Sri Atmaja P. Rosyidi

Wavelet Spectrogram Analysis of Surface Wave Technique for Dynamic Soil Properties Measurement on Soft Marine Clay Site

The surface wave measurement is one of in-situ seismic methods based on the dispersion of Rayleigh waves (R-waves) which is used to determine dynamic soil properties, i.e., the shear wave velocity (VS), shear modulus (G), damping ratio (D) and depth of each layer of the soil profile. Much of the basis of the theoretical and analytical work of this method for soil investigation has also been developed (Stokoe et al., 1994). Seismic data used in surface wave analysis are non-stationary in nature, i.e., varying frequency content in time. Especially in the low frequency range measurement, i.e., in soft soil deposit, the interested frequency of surface wave can be relatively low, i.e., less than 20 Hz. In these frequency values, the noisy signals from the natural or man-made sources may disturb the identical frequency level of the surface wave signals generated from the source. Therefore, a timefrequency decomposition of a seismic signal is needed to obtain the correct information of phase spectrum generated from signal transformation. In most of surface wave methods, the data analysis from time to frequency domain has been carried out by using Fourier transformation. However, some information of non-stationary seismic data in analysis maybe lost due to any arbitrary periodic function of time with period which is expressed as sum a set of sinusoidal in Fourier transform. The Fourier analysis is unable to preserve the time dependence. In addition, it also can not describe the evolutionary spectral characteristics of non-stationary processes. Thus, a new tool, i.e., wavelet analysis is required which allows time and frequency localization of the signals in the surface wave measurement beyond customary Fourier analysis.

Coupled Procedure for Elastic Modulus and Damping Ratio Measurement on Pavement Subgrade Structures Using Surface Wave Method

Limited financial capability of governments for road rehabilitation in developed countries and technical constraints of laboratory tests in assessing pavement quality highlight the need to develop an innovative technique in pavement evaluation. The performance of the Spectral-Analysis-of-Surface-Wave (SASW) method to evaluate the dynamic parameters on the existing road pavements is presented herein. The aim of this paper is to propose a coupled analyses procedure for calculating elastic modulus and damping ratio of soil subgrade layer in pavement. The dynamic elastic modulus was obtained from the shear wave velocity produced from the inversion of an experimental dispersion curve. To validate the modulus obtained from the SASW method, the falling weight deflectometer (FWD) test was used to determine the subgrade modulus at same sites. In this study, a damping ratio of soil layer was also obtained using attenuation coefficient from the modified Bornitz equation. Good agreements were also obtained between the attenuation coefficients from this study and previous studies. The SASW method is able to characterize adequately the in-situ pavement stiffness which can be potentially developed as an innovative evaluation device.

2-D and 3-D Subsurface Liquefaction Potential Profiling Using Tomography Surface Waves Method

A 6.3 Mw earthquake struck Yogyakarta region in 2006 causing many geotechnical damages, e.g., ground cracks, surface displacement, landslides and local liquefactions and soil billings occurred in some regions. From field observations, it was shown that most minor to major structural damages in buildings and bridges were identified near to liquefaction locations. Consequently, a site investigation and advanced analysis for providing the subsurface liquefaction potential information plays important rule in infrastructure design related to structural damage analysis. The aim of this paper is to use of the tomography surface waves method in order to investigate the liquefaction potential in 2-D and 3-D subsurface profile. These seismic surveys were conducted on deep loose sand and sandy soil deposit located inside Universitas Muhammadiyah Yogyakarta (UMY)’s campus, Indonesia which consists of. The liquefaction potential profile was analyzed and generated from combination of the shear wave velocity and soil properties information. Two earthquake scenarios, 6.3 and 8 Mw, were used to simulate the sensitivity of 2-D profile for identifying the liquefaction potential in each soil layer. The results show that the liquefaction potential widely occurs in observed sandy soil and sand deposit layer for stronger earthquake. Finally, the tomography surface waves method is becoming an effective tool for observing liquefaction potential profile in the site investigation, particularly for the purpose of geohazards analysis in the concept of sustainable environmental development.

Effect of input source energy and measurement of flexible pavement deflection using the SASW method

Abstract This paper presents the effect of input source energy on the results of spectral analysis of surface wave (SASW) evaluation of flexible pavements in terms of maximum and minimum wavelength. A series of surface wave tests, namely the SASW test, were done on asphalt pavement using four steel balls with different masses as sources. These sources were dropped from two different heights, 0.25 and 0.50 m. This test was also conducted with two different configurations, i.e. with the receivers positioned 0.15 and 0.30 m apart. This paper also presents the feasibility of using accelerometers to measure flexible pavement deflection. For this purpose, the process of integrating accelerometer time history is described. It is proved that a change in input source energy has some effect on the value of maximum and minimum wavelength. The result for numerical double integration is satisfactory and is congruent with the displacement obtained through finite element analysis.

Use of Wavelet Analysis and Filtration on Impulse Response for SASW Measurement in PCC Slab of Pavement Structure

A quick and efficient of the spectral analysis of surface wave (SASW) has been developed to non-destructively measure the stiffness of PCC slabs. However, in layered PCC slab with strong stiffness contrast, several wave groups were observed due to the refraction and reflections of stress waves at the layer boundaries. As a result, the phase spectrum affected by these different wave groups is to be complicated. In this study, a time-frequency analysis of wavelet transform was then employed to impulse response analysis to overcome identification problem of the non-stationary wave groups and spectral characteristics of phase spectrum. Time-frequency wavelet spectrogram was utilized to select the interested response spectrum from wave groups. A time-frequency wavelet filtering was then used to remove the interference of unnecessary wave groups or background noise based on simple concept of wavelet filtering. Consequently, the phase spectrum was reconstructed from denoised impulse response by inverse wavelet transform. Results showed that the wavelet analysis of impulse response can be used to improve the phase spectrum and reconstruct better phase velocity dispersion curve. A good agreement was also established between the PCC stiffness from SASW measurements compared to ACI formulation.

Lesson Learned from Road Infrastructure Deterioration Caused by Earthquake 7.6 MW and 6.2 MW Padang, September 30, 2009

The huge destruction of the earthquake of 7.6 and 6.2 MW in Padang, West Sumatra, Indonesia on September 30, 2009 caused widespread death of more than 1,200 people and destruction to the heavily populated and relatively prosperous region. In this paper a summary of earthquake effects to structural damage on road infrastructure and geofailures, i.e., landslide and debris flow, during the earthquake were identified based on direct field observation at several districts, i.e. the city of Padang, Padang Pariaman, Pariaman and Agam. The levels of earthquake damage were classified from low to severe destruction level for road pavement and bridges. The earthquake also caused events of landslides and debris flows close to road networks which killed hundreds of people while hundred kilometers of road pavement were made inaccessible. Some road networks were totally collapsed and as a result, several villages became isolated areas.