Section 27-713. Caisson piles

(a) Description. Caisson piles shall denote
  concrete filled pipe piles that are  socketed  into  bedrocks  of  class
  1-65, 2-65 or 3-65 and constructed with steel cores.
    (b)  Materials.  Pipe  or  shell  and  concrete  shall  conform to the
  requirements for concrete filled pipe piles,  except  that  the  minimum
  compressive  strength  of  the  concrete at the age of twenty-eight days
  shall be thirty-five hundred psi.  Steel  cores  shall  conform  to  the
  requirements for steel H piles. Reinforcing steel cages shall be covered
  with at least one and one-half inches of concrete.
    (c)  Design  of  rock  socket.  The design of the rock socket shall be
  predicated on the sum of the allowable bearing pressure on the bottom of
  the socket plus bond along  the  sides  of  the  socket.  The  allowable
  bearing  pressure on the surface of the rock at the bottom of the socket
  shall be as established in  section  27-678  of  article  four  of  this
  subchapter  increased  for  embedment  in  accordance with note eight of
  table 11-2, provided that the strength  of  the  concrete  fill  in  the
  socket,  computed  as  0.45f'c is of comparable magnitude. The allowable
  bond stress between the concrete and the sides of the  socket  shall  be
  taken  as  two hundred psi. The provisions of subdivision (c) of section
  27-700 of article eight  of  this  subchapter  relative  to  penetration
  resistance shall not apply.
    (d) Spacing and minimum dimensions.
    (1)  Minimum  diameter  of  a  caisson shall be eighteen inches with a
  minimum shell thickness of three-eighths of an inch.  Minimum  depth  of
  the rock socket shall be equal to the diameter of the pipe.
    (2) The center-to-center spacing of caissons shall be at least two and
  one-half times the outside diameter of the shell.
    (e) Installation.
    (1)  The  steel  shell  shall  be  installed  through  overburden, the
  material within the shell shall be removed, and the shell seated in  the
  rock  sufficiently  to stop the inflow of soil. Where required to extend
  the shells, splices are to be welded.  A  suitable  steel  driving  shoe
  shall be welded to the bottom of each caisson.
    (2)  A  socket shall then be drilled in the rock to the required depth
  and shall be approximately of the same diameter as the  inside  diameter
  of  the  shell. Before placement of concrete, the socket and shell shall
  be thoroughly cleaned and the rock inspected to verify that the rock  is
  of  the  class  on  which the design has been predicated, or of a better
  class.  In case visual inspection cannot be made because of inability to
  unwater the caissons by standard  pumping  methods,  drilling  logs  and
  screenings from the rock drilling operation may be utilized to determine
  the class of rock in the socket.
    (3)  Where more than one section of steel core is required, the mating
  ends of the sections shall be spliced so  as  to  safely  withstand  the
  handling  stresses  to  which  they  may be subjected. The ends shall be
  milled or field ground to  insure  contact.  The  steel  core  shall  be
  centrally installed in the caisson before grouting and concreting, shall
  not  be  more  than one inch above the rock at the bottom of the socket,
  and shall be full length of the caisson or extend a sufficient  distance
  up  into  the  shaft  to  transmit  the  load in the steel core into the
  concrete of the caisson. A minimum-weight thirty-six  pounds  stub  core
  beam  shall  be installed in the socket for caissons not requiring steel
  cores in order to lock the caissons into the rock. In these  cases,  the
  length of the steel cores shall be twice the socket depth.
    (4) Concrete and grout shall be placed so that it completely fills the
  shell,  the  socket, and the space between the steel core and shell, and
  in a manner that will preclude separation of the ingredients.

    (5) If the leakage of water into the caisson  is  minor,  the  caisson
  shall  be  pumped out and one cubic yard of grout shall be placed in the
  caissons and then the balance of the concrete installed. If the  leakage
  of  water  makes it inadvisable to attempt to place concrete in the dry,
  the  shell shall be filled to its top with clean water, and the concrete
  placed by the tremie method to the top of the caisson in one  continuous
  operation  or  by  using  a  seal  of  grout of the same strength as the
  specified concrete. The grout seal, if used, shall be deposited by means
  of a grout pipe to an elevation of at least three feet above the cutting
  edge, and after a sufficient time has elapsed to allow the grout to set,
  the caisson shall be pumped dry and  the  remaining  space  filled  with
  concrete.