Analisis Stabilitas Lereng di DAS Tirtomoyo Wongiri Akibat Hujan Periode Ulang.
ANALISIS STABILITAS LERENG DI DAS
TIRTOMOYO WONOGIRI AKIBAT HUJAN
PERIODE ULANG
(Studi Kasus Dusun Damon, Hargorejo, Wonogiri)
Analysis of Slope Stability in Wonogiri Tirtomoyo Watershed by The Rain Period
(Case Study : Damon, Hargorejo, Wonogiri)
SKRIPSI
Diajukan Sebagai Salah Satu Syarat Untuk Memperoleh Gelar Sarjana Teknik
Jurusan Teknik Sipil Fakultas Teknik Universitas Sebelas Maret
Disusun Oleh:
TRY DARMA PUTRA
NIM I 1112087
JURUSAN TEKNIK SIPIL FAKULTAS TEKNIK
UNIVERSITAS SEBELAS MARET
SURAKARTA
2015
DAFTAR ISI
DAFTAR ISI...................................................................................................... xii
BAB I PENDAHULUAN .................................................................................
1
1.1 Latar Belakang Masalah ....................................................................
1
1.2 Rumusan Masalah ..............................................................................
3
1.3 Batasan Masalah ................................................................................
4
1.4 Tujuan Penelitian ...............................................................................
4
1.5 Manfaat Penelitian .............................................................................
4
BAB II TINJAUAN PUSTAKA DAN LANDASAN TEORI .......................
5
2.1 Tinjauan Pustaka ................................................................................
5
2.1.1 Stabilitas Lereng .......................................................................
5
2.1.2 Hidrologi ...................................................................................
6
2.2 Landasan Teori ..................................................................................
6
2.2.1 Stabilitas Lereng ........................................................................
6
2.2.2 Hidrologi ................................................................................... 12
BAB III METODE PENELITIAN ................................................................. 21
3.1 Lokasi Penelitian ............................................................................... 21
3.2 Alat .................................................................................................... 22
3.3 Data..................................................................................................... 22
3.4 Tahapan Penelitian.............................................................................. 23
3.4.1 Pengumpulan Data..................................................................... 23
3.4.2 Permodelan Lereng.................................................................... 24
3.4.3 Analisa Mekanika Tanah ........................................................... 29
3.4.4 Analisa Hidrologi....................................................................... 29
3.4.5 Analisa Stabilitas Lereng Karna Pengaruh Hujan ..................... 40
3.5 Diagram Alir Penelitian ...................................................................... 41
xii
BAB IV PEMBAHASAN................................................................................ 42
4.1 Analisa Data Tanah ............................................................................ 42
4.1.1 Hasil Analisa Pengujian Sampel Tanah..................................... 42
4.2 Analisa Hidrologi................................................................................ 42
4.2.1 Data Hujan ................................................................................. 42
4.2.2 Polygon Thiessen....................................................................... 43
4.2.3 Analisa Frekuensi Metode Log Pearson tipe III ........................ 47
4.2.4 Koefisien Tutupan Lahan .......................................................... 49
4.2.5 Metode SCS ............................................................................... 50
4.2.6 Perhitungan Lapisan Tanah Jenuh ............................................. 51
4.3 Analisa Lereng.................................................................................... 52
