Identification Of Liquefaction Hazard In The Coastal Area Of Merak-Anyer, Banten Based On Cpt And Spt Data

The coastal area of Merak-Anyer, Banten is located in the high seismic zone therefore it is highly susceptible to seismic hazard such as liquefaction. Earthquake triggered liquefaction could cause destructions to buildings and infrastructures, thus it can hinder evacuation efforts during an earthquake event.   Knowledge of the spatial distribution of liquefaction hazard potential in the coastal area is required as part of the hazard mitigation measures. This paper presents the results of the liquefaction hazard susceptibility analysis in Merak-Anyer, Banten based on geotechnical investigation. Liquefaction analysis was carried out using cone penetration test (CPT) and N-SPT methods with earthquake magnitude of 7, peak ground acceleration of 0.25 g and local groundwater level.  Analysis results showed that all investigation points in the coastal area of Merak-Anyer are prone to liquefaction and its associated settlement. The high liquefaction zone includes the areas of Rencana Pelabuhan Cilegon, Cigading, Mercu Suar dan Cinangka which correlates with the occurrence of loose sand – loose silt at the surface to the depth of 10 m with cone resistance (qc) < 10 MPa  and N-SPT <10

GEOLOGI TEKNIK SEDIMEN KUARTER DAN BAHAYA AMBLESAN, LIKUIFAKSI DI SERANGAN – TUBAN – TANJUNG BENOA, BALI

Wilayah pesisir pada cekungan sedimen Kuarter di daerah Serangan – Tuban – Tanjung Benoa, Bali Selatan sebagai kawasan pengembangan tataruang dan infrastruktur perlu mendapat perhatian terkait dengan kondisi geologi teknik bawah permukaan dan ancaman bahaya geologinya. Tulisan ini bertujuan untuk mengetahui karakteristik geologi teknik sedimen bawah permukaan berkaitan dengan ancaman bahaya amblesan dan likuifaksi. Metode penelitian meliputi pemboran teknik, pengujian penetrasi konus, pengujian laboratorium geoteknik dan analisis geologi teknik.  Hasil penelitian menunjukkan ketebalan sedimen Kuarter mencapai kurang lebih 20 meter, terdiri dari tanah penutup, lempung, lanau – lempung, perselingan lanau - pasir lempungan, sisipan kerikil, pasir kasar dan batugamping sebagai batuan dasar. Keberadaan lapisan lempung sangat lunak hingga lunak, plastitas tinggi, kuat geser rendah, dicirikan nilai tahanan konus qt  < 2 MPa dan nilai  N-SPT  < 2  pada kedalaman –0,5 hingga –20 meter tersebar di Serangan – Tuban, mengindikasikan ancaman bahaya amblesan. Sedangkan keberadaan lapisan lanau – pasir sangat lepas-lepas, dicirikan nilai tahanan konus qt  < 5 MPa dan nilai  N-SPT  < 10 di permukaan hingga kedalaman -15 m  tersebar di daerah Kedonganan – Tanjung Benoa – Serangan, mengindikasikan kerentanan terhadap likuifaksi akibat gempabumi.  Gambaran sifat keteknikan secara vertikal dan spasial dapat memberikan informasi untuk perencanaan dan pencegahan risiko ancaman amblesan dan likuifaksi pada sedimen cekungan Kuarter Bali Selatan.The rapid development in the coastal area on the Quaternary sedimentary basin of Serangan - Tuban - Tanjung Benoa, South Bali requires attention regarding its subsurface engineering geology and associated geological hazard. This paper presents the characteristics of subsurface sediment from engineering geology related to the potential hazards of subsidence and liquefaction. The utilized methods included geotechnical boring, cone penetration test, geotechnical laboratory tests and engineering geology analysis.  Results showed that the thickness of Quarternary sediment reaches 20 m, consisting of top soil, clay, clayey - silt, intercalation of silt and clayey sand, gravel, coarse sand and limestone as the baserock.  The occurrence of very soft to soft clay, highly plastic with low shear strength at the depth of -0.5 to -10 m, characterized by cone resistance qt< 2 MPa and N-SPT value < 2 is distributed in Serangan – Tuban and indicated to be subsidence prone. Meanwhile the very loose to loose silt-clay of cone resistance qt < 5 MPa and  N-SPT value <10 is distributed in Kedongan – Tanjung Benoa - Serangan, and indicated to be susceptible to earthquake induced liquefaction. The spatial and vertical engineering profiles of the subsurface geology provide valueable information for planning and mitigation of subsidence and liquefaction hazards in the sediment from Quaternary basin of South Bali. 

