N.Y.C. Admin. Code § BC 1803: Section BC 1803: Geotechnical Investigations and Material Classifications

1803.1 General.

Geotechnical investigations shall be subject to special inspections in accordance with Sections 1705.6, 1705.7 and 1705.19 and be conducted in accordance with Sections 1803.2 through 1803.7. An engineer shall scope, supervise and approve the subsurface investigation and the classification of the soil and rock encountered.

1803.2 Where required.

A geotechnical investigation shall be performed and report shall be prepared for:

1. New structures;

2. Horizontal enlargements;

3. Vertical enlargements or alterations necessitating new foundations or resulting in additional loading that exceeds 5 percent of the existing foundation design capacity; or

4. As required by the commissioner or applicant of record.

The geotechnical investigation shall be performed in accordance with Sections 1803.4 through 1803.6. For structures in Seismic Design Category C or D, the requirements of Sections 1803.2.1 and 1803.2.2 shall also apply.

1803.2.1 Seismic Design Category C.

For structures assigned to Seismic Design Category C in accordance with Section 1613, the geotechnical investigation shall include an evaluation of the following potential geologic and seismic hazards:

1. Slope instability.

2. Liquefaction. Peak ground accelerations for use in such analyses shall be determined in accordance with Section 1816.2.1.

3. Total and differential settlement.

4. Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.

1803.2.2 Seismic Design Category D.

For structures assigned to Seismic Design Category D in accordance with Section 1613, the geotechnical investigation shall meet the requirements of Section 1803.2.1 and the following as applicable:

1. A determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1828.8 mm) of in situ soil or backfill height due to design earthquake ground motions. Peak ground acceleration for use in lateral pressure analyses shall be determined in accordance with Section 1816.2.1.

2. The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground accelerations for use in such analyses shall be determined in accordance with Section 1816.2.1.

3. An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:

3.1. Estimation of differential settlement.

3.2. Lateral soil movement.

3.3. Lateral soil loads on foundations.

3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction

3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations.

3.6. Increases in soil lateral pressures on retaining walls.

3.7. Flotation of buried structures.

4. Discussion of mitigation measures such as, but not limited to, the following:

4.1. Selection of appropriate foundation type and depths.

4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.

4.3. Ground stabilization.

4.4. Any combination of these measures and how they shall be considered in the design of the structure.

1802.3 Material classification.

Soil and rock classification shall be based on materials disclosed by borings, test pits or other subsurface exploration methods. Soil classifications shall be determined in accordance with ASTM D 2487 (refer to Table 1803.3) and the supplemental definitions contained herein. Rock classifications shall be determined in accordance with generally accepted engineering practice and the supplemental definitions contained herein. Laboratory tests shall be conducted to ascertain these classifications where deemed necessary by the engineer responsible for the geotechnical investigation or the commissioner.

BEDROCK.

1.

Hard sound rock (Class 1a). Includes crystalline rocks, such as gneiss, granite, diabase and mica schist. Characteristics are as follows: the rock rings when struck with pick or bar; the rock does not disintegrate after exposure to air or water; the rock breaks with sharp fresh fracture; cracks are unweathered, less than 1/8-inch (3.2 mm) wide, and generally no closer than 3 feet (914.4 mm) apart; and the RQD (rock quality designation) with a double tube, NX-size diamond core barrel is generally 85 percent or greater for each 5-foot (1524 mm) run; or core recovery with BX-size core is generally 85 percent or greater for each 5-foot (1524 mm) run.

2.

Medium hard rock (Class 1b). Includes crystalline rocks of paragraph 1 of this subdivision, plus marble and serpentinite. Characteristics are as follows: all those listed in paragraph 1 of this subdivision, except that cracks may be 1/4-inch (6.4 mm) wide and slightly weathered, generally spaced no closer than 2 feet (609.6 mm) apart; and the RQD with a double tube, NX-size diamond core barrel is generally between 50 and 85 percent for each 5-foot (1524 mm) run; or core recovery with BX-size core is generally 50 to 85 percent for each 5-foot (1524 mm) run.

3.

