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ANALISIS STABILITAS FONDASI MESIN PEMBANGKIT HYDRO PADA SUNGAI BAWAH TANAH ZONA KARST Sulha, Sulha; Rifa’i, Ahmad; Sarita, Umran
DINAMIKA – Jurnal Ilmiah Teknik Mesin Vol 7, No 1 (2015)
Publisher : HALUOLEO UNIVERSITY

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Abstract

Penelitian ini bertujuan untuk menganalisis stabilitas fondasi mesin pembangkit listrik hydro pada sungai bawah tanah zona karst di Goa Seropan, menggunakan metode elemen hingga model  plan-strain. Pendekatan analisis dilakukan pada tampang fondasi dengan menggunakan 4 model geometri. Material properti di lokasi konstruksi diambil dari hasil penelitian dan uji laboratorium IWRM Goa Seropan dari tim teknis UGM. Input gemoteri diperoleh dari data pengukuran lapangan yang disederhanakan, sedangkan input parameter tanah, batuan dan beton diperoleh dari data sekunder. Analisis model yakni beban statis dan dinamis menggunakan software PLAXIS  v8.2, yang divalidasi berdasarkan perhitungan manual. Hasil simulasi numeris menunjukkan penambahan bored pile 0,20 meter pada sistem fondasi pembangkit hydro-power mampu melawan tegangan yang terjadi di tanah dasar akibat beban gempa dengan faktor aman sebesar 2,01. Sistem fondasi pada model geometri I, dengan dimensi pelat horisontal sebesar 0,40 meter, dinding vertikal sebesar 0,30 meter, dan bored pile sebesar 0,20 meter, cukup aman dan stabil terhadap beban statik maupun dinamik. Selisih diplacement vertikal maksimum dua titik fondasi pada model gemetri I akibat akumulasi pembebanan menyebabkan angular distortion sebesar 0,2159 cm (1/1112) masih relatif kecil dari angular distortion izin (1/750). Simpangan horisontal maksimum fondasi dan bangunan yang terjadi akibat beban gempa 355,4g adalah sebesar 0,379%,  masih relatif aman jika ditinjau terhadap simpangan izin sebesar 1,54%. Software PLAXIS terbukti mampu memodelkan perilaku dinding goa dan struktur yang memikul beban statik dan dinamik dengan cukup baik.
Analisis Kelongsoran Lereng Akibat Pengaruh Tekanan Air Pori di Saluran Induk Kalibawang Kulonprogo Subiyanti, Hesti; Rifa’i, Ahmad; Jayadi, Rachmad
Jurnal Semesta Teknika Vol 14, No 1 (2011): MEI 2011
Publisher : Jurnal Semesta Teknika

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Abstract

During rainy seasons, landslide occurs every year in Talang Bawong, Kalibawang Irrigation Channel thatcan damage houses, school building, bridge and the channel. Considering this fact, a numerical analysis by modeling the slope at the site was conducted. The objectives of this research were to identify the rain characteristic in the research site and to recognize its influence towards the change of water pressure in soil as well as the slope failure. The input data of this analysis were slope topography, physical and mechanical properties of soil applied. Groundwater flow in the slope model was numerically simulated by using SEEP/W software. Designed rainfall with appropriate return period was determined by analizing the maximum daily rainfall data with the aid of HAVARA software, while rainfall depth distribution was completed by applying frequency analysis. The historical daily rainfall data (1985 – 2004) were obtained from Kalibawang rain stasiun. Six rainfall models, as follow: initial condition (no rain) (model I), heavy rain in a short duration (model II), normal rain 25 mm and 40 mm in a long duration (model III), normal rain 20 mm in a long duration (model IV), heavy rain followed by normal rain 20 mm (model V), and normal rain 20 mm followed by heavy rain (model VI) Were analyzed. The output of the simulation was water pressure distribution data, which in turn being used as input data in analyzing slope stability using the SLOPE/W software. The result of the research showed that the highest rainfall with 2-year-return period was 114 mm while the dominant duration was 4 hours/day, and it was applied in the model II. The result showed that, a normal rain in a long duration is more severely influenced the change in water pressure than a heavy rain in a short duration. The safety factors are 1,444 for no rain condition, 1,418 for 114 mm rain for 4 hours, 1,208 for 25 mm and 40 mm rains, 0,982 for 20 mm rain, 1,397 for heavy rain followed by normal rain, and 1,402 for normal rain followed by heavy rain. In addition, a 20 mm normal rain on the 61st  day resulted in the most severe influence on the slope failure. 
Behavior of Expansive Clay of Ngawi Region (East Java) Under Water Content Variation Sudjianto, Agus Tugas; Suryolelono, Kabul Basah; Rifa’i, Ahmad; B Mochtar, Indrasurya
Civil Engineering Dimension Vol 11, No 2 (2009): SEPTEMBER 2009
Publisher : Institute of Research and Community Outreach - Petra Christian University

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (291.438 KB) | DOI: 10.9744/ced.11.2.pp. 100-105

Abstract

When expansive clay is wetted, deformations occur both vertically and laterally. If it is tested in an oedometer ring apparatus the lateral deformation will be restrained by the wall of the ring. This paper present the results of an experimental investigation using modified oedometer test for measuring the vertical and lateral swelling potential and lateral pressure of disturbed expansive clay soil. Series of modified oedometer tests were conducted with initial water content of 20%, 25% and 30%, to predict the vertical and lateral swelling potential and lateral swell pressure. The results of the test show that the percentages of the vertical swell is bigger than the lateral swell. Both vertical and lateral swell, linearly decrease with increasing initial water content. The lateral swell pressure also decreases with increasing initial water content.
Perbaikan Tanah Dasar Jalan Tol Semarang – Demak Menggunakan Bahan Aditif Dan Perkuatan Kolom Stabilisasi Anggraini, Anindita Dwi; Rifa’i, Ahmad; Faris, Fikri
Rekayasa Sipil Vol 12, No 1 (2018)
Publisher : Department of Civil Engineering, Faculty of Engineering, University of Brawijaya

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Abstract

In Semarang there is often a flood of sea water that swamp the road. This happens because the ground is lower than the water level, load-carrying capacity is deficient. Following up on this, a new road network is needed as a toll road. To accomplish the problem, it is necessary to increase the load-carrying capacity by improve the subgrade on the toll road using additive and strengthen the stabilization column. Additives used in the form of additives made of inorganic materials containing compounds of calciumchloriddihydrat with pH of 8.24 which has ion bonding energy is greater than the metal material on the surface of the soil grains. The general composition consists of carbon elements 72.78%, hydrogen 21.11%, and nitrogen 1.36%. The research was conducted on soil mix, additive material by comparison 1 gram of additive, 1 liter of water and variation of cement content like 4%, 5%, 6%, 7%. To get the optimum mix for soil improvement. Then numerical analysis by using Plaxis Software v.8.6 with variation of soil thickness and column length stabilization. Test results show that the soil is high-plasticity clay. The soil stabilization was eligible for soil compressive strength testing for layers of soil composite cement foundation of 24 kg / cm2. Soil compressive strength testing of soil stabilization is 2,47 kg/cm 2 with 7% cement and addictive. Based on numerical analysis with plaxis v 8.6 software, the deformation value in the model with 5 m thick soil stabilization and 50 m stabilization column length has met the embankment degression limit according to the PU guideline that is 20 mm for the 1st class road. For the value of road stability safety factor, eligible value 1.4.