Strength and Deformation Characteristics of Reconstituted Sand under Different Stress Paths in True Triaxial Tests

To improve the geotechnical stress"“strain analysis, the stress"“strain behavior of geomaterial under general three-dimensional stress conditions prevailing in the field need to be captured. The true triaxial apparatus is an enhanced version of the conventional triaxial apparatus, which allows to simulate stresses by applying loadings independently in 3 orthogonal directions. This study evaluated the strength and deformation behavior of Bangka sand under true triaxial test conditions. The test specimens were prepared by means of the multi-sieve sand pluviation method. Various true triaxial test stress paths were applied under axial compression, lateral extension, axial extension, and lateral compression with the objective of understanding and developing the empirical correlation of coarse-grained soil strength parameters in axial compression stress paths related to other stress paths. The test results showed that an increase in the value of b, the parameter used to quantify the relative magnitude of the intermediate principal stress to the other principal stresses, resulted in an increase of the internal friction angle and a decrease of the peak stress ratio. In addition it was observed that the Lade-Duncan failure criterion fitted the results of this study better than other failure criteria, namely the extended von Mises, Mohr-Coulomb, and Matsuoka-Nakai failure criteria

Excavation Analysis using Stress Path Dependent Soil Parameters

This paper presents numerical analyses of an excavation using stress path dependent soil parameters, where soil elements in a region of an excavation are represented by specific soil parameters that correspond to their specific stress paths. The performance of the M1 excavation pit in Berlin sand was selected as the analysed case. This excavation pit was supported by diaphragm-wall with a single row of pre-stressed anchors. The numerical analyses of the excavation were performed using finite element program PLAXIS 3D. Mohr-Coulomb model and Hardening Soil model were used as the soil constitutive models. The analyses were performed using two approaches, which are: (i) analysis using axial compression soil parameters, and (ii) analysis using stress path dependent soil parameters. A set of conversion ratios were employed to convert the general soil parameters (i.e. axial compression stress path) to the soil parameters of the other stress paths. These conversion ratios were obtained from an experimental program of true triaxial tests conducted on Bangka sand. The comparison of the field records and the analysis results were discussed. The results show that the stress path dependent approach produced better prediction of diaphragm-wall deformation compare to the general approach using axial compression soil parameters

Axial and Lateral Small Strain Measurement of Soils in Compression Test using Local Deformation Transducer

This paper presents the development of a method using local deformation transducers (LDTs) to locally and sensitively measure small axial and lateral strains in soil in a compression test. A local strain measurement system comprising of axial and lateral LDTs was developed referring to the original LDT system and the cantilever LDT system, respectively. The LDTs were calibrated both in air and under water. Their insensitivity to pressurized water was confirmed. The calibration factors for the axial and lateral LDTs were found to be 1.695 mm/volt and 1.001 mm/volt, respectively. The performance in terms of repeatability and stability of the LDT system was evaluated. The repeatability test showed that the average standard deviation of the lateral LDT was 0.015 volt, while the stability test showed that the average standard error of the axial and lateral LDT were 3.13 × 10-5 volt and 2.65 × 10-5 volt, respectively. Unconfined compression tests were conducted on three reconstituted clay samples to examine the proposed axial and lateral LDT system. The stress-strain relationship indicates a nonlinear relationship between the axial and lateral strain of soil instead of the conventionally assumed constant relationship. The results demonstrate this nonlinear behavior even at small strain levels, which were successfully measured using a domestically built axial and lateral LDT system

Reconnaissance on Liquefaction-induced Flow Failure Caused by the 2018 Mw 7.5 Sulawesi Earthquake, Palu, Indonesia

