conset 10 april 2012.pdf
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Transcript of conset 10 april 2012.pdf
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