2012 IEEE Colloquium on Humanities, Science & Engineering Research (CHUSER 2012), December 3-4, 2012, Kota Kinabalu, Sabah, Malaysia Site-Specific Empirical Correlation between Shear Wave Velocity and Standard Penetration Resistance using MASW Method Chee-Ghuan Tan School of Civil Engineering, Universiti Sains Malaysia, Penang, Malaysia [email protected] Taksiah A. Majid Kamar Shah Ariffin Disaster Research Nexus, School of Civil Engineering, Universiti Sains Malaysia, Penang, Malaysia School of Material and Mineral Resources, Universiti Sains Malaysia, Penang,Malaysia II. SURFACE WAVE METHOD Surface wave geophysical methods have been developed few decades ago and lots of application in geotechnical engineering. Surface wave geophysical methods able to determine dynamic properties of soil, particularly the shear wave velocity profile as well as the shear modulus. These properties are main parameters in estimating the soil response and soil-structure interaction to seismic loading [6]. Surface wave methods offer advantages over other surface based in-situ seismic techniques is rapid, cost effective, noninvasive and ability to detect low velocity layer underneath higher velocity layer of deposit provides more accurate site characterization. Keywords- Shear wave velocity profile, Multichannel analysis of surface wave (MASW), Standard penetration resistance, Empirical correlation A. Multichannel Analysis of Surface Waves (MASW) Spectral analysis of surface wave (SASW) method was introduced by Stokoe and Nazarian [7] which focuses on analyzing the ground roll dispersion relation to produce nearsurface S-wave velocity profile. The main drawbacks are time consuming and inherent difficulties when evaluating and distinguishing signal from noise with only a pair of receivers. To overcome the few drawbacks of the SASW method, a new technique Multichannel Analysis of Surface Waves (MASW) was developed by four-phase research project team from Kansas Geological Survey. Multi-station recording permits a single survey of a broad depth range and higher levels of redundancy with a single field configuration compared with SASW [8]. A multichannel shot gather decomposed into a swept frequency record allows the fast generation of an accurate dispersion curve. This dispersion curve is then used to determine the shear-wave velocity profile for the shallow-depth layer of soil [9]. INTRODUCTION The most important aspect in earthquake engineering is to determine the dynamic soil properties. The dynamics soil properties able to provide the important information of the dynamic response of the soil-structure which needed in dynamic structural analysis of the superstructures. The local soil structure also play a major role in the seismic soil amplification of a site which is a critical factor affecting the level of ground shaking [1]. However, lacking of understanding the geological information of the site often responsible for structure and environmental failure occurred. The soil stiffness and soil amplification factor on ground surface are always presented by Vs30. Field measurement of shear wave velocity includes cross-hole test, downhole test, suspension logging, seismic This study was supported by the Postgraduate Research Grant Scheme given by Universiti Sains Malaysia. 978-1-4673-4617-7/12/$31.00 ©2012 IEEE School of Civil Engineering, Universiti Sains Malaysia, Penang, Malaysia Malaysia reflection, seismic refraction and surface wave. However, surface wave test is simpler and efficient technique compared to other in-situ test in measuring the shear wave velocity. It is not economically feasible to conduct test at all sites. Therefore, a reliable empirical correlation between shear wave velocity and standard penetration resistance (Nspt) would be useful since the ease of obtaining the Nspt from site investigation report. Several researchers have proposed empirical correlation for shear wave velocity based on standard penetration test [2-5]. However, these empirical correlations are region specific and cannot be applicable to all regions. Abstract—In seismic engineering, dynamic property of the soil is one of the most important aspects in ground response analysis. It is significantly affected by the presence soil deposits of the site. Generally, the average shear wave velocity at top 30 m (Vs30) of soil deposit is used to represent stiffness of the soil and is one of the important parameters to determine the soil amplification factor on the ground surface and site classification. Vs30 is usually determined by carry out wave propagation test on the field. However, it is not economically feasible to conduct test at all sites. Therefore, a reliable empirical correlation between shear wave velocity and standard penetration resistance (Nspt) would be useful since the ease of obtaining the Nspt from site investigation report. Although there are quite a number of these empirical correlations available in literature, but they are region specific and cannot be applicable to all region. In this study, Multichannel Analysis of Surface Wave (MASW) is employed to obtain the shear wave velocity profile of site which needed to develop the empirical regression equations between Vs and Nspt for sand, silt and clay. MASW test has been carried out on the twenty sites which posses of Nspt profiles around Penang Island. The empirical regression equations developed by the study area are exhibit good prediction performance. It can be used for the area which consist of soft to stiff clay and silt and loose to dense sand. I. Norazura Mohamad Bunnori 94 2012 IEEE Colloquium on Humanities, Science & Engineering Research (CHUSER 2012), December 3-4, 2012, Kota Kinabalu, Sabah, Malaysia B. Field Test Set up and Procedure Extensive MASW tests were carried out o in the Penang Island as shown in Fig. 1. GEOMETR RICS-24 channels seismograph (Geode) with single geode operating o software (SGOS) is used for the MASW tests. 