PREGLED HAZARDA PROUZROČENOGA SLIJEGANJEM POVRŠINE U DELTI PEKALONGAN, SREDIŠNJA JAVA: UVID IZ PODZEMLJA

Land subsidence is a global threat to coastal areas worldwide, including the North Java coastal area. Of many areas experiencing land subsidence in North Java, the rate of land subsidence in Pekalongan has matched the high subsidence rates usually found in big cities. The rate of land subsidence in Pekalongan far exceeds the sea-level rise, resulting in a looming threat of land loss. The devastating impacts of land subsidence are the manifestation of its subsurface movement. Therefore, it is essential to understand the subsurface to elucidate the mechanism of land subsidence. Previous studies on land subsidence in Pekalongan are mainly related to subsidence rate monitoring and have not elaborated on the subsurface condition. This paper reviews the Pekalongan subsurface geology based on available literature to provide insight into the land subsidence problem. The results revealed that the land subsidence occurs in the recent alluvial plain of Pekalongan, consisting of a 30-70 m thick compressible deposit. Possible mechanisms of land subsidence arise from natural compaction, over-exploitation of confined groundwater, and increased built areas. As the seismicity of the study area is low, tectonic influence on land subsidence is considered negligible. It is expected that the offshore, nearshore, and swamp deposits are still naturally compacting. As the surface water supply is minimal, over-exploitation of groundwater resources from the deltaic and Damar Formation aquifers occurs. In the end, future research direction is proposed to reduce the impacts of the subsidence hazard.Slijeganje površine tla prijetnja je svim obalnim područjima, pa tako i obali sjeverne Jave. Niz područja u tome prostoru podložno je takvu slijeganju. Iznos toga spuštanja posebno je izražen u velikim gradovima područja Pekalongan. Taj iznos daleko nadilazi porast morske razine rezultirajući gubitkom kopna. Vrlo velik učinak takvih površinskih spuštanja odražava se također i u dubini. Zato je nužno razumjeti ispodpovršinske pojave kako bi se objasnilo samo spuštanje površine. Prethodna istraživanja tih pojava u Pekalonganu uglavnom su bila usmjerena na praćenje iznosa spuštanja, bez uvida u dubinske odnose. Ovdje je prikazana dubinska geologija istraživanoga područja, pregledom dostupne literature. Rezultati su pokazali kako se spuštanje događa u recentnoj aluvijalnoj ravnici Pekalongana, koja obuhvaća tlo debljine 30 – 70 m. Jedan od mogućih uzroka spuštanja jest prirodno zbijanje, zatim pretjerana eksploatacija podzemnih voda te prevelika izgrađenost. Seizmičnost je prostora mala, stoga je i utjecaj tektonike na taj proces zanemariv. Nadalje, morski, priobalni i močvarni talozi podložni su recentnom, prirodnom zbijanju. Kako je pritok svježe, meteorske vode minimalan, dolazi do pretjerane eksploatacije vodonosnika formacije Damar u delti. Predložena su buduća tematska istraživanja kojima bi se smanjio utjecaj opasnosti proizišlih iz slijeganja

