Allowable Soil Bearing Pressures

NYC Admin. Code tit. 27, ch. 1, subch. 11, art. 4

in effect

NYC Admin. Code § 27-675 Classification of soil materials.

§ 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. Characteristics 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 thoroughly 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.

NYC Admin. Code § 27-676 Satisfactory bearing material.

§ 27-676 Satisfactory bearing material. The following materials, or any combination of them shall be considered as generally satisfactory bearing materials; hard sound, medium hard, intermediate, and soft rock; hardpan; granular soils of G and S groups; dense or medium silt soils of groups ML and MH; and hard or medium clay soils of groups CL and CH. Figure: Table11-1

FIELD IDENTIFICATION PROCEDURES FOR FINE-GRAINED SOILS OR FRACTIONS These procedures are to be performed on the minus No. 40 sieve size particles, approximately 1/1964 in. For field classification purposes, screening is not intended, simply remove by hand the coarse particles that interfere with the tests. Dilatancy (reaction to shaking) After removing particles larger than No. 40 sieve size, prepare a pat of moist soil with a volume of about one-half cubic inch. Add enough water if necessary to make the soil soft but not sticky. Place the pat in the open palm of one hand and shake horizontally, striking vigorously against the other hand several times. A positive reaction consists of the appearance of water on the surface of the pat which changes to a livery consistency and becomes glossy. When the sample is squeezed between the fingers, the water and gloss disappear from the surface, the pat stiffens, and finally it cracks or crumbles. The rapidity of appearance of water during shaking and of its disappearance during squeezing assist in identifying the character of the fines in a soil. Very fine clean sands give the quickest and most distinct reaction whereas a plastic clay has no reaction. Inorganic silts, such as a typical rock flour, show a moderately quick reaction. Dry Strength (crushing characteristics) After removing particles larger than No. 40 sieve size, mold a pat of soil to the consistency of putty, adding water if necessary. Allow the pat to dry completely by oven, sun, or air-drying, and then test its strength by breaking and crumbling between the fingers. This strength is a measure of the character and quantity of the colloidal fraction contained in the soil. The dry strength increases with increasing plasticity. High dry strength is characteristic for clays of the CH group. A typical inorganic silt possesses only very slight dry strength. Silty fine sands and silts have about the same slight dry strength, but can be distinguished by the feel when powdering the dried specimen. Fine sand feels gritty whereas a typical silt has the smooth feel of flour. Toughness (consistency near plastic limit) After particles larger than the No. 40 sieve size are removed, a specimen of soil about one-half inch cube in size, is molded to the consistency of putty. If too dry, water must be added and if sticky, the specimen should be spread out in a thin layer and allowed to lose some moisture by evaporation. Then the specimen is rolled out by hand on a smooth surface or between the palms into a thread about one-eighth inch in diameter. The thread is then folded and rerolled repeatedly. During this manipulation the moisture content is gradually reduced and the specimen stiffens, finally loses its plastic ity, and crumbles when the plastic limit is reached. After the thread crumbles, the pieces should be lumped together and a slight kneading action continued until the lump crumbles. The tougher the thread near the plastic limit and the stiffer the lump when it finally crumbles, the more potent is the colloidal clay fraction in the soil. Weakness of the thread at the plastic limit and quick loss of coherence of the lump below the plastic limit indicate either inorganic clay of low plasticity, or materials such as kaolin-type clays and organic clays which occur below the A-line. Highly organic clays have a very weak and spongy feel at the plastic limit.

NYC Admin. Code § 27-677 Nominally unsatisfactory bearing material.

§ 27-677 Nominally unsatisfactory bearing material. Fill material, peat, (group Pt), organic silts and clays (grouping OL and OH), soft or loose soils of groups ML, CL, HM and CH, varved silt, or satisfactory bearing materials that contain lenses of, or are underlain by, these materials shall be considered as nominally unsatisfactory bearing materials.

NYC Admin. Code § 27-678 Allowable soil bearing pressures.

