PEMODELAN NUMERIK PENENTUAN PANJANG LAJU PENGGALIAN UNTUK TEROWONGAN JALAN

ABSTRAKPanjang laju penggalian terowongan jalan harus direncanakan dengan mempertimbangkan perilaku batuan, bentuk penampang dan tahapan penggalian yang dilakukan. Pendekatan empiris berdasarkan kategori massa batuan umumnya digunakan untuk menentukan panjang laju penggalian. Untuk mengetahui efektivitas dan kesesuaian pendekatan empiris ini, maka dilakukan pemodelan numeric 3 dimensi dengan metode elemen hingga. Dua kategori massa batuan yaitu kelas massa batuan dari Bieniawski (1989) dan klasifikasi dari Jepang (JSCE, 2007) dibandingkan untuk mendapatkan parameter desain yang akan dimodelkan. Terowongan jalan dua lajur dengan diameter 10 m yang melewati jenis batuan dengan kategori V (sangat jelek) digunakan dievaluasi dalam pemodelan. Bentuk penampang penggalian terowongan yang dimodelkan terdiri 3 (tiga) model, yaitu: penggalian muka bidang galian dengan bench tambahan, bench kecil dan bench ganda. Pemodelan dilakukan untuk mengetahui dua kondisi, yaitu kondisi mendekati kondisi keruntuhan (krisis), yaitu FK ≈ 1,dan kondisi diatas FK minimum yang disyaratkan (FK≥1,8). Hasil analisis menunjukkan bahwa metode penggalian bench ganda dengan panjang laju penggalian maksimum 1,00 m memenuhi kriteria faktor keamanan minimum yang disyaratkan. Hal ini juga menunjukkan kriteria panjang laju pengendalian berdasarkan JSCE (2007) lebih mendekati dibandingkan dengan Bieniawski (1989) yang mensyaratkan laju penggalian 1,5 m.Kata kunci :  laju penggalian, terowongan jalan, metode elemen hingga, model 3D, penampang penggalian

Evaluation of Lateral and Axial Deformation for Earth Pressure Balance (EPB) Tunnel Construction Using 3 Dimension Finite Element Method

Mass Rapid Transit Jakarta (MRTJ) phase 1 tunnel construction using the earth pressure balance method has been completed and surface settlement and lateral displacement data according to elevation and inclinometer readings has been collected to evaluate the effect of tunnel’s construction on surrounding infrastructure. Soil stratification along the research area, defined according to boring logs and soil parameters for the hardening soil model (HSM) and the soft soil model (SSM), was determined by optimization of stress-strain curve fitting between CU triaxial test, consolidation test and soil test models in the Plaxis 3D software. Evaluation of the result of surface settlement measurements using an automatic digital level combined with geodetic GPS for elevation and position control points showed that the displacement behavior was affected by vehicle load and stiffness of the pavement. Lateral displacement measurements using inclinometers give a more accurate result since they are placed on the soil and external influences are smaller than surface settlement measurement. The result of 3D finite element modeling showed that surface settlement and lateral displacement during TBM construction can be predicted using HSM with 2% contraction. SSM and the closed-form solutions of Loganathan and Poulos are unable to provide a good result compared to the actual displacement from measurements

