bridge foundation in alluvial soil

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DEEP FOUNDATION WHERE ROCK STRATA/FIRM FOUNDATION IS NOT AVAILABLE THEM THIS TYPE FOUNDATION IS AN GOOD ALTERNATIVE TO PILE

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Page 1: BRIDGE FOUNDATION IN ALLUVIAL SOIL

CBL 571 m

Ground level 558 m

Top of pier cap 568 m

Side slope 12 H:1V

Depth of scour= 5.00 m

Height of overburden Top.El 576.5

Well cap top El 560.00

Height 16.50 m

Height of well= 12.55 m

Angle of internal friction of soil= F= 23 deg

Coeff. Wall friction= 0.424

Pier top width= 2.5 m

Rock level= 547.45 m

Length of pier 5 m

Skin friction 3.40 t/sq.m

Poissons ratio of soil= 0.50

SBC of rock 250.00 t/sq.m

Coeff of subgrade reaction=Cg 2500.00 t/cum

Assumed hor deformation of soil r1= 2.00 cm

Unit weight of soil(sat)= 2.01 t/cum

saturated height= 5.00 m

Unit weight of concrete yc= 2.4 t/cum

Load on the well cap=

Permissible stress in concrete 7 N/mm2

Permissible stress in steel=80% of 2300kg/sq.cm 190 N/mm2

Bond stress in concrete 0.6 N/mm2

Permissible tension 0.2 N/mm2

E for concrete 22400 N/mm2

m= 13.33

k= 0.33

j= 0.89

Q= 10.26 bd2

Bottom width= 4.167

Say 4.200 m

Bottom length=L= 5

say 5.000

Outer Dia of well= L+2t= 5.800 m

Kp= 2.28

Ka= 11.600m 0.44

Page 2: BRIDGE FOUNDATION IN ALLUVIAL SOIL

Thickness based on lateral pressure=

Dia of well= 5.400

K= 0.35

m1= 0.2

m2= 0.15

h= 12.55

P= 58.6116

coeff= 2.645

V= 155.04 t

Intensity of load= 28.71 t/sq.m

Allowabble compressive stress=s_all= 28.71 t/sq.m

Now

p= 7.079 + 5.00 12.08 t/sq.m

ro= 2.7 m

Therefore ri= 2.05 m

Thickness= 0.85 m A

Min thickness of steining= 0.70 m B

Thickness adopted 0.85 m

Thickness of steining in rect. Area:

Height of soil inducing the earth pressure

Height of embankment= 16.50

Depth of sinking= 12.55

Total depth of soil 29.05 m

Intensity of earth pressure 25.58 t/sq.

Efeective length= 4.80 m

Bending moment= 73.67 t-m

Thickness of well= 84.72 cm

Say 85.00 cm

Thickness of steining below 6m 1.00 m

Thickness of steining for rect portion:

Based on skin friction:

0.85 m C

Based on IRC 78 0.88 m

Moment due to lateral loads= 22.71 t-m

prr

all

all

io2

=

'

2

2

2

1'

K

eDP

oDhK

oth

=

=

d

fdt

c

41

2

Hkdt =

Page 3: BRIDGE FOUNDATION IN ALLUVIAL SOIL

Moment due to eccentric load= 58.93 t-m

Total moment= 81.64 t-m

Effective span= 4.75 m

Thickness of steining= 89.19 cm

Therefore max. thickness= 0.89

Overall thickness= 90.00 cm

Diameter based on lateral pressure & vertical loads

HH

NHHFhFhD

wallc

wallc

O

=

5.0

2

Page 4: BRIDGE FOUNDATION IN ALLUVIAL SOIL

F=P= 5.13 t

H= 12.55 m

h= 5.00 m

Therefore Do= 5.85 m

Diameter provided= 5.80 m

Thickness of well cap(assumed) 1.50 m

Perimeter= 35.62 m

Cros sectional area of steining= 32.06 sq.m

Surface area of well cap= 60.06 sq.m

Equivalent dia 8.74 m

Section Modulus I1 94.30 m4

I2 55.55 m4

I=I1+I2= 149.85 m4

Z=I/y 51.67 m3

Length= 17.4 m

Average width=Bo=A/L= 3.45 m

Load from the trough= 1375.72 t

Dead load from pier= 1148.40 t

weight of well cap= 90.09 t

Self weight of well= 1495.91 t

Soil load= 3552.29 t

Add for impact load@ 5% 205.51 t

Total 7867.92 t

Permissible tilt= 0.21 m

Permissible shift= 0.13 m

Moment due to shift 187.74 t-m

Moment due to tilt 312.89 t-m

Moment due to eccen= 4525.28 t-m

Total Moment= 5025.91 t-m

fb= 97.262 t/sq.m

fv= 131.00 t/sq.m

f1= 228.26 t/sq.m

f2= 33.74 t/sq.m

Ka= 0.44

Max. intensity of pressure= 31.89 t/sqm

STEINING REINFORCEMENT:

Hoop stress= 89.74 t/sqm <fc

qall 300.00 t/sq.m

D 5.85

Page 5: BRIDGE FOUNDATION IN ALLUVIAL SOIL

hor steel

Ast= 60.33 sq.cm

dia of bar 25 mm

Area= 4.91

No. tiers 2

Spacing= 16.27 cm

Min. hor steel= 0.04% bdh

3.6 cm2

dia of bar 10 mm

Area= 0.79

No. tiers 1

Spacing= 22 cm

say 200 mm

vert.steel Min steel 0.20% bd

641.18 sq.cm

dia of bar 16 mm

Area= 2.01

No. of bars= 318.9

Say 320

Outer face 214

Spacing= 16.65 cm

say 165 cm

Inner face= 108

Spacing= 32.98 cm

say 150 cm

Reinforcement in the rect reach:

As before construction of the pier the depth of the soilwill be from GL to Rock level. Later

will be filled with sand which offer passive resistence. Hence The depth of soil to be

considered for the design will be higher of the height of embankment or ht of well

Height of embankment= 16.50 m

Depth of sinking= 12.55 m

Max. of the two= 16.50 m

Net height (less ht of plug) 14.00 m

Effective length= 4.80 m

Intensity of earth pressure= 12.33 t/sq.m

Moment 23.67 t-m

Effective depth= 98.00 cm

Area of steel= 142.80 sq.cm

Dia of bar 32

Area= 8.042

Spacing= 5.6320

Page 6: BRIDGE FOUNDATION IN ALLUVIAL SOIL

Design of well Curb

Min Height of curb= 2.10 m

say 2.00 m

Angle of bevel face= 30

mu for above angle= 0.4

Total Hoop tension= 2.56 t

Hoop tension in curb

r 3 m

d= 4.900 m

H= 735.3 t

Hoop compression 214.552 t

Net hoop tension= 520.75 t

Design hoop tension= 781.1312 t

Hoop steel= 188.2 sq.cm

Dia of rods 12 mm

Area 1.131

No. 168

Spacing 9.16 cm

Provide spacing 9.00 cm

Min steel= .72kN/cum

Volume/m height= 19.24 cum

Steel area= 13.85 kg

Area of steel= 17.65 sq.cm Less than above okay

Pier area= 69.72

Intensity of load= 88.45 t/sq.m

M= 66.36 t-m

Moment of resistence= 10.26 D2

There fore d= 80.41 cm

Overall depth= 91.66

Say= 90.00 cm Okay

Thickness provided= 125.00 cm

0.3

3.80F

2.000

5.60F

0.10

A1=Bottom open area= 24.63 sq.m

A2=top open area= 11.34 sq.m

Page 7: BRIDGE FOUNDATION IN ALLUVIAL SOIL

Volume of curb= 52.84 cum

Deduct a 0.76 cum

b 30.58 cum

23.65 cum

Min steelSteel 72.00 kg/cum

1703.01 kg

Dia of rod 12.00 mm

area 1.13 sq.cm

wt/m 0.89 kg/m

Spacing of stirrups 200 mm

No. 92

Total length= 3078.42 m

Wt= 2733.06 kg

2.73 t

Provide hoop steel for balance quantity of 1.37 t

Dia of rod 25.00 mm

area 4.91

wt/m 3.85 kg/m

L= 18.06 m

Qty/ring= 69.61

No. of rings 20.00

Spacing= 10.000 cm c/c

Say @ 10.50 cm c/c

Wt= 2784.31 kg

2.78

Page 8: BRIDGE FOUNDATION IN ALLUVIAL SOIL

Design of plug:

Thickness of bottom plug(As per IRC)= 2.40 m

Thickness of plug= 4.70

Therefore thickness= 2.17 m

Thickness of plug for rect. Portion

6.31 W=total bearing presure

fc 200 t/sq.m

= 0.15

R=radius 5.8 m

q=SBC= 175 t/sq.m

b=width of short side 5

a=short side/long side 1

Therefore t= 2.51 m

Effective length= 4.90 m

Design load fcator 1.5

t2= =1.18R

2q/fc 4.553

Therefore thickness= 2.13 m

Therefore well plug thickness= 2.51 m

say 2.500 m

Thickness of well cap(assumed)(computation in sheet wellcap_pier)

Stability of well:

= 38

32

cf

Wt

a61.114

3 22

=

cf

qbt