PENGARUH LEMPUNG EKSPANSIF TERHADAP POTENSI AMBLESAN TANAH DI DAERAH SEMARANG

ABSTRAK Kota Semarang mengalami amblesan tanah yang intensif setiap tahunnya. Salah satunya penyebab adalah pengaruh faktor kompaksi/konsolidasi batuan di bawah permukaan yang diduga mempunyai keterkaitan dengan keberadaan lapisan lempung. Karakteristik keteknikan batuan erat kaitannya dengan sifat penyusun batuannya, diantaranya adalah sifat ekspansifitas yang sangat dipengaruhi oleh kandungan mineral lempung. Jenis mineral lempung montmorilonit mempunyai daya kembang susut terbesar sehingga kehadirannya merupakan faktor utama yang menentukan sifat ekspansif. Tulisan ini membahas mengenai karakteristik lempung di daerah Semarang terutama mengenai sifat ekspansif lempung melalui pendekatan mineralogi berdasarkan hasil analisis XRD dan SEM-EDX serta pengaruhnya terhadap potensi amblesan tanah. Hasil penelitian menunjukkan bahwa batuan umumnya tersusun atas mineral lempung berupa montmorilonit, illit dan kaolinit/klorit, selain itu juga mengandung fraksi mineral non lempung. Hasil korelasi dengan data lapangan menunjukkan bahwa lempung yang berada relatif di dekat permukaan umumnya mempunyai sifat ekspansif rendah – sedang, sedangkan lapisan lempung yang lebih dalam mempunyai sifat ekspansif sedang – tinggi. Lempung bawah permukaan di daerah Semarang menunjukkan sifat ekspansif yang rendah di bagian barat dengan kecenderungan peningkatan sifat ekspansif semakin ke arah timur. Keberadaan lapisan lempung tersebut diindikasikan mempercepat proses konsolidasi endapan Holosen di bagian timur dan utara Semarang yang memperbesar potensi amblesan tanah

POTENSI LIKUIFAKSI AKIBAT GEMPABUMI BERDASARKAN DATA CPT DAN N-SPT DI DAERAH PATALAN BANTUL, YOGYAKARTA

ABSTRAK Gempabumi dapat menimbulkan bahaya likuifaksi yang dapat merusakkan bangunan dan sarana infrastruktur khususnya di wilayah perkotaan di Indonesia. Investigasi  geoteknik bawah permukaan telah dilakukan di daerah Patalan, Bantul, Yogyakarta, untuk mendapatkan gambaran susunan lapisan tanah dan kekuatannya, menentukan kedalaman dan ketebalan lapisan tanah yang berpotensi likuifaksi dan penurunan lapisan tanah akibat likuifaksi. Analisis potensi likuifaksi dilakukan menggunakan data CPT (cone penetration test) dan N-SPT (standard penetration test), dengan mempertimbangkan nilai percepatan getaran tanah maksimum (p.g.a) sebesar 0,25g, magnitudo gempabumi sebesar 6,2 SR dan muka airtanah setempat. Hasil penyelidikan menunjukkan bahwa lapisan tanah lepas selama gempabumi terdiri dari pasir lanauan dan lanau pasiran pada kedalaman antara 0,2  - 12,8 m. Analisis potensi likuifaksi mengindikasikan bahwa ketebalan lapisan tanah yang berpotensi terlikuifaksi bervariasi antara 0,2 m dan 5,2 m, Sedangkan penurunan total lapisan tanah terutama terkonsentrasi di wilayah bagian tengah yang terletak di jalur Patahan Opak dengan besaran antara 0,21 cm hingga 12,98 cm Zona likuifaksi dan penurunan ini berada pada lapisan sedimen bagian atas yang mengisi pada cekungan Bantul di sekitar Patahan Opak

Microzonation of Soil Amplification Based on Microtremor, Spt and Cptu Data in Bandung Basin