§ 27-678 Allowable soil bearing pressures. The allowable bearing pressures on satisfactory bearing materials shall be those established in table 11-2. The allowable bearing pressures on nominally unsatisfactory bearing materials shall be those established in accordance with section 27-679 of this article. Allowable bearing pressure shall be considered to be the allowable pressure at a point in the soil mass in excess of the stabilized overburden pressure existing at the same point prior to construction operations. The stabilized overburden pressure existing at a point shall be defined as that portion of the weight of the overlying soil material that is supported by granular interaction rather than pore pressure. In general, the magnitude of the stabilized overburden pressure may be approximated as follows: (a) The overlying soil material shall have been in place for an adequate length of time to produce a stable condition of pore pressure in, or below the foundation level. Where the bearing stratum consists of soils of classes 5-65 through 8-65, the bearing stratum shall be considered to be fully consolidated except with regard to the weight of that portion of the overlying soil material that consists of added fill material. (b) Where all or a portion of the overlying soil consists of fill material, the weight of the fill material shall not be included in the stabilized overburden pressure unless the magnitude of stabilized pressure is verified by an architect or engineer on the basis of laboratory or field tests on undisturbed material. (c) Where the bearing stratum consists of soils of classes 9-65 through 11-65, the stabilized overburden pressure shall be considered as zero unless the magnitude of the stabilized pressure is established by an architect or engineer on the basis of laboratory or field tests on undisturbed material. (d) The stabilized overburden pressure shall not include the weight of any soil removed by excavation and not replaced. For footings, the total stabilized overburden pressure shall not exceed the weight of a one square foot column of soil (considering submerged weight where the soil column is partly submerged) measured from the bottom of the footing to the lowest level of the final grade above the footing.For a box foundation, where the strength of the slab is adequate to stabilize the underlying soil, the stabilized overburden pressure shall not exceed the weight of a one square foot column of soil measured from the bottom of the box to the lowest level of the adjacent grade. (e) Where the bearing stratum consists of soils of classes 9-65 through 11-65, the allowable bearing pressure shall be adjusted for the effects of rebound due to excavation as determined from consolidation test data. (f) Where the bearing stratum consists of rock of classes 1-65 through 3-65, the stabilized overburden pressure shall be neglected. TABLE 11-2 Allowable Soil Bearing Pressures Class of Material Description See Notes (1) Basic Allowable Bearing Values (Tons per sq. ft.) See Notes (10), (11) and (12) 1-65 Hard Sound Rock 60 See Notes (2) and (8). 2-65 Medium Hard Rock 40 See Notes (2) and (8). 3-65 Intermediate Rock 20 See Notes (2) and (8). 4-65 Soft Rock 8 5-65 Hardpan — See Notes (3) and (8). 6-65 Gravel and Gravel Soils (Soil Groups, GW, GP, GM & GC and soils of Soil Groups SW, SP, and SM containing more than 10% of material retained on a No. 4 sieve) — See Notes (4) and (8) and (9). 7-65 Sands (other than Fine Sands) (Soil Groups SW, SP & SM but containing not more than 10% of material retained on a No. 4 sieve) — See Notes (5), (8) and (9). 8-65 Fine sand — See Notes (6), (8) and (9). 9-65 Clays and Clay Soils (Soil Groups SC, CL & CH) Hard 5 See Note (7). Medium 2 See Note (7). Soft See Sec. 27-679. 10-65 Silts and Silt Soils (Soil Groups ML & MH) Dense 3 Medium 1.5 Loose See Sec. 27-679. 11-65 Nominally Unsatisfactory Bearing Materials See Sec. 27-679. Notes for Table 11-2: (1) Classification. The soil classifications indicated in this table are those described in section 27-675 of this article. Where there is doubt as to the applicable classification of a soil stratum, the allowable bearing pressure applicable to the lower class of material to which the given stratum might conform shall apply unless the conformance to the higher class of material can be proven by laboratory or field test procedures. (2) Allowable bearing pressure on rock. The tabulated values of basic allowable bearing pressures apply only for massive rocks or, for sedimentary or foliated rocks, where the strata are level or nearly so, and, then only if the area has ample lateral support. Tilted strata and their relation to nearby slopes or excavations shall receive special consideration. (3) Allowable bearing pressure on hardpan. For hardpan consisting of well cemented material composed of a predominantly granular matrix and free of lenses of fine grained material and inclusions of soft rock, the basic allowable bearing pressure shall be twelve tons per square foot. For hardpan consisting of poorly cemented material or containing lenses of fine grained material, inclusions of soft rock, or a fine grained matrix, the basic allowable bearing pressure shall be eight tons per square foot. (4) Allowable bearing pressure on gravel and gravel soils. Values of basic allowable bearing pressure shall be as follows: (a) For soils of Soil Groups GW, GP, GM, and GC: Compact, well graded material – ten tons per square foot. Loose, poorly graded material – six tons per square foot. Intermediate conditions – Estimate by interpolation between indicated extremes. (b) For soils of Soil Groups SW, SP, and SM, containing more than ten percent of material retained on a No. 4 sieve: Compact, well graded material – eight tons per square foot. Loose, poorly graded material – four tons per square foot. Intermediate conditions – Estimate by interpolation between indicated extremes. (5) Allowable bearing pressure on sands. The basic allowable bearing pressure shall be determined from the resistance to penetration of the standard sampling spoon. The basic allowable bearing pressure in tons per square foot shall equal 0.10 times N but not greater than six tons per square foot, nor less than three tons per square foot. The appropriate value for the penetration resistance at various areas of the site shall be made by averaging the