The Mw 7.5 Sulawesi Earthquake 2018 was a catastrophic disaster that resulted in large numbers of casualties. This study aimed to investigate the damages of liquefaction-induced-flow failure in three areas in Palu city, i.e. Petobo, Balaroa, and Jono Oge. It was found that this flow failure occurred on a large scale at a very gentle ground inclination, ranging from 1 to 3%. In order to gain an understanding of the soil conditions in these specific locations, Portable Dynamic Cone Penetration Tests were conducted in Petobo. The results showed that the soil layers in the affected area were in a loose state compared to the non-affected areas. Furthermore, some spots of freshwater inundation were recognized in Petobo and Balaroa, even two weeks after the disaster. Based on this evidence, a mechanism of liquefaction-induced-flow failure caused by a confined aquifer is proposed

Compaction Control Using Degree of Saturation and Plasticity Index on Tropical Soil

Soil compaction in the field is conventionally controlled using maximum dry density, (ρd)max, and optimum moisture content, (w)opt, as the target properties. However, achieving accurate control of these target properties can be difficult due to variation of compaction energy level (CEL) and soil type. Recently, a novel soil compaction control approach using optimum degree of saturation, (Sr)opt, as the target properties has been proposed. It was argued that (Sr)opt can be a better compaction control property as the value is less sensitive to the variation of CEL and soil type. This paper presents an investigation of the compaction characteristics of tropical soils from several locations in Indonesia based on both primary and secondary data. This study was performed by exploring the relationships between (i) dry density (ρd) and Sr, (ii) (ρd) and plasticity index (PI), (iii) (ρd) and CBR, as well as (iv) (ρd) and permeability. This study showed that the (Sr)opt of the soils was 91.2%, with variation between 81.2% and 96.5%. This study also showed that (ρd)max can be related to PI at a given CEL. It is expected that the proposed relationships can be better references for field compaction control practices in Indonesia

Compaction Control Using Degree of Saturation and Plasticity Index on Tropical Soil

Soil compaction in the field is conventionally controlled using maximum dry density, (ρd)max, and optimum moisture content, (w)opt, as the target properties. However, achieving accurate control of these target properties can be difficult due to variation of compaction energy level (CEL) and soil type. Recently, a novel soil compaction control approach using optimum degree of saturation, (Sr)opt, as the target properties has been proposed. It was argued that (Sr)opt can be a better compaction control property as the value is less sensitive to the variation of CEL and soil type. This paper presents an investigation of the compaction characteristics of tropical soils from several locations in Indonesia based on both primary and secondary data. This study was performed by exploring the relationships between (i) dry density (ρd) and Sr, (ii) (ρd) and plasticity index (PI), (iii) (ρd) and CBR, as well as (iv) (ρd) and permeability. This study showed that the (Sr)opt of the soils was 91.2%, with variation between 81.2% and 96.5%. This study also showed that (ρd)max can be related to PI at a given CEL. It is expected that the proposed relationships can be better references for field compaction control practices in Indonesia

Prediksi Penurunan Tanah Menggunakan Prosedur Observasi Asaoka Studi Kasus: Timbunan di Bontang, Kalimantan Timur

Abstrak. Penurunan konsolidasi tanah merupakan masalah geoteknik yang sering ditemukan pada kasus timbunan, terutama pada tanah lunak. Penurunan konsolidasi disebabkan oleh keluarnya air pori dari dalam tanah yang disebabkan oleh peningkatan tegangan pada massa tanah. Untuk memprediksi besar penurunan serta lama waktu konsolidasi umumnya digunakan teori konsolidasi satu dimensi Terzaghi. Prediksi penurunan konsolidasi dengan teori ini, pada banyak kasus, memberikan hasil yang lebih besar dari penurunan aktual. Hal ini, salah satunya, disebabkan adanya pengabaian fenomena perkuatan tanah yang mungkin terjadi akibat proses penimbunan secara bertahap. Selain teori tersebut terdapat pula prediksi penurunan tanah dengan metode elemen hingga yang sudah menganalisis penurunan secara dua dimensi bahkan tiga dimensi. Namun untuk metode ini prediksi penurunan terhadap waktu, terutama untuk kasus perbaikan tanah dengan drainase vertikal, metode ini tidak memberikan hasil yang baik. Observasi Asaoka. Melalui prosedur ini, besarnya penurunan akhir dapat diprediksi dengan menggunakan data observasi penurunan akibat timbunan dengan menggunakan metoda curve fitting. Studi ini juga membahas perbandingan metode perhitungan penurunan dengan menggunakan teori konsolidasi Terzaghi, metode elemen hingga dan metode observasi Asaoka.Abstract. Consolidation settlement is a general geotechnical problem found embankment, particularly those founded on soft soil. Consolidation settlement is caused by the discharge of soil pore water induced by the increas of stress in soil mass. Terzaghi one dimensional theory was used to predict the settlement and time rate of consolidation. In many cases, the settlement prediction from this theory provides results much greater than the observed value due to many factors including the neglection of soil strength gain that may occur during consolidation process. In addition, there is also settlement prediction by using observed settlement data from the site using curve fitting method. This study presents settlement prediction method using Terzaghi consolidation theory, finite element method and Asaoka observational method