4.3.1 Analisa Stabilitas Lereng Sebelum Hujan ................................. 52
4.3.2 Analisa Stabilitas Lereng Setelah Hujan ................................... 55
BAB V KESIMPULAN DAN SARAN ............................................................ 58
5.1 Kesimpulan ........................................................................................ 58
5.2 Saran ................................................................................................... 59
DAFTAR PUSTAKA ....................................................................................... 60
LAMPIRAN
Lampiran A
Lampiran B
Lampiran C
Lampiran D
xiii
DAFTAR TABEL
Hal
Tabel 1.1
Perbedaan Penelitian ..................................................................... 3
Tabel 2.1
Hubungan Nilai Faktor Keamanan Lereng dan Intensitas Longsor 9
Tabel 2.2
Nilai KT untuk Distribusi Pearson III (kemencengan Positif)....... 16
Tabel 2.3
Nilai KT untuk Distribusi Pearson III (kemencengan negatif) ...... 17
Tabel 2.4
Pengelompokan Tanah Hidrologi................................................... 19
Tabel 2.5
Modefikasi Angka-angka Kurve Limpasan Untuk Pulau Jawa
(AMCII) ......................................................................................... 19
Tabel 3.1
Data Curah Hujan Rerata Tiga Stasiun Penakar Hujan.................. 30
Tabel 3.2
Perhitungan Koefisien Thiessen Untuk Stasiun Puter, Ngancar,
dan Watugede................................................................................. 33
Tabel 3.3
Hujan Harian Maksimum Tahunan Dengan Acuan Terbesar Stasiun
Puter ............................................................................................... 34
Tabel 3.4
Hujan Harian Maksimum Tahunan Dengan Acuan Terbesar Stasiun
Ngancar .......................................................................................... 34
Tabel 3.5
Hujan Harian Maksimum Tahunan Dengan Acuan Terbesar Stasiun
Watugede........................................................................................ 35
Tabel 3.6
Hujan Harian MaksimumTahunan Dengan Acuan Terbesar ......... 35
Tabel 3.7
Syarat Jenis Distribusi.................................................................... 37
Tabel 3.8
Perhitungan Data Menggunakan Log Pearson III .......................... 37
Tabel 3.9
Hujan Kala Ulang........................................................................... 38
Tabel 3.10 Variasi Analisis Stabilitas Lereng Setelah Hujan .......................... 39
Tabel 4.1
Hasil Pengujian Sampel Tanah ...................................................... 41
Tabel 4.2
Data Hujan Harian Stasiun Puter Tahun 2004 ............................... 42
Tabel 4.3
Koefisien Thiessen DAS Tirtomoyo .............................................. 44
Tabel 4.4
Hujan Maksimum Rata-rata Ditinjau dari Stasiun Ngancar........... 44
Tabel 4.5
Hujan Maksimum Rata-rata Ditinjau dari Stasiun Puter................ 45
Tabel 4.6
Hujan Maksimum Rata-rata Ditinjau dari Stasiun Watugede ........ 45
Tabel 4.7
Hujan Maksimum Rata-rata ........................................................... 46
Tabel 4.8
Hasil Uji Pemilihan Sebaran yang Sesuai ...................................... 46
xiv
Tabel 4.9
Tinggi Hujan Periode Ulang .......................................................... 48
Tabel 4.10 Curve Number Tutupan Lahan Lokasi Penelitian.......................... 49
Tabel 4.11 Tebal Lapisan Tanah Jenuh Akibat Hujan Periode Ulang ............. 51
Tabel 4.12 Hasil Analisa Lereng Sebelum Hujan ............................................ 53
Tabel 4.13 Rekapitulasi Hasil Perhitungan SF Setelah Hujan ......................... 54
xv
DAFTAR GAMBAR
Hal
Gambar 1.1
Peta DAS Tirtomoyo ............................................................... 2
Gambar 2.1
Bidang Longsor Lereng Infinite Slope..................................... 7
Gambar 2.2
Bidang Longsor Lereng Finite Slope ....................................... 8
Gambar 2.3
Bidang Longsor Circular.......................................................... 10
Gambar 2.4
Bidang Longsor Non-Circular.................................................. 10
