Table 8 Iowa DOT (2011) BDM nominal...

Table 8

Iowa DOT (2011) BDM nominal geotechnical end bearing design chart

LRFD-driven pile foundation geotechnical resistance design chart for end bearing
Soil description	SPT blow count		Estimated nominal resistance values for end bearing pile
	N value		Timber pile: kNa^,c	Steel H, grade 50: MPa			Prestressed concrete with dimension in mm: kNb			Steel pipe with diameter in mm: kNd
	Mean	Range	Timber pile: kNa^,c	HP254	HP305	HP356	305	356	406	254	305	356	457
Granular material
	<15	—	e	e	e	e	e	e	e	e	e	e	e
Fine or medium sand	15	—	142	e	e	e	267	373	480	142	213	284	480
Coarse sand	20	—	196	e	e	e	373	516	658	195	284	391	640
Gravelly sand	21	—	196	e	e	e	373	516	658	195	284	391	640
	25	—	249	e	e	e	g	g	g	g	g	g	g
	—	25–50	f	[13-27]	[13-27]	[13-27]	f^,g	f^,g	f^,g	g	g	g	g
	—	50–100	f	[27-55]	[27-55]	[27-55]	f	f	f	g	g	g	g
	—	100–300	f	[55-16]	[55-16]	[55-16]	f	f	f	g	g	g	g
	—	>300	f	[124]	[124]	[124]	f	f	f	g	g	g	g
Bedrock
	—	100–200	f	[82]	[82]	[82]	f	f	f	g	g	g	g
	—	>200	f	[124]	[124]	[124]	f	f	f	g	g	g	g
Cohesive material
	12	10–50	71	e	e	e	124	178	231	71	106	142	231
	20	—	107	[7]	[7]	[7]	195	284	373	124	160	231	373
	25	—	142	[13]	[13]	[13]	267	373	480	142	213	284	480
	50	—	f	[27]	[27]	[27]	516 f	729 f	943 f	249	427	569	943
	100	—	f	[48]	[48]	[48]	f	f	f	f	f	f	f

LRFD-driven pile foundation geotechnical resistance design chart for end bearing
Soil description	SPT blow count		Estimated nominal resistance values for end bearing pile
	N value		Timber pile: kNa^,c	Steel H, grade 50: MPa			Prestressed concrete with dimension in mm: kNb			Steel pipe with diameter in mm: kNd
	Mean	Range	Timber pile: kNa^,c	HP254	HP305	HP356	305	356	406	254	305	356	457
Granular material
	<15	—	e	e	e	e	e	e	e	e	e	e	e
Fine or medium sand	15	—	142	e	e	e	267	373	480	142	213	284	480
Coarse sand	20	—	196	e	e	e	373	516	658	195	284	391	640
Gravelly sand	21	—	196	e	e	e	373	516	658	195	284	391	640
	25	—	249	e	e	e	g	g	g	g	g	g	g
	—	25–50	f	[13-27]	[13-27]	[13-27]	f^,g	f^,g	f^,g	g	g	g	g
	—	50–100	f	[27-55]	[27-55]	[27-55]	f	f	f	g	g	g	g
	—	100–300	f	[55-16]	[55-16]	[55-16]	f	f	f	g	g	g	g
	—	>300	f	[124]	[124]	[124]	f	f	f	g	g	g	g
Bedrock
	—	100–200	f	[82]	[82]	[82]	f	f	f	g	g	g	g
	—	>200	f	[124]	[124]	[124]	f	f	f	g	g	g	g
Cohesive material
	12	10–50	71	e	e	e	124	178	231	71	106	142	231
	20	—	107	[7]	[7]	[7]	195	284	373	124	160	231	373
	25	—	142	[13]	[13]	[13]	267	373	480	142	213	284	480
	50	—	f	[27]	[27]	[27]	516 f	729 f	943 f	249	427	569	943
	100	—	f	[48]	[48]	[48]	f	f	f	f	f	f	f

Timber piles shall not be driven through soils with N > 25

With prestressed concrete piles, the preferred N for soil at the tip ranges from 25 to 35. Prestressed concrete piles have been proven to be difficult to drive in very firm glacial clay and very firm sandy glacial clay. Prestressed concrete piles should not be driven in glacial clay with consistent N > 30 to 35

End bearing resistance values for timber piles are based on a tip area of 465 cm² (72 in²). Values shall be adjusted for a different tip area

Steel pipe piles should not be driven in soils with consistent N > 40

Neglect end bearing

Use of end bearing is not recommended for timber piles when N > 25 or for prestressed concrete piles when N > 35 or for any condition identified with this note

End bearing resistance shall be 0·0389 × N value (ksi) or 0·2682 × N value (MPa)

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