Perencanaan Perkuatan Lereng menggunakan Spunpile Dengan dan Tanpa Subdrain Studi Kasus: Ruas Jalan BILL - KEK Mandalika Nusa Tengggara Barat

Nurjanah, Ayu (2026) Perencanaan Perkuatan Lereng menggunakan Spunpile Dengan dan Tanpa Subdrain Studi Kasus: Ruas Jalan BILL - KEK Mandalika Nusa Tengggara Barat. Masters thesis, Institut Teknologi Sepuluh Nompember.

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Abstract

Indonesia merupakan wilayah dengan potensi bencana pergerakan massa tanah yang tinggi, termasuk di kawasan Lombok, Nusa Tenggara Barat. Penelitian ini dilatarbelakangi oleh terjadinya kelongsoran berulang pada Ruas Jalan Bypass Bandara Internasional Lombok (BIL) – KEK Mandalika di KM 10+415 hingga KM 10+519 yang mengalami retakan dan penurunan intensif sejak awal tahun 2023. Berdasarkan penyelidikan tanah, statigrafi nilai N-SPT, dan pengujian geolistrik Wenner 2D/3D pada musim hujan dan kemarau, diketahui bahwa lokasi ini didominasi oleh tanah kohesif jenuh air dengan zona lemah (resistivitas < 3 Ωm) yang berfungsi sebagai jalur aliran air tanah alami dari perbukitan di sisi Barat menuju embung di sisi Timur. Infiltrasi air hujan ke dalam retakan tanah (cracked soil) meningkatkan tekanan air pori secara drastis, sehingga menurunkan parameter kekuatan geser tanah dan menjadi penyebab utama kegagalan stabilitas timbunan jalan. Tujuan penelitian ini adalah mengetahui keefektivitasan perkuatan lereng dalam meningkatkan stabilitas lereng pada kasus kelongsoran lereng di Ruas Jalan BIL – KEK Mandalika Nusa Tenggara menggunakan SLOPE/W pada software GeoStudio. Efektivitas perkuatan dinilai berdasarkan pencapaian Faktor Keamanan target (SF) ≥ 1,5. Hasil analisis stabilitas konvensional (kondisi eksisting tanpa retakan) menunjukkan bahwa lereng dalam kondisi aman dengan SF = 1,553 namun ketika disimulasikan dengan pendekatan cracked soil, nilai SF turun drastis menjadi 0,478 yang memvalidasi kondisi runtuh di lapangan. Sebagai upaya penanggulangan, direncanakan dua metode perkuatan. Metode perkuatan pertama (kondisi dengan Crack) memerlukan perkuatan struktur berupa spunpile tipe silinder diameter 600 mm Tipe C sebanyak 5 buah. Metode perkuatan kedua mengintegrasikan sistem manajemen air hujan berupa drainase permukaan dikawasan main road dan kawasan frontage road serta drainase bawah permukaan. Drainase bawah permukaan (subdrain) tebal 3 m dilengkapi pipa HDPE Corrugated Perforated DN 600 mm. Penerapan sistem drainase ini berhasil menurunkan Muka Air Tanah dan menaikkan SF sebesar 123,85 % dari SF yang awalnya 0,478 menjadi 1,070. Dengan adanya penambahan drainase maka kebutuhan perkuatan struktur berkurang menjadi 2 buah spunpile. Dari hasil analisa tersebut maka dapat di rekomendasikan perkuatan untuk lereng jalan yang mengalami kelongsoran pada Ruas Jalan BILL – KEK Mandalika menggunakan perkuatan spunpile tipe silinder dengan diameter 600 mm Tipe C sebanyak 2 buah yang dikombinasikan dengan penggunaan Subdrain untuk mencapai SF ≥ 1,5.
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Indonesia is a region with a high potential for mass soil movement hazards, including the Lombok area in West Nusa Tenggara. This research is motivated by the occurrence of recurring landslides along the Lombok International Airport BIL – KEK Mandalika Bypass Road section from KM 10+415 to KM 10+519, which has experienced intensive cracking and subsidence since early 2023. Based on soil investigations, N-SPT value stratigraphy, and 2D/3D Wenner geoelectrical resistivity testing during the rainy and dry seasons, it was determined that the location is dominated by water-saturated cohesive soil with a weak zone (resistivity < 3 Ωm) that serves as a natural groundwater flow path from the hills on the West side toward the retention basin on the East side. Rainwater infiltration into soil cracks (cracked soil) drastically increases pore water pressure, thereby reducing soil shear strength parameters and acting as the primary cause of road embankment stability failure. The objective of this study is to evaluate the effectiveness of slope reinforcement in improving stability for the landslide case on the BIL – KEK Mandalika Road Section using SLOPE/W within the GeoStudio software. The effectiveness of the reinforcement is assessed based on achieving a target Safety Factor (SF) ≥ 1.5. The results of conventional stability analysis (existing condition without cracks) indicate that the slope is initially stable with an SF of 1.553. However, when simulated using the cracked soil approach, the SF drops drastically to 0.478, which validates the actual failure conditions observed in the field. As a remedial measure, two reinforcement methods were devised. The first reinforcement method (condition with cracks) requires structural reinforcement consisting of 5 units of Type C cylindrical spunpiles with a diameter of 600 mm. The second reinforcement method integrates a rainwater management system comprising surface drainage in the main road and frontage road areas, alongside subsurface drainage. The subsurface drainage (subdrain) is 3 meters thick and equipped with a DN 600 mm Corrugated Perforated HDPE pipe. The implementation of this drainage system successfully lowered the Groundwater Level and increased the SF by 128,85%, from an initial SF of 0.478 to 1.070. With the addition of the drainage system, the structural reinforcement requirement is reduced to 2 units of spunpiles. Based on these analysis results, it is highly recommended to reinforce the unstable road slope on the BILL – KEK Mandalika Road Section using a combination of 2 units of Type C cylindrical spunpiles (600 mm diameter) combined with a Subdrain system to successfully achieve a target SF ≥ 1.5.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Stabilitas Lereng, Cracked Soil, Spunpiles, Subdrain, GeoStudio.
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TA Engineering (General). Civil engineering (General) > TA169.5 Failure analysis
Divisions:	Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Civil Engineering > 22101-(S2) Master Thesis
Depositing User:	Ayu Nurjanah
Date Deposited:	28 Jul 2026 02:04
Last Modified:	28 Jul 2026 02:08
URI:	http://repository.its.ac.id/id/eprint/138060

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