Slope Stability - Frasta - Unikarta
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8/19/2019 Slope Stability - Frasta - Unikarta
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GEOTEKNIK UNTUK
PERENCANAAN
PENAMBANGAN
Dr. Singgih Saptono
Email: [email protected]
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Other Factors
Influencing
Mining
• Technology Change
• Work Practice• Safety
• Poor Weather
• Infrastructure Constrains
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S a p t o n o –
G e o t e c h n i c a l E n g i n e e r i n g W
o r k s h o p ,
2 0 1 5
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nov2015@SS
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S a p t o n o –
G e o t e c h n i c a l
E n g i n e e r i n g W
o r k s h o p ,
2 0 1 5
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nov2015@SS
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S a p t o n o –
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E n g i n e e r i n g W
o r k s h o p ,
2 0 1 5
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G e o t e c h n i c a l
E n g i n e e r i n g W
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E n g i n e e r i n g W
o r k s h o p ,
2 0 1 5
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Open Pit
Slopes
Design
Scales
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Cost Model
Coal Price
‐ royalty
‐ commissions
Cost
‐Development cost
‐Operating cost
‐Overhead cost
‐Land compensation cost
‐Environment cost‐Coal hauling cost
‐Road maintenance cost
‐Coal crushed cost
‐Coal barging cost
Contractor Cost
‐Overburden removal cost
‐Drill & Blast cost
‐Coal cleaning & Coal getting cost
BESR
Q ratio
Expression
Pit Potential
Geotechnical
recommendations
Pit Design
Mineablereserves
Reserves
Classification
ResourcesClassification
RESERVES CALCULATION STEPSRESERVES CALCULATION STEPS
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KEBIJAKAN
DAN
PEDOMAN
PENGATURAN
KEMANTAPAN LERENG PENAMBANGAN DI
INDONESIA
Kepmen Pertambangan dan Energi
No. 555. K/26/M.PE/1995
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Kepmen Pertambangan dan Energi
No.555.
K/26/M.PE/1995
tanggal 12
Mei
1995
• Tujuan dari dikeluarkan Kepmen tersebut adalah untuk melindungi tenaga
kerja, peralatan, pelaksanaan kegiatan penambangan bisa berjalan dengan
aman, terjadi efisiensi biaya, efektif dan produktivitas dari pekerja tinggiserta lancar tanpa terjadi atau seminimal mungkin kecelakaan kerja.
• Menyangkut kemantapan lereng, Kepmen Pertambangan dan Energi No.
555.K/26/M.PE/1995 dalam Bab VI pasal 240 sampai dengan pasal 242
berisi tentang peraturan mengenai tinggi jenjang, lebar jenjang, dan sudutlereng yang sangat tergantung pada ukuran peralatan, jenis batuan, sistem
penambangan yang dipakai serta kondisi dari keadaan geologi tempat
bekerja seperti rekahan, patahan, atau tanda‐tanda tekanan atau tanda‐
tanda kelemahan lainnya.
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Pasal 240 Cara Kerja
1. Kepala Teknik Tambang (KTT) harus menjamin bahwa kemantapanlereng penambangan, penimbunan dan material lainnya telah
diperhitungkan dalam perencanaan tambang2. Penimbunan tanah penutup hanya dapat dilakukan pada jarak
sekurang‐ kurangnya 7,5 m dari ujung teras penambangan
3. Dilarang melakukan penggalian potong bawah (under cutting) padapermuka kerja, teras atau galeri, kecuali mendapat persetujuanKepala Pelaksana Inspeksi Tambang (KAPIT)
4. Permuka kerja harus aman dari batuan menggantung dan padawaktu pengguguran batuan, para pekerja pada tempat tersebutharus menyingkir
5. Permuka kerja tambang permukaan pada bagian atas daerahkegiatan tambang bawah tanah hanya dapat dibuat setelahmendapat persetujuan KAPIT
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6. Dilarang bekerja atau berada di atas timbunan aktif batu
pecah, kecuali:
– berdasarkan perintah seorang pengawas tambang
– curahan batu ke dan dari timbunan telah dihentikan
– telah diperoleh kepastian bahwa corongan di bawah timbunan telah
ditutup – pekerja menggunakan sabuk pengaman yang dihubungkan dengan tali
yang sesuai dengan panjangnya, diikatkan secara kuat dan aman pada
titik tetap diatasnya.
