N.J. Admin. Code § 19:6-2.42 - Pile foundations

(a) The allowable axial load on a pile shall be the least value permitted by consideration of the following factors (for battered piles, the axial load shall be computed from the resultant of all vertical loads and lateral forces occurring simultaneously):

1. The capacity of the pile as a structural member.

2. The allowable bearing pressure on soil strata underlying the pile tips.

3. The resistance to penetration of the piles, including resistance to driving, resistance to jacking, the rate of penetration, or other equivalent criteria as established in this section.

4. The capacity as indicated by load test, where load tests are required.

5. The maximum loads prescribed in this section.

(b) Rules concerning the capacity of the pile as a structural member are:

1. Embedded portion of the pile: The compressive stress on any cross section of a pile produced by that portion of the design load that is considered to be transmitted to that section shall not exceed the allowable values for the construction materials as established in table 615.11. The tensile stress shall not exceed the values established in this article for like material.

2. Portion of the pile that is not embedded: That portion of any pile that is free standing in air or water shall be designed as a column in accordance with the provisions of this subchapter, fixed at a point five feet below the soil contact level in class 8-65 material or better and ten feet below in any other material. The conditions of lateral and rotational restraint offered by the pile cap shall be considered in determining the equivalent unbraced length.

3. Load distribution along embedded portion of the pile: The portion of the design load acting on any cross section of a pile may be determined by analysis, considering time dependent changes in distribution of the load. As an alternative method for the purposes of this section, it may be assumed that:

i. For piles embedded 40 feet or more in materials of class 10-65 or better, and bearing on or in materials of classes 1-65 to 5-65: 75 per cent of the load shall be assumed to be carried by the tip. For shorter piles, with similar conditions of embedment and bearing, 100 per cent of the load shall be assumed carried by the tip.

ii. For piles embedded in materials of class 10-65 or better and bearing on or in materials of classes 6-65 to 10-65, the full load shall be assumed to act as a cross section located at 2/3 of the embedded length of the pile measured up from the tip. Where tapered piles are used, the stress at all sections of the pile shall be determined on the basis that the full load acts at a location 2/3 of the embedded length of the pile measured up from the tip and that 1/3 of the full load acts at the tip. The stresses so computed shall not exceed the allowable values in table 615.11.

iii. For conditions not covered in subparagraphs i and ii of this subsection the provisions relating to analysis shall apply.

(c) Rules concerning allowable bearing pressure on soil strata underlying the pile tips are:

1. Bearing capacity: The allowable pile load shall be limited by the provision that the pressures in materials at and below the pile tips, produced by the loads on individual piles and by the aggregate of all piles in a group or foundation, shall not exceed the allowable bearing values established in section 21 of this subchapter. The provisions of sections 24 and 25 of this subchapter shall apply. The transfer of load from piles and soil shall be determined by the recognized method of analysis. As an alternative, for purposes of this section, piles or pile groups may be assumed to transfer their loads to the underlying materials by spreading the load uniformly at an angle of 60 degrees with the horizontal, starting at a polygon circumscribing the piles, located as follows:

i. For piles embedded entirely in materials of classes 4-65 to 8-65, the polygon shall be circumscribed at a level located 2/3 of the embedded length of the pile, measured up from the tip.

ii. For piles penetrating through soils of classes 9-65, 10-65, or 11-65 into bearing soils of class 8-65 or better, the polygon shall be circumscribed at the bottom of the strata of class 9-65, 10-65, or 11-65 materials.

iii. In the case of piles having enlarged bases, the lateral distribution of the load to the soil may be assumed to begin at the junction of the shaft and the enlarged base and to extend as follows:

(1) In the case where the enlarged base is formed in loose or medium compact (N value less than 30) soils in class 6-65 or 7-65 that extend 20 feet or more below the junction of the base and shaft, or that are of lesser extent but are directly underlain by soil of class 5-65 or better, the bearing area may be taken at the plane six feet below said junction but not lower than the bottom of the soils strata of class 6-65 or 7-65.