Bandung Basin consists of Sunda-Tangkuban Perahu volcanic deposit that is made of lake sediment and an alluvial fan with fine to coarse-grained materials such as clay, silt and sand. The area is surrounded by several earthquake sources such as the Lembang, Cimandiri, and Baribis Faults. Therefore, it is important to understand soil dynamic problems with respect to seismic sources and soil properties. This research aims to investigate velocity amplification of the Bandung Basin using microtremor measurements and site classification based on the Standard Penetration Test (SPT) and Cone Penetrometer Test (CPTu). Velocity amplification was analyzed using the horizonal to vertical H/V spectral ratio, and site classification was determined using and  values. Microzonation maps were developed using Geographical Information System (GIS) to determine the correlation between soil velocity amplification and site class. The results revealed that velocity amplification levels in the Bandung Basin vary with a range of 1.3 to 26.5. Site classification ranges from very dense soil and hard rock (class C), stiff soil (class D) to soft clay soil (class E). Site class E dominates the southeast part of the Bandung Basin with a high value of soil amplification. This scientific information is critical for further spatial planning focusing on infrastructure and residential building. Cekungan Bandung berasal dari endapan vulkanik Sunda-Tangkuban Perahu yang terdiri dari sedimen danau dan kipas aluvial dengan material berbutir halus hingga kasar seperti lempung, lanau, dan pasir. Daerah ini juga dikelilingi oleh beberapa sumber gempa yakni sesar Lembang, Cimandiri, dan Baribis. Oleh karena itu masalah dinamika tanah yang dipengaruhi oleh sumber seismik dan sifat tanah perlu menjadi perhatian. Tujuan penelitian ini adalah untuk mengetahui amplifikasi kecepatan tanah di wilayah cekungan Bandung dengan menggunakan alat mikrotremor dan metode site classification berdasarkan uji SPT dan CPTu. Amplifikasi kecepatan dianalisis menggunakan perbandingan rasio spektral H/V dan site classification yang diperoleh dengan menggunakan nilai  dan . Peta mikrozonasi disusun menggunakan teknik Sistem Informasi Geografis (SIG) untuk menentukan korelasi amplifikasi tanah dan site class tanah. Hasil penelitian menunjukkan bahwa tingkat amplifikasi kecepatan di Cekungan Bandung bervariasi, berkisar 1,3 hingga 26,5. Site classification berkisar dari tanah yang sangat padat dan batuan keras (kelas C), tanah kaku (kelas D) hingga tanah lempung lunak (kelas E). Hasil penelitian menunjukkan site class E mendominasi bagian selatan Cekungan Bandung dengan nilai amplifikasi tanah yang tinggi. Informasi ilmiah ini diperlukan untuk perencanaan tata ruang kedepannya, dengan fokus pada infrastruktur dan bangunan tempat tinggal

KERENTANAN LIKUIFAKSI WILAYAH KOTA BANDA ACEH BERDASARKAN METODE UJI PENETRASI KONUS

Pengetahuan mengenai kerentanan likuifaksi di suatu wilayah kota pesisir yang rawan gempabumi besar sangat diperlukan dalam perencanaan tataruang untuk mengurangi bencana seismik. Makalah ini menyajikan hasil evaluasi potensi likuifaksi di wilayah Kota Banda Aceh berdasarkan metode uji penetrasi konus untuk menghasilkan mikrozonasi kerentanan penurunan lapisan tanah akibat likuifaksi di wilayah ini. Hasil analisis menunjukkan bahwa potensi likuifaksi terdapat pada lapisan tanah pasir dan campuran pasir dan lanau, yang dicirikan oleh nilai tahanan konus dan hambatan setempat masing-masing lebih kecil dari 15 MPa dan 150 kPa pada kedalaman dan ketebalan yang bervariasi. Berdasarkan hasil perhitungan penurunan tanah, wilayah Banda Aceh dapat dibagi menjadi lima zona kerentanan. Zona kerentanan tinggi terutama terdapat di Kecamatan Kuta Alam dan Syah Kuala, sedangkan zona kerentanan rendah terutama terdapat di wilayah Kecamatan Banda Raya. Dengan demikian, investigasi geoteknik detil sangat diperlukan untuk mencegah kerusakan pada bangunan dan infrastruktur akibat likuifaksi di wilayah Kota Banda Aceh. Knowledge of liquefaction susceptibility is very important for spatial planning of a coastal city prone to big earthquakes. This paper presents the results of liquefaction potential evaluation based on cone penetration test to produce a microzonation map of liquefaction-induced ground settlement for Banda Aceh City. Results of the analysis show that liquefaction would occur in layers of loose to medium sand and silt-sand mixtures with the values of tip resistance and sleeve friction of less than 15 MPa and 150 kPa, respectively, at various depths. On the basis of ground settlement calculation, the city can generally be divided into five zones. High susceptible zone to ground settlement is mainly concentrated within the Kuta Alam and Syah Kuala Sub-District. Meanwhile, the zone of low susceptibility is within the Banda Raya Sub-District. Thus, detailed geotechnical investigation is necessary to mitigate liquefaction damage on buildings and infrastructures in Banda Aceh City