Gambar 2.5
Proses perhitungan Faktor Keamanan dalam FEM.................. 11
Gambar 2.6
Polygon Thiessen ..................................................................... 13
Gambar 3.1
Lereng Dusun Damon, Wonogiri ............................................. 21
Gambar 3.2
Pengambilan Sampel Tanah di Dusun Damon ........................ 23
Gambar 3.3
Jendela Pengaturan Project....................................................... 24
Gambar 3.4
Jendela Pengaturan Dimensions............................................... 25
Gambar 3.5
Toolbar ..................................................................................... 25
Gambar 3.6
Jendela Pengaturan Toolbar Material....................................... 26
Gambar 3.7
Permodelan Lereng ................................................................. 26
Gambar 3.8
Mesh-Global Coarseness.......................................................... 27
Gambar 3.9
Preatich Level........................................................................... 28
Gambar 3.10
K0-Procedure ........................................................................... 28
Gambar 3.11
Initial Soil Stresses ................................................................... 29
Gambar 3.12
Peta DAS Tirtomoyo Hulu....................................................... 30
Gambar 3.13
Kurva Massa Ganda Stasiun Penakar Hujan Puter .................. 32
Gambar 3.14
Kurva Massa Ganda Stasiun Penakar Hujan Ngancar ............. 32
Gambar 3.15
Kurva Massa Ganda Stasiun Penakar Hujan Watugede........... 33
Gambar 3.16
Polygon Thiessen DAS Tirtomoyo di Debit Sulingi................ 34
Gambar 4.1
Polygon Thiessen DAS Tirtomoyo, Wonogiri ......................... 44
Gambar 4.2
KOndisi Tutupan Lahan dan Luas Area................................... 49
Gambar 4.3
Bidang Longsor Lereng Kemiringan 30° ................................. 53
Gambar 4.4
Nilai SF Lereng 30° ................................................................. 54
Gambar 4.5
Grafik Hub. Nilai FK Dengan Intensitas Hujan Kala Ulang ... 56
Gambar 4.6
Grafik Hungan Nilai FK Dengan Kemiringan Lereng............. 57
xvi
DAFTAR NOTASI
c
= Nilai kohei tanah (kN/m2)
φ
= Sudut geser dalam tanah (º)
LS
= Lintang selatan (º)
BT
= Bujur timur (º)
τ
= Tahanan geser maksimum yang dapat dikerahkan oleh tanah (kN/m2)
τd
= Tahanan geser yang terjadi akibat gaya berat tanah yang akan longsor
(kN/m2)
P
= Curah hujan (mm)
An
= Luas area Polygon n (km2)
Q
= Air larian (mm)
F
= Infiltrasi (mm)
S
= Abstraksi awal (mm)
CN
= Curve Number
DS
= Disturbed sample
UDS
= Undisturbed sampel
Wn
= Kadar air alami (%)
Gs
= Specific gravity
γb
Berat volume tanah basah (kN/m3)
γsat
= Berat volume tanah jenuh (kN/m3)
PL
= Batas plastis (%)
LL
= Batas cair (%)
e
= Angka pori
FK
= Faktor Keamanan
xvii
TIRTOMOYO WONOGIRI AKIBAT HUJAN
PERIODE ULANG
(Studi Kasus Dusun Damon, Hargorejo, Wonogiri)
Analysis of Slope Stability in Wonogiri Tirtomoyo Watershed by The Rain Period
(Case Study : Damon, Hargorejo, Wonogiri)
SKRIPSI
Diajukan Sebagai Salah Satu Syarat Untuk Memperoleh Gelar Sarjana Teknik
Jurusan Teknik Sipil Fakultas Teknik Universitas Sebelas Maret
Disusun Oleh:
TRY DARMA PUTRA
NIM I 1112087
JURUSAN TEKNIK SIPIL FAKULTAS TEKNIK
UNIVERSITAS SEBELAS MARET
SURAKARTA
2015
DAFTAR ISI
DAFTAR ISI...................................................................................................... xii
BAB I PENDAHULUAN .................................................................................
1
1.1 Latar Belakang Masalah ....................................................................
1
1.2 Rumusan Masalah ..............................................................................
3
1.3 Batasan Masalah ................................................................................
4
1.4 Tujuan Penelitian ...............................................................................
4
1.5 Manfaat Penelitian .............................................................................
4
BAB II TINJAUAN PUSTAKA DAN LANDASAN TEORI .......................