Intermediate rock (Class 1c). Includes rocks described in paragraphs 1 and 2 of this subdivision, plus cemented shales and sandstone. Characteristics are as follows: the rock gives dull sound when struck with pick or bar; does not disintegrate after exposure to air or water; broken pieces may show moderately weathered surfaces; may contain fracture and moderately weathered zones up to 1 inch (25.4 mm) wide spaced as close as 1 foot (304.8 mm) apart; and the RQD with a double tube, NX-size diamond core barrel is generally 35 to 50 percent for each 5-foot (1524 mm) run; or a core recovery with BX-size core of generally 35 to 50 percent for each 5-foot (1524 mm) run.

4.

Soft rock (Class 1d). Includes rocks described in paragraphs 1, 2, and 3 of this subdivision in highly weathered condition, plus talc schist and poorly cemented shales and sandstones. Characteristics are: rock may soften on exposure to air or water; may contain highly weathered zones up to 3 inches (76.2 mm) wide but filled with stiff soil; and either the RQD with a double tube, NX-size diamond core barrel is less than 35 percent for each 5-foot (1524 mm) run or core recovery with BX-size core of generally less than 35 percent for each 5-foot (1524 mm) run, or a value of N

60

greater than 50 blows per foot (0.3 meters).

SANDY GRAVEL AND GRAVELS. Consists of coarse-grained material with more than half of the coarse fraction larger than the #4 size sieve and contains little or no fines (GW and GP). The density of these materials shall be determined in accordance with the following:

Dense (Class 2a). These materials have a value of N

60

greater than 30 blows per 1 foot (0.3 meter).

Medium (Class 2b). These materials have a value of N

60

between 10 and 30 blows per 1 foot (0.3 meter).

Loose (Class 6). These materials have a value of N

60

less than 10 blows per 1 foot (0.3 meter). These materials shall be considered nominally unsatisfactory bearing materials.

GRANULAR SOILS. These materials are coarse-grained soils consisting of gravel and/or sand with appreciable amounts of fines and gravel. Soil types include GM, GC, SW, SP, SM and SC. The density of granular materials shall be determined in accordance with the following:

Dense (Class 3a). These materials have a value of N

60

greater than 30 blows per 1 foot (0.3 meter).

Medium (Class 3b). These materials have a value of N

60

between 10 and 30 blows per 1 foot (0.3 meter).

Loose (Class 6). These materials have a value of N

60

less than 10 blows per 1 foot (0.3 meter). These materials shall be considered nominally unsatisfactory bearing materials.

CLAYS. For soil types SC, CL and CH in the absence of sufficient laboratory data, the consistency of clay materials shall be determined in accordance with the following:

Hard (Class 4a). Clay requiring picking for removal, a fresh sample of which cannot be molded by pressure of the fingers; or having an unconfined compressive strength in excess of 4 TSF (383 kPa); or having a value of N

60

greater than 30 blows per 1 foot (0.3 meter).

Stiff (Class 4b). Clay that can be removed by spading, a fresh sample of which requires substantial pressure of the fingers to create an indentation; or having an unconfined compressive strength of between 1 TSF (95.8 kPa) and 4 TSF (383 kPa); or having a value of N

60

between 8 and 30 blows per 1 foot (0.3 meter).

Medium (Class 4c). Clay that can be removed by spading, a fresh sample of which can be molded by substantial pressure of the fingers; or having an unconfined compressive strength of between 0.5 TSF (47.9 kPa) and 1 TSF (95.8 kPa); or having a value of N

60

between 4 and 8 blows per 1 foot (0.3 meter).

Soft (Class 6). Clay, a fresh sample of which can be molded with slight pressure of the fingers; or having an unconfined compressive strength of less than 0.5 TSF (47.9 kPa); or having a value of N

60

less than 4 blows per 1 foot (0.3 meter). This material shall be considered nominally unsatisfactory bearing material.

SILTS AND CLAYEY SILTS. For soil types ML and MH in the absence of sufficient laboratory data, the consistency of silt materials shall be determined in accordance with the following:

Dense (Class 5a). Silt with a standard penetration test where the value of N

60

greater than 30 blows per 1 foot (0.3 meter).

Medium (Class 5b). Silt with a standard penetration test where the value of N

60

between 10 and 30 blows per 1 foot (0.3 meter).

Loose (Class 6). Silt with a standard penetration test where the value of N

60

fewer than 10 blows per 1 foot (0.3 meters). This material shall be considered nominally unsatisfactory bearing material.