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Pasal 241
Tinggi Permuka Kerja dan Lebar Teras Kerja
1. Kemiringan, tinggi, dan lebar teras harus dibuat denganbaik dan aman untuk keselamatan para pekerja agar
terhindar dari material atau benda jatuh2. Tinggi jenjang (bench) untuk pekerjaan yang dilakukan
pada lapisan yang mengandung pasir, tanah liat, kerikil, dan material lepas lainnya harus:
• tidak boleh lebih dari 2,5 m apabila dilakukan secara manual• tidak boleh lebih dari 6 m apabila dilakukan secara mekanis
• tidak boleh lebih dari 20 m apabila dilakukan dengan menggunakanclamsheel, dragline, bucket wheel excavator atau alat sejenis, kecuali mendapat persetujuan KAPIT
3. Tinggi jenjang untuk pekerjaan yang dilakukan padamaterial kompak tidak boleh lebih dari 6 m apabiladilakukan secara manual
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4. Dalam hal penggalian dilakukan sepenuhnya dengan alat mekanis
yang dilengkapi dengan kabin pengaman yang kuat, maka tinggi
jenjang maksimum untuk jenis material kompak 15 m, kecualimendapat persetujuan KAPIT
5. Studi kemantapan lereng harus dibuat apabila:
• tinggi jenjang keseluruhan pada sistem penambangan berjenjang
lebih dari 15 m
• tinggi setiap jenjang lebih dari 15 m
6. Lebar lantai teras kerja sekurang‐kurangnya 1,5 kali tinggi jenjang
atau disesuaikan dengan alat‐alat yang digunakan sehingga dapat
bekerja dengan aman dan harus dilengkapi dengan tanggulpengaman (safety berm) pada tebing yang terbuka dan diperiksa
pada setiap gilir kerjadari kemungkinan adanya rekahan atau tanda‐
tanda tekanan atau tanda‐tanda kelemahan lainnya.
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Pasal 242
1. Pada waktu membuat sumuran, parit, atau pekerjaan sejenis yang
dinding bukaannya mencapai tinggi lebih dari 1,2 m, harus diberi
penyangga atau dibuat miring dengan sudut yang aman
2. Pembuatan tanggul atau bendungan air yang bersifat sementara atautetap harus cukup kuat dan memenuhi persyaratan yang berlaku.
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Tambang Terbuka FMI - Mineral
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Tambang Terbuka Newmont - Mineral
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Tambang Terbuka Palabora - Mineral
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Tambang Terbuka KPC - Batubara
22
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Tambang Adaro
23
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Tambang Terbuka Adaro - Batubara
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Tambang Terbuka Satui ‐ Batubara
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Tambang Terbuka Senakin ‐ Batubara
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Longsoran Pada Lereng Tambang
Terbuka
27
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Joint In Sediment Rock
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Joint in Igneous Rock
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A large scale slope failure in an open
pit mine
Bingham Canyon mine slope failure Slope failure in which some structural control by faults is evident at the top of the failure but
where the mechanisms involved in the lower part
of the failure are unclear.
A large scale slope failure in an open
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A large scale slope failure in an open
pit
mine
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Candidate Failure Surface Involving A Number
Of Different
Shear
Failure
Mechanisms
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Tanah dan Batuan
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Definisi Batuan• Menurut Talobre (1948)
• Orang yang pertama kali memperkenalkanMekanika Batuan di Perancis pada tahun 1948, batuan adalah material yang membentuk kulitbumi termasuk fluida yang berada didalamnya
(seperti air, minyak dan lain‐lain).• Menurut ASTM
• Batuan adalah suatu bahan yang terdiri dari
mineral padat (solid) berupa massa yang berukuran besar ataupun berupa fragmen‐fragmen.
