subsoil [ˈsʌbˌsɔɪl]

例句:

• Earthworms burrow deep into the subsoil.
  蚯蚓深深地钻进底土.
  来自《简明英汉词典》
• Some movement in the building will occur as It'settles into the subsoil.
  楼房沉到下层土时,楼里就会有动静.
  
• They embedded the pilings deep into the subsoil.
  他们把桩深深打进地基下的土中.
  
• The soil consists of a chalk subsoil, topped by a covering of rubble that is made up of sand, lignite, marl, loam and clay.
  来自WSJ
• It certainly has its roots in the subsoil of the London Literary World and a family connection with the Man Booker.
  来自THETIMES