Earth Cache
You will be walking along The Box Vale Tramway. It was built in 1888 to carry coal mined in the Nattai Gorge to the main southern line at Mittagong. The line passes through several cuttings, a tunnel, and it ends at the "incline" by which coal was brought up from the gorge. The Colliery was closed in 1896 and the tramway was abandoned until 1996 when it was opened as a four-and-a-half kilometer bush walking track. Additional information and maps are available from the Visitors Information Centre in Mittagong.
Mobile phone reception should be available on this part of the trail but may not work inside the tunnel.
Angle of Repose
Angle of Repose is a term used to describe the stability of a sloped surface. By definition it is the angle (relative to the horizontal plane) of the steepest stable slope of a pile of material that can be maintained without sliding or slippage.
Landslides
Landslides, or the more technical term “mass wasting”, is the geomorphic process by which soil, regolith, and rock move downslope under the force of gravity. Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to years. When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. The slope material's strength and cohesion and the amount of internal friction between material help maintain the slope's stability and are known collectively as the slope's shear strength. Again, the steepest angle that a slope can maintain without losing its stability is known as its angle of repose. When a slope possesses this angle, its shear strength perfectly counterbalances the force of gravity acting upon it.
The Box Vale Tramway
As you make your way along the Box Vale Tramway you will observe that the geological engineers of the 1880s aimed to work with a 90 degree angle of repose. Today, some 130 years later, we see evidence of mass wasting. For the most part, this mass wasting is the result of weathering and has taken the form of mudslides and topples (with accompanying talus or scree). These violations of the angle of repose obstruct passage in such a way that the Tramway can no longer be used as it was originally intended.
By the time you reach the posted coordinates you're going to discover that the engineers of yesteryear managed to create a cutting with a seemingly impossible 180 degree angle of repose. Of course, I might be exaggerating just the tiniest of little bits. Once a slope and its angle of repose are greater than ninety degrees we use different names to describe them. In the current instance the phenomenon is known as a tunnel.
Anyway, the question that begs asking is: why build a tunnel instead of a cutting? Tunnel cave-ins are the number one disaster in all mining accidents. Why risk a tunnel here? Wouldn't the thundering vibrations of an old steam locomotive increase the chance of collapse? And yet there is no internal supports or shoring of any kind. What did the construction crews of the 1880s know that gave them the confidence to undertake such a mammoth and risky proposition as this huge tunnel? I mean, just look at the amount of mass wasting along the Tramway so far. Why not just blast their way through with another cutting? And yet here before us is a tunnel that has withstood the test of time for 130 years and which is in pretty much the same condition as the day it was built..... or it is? If you look toward the ceiling at the south entrance of the tunnel you will observe a substantial crack!
To claim this cache:
Yes, my apologies. You have to walk this far and answer questions too. So...
Jump in your time machine and travel back to the mid 1880s to the moment just before the Box Vale Tramway was built. Put on your hard hat because you are now the geological engineer responsible for building a passage along which train loads of coal will be transported. You have already cleared a half dozen or more cuttings when you come up against yet another huge obstruction in your path.
1. How are you going to create a route to the other side? Will you tunnel through, dig yet another cutting, or will you devise some other manner of getting past this roadblock?
Hints to help you decide. Examine the surrounding terrain. Do you notice anything that might impact your decision about what to build? Examine the tunnel (something you can do today but could not do in the mid 1880s). Do you notice anything about the walls and ceiling that might influence your decisions?
2. Once you determine your course of action (tunnel, cutting, or something else) how will you proceed to build it? Please provide a brief explanation to justify your decisions.
2a. If you tunnel, consider that dynamite blasting will be the fastest way to clear your path but may weaken and cause faulting in the rock above the ceiling. Also, manual digging with pick and shovel "may" not disturb the surrounding rock but is labor intensive and very slow. If there are any mistakes or slipups, gravity will make its presence felt.
2b. If you create a cutting, what will be a safe angle of repose? Consider the many collapses you saw in the cuttings you walked along on your way to the tunnel.
2c. If you devise an alternate plan, keep in mind that trains must have safe, easy passage through this area.
Optional
3. Predict when you think the tunnel will collapse. You may include your prediction as part of your log.
Please send your answers to me via the geocaching website - e-mail or message. The answers to these questions (except number 3) should not be included in your log. You do not need to wait for a reply from me to log your find.
Beware of falling rocks, trees, and branches. Please be careful.