When soil is loaded to a stress level greater than it ever ‘experienced’ in the past, the soil structure is no longer able to sustain the increased load, and start to breakdown.

Preconsolidation Pressure - Pc: Maximum pressure experienced by soil in the past

Normal Consolidation: OCR = 1 when the preconsolidation pressure is equal to the existing effective

vertical overburden pressure Pc = p’o

present effective overburden pressure is the maximum pressure that soil has been subjected in the past

Over Consolidation: OCR > 1 when the preconsolidation pressure is greater than the existing

effective vertical overburden pressure Pc > p’o

present effective overburden pressure is less than that which soil has been subjected in the past

It also said soil is in preconsolidated condition

OCR (over consolidation ratio) =

Under Consolidation: OCR < 1 when the preconsolidation pressure is less than the existing effective

vertical overburden pressure Pc < p’o,

e.g : recently deposited soil geologically or manually.

Pc = p’o

p’o

Pc

Effective Consolidation Stress p’o

Void

ratio

e

Pc

'

c

o

P

p

Pc > p’o

p’o

Pc

p’o

Pc < p’o

Pc

DETERMINATION OF EFFECTIVE PRESSURE

CONSOLIDATION

Normal Consolidation

Over consolidation

oc pp OR 1p

p

o

c o

occ

p

pplog.H.

eo1

CcS

oc pp OR 1p

p

o

c

po + p < pc

o

occ

p

pplog.H.

eo1

CsS

po < pc < po+p c

oc

o

ccc

p

pplog.H.

eo1

Cc

p

plog.H.

eo1

CsS

DETERMINATION OF COMPRESSIVE PARAMETER

CONSOLIDATION TIME :

%U100log.933,0781,1Tv

%100xS

SU

c

i,c

Where : t = consolidation time Tv = consolidation factor depended on consolidation degree (U) U = consolidation degree in percent, descript as ratio of design settlement to total settlement Cv = coefficient of consolidation, get from consolidation test

2

v100

%U

4T

U = 0 – 60%

U > 60%

t = (Tv . H2 ) / Cv

Consolidation Settlement

Hitunglah penurunan

konsolidasi primer pada

lapisan lempung N/C

setebal 5m akibat

pembebanan 50kPa

diatas permukaan tanah.

Hitunglah waktu

penurunan konsolidasi

primer bila diketahui nilai

cv = 0.85m2/tahun

5m

5m

2m

Rock

Sand

Gs=2.65, e=0.7

Sand

50% saturation

Clay, Cv=0.85m2/yrs

Cc=0.45, eo=0.9

sat=15kPa

Ground water table

Surcharge = 50kPa

5m

5m

2m

Rock

Sand

Gs=2.65, e=0.7

Sand

50% saturation

Clay, Cv=0.85m2/yrs

Cc=0.45, eo=0.9

sat=15kPa

Ground water table

Surcharge = 50kPa Perhitungan Overburden

Pressure (po)

Berat Volume Lapisan Pasir diatas

m.a.t.

Berat Volume Effektif lapisan

Pasir dibawah m.a.t.

2.650.50.79.81

1 10.7

22.21kPa

sw wsand

GSre

e

( )' '

1

1 1

2.6519.819.516kPa

10.7

sand satsand w

s ws w ww

GG e

e e

Contoh : Consolidation Settlement

5m

5m

2m

Rock

Sand

Gs=2.65, e=0.7

Sand

50% saturation

Clay, Cv=0.85m2/yrs

Cc=0.45, eo=0.9

sat=15kPa

Ground water table

Surcharge = 50kPa Berat Volume effektif

Lapisan lempung dibawah

m.a.t.

Sehingga didapat Po :

Perhitungan Penurunan :

( )

o sand sand clay

' '

15 9.81 5.19kPa

5p' 2 +3 ' + '

2

5222.21+39.516+ 5.19 85.94 kPa

2

clay sat clay w

'log

1 '

2.5 85.94500.45 log

10.9 85.94

0.592m0.199m0.792m0.8m

o oc c

o o

H p pS C

e p

Contoh : Consolidation Settlement

Berat Volume effektif

Lapisan lempung dibawah

m.a.t.