EVALUASI NUMERIK METODE PENGGALIAN TEROWONGAN CISUMDAWU

This paper presents results of research works carried out to evaluate the excavation method of the left (west) side of the Cisumdawu Tunnel by a numerical method. Using data obtained from site investigation during design process and face mapping at eight observation points, tunnel excavations by bench cut (multiple), full face with bench cut, and centre diaphragm methods were numerically modelled in two dimension using a finite element method. The numerical modelling results were compared with field measurement results to determine the most suitable excavation method applied in Cisumdawu Tunnel. Results of this research showed that roof displacements induced by the bench cut (multiple) excavation method obtained in the numerical modelling was close to that obtained in the field measurement. The bench cut (multiple) excavation method applied in the field induced lower roof displacement value than the full face with bench cut and centre diaphragm methods. However, the three excavation methods induced roof displacements lower than a 10 cm maximum displacement specified in the JSCE (2007) and roof strength factor > 1.25, indicating stable tunnel condition.Makalah ini menampilkan hasil penelitian yang dilakukan untuk mengevaluasi metode penggalian Terowongan Cisumdawu sisi kiri (barat) menggunakan metode numerik. Menggunakan data hasil penyelidikan tapak dalam proses perancangan dan data hasil face mapping di delapan stasiun titik amat, penggalian terowongan dengan metode bench cut (multiple), full face with bench cut dan centre diaphragm dimodelkan secara numerik dalam dua dimensi menggunakan metode elemen hingga. Hasil pemodelan numerik dibandingkan dengan hasil pengukuran lapangan untuk menentukan metode penggalian yang paling sesuai diterapkan di Terowongan Cisumdawu. Hasil penelitian menunjukkan roof displacement terowongan dengan metode penggalian bench cut (multiple) yang diperoleh dalam pemodelan numerik mendekati roof displacement pada pengukuran lapangan. Metode penggalian bench cut (multiple) yang diterapkan di lapangan menghasilkan nilai roof displacement lebih rendah dibandingkan metode full face with bench cut dan centre diaphragm. Namun demikian, ketiga metode penggalian tersebut masih memenuhi batasan nilai displacement maksimum 10 cm yang ditentukan dalam JSCE (2007) dan menghasilkan nilai roof strength factor > 1,25 yang menunjukkan terowongan  dalam kondisi stabil

Evaluation of Face Support Pressure Prediction for Earth Pressure Balance (EPB) Tunnelling using Analytical and 3-Dimensional Finite Element Modelling

A shield tunnelling technique is usually selected using earth pressure balance or slurry methods for tunnel construction in urban areas with soft and saturated ground. Although shield tunnelling has many advantages, incorrect determination of face pressure could cause ground surface settlement or lifting during tunnel construction. Numerous approaches for determining face support pressure have been published internationally, but a suitability evaluation based on local ground conditions in Indonesia has not been conducted yet. The completion of Mass Rapid Transit Jakarta (MRTJ) tunnel construction project using the earth pressure balance method, along with its adequate data, has become a sample case of the effectiveness of each method to determine face support pressure. The study discussed in this paper aimed to determine the linear relationship between the calculated value and the actual measurement of face support pressure and to identify which method most closely represents the actual condition according to the MRTJ case study. An analytical approach using the limit equilibrium method and the numerical approach using Plaxis 3D were conducted, followed by statistical evaluation in the terms of coefficient of variation. The result shows that the limit equilibrium method is effective in predicting the mean value face support pressure and the upper and lower perimeters for tunnel construction, while the overall face support pressure result using the shell model of the finite element method are lower than the actual measured values. The result probably indicates the balance state condition at the tunnel face, and the additional 80 kPa after the second phase of excavation could indicate the need for greater pressure for tunnel boring machine movement

EVALUASI PETA PERCEPATAN GEMPA SUMATERA (SNI-1726-2002) TERHADAP PETA PERCEPATAN GEMPA MENGGUNAKAN SOFTWARE PSHA

Evaluation on seismic hazard map in Sumatra bedrock was needed because the Indonesian seismic hazard map standard (SNI-1726-2002) was built using the 2D seismic source model and a lot of seismic activity around Sumatera occurred after the 8N1-1 7 26-2002 was published. Probabilistic Seismic Hazard (PSHA) software was developed by USGS in 2007 to gain bedrock acceleration value derivedf rom Probabilistic calculation on 3D seismic source using the Next Generation Attenuation (NGA). Therefore this software represented the newest theory to build seismic hazard map and it was used in this research to evaluate and validate the Indonesian standard, particularly Sumatra seismic hazard map. Several phases were done to gain the seismic hazard map, such as collecting and processing earthquake data, calculating seismic risk parameter, acceleration calculation using PSHA software and developing a seismic hazard map using ArcGis Software. Evaluation result indicated that SNI-1726-2002 seismic hazard map in Sumatera bedrock, particularly in region 3,4 and 5 was lower than seismic hazard map developed using PSHA software. The deviation was range between ± 0.05-0.20g.  