Cl ifi ti f k d il t th
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Classification of rock and soil strengths
(ISRM,
1981)Class Description Unconfined Compressive
Strength (MPa)
Examples
S1 Very soft soil ‐ Easily penetrated several inches by fist.
0,5
Classification of rock and soil strengths
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Class Description Unconfined
Compressive Strength
(MPa)
Examples
R0 Extremely weak rock ‐ Indented by thumbnail.
0,25–1,0
R1 Very weak rock ‐ Crumbles under firm
blows with point of geological
hammer and can be peeled by a
pocket knife
1,0–5,0 Chalk,
Rocksalt
R2 Weak rock ‐ Can be peeled by a
pocket knife with difficulty, shallow
indentations made by firm blow with
point of geological hammer.
5,0–25 Coal,
Schist,
Siltstone
R3 Medium strong rock ‐ Cannot be
scraped or peeled with a pocket knife,
specimen can be fractured with single
firm blow of geological hammer.
25–50 Sandston
e Slate
Classification of rock and soil strengths
(ISRM,
1981)
Classification of rock and soil strengths
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Class Description Unconfined
Compressive Strength
(MPa)
Examples
R4 Strong rock ‐ Specimen requires more
than one blow of geological hammer
to fracture it.
50–100 Gneiss
R5 Very strong rock ‐ Specimen requires many blows of geological
hammer to fracture it.
100–250 Marble,Granite
R6 Extremely strong rock ‐ Specimen can
only be chipped with geological
hammer.
>250 Quartzite,
dolerite,
Gabbro,
Basalt
Classification of rock and soil strengths
(ISRM,
1981)
Klasifikasi Batuan Berdasarkan UCS (Bieniawski
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Klasifikasi Batuan Berdasarkan UCS (Bieniawski,
1989)
39
Batuan kerasBatuan lunak
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l E n g i n e e r i n g W o r k s h o p ,
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Massa Batuan
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l E n g i n e e r i n g W o r k s h o p ,
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Struktur Geologi
i
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l E n g i n e e r i n g W o r k s h o p ,
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Joint
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Fault
Analisis
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stereografis
(Hoek & Bray, 1981)
Preliminary evaluation of slope stability of
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– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Preliminary evaluation of slope stability of
proposed open
pit
mine
Schimdt Net
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Sc dt et
Wulff Net
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Kalsberg
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Kalsberg
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Plotting Bidang Kekar
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– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Kondisi
Potensial
Kelongsoran
pada suatu
tambang
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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Uncertainty of Rocks
Relation of Discontinuity Spacing and Size of The Problem
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g W o r k s h o p ,
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When the problem domain is
much smaller than rock blocks(excavation of rock by drilling)
Discontinuity propertiesgovern
Intact rock material
Rock mass properties
When the structure is much larger
than the blocks
Uncertainty of Rocks
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g
W o r k s h o p , 2 0
1 5
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Uncertainty of Rocks
Intact rock
Uncertainty of Rocks
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S a p t o n o
– G e o t e c h n i c a
l E n g i n e e r i n g
W o r k s h o p , 2 0
1 5
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Pengaruh Skala
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S a p t o n o
– G e o t e c h n i c a l E n g i n e e r i n g
W o r k s h o p , 2 0
1 5
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g
55
Pengaruh efek skala (Cunha, 1990)
0
100
200
300
400
500
0 25 50 75 100 125 150 175
U C S , M P
a
Diameter, mm
Basaltprophyry
Basalt mafic
UCS = 2630 D-0,58
UCS = 6025 D‐0,85
Kekuatan batuan terhadap Pengaruh skala
(Kramadibrata & Jones, 1993)
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1 5
‐
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Kelongsoran Lereng Tunggal
56
Longsor lereng tunggal mudstone pada
22 Maret 2010 di Lowwall PIT RA ,
Tinggi lereng = 12 m , = 48o
Beberapa boulder terdapat diantara
material longsoran.
