14B-18-1806 Presumptive load-bearing values of soils.

The provisions of Section 1806 of IBC are adopted by reference with the following modifications:

1.   Revise Section 1806.1 by replacing "Table 1806.2" with "Table 1806.2(1) or 1806.2(2), as applicable" and deleting the second sentence.

2.   Revise Section 1806.2 to read:

"1806.2 Presumptive load-bearing values.

Where only a limited geotechnical investigation in accordance with Section 1803.1, exception 3, is performed, the load-bearing values used in design for supporting soils near the surface shall not exceed the values specified in Table 1806.2(1). Where the building official has reason to doubt the classification, strength or compressibility of the soil, the requirements of Section 1803.5.2 shall be satisfied.

Where a full geotechnical investigation is performed in accordance with Section 1803, the load-bearing values used in design for supporting soils near the surface shall not exceed the values specified in Table 1806.2(2), unless the use of higher values is recommended by the registered geotechnical engineer.

Presumptive load-bearing values shall apply to materials with similar physical characteristics and dispositions. Mud, organic silt, organic clays, peat or unprepared fill shall not be assumed to have a presumptive load-bearing capacity unless data to substantiate the use of such a value are submitted."

3.   Delete Table 1806.2.

4.   Insert Tables 1806.2(1), 1806.2(2) and 1806.2(3) to read:

TABLE 1806.2(1)
PRESUMPTIVE LOAD-BEARING VALUES WITHOUT FULL GEOTECHNICAL INVESTIGATION

 

CLASS OF MATERIALS	VERTICAL FOUNDATION PRESSURE (psf)	LATERAL BEARING PRESSURE (psf/ft below natural grade)	LATERAL SLIDING RESISTANCE
			Coefficient of friction a	Cohesion (psf) b
Sandy gravel and gravel (GW and GP)	3,000	200	0.35	–
Sand, silty sand, clayey sand, silty gravel and clayey gravel (SW, SP, SM, SC, GM and GC)	2,000	150	0.25	–
Clay, sandy clay, silty clay, clayey silt, silt and sandy silt (CL, ML, MH and CH)	1,500	100	–	130
Non-engineered fill	500	50	0.1	–

 

For SI: 1 pound per square foot = 0.0479 kPa, 1 pound per square foot per foot = 0.157 kPa/m.

a.   Coefficient to be multiplied by the dead load.

b.   Cohesion value to be multiplied by the contact area, as limited by Section 1806.3.2.

TABLE 1806.2(2)
PRESUMPTIVE VERTICAL FOUNDATION PRESSURE VALUES WITH GEOTECHNICAL INVESTIGATION

CLASS	DESCRIPTION	NOTES	CONSISTENCY OR RELATIVE DENSITY a	ALLOWABLE NET BEARING PRESSURE (psf)
1	DOLOMITE bedrock	c	Hard, sound rock, minor jointing	200,000
2a	Fractured DOLOMITE surface	d, h	Blocky limestone with soil filled seams and fractures	60,000
2b	Fractured DOLOMITE surface	e, h	Blocky limestone with soil filled seams and fractures	100,000
2c	DOLOMITE surface	f, h	Rock with minor fractures and jointing	120,000
2d	DOLOMITE surface	g, h	Rock with minor fractures and jointing	150,000
3	HARDPAN, hard silty clay, or very dense clayey silt, (CL, CL-ML)	i	Very hard or very dense	20,000
		j	Hard or dense	12,000
4	SAND, GRAVEL or SILT, silty sand, clayey sand, silty gravel or clayey gravel (SW, SP, GW, GP, SC, SM, GC, GM, ML)	k	Dense	3,000
			Medium dense	2,000
			Loose	1,000
			Very loose	Note b
5	Silty CLAY, Clayey SILT (CH, CL, ML-CL, MH)	–	Hard	4,000
			Very stiff	3,000
			Stiff	2,000
			Medium	1,500
			Soft	Note b
			Very soft	Note b
6	Organic SILT, CLAY or PEAT	m	–	Note b
7	Non-Engineered FILL	n	–	500
8	CONTROLLED FILL	o	95% Modified Proctor	3,000
9	Improved In-Situ Soil or Fill	p	–	Note b

