ANALISIS NEGATIVE SKIN FRICTION PADA PONDASI SPUN PILE MENGGUNAKAN SETTLE3D (Studi Kasus : Proyek Rusun Dosen Poltek PU Semarang)

ABSTRAK

Spun pile merupakan salah satu jenis pondasi dalam yang umum digunakan pada konstruksi bangunan bertingkat maupun infrastruktur karena kekuatan tekan yang tinggi dan kemudahan dalam pelaksanaan. Namun, pada kondisi tanah lunak yang mengalami penurunan primer, fenomena negative skin friction (NSF) dapat terjadi dan menyebabkan penambahan beban aksial pada spun pile. NSF timbul akibat pergerakan vertikal tanah yang lebih besar daripada pergerakan tiang, sehingga tanah memberikan gaya ke bawah pada permukaan tiang. Penelitian ini bertujuan untuk menganalisis besar penurunan tanah terhadap struktur pondasi spun pile menggunakan program Settle3D, mengevaluasi pengaruh gaya negative skin friction (NSF) terhadap kapasitas daya dukung pondasi berdasarkan hasil analisis daya dukung, serta mengkaji peran faktor keamanan (safety factor) dalam menjamin kestabilan pondasi spun pile terhadap risiko penurunan dan pengaruh gaya NSF. Parameter tanah seperti undrained shear strength (Cu), modulus elastisitas (Es), serta karakteristik penurunan tanah digunakan untuk menghitung nilai NSF pada tiap lapisan tanah yang mengalami penurunan. Pemodelan dengan program Settle3D
menghasilkan total settlement maksimum sebesar 139,2 mm pada group pile, dan 147,89 mm pada model single pile, dengan penurunan signifikan hingga kedalaman 20 meter. Penurunan ini menghasilkan gaya NSF sebesar 57,645 ton. Evaluasi terhadap kapasitas spun pile menunjukkan bahwa bila menggunakan daya dukung izin (Qa), pondasi dalam kondisi tidak aman karena nilai Qa (70.5 T) < Pult + NSF (124.745 T). Namun, evaluasi menggunakan daya dukung ultimit (Qu) menunjukkan kondisi masih aman, yaitu Qu (208.09 T ) > Pult + NSF (124.745 T). Hasil ini juga diperkuat oleh uji PDA, di mana nilai Ru (209 T) > Pult + NSF (124.745 T), menunjukkan struktur pondasi masih dalam
kondisi aman terhadap beban kerja dan NSF. Kesimpulan menunjukkan pentingnya mempertimbangkan efek NSF dalam perencanaan pondasi dalam, khususnya pada tanah lunak. Penggunaan Settle3D efektif mengidentifikasi besar settlement yang memicu NSF, sehingga meningkatkan akurasi evaluasi keamanan pondasi.

Kata kunci: Pondasi Spun Pile, penurunan tanah, NSF, tiang pancang

===============================================================

ABSTRACT

Spun piles are a type of deep foundation commonly used in the construction of multi-story buildings and infrastructure due to their high compressive strength and ease of installation. However, in soft soil conditions undergoing primary consolidation, the phenomenon of negative skin friction (NSF) may occur, resulting in additional axial loads on the spun piles. NSF arises when the vertical movement of the soil exceeds that of the pile, causing the soil to exert a downward force along the pile surface. This study aims to analyze the magnitude of soil settlement due to consolidation on spun pile foundations using the Settle3D program, evaluate the influence of NSF on the pile's bearing capacity based on capacity analysis results, and assess the role of the safety factor in ensuring the stability of spun pile foundations against settlement and NSF effects. Soil parameters such as undrained shear strength (Cu), elastic modulus (Es), and consolidation characteristics were used to calculate NSF values for each settling soil layer. Modeling using Settle3D produced a maximum total settlement of 139.2 mm for the group pile and 147.89 mm for the single pile model, with significant settlement occurring up to a depth of 20 meters. This settlement generated an NSF force of 57.645 tons. Evaluation of the pile capacity showed that when using allowable bearing capacity (Qa), the foundation is unsafe since Qa (70.5 T) < Pult + NSF (124.745 T). However, evaluation using ultimate bearing capacity (Qu)
indicated a safe condition, with Qu (208.09 T) > Pult + NSF (124.745 T). This result is supported by PDA test results, where Ru (209 T) > Pult + NSF, indicating that the foundation remains safe under working loads and NSF. The findings highlight the importance of considering NSF effects in deep foundation design, particularly in soft soils. The use of Settle3D is effective in identifying settlement that triggers NSF, thus improving the accuracy of foundation safety evaluations.

Keywords: Spun Pile Foundation, Settlement, NSF, Deep Pile