Massa batuan longsor dan pecah
akibat kekar berkembang yang
dibuktikan akibat faktor cuaca.
Pengaruh Kekar pada Longsoran Lereng
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– G e o t e c h n i c a l E n g i n e e r i n g
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1 5
‐
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g p g g
57
Fn
Fs
H
S2
Keterangan: S1 = spasi kekar 1
S2 = spasi kekar 2
S3 = spasi kekar 3
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S .
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– G e o t e c h n i c a l E n g i n e e r i n g
W o r k s h o p , 2 0
1 5
‐
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Kegiatan Laboratorium
UNCONFINED COMPRESSIVE STRENGTH TEST
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– G e o t e c h n i c a l E n g i n e e r i n g
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59
DIRECT SHEAR TEST
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DIRECT SHEAR TEST
60
‐
HOEK CELL ‐ TRIAXIAL TEST
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61
‐
TRIAXIAL TEST
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62
‐ DIRECT SHEAR TEST FOR SOIL
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DIRECT SHEAR TEST FOR SOIL
‐ DIRECT SHEAR TEST FOR SOFT ROCK
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W o r k s h o p , 2 0
1 5
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DIRECT SHEAR TEST FOR SOFT ROCK
‐
CREEP DIRECT SHEAR TEST
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FOR SOFT
ROCK
‐
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– G e o t e c h n i c a l E n g i n e e r i n g
W o r k s h o p , 2 0
1 5
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UJI GESER SKALA BESAR
5 ‐
Gambar Proses Kalibrasi Tekanan Piston Terhadap Force Load
(kN)
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Kalibrasi piston pemberi
gaya normal
Kalibrasi piston pemberi
gaya geser
Piston gaya normal
Loadcell 1000 kN
Piston gaya geser
Strain indicator
manometer
(kN)
ManometerPower Pack
5 ‐
Alat Uji Geser Langsung Skala Besar (dirancang oleh: Kramadibrata. S; Suparman. Y dan Saptono. S; Tahun 2009;
L b i G k ik d P l T b R k T k ik P b ITB)
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Spesifikasi alat:
Tinggi = 1,85 m
Lebar = 1,10 m
Panjang = 2,35 m
Berat = 2,50 ton
Gaya geser maksimum = 500 kNGaya normal maksimum = 500 kN
Piston gaya normal:
Jumlah piston = 9 buah
Diamater piston = 7 cm
Panjang stroke = 15 cm
Kapasitas piston = 300 kN
Piston untuk gaya geser:
Jumlah piston = 2 buah
Diamater piston = 17 cm
Panjang stroke = 30 cm
Kapasitas piston = 350 kN
Spesikasi Power Pack:
Horse Power = 5,5 kW
Tekanan untuk gaya = 500 kN
Laboratorium Geomekanika dan Peralatan Tambang, Rekayasa Teknik Pertambangan, ITB)
5 ‐
Alat Uji Geser Langsung Skala Besar
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5 ‐
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– G e o t e c h n i c
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PENYELIDIKAN LAPANGAN
5 ‐
PERALATAN PENGUKURAN ORIENTASI BIDANG KEKAR
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– G e o t e c h n i c
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W o r k s h o p , 2 0
1 5
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Palu Geologi
Meteran 5 m
Meteran 25 m
Clipbroad
Kompas Geologi
Kompas Geologi
5 ‐
PENGUKURAN KARAKTERISASI MASSA BATUAN
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– G e o t e c h n i c
a l E n g i n e e r i n g
W o r k s h o p , 2 0
1
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• Pengukuran orientasi kekar dengan menggunakan kompas
geologi dan yang diukur adalah kemiringan dan arah
kemiringan (dip and dip direction),
• Pengukuran jarak antar kekar dengan menggunakan
meteran dengan metoda scanline. Pada metoda ini, meteran
dibentangkan sepanjang dinding pengamatan. Hasil dari
pengamatan ini adalah berupa arah dan kemiringan kekar serta jarak semu antar bidang kekar
• Prosedur pengukuran jarak kekar menggunakan sistem
pembobotan pada sudut normal dari bidang kekar.
