Section 27-663. Borings

(a) Number. At least one boring shall be made for
  every twenty-five hundred square  feet  of  building  area  or  fraction
  thereof  and, for buildings supported on piling of such type or capacity
  that load tests are required, one boring shall be made for every sixteen
  hundred square feet of building  area  or  fraction  thereof  except  as
  indicated in paragraphs one through three of this subdivision.
    (1)  For one- and two-family dwellings (appurtenant structures such as
  garages,  sheds,  and  porches  shall  be  considered  as  part  of  the
  dwelling):
    a.  Buildings  supported  on footings founded on soil of class 8-65 or
  better--For contiguous groups of four or more  dwellings  at  least  one
  boring  shall  be  made for every four buildings. For isolated dwellings
  and for contiguous groups of two or three dwellings,  the  overall  site
  shall  be  explored  by  at  least  one  boring  or  auger  probing  or,
  alternately, the site of each building shall be explored by one test pit
  carried to a depth of at least eight feet below the level of the  bottom
  of the proposed footings.
    b.  Buildings supported on piles or on footings founded in soil strata
  of class 9-65, or poorer--The site shall be explored  by  at  least  one
  boring  for  every four buildings in contiguous groups or one boring for
  each building in the case of isolated dwellings.
    (2) For buildings having a plan area in excess of ten thousand  square
  feet  and  where  subsurface  conditions  as determined from preliminary
  borings or from borings on neighboring sites consist of uniform deposits
  of materials of class 1-65, 2-65, 3-65, 6-65, 7-65, or 8-65, subject  to
  the approval of the commissioner, the required borings may be reduced to
  one  for  every  five  thousand square feet of building area or fraction
  thereof except where the foundation is to be supported on piles.
    (3) Where foundations are to rest on rock of class 1-65, 2-65, or 3-65
  and such rock is exposed prior to construction over a part or all of the
  area of the buildings, borings will not be required in those areas where
  rock is exposed, and the area (within the limits of the building) of the
  exposed rock surface shall not be included in the area used  to  compute
  the  required number of borings, provided the following requirements are
  met:
    a. The presence of defects or the inclination of bedding planes in the
  rock are of such size and location as to not affect the stability of the
  foundation.
    b. The foundation is designed  for  bearing  pressures  not  exceeding
  those permitted in table 11-2 without increase for embedment.
    (b)  Location.  At  least two-thirds of the required number of borings
  shall be located within the area under the building. Those  outside  the
  area  shall  not  be  more  than twenty-five feet from the limits of the
  building. Borings shall  be  uniformly  distributed  or  distributed  in
  accordance with the loading pattern imposed by the building.
    (c)  Depth.  (1)  Unless  soil  material of class 1-65 through 3-65 is
  encountered at shallower depth, borings shall extend below  the  deepest
  part  of  the excavation as necessary to satisfy the more restrictive of
  the following requirements:
    a. Borings  shall  extend  deep  enough  into  nominally  satisfactory
  bearing  material to establish its character and thickness, but not less
  than the following:
    1. Where the soil material is class 5-65--ten feet.
    2. For one and two family residences, two stories or less in  height--
  fifteen feet.
    3. For other cases-- twenty-five feet.
    b.  Borings  shall  extend  to  the depth at which the vertical stress
  caused by the proposed construction is reduced to ten percent or less of