(2) Where the enlarged base is formed in compact (N value 30 to 60) soils of class 6-65 or 7-65 or in any soil of these classes that extends less than 20 feet below the junction of the base and the shaft and that is underlain by soil of class 8-65 or poorer, the bearing area shall be taken at planes less than six feet below said junction, with a lower limit of three feet where the material is very compact (N value 60, or greater) and the extent of the class 6-65 or 7-65 material is ten feet below the junction of shaft and base. (Provisions of section 48 of this subchapter relating to the minimum depth of bearing stratum below the junction of base and shaft shall apply.) For conditions intermediate between that described in item (1) above and the lower limit conditions described here, the location of the bearing area may be determined by linear interpolation between the indicated limits of N value and extent of bearing material below the junction of shaft and base, giving equal weight to both variables.

(3) Where the enlarged base is formed in or on soils of class 4-65 or 5-65, the bearing area shall be taken at a depth below the junction of the shaft and base consonant with the size and depth of the base formed, and as evaluated from the required test piles.

iv. For all piles bearing on soils of classes 1-65 to 3-65, analysis of load distribution will not be required if the requirements relating to capacity of the pile as a structural member, to resistance to penetration, to load test where required, and to maximum tabulated loads are satisfied.

v. For piles in soils of classes 9-65 and 10-65, for cases not described above, or for any case where the method of installing the pile utilizes a temporary casing, the provisions relating to analysis shall apply.

vi. In no case shall the area considered as supporting the load extend beyond the intersection of the 60 degrees planes of adjacent piles or pile groups.

2. Bearing stratum: The plans for the proposed work shall establish, in accordance with the requirements relating to allowable bearing pressure, the bearing strata to which the piles in the various sections of the building are to be penetrated and the approximate elevations of the top of such bearing strata. Where penetration of a given distance into the bearing strata is required for adequate distribution of the loads, such penetration shall be shown on the plans. The indicated elevations of the top of the bearing strata shall be modified by such additional data as may be obtained during construction. All piles shall penetrate to or into the designated bearing strata.

(d) Where subsurface investigation, as described in this subchapter, or general experience in the area indicates that the soil must be penetrated by the pile, consists of glacial deposits containing boulders, or fills containing riprap, excavated detritus, masonry, concrete, or other obstructions in sufficient numbers to present a hazard to the installation of the piles, the selection of type of pile and penetration criteria shall be subject to the approval of the chief engineer, but in no case shall the minimum penetration resistance be less than that stipulated in tables 617.3 and 617.4.

1. Piles installed by use of steam-powered, air-powered, diesel-powered or hydraulic impact hammers:

i. The minimum required driving resistance and the requirements for hammer energies for various types and capacities of piles are given in tables 617.3 and 617.4. To obtain the required total driving resistance, the indicated driving resistances shall be added to any driving resistance experienced by the pile during installation, but which will be dissipated with time (resistance exerted by nonbearing materials or by materials which are to be excavated). For purposes of this section, the resistance exerted by nonbearing materials may be approximated as the resistance to penetration of the pile recorded when the pile has penetrated to the bottom of the lowest stratum of nominally unsatisfactory bearing material. (Class 11-65 or to the bottom of the lowest stratum of soft or loose deposits of class 9-65, but only where such strata are completely penetrated by the pile. The provisions of sections 44 through 48 of this subchapter shall also apply.)

ii. Alternate for similitude method: The requirement of piling to the penetration resistances given in tables 617.3 and 617.4 will be waived where the following five conditions prevail:

(1) The piles bear on, or in, soil of class 5-65 through class 10-65;

(2) The stratigraphy, as defined by not less than one boring for every 4,000 square feet of building area, shall be reasonably uniform or divisible into areas of uniform conditions;

(3) Regardless of pile type or capacity, one load test, as described in this section, shall be conducted in each area of uniform conditions, but not less than two typical piles for the entire foundation installation of the building or group of buildings on the site, nor less than one pile for every 15,000 square feet of building area, or one pile for every 100 piles installed, whichever is less, shall be load tested;