5
2.1 Tinjauan Pustaka ................................................................................
5
2.1.1 Stabilitas Lereng .......................................................................
5
2.1.2 Hidrologi ...................................................................................
6
2.2 Landasan Teori ..................................................................................
6
2.2.1 Stabilitas Lereng ........................................................................
6
2.2.2 Hidrologi ................................................................................... 12
BAB III METODE PENELITIAN ................................................................. 21
3.1 Lokasi Penelitian ............................................................................... 21
3.2 Alat .................................................................................................... 22
3.3 Data..................................................................................................... 22
3.4 Tahapan Penelitian.............................................................................. 23
3.4.1 Pengumpulan Data..................................................................... 23
3.4.2 Permodelan Lereng.................................................................... 24
3.4.3 Analisa Mekanika Tanah ........................................................... 29
3.4.4 Analisa Hidrologi....................................................................... 29
3.4.5 Analisa Stabilitas Lereng Karna Pengaruh Hujan ..................... 40
3.5 Diagram Alir Penelitian ...................................................................... 41
xii
BAB IV PEMBAHASAN................................................................................ 42
4.1 Analisa Data Tanah ............................................................................ 42
4.1.1 Hasil Analisa Pengujian Sampel Tanah..................................... 42
4.2 Analisa Hidrologi................................................................................ 42
4.2.1 Data Hujan ................................................................................. 42
4.2.2 Polygon Thiessen....................................................................... 43
4.2.3 Analisa Frekuensi Metode Log Pearson tipe III ........................ 47
4.2.4 Koefisien Tutupan Lahan .......................................................... 49
4.2.5 Metode SCS ............................................................................... 50
4.2.6 Perhitungan Lapisan Tanah Jenuh ............................................. 51
4.3 Analisa Lereng.................................................................................... 52
4.3.1 Analisa Stabilitas Lereng Sebelum Hujan ................................. 52
4.3.2 Analisa Stabilitas Lereng Setelah Hujan ................................... 55
BAB V KESIMPULAN DAN SARAN ............................................................ 58
5.1 Kesimpulan ........................................................................................ 58
5.2 Saran ................................................................................................... 59
DAFTAR PUSTAKA ....................................................................................... 60
LAMPIRAN
Lampiran A
Lampiran B
Lampiran C
Lampiran D
xiii
DAFTAR TABEL
Hal
Tabel 1.1
Perbedaan Penelitian ..................................................................... 3
Tabel 2.1
Hubungan Nilai Faktor Keamanan Lereng dan Intensitas Longsor 9
Tabel 2.2
Nilai KT untuk Distribusi Pearson III (kemencengan Positif)....... 16
Tabel 2.3
Nilai KT untuk Distribusi Pearson III (kemencengan negatif) ...... 17
Tabel 2.4
Pengelompokan Tanah Hidrologi................................................... 19
Tabel 2.5
Modefikasi Angka-angka Kurve Limpasan Untuk Pulau Jawa
(AMCII) ......................................................................................... 19
Tabel 3.1
Data Curah Hujan Rerata Tiga Stasiun Penakar Hujan.................. 30
Tabel 3.2
Perhitungan Koefisien Thiessen Untuk Stasiun Puter, Ngancar,
dan Watugede................................................................................. 33
Tabel 3.3
Hujan Harian Maksimum Tahunan Dengan Acuan Terbesar Stasiun
Puter ............................................................................................... 34
Tabel 3.4
Hujan Harian Maksimum Tahunan Dengan Acuan Terbesar Stasiun
Ngancar .......................................................................................... 34
Tabel 3.5
Hujan Harian Maksimum Tahunan Dengan Acuan Terbesar Stasiun
Watugede........................................................................................ 35
Tabel 3.6
Hujan Harian MaksimumTahunan Dengan Acuan Terbesar ......... 35
