Development of Ballast Settlement Equation: Ballast Settlement under Different Axle Loads and Train Speeds

Muhammad Danu Prawira, Prof. Ir. Suryo Hapsoro Tri Utomo, Ph.D.; Taqia Rahman, ST., M.Sc., Ph.D.

2024 | Tesis | S2 Mag. S. & T.Transportasi

Jalur kereta api berdiri sebagai sistem infrastruktur penting yang disediakan untuk memfasilitasi kelancaran pergerakan kereta api. Aspek keselamatan dan keamanan jalur kereta api sangatlah penting mengingat jalur kereta api menerima beban besar dan berulang secara terus menerus. Pembebanan yang berulang ini menyebabkan jalur kereta api mengalami deformasi plastis (settlement), terutama pada lapisan ballast. Deformasi plastis dapat berdampak buruk pada geometri jalur jika melebihi ambang batas yang diizinkan. Namun, memahami ballast settlement terbukti menjadi upaya yang menantang karena pengaruh berbagai faktor. Beberapa rumus empiris telah dikembangkan untuk memprediksi ballast settlement. Namun, persamaan empiris yang dikembangkan dalam 30 tahun terakhir menghadapi tantangan dengan meningkatnya beban gandar dan kecepatan kereta api saat ini. Oleh karena itu, tesis bertujuan untuk mengembangkan rumus empiris untuk memprediksi ballast settlement dengan mempertimbangkan faktor beban gandar dan kecepatan kereta api.

Tesis ini memanfaatkan beberapa data yang diperoleh dari pengujian ballast settlement yang dilakukan pada beberapa penelitian sebelumnya. Metode systematic literature review digunakan untuk mengidentifikasi kumpulan data hasil pengujian ballast settlement pada beban gandar dan kecepatan kereta api yang berbeda. Kumpulan data yang terpilih akan dianalisis di Microsoft Excel untuk mendapatkan best-fit curve dan best-fit equation. Kemudian, rumus baru tersebut akan divalidasi menggunakan metode Mean Absolute Percentage Error (MAPE) untuk menilai tingkat akurasi dalam memprediksi ballast settlement pada beban gandar dan kecepatan kereta api yang berbeda.

Rumus logaritmik dipilih sebagai dasar pengembangan karena kemampuannya untuk memprediksi ballast settlement yang relevan dengan hasil pengujian ballast settlement. Rumus empiris baru mampu menghasilkan pola ballast settlement pada beban gandar dan kecepatan kereta api yang berbeda. Selain itu, rumus empiris baru ini berada pada kategori “Baik” untuk memprediksi ballast settlement berdasarkan nilai Mean Absolute Percentage Error (MAPE). Namun, rumus baru ini lebih kompatibel bila diterapkan pada kondisi parameter jalur yang paling umum. Kondisi partikel ballast, penggunaan geosintetik, dimensi bantalan dan kekuatan subgrade berpotensi mempengaruhi ballast settlement. Oleh karena itu, penelitian yang akan datang perlu mempertimbangkan faktor-faktor tersebut untuk mendapatkan rumus ballast settlement yang lebih akurat.

The railway track stands as an essential infrastructure system provided to facilitate the seamless movement of trains between two locations. The aspect of safety and security relating to the railway track are very important, given its continuous exposure to large repeated loads. These repeated loads cause the railway track to plastic deformations (track settlement), especially the ballast layer which has granular characteristics. The plastic deformation can adversely impact the track geometry when it exceeds the permissible threshold. However, comprehending ballast settlement has proven to be a challenging effort due to the role of many factors. Numerous empirical formulas have been developed in attempts to understand and predict ballast settlement. Nevertheless, the empirical equation has been developed in the last 30 years are no longer aligns with the current train load and speed conditions. Therefore, this thesis aims to develop an empirical equation to predict ballast settlement by considering the passing axle load and train speed factor.

This thesis utilises some data derived from ballast settlement tests conducted in previous studies. A qualitative approach with a systematic literature review method was used to identify comprehensive datasets of ballast settlement test result under different axle loads and train speeds. The selected datasets will be analysed in Microsoft Excel to derive the best-fit curve and the best-fit equation that aligns with the observed ballast settlement pattern. Then, the new equation will be validated using the Mean Absolute Percentage Error (MAPE) method to assess the level of accuracy in predicting ballast settlement under different axle loads and train speeds.

The logarithmic equation was selected as the basis for the new equation, rooted in its ability to predict non-linear ballast settlement patterns similar to the ballast settlement test results. The new empirical equation has demonstrated an ability to produce ballast settlement patterns under different axle loads and train speeds. In addition, the new empirical equation is in the “Good” category for predicting ballast settlement based on Mean Absolute Percentage Error (MAPE) values. However, it is important to note that the new equation is more compatible when applied under the conditions of most commonly track parameters. Variations in track parameters, such as the condition of ballast particles, the implementation of geosynthetics and sleeper pads, sleeper dimensions and subgrade stiffness have the potential to influence the ballast settlement rate. Therefore, forthcoming research needs to consider the inclusion of these factors to obtain a more accurate prediction equation for ballast settlement.

Kata Kunci : Ballast Settlement, Axle Load, Train Speed, Laboratory Test, Dynamic Load