(4) Except as permitted by the provisions of item (6) below, all building piles within the area of influence of a given load-tested pile of satisfactory performance shall be installed to the same or greater driving resistance as the successful load-tested pile. The same equipment that was used to install the load-tested pile shall be used to install all other building piles, and the equipment shall be operated identically with respect to steam or air pressure, type and condition of cap block, length of hose, accessories, and all other variables. Also, all other piles shall be of same type, size and shape as the load-tested pile. All building piles within the area of influence represented by a given satisfactory load-tested pile shall bear in, or on, the same bearing stratum as the load-tested pile;

(5) A report by the architect or engineer shall be submitted establishing to the satisfaction of the chief engineer that the soil bearing pressures do not exceed the values permitted by the provisions of this subchapter and that the probable differential settlements will not cause stress conditions in the building in excess of those permitted by the provisions of this subchapter.

(6) Where the structure of the building or the spacing and length of the piling is such as to cause the building and its foundation to act as an essentially rigid body, the building piles may be driven to length and/or penetration into the bearing stratum without regard to penetration resistance, subject to the requirements of item (5) above relating to submission of report.

2. Piles installed by jacking or static forces: The carrying capacity of a pile installed by jacking or static forces shall be not more than 50 per cent of the load or force used to install the pile to the required penetration, except for piles jacked into position for underpinning. The working load of a temporary underpinning shall not exceed the total jacking force at final penetration. The working load of each permanent underpinning pile shall not exceed the larger of the following values: 2/3 of the total jacking force used to obtain the required penetration if the load is held constant for seven hours without measurable settlement; or 1/2 of the total jacking force at final penetration if the load is held for a period of one hour without measurable settlement. The jacking resistance used to determine the working load shall not include the resistance offered by nonbearing materials which will be dissipated with time.

3. Piles installed by use of vibratory hammer: The capacity of piles installed by vibratory hammers shall not exceed the value established by the principle of similitude as follows:

i. Comparison piles, as required by the provisions of subsection (e) of this section, shall be installed using an impact hammer and driving resistance corresponding to the proposed pile capacities as determined in subsection (d) of this section, or to tip elevations and driving resistances as determined by the architect or engineer.

ii. For each comparison pile, install an identical index pile by use of the vibratory hammer at a location at least four feet, but not more than six feet, from each comparison pile. The index piles shall be installed to the same tip elevation as the comparison pile, except that where the comparison piles bear on soils of classes 1-65 to 5-65, the index piles shall bear in, or on, similar material. All driving data for the index piles shall be recorded.

iii. The index piles shall be load tested in accordance with the provisions of subsection (e) of this section. Should the specified load test criteria indicate inadequate capacity of the index piles, steps i, ii and iii of this paragraph shall be repeated, using longer, larger, or other types of piles.

iv. All building piles within the area of influence of a given satisfactorily tested index pile shall be installed to the same or lesser rate of penetration (inches per minute) as the successful index pile. The same equipment that was used to install the index pile, identically operated as to rpm, manifold pressure, and so forth, shall be used to install the building piles. Also, all building piles shall be of the same type, size and shape as the index pile. All building piles within the area of influence as represented by a given satisfactory tested index pile bear in, or on, the same bearing stratum as the index pile.

(e) Load test of piling shall be required as follows:

1. Piles installed by static forces and piles installed by bored holes: The load bearing capacity of all types and capacities of piles installed by static forces or in bored holes (other than underpinning piles installed by jacking) shall be demonstrated by load test.