Table 1803.3 Unified Soil Classification (Including Identification and Description)

1803.4 Investigation.

An engineer shall scope and supervise the geotechnical investigation. The geotechnical investigation shall be sufficient for evaluating soil and rock conditions including but not limited to material classification, stratigraphy, groundwater, slope stability, soil and rock strength, adequacy of load-bearing soils and rock, the effect of moisture variation on soil-bearing capacity, compressibility, liquefaction and expansiveness. The investigation shall comply with Sections 1803.4.1 through 1803.4.4.

1803.4.1 Scope of investigation.

The scope of the geotechnical investigation, including the number, types and depths of borings, the number of test pits or the number of alternative test methods; the equipment used to drill and sample; the in-situ testing; and the laboratory testing program shall be determined by the engineer responsible for the investigation, subject to the requirements of this chapter.

1. Borings shall be uniformly distributed under the structure or distributed in accordance with load patterns imposed by the structure.

2. At a minimum, investigations for structures shall include:

2.1. one exploratory boring for built-over areas up to and including 750 square feet (69.7 m

2

)

2.2. two exploratory borings for built-over areas greater than 750 square feet (69.7 m

2

) but less than 5,000 square feet (464.5 m

2

), and at least one additional boring for each additional 2,500 square feet (232.3 m

2

), or part thereof, of built-over areas up to 20,000 square feet (1858.1 m

2

).

2.3. at least one boring for each additional 5,000 square feet (464.5 m

2

), or part thereof, of built-over areas in excess of 20,000 square feet (1858.1 m

2

).

3. At a minimum, investigations for retaining walls greater than 10 feet (3048 mm) in height shall include one exploratory boring for every 50 linear feet (15 204 mm) of wall.

4. Borings shall be taken into bedrock, or to an adequate depth below the top of the load-bearing strata to demonstrate that the foundation loads have been sufficiently dissipated and to evaluate global stability of retaining walls.

5. For structures having an average area load (dead plus live) of 1,000 pounds per square foot (47.9 kN/m

2

) or more, at least one boring for every 10,000 square feet (929 m

2

) of footprint area shall penetrate at least 100 feet (30 480 mm) below the curb grade or 5 feet (1524 mm) into bedrock of Class 1c or better, whichever is less.

6. At least one-half of the borings satisfying this requirement shall be located within the limits of the built-up area and the remainder shall be within 25 feet (7620 mm) of the built-up area limits.

7. For structures to be supported on deep foundations, the required number of borings shall be not less than two borings, and based on a minimum of one boring per 2,000 square feet (184.8 m

2

) for the first 20,000 square feet (1858.1 m

2

) and one boring per every additional 4,000 square feet (371.6 m

2

).

8. All boring, sampling, and in-situ testing operations shall be subject to special inspection in accordance with Table 1705.6.

Exception: Test pits may be substituted for borings for one and two-story structures. The registered design professional shall submit a test pit observation report to the commissioner.

1803.4.2 Existing data.

Suitable borings, test pits, probings, and the logs and records that were obtained as part of earlier exploration programs by an engineer other than the engineer performing the geotechnical investigation and that meet the requirements of this section may only be used as partial fulfillment of the requirements of Section 1803.4.1. Additional boring(s) shall be made to fulfill the requirements of Section 1803.4.1, with a minimum of one additional boring required.

1803.4.3 Groundwater table.

The geotechnical investigation shall determine the existing groundwater table.

1803.4.4 Compressible soils.

In areas containing compressible soils, the geotechnical investigation shall determine the extent of these soils in the plan area of the structure and shall be subject to the requirements of Section 1803.3.

1803.5 Soil and rock sampling.

The soil boring and sampling procedures and apparatus shall be in accordance with ASTM D 1586 and ASTM D 1587 and generally accepted engineering practice. The rock coring, sampling procedure and apparatus shall be in accordance with ASTM D 2113 and generally accepted engineering practice. Rock cores shall be obtained with a double-tube core barrel with a minimum outside diameter of 2 7/8 inches (73 mm). With the approval of the engineer responsible for the geotechnical investigation, smaller-diameter double-tube core barrels may be used under special circumstances such as telescoping casing to penetrate boulders, or space limitations requiring the use of drill rigs incapable of obtaining large-diameter cores.

