Abstract
Infiltration causes a decrease in soil shear strength parameters. Decrease in soil shear strength parameters can cause landslides. Landslides often occur in Bogor Regency, one of the landslide locations is Puncak, Bogor. Landslides in Puncak, Bogor on 05 February 2018 at 09.20 WIB must have a safety factor 1.07. Changes in safety factors due to rainfall are observed from 03 February 2018 at 05.00 WIB until 05 February 2018 at 09.20 WIB. This research includes testing soil samples, pore water pressure analysis and slope stability analysis. The software used for this analysis is GeoStudio. The analysis results are the changes in safety factor due to rainfall. The safety factor on 03 February 2018 at 05.00 WIB is 1.602. Safety factor until 05 February 2018 at 03.40 WIB are still above 1.25. So, the slopes are still safe. The decline in safety factor continued until 1.070 due to a decrease in cohesion on 05 February 2018 at 09.20 WIB with cohesion on SW-SM soil and SM soil at 4.01 kPa and 9.18 kPa. So, the duration needed to change a safe slope to landslide is only 5 hours 40 minutes. This can occur because of the intensity of the rain on 05 February 2018 at 07.00 WIB and 08.00 WIB are 34.1 mm/hour and 34.9 mm/hour. Key words: cohesion, landslides, rainfall, safety factor
Highlights
Air hujan yang membasahi permukaan tanah akan mengalami infiltrasi ke bawah permukaan tanah
Infiltration causes a decrease in soil shear strength parameters
Landslides often occur in Bogor Regency
Summary
Properties Tanah Pengambilan sampel tanah dilakukan pada dua lapisan tanah pada lokasi longsor. Sampel tanah ini akan menghasilkan beberapa properties tanah seperti kadar air, berat jenis tanah, kepadatan, porositas, angka pori, permeabilitas, Atterberg limit, analisis saringan dan klasifikasi jenis tanah. Kurva karakteristik air tanah dapat diperkirakan dengan metode modified Kovacs yang tersedia pada SEEP/W. Metode ini dikembangkan oleh Aubertin et al (2013). Metode ini digunakan karena dapat memperkirakan kurva karakteristik air tanah menggunakan properties tanah yang umum (Aubertin et al 2013). Properties tanah yang digunakan untuk memperkirakan kurva karakteristik air tanah meliputi kadar air saat jenuh, D10, D60, dan batas cair. Kurva karakteristik air tanah untuk tanah SW-SM dan tanah SM dapat dilihat pada Gambar 1. Hydraulic conductivity function diperkirakan dengan menggunakan model Van Genucthen yang tersedia pada SEEP/W. Hydraulic conductivity function untuk tanah SW-SM dan tanah SM dapat dilihat pada Gambar 2
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