Download - Kuliah Mektan II 05
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SI-215MEKANIKA TANAH II
DOSEN:
Analisis Penurunan danKonsolidasi
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DOSEN:DR. techn. INDRA NOER HAMDHAN, ST., MT.DR. Ir. IMAM ASCHURI, MT.DR. YUKI ACHMAD YAKIN, ST, MT
JURUSAN TEKNIK SIPILINSTITUT TEKNOLOGI NASIONAL
BANDUNG 2012
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Pendahuluan
1) Tegangan tanah yg terjadi< daya dukung tanah ijin
2) Penurunan yg terjadi <penurunan ijin
Persyaratan StabilitasKonstruksi Bangunan Sipil:
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penurunan ijin
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Penurunan Ijin
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Penurunan (Settlement)
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Penurunan bangunan dapat terjadi akibat:
• Penurunan seketika (Immediately settlement)
• Penurunan konsolidasi (Consolidation settlement)
• Konsolidasi primer
• Konsolidasi sekunder
Penurunan (Settlement)
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• Konsolidasi sekunder
Penurunan Seketika (Immediately settlement):
Penurunan yang terjadi akibat tambahan teganganefektif pada tanah tetapi air pori dalam tanah belumterdisipasi (sifat elastis tanah)
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Penurunan Konsolidasi (Consolidation settlement):
Penurunan yang terjadi akibat tambahan tegangan efektifpada tanah sehingga air pori dalam tanah terdisipasi
Hasil proses konsolidasi:
Penurunan (Settlement)
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• Besarnya penurunan (settlement), mm, cm
• Kecepatan penurunan ( settlement), hari, bln, tahun
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Faktor yang mempengaruhi besarnya penurunan:
1. Sifat kompresibilitas tanah
2. Tebal lapisan tanah yang kompresibel
3. Besarnya tekanan efektif tanah
Faktor yang mempengaruhi kecepatan proses
Penurunan (Settlement)
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Faktor yang mempengaruhi kecepatan prosespenurunan:
1. Tebal lapisan tanah yang kompresibel
2. Kondisi drainase
3. Waktu beban bekerja
4. Keberadaan permeable tanah
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Penurunan Konsolidasi
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Time-Consolidation Relationship UnderConstant Load
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Jenis tanah berdasarkan tegangan yangdialami:
1. Normally Consolidated soils
2. Over Consolidated soilsPo = . ho
Pc = . hc
Penurunan Konsolidasi
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hc ho
Po = . ho
Pc = . hc
Po = Pc
hc
ho
Pc = . hc
Po < Pc
Normally Consolidated soils Over Consolidated soils
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Analogi proses konsolidasi dari Terzaghi
Konsolidasi Terzaghi
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Ditinjau dari beberapa kondisi:
1. Tidak air dalam piston
2. Ada air dalam piston tapi katub ditutup
3. Ada air dalam piston tapi katup dibuka penuh
4. Ada air dalam piston tapi katup dibuka tidak penuh
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Consolidometer atauOedometer
Maksud :
mempelajari karakteristik
Uji Konsolidasi di Laboratorium
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mempelajari karakteristikkompresibiltas tanah
• Menganalisis besarnya penurunan melalui grafikhubungan tegangan dan angka pori
• Menganalisis waktu proses konsolidasi melalui grafikhubungan penurunan dan waktu
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Hasil pengujian:
Uji Konsolidasi di Laboratorium
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Time vs Consolidation Rate
Pressure vs Void Ratio
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Calculation of consolidation settlementdibagi 2 case:
1. Normally consolidated
Calculation of Consolidation Settlement
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1. Normally consolidated
2. Over consolidated
How to determine whether the soils will beclassified normally consolidated or overconsolidated ????????
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Tegangan Prakonsolidasi
Uji Konsolidasi di Laboratorium
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Casagandre Procedure for determining preconsolidation pressure
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Step penentuan NC atau OC :
1. Tentukan overburden pressure(Po= . ho)
2. Tentukan Tegangan Prakonsolidasi (Pc)
3. Tentukan rasio Teg. Prakonsolidasi (Pc)
Penurunan Konsolidasi
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3. Tentukan rasio Teg. Prakonsolidasi (Pc)dengan Teg. Overburden (Po),
OCR= Pc/Po
4. Normal Consolidated (OCR≤1) dan OverConsolidated (OCR>1)
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Penurunan Konsolidasi
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2
1
o
21
)/(
1
e1
HCc.S
)/(.