ANALISIS RESIKO GEMPA DI BATUAN DASAR

Peta percepatan gempa maksimum di batuan dasar Indonesia merupakan salah satu bagian dari Standar Nasional Indonesia tentang Perencanaan Ketahanan Gempa untuk Rumah dan Gedung yang menggambarkan tingkat resiko kegempaan untuk wilayah Indonesia yang digunakan sebagai dasar perhitungan beban gempa pada struktur. Dengan banyaknya kejadian gempa-gempa besar dalam beberapa tahun terakhir ini yang tentu sangat mempengaruhi tingkat resiko kegempaan Indonesia. Untuk itu, dilakukan pembuatan peta percepatan gempa di Sumatera, Jawa-Sumba dan Kalimantan sebagai bagian dari analisa resiko gempa untuk seluruh Indonesia berdasarkan data-data terbaru dengan menggunakan permodelan sumber gempa 3D dan bantuan piranti lunak PSHA-07-USGS. Berdasarkan hasil analisis yang mengacu pada Unified Building Code 97 yaitu untuk periode ulang 475 tahun diperoleh rentang PGA maksimum untuk Sumatera yaitu 0.02-0.85g. Jawa-Sumba yaitu 0.02-0.65g dan Kalimantan yaitu 0.005-0.2g. Keseluruhan hasil menunjukkan nilai yang lebih besar dibandingka peta percepatan gempa yang terdapat di Standar Nasional Indonesia tentang Perencanaan Ketahanan Gempa untuk Rumah dan Gedung. Hasil penelitian menunjukkan nilai yang cukup komparatif hanya di wilayah Sumatera dengan penelitian-penelitian lain yang belum lama ini dipublikasikan. Beberapa faktor yang sangat mempengaruhi hasil perhitungan antara lain : data gempa, permodelan sumber gempa dan pemilihan fungsi atenuasi.   Kata kunci : Analisis resiko gempa, peta percepatan gempa, batuan dasar, permodelan sumber gempa 3D, pemilihan fungsi atenuasi, sumber gempa Seismic hazard map in Indonesian bedrock was part of the Indonesian standart descrebing seisic hazard for Indonesia territory and used as one of significant load in structure design. Recent earthquake with big intensity surely can effect the seismic hazard in Indonesia. Therefore, seismic hazard map in Sumatera, Java-Sumba and Kalimantan was developed as part of seismic hazard analysis in Indonesia using the latest data, 3D seismic source model and PSHA-07-USGS software and publicized in this paper. The seismic hazard analysis was refer to Unified Building Code 97 and represnt the 475 year return period seismic hazard map in Sumatera, Java-Sumba and Kalimantan. The result showed that maximum PGA for Sumatera ranges between 0.02-0.65g, Java-Sumba 0.02-0.65g and Kalimantan 0.005-0.2g. All result showed a larger value than seismic hazard map in the than Indonesian Standard (SNI 03-1726-2002). Comparison with the other studies showed a comparative result only in Sumatera, while in Java-Suma and Kalimantan shown a disagree result. Some factors can affect the result, such as seismic data, seismic source model and attenuation function selection.   Keyword : Seismic hazard analysis, seismic hazard map, bedrock, 3D seismic source model, attenuation function selection, seismic dat

Assessment on earthquake resistance spectral design load criteria for buildings and infrastructures in Indonesia