2. Piles driven by impact hammers: The load bearing capacity of piles installed by impact hammers shall be demonstrated by load test when the proposed pile capacity exceeds the following values.

i. Caisson piles: No load test required.

ii. Piles installed upon end to rock of class 1-65, 2-65 or 3-65--100 tons, except as provided in subparagraph iv of this paragraph, and except that no load tests will be required for piles up to 200 tons capacity wherein the pile load does not exceed 80 per cent of the load determined on the basis of limiting stresses in the pile materials and provided that the pipe or shell be driven to the resistance indicated in table 617.3;

iii. Piles bearing on rock or hardpan (soil classes 1-65 to 5-65) other than as described in subparagraph ii above and except as provided in subparagraph iv below.

iv. Piles bearing on materials of class 8 or better, wherein, on the assumption that 100 per cent of the load reaches the pile tip (or, in the case of piles having an enlarged base or other enlargement of the bearing area, the top of the enlargement), the bearing pressure on the soil underlying the tips or bases can be demonstrated to be equal to or less than the values of basic allowable pressure indicated in table 613.7, provided that the class and density of the bearing material supporting the piles be confirmed by not less than one boring at each column location, then the chief engineer may reduce the required number of load tests.

v. All other types of piles: 30 tons.

3. Piles installed by use of vibratory hammers: The load bearing capacity of all types and capacities of piles (other than caisson piles) shall be demonstrated by load test.

4. Load test procedures: Before any load test is made, the proposed apparatus and structure to be used in making the load test shall be satisfactory to the chief engineer and, when required by the chief engineer, all load tests shall be made under the surveillance of the chief engineer or his representative. A complete record of such tests shall be filed with the chief engineer:

i. Areas of the foundation site within which the subsurface soil conditions are substantially similar in character shall be established. In addition, for friction piles bearing on soil materials of class 6-65 or poorer, the uniformity of each such area shall be verified by installing at least three penetration test piles, distributed over the area. Continuous records of penetration resistance shall be made for such piles. If the records of penetration resistance are not similar or are not in reasonable agreement with the information obtained from the borings, the assumed areas of similar subsurface conditions shall be modified in accordance with the information derived from the penetration-test piles and additional penetration-test piles shall be installed as required to verify the uniformity of such areas.

ii. For piles installed by jacking or static forces or by impact hammers, one load test shall be conducted in each area of uniform conditions, but not less than two typical piles for the entire foundation installation of the building or group of buildings on the site, and not less than one pile for each 15,000 square feet of the area of the building wherein said piles are to be used shall be load tested. For piles installed by use of vibratory hammers, one comparison pile shall be installed and one index pile shall be load tested in each area of uniform conditions, but not less than two index piles shall be tested for the entire foundation installation of the building or group of buildings on the site, nor less than one index pile tested for every 7,500 square feet of the area of the building wherein said piles are to be used. For piles whose capacity is determined on the basis of similitude, the provisions of this subsection shall apply.

iii. The load test shall be conducted by a method that will maintain constant load under increasing settlement. Settlement observations shall be made by means of dial extensometers. The extensometers shall provide readings to the nearest 0.001 inch. In addition, settlement observations shall be taken using an engineer's level reading to 0.001 foot, properly referenced to a well established benchmark:

(1) Test loads shall be applied by direct weight or by means of a hydraulic jack acting against a deadweight or a reaction frame supported by anchor piles. The loading platform or box shall be carefully constructed to provide a concentric load on the pile. If direct weight is employed, the loading increments shall be applied without impact or jar. The weight of the loading platform or box shall be obtained prior to the test and this weight shall be considered as the first increment of load. If a hydraulic jack is employed, facilities for maintaining each increment of desired load constant under increasing settlement shall be provided. The gauge and the jack shall be calibrated as a unit for each project.

(2) The test load shall be twice the proposed working load of the pile. The test load shall be applied in seven increments at a load of 50 per cent, 75 per cent, 100 per cent, 125 per cent, 150 per cent, 175 per cent and 200 per cent of the proposed working load. After the proposed working load has been applied and for each increment thereafter, the test load shall remain in place until there is no measurable settlement in a two-hour period. The total test load shall remain in place until settlement does not exceed 0.001 foot in 48 hours. The total load shall be removed in decrements not exceeding 25 per cent of the total load at one-hour intervals or longer. The rebound shall be recorded after each decrement is removed, and the final rebound shall be recorded 24 hours after the entire test load has been removed.