measured resistance within a depth of soil below the proposed footing level equal to the width of the footing. Where the average values so obtained do not vary by more than twenty-five percent of the minimum of the average values over the site of the proposed building, the lowest average value shall be used for the design of the entire building. Where the variation exceeds twenty-five percent, the allowable bearing pressure shall be predicated on the lowest average value unless appropriate measures are taken to avoid detrimental amounts of differential settlements of the footings. Where the design bearing pressure on soils of class 7-65 exceeds three tons per square foot, the embedment of the loaded area below the adjacent grade shall not be less than four feet and the width of the loaded area not less than three feet, unless analysis shall demonstrate the proposed construction to have a minimum factor of safety of 2.0 against shear failure of the soil. (6) Allowable bearing pressure on fine sand. The basic allowable bearing pressure shall be determined from the resistance to penetration of the standard sampling spoon. The basic allowable bearing pressure in tons per square foot shall equal 0.10 times N but not greater than four tons per square foot nor less than two tons per square foot, except that, for loose materials (resistance to penetration of the standard sampling spoon ten blows per foot or less), where the foundation is subjected to vibratory loads from machinery or similar cause, the indicated basic values shall not apply. The allowable bearing pressure shall be established by analysis applying accepted principles of soil mechanics and a report of such analysis satisfactory to the commissioner shall be submitted as a part of the application for the acceptance of the plans. (7) Allowable bearing pressure on clays and clay soils. The bearing capacity of medium and hard clays and clay soils shall be established on the basis of the strength of such soils as determined by field or laboratory tests and shall provide a factor of safety against failure of the soil of not less than 2.0 computed on the basis of a recognized procedure of soils analysis, shall consider probable settlements of the building, and shall not exceed the tabulated maximum values. (8) Increases in allowable bearing pressure due to embedment of the foundation. (a) The basic allowable bearing values for rock of classes 1-65, 2-65 and 3-65 shall apply where the loaded area is on the surface of sound rock. Where the loaded area is below the adjacent rock surface and is fully confined by the adjacent rock mass and provided that the rock mass has not been shattered by blasting or otherwise is or has been rendered unsound, these values may be increased ten percent of the base value for each foot of embedment below the surface of the adjacent rock surface in excess of one foot, but shall not exceed twice the basic values. (b) The basic allowable bearing values for soils of classes 5-65 through 8-65 determined in accordance with notes three, four and five above, shall apply where the loaded area is embedded four feet or less in the bearing stratum. Where the loaded area is embedded more than four feet below the adjacent surface of the bearing stratum, and is fully confined by the weight of the adjacent soil, these values may be increased five percent of the base value for each foot of additional embedment, but shall not exceed twice the basic values. Increases in allowable bearing pressure due to embedment shall not apply to soils of classes 4-65, 9-65, 10-65, or 11-65. (9) Increase in allowable bearing pressure for limited depth of bearing stratum: The allowable bearing values for soils of classes 6-65, 7-65 and 8-65 determined in accordance with this table and the notes thereto (including note eight), may be increased up to one-third where the density of the bearing stratum below the bottom of the footings or the tips of the piles increases with depth provided that: (a) The bearing stratum is not underlain by materials of a lower class. (b) The allowable bearing value of the soil material underlying the bottom of the footings or the tips of the piles increases at least fifty percent within a depth below the footing or the tips of the piles which is not greater than the width of the footing or the width of the polygon circumscribing the pile group. (c) It shall be demonstrated by a recognized means of analysis that the probable settlement of the foundation due to compression, and/or consolidation do not exceed acceptable limits for the proposed building. (10) Combination of loads. The provisions of section 27-594 of article two of subchapter ten of this chapter shall apply. (11) Correction for foundations bearing on materials of varying bearing capacities. Where it is shown by borings or otherwise that materials of varying bearing value will be used for support of a building: (1) Where the weakest material does not rank below class 5-65, no modifications shall be required. (2) Where the weakest materials rank as classes 6-65 through 8-65, if the difference in basic allowable bearing values for the several materials does not exceed thirty percent of the allowable value for the poorest material which is to support the foundation, the foundations may be proportioned in direct conformance with the allowable bearing pressures. Where the difference in basic allowable bearing values exceeds thirty percent, appropriate measures shall be taken to limit the differential settlements of the different portions of the structure to tolerable values. (3) For materials of classes 9-65 and 10-65, in all cases, appropriate measures shall be taken to equalize the settlements of the different portions of the structure. (12) Inundated footings. The provisions of this section relating to materials of classes 1-65 through 7-65, shall be deemed equally applicable both to the dry and to the inundated condition of the soil provided: (a) That the subgrade is undisturbed by the construction operations, (b) The bearing area is in a confined condition. For such cases, no reduction in allowable bearing value will be required where the soil supporting the foundation is subject to a rising level of inundation. However, the effects on settlement of a falling level of inundation occurring after construction of the foundation shall be considered in the design.