72
1 5
‐
PENENTUAN ORIENTASI DENGAN KOMPAS
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1
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73
N dip Dip direction
Dip direction
+ 90o
Dip
1 5
‐
ANALISIS LERENG DARI HASIL PENGUKURAN
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BIDANG DISKONTINUITAS
1 5
‐PROSEDUR PENGUKURAN KEKAR
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1
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• Garis bentangan, membentuk arah dan kemiringan
• Setinggi mata pengamat
• 10 kali jarak rata-rata kekar atau panjang minimum 30 m• Variasi orientasi keluarga kekar
• Kerataan permukaan singkapan massa batuan
• Ketersediaan muka singkapan massa batuan lain yang saling tegaklurus
• Jenis batuan
• Keadaan air tanah
• Cuaca
• Ketersediaan peralatan
1 5
‐Penentuan spasi (ISRM, 1981)
S3
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1
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J1
J1
J1
J2
J2S1
S1
S2
76
S3
Scanline
d3
S3 = d3 sin
Set no. 2
Set no. 1
Set no.3
1 5
‐
Pengukuran Kekar Dengan Scanline
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0 1
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77
SCANLINE
J14
d14
41
A B1 2 3 4 5 6 7 8 9 10 11 12 13
1 5
‐
Penggunaan faktor koreksi untuk jarak kekar
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S a p t o n o – G e o t e c h n i c
a l E n g i n e e r i n g
W o r k s h o p , 2
0
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• f/f = arah dip dan dip muka lereng
• s/s = arah dip dan dip garis bentangan
• d/d = arah dip dan dip bidang kekar • n/n = arah dip dan dip yang normal terhadap bidang kekar
• = sudut normal terhadap kekar dan garis bentangan
• – = Nilai rata-rata untuk kekar keluarga A
• W = faktor bobot Terzaghi = 1/cos • i-m = Nomor jalur
• Ji-m = jarak semu kekar untuk nomor jalur im
• d(im)= jarak duga kekar atau sebenarnya untuk jalur im
• dxw = jarak duga kekar rata-rata dari satu keluarga kekar
• dsw = bobot rata-rata jarak sebenarnya kekar dari garis bentangan
78
0 1 5
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Blangko Pengambilan Data Pengukuran Jarak Kekar
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0
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79
Pengukuran kekar
Scanline s : ……… s : ………..
Face f : ……… f : …………
No. Dip Direction
dDip d Jarak semu n
dn
90-d i-m ji-m di-m
N…oE o m o o o m m
0 1 5
‐
Contoh, Penentuan Jarak Antar Kekar
f =195 f =50 s =285 s =2
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0
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80
f =195 f =50 s =285 s =2
bid diskont Joint no. d d Jarak Joint n n cos(n‐s) cos n cos s sin n sin s abs[cos ] i‐m ji‐m d(im) dxw
o o terukur, m d + 180 90 ‐ d ( o ) m m m
A 1 75 61 255 29 0.87 0.87 1.00 0.48 0.03 0.77 39.29
A 2 40 54 0.15 220 36 0.42 0.81 1.00 0.59 0.03 0.36 68.76 1 ‐ 2 0.15 0.09
