Geotechnical Formulas PDF

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Formulas for Soil Mechanics...

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1

GEOTECHNICAL Index and Classification Properties of Soils Unit weight :

 

W V

Gs γw 1+ e Moist unit weight :  = dry  1 +  (Gs + e) γ w Saturated unit weight: sat = 1+ e Zero air void unit weight:  Gsγ w zav = 1+ e Moisture content (water content) Ww  Ws ωG s Degree of saturation : s = e

Dry unit weight :

Porosity :

d =

n =

e 1+ e

DRY

H1

MOI ST

H2 G. W. T .

SATURATED

Phases of Soil

Air void ratio = n (1 – s) G.W.T. = ground water table where : W = total weight V = volume Gs = specific gravity e = void ratio w = unit weight of water = 9.81 kN/m3 ( 1gram/cm3 )

H3

2

GEOTECHNICAL Relative density ( Density index ) Dr =

e max - e e max - e min

Dr =

1/ d min -1/ d 1/ d min -1/ d max

or

e = in-situ void ratio emax = void ratio in loosest condition emin = void ratio in densest condition d = dry unit weight in the field d(max) = dry unit weight in densest condition d(min) = dry unit weight in loosest condition

Soil Characteristic brittle solid plastic liquid

Liquidity Index 2mm

2t o0 . 0 5 mm

0 . 0 5t o0 . 0 0 2 mm

4 C

Qb

0.25 H

H

a s s u me d h i n g e

Design Load :

Qall =

Qb + Q f F.S.

Qall

 method Pa= H – 4C Cuts in Clay when

 50 Pa qp = 0.59[ Nvalue ( )]0.8 Pvb

tan  =

D S

D = diameter of pile S = spacing of piles center to center

Pa = 100 kPa Pvb = effective vertical pressure at base elevation Frictional capcity : Qf =   Pv P L a. Nvalue  15  = 1.5 – n (z)0.5 (drilled on sand)  = 2 – 0.15 (z)0.5 (drilled on gravel) b. Nvalue  15 N  = value [ 1.5 – n (z)0.5 ] 1 5 Pv = effective vertical overburden pressure at depth z. z = height from ground surface to mid-height of a given layer n = 0.245 P = perimeter of pile L = length of pile

Settlement of Piles Se = Se1 + Se2 + Se3 Elastic Settlement of Pile, Se1 Se1 =

( Q wp + ξ Q ws ) L Ap Ep

Qwp = load carried at the pile point under working load condition Qws = load carried by frictional resistance under working load condition Ap = cross sectional area of pile L = length of pile

GEOTECHNICAL Settlement of Pile caused by the Load at the Pile Tip , Se2

Se2 =

qwp D Es

(1 - s2 ) Iwp

Settlement of Group of Piles

13

qwp =

Qwp Ap

Es = modulus of elasticity of soil s = Poisson’s ratio of soil Iwp = influence factor Settlement of Pile caused by the Load transmitted along of the pile shaft , Se3 Se3 =

Q ws D (1 - s2 ) Iws PLEs

Iws = 2 + 0.35

L D

P = perimeter of pile L = length of pile Iws = influence factor D = diameter of pile

S= Σ

C cH Po + ΔP log + eo Po 1

Cc = compression index H = thickness of clay layer eo = initial void ratio P = average increase in pressure on clay Po = effective overburden pressure at the midheight of the clay layer...