Tabel 3.7
Syarat Jenis Distribusi.................................................................... 37
Tabel 3.8
Perhitungan Data Menggunakan Log Pearson III .......................... 37
Tabel 3.9
Hujan Kala Ulang........................................................................... 38
Tabel 3.10 Variasi Analisis Stabilitas Lereng Setelah Hujan .......................... 39
Tabel 4.1
Hasil Pengujian Sampel Tanah ...................................................... 41
Tabel 4.2
Data Hujan Harian Stasiun Puter Tahun 2004 ............................... 42
Tabel 4.3
Koefisien Thiessen DAS Tirtomoyo .............................................. 44
Tabel 4.4
Hujan Maksimum Rata-rata Ditinjau dari Stasiun Ngancar........... 44
Tabel 4.5
Hujan Maksimum Rata-rata Ditinjau dari Stasiun Puter................ 45
Tabel 4.6
Hujan Maksimum Rata-rata Ditinjau dari Stasiun Watugede ........ 45
Tabel 4.7
Hujan Maksimum Rata-rata ........................................................... 46
Tabel 4.8
Hasil Uji Pemilihan Sebaran yang Sesuai ...................................... 46
xiv
Tabel 4.9
Tinggi Hujan Periode Ulang .......................................................... 48
Tabel 4.10 Curve Number Tutupan Lahan Lokasi Penelitian.......................... 49
Tabel 4.11 Tebal Lapisan Tanah Jenuh Akibat Hujan Periode Ulang ............. 51
Tabel 4.12 Hasil Analisa Lereng Sebelum Hujan ............................................ 53
Tabel 4.13 Rekapitulasi Hasil Perhitungan SF Setelah Hujan ......................... 54
xv
DAFTAR GAMBAR
Hal
Gambar 1.1
Peta DAS Tirtomoyo ............................................................... 2
Gambar 2.1
Bidang Longsor Lereng Infinite Slope..................................... 7
Gambar 2.2
Bidang Longsor Lereng Finite Slope ....................................... 8
Gambar 2.3
Bidang Longsor Circular.......................................................... 10
Gambar 2.4
Bidang Longsor Non-Circular.................................................. 10
Gambar 2.5
Proses perhitungan Faktor Keamanan dalam FEM.................. 11
Gambar 2.6
Polygon Thiessen ..................................................................... 13
Gambar 3.1
Lereng Dusun Damon, Wonogiri ............................................. 21
Gambar 3.2
Pengambilan Sampel Tanah di Dusun Damon ........................ 23
Gambar 3.3
Jendela Pengaturan Project....................................................... 24
Gambar 3.4
Jendela Pengaturan Dimensions............................................... 25
Gambar 3.5
Toolbar ..................................................................................... 25
Gambar 3.6
Jendela Pengaturan Toolbar Material....................................... 26
Gambar 3.7
Permodelan Lereng ................................................................. 26
Gambar 3.8
Mesh-Global Coarseness.......................................................... 27
Gambar 3.9
Preatich Level........................................................................... 28
Gambar 3.10
K0-Procedure ........................................................................... 28
Gambar 3.11
Initial Soil Stresses ................................................................... 29
Gambar 3.12
Peta DAS Tirtomoyo Hulu....................................................... 30
Gambar 3.13
Kurva Massa Ganda Stasiun Penakar Hujan Puter .................. 32
Gambar 3.14
Kurva Massa Ganda Stasiun Penakar Hujan Ngancar ............. 32
Gambar 3.15
Kurva Massa Ganda Stasiun Penakar Hujan Watugede........... 33
Gambar 3.16
Polygon Thiessen DAS Tirtomoyo di Debit Sulingi................ 34
Gambar 4.1
Polygon Thiessen DAS Tirtomoyo, Wonogiri ......................... 44
Gambar 4.2
KOndisi Tutupan Lahan dan Luas Area................................... 49
Gambar 4.3
Bidang Longsor Lereng Kemiringan 30° ................................. 53
Gambar 4.4
Nilai SF Lereng 30° ................................................................. 54
Gambar 4.5
Grafik Hub. Nilai FK Dengan Intensitas Hujan Kala Ulang ... 56
Gambar 4.6
Grafik Hungan Nilai FK Dengan Kemiringan Lereng............. 57
xvi
DAFTAR NOTASI
c
= Nilai kohei tanah (kN/m2)
φ
= Sudut geser dalam tanah (º)
LS
= Lintang selatan (º)
BT
= Bujur timur (º)
τ
= Tahanan geser maksimum yang dapat dikerahkan oleh tanah (kN/m2)
τd
= Tahanan geser yang terjadi akibat gaya berat tanah yang akan longsor
(kN/m2)
P
= Curah hujan (mm)
An
= Luas area Polygon n (km2)
Q
= Air larian (mm)
F
= Infiltrasi (mm)
S
= Abstraksi awal (mm)
CN
= Curve Number
DS
= Disturbed sample
UDS
= Undisturbed sampel
Wn
= Kadar air alami (%)
Gs
= Specific gravity
γb
Berat volume tanah basah (kN/m3)
γsat
= Berat volume tanah jenuh (kN/m3)
PL
= Batas plastis (%)
LL
= Batas cair (%)
e
= Angka pori
FK
= Faktor Keamanan
xvii