Trackbed liner and related methods

A trackbed liner of a railway trackbed comprising ballast and a track, the trackbed liner comprising:

• an upper support layer;
• a lower support layer;
• and
• at least one filtration layer located between the upper and lower support layers, the filtration layer comprising a material that is water vapour permeable and that is liquid water impermeable under a pressure load imposed on the filtration layer by the railway trackbed until it becomes permeable to liquid passing upwardly through the filtration layer upon a pressure;
• load imposed by a vehicle of at least about 10 kN/m2 acting on the trackbed, and wherein the filtration layer restricts the passage of solids materials, so as to restrict pumping erosion of material located beneath the liner.

A method of renovating a trackbed comprising ballast contaminated with clay particles, the method comprising the steps of:

• removing contaminated ballast;
• following removal of contaminated ballast, laying a trackbed liner having:
• an upper support layer, a lower support layer, and at least one filtration layer located between the upper and lower support layers, the filtration layer comprising a material having a plurality of pores and which is impermeable to liquid water;
• and
• locating fresh ballast on an upper surface of the trackbed liner to provide a renovated trackbed;
• wherein the trackbed liner is impermeable to liquid water under a pressure load imposed on the liner by a railway trackbed that includes a track and ballast until the trackbed liner becomes permeable to liquid passing upwardly through the filtration layer upon a pressure load imposed by a vehicle of at least about 10 kN/m2 acting on the trackbed, and wherein the filtration layer restricts the passage of solids materials, so as to restrict pumping erosion of material located beneath the liner.

A method of laying a track comprising the steps of:

• laying a trackbed liner on a subgrade, wherein the liner has an upper support layer, a lower support layer, and at least one filtration layer located between the upper and lower support layers, the filtration layer comprising a material having a plurality of pores and which is impermeable to liquid water based upon a pressure load imposed upon the filtration layer;
• following laying of the liner, locating ballast on an upper surface of the liner to provide a trackbed;
• and
• laying a track on the trackbed;
• wherein the filtration layer is impermeable to liquid water under a pressure load imposed on the filtration layer by the trackbed until it becomes permeable to liquid water passing upwardly through the filtration layer upon a pressure load of a vehicle of at least about 10 kN/m2 acting on the trackbed, and wherein the liner filtration layer restricts the passage of solids materials, so as to restrict pumping erosion of the subgrade.

A method of displacing water from a trackbed in use during passage of a vehicle along a track laid on the trackbed, the method comprising the steps of:

• providing a trackbed liner above a subgrade and beneath ballast of the trackbed upon which the track is located, the liner comprising:
• an upper support layer;
• a lower support layer;
• and at least one filtration layer located between the upper and lower support layers, the filtration layer comprising a material having a plurality of pores and which is impermeable to liquid water based upon a pressure load imposed upon the filtration layer;
• wherein the filtration layer is impermeable to liquid water under a pressure load imposed on the filtration layer by the trackbed until it becomes permeable to liquid water passing upwardly through the filtration layer upon a pressure load of a vehicle of at least about 10 kN/m2 acting on the trackbed, and wherein the filtration layer restricts the passage of solids materials from the subgrade, so as to restrict pumping erosion of the subgrade.

A method of providing a trackbed liner, the method comprising the steps of:

• providing upper and lower support layers;
• providing at least one filtration layer, said filtration layer being of a material having a plurality of pores which are dimensioned so that the filtration layer is impermeable to liquid water under a pressure load imposed on the filtration layer by a railway trackbed comprising a track and ballast overlying the filtration layer until it becomes permeable to liquid water passing upwardly through the filtration layer upon a pressure load of a vehicle of at least about 10 kN/m2 acting on the trackbed, and wherein the filtration layer restricts the passage of solids materials, so as to restrict pumping erosion of material located beneath the liner;
• and
• locating said filtration layer between the upper and lower support layers.