Nilai Derajat Kejenuhan Tanah Pada Penilaian Ancaman Longsor Rombakan (Debris Flow) Pada Batuan Vulkanik

Abstract

Flow landslides are spatial movements that occur continuously due to the soil surface's direction usually, a short distance away, and the occurrence is not too long. The flow avalanche gradation depends on the intensity of rain, soil type, and vegetation. In contrast, the direction of mobility depends on the slope of the slope and surface soil type. Soil types that are quickly saturated due to high-intensity rain and briefly on the slopes cause the soil layer to be eroded under its weight soon into the valley. This was what makes it difficult for residents to avoid and evacuate. In this case, analysis and technical studies need to be carried out on the effect of the soil's degree of saturation, which causes the threat of landslide of the rubble. Observations were made with borehole, and geoelectric samples carried out in Abang Batu Dinding Village, Kintamani. The surface morphology is hilly, soil type at an average depth of 1-1.5 m sandy silt, and bedrock is volcanic breccia. The hydrological analysis was modeled based on the Thiessen polygon, where the average effective rainfall for 10-50 years is 238 mm/day. The negative pore water stress value increases from 35 kPa-72.44 kPa. There is still water in the soil pores that can keep the bonds of soil grains when the degree of low saturation is around 40%, and then it increases to 78.46%. In this study, the degree of saturation of 40% to 56% of the value of soil shear strength increased and then the shear strength of the soil decreased to 37.62 o with a degree of saturation of 78.46%. Rapid changes in the soil surface with minimal vegetation will cause erosion on the soil surface, in spatial conditions with a soil thickness of 1-1.5 m will cause landslides or debris.

Analysis of Soil Movement Hazards Trigger on Main Road Segment Denpasar-Singaraja in Baturiti District, Tabanan

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“…Konsep penguatan tanah adalah teknik kuno dan banyak didemonstrasikan dialam oleh hewan, burung, dan aksi akar pohon. Konstruksi yang menggunakan teknik ini diketahui telah ada pada milenium kelima dan keempat SM [4]. Konsep ini digunakan untuk perbaikan sifat tanah tertentu yang diinginkan seperti daya dukung, kuat geser (c dan ϕ), permeabilitas, dll.…”

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“…Selain gerakan tanah dan longsoran batuan, terdapat jenis longsoran dengan material cair yang diakibatkan oleh hasil endapan yang bergerak menuju bawah akibat terbawanya oleh aliran air yang disebut dengan debris flow [7]. Material yang terdapat pada debris flow dapat berupa aliran dengan banyaknya bebatuan besar ataupun aliran cair seperti lumpur dengan kandungan batu yang lebih sedikit serta didominasi oleh material tanah dan pasir [8]. Sedangkan pada lereng buatan seperti lereng timbunan, untuk penyebab terjadinya kelongsoran pada lereng ini biasanya diakibatkan oleh kemiringan timbunan yang terlalu curam dan juga karakteristik material tanah yang digunakan sebagai bahan timbunan tidak terlalu bagus sehingga diperlukan analisis stabilitas lereng dengan bantuan software [9].…”