(3) Under each load increment, settlement observations shall be made and recorded at one-half minute, one minute, two minutes, four minutes, and each four minutes thereafter after application of load increment, except in the instance of the total load, where, after the four minutes reading, the time interval shall be successively doubled until the final settlement limitation is reached and the load is removed.

(4) The allowable pile load shall be the lesser of the two values computed as follows:

(A) Fifty per cent of the applied load causing a net settlement of the pile of not more than 0.01 inch per ton of applied load. Net settlement in this paragraph means gross settlement due to the total test load minus the rebound after removing 100 per cent of the test load.

(B) Fifty per cent of the applied load causing a net settlement of the pile of 0.75 inch. Net settlement in this paragraph means gross settlement as defined in paragraph 1 of this subsection, less the amount of elastic shortening in the pile section due to total test load.

5. Foundation piles: Except as provided in subsection (d) of this section, all building piles within the area of influence of a given load-tested pile of satisfactory performances shall be installed to the same or greater penetration resistance (or static load) as the successful load-tested pile. The same equipment that was used to install the load-tested pile shall be used to install all other building piles, and the equipment shall be operated identically with respect to speed, height of fall, stroke, pressure, type and conditions of cap block, length of hose, accessories, and all other variables. Also all other piles shall be of the same type, size, and shape as the load-tested pile. All building piles within the area of influence represented by a given satisfactory load-tested pile shall bear in, or on, the same bearing stratum as the load-tested pile. For friction piles where the actual pile lengths vary more than 50 per cent from that of the test pile, the chief engineer may require investigation to determine the adequacy of the piles.

6. Pile groups: When the chief engineer has reason to doubt the safe load sustaining capacity of pile groups, he may require, at the expense of the owner, group load tests up to 150 per cent of the proposed group load.

7. "Casing off": Any temporary supporting capacity that the soil might provide to the pile during a load test, but which would be dissipated with time, shall be obviated by "casing off" or by other suitable means. For purposes of this section, temporary supporting capacity shall include the resistances offered by any strata of nominally unsatisfactory bearing materials (class 11-65) or of soft or loose deposits of class 9-65 or 10-65 that are completely penetrated by the pile, or any resistance offered by granular soils that will be dissipated by reason of vibration.

(f) Rules concerning maximum loads are:

1. Basic maximum loads: except as permitted by the provisions of paragraph 2 below, the maximum allowable pile load, determined in accordance with the provisions of this subchapter, shall not exceed the values specified in table 617.5

2. Substantiation of higher allowable loads: The pile capacities tabulated in table 617.5 may be exceeded where a higher value can be substantiated on the basis of test and analysis as follows:

i. Load tests: The provisions of subsection (e) of this section shall be supplemented as follows:

(1) Not less than one single-pile test shall be conducted for each 10,000 square feet of pile foundation area, or one such load test for every 100 piles installed, whichever is less;

(2) Final load increments shall remain in place for a total of not less than 96 hours;

(3) Single test piles shall be subjected to cyclical loading or suitably instrumented so that the movements of the pile tip and butt may be independently determined. Other alternate methods or devices, acceptable to the chief engineer, which will permit evaluation to the transfer of load from piles to soil may be used;

(4) If required, group load tests shall be performed in groups of numerically average size. Except where the proposed foundation is limited to a single and/or two-pile groups, each test group shall contain not less than three piles;

(5) Individual pile loadings shall not exceed those determined from a single-pile load test;

(6) The provisions of subsection (e) of this section shall apply.

ii. Analysis and report: A report shall be submitted by the architect or engineer establishing to the satisfaction of the chief engineer (on the basis of soil and load tests and foundation analysis, including analysis of the group action of the piles) that the proposed construction under a 100 per cent overload of the foundation is safe against failure of the pile and soil materials, and showing 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.

iii. Penetration resistance: The penetration resistance shall not be less than that required by the provisions of subsection (d) of this section or, where applicable values are not indicated therein, shall be determined from the required load tests. The pile material shall be capable of withstanding the driving stresses without being damaged.

Notes

N.J. Admin. Code § 19:6-2.42