Prediction of Soil Settlement using Numerical Modelling Based on Shear Wave Velocity Measurement

The method of Spectral Analysis of Surface Wave (SASW) is a seismic method that consider as a non-destructive geotechnical technique to determine the soil profile based on the shear wave velocity profile by utilizing the dispersive characteristic of Rayleigh wave through the soil medium. The shear wave velocity was found to be directly proportional to the strength of the soil. In this research, SASW measurement had been proposed to predict the soil settlements using numerical modelling. The frequency responses from SASW were acquired for shear wave profile analysis using WinSASW software. Thus, the borehole information which near to the conventional pile method and SASW were taken as the reference of the study. In obtaining the correlated N-value, equation that developed from previous research was used with the reference of N-SPT value. Hence, the correlated N-values were carried forward to obtaining the bearing capacity of foundation. Meanwhile, the numerical modelling has been developed in PLAXIS software in obtaining the soil settlement. The prediction of soil settlements of Site 1, Site 2 and Site 3 that calculated by conventional equation and modelled using PLAXIS were 0.003mm and 0.001mm, 0.002mm and 0.004mm, 0.003mm and 0.004m respectively. Based on the result obtained, this research has shown the potential used of shear wave velocity in the prediction of soil settlement.

Scholte Wave Dispersion Modeling and Subsequent Application in Seabed Shear-Wave Velocity Profile Inversion

Recent studies have illustrated that the Multichannel Analysis of Surface Waves (MASW) method is an effective geoacoustic parameter inversion tool. This particular tool employs the dispersion property of broadband Scholte-type surface wave signals, which propagate along the interface between the sea water and seafloor. It is of critical importance to establish the theoretical Scholte wave dispersion curve computation model. In this typical study, the stiffness matrix method is introduced to compute the phase speed of the Scholte wave in a layered ocean environment with an elastic bottom. By computing the phase velocity in environments with a typical complexly varying seabed, it is observed that the coupling phenomenon occurs among Scholte waves corresponding to the fundamental mode and the first higher-order mode for the model with a low shear-velocity layer. Afterwards, few differences are highlighted, which should be taken into consideration while applying the MASW method in the seabed. Finally, based on the ingeniously developed nonlinear Bayesian inversion theory, the seafloor shear wave velocity profile in the southern Yellow Sea of China is inverted by employing multi-order Scholte wave dispersion curves. These inversion results illustrate that the shear wave speed is below 700 m/s in the upper layers of bottom sediments. Due to the alternation of argillaceous layers and sandy layers in the experimental area, there are several low-shear-wave-velocity layers in the inversion profile.

Seismic hazard microzonation of Bengkulu City, Indonesia

It has been known that Bengkulu City (Indonesia) is vulnerable to undergo seismic damage. This study is initiated by measuring horizontal to vertical spectral ratio (H/V) to sites in Bengkulu City using microtremor. The inversion analysis is performed to generate shear wave velocity profile. Hundreds of sites are investigated in this study. The results show that observed H/V is consistent with the theoretical H/V. National Earthquake Hazard Reduction Program code is adopted to classify the site class. The results also exhibit that Bengkulu City is dominated by Site Classes C and D. In general, this study could lead local government to consider seismic hazard mitigation for spatial plan.