NYC Admin. Code § 27-679 Bearing capacity of nominally unsatisfactory bearing materials.

§ 27-679 Bearing capacity of nominally unsatisfactory bearing materials. Whenever soils exploration shows that the proposed foundation would rest on, or be underlain by, nominally unsatisfactory bearing materials, a report based on soil tests and foundation analysis (including analysis of undisturbed samples) shall be submitted by an architect or engineer, demonstrating, subject to the approval of the commissioner, that the proposed construction, under a condition of one hundred percent over load, is safe against failure of the soil materials. The report shall also show that the probable total magnitude and distribution of settlement to be expected under design conditions will not result in instability of the building or stresses in the structure in excess of the allowable values established in subchapter ten of this chapter. In addition, the following provisions shall apply: (a) Fill materials. (1) CONTROLLED FILLS. Fills shall be considered as satisfactory bearing materials of class 6-65 or 7-65 when placed in accordance with the following procedures, under the provisions for controlled inspection. a. Before placement of fill, the existing ground surface shall be stripped of all organic growth, timber, rubbish, and debris. After stripping, the ground surface shall be compacted to the density in subparagraph d of this paragraph. b. Materials for fill shall consist of sand, gravel, crushed stone, crushed gravel, or a mixture of these, and shall contain no organic matter. The fill materials shall contain no particles exceeding four inches in the largest dimension. No more than thirty per cent of the material shall be retained on a three-quarter inch sieve. The material passing the three quarter inch sieve shall contain, by weight, no more than forty percent passing the one hundred sieve, or twelve percent passing the two hundred sieve. c. The grading of the fill shall be determined in accordance with the applicable procedures of reference standards RS 11-1 and RS 11-2. d. Fill shall be placed and compacted at its optimum moisture content, in uniform layers not more than twelve inches thick (after compaction) and each layer shall be thoroughly compacted to a density not less than ninety-five percent of the density prescribed in reference standard RS 11-3. The field density shall be verified by in-place density tests made on each lift of the embankment. Fill shall not be placed when frozen or placed on a frozen or wet sub-grade. (2) UNCONTROLLED FILLS. Fill material, other than controlled fill, may be used for the support of buildings, other than one- and two-family dwellings, and may be considered as satisfactory bearing material of applicable class, subject to the following: a. The soil within the building area shall be explored using test pits. At least one test pit, penetrating at least eight feet below the level of the bottom of the proposed footings, shall be provided for every twenty-five hundred square feet of building area. Where such test pits consistently indicate that the fill is composed of material that is free of voids and free of extensive inclusions of mud, organic materials such as paper, garbage, cans, or metallic objects, and debris, the provisions of subparagraphs b and c of this paragraph shall apply. Where the test pits show such voids or inclusions, the additional provisions of subparagraph d of this paragraph shall apply. Borings may be used in lieu of test pits, provided that continuous samples at least four inches in diameter are recovered. b. The building area shall be additionally explored using one standard boring under each column. These borings shall be carried to a depth sufficient to penetrate into natural ground, but not less than twenty feet below grade, and a sufficient number shall penetrate deeper than twenty feet as required to meet the provisions of section 27-663 of article two of this subchapter. Where such borings show voids or inclusions, the provisions of subparagraph d of this paragraph shall apply. c. The allowable soil bearing pressure on the fill material shall not exceed two tons per square foot. d. Wherever the fill shows voids or inclusions as described in subparagraphs a and b of this paragraph either the fill shall be treated as having no presumptive bearing capacity, or the building shall incorporate adequate strength and stiffness to bridge such voids or inclusions or shall be articulated to prevent damage due to differential or localized settlement of the fill. (b) Organic silts, organic clays, soft inorganic clay, loose inorganic silt, and varved silt. (1) The allowable bearing pressure shall be determined