The Collaborative International Dictionary of English v.0.48:

muck pile \muck" pile`\ (m[u^]k" p[imac]l`), n.
   1. (Construction) The broken material at the face of a tunnel
      being bored, after being crushed by blasting.
      [RDH]

   2. (Mining) Muck[5] that has been placed in a spoil area.
      [RDH]

The Collaborative International Dictionary of English v.0.48:

Muck \Muck\, n. [Icel. myki; akin to D. m["o]g. Cf. Midden.]
   1. Dung in a moist state; manure. --Bacon.
      [1913 Webster]

   2. Vegetable mold mixed with earth, as found in low, damp
      places and swamps.
      [1913 Webster]

   3. Anything filthy or vile. --Spenser.
      [1913 Webster]

   4. Money; -- in contempt.
      [1913 Webster]

            The fatal muck we quarreled for.      --Beau. & Fl.
      [1913 Webster]

   5. (Mining) The unwanted material, especially rock or soil,
      that must be excavated in order to reach the valuable ore;
      also, the unwanted material after being excavated or
      crushed by blasting, or after being removed to a waste
      pile. In the latter sense, also called a muck pile.
      [RDH]

   Muck bar, bar iron which has been through the rolls only
      once.

   Muck iron, crude puddled iron ready for the squeezer or
      rollers. --Knight.

   muck pile see muck pile in the vocabulary.
      [1913 Webster +RDH]