggregate quality to simulated ballasted track formation response using a 0.9 m long by 250 mm wide tie to represent a typical loaded rail seat. The large-scale testing was restricted to one aggregate that was subjected to a range of load levels and artificial subgrade stiffness. Similar related work on coarse, single-sized aggregates recommended for drainage layers in highway pavements is reviewed to illustrate the trade-offs between support compressibility and quality of aggregate defined by the aggregate index value. The laboratory tests and model performance are compared with published data to establish a laboratory performance rating in the form of an aggregate index for prediction of those track quality indices that relate to deformation as a function of aggregate type. Key words : ballast, aggregate, hardness, toughness, railway, track quality.

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