Abstract
There are many roadbeds which are insufficient of their quality in existing lines and so the occurrence of mud-pumping together with penetrative settlement causes track irregularity. This is why track maintenance labor has increased. Therefore, this paper elucidates the primary factors of ballast penetrating phenomena and made clear the contribution degree of the factors to the formulas of penetrating settlement. To be more specific, the determination of the causes of ballast penetrating settlement is conducted in indoor tests.
Finally, field surveys are made in a broad area to determine the causes of the phenomena and to confirm the formulas of penetrating settlement.
