Sains Malaysiana 37(2):  177-184(2008)

Penggunaan Kaedah Analisi Spektrum Gelombang

Permukaan (SASW) Sebagai Teknik Baru Pengelasan

Jasad Batuan Untuk Geologi Kejuruteraan

(The Application of Spectral Analysis of Surface Wave (SASW) Method as a New Rock Mass Classification Technique in Engineering Geology) 

Abdul Rahim Samsuddin, Abdul Ghani Rafek & Umar Hamzah

Pusat Pengajian Sains Sekitaran dan Sumber Alam

Fakulti Sains dan Teknologi, Uiversiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor, Malaysia

Suharsono & Khairul Anuar Mohd Nayan

Jabatan Kejuruteraan Awam dan Struktur

Fakulti Kejuruteraan, Universiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor, Malaysia

Diserahkan: 25 Mei 2007 / Diterima: 26 Julai 2007

ABSTRAK

Analisis spektrum gelombang permukaan (SASW) adalah kaedah seismos yang menggunakan ciri serakan gelombang Rayleigh yang merambat pada lapisan bahan bagi memperolehi profil halaju gelombang ricih. Kaedah SASW merupakan satu kaedah insitu tanpa musnah untuk pencirian tapak geoteknik yang lebih kos efektif berbanding kaedah konvensyenal secara penggerudian. Dalam kajian ini sebanyak 20 stesen yang terdiri daripada 13 tapak kajian telah dipilih. Perisian (WINSASW 2.0) telah digunakan dalam proses penyongsangan untuk menghasilkan profil halaju gelombang ricih melawan kedalaman. Profil-profil ini kemudian dianalisis secara berasingan bagi memperolehi beberapa parameter geologi kejuruteraan jasad batuan seperti kekukuhan, nilai Penanda Mutu Batuan (RQD), anisotropi dan sifat kebolehkorekan. Analisis data SASW dijalankan dengan menganggap bahawa jasad batuan adalah homogen dan isotrop serta mengandungi pelbagai intensiti ketakselanjaran yang mempengaruhi perambatan halaju gelombang permukaan. Pengukuran sifat kedinamikan tanah dijalankan dengan menggunakan halaju gelombang ricih dan nilai ketukan N daripada Ujian Penusukan Piawai (N_SPT) dalam lubang gerudi. Satu persamaan linear baharu, Vs = 4.44 N_SPT  + 213.84 yang mengaitkan halaju gelombang ricih dan N_SPT telah diperolehi. Satu persamaan empirik telah dikemukakan bagi mengukur nilai Penanda Mutu Batuan (RQD) berasaskan  halaju gelombang ricih yang diperolehi daripada kaedah SASW dan halaju daripada ujian ultrasonik. Persamaan ini memberikan hasil yang perbezaannya kurang daripada 10% berbanding data RQD daripada lubang gerudi. Analisis keanisotropan jasad batuan dijalankan menggunakan halaju gelombang ricih yang diperolehi berdasarkan kaedah SASW yang diukur dalam empat arah. Plot nisbah halaju gelombang ricih - halaju ultrasonik melawan halaju ultrasonik telah digunakan untuk menentukan sifat kebolehkorekan jasad batuan. Sebanyak lima kelas lengkungan kebolehkorekan jasad batuan telah dapat dikemukakan iaitu lengkungan Mudah korek, Mudah koyak, Susah koyak, Pemecah hidraulik dan Peletupan.

Kata kunci: Analisis spektrum; gelombang permukaan; ketakselanjaran; keanisotropan; penanda mutu batuan;  jasad batuan

ABSTRACT

Spectral analysis of surface waves (SASW) is a seismic method that uses the dispersive characteristics of Rayleigh waves propagating through layered material to evaluate S-wave velocity profile. The SASW is an insitu nonintrusive method for geotechnical site characterization which is cost effective as compared to the conventional drilling method. In this study, a total of 20 stations from 13 sites were selected. A software (WINSASW 2.0) was used for the inversion process to produce S-wave velocity versus depth profiles. These profiles were then separately analyzed in relation to several engineering rock mass geological parameters such as stiffness, rock quality designation (RQD), anisotropy and the excavability properties. The analysis of the SASW data was based on the assumption that the rock mass is an isotropic homogeneous material with various intensity of discontinuity which influenced the velocity of surface wave propagation within the rock mass. Measurement of dynamic soil properties was carried out employing the shear wave velocities and the N values of the Standard Penetration Test (N_SPT) from borehole data. A new linear equation Vs = 4.44 N_SPT + 213.84 which relates S-wave and N_SPT was deduced. An empirical equation is also proposed to calculate Rock Quality Designation (RQD) values based on S-wave velocity derived from SASW and that of ultrasonic tests. The result of this equation was found to be less than 10% in comparison to the RQD obtained from actual borehole data. An isotropic analysis of the rock mass was carried out using S-wave velocities derived from SASW measurements in four directions. The plots of S-wave - ultrasonic velocity ratio versus ultrasonic velocity were used to evaluate the excavability properties of rock mass. Five classes of rock mass excavability curves were finally proposed in relation to easy digging, easy ripping, hard ripping, hydraulic breaking and blasting.    

Keywords: Spectrum analysis; surface wave; discontinuity; anisotropy; rock quality designation; rock mass

 RUJUKAN/REFERENCES 

Athanasopoulos, G.A., Pelekis, P.C. & Anagnostopoulos, G.A. 2000. Effect of soil stiffness in the attenuation of Rayleigh wave motions from field measurements. Soil Dynamics and Earthquake Engineering  19: 277-288.

Caterpillar. 1988. Caterpillar handbook of ripping, Ed. ke-8. Illinois: Caterpillar, Inc.

Cho, Y.S. & Lin, F.B., 2001. Spectral analysis of surface wave response of multi-layer thin cement mortar slab structures with finite thickness. NDT&E International 34: 115-122.

Cunha, A.P., (Ed), 1990. Scale effects in Rock Masses. Proceedings of the first International Workshop on scale effects in rock masse. Rotterdam: A.A. Balkema.

Deere, D.U., 1968, Geological Considerations, Rock Mechanics in Engineering Practice, Wiley, New York, 1-20.

Franklin, J.A., Broch, E. & Walton, G. 1971. Logging the mechanical character  of rock. Trans. Institute Mining and Metallurgy 80: 1-9.

Goodman, R.E., 1976.  Methods of Geological Engineering in Discontinuous Rocks. West: St. Paul.