APPROXIMATE CALCULATION OF MODULUS OF SUBGRADE REACTION

 APPROXIMATE CALCULATION OF MODULUS OF SUBGRADE REACTION (Ks)

Soil Properties

Ks = qult / DH

Where,

q_ult = q_a x SF

Ultimate Soil Pressure is at a Settlement, DH = 0.0254m  (If Soil Investigation Report is not Available)

Ks = 40 x SF x q_a  KN/m3 .......... As per (Foundation Analysis and Design - Fifth Edition ) by Joseph E. Bowles (Chapter 9.6 - Page 503 - Modulus of Subgrade Reaction)

Allowable Bearing Capacity, q_a = 300 KN/m2

Factor of Safety, SF = 1.5 (Chapter 4.15 - Page 276 - Safety Factors in Foundation Design )

Modulus of Subgrade Reaction, Ks = 18000 KN/m³

Table 9-1 Range of Modulus of Subgrade Reaction ks Use Values as Guide and for Comparison when Using Approximate Equations
Soil	Ks (kN/m3)
Loose Sand	4800 - 16000
Medium Dense Sand	9600 - 80000
Dense Sand	64000 - 128000
Clayey Medium Dense Sand	32000 - 80000
Silty Medium Dense Sand	24000 - 48000
Clayey Soil:
qa ≤ 200 kPa	12000 - 24000
200 ≤ qa ≤ 800 kPa	24000 - 48000
qa > 800 kPa	> 48000

 

Table 4-9 Values of Stability Numbers (or Safety Factors) Usually Used
Failure Mode	Foundation Type	SF
Shear	Earthworks Dams, Fills, etc.	1.2 -1.6
Shear	Retaining Structure Walls	1.5 - 2.0
Shear	Sheetpiling Cofferdams Temporary Braced	1.2 - 1.6
Shear	Excavations	1.2 - 1.5
	Footings
Shear	Spread	2.0 - 3.0
Shear	Mat and Uplift	1.7 - 2.5
Seepage	Uplift, Heaving	1.5 - 2.5
Seepage	Piping	3.0 - 5.0