  the original vertical stress at this depth due  to  the  weight  of  the
  overburden,  except that where strata of soil materials of class 9-65 or
  poorer are encountered within this depth, the  borings  shall  penetrate
  such  strata and be carried to a depth that shows penetration continuous
  of material of class 8-65 or better as required in paragraph a  of  this
  subdivision.
    c.  In  addition  to  the  requirements  of paragraphs a and b of this
  subdivision, at least one boring in every ten thousand  square  feet  of
  building  area,  but  not  less  than  one boring per building, shall be
  carried to a depth of one hundred feet  below  the  curb  for  buildings
  having an average area load exceeding one thousand psf. The average load
  shall  be  computed  as  the sum of all dead loads and live loads of the
  building, divided by the area of the building at ground level.
    (2) Where rock is encountered in borings within the  depths  noted  in
  paragraph  one  the  borings  shall be cored a minimum of five feet into
  rock, or farther where necessary or  required,  to  obtain  at  least  a
  recovery  of thirty-five per cent core from five feet of penetration but
  not to exceed the depth in paragraph one of this  subdivision.  However,
  for foundations supported on piles or drilled-in caissons bearing on the
  rock  and  having  a  capacity  in  excess  of eighty tons per unit, the
  capacity of the rock to support the applied load shall  be  demonstrated
  by increasing the length of coring to ten feet.
    (d) Types.
    (1)  SOIL BORINGS. Soil samples shall be recovered at intervals not to
  exceed five feet and at every change of soil strata. Such samples  shall
  be  recovered using a two inch O.D. split spoon sampler having an inside
  diameter of one and three-eighths inches and a constant  internal  cross
  section. The sampler shall be at least twenty-four inches long and shall
  be  tipped with a heat treated, sharp cutting shoe. It shall be straight
  and sound, with an undistorted cross section.  The  rods  to  which  the
  sampler  is  attached  shall  be  one  inch  extra heavy pipe or one and
  five-eighths O.D. drill rods. The sampling tools shall be driven with  a
  one hundred forty pound hammer having a fall of thirty inches. The blows
  per foot so recorded shall be designated, hereinafter, by the symbol, N.
  The  fall  of  the  hammer shall be a free fall and the energy of impact
  shall not be mitigated by friction of the hoisting  line  on  the  drum,
  friction  of the hammer against its guide, or other similar effects. All
  samples, except those of rock, shall be preserved in air  tight  bottles
  having a capacity of at least eight ounces.
    (2)  ROCK  BORINGS.  Where borings are required to penetrate rock they
  shall be advanced by core drilling, and core samples shall be  recovered
  using  a  double tube core barrel and diamond bits that provide cores at
  least one and three-eighths inches in diameter.
    (e) Data to be reported.  Records  of  all  borings  required  by  the
  provisions  of  subdivision  (a)  of  this  section  shall accompany the
  application for approval of the foundation  plans.  Such  records  shall
  show,  as a minimum, the size of casing and the number of blows per foot
  required to advance the casing (to the depth that casing is  used);  the
  weight of hammer and the distance of fall; a description of the sampler;
  a  description  of  the drill tools and equipment including, where used,
  the size of diamond bits and type of core barrels; the number  of  blows
  required  to  drive  the sampling spoon for each six inches increment of
  penetration; the elevation  of  the  ground  surface  referenced  to  an
  established datum; the location and depth of the boring and its relation
  to  the  proposed  construction;  the  elevations  at which samples were
  taken; the elevations at which core drilling was started and stopped for
  each "run"; the elevations of the boundaries  of  soil  strata;  percent
  recovery for each "run" of core drilling; description of the soil strata

  encountered  and  geological  classification  of  rock drilled (based on
  visual examination  of  cores);  any  particular,  unusual,  or  special
  conditions such as loss of water in the earth and rock strata, boulders,
  cavities,  and  obstructions,  use  of  special type of samplers, traps,
  etc.; and the level of ground water together with a description  of  how
  and  when  the  ground  water  level  was  observed.  All  abandoned  or
  unsuccessful attempts at borings or rock drilling shall be reported.
    (f) Disposition of samples and cores.  Soil  samples  and  rock  cores
  shall  be  retained  in  an  accessible location by the owner, or by the
  party making application for approval of  the  foundation  plans  for  a
  period  of  one  year  after  the  date  of issuance of a certificate of
  occupancy, and shall be available upon reasonable notice for  inspection
  by the commissioner.