PENGEMBANGAN SISTEM PENGUKURAN PERUBAHAN DIMENSI SAMPEL PADA UJI TRIAKSIAL

Gejala alam dan aktivitas pembangunan oleh manusia secara langsung maupun tidak langsung dapat menimbulkan deformasi tanah. Peristiwa deformasi tanah merupakan salah satu karakteristik fisik tanah yang penting untuk dipelajari. Deformasi tanah dapat menimbulkan efek yang merugikan secara fisik maupun ekonomi. Berbagai penelitian berbasis perubahan dimensi atau deformasi tanah baik secara pendekatan teoritis maupun eksperimen di laboratorium dan lapangan menjadi sangat penting dilakukan. Penelitian pengembangan sistem pengukuran perubahan dimensi pada uji kompresi telah dilakukan. Sistem yang dibangun menggunakan metoda tidak langsung dan metoda langsung. Metoda tidak langsung yaitu transduser pengukur deformasi tidak langsung bersentuhan dengan objek yang terdeformasi selama uji kompresi, sebaliknya dengan metoda langsung transduser bersentuhan dengan objek yang mengalami perubahan dimensi. Pada metoda tidak langsung menggunakan teknik image processing dan rotary potentiometer. Pembacaan deformasi dengan teknik image processing yaitu membaca perubahan ukuran sampel selama uji kompresi pada beberapa foto. Ukuran tinggi sampel dalam foto dihitung berdasarkan jumlah piksel yang kemudian dikonversi ke satuan jarak (mm) sehingga diperoleh nilai deformasi. Dengan teknik image processing resolusi 1 mm setara dengan 11,62 piksel. Sistem rotary potentiometer digunakan untuk mengukur deformasi pada arah vertikal. Sistem ini bekerja dengan gerak rotasi yang terjadi pada potentiometer karena adanya perubahan ukuran sampel. Resolusi pengolah sinyal analog ke digital dan rentang pengukuran dari sistem rotary potentiometer berturut-turut adalah 0,038 mm dan 25 mm. Pengukuran perubahan dimensi dengan metoda langsung menggunakan sensor magi netostrictive dan sensor local deformation transducer (LDT). Dengan pengukuran metoda langsung ini regangan yang terukur tidak hanya arah vertikal seperti hal pada alat konvensional tetapi juga skala volum sampel. Perubahan dimensi volum ditransformasikan ke suatu gerak linear dengan menggunakan sensor magnetostrictive. Pengukuran perubahan dimensi sampel dengan sensor ini diawali dengan proses menjenuhkan sampel agar semua pori terisi air. Pada saat diberi kompresi, air yang mengisi pori-pori mengalir keluar dari sampel dan akan dideteksi oleh sensor sebagai perubahan dimensi yang terjadi pada sampel. Tegangan analog dari sensor akan diolah oleh bagian sistem elektronik dan hasilnya dapat ditampilkan pada seven segment dan komputer. Sensitivitas rancangan sensor ini adalah 0,007 ml/digital bit. Dilakukan proses kalibrasi dan pengujian sistem dengan perolehan kesalahan relatif sebesar 2%. Hasil pengukuran perubahan dimensi volum sampel dengan sensor agnetostrictive dibandingkan dengan pengukuran menggunakan alat konvensional dan diperoleh perbedaan sebesar 1,6%. Metoda langsung berikutnya adalah dengan menggunakan beberapa local deformation transducer. Pengukuran berbasis LDT yang dirancang berbeda dengan sistem pengukuran deformasi menggunakan triaksial konvensional, dimana deformasi yang terukur dengan LDT tidak hanya dalam arah vertikal, tetapi juga dalam arah lateral dan metoda pengukuran yang bersifat otomatis. LDT adalah plat tipis dengan ukuran tertentu yang ditempeli dengan strain gage. Perubahan yang terdeteksi dengan sensor ini lebih baik karena pengukuran tidak hanya pada pada arah vertikal tetapi juga arah lateral. Digunakan 4 sensor LDT lateral untuk mengukur deformasi arah lateral dan 1 LDT vertikal untuk mengukur deformasi arah vertikal. Sensor ini mengalami regangan dan memberikan respon perubahan resistansi ketika terjadi deformasi pada sampel. Perubahan resistansi akan diolah oleh bagian sistem elektronik yang terdiri dari rangkaian jembatan Wheatstone, penguat instrumentasi, analog to digital converter, dan mikrokontroler. Hasil deformasi yang terukur oleh LDT ditampilkan melalui Graphical User Interface (GUI) yang terdapat pada komputer. Berdasarkan bit ADC dan tegangan referensi yang digunakan, maka diperoleh nilai resolusi ADC 5 x 1

