N.J. Admin. Code § 19:6-2.8

Current through Register Vol. 56, No. 21, November 4, 2024

Section 19:6-2.8 - Borings

(a) Except for one and two-family dwellings with plan dimension not exceeding 2,500 square feet and where soil conditions are essentially uniform, at least five borings shall be made for each building, one in each corner and one in the center. For one and two-family dwellings of a size not to exceed 2,500 square feet, one boring shall be made for each such building. For buildings supported on piling, one boring shall be made for every 4,000 square feet of building area or fraction thereof, but not less than five borings for each building. Additional borings may be necessary if soil conditions are not found to be uniform. The boring program shall be expanded by probes as described in section 10 of this subchapter.

1. 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:

i. 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;

ii. The foundation is designed for bearing pressures not exceeding those permitted in table 613.6 of this subchapter, without increase for embedment.

(b) At least two thirds of the required number of borings shall be located within the area under the building. Those outside of the area shall not be more than 25 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) Rules concerning depth are:

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, or in the case of pile supported buildings, below anticipated tip elevations of piling as necessary to satisfy the more restrictive of the following requirements:

i. 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 other classes: 25 feet.

ii. Except as noted in subparagraphs i, iii and iv of this subsection, in order to determine the full depth of the organic silt strata and the underlying depth of sand or desiccated clay, all borings shall penetrate to a depth of at least 25 feet below the top of the organic soil or to such depth that the penetration resistance to the sample spoon decreases significantly, whichever is deeper;

iii. Borings shall extend to the depth at which the vertical stress caused by the proposed construction is reduced to ten per cent 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 subsection (a) of this section;

iv. At least one boring for each building or one boring for each 100,000 square feet of building area or fraction thereof, whichever is greater, shall extend as a minimum depth to the lower limit of the compressible material, defined as varved clay or silt, or material of classes 9-65 and 10-65. For buildings supported on piles, all borings shall be carried to the foregoing criteria;

v. For piling deriving their support in end bearing, the borings shall penetrate to at least ten feet into the compact glacial till that overlies bedrock.

2. Where rock is encountered in borings within the depth noted in paragraph 1 of this subsection, the borings shall be cored to a minimum of five feet into rock, or farther where necessary or required, to obtain at least a recovery of 35 per cent from five feet of penetration, but not to exceed the depth noted in paragraph 1 of this subsection. However, for foundations supported on piles bearing on the rock and having a capacity in excess of 80 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) Rules concerning types are:

1. Soil borings: Soil samples shall be recovered at intervals not to exceed five feet and at every change of soil strata, except that sampling in the upper 25 feet shall be continuous. Such samples shall be recovered using a two-inch split spoon sampler having an inside diameter of 1-3/8 inches and a constant internal cross section. The sampler shall be at least 24 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 1-5/8- inch O.D. drill rods. The sampling tools shall be driven with a 140-pound hammer having a fall of 30 inches. The blows per foot so recorded shall be designated hereinafter by the symbol N. The fall of the hammer shall be 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 similar effects. All samples, except those of rock, shall be preserved in airtight 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 1-3/8 inches in diameter.

(e) Records of all borings required by the provisions of subsection (a) of this section shall accompany the application for approval of the building 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 the casing is used); the weight of the 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-inch increment of penetration; the elevation of the ground surface referenced to an established datum that is not subject to subsidence or lateral movement; 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; per cent 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 sampling traps, and so forth; 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) 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 building 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.

N.J. Admin. Code § 19:6-2.8