A 3 18 32 0.22 198 58 0.05 0.53 1.00 0.85 0.03 0.06 86.71 2 ‐ 3 0.22 0.05
A 4 50 80 0.50 230 10 0.57 0.98 1.00 0.17 0.03 0.57 55.21 3 ‐ 4 0.50 0.16
A 5 45 89 0.13 225 1 0.50 1.00 1.00 0.02 0.03 0.50 59.98 4 ‐ 5 0.13 0.07
B 48 136 75 316 15 0.86 0.97 1.00 0.26 0.03 0.84 33.23 A 0.18
B 49 152 85 0.30 332 5 0.68 1.00 1.00 0.09 0.03 0.68 47.00 48 ‐ 49 0.30 0.23
B 50 145 58 0.25 325 32 0.77 0.85 1.00 0.53 0.03 0.67 48.11 49 ‐ 50 0.25 0.17
B 51 150 60 0.20 330 30 0.71 0.87 1.00 0.50 0.03 0.63 50.99 50 ‐ 51 0.20 0.13
B 52 105 80 0.20 285 10 1.00 0.98 1.00 0.17 0.03 0.99 8.00 51 ‐ 52 0.20 0.17
C 78 215 63 35 27 ‐0.34 0.89 1.00 0.45 0.03 0.29 73.22 B 0.31
C 79 232 82 0.50 52 8 ‐0.60 0.99 1.00 0.14 0.03 0.59 53.79 78 ‐ 79 0.50 0.22
C 80 208 66 0.15 28 24 ‐0.22 0.91 1.00 0.41 0.03 0.19 78.98 79 ‐ 80 0.15 0.06
C 81 221 56 0.42 41 34 ‐0.44 0.83 1.00 0.56 0.03 0.34 69.90 80 ‐ 81 0.42 0.11
C 82 196 47 0.27 16 43 ‐0.02 0.73 1.00 0.68 0.03 0.01 89.37 81 ‐ 82 0.27 0.05
D 116 274 50 94 40 ‐0.98 0.77 1.00 0.64 0.03 0.73 43.19 C 0.21
D 117 320 48 0.20 140 42 ‐0.82 0.74 1.00 0.67 0.03 0.59 54.20 116 ‐ 117 0.20 0.13
D 118 334 60 0.16 154 30 ‐0.66 0.87 1.00 0.50 0.03 0.55 56.61 117 ‐ 118 0.16 0.09D 119 334 38 0.40 154 52 ‐0.66 0.62 1.00 0.79 0.03 0.38 67.90 118 ‐ 119 0.40 0.19
C 0.27
teta‐A = 63.33 w‐A = 2.23
teta‐B = 45.27 w‐B = 1.42 0.44 dsw 0.24
teta‐C = 63.01 w‐C = 2.20
teta‐D = 48.80 w‐D = 1.52
0 1 5
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Keterangan :
81
cos = abs [cos(n – s) cos n cos s + sin n sin s]s = arah dip garis bentangan
s = dip garis bentangand = arah dip kekar d = dip kekar d < 180, n = d + 180
d > 180, n = d – 180n , n = 90 – d
0 1 5
‐
RQD Hasil Pengukuran Kekar Adalah:
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82
)11.0(100 1.0 e RQD
Spasi kekar, A = 0.18 m
Spasi kekar, B = 0.31 m
Spasi kekar, C = 0.21 m
Spasi kekar, D = 0.27 m
Spasi kekar rata-rata sebenarnya = 0.24 m
Frekuensi kekar, spasi = 4.17 kekar/m
RQD, = 93.38%
0 1 5
‐
Cara penentuan kekasaran (JRC)
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Joint Roughness Coefficient JRC, (Barton, 1977)
1 0 c m
1 0
c m
83
0 1 5
‐
Contoh Profil Kekasaran
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W o r k s h o p , 2
0
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0 1 5
‐
Peralatan Penentuan Joint Compressive Strength
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Schmidt hammer
0 1 5
‐
Kemenerusan
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86
Kemenerusan diukur sebagai panjang kemenerusan
bidang kekar yang nampak pada daerah lereng
yang dibedakan menjadi dua kemenerusan yaitu:
< 0.6 H dan > 0.6 H,
H = tinggi lereng (m)
< 0,6 H
< 0,6 H
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0 1 5
‐
Penentuan Lebar Celah Dan Material Pengisi
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• Lebar celah (aperture) adalah jarak tegak
lurus pemisahan pada kekar yang terbuka.
