Widjojo Adi Prakoso
Civil Engineering Department, Faculty of Engineering, Universitas Indonesia, Depok 16424, Indonesia

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PEMETAAN VS30 DENGAN MENGGUNAKAN KORELASI ZHAO DI PESISIR CILACAP Robert Edison; Widjojo Adi Prakoso; Supriyanto Rohadi
Jurnal Geosaintek Vol 8, No 1 (2022)
Publisher : Institut Teknologi Sepuluh Nopember

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j25023659.v8i1.12601

Abstract

Pada gempa Pangandaran 2006, pesisir Kabupaten Cilacap merupakan salah satu daerah yang mengalami kerusakan paling parah. Hal ini dikarenakan Kabupaten Cilacap terletak dekat dengan zona subduksi yang juga ditandai dengan tingginya aktivitas seismik di daerah tersebut. Salah satu faktor yang mempengaruhi tingkat kerusakan pada saat gempa adalah kelas tanah. Salah satu cara untuk mengklasifikasikan jenis tanah adalah dengan menggunakan metode mikrotremor dan metode MASW, dimana dalam pengolahannya mikrotremor memanfaatkan respon tanah terhadap getaran untuk memberikan informasi tentang jenis tanah di daerah tersebut, sedangkan MASW menggunakan propagasi gelombang Rayleigh pada permukaan. Setelah itu, periode dominan hasil pengolahan mikrotremor dan Vs30 hasil pengolahan MASW dikorelasikan menggunakan Zhao’s Classification, menghasilkan Vs30 berdasarkan analisis regresi. Nilai periode dominan berkisar antara 0,10-1,07 s, sedangkan Vs30 dari korelasi berkisar antara 6,68-461,34 m/s. Kedua analisis menunjukkan bahwa Tritih Kulon terbukti memiliki kerusakan yang lebih parah pada saat gempa karena terdiri dari Tanah Lunak (SE) yang ditunjukkan oleh nilai periode dominan terpanjang dan nilai Vs30 terendah.
Lower Bound Capacity of Strip Footings on Rock Masses with Two Discontinuity Sets Widjojo Adi Prakoso
Indonesian Geotechnical Journal Vol. 1 No. 2 (2022): Vol.1 , No.2, August 2022
Publisher : Himpunan Ahli Teknik Tanah Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (520.352 KB) | DOI: 10.56144/igj.v1i2.10

Abstract

This paper presents a lower bound model for predicting the rock strip footing bearing capacity. The model is based on strip footings on rock masses with two sets of ubiquitous, closed discontinuities.  The model considers explicitly the strength of the intact rock and the discontinuities, as well as the number and orientation of the discontinuities.  The validation of the model is presented.  The parametric study of footings on rock masses with two discontinuity sets having the same strength is performed, and the results are reported graphically in detail. The bearing capacity is controlled primarily by the rock structures (number of discontinuity sets and orientation) and the discontinuity strength, and it is controlled by the intact rock strength for a very limited number of cases.  The minimum bearing capacity factor is independent of the intact rock friction angle, but it is a linear function of discontinuity cohesion.  The bearing capacity factor is also presented in terms of its ratio to UCS; the ratio for the maximum bearing capacity is rather insignificantly affected by intact rock friction angle, and not linearly correlated to discontinuity cohesion.  The bearing capacity factor for rock masses with low discontinuity strengths tends to be more sensitive to any variation in discontinuity orientation. There are some exceptions to the above points, suggesting that there would always be some rock mass conditions leading to unexpected rock footing bearing capacities and therefore good characterization processes of rock masses would always be essential.  The practical significant of this study is briefly discussed.
Studi Karakteristik Aliran Tanah Terlikuefaksi Berdasarkan Uji Viskositas Wiwik Rahayu; Widjojo Adi Prakoso; Anisya Purwandari; Dian Sih Pusporini; Natasha Gilbert
Jurnal Teknik Sipil Vol 30 No 1 (2023): Jurnal Teknik Sipil
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/jts.2023.30.1.6

Abstract

Abstrak Gempa bumi di Kota Palu sebesar 7,5 Mw pada tahun 2018 menyebabkan likuefaksi di Desa Lolu dengan pergerakan lateral tanah hingga 150 meter. Pergerakan ini terjadi akibat perilaku mencairnya tanah atau disebut likuefaksi. Beberapa peneliti telah membuktikan bahwa perilaku tanah terlikuefaksi dapat dianalisis dengan cara mensimulasikan tanah sebagai cairan yang memiliki kekentalan (viscous fluid). Perilaku pergerakan tanah pada saat likuefaksi terjadi dapat dipelajari melalui karakteristik aliran tanah. Karakteristik aliran tanah terlikuefaksi dianalisis dari nilai viskositas terhadap gaya yang diberikan. Dilakukan pengujian di laboratorium menggunakan alat rotational rheometer untuk mendapatkan nilai viskositas. Terdapat 6 (enam) sampel tanah uji yang digunakan pada penelitian ini, yaitu 3 (tiga) sampel dari area aliran dan 3 (tiga) sampel dari area terdampak. Tanah dari area aliran terdiri dari silty sand, coarse sand, dan fine sand. Sementara tanah dari area terdampak terdiri dari sand gravel, sand gravel boulder, dan silty sand. Seluruh sampel tanah uji menunjukkan karakteristik aliran tanah terlikuefaksi Non-Newtonian, yaitu shear thinning. Variasi kadar air dan suhu yang diterapkan pada seluruh sampel tanah uji menunjukkan bahwa semakin tinggi nilai kadar air dan suhu, maka semakin rendah nilai viskositas yang dihasilkan. Berdasarkan komposisi tanah, semakin besar persentase butir halus yang terkandung maka semakin besar nilai viskositas atau dapat dikatakan tanah mengalir dengan lebih lambat. Kata-kata Kunci: Likuefaksi, rotational rheometer ,   laju geser viskositas, kadar air suhu. Abstract An earthquake in Palu City of 7.5 Mw in 2018 caused liquefaction in Lolu Village with lateral ground movement up to 150 meters. This movement occurs due to the behavior of melting soil, called liquefaction. Several researchers have proven that the behavior of liquefied soil can be analyzed by simulating the soil as a viscous fluid. The behavior of soil movement when liquefaction occurs can be studied through the characteristics of soil flow. The characteristics of liquefied soil flow were analyzed, from the value of the viscosity due to the applied force. Laboratory tests were carried out using a rotational rheometer to obtain the viscosity value. There were 6 (six) soil samples used in this study, namely 3 (three) samples from the flow area and 3 (three) samples from the affected area. The soil of the flow area consists of silty sand, coarse sand, and fine sand. The soil from the affected area consists of sand gravel, sand gravel boulders, and silty sand. All of the tested soil samples showed non-Newtonian soil flow characteristics, namely shear thinning. Variations in water content and temperature applied to all tested soil samples indicate that the higher the water content and temperature values, the lower the resulting viscosity value. Based on the composition of the soil, the greater the percentage of fine grains contained, the greater the value of viscosity, or it can be said that the soil flows more slowly. Keywords: Liquefaction, rotational rheometer, viscosity shear rate, temperature water content