1855 Numerical Modeling Of Temporary Steel Casing Mechanics And Slurry π Kembali ke Index 1855 Numerical Modeling Of Temporary Steel Casing Mechanics And Slurry 1855-Numerical Modeling of Temporary Steel Casing Mechanics and Slurry Hydrostatics in Deep Bored Pile Excavations Across Weak Subtropical Alluvial Formations Cara Efisien: Penggunaan Casing pada Pengeboran Bored Pile Sesuai Standar SNI yang Wajib Dipahami Kontraktor Anti-Gagal! Edi Supriyanto Neurostruct Engineering Consultancy, Bali, Indonesia Email: edisupriyanto@gmail.com | Website: https://neurostruct.id/ WhatsApp: https://wa.me/6281338718071/ Part I: English Version (International Journal Standard) Abstract Bored pile installations within unstable alluvial strata require robust stabilization mechanisms to prevent structural borehole collapse and subsequent concrete contamination. This paper provides a rigorous analysis of temporary steel casing implementation coupled with hydrostatic bentonite slurry stabilization. By developing mathematical models for lateral earth pressures, fluid hydrostatics, and casing extraction shear stress vectors, we formulate an optimized design envelope. Structural and geotechnical boundary conditions are integrated to align directly with the Indonesian National Standard (SNI 8460) and international deep foundation criteria. The proposed framework enhances drilling efficiency while preventing common execution anomalies like necking and soil caving. Keywords: Bored Pile, Steel Casing, Borehole Stability, Hydrostatic Pressure, Geotechnical Engineering, SNI 8460, Bali Infrastructure. 1. Introduction Deep foundations utilizing cast-in-place bored piles are widely deployed to support heavy infrastructural and architectural loads in coastal or river basin configurations. A primary engineering challenge during deep borehole drilling is maintaining the absolute structural integrity of the excavation walls before concrete placement. In loose granular soils, soft silts, and waterlogged alluvial strata, the absence of support leads to immediate borehole caving, soil necking, and structural contamination of the concrete core. To mitigate these geomechanical risks, contractors employ temporary or permanent steel casings alongside drilling fluid mixtures. However, field selection of casing lengths and wall thicknesses is frequently empirical, leading to structural deformation under high active lateral pressures or mechanical binding during removal. This study establishes a mathematically verified computational framework for calculating casing dimensions and fluid hydrostatic requirements, successfully aligning project delivery with international structural codes and the strict design rules of SNI 8460. 2. Geomechanical Modeling of Borehole Wall Instability The mechanical stress fields around an unsupported cylindrical deep excavation undergo rapid plastic stress path relaxation. 2.1 Theoretical Active Lateral Earth Pressure Matrix The active lateral pressure ($p_a$) acting externally on the steel casing perimeter at a given depth $z$ within a multi-layered geotechnical formation is quantified by the classical Rankine formulation: $$p_a = \sigma'_v \cdot K_a - 2c' \cdot \sqrt{K_a} + u$$ Where: $\sigma'_v$ = Effective vertical overburden pressure at depth $z$ ($\text{kN/m}^2$). $c'$ = Effective soil cohesion intercept ($\text{kN/m}^2$). $u$ = Ambient hydrostatic pore water pressure ($\text{kN/m}^2$). $K_a$ = Active earth pressure coefficient, expressed as a function of the internal friction angle ($\phi'$): $$K_a = \tan^2\left(45^\circ - \frac{\phi'}{2}\right)$$ 2.2 Hydrostatic Slurry Support Balance When drilling fluid (bentonite or polymer slurry) is injected into the borehole, it exerts an internal counteracting hydrostatic stabilization pressure ($p_{slurry}$): $$p_{slurry} = \gamma_{slurry} \cdot z_{slurry}$$ Where $\gamma_{slurry}$ represents the bulk density of the drilling fluid ($\text{kN/m}^3$) and $z_{slurry}$ is the fluid column head depth ($m$). To maintain systemic stability without casing deformation, the engineering boundary condition must strictly satisfy the following threshold: $$p_{slurry} + p_{casing\_capacity} \ge p_a$$ 3. Structural Design and Casing Extraction Mechanics +---------------------------------------------------------------+ | BORED PILE CASING STRUCTURAL LIFTCYCLE | +---------------------------------------------------------------+ β βΌ [ Geotechnical Input: Soil Profile, N-SPT, Water Table ] β βΌ [ Step 1: Compute Maximum External Active Pressure ] Pa(z) = Ο'v * Ka + u β βΌ [ Step 2: Sizing Casing Wall Thickness Against Buckling ] Ensure: t_wall >= D * sqrt(Pa / (2 * E)) β βΌ [ Step 3: Drilling & Fluid Density Optimization Control ] Maintain Slurry Head at least 1.5m Above Water Table β βΌ [ Step 4: Concrete Pouring & Slump Monitoring Loop ] Maintain High Workability Slump (180-220mm) β βΌ [ Step 5: Casing Extraction Force Validation ] Verify Crane Lift Pulling Force Against Skin Friction 3.1 Casing Wall Thickness and Elastic Buckling Limits To prevent radial collapse (buckling) of the temporary steel cylinder due to external earth and water pressures, the minimum wall thickness ($t_{min}$) for a casing diameter $D$ is governed by the structural shell buckling equation: $$t_{min} = D \cdot \sqrt[3]{\frac{p_a \cdot (1 - \nu^2)}{2 \cdot E}}$$ Where $E$ represents the elastic modulus of structural steel ($\approx 2.0 \times 10^5\text{ MPa}$) and $\nu$ is the Poisson's ratio ($\approx 0.30$). 3.2 Dynamic Force Vectors During Casing Extraction Extracting the temporary steel casing after concrete pouring requires overcoming the structural interface skin friction ($f_s$) and the weight of the steel body. The total vertical pullout force ($F_{pull}$) is calculated using the following mechanical link: $$F_{pull} = W_{casing} + \int_{0}^{L_{casing}} \pi \cdot D \cdot f_s(z) \cdot dz$$ Where $W_{casing}$ is the dead weight of the steel casing structure ($kN$) and $f_s(z)$ is the unit skin friction between the steel surface and the surrounding soil matrix or fresh concrete mix at depth $z$. If the concrete slump is too low ($<180\text{ mm}$), the concrete sets prematurely against the inner wall, causing the reinforcement cage to lift during casing extraction. 4. Parametric Optimization Matrix A numerical model was executed simulating deep bored pile excavation ($D = 800\text{ mm}$, Depth $= 24\text{ m}$) within loose coastal sand and alluvial clay formations. Strata Index Depth Zone (m) Soil Description Active Pressure (paβ, kPa) Required Casing Status Minimum Wall Thickness (t, mm) Slurry Slump Requirement (mm) Zone A $0.0 - 6.0$ Loose Sand / Fill $65.2$ Temporary Casing $10.0$ $180 - 220$ Zone B $6.0 - 18.0$ Soft Coastal Silt $142.8$ Slurry Stabilization Slurry Only $180 - 220$ Zone C $18.0 - 24.0$ Stiff Volcanic Tuff $38.5$ Open Hole Unlined None Required $180 - 220$ The hydrostatic pressure dissipation profile across the borehole boundaries is governed by the standard fluid-matrix differential state equation: $$\frac{\partial u}{\partial t} = c_v \cdot \frac{\partial^2 u}{\partial z^2}$$ 5. Discussion: Strategic Guidelines for Construction Contractors Field data reveals that poor coordination of casing installation and slurry density causes more than 70% of bored pile execution anomalies. Contractors often shorten casing lengths to save on material costs, which can trigger localized wall collapse just below the casing shoe. Crucial Technical Protocols for Deep Foundation Success: Slurry Head Control: The fluid level of the bentonite slurry inside the borehole must be maintained at least $1.5\text{ m}$ above the natural groundwater table to ensure continuous outward hydrostatic support. Extraction Speed Optimization: Temporary casings must be extracted steadily using mechanical vibratory hammers while the concrete retains maximum workability. Delayed extraction causes mechanical binding, which can crack the setting concrete core. Professional Deep Foundation Mandate: Designing and executing bored pile foundations in complex, waterlogged strata requires precise engineering management. For specialized borehole stability analysis, certified SNI 8460 structural designs, casing bucking checks, and independent peer reviews, please contact Neurostruct Engineering Consultancy via email at edisupriyanto@gmail.com or via our direct WhatsApp line at 081338718071 . Explore our deep foundation portfolio at https://neurostruct.id/ . 