Kondisi lebar celah ini dapat terisi oleh
material
88
Cloced discontinuity Open discontinuity
Filled discontinuity
0 1 5
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Penentuan kondisi air
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• Prosedur penentuan kondisi air
berdasarkan pada kondisi massa batuan,
pada kasus ini yaitu pada dinding lereng
89
Kondisi air Deskripsi
I Dinding kekar kering
II Ada tetesan air di bidang kekar
III Aliran kecil
IV Aliran kuat
V Aliran besar
kering
menetes
Mengalir
kecil
0 1 5
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ANALISIS LERENG
0 1 5
‐ PLANE FAILURE
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0 1 5
‐
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2
0 1 5
‐
The following assumptions are made
i l f il l i
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in plane failure analysis:1. Both sliding surface and tension crack strike parallel to the slope.
2. The tension crack is vertical and is filled with water to a depth zw.
3. Water enters the sliding surface along the base of the tension crack and
seeps along the sliding surface, escaping at atmospheric pressure where the sliding surface daylights in the slope face. The pressure distributions induced by the presence of water in the tension crack and along the sliding surface are illustrated in Figure.
4. The forces W (the weight of the sliding block), U (uplift force due to
water pressure on the sliding surface) and V (force due to water pressure in the tension crack) all act through the centroid of the sliding mass. In other words, it is assumed that there are no moments that would tend to cause rotation of the block, and hence failure is by sliding only. While this assumption may no be strictly true for actual slopes, the errors introduced by ignoring moments are small enough to neglect. However, in steep slopes with steeply dipping discontinuities, the possibility of toppling failure should be kept in mind.
2
0 1 5
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5. The shear strength τ of the sliding surface is defined by cohesion c and friction angle φ that are related by the equation
τ = c + σ tan φ. In the case of a rough surface or a rock mass
having a curvilinear shear strength envelope, the apparent cohesion and apparent friction angle are defined by a tangent that takes into account the normal stress acting on the sliding surface. The normal stress σ acting on a sliding surface can be determined from the curves given in Figure. It is assumed that release surfaces
are present so that there is no resistance to sliding at the lateral boundaries of the failing rock mass (Figure (b)).
5. In analyzing two‐dimensional slope problems, it is usual to consider a slice of unit thickness taken at right angles to the slope face. This means that on a vertical section through the slope, the area of the sliding surface can be represented by the length of the surface, and the volume of the sliding block is represented by the cross‐section area of the block (Figure (c)).
2
0 1 5
‐Geometries of plane slope failure: (a) tension crack in
the upper slope; (b) tension crack in the face
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,2
0 1 5
‐
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p,2
0 1 5
‐ WEDGE FAILURE
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p,2
0 1 5
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o – G e o t e c h n i
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p , 2
0 1 5
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o – G e o t e c h n i
c a l E n g i n e e r i n g W o r k s h o p
nov2015@SS
FSW
= KFSP
p , 2
0 1 5
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Wedge factor K as a function of wedge
geometry
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o – G e o t e c h n i c a l E n g i n e e r i n
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p , 2
0 1 5
‐
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S .
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p , 2
0 1 5
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Stereoplot of data required for wedge
stability analysis
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stability analysis
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o p , 2
0 1 5
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THE SHAPE OF TYPICAL SLIDING
SURFACES
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SURFACES
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0 1 5
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0 1 5
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C R PERHITUNG N
F KTOR KE M N N
o p , 2
0 1 5
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Model Lereng
ϒ : 17,5 kN/m3
ϕ : 47 °c : 42,6 kPa
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10 m
60°
,
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0 1 5
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Geometri Bidang Longsor
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o p , 2
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CARA PERHITUNGAN BISHOP
1. Buat tabulasi geometri tiap irisan
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g pirisan b (m) R xi h (m) α (º)
1 0,94 16,59 6,85 0,74 24,387
2 0,94 16,59 7,79 1,78 28,006
3 0,94 16,59 8,73 2,91 31,750
4 0,94 16,59 9,67 3,88 35,653
5 0,94 16,59 10,47 4,76 39,132
6 0,94 16,59 11,56 5,59 44,171
7 0,94 16,59 12,5 5,69 48,892
8 0,94 16,59 13,44 4,43 54,108
9 0,94 16,59 14,38 3,07 60,087
10 0,94 16,59 15,32 1,32 67,435
h o p , 2
0 1 5
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2. Asumsikan nilai F awal untuk menghitung
FK Bishop, misalkan F = 0,8
3. Gunakan rumus FK Bishop untuk
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p
menghitung nilai tiap irisan.
