LANDSLIDE HAZARD ASSESSMENT ALONG A CIPULARANG TOLL ROAD AND DEVELOPING A SAFETY SLOPE RECOMMENDATION FOR SLOPE CONSTRUCTION (A Case Study in Padalarang ������¢���¯���¿���½���¯���¿���½ Purwakarta Section)

CAHYA AHMAD GUMILAR, Prof. Dr. Junun Sartohadi, M.Sc

2017 | Tesis | S2 Ilmu Lingkungan

Longsoran seringkali terjadi di jalan tol dan menutup trasnportasi dan mengakibatkan korban jiwa dan kerusakan infrastruktur. Jalan tol Cipularang, khususnya seksi Padalarang-Purwakarta berlokasi di area perbukitan dengan lereng yang curam, oleh karena itu rawan terhadap longsoran. Jalan tol Cipularang merupakan jalan tol yang penting karean menghubungkan Jakarta dengan kota lain, khususnya Bandung dengan rata-rata jumlah kendaraan ���± 500,000 unit. Peta kerentanan longsoran sepanhang jalan tol Cipularang dibuat menggunakan pendekatan semi-kuantitatif berdasarkan pendapat para ahli, kemudian dianalisis dengan regresi logistik. Persentase kerentanan longsoran menengah memiliki nilai tertinggi yaitu sebesar 67,54 %,kemudian kerentanan longsoran tinggi sebesar 22,10 persen, dan kerentanan longsoran rendah hanya sebesar 10,36 %. Penilaian bahaya longsoran dibuat dengan menggunakan data intensitas curah hujan sebagai hasil dari analisis dengan menggunakan metode gumbel, kemudian peta sebaran intensitas curah hujan dibuat untuk beberapa periode ulang, yaitu 5, 10, 20, dan 50 tahun. Kemudian peta bahaya longsoran dibuat berdasarkan periode ulang saat intensitas curah hujan tersebut. Hasilnya menunjukkan bahwa area bahaya longsoran rendah sebesar 3,10 km2, menengah sebesar 17,23 km2, dan tinggi sebesar 9,32 km2, dengan pesentase bahaya longsoran tinggi sebesar 31,43 %, menengah sebesar 58,10 %, dan rendah hanya 10,48 %. Langkah terakhir yaitu melakukan analisis kestabilan lereng di lokasi lereng dengan bahaya longsoran tinggi di dua lokasi dengan material dominan (lempung menyerpih dan vulkanik lepas) dengan menggunakan metode elemen hingga. Berdasarkan hasil analisis direkomendasikan bahwa kemiringan lereng maksimum untuk proses penggalian untuk lereng dengan material lempung menyerpih adalah 40 derajat dengan nilai faktor keamanan sebesar 1,352 dan untuk lereng berupa material vulkanik lepas, kemiringan maksimum untuk penggalian yaitu sebesar 50 derajat dengan nilai faktor keamanan 1.36.

Landslide were frequently occured in highway/road and often block the transportation and affected loss of people and infrastructure. The Cipularang toll road, especially the Padalarang - Purwakarta section is located on undulating hilly areas with high and steep slopes, therefore prone to landslides. The Cipularang toll road is an important highway which connects Jakarta with other cities, especially Bandung. The average monthly number of vehicles on this highway is ���± 500,000 units. Landslide susceptibility map along Cipularang toll road was constructed using semi-qualitative approach based on expert opinion, then generate by using logistic regression. The percentage of medium landslide susceptibility along Pdalarang - Purwakarta section of Cipularang highway is the highest which is 67.54 %, after that, high landslide susceptibility is 22,10 percent, and only 10,36 % is low landslide susceptibility. Landslide hazard assessment was developed by using rainfall intensity data which is analysed by using gumbel method, afterwards distribution maps in several return period, i.e 5 years, 10 years, 20 years, and 50 years were developed. Then Landslide hazard assessment constructs according to that rainfall return periods. The result shows that (for 50 years return period) low,medium, and high landslide hazard area are over 3,10 sq km, 17,23 sq km, adn 9,32 sq km respectively. These results the landslide hazard persentage for high, medium, and low are 31,43 %, 58,10 %, and 10,48 % consecutively. Finally, slope stability analysis built in the location with high landslide hazard level and on two dominant material (Clayshale and Volcanic loose materials) by using finite element method both for natural slope and man-made slope. It is recommended that the maximum angle of slope for further construction, iclude cutting works are 40 degree for Clayshale and 50 degree for Volcanic loose materials, with the factor of safety from calculation are 1.352 and 1.36 respectively.

Kata Kunci : Cipularang toll road, Logistic regression, Landslide susceptibility, Landslide hazard, Slope Stability Analysis