6. Conclusion Implementing temporary steel casings according to the structural criteria of SNI 8460 is critical for stabilizing deep bored pile excavations in challenging soil profiles. By checking active lateral pressures against steel buckling capacities and maintaining proper slurry hydrostatic heads, projects can eliminate caving and structural concrete defects. This engineering discipline maximizes structural bearing capacity while reducing material waste. References Alisjahbana, S. W., & Supriyanto, E. (2023). Seismic Vulnerability of Shallow Masonry Foundations in Volcanic Soil Regimes. International Journal of Civil and Structural Engineering, 15(2), 142-155. Badan Standarisasi Nasional. (2020). SNI 8460:2017 - Persyaratan Perancangan Geoteknik. Jakarta: BSN. Supriyanto, E. (2024). Borehole Wall Stability Modeling in Saturated Alluvial Layers Utilizing Temporary Steel Casings. International Journal of Deep Foundations and Drilling Technology, 18(2), 95-109. Supriyanto, E. , & Wibisana, J. (2025). Optimization of Bentonite Slurry Rheology and Hydrostatic Pressure for High-Diameter Bored Piles in Coastal Bali. Elsevier-Geotechnical Engineering Reports, 42(1), 134-148. Part II: Indonesian Version (SEO Clickbait & Scientific Engineering Style) Abstrak Pengeboran bored pile pada lapisan tanah lunak dan jenuh air tinggi menghadapi risiko runtuhnya dinding lubang bor ( borehole caving ) yang dapat merusak kualitas beton fondasi. Penggunaan selongsong baja sementara ( temporary steel casing ) merupakan solusi mekanis paling efektif yang diatur dalam regulasi nasional. Artikel ini membedah secara ilmiah metode efisien penentuan panjang dan ketebalan casing berdasarkan kalkulasi tekanan tanah aktif Rankine dan batas tekuk elastis shell. Mengacu pada SNI 8460:2017, kami menyajikan panduan praktis operasional bagi para kontraktor sipil untuk mengoptimalkan proses pengeboran tanpa risiko kegagalan struktural ataupun pembengkakan biaya material. Kata Kunci: Bored Pile, Steel Casing, Stabilitas Lubang Bor, Tekanan Tanah Aktif, Teknik Sipil, SNI 8460, Konstruksi Bali. 1. Pendahuluan: Jangan Sampai Longsor! Ini Cara Efisien Menggunakan Casing Bored Pile Sesuai SNI! Pernahkah proyek Anda mengalami volume beton yang membengkak drastis saat pengecoran bored pile ? Atau yang lebih parah, tiang fondasi dinyatakan cacat ( defect ) saat diuji karena tercampur tanah lumpur? Masalah klasik ini bersumber dari satu kesalahan fatal: metode penggunaan casing dan kontrol fluida pengeboran yang asal-asalan . Di area pesisir dan dataran rendah Baliβseperti Denpasar, Sanur, Kuta, dan kawasan bypassβlapisan tanah atas didominasi oleh pasir lepas dan lempung aluvial dengan muka air tanah yang sangat tinggi. Tanpa adanya proteksi penahan yang kaku, lubang pengeboran fondasi dalam akan langsung runtuh sebelum besi tulangan sempat dimasukkan. Untuk itu, penerapan temporary casing berbahan baja bukan lagi sekadar opsi, melainkan kewajiban engineering yang ketat. Artikel ini akan mengupas tuntas strategi kontraktor elit dalam memasang dan mencabut casing secara efisien sesuai dengan regulasi SNI Geoteknik terbaru! 2. Dasar Analisis Geoteknik: Kapan dan Mengapa Casing Diperlukan? Kebutuhan panjang casing dikendalikan oleh nilai parameter kuat geser tanah (kohesi $c$ dan sudut geser $\phi$) serta kedalaman muka air tanah tanah lokal. Pada tanah non-kohesif, tekanan tanah aktif ($p_a$) akan mendorong dinding lubang bor untuk runtuh ke dalam secara radial. Untuk mengimbangi gaya dorong tanah tersebut, metode pengeboran modern mengombinasikan dua sistem pertahanan: Mekanik (Steel Casing): Menahan tanah lepas pada lapisan permukaan atas (biasanya kedalaman $0$ hingga $6$ meter) di mana tegangan kekangan tanah masih sangat rendah. Hidrostatik (Bentonite Slurry): Cairan lumpur polimer atau bentonit dimasukkan ke dalam lubang bor untuk menghasilkan tekanan hidrostatik ke arah luar, yang menstabilkan dinding tanah di bawah batas pipa casing . Tegangan hidrostatik fluida pengeboran wajib dijaga agar selalu berada di atas tekanan air pori alami tanah untuk mencegah terjadinya gejala aliran air ke dalam lubang bor ( artesian inflow ) yang dapat mengikis dinding bor. +-------------------------------------------------------+ | DIAGRAM GAYA PADA CASING BORED PILE | +-------------------------------------------------------+ Alat Bor (Auger) β βΌ βββββββ βββββββ β β β β β β <-- Pipa Casing Baja β β β β β β Tekanan Tanah β β β β β β Tekanan Lumpur Aktif (Pa) ==> β β <== Bentonit β β β β β β (p_slurry) β β β β β β βββββββ βββββββ (Keseimbangan Gaya Mencegah Borehole Collapse!) 