KLASIFIKASI MASSA BATUAN RMI (ROCK MASS INDEX) UNTUK ANALISIS KESTABILAN LERENG DENGAN METODE ELEMEN HINGGA

ABSTRAK - Pada penelitian ini akan digunakan studi klasifikasi massa batuan terhadap lereng alami, yaitu klasifikasi RMi dengan objek penelitian pada lokasi lereng batuan yang berada di Cipatat, Kabupaten Bandung Barat, Provinsi Jawa Barat. Lokasi penelitian memiliki morfologi bentuk lereng terjal dengan litologi dominan berupa batugamping. Klasifikasi RMi ini jarang digunakan karena memiliki beberapa parameter yang cukup rumit untuk dilakukan pembobotan. Untuk mendapatkan nilai bobot dari klasifikasi massa batuan dilakukan pengamatan lapangan dengan scanline dan pengambilan sampel batuan utuh. Hasil properti keteknikan dari klasifikasi massa batuan RMi dianalisis menggunakan metode elemen hingga (finite element method). Massa batuan di lokasi penelitian memiliki litologi dominan berupa batugamping kalkarenit, kalsirudit, dan kalsilutit dengan tingkat pelapukan rendah hingga sedang. Bobot massa batuan berdasarkan klasifikasi RMi berkisar 2,09 – 6,228 (high). Properti keteknikan dari massa batuan dari lima lokasi memiliki modulus deformasi (Em) berkisar 3.068 – 11.550 MPa, kohesi (c) berkisar 0.236 – 2.334 MPa, sudut geser dalam (ɸ) 37o – 57o, dan kuat tarik (σt) berkisar 0,04 – 0.80 MPa. Dari hasil analisis tersebut, properti keteknikan dari klasifikasi massa batuan RMi dapat diterapkan untuk analisis kestabilan lereng menggunakan metode elemen hingga. Rekomendasi penyangga dari klasifikasi RMi cukup signifikan berpengaruh pada faktor keamanan dan perpindahan kestabilan lereng. Kata kunci: Klasifikasi massa batuan RMi, kestabilan lereng, volume blok, metode elemen hingga ABSTRACT - In this research, a rock mass classification study on rock slopes will be used, the RMi classification with the research object on rock slope locations in Cipatat, West Bandung Regency, West Java Province. The research location has a steep slope morphology with dominant lithology in the form of limestone. The RMi classification is rarely used because it has several parameters that are quite complicated to weight. To obtain weight values from rock mass classification, field observations were carried out with a scanline and intact rock samples were taken. The results of the engineering properties of the RMi rock mass classification were analyzed using the finite element method. The rock mass at the study site has dominant lithology in the form of calcarenite, calcirudite, and calcilutite limestones with low to moderate weathering levels. The rock mass weight based on the RMi classification ranges from 2.09 to 6.228 (high). The engineering properties of the rock masses from five locations have a deformation modulus (Em) ranging from 3,068 – 11,550 MPa, cohesion (c) ranging from 0,236 – 2,334 MPa, internal friction angle (ɸ) 37o – 57o, and tensile strength (σt) ranging from 0,04 – 0.80 MPa. From the results of this analysis, the engineering properties of the RMi rock mass classification can be applied to slope stability analysis using the finite element method. Support recommendations from RMi classifications have quite an effect on the safety factor and slope stability, while another recommendation to make the slope more stable is to make a cut-off slope for each slope so that the slope is more stable

ANALIZA REZULTATA NISKOFREKVENTNIH PASIVNIH SEIZMIČKIH ISTRAŽIVANJA U SVRHU KARAKTERIZACIJE PRISUTNOSTI UGLJIKOVODIKA U SUBBAZENU KENDAL

