Recommended Values of Bond Strength

The table is based on field and laboratory tests.

Bond strength: Classic drilled nails

q_s,k[kPa]¹⁾ according to EA Pfähle
Cohesionless soils			Cohesive soils			Rocks
q_c ²⁾ [MN/m²]			c_u ³⁾ [kN/m²]			q_u,k ⁴⁾ [MN/m²]
7.5	15	25	60	150	250	0.5	5	20
55 -80	105 - 140	130 -170	30 - 40	50 -65	65 - 85	70 - 250	500 -1000	500 - 2000

Notes:

1) Determination of bond strength should be part of the geological survey

2) Cone resistance, CPT test (according to DIN EN ISO 22476-1)

3) Total cohesion of the soil

4) Uniaxial compression strength

Literature:

EA-Pfähle, ISBN: 978-3-433-03005-9

Values in the table based on soil and rock classification.

Estimated bond strength of soil nails in soil and rock (source: Elias a Juran, 1991)

Material	Construction method	Soil / rock type	Ultimate bond strength q_s[kPa]
Rock	Rotary drilled	Marl / limestone	300 - 400
		Phyllite	100 - 300
		Chalk	500 - 600
		Soft dolomite	400 - 600
		Fissured dolomite	600 - 1000
		Weathered sandstone	200 - 300
		Weathered shale	100 - 150
		Weathered schist	100 - 175
		Basalt	500 - 600
		Slate / hard shale	300 - 400
Cohesionless soils	Rotary drilled	Sand / gravel	100 - 180
		Silty sand	100 - 150
		Silt	40 - 120
		Piedmont residual	40 - 120
		Fine colluvium	75 - 150
	Driven casing	Sand / gravel -low overburden -high overburden	190 - 240 280 - 430
		Dense moraine	380 - 480
		Colluvium	100 - 180
	Augered	Silty sand fill	20 - 40
		Silty fine sand	55 - 90
		Silty clayey sand	60 - 140
	Jet grouted	Sand	380
		Sand gravel	700
Fine - grained soils	Rotary drilled	Silty clay	35 - 50
	Driven casing	Clayey silt	90 - 140
	Augered	Loess	25 - 75
		Soft clay	20 - 30
		Stiff clay	40 - 60
		Stiff clayey silt	40 - 100
		Calcareous sandy clay	90 - 140

Note: Convert values in kPa to psf by multiplying by 20.9. Convert values in kPa to psi by multiplying by 0.145.

GEO5