Settlement and Consolidation, 1-25-00

Published on May 2016 | Categories: Types, School Work | Downloads: 22 | Comments: 0 | Views: 100
of 5
Download PDF   Embed   Report

Comments

Content


1-25-00, Settlement and Consolidation
Ref: Principles of Geotechnical Engineering, Braa !" #as, 1$$%
Coastal Engineering &and'oo(, )"B" &er'ich, 1$$1
*opics:
Effecti+e Stress
Compression and Consolidation Process
Settlement Categories
Preconsolidation Condition
Calc,lation of Primar- Consolidation Settlement
*ime Rate of Consolidation
---------------------------------------------------------------------------------------------------------------------
Effecti+e Stress
*otal stress at point A 'elo. the soil s,rface is e/,al to 011 the stress carried '- the .ater
in the contin,o,s +oid spaces 0i"e" pore .ater press,re, u1 and 021 the stress carried '- the
soil solids at their points of contact 0i"e" the soil s(eleton1" 2ppro3imatel- the effective
stress 0σ'1
( )
sat A w
H H H γ − + γ · σ
.here
total
w s
sat
V
W W +
· γ · γ
( ) a u − + σ · σ 1 4
.here a is the fractional s,rface area of solids 0,s,all- a551 for all
practical conditions1 so u + σ ≈ σ 4
rearranging and s,'tracting the pore press,re 0 w A
H u γ ·
, i"e" h-drostatic press,re1
( ) [ ] ( ) γ′ − · γ − γ − + γ · σ′ H H H H H H
A w A sat A w
, .here
w
γ − γ · γ′
Compression of soil la-ers d,e to stress increase '- constr,ction of fo,ndations or other loads"
Compression is ca,sed '-:
1" #eformation of soil particles
2" Relocation of soil particles
6" E3p,lsion of .ater or air from +oid spaces
Consolidation - Process the red,ction of ',l( soil +ol,me ,nder loading d,e to flo. of pore
.ater" 7or sat,rated soils, an- increment of loading 0∆σ, called s,rcharge1 .ill 'e initiall- ta(en
,p '- the pore press,re and res,lt in consolidation ,ntil a ne. e/,ili'ri,m is reached .here the
soil solids 0or s(eleton1 ta(es ,p the added load"
s,rcharge: u ∆ + σ ∆ · σ ∆ 4
A
H
A
H
7or cohesi+e soils: at t 8 0, u ∆ · σ ∆ 9 t8∞, 4 σ ∆ · σ ∆
7or non-cohesi+e soils: .ater drains faster and the load is transferred immediatel-
Categories:
1" :mmediate settlement - elastic deformation of dr- soil and moist and sat,rated soils
.itho,t change to moist,re content
a" d,e to high permea'ilit-, pore press,re in cla-s s,pport the entire added load and no
immediate settlement occ,rs
'" generall-, d,e to the constr,ction process, immediate settlement is not important
2" Primar- consolidation settlement - +ol,me change in sat,rated cohesi+e soils 'eca,se of
the e3p,lsion of .ater from +oid spaces
a" high permea'ilit- of sand-, cohesionless soils res,lt in near immediate drainage d,e
to the increase in pore .ater press,re and no primar- consolidation settlement occ,rs
6" Secondar- compression settlement - plastic ad,stment of soil fa'ric in cohesi+e soils
Preconsolidation Condition
1" normall- consolidated - present effecti+e o+er',rden press,re 8 ma3im,m press,re the
soil has 'een s,'ected to in the past 0pc1
2" o+erconsolidated - present effecti+e o+er',rden press,re 5 ma3im,m press,re the soil
has 'een s,'ected to in the past 0pc1
e
log p
;ormall- consolidated
e
log p
<+erconsolidated
p
c
!a3im,m
past load
;on-linear
re'o,nd .hen
load is remo+ed
Preconsolidation press,re determination
0Casagrande, 1$6=1
1. Esta'lish point a at .hich e-log p has
minim,m radi,s of c,r+at,re
2. #ra. hori>ontal line from a 0line ab1
3. #ra. tangent to c,r+e at a 0line ac1
4. #ra. line ad to 'isect angle bac
5. Proect the straight-line portion of gh
'ac( to intersect ad at f
6. 2'scissa of point f is the
preconsolidation press,re, pc
log p
?
o
i
d

r
a
t
i
o
,

e
a
h
b
c
d
f
pc
g
Calc,lation of @ltimate Primar- Consolidation Settlement
Sat,rated cla- soil la-er of thic(ness H, cross-sectional area A, e3isting o+er',rden
press,re po, increase in press,re ∆p, and res,lting ,ltimate primar- consolidation
settlement
Change in +ol,me is A V · ∆ , change in +ol,me is e/,al to the change in +ol,me of the
+oids 0definition of settlement1 and '- the definition of the +oid ratio:
v
eV V A V ∆ · ∆ · · ∆
@sing the initial +oid ratio and total +ol,me 0eo and Vo1 gi+es
o o
o

e
AH
e
V
V
+
·
+
·
1 1
Com'ining and rearranging gi+es
e
e
AH
eV A V
o


+
· ∆ · · ∆
1

o
e
e
H
+

·
1
Compression inde3 !c 8 slope of the e-log p c,r+e:

,
_

¸
¸ ∆ +

·

,
_

¸
¸

·
o
o
c
p
p p
e
p
p
e e
!
log log
1
2
2 1


,
_


¸
¸ ∆ +
+
·
o
o
o
c
p
p p
e
H !
log
1
• 7or thic( cla-, more acc,rate to di+ide m,ltiple la-ers
• Consider depth to 2B for s/,are fo,ndation 0B3B1 or %B for strip fo,ndations
0B3A1, B is the .idth
Compression +s" S.ell :nde3
normall- consolidated cla-s 0pc 8 po B ∆p"
( ) ( )
( )



,
_


¸
¸ ∆ +
+
·
i o
i i o
o
i c
p
p p
e
H !
log
1
o+erconsolidated cla- 0pc ≥ po B ∆p1 ,se the S.ell :nde3 0!s1


,
_


¸
¸ ∆ +
+
·
o
o
o
s
p
p p
e
H !
log
1
;<*E: ,se of !c +ice !s is conser+ati+e
most marine soils are o+erconsolidated - sedimentation increases the s,rcharge on
the soil, ',t s,'se/,ent erosion remo+es m,ch of the load
,nderconsolidated cla- 0pc ≤ po B ∆p1 0R2RE C<;#:*:<;1


,
_


¸
¸ ∆ +
+
+


,
_


¸
¸
+
·
c
o
o
c
o
c
o

p
p p
e
H !
p
p
e
H !
log
1
log
1
0partiall- on 'oth c,r+es1
• :f the e-log p plot is (no.n, can simpl- find ∆e o+er the appropriate range of
press,res and ,se
o
e
e
H
+

·
1
0.or(s for all conditions1
Good
conditionC
Compression inde3 determination
1" Graphicall- from la'orator- e-log p plot, ,se D+irgin compression c,r+eD 0i"e"
straight line portion of the c,r+e1
2" Rendon-&errero 01$E61
6E " 2
2 " 1
1
1%1 " 0


,
_


¸
¸ +
·
s
o
s c
#
e
# !
6" ;agara and !,rt- 01$E51
( )
s c
#
$$
!
1
]
1

¸

·
100
F
26%6 " 0
S.ell :nde3G determined from la' tests, generall-
! !
! ! !
5
1
10
1
to ≅
*ime Rate of Consolidation
#eri+ation ass,mptions
1" &omogeneo,s cla--.ater s-stem
2" Sat,rated
6" Hater and soil grains are incompressi'le
%" 7lo. of .ater is ,nidirectional and in the direction of consolidation
5" #arc-4s la. ass,med - i% v · , v 8 discharge +elocit-, % 8 coeff of
permea'ilit-, i 8 h-dra,lic gradient,
$ h i ∆ ·
2&
dr
cla-
sand
sand
>
h 8 ,Iγ
.
∆p
d3
d-
d>
+
>
d3d-
J+
>
B 0d+
>
Id>1d>Kd3d-
Jrate of .ater o,tflo.K - Jrate of .ater inflo.K 8 Jrate of change of +ol,meK
restrict flo. to +ertical 0>1 direction 0ass,mption %1
t
V
d&d' v d&d' d(
(
v
v
(
(
(


· −
,
_

¸
¸


+
t
V
d&d'd(
(
v
(


·


#arc-4s la. gi+es
(
u
%
(
h
% %i v
(


− ·


− · ·
since
h u
w
γ ·
com'ining gi+es
t
V
d&d'd( (
u %
w


·


γ

1
2
2
d,ring settlement
( )
t
e
e
d&d'd(
t
eV V
t
V
t
V
o
v


+
·

+ ∂
·


·


1
, since 0 ·


t
V

and
o o

e
d&d'd(
e
V
V
+
·
+
·
1 1

t
e
e (
u %
o w


+
·


γ

1
1
2
2
ass,me that the decrease in +oid ratio is proportional to the increase in effecti+e stress 0or
the decrease in pore press,re1
u a e
v
∂ − · ∂
, av 8 coeff" of compressi'ilit-
define the coeff" of +ol,me compressi'ilit-
o
v
v
e
a
)
+
·
1
t
u
)
(
u %
v
w


− ·


γ

2
2
, define coeff" of consolidation
v w
v
)
%
c
γ
·

t
u
c
(
u
v


·


2
2
,
sol+ing gi+es a time factor
2
dr
v
v
H
t c
* ·
estimate )v from e-log p plot at appropriate press,res,
p
e
e
)
av
v


+
·
1
1
,
2
2 1
e e
e
av
+
·
Variation of Degree of Consolidation with Time Factor
0
0"1
0"2
0"6
0"%
0"5
0"=
0"L
0"E
0"$
1
0"001 0"01 0"1 1
Time Factor, T
v
=C
v
t/H
2
d
e
g
r
e
e

o
f

c
o
n
s
o
l
i
d
a
t
i
o
n
,

U
(
%

/
!
"
"
Si+aram M S.amee 01$LL1 empirical relationship for @ 0degree of settlement1 from 0-100F
1L$ " 0
E " 2
%
1
%
100
F
1
1
]
1


¸


,
_

¸
¸
π
+
π
·
v
v
*
*
+
and
65L " 0
= " 5
2
100
F
1
100
F
%
1
1
]
1


¸


,
_

¸
¸


,
_

¸
¸

,
_

¸
¸ π
·
+
+
*
v

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close