 

For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.

a.   Classified in accordance with Table 1806.2(3).

b.   Requires engineering analysis and testing by a registered geotechnical engineer.

c.   1 foot into sound rock (recovery greater than 95% and RQD greater than 70%) with 20% increase per foot of additional penetration up to a maximum of 400,000 pounds per square foot.

d.   Surface of refusal to standard caisson rig rock auger, correlated to borings with recovery greater than 90% and RQD greater 40%, rock unconfined compressive strength greater than 2,000 pounds per square inch.

e.   Surface of refusal to standard caisson rig rock auger, correlated to borings with recovery greater than 90% and RQD greater than 50%, rock unconfined compressive strength greater than 2,500 pounds per square inch.

f.   Surface of refusal to standard caisson rig rock auger, correlated to borings with recovery greater than 95% and RQD greater than 60%, rock unconfined compressive strength greater than 3,000 pounds per square inch.

g.   Surface of refusal to standard caisson rig rock auger, correlated to borings with recovery greater than 95% and RQD greater than 70%, rock unconfined compressive strength greater than 3,500 pounds per square inch.

h.   No load tests are required up to presumptive bearing pressures. If higher bearing pressures are required than shown in table or RQD or rock compressive strength does not meet values shown, load tests are required to confirm allowable bearing pressure.

i.   Where qu is greater than 14,000 pounds per square foot, or N is greater than or equal to 50.

j.   Where qu is greater than or equal to 8,000 pounds per square foot, or N is greater than or equal to 30.

k.   Allowable net bearing value assumes minimum depth of embedment is 2.5 feet and a minimum width of 1.5 feet. Allowable bearing values shall be reduced proportionally for less depth of embedment, or the effect of reduced confinement from a rise in the water table above the foundation level.

l.   [Reserved.]

m.   Organic means more than 10% organic matter as determined in accordance with ASTM D2974.

n.   Presumptive value for light or temporary structure. Otherwise engineering analysis required.

o.   Controlled fill shall be placed in specified lifts with moisture control, under full time observation of a registered geotechnical engineer or their qualified representative in accordance with ASTM D1557.

p.   Improved fill or soil in-situ by dynamic compaction, compaction grouting, or other methods.

TABLE 1806.2(3)
STANDARDS FOR CLASSIFYING SOIL CONSISTENCY AND RELATIVE DENSITY

Clay		Sand and Gravel
DESCRIPTIVE TERM	UNCONFINED STRENGTH (psf)	DESCRIPTIVE TERM	SPT N VALUE
Very soft	< 500	Very loose	0 - 3
Soft	500 - 1,000	Loose	4 - 9
Medium	1,000 - 2,000	Medium	10 - 29
Stiff	2,000 - 4,000	Dense	30 - 49
Very stiff	4,000 - 8,000	Very Dense	≥ 50
Hard	> 8,000

 

For SI: 1 pound per square foot = 0.0479 kPa.

5.   Revise Section 1806.3 to read:

"1806.3 Lateral load resistance.

Where the presumptive values of Table 1806.2(1) are used to determine resistance to lateral loads, the calculations shall be in accordance with Sections 1806.3.1 through 1806.3.4. Where the presumptive values of Table 1806.2(2) are used, resistance to lateral loads shall be as provided in the geotechnical report."

6.   Revise Section 1806.3.1 by replacing "Table 1806.2" with "Table 1806.2(1)."

7.   Revise Section 1806.3.3 by replacing "Table 1806.2" with "Table 1806.2(1)."

(Amend Coun. J. 10-7-20, p. 21791, Art. II, § 29)