2121
P
PLogsehingga
ppLogCce
Cc
HSH
ppLoge
LogPLogPe
ee
o
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00
log1 P
PPH
e
CS oc
Normally Consolidated Soils
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001 Pe
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Over Consolidated Soils
00
log1 P
PPH
e
CS or
Case 1 (Po+P)< Pc
Case 2
Case 1
Over Consolidated Soils
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)(log
1)(log
1 000 c
cccr
P
PPH
e
C
P
PH
e
CS
Case 2 (Po+P)> Pc
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Soil Compressibility
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)1/('
log'1
2
peCC
t
tHCS
Penurunan Konsolidasi Sekunder
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p
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Kecepatan proses konsolidasi dipengaruhi:
• Koefisien konsolidasi (sifat tanah)
• Tebal lapisan tanah kompresibel
• Drainase tanah (1 arah atau 2 arah)
Waktu dan Derajat Konsolidasi
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Penurunan akibat proses konsolidasi telah selesai,maka derajat konsolidasinya 100% (U=100%)
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Jika suatu saat (waktu, t), besar penurunannyaSt, maka Derajat Konsolidasi nya :
%100xS
U t
Waktu dan Derajat Konsolidasi
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%100xS
U t
U = 60% artinya bahwa saat itu penurunan yangterjadi 60% dari S (penurunan total konsolidasiprimer) dan waktu yang dibutuhkan disebut t60
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Assumptions:
• Clay-water system is homogeneous
• Saturation is complete
• Compressibility of water is negligible
• Compressibility of soil grains is negligible
• Water flows only in one direction (in direction of loading)
Teori Konsolidasi Terzaghi
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• Water flows only in one direction (in direction of loading)
• Darcy’s law is valid
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y wx z
w 0
v Wv v 1 1 e
x y z t 1 e t
x x x x
y y y y
hv k i k
x
hv k i k
y
Mathematical Derivation (1)
Teori Konsolidasi 1D
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y y y y
z z z z
v k i ky
hv k i k
z
t
e
ez
hk
y
hk
x
hk w
zyx
02
2
2
2
2
2
1
t
e
ez
uk
y
uk
x
uk w
zyx
02
2
2
2
2
2
1
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t
e
ez
uk w
z
02
2
1
t
u
ta
t
u
tau
ta
ta
t
ev
wvwvv
Mathematical Derivation (2)
Teori Konsolidasi 1D
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t
u
tek
a
z
u
z
vw
02
2
1
t
u
ct
u
ek
a
z
u
vz
vw
1
1 02
2
2
2
z
uc
t
uv
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Mathematical Derivation (3)
wv
z
vw
zv
m
k
a
ekc
)1( 0
)1( 0e
am v
v
Dengan menggunakan deret Fourier
Teori Konsolidasi 1D
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Dengan menggunakan deret Fourier
td
CT v
v 2
Tv = Faktor waktu
Cv = Koefisien konsolidasi
t = Waktu
d = Panjang lintasan
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d = 1/2H d = H
Teori Konsolidasi 1D
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(a) Double Drainage (b) Single Drainage
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td
CT v
v 2
Teori Konsolidasi 1D
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Untuk menentukan nilai Cv (Coefficient ofconsolidation) di laboratorium digunakan beberapacara, diantaranya:
1) Log Time method2) Root Time Method
Koefisien Konsolidasi (Cv)
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2) Root Time Method
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Log Time Method
2
50
VV d
t
TC
Koefisien Konsolidasi (Cv)
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196,050
50
VTU
t
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Root Time Method
2 VV d
t
TC
Koefisien Konsolidasi (Cv)
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848,090
90
V
V
TU
dt
C
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Metode yang sering digunakan untukmempercepat proses konsolidasi adalah:1) Preloading2) Drainase vertikal3) Kombinasi
Drainase Vertikal
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3) Kombinasi
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Vertical Drains
Vertical Drains
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Vertical Drains
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Vertical Drains
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Vertical Drains
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Vertical Drains
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