The Effect of Degree of Fouling of Coal Dust on Railway Foundation Stability
Railway ballasts and large aggregates can be fouled internally by inter particle weathering and externally by soil pumping and deposition of rail fright particles. The gradual accumulation of soil fines and coal particles on road pavements, rail ballast and sleepers affect the aggregate interlocking properties. Track maintenance and ballast replacement schedule are dependent on the different classification methods used to evaluate the degree of fouling. Uniformly graded large aggregates were fouled with different percentages of residual fines of coal dusts that were prepared at different moisture content (w). The degree of fouling of the coal dust fouled aggregates (CDFA) were classified according to the percentage of fouling (PF) and Relative ballast fouling ratio (RBFR). The interlocking properties of the fouled aggregates were investigated in a large direct shear device and the Intergranular Friction Angles (IFA) were determined. Degree of fouling up to 8% had no effect on the dry density of the aggregate, between 8 and 16% the effect of fouling was marginal, however linear relationship was indicated beyond 16% fouling. The rate of decrease of IFA was found to be dependent on the degree of fouling and moisture content of the coal material. The IFA of the CDFA tend towards the IFA of the wet coal materials as the degree of fouling increase to 20% of the dry mass of the aggregate. 20% fouling represent moderately fouled and fouled conditions in accordance with PF and RBFR fouling classifications respectively. RBFR is based on the inter aggregate void volume occupied by the fouling material and specific gravity of coal. It was found to be more sensitive to the changes in IFA than PF. Regression models of the effect of coal dust fouling on aggregate integranular and interface friction based on IFA, MC, PF and RBFR were formulated and proposed for the development of track maintenance scheme, ballast replacement schedule and standard track inspection routines.
KeywordsAngle of friction Gravels Direct shear strength Interface shear strength Fouling Railway ballasts Percentage of fouling (PF) and relative ballast fouling ratio (RBFR) Shear box apparatus Optimum moisture content Maximum dry unit weight Coal dust
The field work and fabrication of shear box was funded by Rand Coal Engineering PLc. The author is grateful.
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