Huda, Nur Muhammad Aquana Akhsanul (2026) Analisis Rembesan Dan Stabilitas Bendungan Pidekso Berdasarkan Analisis Balik Data Instrumentasi Dan Pemodelan Numerik. Masters thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Keamanan bendungan urugan dipengaruhi oleh rembesan, tekanan air pori, tegangan efektif, dan stabilitas lereng. Parameter geoteknik hasil investigasi awal belum tentu sepenuhnya mewakili kondisi bendungan setelah mengalami penggenangan dan pembebanan selama masa operasi. Penelitian ini bertujuan menganalisis karakteristik rembesan Bendungan Pidekso, mengevaluasi pengaruh tekanan air pori terhadap tegangan efektif dan stabilitas lereng, memperoleh parameter geoteknik terkalibrasi melalui analisis balik data instrumentasi, serta mengevaluasi tingkat keamanan bendungan berdasarkan parameter tersebut. Analisis dilakukan pada STA 0+180, STA 0+280, dan STA 0+320 untuk muka air waduk +174,00 m, +185,00 m, dan +186,67 m. Data penelitian meliputi parameter geoteknik, elevasi muka air waduk, piezometer, pressure cell, V-notch, dan patok geser. Analisis rembesan menggunakan metode elemen hingga pada SEEP/W, sedangkan stabilitas lereng dianalisis menggunakan metode keseimbangan batas Morgenstern-Price pada SLOPE/W. Kalibrasi hidraulik dilakukan terlebih dahulu melalui penyesuaian koefisien permeabilitas terhadap tekanan air pori dan kecenderungan debit rembesan, kemudian dilanjutkan dengan kalibrasi parameter mekanik berdasarkan tegangan efektif, faktor keamanan, dan kewajaran bidang longsoran. Hasil analisis balik menghasilkan parameter inti terkalibrasi berupa k = 1,65 × 10⁻¹⁰ m/det, γsat = 19,50 kN/m³, c′ = 29,00 kPa, dan φ′ = 24,00°. Pada muka air +186,67 m, debit rembesan terkalibrasi sebesar 5,42 × 10⁻⁶ m³/det/m pada STA 0+180, 5,15 × 10⁻⁶ m³/det/m pada STA 0+280, dan 5,30 × 10⁻⁶ m³/det/m pada STA 0+320. Kenaikan muka air waduk meningkatkan tekanan air pori dan debit rembesan sehingga menurunkan tegangan efektif dan dapat menurunkan faktor keamanan. Faktor keamanan pada kondisi statis berada pada rentang 2,452-2,588, rapid drawdown 2,396-2,584, OBE 1,773-1,911, dan MDE 1,554-1,773. Seluruh kondisi yang dianalisis memenuhi kriteria keamanan yang digunakan dalam penelitian, dengan MDE sebagai kondisi paling kritis. Data V-notch dapat digunakan untuk mengevaluasi kecenderungan rembesan pada rentang muka air operasi, tetapi belum dapat memvalidasi langsung kondisi banjir +186,67 m karena data representatif pada elevasi tersebut belum tersedia. Model terkalibrasi dapat digunakan sebagai baseline evaluasi berkala terhadap tekanan air pori, debit rembesan, dan stabilitas Bendungan Pidekso.
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The safety of an embankment dam is influenced by seepage, pore-water pressure, effective stress, and slope stability. Geotechnical parameters obtained from the initial investigation may not fully represent dam conditions after reservoir impoundment and operational loading. This study aims to analyse seepage characteristics at Pidekso Dam, evaluate the influence of pore-water pressure on effective stress and slope stability, determine calibrated geotechnical parameters through back analysis of instrumentation data, and assess dam safety using the calibrated parameters. The analyses were conducted at STA 0+180, STA 0+280, and STA 0+320 for reservoir water levels of +174.00 m, +185.00 m, and +186.67 m. The data included geotechnical parameters, reservoir water levels, piezometer readings, pressure-cell measurements, V-notch discharge records, and surface displacement observations. Seepage was analysed using the finite element method in SEEP/W, while slope stability was evaluated using the Morgenstern-Price limit equilibrium method in SLOPE/W. Hydraulic calibration was first performed by adjusting the permeability coefficient against pore-water pressure and seepage discharge trends, followed by mechanical calibration based on effective stress, factor of safety, and the reasonableness of the critical slip surface. The back analysis produced calibrated core parameters of k = 1.65 × 10⁻¹⁰ m/s, γsat = 19.50 kN/m³, c′ = 29.00 kPa, and φ′ = 24.00°. At the reservoir level of +186.67 m, the calibrated seepage discharges were 5.42 × 10⁻⁶ m³/s/m at STA 0+180, 5.15 × 10⁻⁶ m³/s/m at STA 0+280, and 5.30 × 10⁻⁶ m³/s/m at STA 0+320. Increasing reservoir water level increased pore-water pressure and seepage discharge, thereby reducing effective stress and potentially decreasing the factor of safety. The factors of safety ranged from 2.452 to 2.588 under static conditions, 2.396 to 2.584 under rapid drawdown, 1.773 to 1.911 under the Operating Basis Earthquake, and 1.554 to 1.773 under the Maximum Design Earthquake. All analysed conditions satisfied the safety criteria adopted in this study, with the Maximum Design Earthquake representing the most critical condition. V-notch measurements were suitable for evaluating seepage trends within the monitored operating range but could not directly validate the +186.67 m flood-level scenario because representative measurements at that level were unavailable. The calibrated model can serve as a baseline for periodic evaluation of pore-water pressure, seepage discharge, and the stability of Pidekso Dam.
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