This study explores the characteristics of hydrocarbon presence in the Kendal subbasin, Central Java, using low-frequency passive seismic (LFPS) techniques as a direct hydrocarbon indicator. Waveform data were collected in 2024 using five deployed stations, including areas near oil wells, oil seeps, and non-seepage zones, to assess the presence of hydrocarbons trapped within fault-bounded anticlines. The thrust faults in the study area significantly influence the Kerek Formation, creating structural folds that serve as potential hydrocarbon traps. In analysing that potential trap system, the waveform data is processed following the time windowing and bandpass filtering to enhance signal clarity and isolate relevant seismic responses. This study identified significant Power Spectral Density (PSD) anomalies within the 1-4 Hz frequency range, which aligns with anomalies observed in Vertical-to-Horizontal Spectral Ratio (VHSR) data. The consistent occurrence of these anomalies in both PSD and VHSR data highlights the potential of LFPS as a reliable tool for detecting subsurface hydrocarbons in geologically complex regions like the Kendal subbasin. The polarity analysis was also performed, resulting in an average azimuth of 0.430 NNE, with an average dip of 0.680. These results inform us that the hydrocarbon flows from the border fault in the north to the well. This method complements the other geophysical method analysis to find new hydrocarbon opportunities.Ovaj rad obuhvaća istraživanje karakteristika prisustva ugljikovodika u subbazenu Kendal, središnja Java, na temelju tehnika niskofrekventne pasivne seizmike (engl. low-frequency passive seismic, LFPS) kao izravnih indikatora ugljikovodika. Podatci o oblicima seizmičkih valova prikupljeni su 2024. godine putem pet postavljenih stanica, uključujući područja u blizini naftnih bušotina, prirodne izdanke nafte i zone u kojima nije bilo prirodnih izdanaka nafte, kako bi se procijenila prisutnost ugljikovodika zarobljenih unutar antiklinala omeđenih rasjedima. Na području istraživanja reverzni rasjedi s blagim nagibom znatno utječu na formaciju Kerek stvarajući strukturne nabore koji su potencijalne zamke ugljikovodika. U analizi toga potencijalnog sustava zamki oblici valova obrađuju se nakon određenoga vremenskog razdoblja i filtriranja prolaska kroj proslojke kako bi se poboljšala jasnoća signala i izdvojili relevantni seizmički odgovori. Ovo istraživanje identificiralo je znatne anomalije gustoće spektralne snage (engl. power spectral density, PSD) unutar frekvencijskoga raspona od 1 do 4 Hz, što je u skladu s anomalijama uočenim u podatcima o vertikalno-horizontalnome spektralnom omjeru (engl. vertical-to-horizontal spectral ratio, VHSR). Učestala pojava ovih anomalija u PSD i VHSR podatcima naglašava potencijal LFPS-a kao pouzdanoga alata za otkrivanje prisutnosti ugljikovodika u geološki složenim regijama kao što je subbazen Kendal. Također je provedena i analiza polariteta, iz koje proizlazi da je prosječni azimut 0,430 S-SI, s prosječnim padom od 0,680. Ti rezultati upućuju na dotok ugljikovodika od graničnoga rasjeda na sjeveru do bušotine. Ovom je metodom moguće dopuniti analize koje se temelje na drugim geofizičkim metodama, kako bi se pronašla nova nalazišta ugljikovodika

KOMPARATIVNA ANALIZA I EVALUACIJA FORMULE ZA PRETVORBU BROJA ODSKOKA SCHMIDTOVA ČEKIĆA U JEDNOOSNU TLAČNU ČVRSTOĆU – STUDIJA SLUČAJA: KOSINA ANDEZITNE STIJENE NA LOKACIJI GRAHA PUSPA, RASJED LEMBANG

