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In this video, at the 6:25 mark, you can see a truck drive in front of the crawler, spraying water on the gravel ahead of the treads. Why did they do this?

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    $\begingroup$ Drifting is easier on a slippery surface. $\endgroup$ – ceejayoz Jun 26 at 20:11
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According to https://www.popularmechanics.com/space/rockets/a15777930/launching-to-space-at-a-crawl/
it is to reduce dust created as the crawler crushes some of the "Alabama River Rock".

Photo showing the crushed rock behind the crawler. enter image description here (Source - Organic Marble)

Addendum:
According to the documentary 'When We Were Apollo', the gravel was not part of the original design, but added as a sacrificial bearing surface to stop damage that was occurring to the internal bearings. (Which raises the question: is it raked after use, and periodically replaced?)

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    $\begingroup$ Is "reduce dust" ever not the reason to spray water on a gravel road? $\endgroup$ – RonJohn Jun 26 at 14:26
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    $\begingroup$ @RonJohn, perhaps "prevent sparking" could be a reason, but in this case the specific type of rock was chosen to prevent sparking. Don't know where in the world sparking on a gravel road might happen. $\endgroup$ – NeutronStar Jun 26 at 17:49
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    $\begingroup$ This is a good reminder that this crawler is insanely heavy. It is listed as weighing 6 million pounds (~2.7 million kgs) $\endgroup$ – Kevin Wells Jun 26 at 18:01
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    $\begingroup$ @NeutronStar quartz is piezoelectric and produces electric sparks when quartz pebbles are rubbed/banged together. In some places quartz is a common component of gravel. $\endgroup$ – Skyler Jun 26 at 18:16
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    $\begingroup$ 2,721 t (6,000,000 lb) is the curb weight of the crawler with all tanks filled to the top but no payload. The lifting capacity was increased from 5,400,000 to 8,200,000 kg (12,000,000 to 18,000,000 lb). So a total weight including payload may be up to 10,921,000 kg or 24,000,000 lb. Ground pressure will be much more 14.6 bar, I calculated 59 bar, that is four times the pressure of the crawler alone with no payload. $\endgroup$ – Uwe Jun 28 at 10:53

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