Recently, there's been a buzz in the railway industry. The passenger volume of the national railway in the first three quarters broke the record, heading towards the highest level in the same period in history. People are crowding onto the trains one after another, and the trains are moving forward one after another. The excitement is all up top, yet I keep wanting to look down.
When the wheel rolls over the steel rail, the force is not directly applied into the ground, but is gradually released layer by layer. The steel rail presses down on the cushion layer, which in turn presses down on the ballast. At the very bottom, there is that black wooden piece.
How can a piece of wood catch it? It relies on its softness. This is not just a polite remark. No matter how heavy the train is, and how soft a piece of pine is, they just don't seem to match. Yet, it is precisely this soft piece of wood that manages to catch the relentless momentum of the train.
When it comes to absorbing force, the key is "yielding". When the wheel presses down, the wood yields a bit first, sinks down, catches the momentum of the impact, and then gradually returns it. You may see it remain motionless, but in fact, every time it passes through, it secretly bends a little and then straightens up again. Hard objects cannot do this. If you put a steel plate underneath, the force will bounce back intact. The steel rail will support the wheel, and the wheel will support the car body, causing both ends to suffer. Soft wood chews up the force, swallows it down, and then spits out something much gentler.
It's similar to stepping on mud. When you step on a hard concrete floor, your sole feels numb. That numbness is exactly what the mud saves you from. The wood is like that layer of mud that relieves the pressure for you.
Softness is acceptable, but it cannot be excessive. If it's too soft, a pit will form under every pressure, and the rail will collapse. The softness of the sleeper is measured, allowing it to give yet withstand. This measure is inherent in pine wood. Its long fibers are tough and resilient, and cannot be scattered under pressure. If you repeatedly bend a fresh willow branch, it will not break, because the fibers can stretch but not break, and the strength is distributed along the fibers. If you use a dry stick, it will break at once because it lacks that toughness. The sleeper requires the toughness of pine wood.
Merely having resilience is not enough. Wood is susceptible to moisture and insects, and if left untreated, it will deteriorate in just two years. Therefore, before being finished, it is first soaked in oil, which penetrates into the fiber seams, keeping moisture and insects out. The necessary elasticity is not diminished at all, but rather, a layer of moisture-proof and anti-corrosive base is added. Therefore, it can give way, beautifully, for decades.
When the traffic gets denser, this skill becomes more valuable. One trip a day and dozens of trips a day are two different things. When the number of trips increases, that light work of unloading becomes a tiring task of repeatedly bending and straightening a piece of wood. Wood doesn't fear this, but it fears not being soaked with oil. Once soaked with oil, the fibers of the sleeper are protected both inside and out, making it unbreakable and impervious to soaking. Whether bent a hundred times or just once, its elasticity remains unchanged. This is also why the busier the line, the more they dare not save that little bit of oil money on the sleepers.
The strength of the ties varies in different places. Passenger trains running on main lines have thin wheels and run fast, exerting a sharp and brittle force that chisels away one after another. The special lines in mining areas are used for heavy-haul coal trains, which run slowly but have a substantial weight, exerting a slow and steady downward pressure. The ties have to be supported with their entire body, and each support can last for a long stretch. Bridges are even more complicated. The wind blows, the beams tremble, and the wheels bounce up when they reach the bridge. The ties have to withstand three types of forces there. Different places have different tasks, but one thing is common: they all rely on that soft wood to firmly support the forces. The soft wood can withstand all these forces because its softness is protected by oil immersion, not a lack of strength.
So don't underestimate that black log. The more people and cars jostle above, the more it shows how sturdily the log holds its ground below. While the bustle is above, stability is its due. Train after train passes overhead, and it catches each one, as if nothing's amiss, then waits for the next.
This sleeper has never been about showing off. What it wants is to be able to catch the next train with stability and strength.