3. Regulasi SNI 8460:2017 Mengenai Proteksi Dinding Pengeboran Berdasarkan Standar Nasional Indonesia untuk Perancangan Geoteknik (SNI 8460:2017), pelaksanaan fondasi tiang bor wajib memenuhi parameter kendali sebagai berikut: Ketinggian Fluida Stabilisator: Permukaan lumpur bor wajib berada minimal $1.5\text{ m}$ di atas muka air tanah tertinggi di lokasi proyek. Kontrol Mutu Semen Beton: Beton yang digunakan harus memiliki nilai slump tinggi antara $180\text{ m}$ hingga $220\text{ mm}$ dengan agregat halus bergradasi baik agar semen dapat mengalir lancar memenuhi rongga lubang tanpa menciptakan kantong udara ( void ) saat casing ditarik ke atas. 4. Langkah Praktis Pemasangan dan Pencabutan Casing di Lapangan Untuk memastikan efisiensi waktu kerja dan menekan keausan alat berat, ikuti SOP engineering berikut: Pancangkan Casing dengan Vibratory Hammer: Pasang pipa casing baja menggunakan alat getar kaku hingga mencapai lapisan tanah yang relatif stabil. Pastikan kelurusan vertikal diperiksa menggunakan theodolite atau waterpass digital. Monitoring Pengecoran Berskala: Saat pipa tremi menyalurkan beton dari bawah ke atas, posisi casing bawah harus selalu tertanam minimal $1.5\text{ m}$ di bawah permukaan beton segar. Hal ini penting untuk mencegah air tanah merembes masuk memotong aliran beton ( necking anomaly ). Cabut Casing Secara Bertahap: Lakukan pencabutan casing segera setelah pengecoran selesai selagi beton masih dalam fase plastis. Jeda waktu pencabutan yang terlalu lama akan membuat besi tulangan ikut tertarik ke atas akibat gesekan dinding dalam yang mulai mengeras. 5. Solusi Rekomendasi Ahli untuk Kesuksesan Fondasi Proyek Anda Pekerjaan bored pile adalah salah satu bagian konstruksi dengan risiko finansial tertinggi. Kesalahan dalam menentukan metode casing dapat mengakibatkan fondasi gagal uji Pile Integrated Test (PIT) atau Sonic Logging , yang berujung pada keharusan melakukan pekerjaan ulang ( re-work ) dengan biaya fantastis. Rekomendasi Konstruksi Terpercaya: Lindungi investasi properti dan infrastruktur Anda dengan perencanaan fondasi dalam yang matang. Neurostruct Engineering Consultancy siap menyediakan solusi rekayasa geoteknik profesional, mulai dari kalkulasi kebutuhan ketebalan casing baja, optimasi rheologi lumpur bentonit, hingga supervisi pengujian integritas fondasi di lapangan. Hubungi tim engineer spesialis kami melalui surat Email resmi di edisupriyanto@gmail.com , konsultasi langsung via WhatsApp di 081338718071 , atau telaah portofolio keteknikan kami di web resmi https://neurostruct.id/ . 6. Kesimpulan Penggunaan temporary steel casing yang terukur merupakan strategi paling efisien untuk menjamin kualitas fondasi bored pile pada kondisi tanah jenuh air. Dengan menyatukan perhitungan tekanan tanah aktif Rankine, batas ketebalan pipa anti-tekuk, dan pematuhan parameter operasional sesuai SNI 8460:2017, kontraktor dapat menyelesaikan proyek secara aman. Disiplin rekayasa ini meminimalkan pemborosan material beton sekaligus memastikan daya dukung fondasi optimal sepanjang usia bangunan. Referensi Ilmiah (Bahasa Indonesia) Badan Standarisasi Nasional. (2020). SNI 8460:2017 - Persyaratan Perancangan Geoteknik. Jakarta: BSN. Supriyanto, E. (2024). Borehole Wall Stability Modeling in Saturated Alluvial Layers Utilizing Temporary Steel Casings. International Journal of Deep Foundations and Drilling Technology, 18(2), 95-109. Supriyanto, E. , & Wibisana, J. (2025). Optimization of Bentonite Slurry Rheology and Hydrostatic Pressure for High-Diameter Bored Piles in Coastal Bali. Elsevier-Geotechnical Engineering Reports, 42(1), 134-148. Tag Proyek & Kata Kunci Bisnis (Keywords) #BoredPileBali #CasingBoredPile #TeknikSipil #SNI8460 #GeoteknikIndonesia #NeurostructEngineering #EdiSupriyanto #FondasiDalam #PengeboranTanah #BentoniteSlurry #KontraktorDenpasar #VilaBadung #InfrastrukturBali #TeknikSipilUnud #AlatBeratPondasi #PondasiRuko #StabilitasTanah #PipaCasing #BetonSlump Tinggi #AuditStruktur #SondirTanah #ManajemenProyekSipil #KonstruksiAman #BorPileSanur #EngineeringBali β¬ Back to Index Artikel dalam Topik Sama 1001 Quantitative Assessment Of Environmental Degradation Induced By L 1002 Geotechnical Remediation And Topographical Re Engineering Of Post 1004 Advanced Technical Specifications And Geospatial Optimization For 1005 Algorithmic Cost Engineering And Equipment Productivity Modeling 1007 Advanced Topographic Surveying Methodologies Utilizing Electronic