Geotechnical Aspects of the Sumatra Earthquake of September 30, 2009, Indonesia

This paper reports and discusses the results of a field survey conducted by a joint scientific group from Japan and Indonesia to assess the geotechnical aspects of the Sumatra earthquake (Mw=7.6) of September 30, 2009. The studied area included the Padang and Pariaman cities, where a number of buildings collapsed as a result of strong shaking, and a mountainous part of the Pariaman district, a place where massive landslides buried several villages, claiming more than 400 human lives. The main objective of the survey was to investigate the causes and mechanisms of catastrophic landslides; however, other geotechnical problems such as lateral spread and liquefaction were also addressed. Field observations indicated that the catastrophic landslides occurred on relatively gentle slopes, then mobilized into debris flows, and traveled several hundred meters from their points of origin. The failure surfaces developed along the boundary of highly weathered pumice tuff with more intact and less weathered bedrock. Data from a portable cone penetration test showed that the sliding material was rather weak, having SPT N-values in the range of 5-10. The results of the field survey suggested that the main cause of slope instability was high pore-water pressures that generated in the soil mass during the earthquake.Griffith Sciences, Griffith School of EngineeringNo Full Tex

Reconnaissance on Liquefaction-induced Flow Failure Caused by the 2018 Mw 7.5 Sulawesi Earthquake, Palu, Indonesia

The Mw 7.5 Sulawesi Earthquake 2018 was a catastrophic disaster that resulted in large numbers of casualties. This study aimed to investigate the damages of liquefaction-induced-flow failure in three areas in Palu city, i.e. Petobo, Balaroa, and Jono Oge. It was found that this flow failure occurred on a large scale at a very gentle ground inclination, ranging from 1 to 3%. In order to gain an understanding of the soil conditions in these specific locations, Portable Dynamic Cone Penetration Tests were conducted in Petobo. The results showed that the soil layers in the affected area were in a loose state compared to the non-affected areas. Furthermore, some spots of freshwater inundation were recognized in Petobo and Balaroa, even two weeks after the disaster. Based on this evidence, a mechanism of liquefaction-induced-flow failure caused by a confined aquifer is proposed