1803.5.1 Bedrock support.

Where the foundation design relies on rock to support footings, deep foundations or caisson sockets, or permanent prestressed rock anchors, a sufficient number of rock corings shall be drilled to sufficient depths to assess the competency of the rock and its load-bearing capacity, but no less than 10 feet (3048 mm) below the lowest level of bearing.

1803.5.2 Alternative investigative methods.

The engineer responsible for the geotechnical investigation may engage specialized technicians to conduct alternative investigative methods such as cone penetrometer testing (CPT) performed in accordance with ASTM D 3441 or ASTM D 5778. Data from these investigations may be used to (i) supplement soil boring and rock coring information, provided there is a demonstrated correlation between the findings, and (ii) determine material properties for static and seismic or liquefaction analyses. CPTs may replace borings on a one to one basis, but in no case shall there be fewer than half the required standard borings as per Section 1803.4.1, and no less than two standard borings. The boring depth requirements of Section 1803.4.1 shall be accomplished with borings. The alternative investigative methods must be capable of extending to the depths of the required borings. Other in-situ testing methods, such as geophysical, vane shear, and pressure meter, may be used to determine engineering design parameters, but may not be used as a substitute for the required number of borings.

1803.5.3 Material disposition.

Soil and rock samples shall be maintained in an accessible location by the permit holder or owner and made available to the engineer responsible for the geotechnical investigation and to the department, until the foundation work has been completed and accepted, or until 1 year after the investigation is complete, whichever is longer.

1803.6 Geotechnical reports.

A geotechnical engineering report shall be prepared for all sites and submitted to the commissioner.

Exception: One- and two-family dwellings no more than three stories in height shall not require a geotechnical report except where any of the following exist:

1. Shallow foundations are used that bear on or above compressible soils (see Section 1803.4.4), uncontrolled fill (see Section 1806.2.3), or artificially treated soils (see Section 1806.2.4);

2. Underpinning is required;

3. The structure is within the special flood hazard area;

4. Dewatering is required;

5. Test pits are implemented in lieu of borings as per Section 1803.4.1; or

6. As required by the commissioner.

1803.6.1 Information required in geotechnical reports.

The geotechnical report shall be prepared by the engineer responsible for the geotechnical investigation and shall be signed and sealed. The geotechnical report submitted to the commissioner shall include the foundation system shown on the drawings submitted to the department. The report shall include, but need not be limited to, the following information:

1. A description of the planned structure.

2. A plot showing the location of test borings, excavations, probes, and/or other exploration techniques.

3. A complete record of the soil and/or rock sample descriptions.

4. A record of the soil and/or rock profile.

5. Elevation of the groundwater table (if encountered), base flood elevation (if applicable), and design flood elevation.

6. Results of in-situ or geophysical testing.

7. Results of laboratory testing.

8. Recommendations for foundation type and design criteria, including but not limited to allowable bearing capacity of natural or compacted soil and/or rock; soil stiffness parameters required for design of the foundations; mitigation of the effects of liquefaction (if applicable); site class; Mapped MCE

R

spectral acceleration parameters (S

S

and S

1

); design spectral response acceleration parameters (S

DS

and S

D1

); site adjusted peak ground acceleration (PGA

M

); differential settlement and varying soil and/or rock strength; and the effects of adjacent loads.

9. Design lateral earth pressures on foundation walls and other retaining walls.

10. Recommendations for the evaluation of adjacent properties potentially impacted by the proposed construction.

11. Where dewatering is required, recommendations for the maximum permissible drawdown outside the site.

12. Expected total and differential settlement.

13. Special design and construction provisions for footings or foundations founded on expansive soils, as necessary.

14. Compacted fill material properties and testing in accordance with Section 1804.6.

15. Controlled low-strength material properties and testing in accordance with Section 1804.7.

16. A list of anticipated special inspections required for construction of earthwork and foundations.

17. For deep foundations reports, the requirements outlined in Section 1810.2.2.

18. For permanent prestressed rock and soil anchor reports, the requirements outlined in Section 1815.2.

19. Soil and rock parameters to be used to determine the safe slope of temporary excavations pursuant to Section 3304.4.1.

1803.7 Construction documents.

Construction documents shall be prepared in accordance with Section 107.7.1.