independently of table 11-2 subject to the following: a. For varved silts, the soil bearing pressure produced by the proposed building shall not exceed two tons per square foot, except that for desiccated or preconsolidated soils, higher bearing pressures will be allowed. b. For organic silts or clays (groups OL and OH) or for soft or loose soils of groups ML, CL, MH, and CH, the soil bearing pressure produced by the proposed building shall not exceed one ton per square foot except that a value of two tons per square foot will be permitted on soils that are adequately preconsolidated or artificially treated. (2) The report required in this section shall contain, as a minimum, the following information: a. Geological profiles through the area defining the stratigraphy. b. Sufficient laboratory test data on the compressible material to indicate the coefficient of consolidation, coefficient of compressibility, permeability, secondary compression characteristics, and Atterberg limits. c. Where the design contemplates improvement of the natural bearing capacity and/or reduction in settlements by virtue of preloading, cross sections showing the amount of fill and surcharge to be placed on design details showing the required time for surcharging shall be indicated, and computations showing the amount of settlement to be expected during surcharging. Records of settlement plate elevations and pore pressure readings, before, during, and after surcharging, shall be filed with the commissioner. d. The estimated amount and rate of settlement expected to occur after the structure has been completed, including the influence of dead and live loads of the structure. e. A detailed analysis showing that the anticipated future settlement will not adversely affect the performance of the structure. f. Where sand drains are to be used, computations showing the diameter, spacing, and method of installation of such drains, shall be provided. (c) Artificially treated soils. Nominally unsatisfactory soil materials that are artificially compacted, cemented, or preconsolidated (including soils compacted by vibration, cemented by chemical injection, or preconsolidated by use of electric current, but not including cases where preconsolidation consists solely of the use of surcharge with or without sand drains) may be used for the support of buildings, and nominally satisfactory soil materials that are similarly treated may be used to resist soil bearing pressures in excess of those indicated in table 11-2 for the soil in its natural state, subject to the following: (1) The vertical and lateral extent of the soil that is compacted, cemented, or preconsolidated shall conform to the full extent of the distribution of loading that is assumed for purposes of computing the intensities of the soil bearing pressure. The actual soil bearing pressure shall not exceed the limitations of subdivisions (a) and (b) of this section for nominally unsatisfactory bearing materials or, for satisfactory bearing materials, shall not exceed the limitations of table 11-2. (2) After the treatment procedure, a minimum of one boring shall be made for every sixteen hundred square feet of that portion of the building area that is supported on treated soil, and a sufficient number of samples shall be recovered from the treated soil to demonstrate the efficacy of the treatment.

NYC Admin. Code § 27-680 Utility services.

§ 27-680 Utility services. Where utility service lines are to be laid in soil materials of class 11-65, provision shall be made to prevent damage to such service lines as follows: (a) Where the lines enter a structure, including a building, a manhole, or a junction chamber, that is rigidly supported on piles or in firm bearing material, the services shall be supported on piles or bearing materials of adequate firmness to prevent differential settlement of the service lines with respect to the structure; otherwise, provisions, such as oversized sleeves, flexible connections, utility tunnels, or other approved device, shall be made to permit the anticipated differential movement to occur without damage to the service lines. (b) Where the lines enter a structure that is supported on soil materials of class 11-65 or on soft clay or loose silt deposits, and engineering analysis shall be made of the probable differential settlement of the utility service line with respect to the structure, and provision shall be made to accommodate such displacement, as described in subdivision (a) of this section.

Source: City of New York, Charter, Administrative Code and Rules (American Legal Publishing XML export, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/newyorkcity/latest/NYCadmin/0-0-0-51299Fetched: 10/24/2026