General assessment on earthquake resistance spectral design load criteria for buildings and infrastructures associated with the recent development of Indonesian seismic hazard maps is presented in this paper. The assessment is directed toward general identification of their associated risks for input to policy formulation of disaster risk reduction management plans or strategies. Indonesian seismic hazard maps haveevolved for the last three decades. This is originated from an early development map before 2002, where a seismic hazard map particularly for buildings (1983) was developed adopting the early process of probabilisticseismic hazard analysis (PSHA) for 200 years return period (RP). Further, a 2002 version seismic hazard maphas been developed in the form of peak ground acceleration (PGA) for 500 years RP. Spectral design criteriafor buildings and bridges have been later developed by updating PSHA involving new seismic source zones, ground-motion predictive equations, and various earthquake RP, accommodating seismic codes for buildings(2500 years RP), for bridges (1000 years RP) and dams involving various RP up to 10,000 years RP correspond to its design level. The spectral accelerations also have included PGA, short (0.2s) period, and 1-s period. The latest update hazard maps (2017) have been developed and adopted for seismic codes for buildings, bridges, dams, and other related infrastructures. The increase in spectral design load criteria is identified to assess the general risk of existing constructions, considering the results of several recent building damage surveys. Adoption of new seismic codes based on the most recent hazard maps along with its enforcement is expected to contribute to seismic disaster risk reduction in Indonesia

ANALYSIS AND EVALUATION OF PEAK GROUND ACCELERATION AMPLIFICATION FACTOR ON GROUND SURFACE

Perencanaan infrastruktur tahan gempa, umumnya memerlukan data percepatan di permukaan tanah. Saat ini American Society of Civil Engineers (ASCE) 07-2010 memberikan faktor amplifikasi untuk kebutuhan perencanaan bangunan tahan gempa sehingga perencana bisa mendapatkan percepatan dipermukaan dengan mengalikan nilai percepatan Peta Gempa Indonesia 2010 dengan faktor amplifikasi tersebut. Untuk mengetahui kesesuaian faktor amplifikasi tersebut terhadap analisis seismic hazard menggunakan piranti luak PSHA-07-USGS maka dilakukan kajian dengan analisis grid di Sumatera menggunakan variasi kecepatan gelombang geser (VS) yang mewakili Klasifikasi jenis tanah ASCE 07-10 untuk tanah sangat padat dan batuan luak (SC), tanah sedang (SD) dan tanah lunak (SE). Perbandingan faktor amplifikasi antara hasil analisis dan ASCE 07-2010 terhadap 2 (dua) tinjauan periode (PGA dan 0.2 detik) menunjukkan bahwa utuk site SC  dan SD, hasil analisis menunjukkan hasil yang cukup mendekati ASCE 07-2010. Untuk site SE dan periode T = 1 detik, untuk permodelan dengan VS30 < 175m/detik diperoleh deviasi yang cukup besar antara analisis dan ASCE 07-2010. Hal ini kemungkinkan disebabkan oleh keterbatasan permodelan, yaitu hanya dapat menggunakan persamaan atenuasi tertentu yang hanya mewakili sumber gempa sesar. Untuk mendapatkan faktor amplifikasi yang baik disarankanuntuk melakukan analisis respon dinamik spesifik berdasarkan kondisi tanah lokal yang sesuai dengan klasifikasi ASCE 07-2010.   Kata kunci : Analisis seismic hazard, faktor amplifikasi, percepatan puncak di permukaan, respon spektra di permukaan.Earthquake resistant infrastructure planning, generally require the acceleration data at ground level. Currently, the American Society of Civil (ASCE) 07-2010 provides amplification factor for earthquake resistant building design needs so that planners can get the acceleration of the surface by multiplying the value of the accelaration of Infonsesian Earthquake Maps 2010 with the amplification factor. To evaluate the amplification facttor with the seismic hazard analysis using software USGS PSHA-07, evaluation using grid analysis in Sumatra was done using variations of shear wave velocity(VS) which represents the ASCE 07-10 sites classification for very dense soil and soft rock (SC), the soil medium (SD) and soft soil (SE). According to the amplification factor comparison between analysis result and the ASCE 07-2010 at two reviewed period (PGA and 0.2 sec), the SC and SD  site result show a close amplification factor to ASCE 07-2010. While large deviation occur between analysis and ASCE 07-2010 at SE  site and period T = 1sec with VS30 < 175m/sec. The large deviation probably caused by modeling limitation which only can used specified attenuation function that represent fault zone only. To gain the good quality amplification factor, it is advice to do specific dynamic reponse analysis using local soil condition according to ASCE-07-2010 classification.   Keyword : Seismic hazard analysis, amplification factor, peak surface acceleration, surface spectrum response