APAKAH VERTIVER EFEKTIF DALAM MENINGKATKAN STABILITAS LERENG JALAN TOL? (STUDI KASUS PROYEK JALAN TOL SOLO – YOGYAKARTA – NYIA SEKSI II PAKET 2.2B)

Annisa Nur Partiadewi, 2. Prof. Ir. T. Faisal Fathani, S.T., M.T., Ph.D., IPU., ASEAN.Eng.

2025 | Skripsi | TEKNIK SIPIL

Ketidakstabilan lereng timbunan merupakan salah satu permasalahan utama dalam pembangunan infrastruktur, terutama pada jalan raya dan jalur kereta api. Metode stabilisasi struktural efektif secara teknis, tetapi berdampak negatif terhadap lingkungan dan memerlukan biaya pemeliharaan yang tinggi. Sebagai solusi, pendekatan vegetatif melalui teknik rekayasa bioengineering mulai banyak diterapkan. Vetiver (Chrysopogon zizanioides) merupakan salah satu spesies yang potensial digunakan karena memiliki sistem perakaran yang dalam dan kuat. Akar tanaman ini dapat meningkatkan kohesi tanah, yang dikenal sebagai kohesi akar. Namun, kohesi akar sangat dipengaruhi oleh siklus hidup tanaman. Meskipun berbagai penelitian telah mengevaluasi pengaruh sistem perakaran terhadap stabilitas lereng, nilai kohesi akar diasumsikan konstan tanpa mempertimbangkan perubahan karakteristik akar di sepanjang siklus hidupnya. Penelitian ini bertujuan untuk mengevaluasi pengaruh siklus hidup vetiver terhadap kohesi akar dan stabilitas lereng. Penelitian ini menggunakan Proyek Jalan Tol Solo-Yogyakarta-NYIA Seksi II Paket 2.2B sebagai studi kasus yang mengharapkan hasil dapat memperkuat dasar teknis penggunaan vetiver dalam rekayasa bioengineering serta menyempurnakan pedoman perkuatan lereng yang telah ada.

Pemodelan kohesi akar dilakukan dengan menggunakan pendekatan teoritis Wu-Waldron Model (WWM) dan Root Bundle Model dengan distribusi Weibull (RBMw), yang masing-masing diformulasikan dalam empat variasi model untuk menghitung kontribusi akar terhadap perkuatan lereng. Selain itu, variasi pola pertumbuhan dan kelangsungan hidup tanaman juga diperhitungkan untuk mengevaluasi efektivitas vegetasi dalam menjaga stabilitas lereng secara jangka panjang. Tiga skenario siklus hidup digunakan untuk merepresentasikan pengaruh kondisi lingkungan terhadap umur dan kemampuan regenerasi tanaman vetiver. Pemodelan stabilitas dilakukan menggunakan perangkat lunak Plaxis 2D dengan asumsi kondisi plane-strain, di mana lereng timbunan diidealisasikan dalam analisis dua dimensi tanpa mempertimbangkan deformasi melintang sepanjang arah lereng, guna menyederhanakan proses simulasi. Analisis Safety Factor (SF) dilakukan pada berbagai fase dalam siklus hidup vetiver untuk mengakomodir efek temporal perubahan perkuatan akar terhadap stabilitas lereng timbunan, karakteristik longsor, dan waktu penyemaian untuk mempertahankan fungsi jangka panjang sistem perakaran.

Berdasarkan hasil analisis, akar vetiver berperan penting dalam meningkatkan kohesi tanah timbunan sebesar 233-978%. Peningkatan kohesi tanah dapat meningkatkan stabilitas lereng timbunan juga ditandai dengan meningkatnya SF pada lereng bervegetasi sebesar 5,59-26,35%. Nilai SF tersebut juga sangat bergantung pada siklus hidup tanaman yang ditandai dengan peningkatan SF pada fase hidup sebesar 11,8-19,9?ri fase tumbuh vetiver. Namun, dikarenakan vetiver termasuk makhluk hidup yang dapat mati, regenerasi tanaman untuk keberlanjutan stabilitas lereng perlu dipertimbangkan dengan menentukan waktu penyemaian tanaman. Hal ini dikarenakan setelah vetiver memasuki fase mati, nilai SF akan menurun sebesar 5,3-19,7%. Penyemaian dapat dilakukan pada 0,1-84,06?ri total siklus vetiver, tergantung kohesi akar, dan lingkungan tempat vetiver tersebut tumbuh.

Slope instability in embankments is one of the main challenges in infrastructure development, particularly in roadways and railway lines. Structural stabilization methods are technically effective, but they often have negative environmental impacts and require high maintenance costs. As an alternative solution, vegetative approaches using bioengineering techniques have been increasingly adopted. Vetiver grass (Chrysopogon zizanioides) is one of the potential species used due to its deep and strong root system. These roots can enhance soil cohesion, commonly referred to as root cohesion. However, root cohesion is significantly influenced by the plant's life cycle. Although numerous studies have evaluated the effect of root systems on slope stability, root cohesion is often assumed to be constant without considering the changes in root characteristics throughout the plant’s life cycle. This research aims to evaluate the influence of the vetiver life cycle on root cohesion and slope stability. The study uses the Solo-Yogyakarta-NYIA Toll Road Project, Section II Package 2.2B, as a case study, with the expectation that the findings can strengthen the technical foundation for the use of vetiver in bioengineering and improve existing slope reinforcement guidelines.

Root cohesion modeling was conducted using two theoretical approaches: the Wu-Waldron Model (WWM) and the Root Bundle Model with Weibull distribution (RBMw), each formulated in four model variations to calculate the contribution of roots to slope reinforcement. In addition, variations in growth patterns and plant survival were also considered to evaluate the long-term effectiveness of vegetation in maintaining slope stability. Three life cycle scenarios were used to represent the impact of environmental conditions on the lifespan and regeneration capacity of vetiver. Stability modeling was carried out using Plaxis 2D software under the assumption of plane-strain conditions, in which the embankment slope was idealized in a two-dimensional analysis without accounting for transverse deformation along the slope, to simplify the simulation process. A Safety Factor (SF) analysis was performed at various stages in the vetiver life cycle to accommodate the temporal effects of root reinforcement changes on embankment slope stability, landslide characteristics, and seeding timing to maintain long-term root system function.

Based on the analysis results, vetiver roots played a significant role in increasing the cohesion of embankment soil by 233–978%. The increase in soil cohesion led to improved slope stability, as indicated by an increase in the SF of vegetated slopes by 5.59–26.35%. The SF values were also highly dependent on the plant's life cycle, as shown by an SF increase of 11.8–19.9% during the mature phase compared to the early growth phase of vetiver. However, since vetiver was a living organism that could die, plant regeneration for sustainable slope stability needed to be considered by determining appropriate seeding times. This was crucial because once vetiver entered its senescence phase, the SF could decrease by 5.3–19.7%. Seeding was conducted at 0.1–84.06% of the total vetiver life cycle, depending on root cohesion and the environmental conditions in which the vetiver was grown.

Kata Kunci : stabilitas lereng, Chrysopogon Zizanioides, WWM, RBMw, Plaxis 2D