EVALUASI KARAKTERISTIK KUAT¬ GESER MATERIAL TEBING SUNGAI DI LOKASI KELONGSORAN PENAMBANGAN PASIR KALI PUTIH, KECAMATAN GARUM KABUPATEN BLITAR - Sudewo, Gatot Iman; Hendrawan, Andre Primantyo; Sisinggih, Dian (Jurnal Mahasiswa Jurusan Teknik Pengairan, 2019)
ABSTRAK Studi ini mengidentifikasi karakteristik fisik dan kuat geser material tanah di beberapa lokasi kelongsoran tebing sungai di area penambangan pasir Kali Putih, Kecamatan Garum Kabupaten Blitar. Analisa gradasi butiran, berat jenis tanah, kerapatan tanah berbutir dan angka pori digunakan untuk mengevaluasi karakteristik fisik dari material ini. Sedangkan untuk pengujian karakteristik mekanik berupa pengujian geser langsung dan penentuan sudut tenang tanah. Dari hasil pengujian karakteristik fisik didapatkan hasil uji gradasi butiran tanah memiliki gradasi butiran baik dan sedikit baik. Nilai berat jenis tanah (Gs) didapatkan rentang harga 2,65 - 2,68. Dari pengujian angka pori tanah menggunakan pemodelan kerapatan Dr 50% dan Dr 70%, didapatkan rentang antara 0,525–0,733 (untuk Dr 50%) dan 0,469–0,674 (untuk Dr 70%). Klasifikasi tanah dengan sistem USCS diklasifikasikan sebagai SW yaitu pasir bergradasi baik (sand well-graded). Dari sistem AASTHO diklasifikasikan sebagai pasir berkerikil dengan simbol A-1b dan dengan metode JGS diklasifikasikan sebagai tanah coarse-grained volcanic soil (V) dan sand volcanic (S-V). Dari pengujian geser langsung diperoleh harga sudut geser dalam berkisar  35,59˚- 44,427˚ (untuk Dr 50%) dan rentang 38,432˚- 47,848˚ (untuk Dr 70%)  sehingga diklasifikasikan sebagai kerikil bercampur pasir. Nilai sudut tenang melalui perhitungan sebesar 27,58˚- 34,25˚, sedangkan nilai sudut tenang melalui observasi sebesar 28,33˚-32,33˚ dan diklasifikasikan sebagai sand (dry) dan gravel (natural with sand). Kata kunci : kelongsoran, tebing sungai, penambangan pasir, kuat geser.  ABSTRACT This study identified the physical characteristics and shear strength of soil materials at some locations of river bank landslides in the Kali Putih sand mining area, Garum-Blitar. The analysis of sieve test, specific gravity, relative density, and void ratio were used to evaluate the physical characteristics of these materials. To evaluate their mechanical characteristics, direct shear test and determination of angle of repose also have been conducted. From the results of physical characteristics, it can be obtained from sieve test that they were well-graded and nearly well-graded materials. The value of specific gravity (Gs) is 2.65-2.68. From determination of void ratio with different relative density, it can be ranged from 0,525-0,733 and 0,469-0,674, for Dr 50% and Dr 70%, respectively. Soil classification obtained from the USCS system is classified as well-graded sand (SW). From AASTHO system it can be classified as gravel sand (A-1b), as for JGS system it can be classified as a coarse-grained volcanic soil (V) and sand volcanic (S-V). From the results of direct sheat test, the angle of internal friction were obtained around 35,591˚-44,427˚ (for Dr 50%) and between a range of 38,432˚-47,848˚ for Dr 70% and can be classified as gravel mixed with sand. The angle of repose value through the calculations were determined around 27,58˚- 34,25˚ while from observations their value were in a range of 28.33˚-32.33˚ and classified as sand (dry) and gravel (natural with sand). Keywords : landslide, river bank, sand mining, shear strength.