ANALISIS STABILITAS TEBING AKIBAT KENAIKAN MUKA AIR SUNGAI MENGGUNAKAN SOFTWARE PLAXIS 2D (STUDI KASUS SUNGAI BLUKAR, KABUPATEN KENDAL)

ABSTRAK

Ketidakstabilan tebing sungai merupakan salah satu permasalahan geoteknik yang sering terjadi, terutama di wilayah yang rentan terhadap erosi dan perubahan morfologi sungai. Kondisi ini dapat menyebabkan kelongsoran, peningkatan sedimentasi, dan berkurangnya kapasitas aliran sungai. Penelitian ini dilakukan
pada segmen Sungai Blukar, Kabupaten Kendal, yang diketahui mengalami ketidakstabilan tebing akibat erosi dan sedimentasi. Tujuan penelitian adalah mengkaji karakteristik tanah di lokasi studi dan menganalisis kestabilan tebing dengan membandingkan kondisi muka air sungai normal dan saat banjir menggunakan software Plaxis 2D. Data yang digunakan merupakan hasil
investigasi lapangan dan uji laboratorium tanah yang mencakup uji sondir, pengeboran, dan pengujian mekanika tanah. Pemodelan dilakukan dengan metode elemen hingga (finite element method) pada Plaxis 2D Connect Edition, dengan ketinggian muka air normal sebesar +2,459 m dari dasar sungai, serta kondisi banjir
dengan kenaikan 1,5 m dari muka air normal. Analisis dilakukan pada empat skenario: muka air normal, fast flooding, slow flooding, dan muka air banjir. Hasil penelitian menunjukkan nilai faktor keamanan (safety factor/SF) berturut sebesar
1,344; 1,234; 1,234; dan 1,208, di mana SF ≥ 1,25 menunjukkan lereng relatif stabil sesuai SNI 8460:2017. Nilai SF cenderung menurun seiring kenaikan muka air, dengan kondisi paling kritis terjadi pada muka air banjir. Selain itu, pola deformasi
menunjukkan perpindahan terbesar terjadi di kaki tebing akibat peningkatan tekanan air pori yang mengurangi kekuatan geser tanah, dengan perubahan paling signifikan pada skenario muka air banjir.

Kata kunci: kestabilan tebing, Sungai Blukar, Plaxis 2D, muka air banjir, faktor keamanan.

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ABSTRACT

Riverbank instability is one of the common geotechnical issues, particularly in areas prone to erosion and changes in river morphology. This condition can lead to slope failure, increased sedimentation, and reduced river flow capacity. This study was conducted on a segment of the Blukar River, Kendal Regency, which has been identified as experiencing riverbank instability due to erosion and sedimentation. The objective of this research is to examine the soil characteristics at the study site and analyze the stability of the riverbank by comparing normal and flood water level conditions using Plaxis 2D software. The data used include field investigations and laboratory soil testing, such as cone penetration tests, borehole drilling, and soil mechanics testing. Modeling was performed using the finite element method (FEM) in Plaxis 2D Connect Edition, with the normal water level assumed at +2.459 m from the riverbed and the flood water level represented by a
1.5 m increase from the normal water level. The analysis was carried out for four scenarios: normal water level, fast flooding, slow flooding, and flood water level. The results showed safety factor (SF) values of 1.344, 1.234, 1.234, and 1.208, respectively, where SF ≥ 1.25 indicates a relatively stable slope according to SNI 8460:2017. The SF values tended to decrease with rising water levels, with the most critical condition occurring during the flood water level scenario. Furthermore, the deformation pattern indicated the largest displacement occurred at the riverbank toe due to increased pore water pressure, which reduced the soil shear strength,
with the most significant changes observed under the flood water level scenario.

Keywords: riverbank stability, Blukar River, Plaxis 2D, flood water level, safety factor.