Penggunaan Kombinasi Material Lempung dan Geomembrane Sebagai Alternatif Perencanaan Zona Inti Bendungan Bagong Trenggalek, Jawa Timur

Ilham, Andi Muhammad (2024) Penggunaan Kombinasi Material Lempung dan Geomembrane Sebagai Alternatif Perencanaan Zona Inti Bendungan Bagong Trenggalek, Jawa Timur. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Bendungan Bagong merupakan bendungan yang terletak di Kabupaten Trenggalek Provinsi
Jawa Timur dan memiliki 4 fungsi utama, yaitu sebagai pengendali debit banjir dengan retensi
sebesar 13,59%, pemenuhan kebutuhan air irigasi, suplai air bersih, serta menjadi destinasi
wisata. Bendungan Bagong dikategorikan sebagai bendungan urugan tipe zonal dengan panjang
total mercu main dam 620 meter dan tinggi 82 meter dengan elevasi puncak +330 m. Dengan
besarnya dimensi dan perbedaan spesifikasi material di setiap zona, diperlukan sumber material
alam yang sangat besar untuk memenuhi kriteria desain yang ditetapkan, sedangkan
ketersediaan lahan sebagai sumber material konstruksi mulai menjadi isu di dunia konstruksi.
Untuk mengatasi masalah di atas, diperlukan alternatif pengganti material alam seperti
geomembrane yang bersifat impermeable sehingga cocok diterapkan pada zona inti main dam
dengan syarat stabilitas dan rembesan pada bendungan tetap terpenuhi.
Untuk mendapatkan desain alternatif paling optimum, digunakan pra-desain pemasangan
geomembrane pada main dam dengan lebar zona inti 80%, 60%, dan 40%. Dengan desain
tersebut, dilakukan analisis terhadap rembesan dan stabilitas pada kondisi non gempa dan
kondisi gempa, menggunakan beban gempa OBE dengan koefisien 0,180 serta gempa MDE
dengan koefisien 0,224. Pada semua desain alternatif, didapatkan stabilitas paling kritis pada
kondisi MAB dengan gempa MDE menghasilkan SF 1,11 pada kombinasi dengan lebar zona
inti 80% dan 60% serta 1,10 pada lebar zona inti 40%. Pemasangan geomembrane juga terbukti
efektif dalam menurunkan garis kejenuhan dan debit rembesan hingga 8 kali lebih kecil
dibandingkan desain inisial. Akan tetapi, pada alternatif dengan lebar dasar zona inti 40%,
ditemukan indikasi kebocoran pada kondisi rapid drawdown yang ditandai dengan debit
rembesan yang melampaui kriteria debit maksimum (0,0043l/det/m’) dan faktor keamanan
terhadap piping yang tidak terpenuhi. Sebagai alternatif tambahan, dilakukan permodelan
dengan pemasangan geomembrane pada main dam dengan lebar dasar zona inti 50%.
Kriteria rembesan dan stabilitas pada main dam dengan lebar zona inti 50% telah terpenuhi
dengan debit rembesan maksimum 0,000057 liter/detik/meter pada kondisi MAB, indeks
rembesan 0,14, dan angka kemanan terhadap potensi piping 54,33. Selain itu, didapatkan angka
kemanan paling kritis 1,11 pada kondisi MAB dengan pengaruh gempa MDE. Dengan lebar
dasar zona inti 50%, kebutuhan material lempung dapat direduksi hingga 40,91% dan
berpotensi mereduksi blanket grout hingga 44%, sehingga desain tersebut dipilih sebagai
alternatif desain optimum dari Bendungan Bagong dengan kriteria desain yang terpenuhi.
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Bagong Dam is located in Trenggalek Regency, East Java that has 4 main functions, as a
flood discharge controller with 13,59% retention, irrigation water needs supply, clean water
supply, and becoming a tourist destination. Bagong Dam is clasified as a zonal earthfill dam
with a total length of crest is 620 meters and a height of 82 meters with +330 m top elevation.
With the large dimensions and differences in material specifications in each zone, huge source
of natural materials is needed to reach the established design criteria while the availability of
land as a source of construction materials to become an issue in the construction world. To
overcome problems above, an alternative to natural materials such as geomembranes is needed
which is impermeable, so it is suitable to be applied to the main dam core zone, provided that
the stability and seepage of the dam are still reached.
To obtain the most optimum alternative design, pre-design of geomembrane installation in
the main dam with a core zone width of 80%, 60%, and 40% was used. With this design,
seepage and stability analyses were conducted under non-seismic and seismic conditions, using
OBE earthquake loads with a coefficient of 0,180 and MDE earthquakes with a coefficient of
0,224. Of all alternative designs, the most critical stability was obtained in MAB condition with
the MDE earthquake generate safety factors of 1,11 in combination with a core zone width of
80% and 60%, 1,10 at a core zone width of 40%. The installation of geomembrane also proved
effective in reducing the saturation line and seepage discharge up to 8 times smaller than the
initial design. However, in the alternative with a core zone bottom width of 40%, there were
indications of leakage under rapid drawdown conditions characterized by seepage discharge
exceeding the maximum discharge criterion (0.0043l/det/m') and unmet piping safety factors.
As an additional alternative, geomembrane was modeled on the main dam with a base width of
50% core zone.
The seepage and stability criteria for the main dam with a 50% core zone width were met
with a maximum seepage discharge of 0.000057 liters/second/meter on MAB conditions, a
seepage index of 0.14, and a piping safety factor of 54.33. In addition, the most critical safety
number of 1.11 was obtained in the MAB condition with the influence of the MDE earthquake.
With a core zone width of 50%, the need for clay material can be reduced up to 40,91% and
potentially reducing blanket grout up to 44%, so that the design was chosen as an optimal design
alternative to the Bagong Dam with achieved seepage and stability criterias.

Item Type: Thesis (Other)
Uncontrolled Keywords: Bagong Dam, dam core zone, dam stability, seepage, geomembrane, Bendungan Bagong, zona inti bendungan, stabilitas bendungan, rembesan, geomembran
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TA Engineering (General). Civil engineering (General) > TA749 Soil stabilization
T Technology > TC Hydraulic engineering. Ocean engineering > TC167 Dams, reservoirs
Divisions: Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Architecture > 23201-(S1) Undergraduate Thesis
Depositing User: Andi Muhammad Ilham
Date Deposited: 31 Jul 2024 05:30
Last Modified: 31 Jul 2024 05:30
URI: http://repository.its.ac.id/id/eprint/110073

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