EVALUASI KERUNTUHAN FONDASI TIANG VERTICAL BREAKWATER AKIBAT GAYA GELOMBANG PADA TAHAP KONSTRUKSI MENGGUNAKAN PEMODELAN NUMERIS

Abla Salsabila, Rozaqqa Noviandi, S.T., M.Agr., Ph.D.

2026 | Skripsi | TEKNIK SIPIL

Fondasi tiang pancang pada struktur vertical breakwater berperan penting dalam menjaga stabilitas struktur terhadap beban gelombang. Pada tahap konstruksi, fondasi belum didukung oleh sistem pengikat permanen seperti pilecap, sehingga lebih rentan mengalami keruntuhan akibat beban siklis lateral akibat gaya gelombang. Kondisi tersebut menjadikan evaluasi mekanisme keruntuhan fondasi pada tahap konstruksi penting dilakukan. Penelitian ini bertujuan mengevaluasi keruntuhan fondasi tiang vertical breakwater akibat gaya gelombang melalui analisis interaksi tanah–tiang, perubahan kapasitas lateral fondasi, distribusi momen lentur, serta mengevaluasi penggunaan clutch sebagai pengikat sementara selama tahap konstruksi.

Penelitian dilakukan menggunakan metode elemen hingga (Finite Element Method/FEM) dengan perangkat lunak PLAXIS 2D. Analisis dilakukan pada model tiang tunggal vertikal dan miring serta kelompok tiang dengan menggunakan data sekunder dari Proyek Pembangunan Vertical Breakwater di Tuban. Beban gelombang dimodelkan sebagai beban siklis lateral untuk mengevaluasi respons fondasi selama tahap konstruksi.

Hasil penelitian menunjukkan bahwa beban gelombang siklis meningkatkan excess pore pressure sehingga menyebabkan degradasi kekakuan tanah di sekitar fondasi. Kondisi tersebut mengakibatkan penurunan kapasitas lateral fondasi dan peningkatan respons lentur tiang. Meskipun demikian, respons lentur yang terjadi masih berada di bawah kapasitas nominal material tiang, sehingga keruntuhan fondasi tidak disebabkan oleh kegagalan struktur tiang, melainkan oleh degradasi kekakuan tanah yang menurunkan kemampuan tanah dalam memberikan tahanan lateral terhadap beban gelombang. Dengan demikian, mekanisme keruntuhan fondasi pada tahap konstruksi didominasi oleh hilangnya kapasitas dukung lateral akibat degradasi interaksi tanah–tiang. Penggunaan clutch sebagai pengikat sementara dapat menjadi salah satu alternatif untuk meningkatkan stabilitas sistem fondasi dan mengurangi potensi keruntuhan selama tahap konstruksi.

Pile foundations play a critical role in maintaining the stability of vertical breakwater structures under wave loading. During the construction stage, the foundation system has not yet been supported by permanent bracing elements, making it more susceptible to failure under cyclic lateral loading induced by waves. Therefore, evaluating the foundation failure mechanism during the construction stage is essential. This study aims to evaluate the failure of vertical breakwater pile foundations under wave loading by analyzing soil–pile interaction, changes in lateral bearing capacity, bending moment distribution, and the effectiveness of a clutch as a temporary connecting element during construction.

The study employed the Finite Element Method (FEM) using PLAXIS 2D. Numerical analyses were conducted on both single-pile and pile-group models using secondary data obtained from a vertical breakwater construction project in Tuban, Indonesia. Wave loading was modeled as cyclic lateral loading to evaluate the foundation response during the construction stage.

The results indicate that cyclic wave loading increases excess pore pressure and soil deformation, leading to degradation of the soil stiffness surrounding the foundation. Consequently, the lateral bearing capacity of the pile foundation decreases, accompanied by an increase in the pile bending response. However, the induced bending moment remains below the nominal bending capacity of the pile material, indicating that the foundation failure is not governed by structural failure of the pile but by soil stiffness degradation, which reduces the soil's ability to provide lateral resistance against wave loading. Therefore, the failure mechanism of the pile foundation during the construction stage is predominantly governed by the loss of lateral bearing capacity resulting from the degradation of soil–pile interaction. The use of a clutch as a temporary connecting element may serve as an alternative measure to improve the stability of the foundation system and reduce the potential for foundation failure during the construction stage.

Kata Kunci : Vertical breakwater, tiang pancang, gaya gelombang, beban siklis, kapasitas lateral.