The Unconfined Compressive Strength (UCS) test is one of the most common methods for determining the rock material strength value. However, the size and complexity of the instrument do not allow UCS testing to be carried out in the field. The UCS value can be estimated in the field by converting the rebound number using the Schmidt hammer test. This research aims to carry out a comparative analysis and evaluation of the conversion formula for rock compressive strength values resulting from the Schmidt hammer test and UCS test in a case study of andesite rock slopes at Graha Puspa, Lembang Fault, Bandung, Indonesia. Rock hardness testing was carried out using the Schmidt hammer test on five segments at Graha Puspa. UCS testing was carried out using a compressive strength machine on four samples in Graha Puspa. The test results show a rebound number value ranging from 31.67 - 45, while the UCS test results show a value range of 134.96 – 171.60 MPa. The results of the previously published empirical equations differed considerably from the results of the UCS tests on rock samples in the laboratory when estimating the UCS values. From this evaluation, this research proposed formulation development of andesite rock formulation in the Lembang Fault area. However, UCS testing on more samples is highly recommended in order to obtain a compressive strength conversion formula that is more suitable for the case study at this location.Ispitivanje jednoosne tlačne čvrstoće (UCS) jedna je od najtočnijih metoda za određivanje čvrstoće stijenskoga materijala. Međutim, veličina i složenost instrumenta za to ispitivanje ne dopuštaju provođenje takvih testiranja na terenu. Vrijednost UCS-a može se procijeniti na temelju broja odskoka Schmidtova čekića. Cilj je ovoga istraživanja provesti komparativnu analizu i evaluaciju formule za procjenu vrijednosti jednoosne tlačne čvrstoće stijene na temelju određivanja Schmidtove tvrdoće i samoga ispitivanja UCS-a u studiji slučaja za kosine andezitnih stijena na lokaciji Graha Puspa, rasjed Lembang, u blizini grada Bandung u Indoneziji. Ispitivanje tvrdoće stijene provedeno je Schmidtovim čekićem na pet uzoraka na lokaciji Graha Puspa. Ispitivanje jednoosne tlačne čvrstoće provedeno je u laboratoriju pomoću stroja za tlačnu čvrstoću na četirima uzorcima s lokacije Graha Puspa. Rezultati ispitivanja čvrstoće stijene pokazuju vrijednost broja odskoka u rasponu od 31,67 do 45, dok rezultati ispitivanja UCS-a pokazuju raspon vrijednosti od 134,96 do 171,6 MPa. Rezultati prije objavljenih empirijskih jednadžbi znatno su odstupali u procjeni vrijednosti UCS-a u usporedbi s rezultatima ispitivanja UCS-a na uzorcima stijene u laboratoriju. Na temelju ove evaluacije predložena je formula za procjenu čvrstoće andezitne stijene u području rasjeda Lembang. Međutim, preporučuju se daljnja istraživanja koja treba usmjeriti na veći broj testiranja UCS-a kako bi se dobila relevantnija formula za procjenu u studiji slučaja na ovoj lokaciji

ANALISIS PERHITUNGAN WAKTU RUNTUH DAN DIMENSI KERUNTUHAN TEROWONGAN BAWAH TANAH BERDASARKAN PERHITUNGAN RMR DI LOKASI CIBITUNG, KABUPATEN PANDEGLANG, PROVINSI BANTEN

