I have periodic dreams containing quicksand, including some over these past weeks.
In one dream, I was walking along a shoreline, water to my left, and at the end of the beach, it narrowed, and was littered with loose chunks/piles of sand, likely fallen from a sandy cliff or embankment to my right. Because it had fallen onto the shore by the water, it easily saturated with water, turning into quicksand, but it was just very shallow, the depth being the height of the pieces that had fallen, perhaps only around 6 to 8 inches at most. But, just a little ways further down the shoreline, the area below the embankment widened, and instead of a shoreline covered with loosely fallen sand, it was flat ground with more of a darker type of soil, almost peaty looking. To my right, away from the shoreline, it seemed as though I remembered that area from another time in my "dream world". There were a few raised circular patches of peaty mud, raised like mud volcanoes, but peaty instead of clay. I leaned over to examine and probe the one farthest from shore with my hand, noticing that it seemed to be very watery with some thicker chunks of peat mud floating in it, not really worth sinking into. I then walked around to the other side between that one, the backside of an adjacent one closer to shore, and the embankment that led back towards the water, and suddenly found that the ground beneath my feet, between the outside of those mud holes and the embankment, began to quake and give way, causing me to begin sinking. It looked like peat, but gave way like quicksand. But, no sooner had I started to sink, when I woke up.
Several nights later, I was having another dream, where I was walking around some buildings somewhere that seemed rural, when all of a sudden, I became "lucid"!
I seemed to recognize the area, and headed straight towards a spot behind (to the left of) some old dark wooden building/structure, and there before me, were three mudpits, which looked like clay. I looked at them again, and one to my right looked slightly dried on the very top surface. Because I was "lucid" this time, I remembered how in so many of my dreams I had encountered mud and would avoid it because of fear of being caught, since someone was always around, or I would be someplace near residences. But, this time I was going to do it!
I jumped into one (I think I meant to jump into the one to my right, but wound up in the one to my left), and sunk right down to my waist, the soft clay feeling soooooo wonderful!
I tried to struggle to sink deeper, and because I was lucid, I tried using my imagination to make myself sink deeper, picturing it in my mind. But, my "feelings" from the experience started to get above a certain threshold, causing me to wake up.
The most recent one, just the other night, I had a shallow rectangular pit dug (perhaps only a foot deep, 4 feet wide and 7 feet long, but just rough guesses), prepared for mixing sand and water into it, but I never got to that point (or I did it partially previously, but then it was undone and I wasn't able to do it over again). There were other bits of things concerning walking around muddy areas, but it was more like very shallow mud in a field, and nothing deep.
It's probably for the best though, as my wife tells me I talk in my sleep. 