Rock slope stability monitoring system in the Batu Mountain area, Lembang, West Bandung

Gunung Batu is placed in Lembang, Langensari, West Bandung right of Lembang Fault line. Lembang Fault is an active fault with a slip rate between 1.95 – 3.45 mm/year and is expected to initiate an earthquake of Mw 6.5 – 7. Earthquakes in the Lembang Fault zone occurred in the 15th and 60th centuries BC, with an earthquake cycle every 170 – 670 years. From this, earthquake cycle estimates indicate that the Lembang Fault is in the final stage of the earthquake cycle. Gunung Batu is a populous area and has grown as a recreational area. Gunung Batu has a complex geological structure with potential rock slides. The observation and kinematic analysis results of the Gunung Batu area suggested that this area partly has an unstable slope and potentially has wedge and toppling failure. This condition of instability requires further monitoring to minimize damage and losses to populations around the Gunung Batu area. The development of slope stability monitoring tools has progressed significantly recently. Selecting the proper monitoring tool is the main component of data input to prevent possible hazards. The monitoring elements include rainfall, slope movement, and tilt movement. Sensor types that will be used in this monitoring system are integrated wireless monitoring systems. This system was developed to monitor the activity of the slopes of Gunung Batu, Lembang, West Bandung. The monitoring results for the last six months show the system is running well without errors

Liquefaction due to the 2006 Yogyakarta Earthquake: Field Occurrence and Geotechnical Analysis

AbstractThe event of earthquake may induce the occurrence of liquefaction hazard. Liquefaction could cause damage to buildings and infrastructure due to the sudden increase of pore pressure at the loose uncompacted layers causing the loss of support or bearing capacity. The Yogyakarta earthquake on May 27, 2006 of magnitude 6.2 had resulted in liquefaction phenomenon to occur in several affected areas. During this earthquake liquefaction occurrences were observed near the Opak Fault area. Mapping of liquefaction along with geotechnical investigation and analysis had been carried out in Bantul region, Yogyakarta. Geotechnic al investigation consisted of a series of cone penetration tests and drillings was carried out in Patalan region, Bantul, Yogyakarta. Analysis of liquefaction potential was conducted by analyzing CPT data by Robertson and Wride (1989) method. Analysis results revealed that the loose layer consists of silty sand and sandy silt at the depth between 0.2- 12.8 m are potentially liquefied during the earthquake. Results of liquefaction analysis indicated that the thickness of potentially liquefied soil layer vari es between 0.2 -5.2 m and total settlement induced by the liquefaction is varied from 1.0 - 10.8cm concentrated at the middle part of Opak Fault. Geotechnical analysis suggested that the liquefaction had occurred within the upper Quaternary sediment fillin g the Bantulgraben

Abdullatif Harputi`nin Tarih-i İlm-i Kelam adlı eseri ve kelam ilmi açısından analizi / The Work the history of the theology of Abdullatif Harputi and the analysis of it from the perspective of the theology

ABSTRACT The September 30, 2009 Padang earthquake has resulted in damages to infrastructures and buildings and a death toll of 383 in Padang City. Numerous liquefaction and ground deformations caused by the earthquake were particularly evidence in the areas few kilometers from the coast. The paper presents results of the previous field geotechnical investigations of liquefaction potential and the recent liquefaction observations in Padang City. A microzonation map was created using the data from liquefaction potential analyses and liquefaction potential indexes. The predicted liquefaction susceptibility zones showed a good agreement with site observations. The assessment suggests that the liquefaction susceptibility decreases to the northeast away from the coastal line