The Tunnel and Retaining Walls are all KS Laser Cut Products. They are all MDF and available off the shelf. Although I did modify some parts to suit my needs, especially on the tunnel.
After forming the parts with PVA, I then ensured all parts slotted together on the backscene as required.
I painted all parts with Railmatch Enamel as required. I use at least four different colours for the bricks. After drying overnight, I mixed up some runny Polyfilla and forced it between the bricks to form the mortar. After leaving to dry well, I wiped off all the unwanted Polyfilla and then coated the whole area with Coloron Wood Dye. This dries very quickly and the final coating was Matt Varnish to seal the whole process.
I have now also added a very fine mist of grime overall and a little extra around bases of structures that are at track level. All that is needed to the Walls and Tunnel now is blending with the surrounding areas after they have been weathered.