ABSTRAK - Pengamanan kegiatan penambangan bawah tanah dilakukan bertujuan untuk menjaga stabilitas dan keamanan lubang bukaan terowongan dari reruntuhan batuan. Pengamanan kegiatan penambangan bawah tanah diperlukan kajian rekayasa geologi teknik seperti pemetaan lapangan, perhitungan Rock Mass Rating (RMR), tinggi bukaan terowongan bawah tanah, waktu runtuh (stand-up time), serta dimensi keruntuhan (beban runtuh, tinggi runtuh, dan beban luas atap). Penelitian ini menggunakan data kondisi geologi secara umum, pemetaan lapangan, perhitungan Rock Mass Rating (RMR), waktu runtuh (stand-up time), dimensi keruntuhan (beban runtuh, tinggi runtuh, dan beban luas atap). Kondisi geologi secara umum di daerah produksi CBT_1106_RMU_NTH dan CBT_1106_RMU_STH berupa batuan porfiritik andesit dengan dominan mineral kuarsa, memiliki jenis tekstur kuarsa crusiform, terdapat beberapa kekar menerus dengan panjang 1-3 m yang terisi dengan mineral hard filling lebar 1-5 mm, kekuatan batuan termasuk medium strong, sebagian teralterasi oleh mineral silika. Nilai RMR untuk daerah CBT_1106_RMU_NTH lebih tinggi dibandingkan CBT_1106_RMU_STH karena adanya pengaruh kondisi air tanah dengan tingkat pelapukan yang berbeda. Waktu runtuh daerah CBT_1106_RMU_NTH dapat bertahan lebih lama dibandingkan CBT_1106_RMU_STH karena daerah tersebut lebih stabil. Dimensi keruntuhan CBT_1106_RMU_NTH lebih pendek dan lebih ringan dibandingkan daerah CBT_1106_RMU_STH. Penelitian ini memberikan rekomendasi tinggi bukaan efektif tanpa penguatan.Kata kunci: geologi teknik, RMR, waktu runtuh, tinggi runtuh, beban runtuh. ABSTRACT - Securing underground mining activities is done purposely to maintain the stability and safety of underground mining openings from rock debris. Securing underground mining activities requires geological engineering studies such as field mapping, calculation of Rock Mass Rating (RMR), underground tunnel height, stand-up time, and collapse dimensions (collapse load, collapse height, and roof area load). This study uses data on general geological conditions, field mapping, calculation of Rock Mass Rating (RMR), stand-up time, collapse dimensions (collapse load, collapse height, and roof area load). The general geological conditions in the CBT_1106_RMU_NTH and CBT_1106_RMU_STH production areas are porphyritic andesitic rocks with dominant quartz minerals, have a crusiform quartz texture type, there are several continuous joints with a length of 1-3 m filled with hard filling minerals 1-5 mm wide, rock strength including medium strong, partially altered by silica minerals. The RMR value for the CBT_1106_RMU_NTH area is higher than CBT_1106_RMU_STH due to the influence of groundwater conditions with different levels of weathering. The collapse time for the CBT_1106_RMU_NTH area can last longer than CBT_1106_RMU_STH because this area is more stable. The CBT_1106_RMU_NTH collapse dimension is shorter and lighter than the CBT_1106_RMU_STH region. This study provides a high recommendation of effective aperture without reinforcement.Keywords: engineering geology, RMR, stand-up time, collapse height, collapse loa

Scenario Seismic Hazard Analysis of the Mataram “Fault”: An Initial Study of Geophysical Approach

Indonesia, as a country in the Ring of Fire, has negative impacts in terms of tectonic and volcanic hazards. As an example of an area frequently hit by earthquakes, One of the area in the country frequently hit by earthquakes is the Special Region of Yogyakarta (DIY). Based on the latest studies, a new source has been discovered, which is the east-west trending “fault” called the Mataram or Tambakboyo “Fault”. This “fault” is still in the initial phase of research. This study aims to provide additional information on the Mataram “Fault” from a geophysical point of view, namely by using the gravimetric method. This method provides an understanding of the existence of a fault, namely the indication of a clear contrast difference (order of km) so that the geometry of the Mataram “fault” can be obtained. This parameter will be used in earthquake hazard modeling by using OpenQuake software. It is hoped that with this research, the geometric characteristics of the Mataram “Fault” and the earthquake hazard can be obtained

Comparison of earthquake acceleration amplification values based on the CPTu and geomorphology approach in the area around the Lembang Fault, Indonesia

The Lembang Fault is one of the sources of earthquakes in the Bandung Basin area, Indonesia. Located at coordinates -6.795075°, 107.463449° to -6.865538°, 107.737159° and has a segment length of approximately 29 km, this fault has a potential earthquake hazard that needs to be taken into account. Earthquake hazards originating from its source, namely bedrock, must be analyzed up to the surface. For this reason, a study of the amplification value needs to be carried out. To date, an easy method for analyzing amplification is using the Vs30 approach based on CPTu and geomorphology. This paper aims to obtain amplification values based on the CPTu (electric sondir) and geomorphological methods. This study obtained a 43% agreement, which was indicated by the similarity of the amplification value, which was close to 1. The geomorphology method showed a larger value (more than 1.6). This finding indicates that the equation is used as if it were in an area with a PGA value below 0.1g. Meanwhile, the average value of the two methods is considered relevant, close to 1 or the same as at the earthquake's epicenter. In the future, a more comprehensive method is needed to evaluate the geomorphology equation and the CPTu correlation to the Vs