Section 27-662
§ 27-662 General. Borings in earth or rock, recovery of samples, tests
of soil samples, load tests, or other investigations or exploratory
procedures shall be performed as necessary for the design and
construction of a safe foundation subject to inspection in accordance
with the requirements of article thirteen of this subchapter.
Section 27-663
§ 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.
Section 27-664
§ 27-664 Test pits. (a) Test pits may be substituted for boring on a
one-for-one basis. All applicable requirements as to depth, numbers of
samples, data to be reported, and disposition of samples shall be
observed, except that the use of sample spoon, recording of driving
resistance, and recovery of rock cores is not required in test pit
investigations, and except as provided in subdivision (b) of this
section.
(b) Test pits for buildings not more than one story in height or for
one or two-family residences not more than two stories in height need
only extend four feet below the deepest part of the excavation for the
construction of footings, or a minimum of four feet when foundation
elements rest on grade pursuant to paragraph four of subdivision (a) of
section 27-658 of article one of this subchapter, provided that such
structures are supported by footings bearing on nominally satisfactory
bearing materials of class 9-65 (except soft clay) soil or better.
Section 27-665
§ 27-665 Boring methods. Borings shall be made by continuous driving
and cleaning out of a pipe casing (including telescoping of smaller
sizes inside of larger casing) except as permitted in subdivisions (a),
(b), and (c) of this section. Where casing is used, it shall be cleaned
out to undisturbed soil prior to sampling and the sample spoon driven
into soil that has not been affected by chopping, washing, or
hydrostatic imbalance.
(a) Uncased borings. Uncased borings, including borings where the
casing is omitted for part of the depth, may be used if the mud slurry
method is followed. The requirements for soil sampling and rock coring
shall be the same for uncased borings as for borings made using casing,
except that prior to each soil sampling operation the boring shall be
substantially cleaned of disturbed material and the sample spoon shall
be advanced through any settled solids before counting the blows
required to drive the spoon. Longer sample spoons, having a sludge
chamber, shall be used where settled solids exceed six inches In
determining ground water levels, methods shall be used to reduce and
replace the mud slurry so that the hydrostatic head may be measured. The
procedures shall be described in detail in the records.
(b) Auger borings. Borings may be made with augers except that short
flight augers shall not be used in granular soils below the water level.
Sampling procedures in auger borings for both soil and rock shall be the
same as for cased borings. Full hydrostatic head shall be maintained in
granular soils below the ground water level during the boring operation.
(c) Maximum diameter. Where the bore hole, as drilled by any method,
is in excess of four inches in diameter, sampling operations shall be
performed through a temporary casing having a four inch inside diameter
or less.
Section 27-666
§ 27-666 Probings and geophysical explorations. (a) Footings, pier or
wall designs. Where the foundations for a proposed building consist of
footings or foundation piers or walls bearing on rock of class 1-65,
2-65 or 3-65, the use of probings, auger borings or geophysical methods,
made without the recovery of soil samples or rock cores, may (except as
hereafter specified) be substituted for up to one-half of the number of
borings required by the provisions of subdivision (a) of section 27-663
of this article, provided that such probings, borings, etc. are carried
to adequate depth and are of a nature that will reasonably define the
surface contours of the rock. The accuracy of such surface contour
definition shall be confirmed by recovering rock cores at the locations
of at least one-fifth of the probings or auger borings or, in the case
where geophysical methods are used, those borings which are made shall
be so distributed as to permit confirmation of the accuracy of the
geophysical investigations. The provisions of paragraph two of
subdivision (a) of section 27-663 of this article, shall not apply where
the provisions of this section are invoked.
(b) Pile support. Where the foundation for the proposed building
consists of piling bearing on rock of class 1-65, 2-65 or 3-65, the
provisions of subdivision (a) of this section shall apply, provided that
the borings consistently show that the soil overlying the rock consists
solely of deposits of class 6-65 through 11-65 and is free of boulders
or other obstructions.
(c) Geophysical methods. Geophysical investigations shall be conducted
by experienced and qualified personnel acceptable to the commissioner
who may reject the results and require additional exploration by borings
if the results of the geophysical explorations cannot be satisfactorily
correlated to the logs of the borings.
Section 27-667
§ 27-667 Existing borings. Existing boring data may be utilized
subject to the following:
(1) Borings, test pits, probings, etc., that have been made in
accordance with all requirements of this section, but not necessarily
for the investigation of the specific project for which application is
being made, may be utilized in fulfillment of these provisions.
(2) The logs of borings, test pits, probings, etc., that have been
made in accordance with all requirements of this section, but wherein
the soil samples and/or rock cores are not available for examination,
may be utilized in fulfillment of these provisions to an extent not to
exceed one-half of the required number of borings.
(3) Borings, test pits, probings, etc., or the logs thereof, that do
not meet the specific requirements of this subchapter, but which are of
suitable type and adequate penetration to provide the data required for
the safe design and construction of the proposed foundation, may be
utilized in fulfillment of the provisions of this section, subject to
the approval of the commissioner.
To the extent possible under law, Friends of Devin Balkind for Public Advocate has waived all copyright and related or neighboring rights to New York City Administrative Code. This work is published from: United States.
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