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Bengkulu City in Indonesia is one of the areas prone to earthquakes, yet it has developed increasingly in the last five years. One of the prospective areas in Bengkulu City, called Singaran Pati, is located close to the Dendam Tak Sudah Lake, a natural tropical lake. This research aims to interpret geological characteristics for the spatial plan development in the study area. Microtremor measurement and site investigation are implemented to observe the geophysical and geological characteristics of the study site. Inversion analysis using Monte Carlo simulated annealing is conducted to generate a shear wave velocity profile. Based on the shear wave velocity, the identified bedrock surface is illustrated in a 3D geological model. A simple analysis of the natural period to estimate allowable structural building storeys is also performed. Results show that the depth of the bedrock surface is around 4.5–147 m. The study area is dominantly categorised as Site Classes C and D. Low- to medium-rise buildings are appropriate to construct based on the geophysical and geotechnical information. The findings can provide preliminary guidelines on geotechnical and geological information for the seismic site conditions in the study area in Bengkulu City. [ABSTRACT FROM AUTHOR]

Current geotechnical design requires an appropriate number of in-situ tests to obtain sufficient underground information. Subsoil properties are known to have high spatial variability and often fluctuate with location. Random field model considering soil spatial variability for reliability analysis in geotechnical engineering requires site statistical data. This study presents a statistical characterisation of subsoil properties in Bangkok. The boring log data of Bangkok subsoil was gathered and used to develop a 3D geological model. The statistical analysis of geotechnical data was performed to describe the spatial variability of soil properties. The mean, coefficient of variation, and scale of fluctuation of the undrained shear strength, standard penetration test, total unit weight, plasticity index, and thickness of soil layers were evaluated in detail using random field model. The lognormal distribution and decay exponential function were adopted to describe the fluctuation trend of soil properties. Based on the data, the empirical correlations between soil shear strength and index properties can be also established. The results of this research can help civil engineers to describe the influence of spatial variability of soil properties in geotechnical engineering analysis. [ABSTRACT FROM AUTHOR]

This paper presents the variations in subsoil conditions of the Bangkok Metropolitan Area of Thailand. The study was initiated by measuring ambient noise with a seismometer. A total of twenty sites was investigated by microtremor measurements. The typical subsoils of Bangkok were presented on the basis of site investigation reports. Furthermore, inversion analysis was conducted to determine subsoil properties in Bangkok. Geotechnical parameters for seismic analyses, such as soil layer thickness, undrained (su), unit weight, time-averaged shear wave velocities at 30 m (Vs30), 100 m (Vs100), and 500 m (Vs500), and engineering bedrock surface depth were reported. Results shows that clay layer thickness varies from 17 - 25 m with the su of approximately 10 - 60 kPa and unit weight of approximately 15 - 17.5 kN/m3. The results also show that Vs30, Vs100, and Vs500 fall in the ranges of 100 - 225, 175 - 300, and 325 - 450 m/s, respectively. Engineering bedrock with the Vs of 760 m/s is found at 375 - 625 m below the ground. This result also indicates that a thick sediment is generally found in the Bangkok Metropolitan Area. In general, the results of this work could be used for civil engineering practice, especially seismic design and analysis in the studied area. [ABSTRACT FROM AUTHOR]

This paper investigates the effects that the spatial variability of a soil's undrained shear strength has on lateral wall movements and ground surface settlements when performing a deep excavation stability analysis. A random finite-element method is employed to statistically assess a deep excavation. A case study based on an actual deep excavation project in Bangkok's subsoils was used to validate the methodology. The two-dimensional spatial variability of the undrained shear strength in the clay layers of Bangkok's subsoil is simulated using the random field theory and Monte Carlo simulation. The Mohr–Coulomb model is used to predict lateral wall movements and ground surface settlements, while the stability analysis of the deep excavation is evaluated by the factor of safety using the strength reduction approach. The results show that spatial variability highly affects the distribution of lateral wall movements and ground surface settlements, as well as the scatter of the factor of safety corresponding to progressing stages of excavation. [ABSTRACT FROM AUTHOR]

The objective of this study was to observe the spatial variation in the geological subsoil condition on the seismic ground response of Bangkok subsoils during the remote 6.8 Mw Tarlay earthquake in 2011 in Northern Thailand. A simulation of random locations was initially performed to define the studied locations. The dynamic parameters, such as the soil index properties, shear modulus, and shear wave velocity, were determined from the subsurface modeling of Bangkok subsoils. Next-generation attenuation analysis was performed to define the input ground motion at each investigated site. Non-linear one-dimensional site response analysis was performed to investigate the surface ground motion, amplification factor, and spectral acceleration during short (0.2 s) and long (1 s) time periods. In general, it is important to consider the ground spatial variation in any seismic ground response analysis. The results show that Bangkok subsoils could magnify the seismic wave during an earthquake. For example, in the 2011 Tarlay earthquake, the magnification varied from two- to four-fold. The results from this study can be used to define the microzonation of the ground motion characteristic of Bangkok subsoils, such as the peak ground acceleration and the spectral acceleration, at short and long periods. [ABSTRACT FROM AUTHOR]

Recently, several mass rapid transit projects have been launched to improve the logistics of trade in Thailand. The railway construction projects linked from Bangkok will be a challenging task for civil engineers since they are located on soft ground conditions. Consequently, an understanding of geomaterial properties and subsoil conditions is important in the design phase. This paper presents a numerical study of railway embankment behaviour when constructed on soft soil. Simplified finite-element modelling was performed to predict stability and deformation characteristics of railway embankments under high-speed design requirements. The construction materials, including ballasts and subgrade soils were selected and tested to characterise their engineering properties. It was found that existing railway embankment conditions exhibit a large degree of movement under a high-speed train load. The study recommends improvements of subgrade conditions, using methods such as cement stabilisation to enhance stability and reduce settlement of the railway embankments. [ABSTRACT FROM AUTHOR]

This study provides evidence that three-dimensional finite element modelling can be effectively applied for deep excavation analysis in Bangkok. The Bangkok subsoils were modelled using the hardening soil model and their parameters were calibrated against the results of laboratory and field tests. A study of a MRT station excavation was initially used to validate the model. The predicted wall movements and surface settlements were compared with the instrument data and two-dimensional analysis from a previous study. Another deep excavation project was selected as an independent study. The result shows that the model can be confidently used for deep excavation analysis. [ABSTRACT FROM AUTHOR]