irisan RM DM
1 36,26 5,03
2 47,24 13,75
3 58,74 25,19
4 68,07 37,205 76,47 49,42
6 83,97 64,08
7 84,21 70,52
8 70,68 59,049 56,73 43,77
10 39,05 20,05
621,42 388,05
F Baru 1,601
h o p , 2
0 1 5
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4. Gunakan metode iterasi untuk
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mendapatkan F-FK ≤ 0,001. Hasil
perhitungan FK=1,601 digunakan sebagai
pengganti nilai F untuk menghitung FK
selanjutnya.
sin
/tantan1(cos
1'tan).(.
601,1
W
F buW bc
DM
RM i
h o p , 2 0 1 5
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5. Lanjutkan perhitungan FK sampai
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didapatkan FK Bishop dengan selisih ≤
0,001Iterasi FK
0 0,8
1 1,601
2 2,235
3 2,525
4 2,626
5 2,657
6 2,667
7 2,67
8 2,671
9 2,671
h o p , 2 0 1 5
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Use of the stability charts presented requires
that the conditions in the slope meet the
following assumptions:
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1. The material forming the slope is homogeneous,
with uniform shear strength properties along the
slide surface.
2. The shear strength τ of the material is characterized
by cohesion: c and a friction angle φ, that are
related by the equation τ = c + σ tan φ
3. Failure occurs on a circular slide surface, which
passes through the toe of the slope.4. A vertical tension crack occurs in the upper surface
or in the face of the slope.
h o p , 2 0 1 5
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Ground water
flow
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models used
with circularfailure analysis
chart.
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Circular failure chart
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failure chart
number 1—
fully drained
slope.
s h o p , 2 0 1 5
‐Use of the circular failure charts
Step 1: Decide upon the ground water conditions which are believed to exist in the
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slope and choose the chart which is closest to these conditions, using Figure.
Step 2: Select rock strength parameters
applicable to the material forming the slope.Step 3: Calculate the value of the dimensionless
ratio c/(γ H tan φ) and find this value on the outer circular scale of the chart.
Step 4: Follow the radial line from the value found in step to its intersection with the curve which corresponds to the slope angle.
Step 5: Find the corresponding value of tan φ/FS or c/(γ H FS), depending upon which is more convenient, and calculate the factor of safety.
s h o p , 2 0 1 5
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Circular failure chart number 2—
ground water condition 2
Circular failure chart number 3—
ground water condition 3
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Circular failure chart number 5—
fully saturated slope.
Circular failure chart number 4—
ground water condition 4
s h o p , 2 0 1 5
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Location of critical sliding surface and critical
tension crack for drained slopes
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s h o p , 2 0 1 5
‐
Bishop’s simplified method of slices for the analysis of non‐circular failure in
slopes cut into materials in which failure is defined by the Mohr–Coulomb
failure criterion
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k s h o p , 2 0 1 5
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Li dkk (2002)
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k s h o p , 2 0 1 5
‐ Toppling failure
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Suggested toppling mechanism of the north face of Vaiont slide (Muller, 1968)
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Common classes of toppling failures: (a) block toppling of columns of rock containing
widely spaced orthogonal joints; (b) flexural toppling of slabs of rock dipping steeply into face; (c) block flexure toppling characterized by pseudo‐continuous flexure of
long columns through accumulated motions along numerous cross‐ joints (Goodman
and Bray 1976).
k s h o p , 2 0 1 5
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