Sehingga didapat Po :

Perhitungan Penurunan :

Penyelesaian :

Perhitungan Overburden

Pressure (po)

Berat Volume Lapisan Pasir diatas

m.a.t.

Berat Volume Effektif lapisan

Pasir dibawah m.a.t.

( )' '

1

1 1

2.6519.819.516kPa

10.7

sand satsand w

s ws w ww

GG e

e e

2.650.50.79.81

1 10.7

22.21kPa

sw wsand

GSre

e

( )

o sand sand clay

' '

15 9.81 5.19kPa

5p' 2 +3 ' + '

2

5222.21+39.516+ 5.19 85.94 kPa

2

clay sat clay w

'log

1 '

2.5 85.94500.45 log

10.9 85.94

0.592m0.199m0.792m0.8m

o oc c

o o

H p pS C

e p

Kecepatan waktu Konsolidasi

2

2

2

%0 to 60%,

4 100

60%, 1.7810.933log(100 %)

or

tt

tt v

t v

v v drv v v

dr v

SU

S

UforU T

forU T U

t THT c t

H c

Ut = rata2 derajat konsolidasi(%)

St = besar penurunan lapisan pada waktu t

S = penurunan total (U90) lapisan akibat konsolidasi

Tv = faktor waktu (time factor)

Hdr = rata2 jarak pengaliran air selama konsolidasi

cv = koefisien konsolidatsi

tv = lama waktu konsolidasi

Time rate of settlement

8.55 0.76 1.163 95

∞ 0.80 ∞ 100

6.24 0.72 0.848 90

4.17 0.64 0.567 80

2.96 0.56 0.403 70

2.11 0.48 0.287 60

1.45 0.40 0.197 50

0.93 0.32 0.126 40

0.52 0.24 0.071 30

0.23 0.16 0.031 20

0.06 0.08 0.008 10

t (yr) St

(m) Tv Uavg

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8 9

Time (yr)

Sett

ele

men

t (m

)

2

2

2

%0 to 60%,

4 100

60%, 1.7810.933log(100 %)

or

tt

tt v

t v

v v drv v v

dr v

SU

S

UforU T

forU T U

t THT c t

H c

More to come…

Hitunglah besarnya penurunan total akibat adanya

beban tanah timbunan jalan dan berapa lama waktu

dibutuhkan untuk penurunan tersebut bila sudah

dapat dianggap mencapai derajat konsolidasi 90%?

Lapisan Impermeable

Hitunglah besarnya penurunan TOTAL apabila :

Δσ = 87,14 kN/m2 ; H1 = 4m ; H2 = 3,2m ; H3 = 1m,

Lapisan pasir : γd =14,6kN/m3 ; γsat = 17,3 kN/m3,

Lapisan lempung N/C : γsat = 19,3 kN/m3 ; LL = 38,

e = 0,50 ; µs = 0,50 ; Es = 6000 kN/m2 ; Cc = 0,32

Task 1

Task 2

o

Methods for Calculating Induced Stresses

Boussinesq’s Method

Simplified Method

60o Approximation

)(qIz

Boussinesq’s Method

Boussinesq’s Method

Boussinesq’s Method

Influence Factor Chart

Elastic Settlement Chart

Approximate Methods

1:2 method (60° approximation)

DEPARTEMEN PENDIDIKAN NASIONAL UNIVERSITAS LAMBUNG MANGKURAT

FAKULTAS TEKNIK

PROGRAM S-1 NON REGULER - PROGRAM STUDI TEKNIK SIPIL Jl. Brig.Jend. H. Hasan Basry, Kampus Fakultas Teknik Unlam Banjarmasin Kal.Sel

Telepon : (0511) 3303802 Faksimili : (0511) 3303802 Kode Pos : 70123

Dengan menggunakan konsep penentuan surcharge ()

dari grafik hubungan antara ; (/qo dan z/B), variasi (Iz

dengan m dan n), dan/atau (average); Hitunglah besarnya

penurunan : elastis (Se) dan/atau konsolidasi (Sc) pada

lapisan tanah lempung N/C.

Impermeable layer