scope:

Introduction

This Track Work Instruction gives an understanding of how a track blanket is designed.

A track blanket is a layer of material including a membrane placed under the ballast in order to prevent water, slurry or clay from pumping up into the ballast and prevent ballast damaging a weak formation, but at the same time allowing the surface water to drain away.

A blanket is usually required in circumstances where the formation has failed, causing the ballast to become contaminated thus making it impossible to pack the track adequately - with consequent loss of top and line.

See also the separate instruction:

TWI 3B002 How to decide on ballast depth

TWI 3B018 How (& when) to use geotextile