244 units of vertical geophones with natural frequency of 4.5 Hz were used to receive the wave signal generated by an actiive source of 8 kg sledgehammer vertically hit on a striker platee. Geophones were deployed linearly with equal spacing in the range r of 0.5 to 2 m interval as suggested by Maheswari et al.. [1]. The nearest source to geophone offsets are in the range off 5 to 15 m to meet the requirement of different type of soil harddness suggested by Xu et al. [10]. The planer characteristic of surface waves evolve only after some distant from the soource and hence it normally need to be greater than half of the maximum desired SW is illustrated in wavelength. The field configuration of MAS Fig. 2. The acquired wave data from the field f measurement were analysis using SeisImager softwaare and can be summarized to two main steps: (i) develoop the dispersion curves of Rayleigh wave phase velocity and (ii) inversion of dispersion curve to obtain the shear wave veelocity profiles. At first, the raw wiggle plot obtained from the t field test was filtered to reduce the random noise effect andd interference with other waves as shown in Fig. 3(a). After filttered, only surface wave is used in generating the dispersion cuurve analysis. The amplitude of body wave and higher mode of Rayleigh wave a high frequencies may dominate over the fundamental mode at range if the raw data is not well filtered. Only fundamental mode of Rayleigh wave is picked from the frequencies of 5-8 to 40-50 Hz as shown in Fig. 3(b) to generatte dispersion curve with signal to noise ratio (S/N) (Fig. 3(c))). The dispersion curve was inverted to estimate the shear wavve velocity profile as shown in Fig. 4. Fig. 5 shows the tyypical shear wave velocity profile and Nspt. Sledgehammer with trigger switch Geo ophones (4.5 5 Hz) Multichannel Seismograph (GEODE) Laptop Vs1 Vs2 Vs3 Figure 2. Field configuuration of MASW method Time (ms) Disttance (m) ( (a) Frequency (Hz) Phase velocity v (m/s) ( (b) Phase velocity (m/s) Frequuency (Hz) ( (c) Figure 3. Development of the disperrsion curves: (a) typical raw wiggle plot obtained from the field test (b) picking of maximum wave signal (c) dispersion curve with quality curvve (signal to noise ratio) Figure 1. Location of geophysical invesstigation 95 2012 IEEE Colloquium on Humanities, Science & Engineering Research (CHUSER 2012), December 3-4, 2012, Kota Kinabalu, Sabah, Malaysia Depth (m) S-velocity (m/s) Figure 6. Correlation between Vs and Nspt for sand, silt and clay Figure 4. Typical shear wave velocity profile obtainned from MASW test III. The shear wave velocity obtained o from Equation 1-3 for sand, silt and clay are coompared with some selected correlations proposed by earlieer researcher which have closest correlation curve with the prroposed equation (Table 1) as shown in Fig. 7. However, the correlation for clay gives slightly higher shear wave velocity v compared to existing correlation. Some discrepanccy between the proposed and previous correlations may duee to different site geotechnical conditions and the proceduress during carry out the MASW survey in site. DEVELOPMENT OF EMPIRICAL CORREELATIONS FOR VS AND NSPT In-situ test to determine the shear wave velocity profile is f to conduct always preferable but it is not economically feasible test at all sites. A reliable empirical correlatioon between Vs and Nspt would be in advantage. In this study, Vs and Nspt data were collected from twenty sites in the generatioon of its empirical correlations. Simple regression analysis was used to develop these correlations. The new empirical correelations with their correlation coefficient (R2) for sand, silt and clay are proposed as follows: Vs = 150.00 Nspt 0.2292 (R2 = 0.6874), Sand (1) Vs = 111.62 Nspt 0.3233(R² = 0.7175), Silt (2) Vs = 118.33 Nspt 0.3276 (R² = 0.7142), Clay (3) IV. O CONCLUSION In summary, an extensive meassurement of shear wave velocity by employing MASW geophysical technique was carried out in Penang Island. The correlationns between Vs and Nspt for sand, silt and clay were developed. The T results proved the previous finding that Nspt is the main parrameter to determine shear wave velocity. Generally the shear wave velocity curves proposed are closely lying to the existting correlation. Therefore, the proposed correlations for sand,, silt and clay are recommended to be used in the studied area. Fig. 6 shows the Vs-Nspt raw data annd the regression correlations for sand, silt and clay. The results r proved the previous finding that Nspt is main parameter while w soil material gives less significant effect on shear wave vellocity estimation. TABLE I. No. Authors (year) 1 Okamato et al. (1989) Lee (1990) 2 3 4 Figure 5. Typical shear wave velocity profile and Nspt variation for site 96 Hanumantharao and Ramana (2008) Maheswari and Boominathan (2009) CORRELATIONS BETWEEN VS AND NSPT Vs Correlation Sand Vs = 125 N 0.33 Vs = 79 N 0.43 Silt Clay Vs = 105.6 N 0.32 Vs = 114.4 N 0.31 Vs = 86.0 N 0.42 Vs = 89.3 N0.36 2012 IEEE Colloquium on Humanities, Science & Engineering Research (CHUSER 2012), December 3-4, 2012, Kota Kinabalu, Sabah, Malaysia RENCES REFER [1] [2] [3] (a) [4] [5] [6] (b) [7] [8] [9] (c) Figure 7. Comparison between proposed and existing correlations for Vs and Nspt for: (a) sand (b) silt (c) clay [10] ACKNOWLEDGEMENTS: This study was supported by the Postgraduaate Research Grant Scheme given by Universiti Sains Malaysia. The T authors would like to extend their gratitude to the Ministrry of Education of Malaysia for permission to collect data from m both primary and secondary schools. 97 R. U. Maheswari, A. Boominathan, and G. R. 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