ballast blue metal bolts gravel parallel rail rails rust secure shine sleepers stable tracks transport triple bucket deep dig digger Dirt earth equipment excavator excavators ground grounded iron metal rusty scoop abstact boat colors decay nails pebbles rocks rotten sand sea ship sky textures water background bolt corroded corrosion engineering grunge grungy line old plate rivet row series construction drip dripping drips paint rusting splatter splatters surface texture urban abstract design elevator gear mechanics reduction steel teeth tooth winch break broken decommission harbour HDR Nyberg scrap sub wreck