Let's say there is this a very large industrial-era quadruped machine, somewhere on the order of magnitude of the Bagger 288. Construction is probably similar the Eiffel Tower. For more scale reference points, it's legs have enough throw to at least clear a 4 story building, and it's feet can fit between the buildings of an average-to-wide street.

Let's pretend that this machine is possible in this world (I may ask further questions regarding this) and that it it's existence is somehow justified.

As it takes a step onto the street...

  1. How much damage does it do via impact? The people in the city can put up with routinely filling in a shallow crater the street and re-laying some cobblestone pavers in its wake, maybe some other minor repairs, but not much more.

  2. Would the ground "shake" or bounce like in a cartoon/movie in proximity to the impact? Enough to cause a bit of a nuisance, maybe free some produce from their stands, or cause some people to lose a bit of balance?

  3. Loosely, what is the radius/drop off of these effects?

  4. Out of curiosity, if the ground wouldn't bounce or shake, is that possible at all? How big (roughly) would my walker need to be?

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    $\begingroup$ Too many questions and not enough information. Are you aware that solid rock and loose ground behave differently when loaded? $\endgroup$ – L.Dutch - Reinstate Monica Nov 29 '17 at 4:05
  • $\begingroup$ @L.Dutch I'll scrap 3 & 4 if it helps shrink the scope. And I'd imagine they would respond differently - but if I knew how why would I ask this question? Shouldn't part of a good answer include ground composition if it is indeed a factor? Also I figured an industrial era cobblestone street was at least a starting point there. $\endgroup$ – plast1k Nov 29 '17 at 4:10
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    $\begingroup$ Would the ground shake? Certainly. How much damage would it do? Quality of construction, nature of ground beneath the building, nature of ground beneath the step, nature of gournd between step and building. Has it been raining? Has it been snowing? What's the distance between the two (is the building in a seismic shadow)? And that's just off the top of my head. Easy answer: such a machine's movement through a populated area would be devestating; otherwise, the question is too broad. $\endgroup$ – JBH Nov 29 '17 at 5:18
  • $\begingroup$ Pounding a stake into the ground with a 12 lb sledgehammer shakes the ground. $\endgroup$ – JDługosz Nov 29 '17 at 5:32
  • $\begingroup$ I've gotta ask and I apologize for doing so, but were you thinking of Will Smith's steampunk tragedy Wild Wild West when you wrote your question? $\endgroup$ – JBH Nov 29 '17 at 5:44

It's really not possible to give hard & fast answers, but some thoughts.

1) Damage depends on the strength of the surface, and how hard the legs come down. Compare to a person walking on concrete, dirt or muddy ground, and stepping gently vs stamping their feet.

2 & 3) The ground doesn't actually bounce like in a cartoon. It just transmits the vibration. You can feel the vibrations from say large tracked equipment like a D-9 Cat for a hundred feet (30 m) or so.

4) To actually cause the ground to visibly move, you'd need something on the order of a largish earthquake.

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As for 2 and 3, consider what a train does. A single car weighs nowhere near as much as 13,500 tons, yet repeatedly(effectively, since each car is the same force as repeatedly dropping the same one) dropping an inch (due to track misalignment) can be felt for 5 miles and buildings near tracks can be felt to sway significant amounts, and must be designed to withstand the vibration.

If we assume each leg is roughly 3 train cars in weight, I definitely don't want to live next to it when it is lowered at any speed from a height above the largest buildings.

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Your main concerns would be impact and sinking. The speed of impact of the "foot" hitting the ground would determine the strength of any tremors. After determining if your machine would cause an earthquake with each step, you would determine what terrains would be able to support it.

To do this, divide the weight of your machine by the surface area of the bottoms of the minimum number of feet "on the ground" during your walk-cycle. (If you want more than one foot in the air at a time, hexapodal walkers are more stable and can move half their legs at a time.)

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