Earth Pressures

H

0.65*KA*t*H

Lateral pressure (earth & water)distribution to be applied on walls

Theoretical methods

Methods based onfield measurements

Rankine

Coulomb

earth pressure cells

Load cells etc. installed on struts

Japanese A, F

Japanese B

Terzaghi & Peck

Tschebotarioff

Japanese C, D, G, H

Japanese A

CHAPTER 4 EARTH PRESSURE ACTING ON RETAINING SYSTEMSTheoretical approaches need to be checked by field measurements.Two alternative field measurements are possible: 1. Strut load measurements2. (Total) earth pressure cell measurements  Pressure distributions are recommended for the two basic types of soils: cohesionless & cohesive

A..SANDY SOILS i) LATERAL PRESSURE DISTRIBUTION DIAGRAMS BASED ON FIELD MEASUREMENTS   I..Load cells (or similar) on struts 1. Terzaghi & Peck (1967)

t = wet unit weight of soil  KA=(1-sin’)/(1+sin’) = tan2(45-/2)

  = angle of internal friction

+ water pressure

0.2*t*H

Hh2

h1

h2/2

h1/2

0.25**H

0.7*H

0.1*H

0.2*H

a*b*t

H

2. Tschebtrarioff (1973)

(Japanese ref. 0.2H)

3. Japanese codes (C D G H)

+ water pressure

+ water pressure

t = wet unit weight of soil a=coefficient of excavation depth 5m>H3m, a=(H-1)/45mH, a=1 b=coefficient of soil type for sand b=2

4. Japanese Code A

t = wet unit weight of soil

H

K*t*H

K*t*H

H

0.4*H

0.6*H

II..Earth pressure cells on walls

1. Japanese Codes A & F

2. Japanese Code B

K=coefficient of lateral pressuresand: 0.2~0.3

 when GWL is high add water pressure.

t = wet unit weight of soilK=coefficient of lateral pressure (by GWL) GWL high 0.3~0.7GWL low 0.2~0.4 Combined: earth press. + water press.

Pa=KA*(t*H1+'H2)-2cKa

H1

H2

Pw=H2* w

PA

H German+water pressure

ii) LATERAL PRESSURE DISTRIBUTION BASED ON THE EARTH PRESSURE DISTRIBUTION (Theory)

PA=KA(H-2cKA)

effective

1.0*KAT*t*H

H

0.25*H

0.75*HH

0.2~0.4*t*H

0.5*H

0.25*H

0.25*H

B..COHESIVE SOILS i) BASED ON FIELD MEASUREMENTS I..Load cell (etc) measurements on struts 1.Terzaghi and Peck (1967)

65.

orC

HN

u

4.

uC

HN

H

cmK

t

uAT .

.41

4.

u

t

c

H

Soft to medium clays Stiff fissured clays

when m is taken as 1.0

0.5*t*H

H

0.25*H0.40*H

0.5*t*H

H

2.Tschebtarioff

Medium clays Stiff Clays

5 m

a*c*t

H

Lateral earth pressure and water pressure

3.Codes C D G H

+water pressure

a: coefficient of excavation depth

5m>H3m a=(H-1)/4

5mH a=1

c: coefficient of soil type

N5 c=6

N>5 c=4

4.Code A (~Terzaghi & Peck)

0.2~0.3*t*H

0.75*H

0.25*H

K*t*H

H H

0.25*H

0.25*H

0.5*H

t = wet unit weight of soil K0.3 cu=qu/2 H

cK

t

u

4

1

II..(By) Earth Pressure cell measurements on walls 

1.Japanese Codes A, F

H

K*t*H

K: coefficient of lateral pressure

Soft clay 0.5~0.8

Stiff clay 0.2~0.5

2. Japanese Codes B

K*t*H

H

0.4*H

0.6*H

K: coefficient of lateral pressure

Soft clayN4

0.4~0.5

Stiff clayN>4

0.2~0.4

N: SPT blow count

H

ii) LATERAL EARTH PRESSURE DISTRIBUTION BASED ON THE EARTH PRESSURE THEORY

KacHKaPa t 2

)2

45(tan2 Ka

Deep and large excavations: H15 m Braced Walls : -Theoretical distribution -Cell pressure records

  Medium 10<H<15 Braced Walls: -Theoretical distribution

-Cell pressure records  

H<10 Braced Walls: -Cell pressure records-Strut load measurements

A Architectural Institute of Japan 1974,11 (1988,01 rev.)B Japan Soc. Of Civ. Eng. 1977,01 (1986,06)C Japan Road Association (Earth works) 1977,01 (1987,05)D Japan Road Association (Utilities Conduits) 1980,04 (1986,03)E Subway Tech. Council 1974,08 (1978,03)F Japan Sewage Works Agency 1976,04 (1988,10)G Metropolitan Expressway Public Corp. 1972,09 (1990,10)H Japan Highway Public Corp. 1977,11 (1990,07)I Railway Tech. Res. Inst. 1979,12 (1987,09)