Alpha

Classification

Repute

Property	Type	Description	Default	Example/range of values
General
Name		The item's name	Algorithm x	any number
Type		The item's type	Alpha
Category		The item's sub group	Option
Kind		The item's group	Algorithms
Notes		Free-form notes regarding this item		any text
Reference		Academic reference from which the algorithm has been derived		any text
Algorithm
Option		Choice of implementations of this algorithm	Skempton's alpha
Alpha	[-]	<to be added>	0.45	> 0 and £ 1
Ready Reckoner
Undrained strength		<to be added>	previously added value (kPa)
Vertical effective stress		<to be added>	previously added value (kPa)
Slenderness ratio	[-]	<to be added>	previously added value
Help
Help file		Help file providing further information about this item	Rex.chm
Web site		Web site for the program	www.geocentrix.co.uk/help/

The alpha algorithm allows you to override the calculation of skin friction against the pile shaft in cohesive soils.

Skin friction (f_s) in cohesive soils is calculated from the expression:

f_s = a C_u

where

C_u = the undrained shear strength of the soil in contact with the pile shaft; and

a = a dimensionless factor.

Alpha is calculated according to one of the following expressions (depending on which Option is selected):

Custom

a = any value between 0.0 and 1.0

Skempton

a = 0.45

One-half

a = 0.5

London Clay

a = 0.6

Randolph

For (C_u/s'_v) >= 1, a = 0.5 (C_u/s'_v)^-0.75

For (C_u/s'_v) < 1, a = 0.5 (C_u/s'_v)^-0.5

Semple & Rigden

For C_u < 35 kPa , a = 1.0

For 35 kPa <= C_u < 80 kPa , a = 1.39 - C_u / 90 kPa

For 80 kPa <= C_u, a = 0.5

Bowles

For C_u < 75 kPa , a = 1.1 - 0.3 x C_u / 75 kPa

For 75 kPa <= C_u < 200 kPa , a = 0.98 - 0.3 x C_u / 125 kPa

For 200 kPa <= C_u, a = 0.5

Sladen

a = 0.4 (s'_v/C_u)^-0.45

O'Neill & Reese

For (C_u/p _a) <= 1.5, a = 0.55

For 1.5 < (C_u/p _a) <= 2.5, a = 0.55 - 0.1 x ( C_u/p _a - 1.5)

For 2.5 < (C_u/p _a) , a is undefined