PSHA Compatible Probabilistic Seismic Site Response Analysis for Oslo, Norway

ABSTRACT This article describes a probabilistic site-response analysis for the city of Oslo, Norway. We first perform a probabilistic seismic hazard analysis (PSHA) for hard rock. Then, we conduct site-response analyses using Monte Carlo simulations to capture uncertainty in the site profile. We include four base-case soil profiles to incorporate epistemic uncertainty, and we vary the shear-wave velocity profile and shear-modulus reduction and damping curves to account for aleatory variability. We base the soil profiles on over 7000 in situ tests, and the shear-wave velocity profile median, standard deviation, and interlayer correlation on over 559 cone penetration tests. Next, we perform regression analyses to estimate medians and standard deviations of site-specific amplification factors (AFs). Finally, we modify the ground-motion models for rock with the AFs and recompute the PSHA for the soil surface. The analyses show that (1) shallower soil profiles have larger uniform hazard spectra (UHS) values at short periods and smaller UHS values at long periods; (2) epistemic uncertainty of the base-case soil shear-wave velocity profile leads to alternative UHS values with a difference of a factor of 2 at short periods; (3) there is only a small difference in the mean magnitudes and distances controlling the hazard for the PSHA conducted for rock compared to soil; (4) response spectra calculated from site-response analyses with no aleatory variability of the soil properties predict significantly smaller spectral acceleration values at periods shorter than the natural site period; (5) using site amplification standard deviations based on ground-motion recordings, instead of site-response analyses, results in a 10%–20% reduction in the soil surface UHS at short periods and a 5%–10% increase at long periods; and (6) the Eurocode 8 AFs are, in general, conservative for Oslo.

Seismic Hazard Microzonation of Bengkulu City, Indonesia

It has been known that Bengkulu City (Indonesia) is vulnerable to undergo seismic damage. This study is initiated by measuring horizontal to vertical spectral ratio (H/V) to sites in Bengkulu City using microtremor. The inversion analysis is performed to generate shear wave velocity profile. Hundreds of sites are investigated in this study. The results show that observed H/V is consistent with the theoretical H/V. National Earthquake Hazard Reduction Program code is adopted to classify the site class. The results also exhibit that Bengkulu City is dominated by Site Classes C and D. In general, this study could lead local government to reconsider seismic hazard mitigation for spatial plan.

Geotechnical Site Characterization via Deep Neural Networks: Recovering the Shear Wave Velocity Profile of Layered Soils

The mechanical property of soils is a vital part of seismic hazard analysis of a site. Such properties are obtained by either in-situ (destructive) experiments such as crosshole or downhole tests, or by non-destructive tests using surface wave inversion methods. While the latter is more favorable due to the cost-efficiency, there are challenges mostly due to computational need, non-uniqueness of inversion results, and fine-tuning parameters. In this article, we use a deep learning framework to circumvent the above-mentioned limitations to output soil mechanical properties, requiring dispersion data as input. Our trained model performs with high accuracy on the test dataset and shows satisfactory performance compared to the ensemble Kalman inversion technique. We finally propose a framework to extend the method to higher dimensions by numerically solving the wave equation in a two-dimensional medium.

Open-Source MASW Inversion Tool Aimed at Shear Wave Velocity Profiling for Soil Site Explorations

The shear wave velocity profile is of primary interest for geological characterization of soil sites and elucidation of near-surface structures. Multichannel Analysis of Surface Waves (MASW) is a seismic exploration method for determination of near-surface shear wave velocity profiles by analyzing Rayleigh wave propagation over a wide range of wavelengths. The inverse problem faced during the application of MASW involves finding one or more layered soil models whose theoretical dispersion curves match the observed dispersion characteristics. A set of open-source MATLAB-based tools for acquiring and analyzing MASW field data, MASWaves, has been under development in recent years. In this paper, a new tool, using an efficient Monte Carlo search technique, is introduced to conduct the inversion analysis in order to provide the shear wave velocity profile. The performance and applicability of the inversion scheme is demonstrated with synthetic datasets and field data acquired at a well-characterized geotechnical research site.

Seismic Hazard Microzonation of Bengkulu City, Indonesia

It has been known that Bengkulu City (Indonesia) is vulnerable to undergo seismic damage. This study is initiated by measuring horizontal to vertical spectral ratio (H/V) to sites in Bengkulu City using microtremor. The inversion analysis is performed to generate shear wave velocity profile. A total of 218 sites is investigated in this study. The results show that observed H/V is consistent with the theoretical H/V. National Earthquake Hazard Reduction Program (NEHRP) code is adopted to classify the site class. The results also exhibit that Bengkulu City is dominated by Site Classes C and D. In general, this study could lead local government to reconsider seismic hazard mitigation for spatial plan.