Section 27-675. Classification of soil materials

For  purposes of this
  subchapter,  soil  materials  shall  be  classified  and  identified  in
  accordance  with  table  11-1.  In addition, the following supplementary
  definitions shall apply.
    (a) Rock.
    (1) HARD SOUND  ROCK.  Includes  crystalline  rocks  such  as  Fordham
  geniss,   Ravenswood   geniss,   Palisades  diabase,  Manhattan  schist.
  Charateristics are: The rock rings when struck with pick  or  bar;  does
  not disintegrate after exposure to air or water; breaks with sharp fresh
  fracture;  cracks  are  unweathered  and less than one-eighth inch wide,
  generally no closer than three feet apart; core recovery with  a  double
  tube,  diamond  core  barrel is generally eighty-five percent or greater
  for each five foot run.
    (2) MEDIUM HARD ROCK. Includes crystalline rocks of paragraph  one  of
  this  subdivision,  plus  Inwood  marble and serpentine. Characteristics
  are: all those listed in paragraph one of this subdivision, except  that
  cracks  may  be  one-quarter inch wide and slightly weathered, generally
  spaced no closer than two feet apart; core recovery with a double  tube,
  diamond  core barrel is generally fifty percent or greater for each five
  foot run.
    (3) INTERMEDIATE ROCK. Includes rocks of paragraphs  one  and  two  of
  this  subdivision,  plus  cemented  shales  and  sandstone of the Newark
  formation.  Characteristics are: the rock gives dull sound  when  struck
  with  pick or bar; does not disintegrate after exposure to air or water;
  broken pieces may show weathered  surfaces;  may  contain  fracture  and
  weathered  zones  up  to one inch wide spaced as close as one foot; core
  recovery  with  a  double  tube,  diamond  core  barrel   is   generally
  thirty-five per cent or greater for each five foot run.
    (4) SOFT ROCK. Includes rocks of paragraphs one, two and three of this
  subdivision in partially weathered condition, plus uncemented shales and
  sandstones.  Characteristics  are: rock may soften on exposure to air or
  water; may contain throughly weathered zones up to three inches wide but
  filled with stiff soil; core recovery with a double tube,  diamond  core
  barrel  is  less  than  thirty-five  percent for each five foot run, but
  standard penetration resistance in soil  sampling  is  more  than  fifty
  blows  per  foot. Where core recoveries are less than twenty percent and
  the material is to be used for bearing, a minimum three inches  diameter
  core  shall  be recovered and the material recovered shall be classified
  in accordance with table 11-1.
    (b) Special soil types.
    (1) FINE SAND. Soils of group SM, containing more than  fifty  percent
  (by weight) of particles passing a number sixty mesh sieve.
    (2)  HARDPAN.  Soils  of  groups  GM,  GC,  and SW, generally directly
  overlying rock, and which are sufficiently cemented to be  difficult  to
  remove by picking.
    (3) CLAY SOILS. Soils of each group SC, CL, and CH shall be classified
  according to consistency as hard, medium, or soft in accordance with the
  following:
    a.  Hard clay. A clay requiring picking for removal, a fresh sample of
  which cannot be molded by pressure of the fingers.
    b. Medium clay. A clay that can be removed by spading, a fresh  sample
  of which can be molded by a substantial pressure of the fingers.
    c.  Soft  clay.  A  clay,  a  fresh sample of which can be molded with
  slight pressure of the fingers.
    (4) SILT SOILS. Soils of each group ML and MH shall be  classified  as
  dense, medium, or loose depending on relative difficulties of removal as
  described  for  hard,  medium, and soft clays in paragraph three of this
  subdivision.

    (5) VARVED SILT. A natural soil deposit consisting of alternating thin
  layers of silt, clay, and sand in which  the  silt  or  silt  plus  sand
  layers predominate.