Sains Malaysiana 40(6)(2011): 561–568

Pencirian Geomekanik Jasad Batuan dengan Menggunakan Kaedah Seismos: Nisbah Poisson

(Rock Mass Geomechanical Characterization by Seismic Methods: Poisson’s Ratio)

T. L. Goh,* A. Ghani Rafek, A. Rahim Samsudin,

M. Hariri Ariffin & N. Baizura Yunus

Program Geologi, Pusat Pengajian Sains Sekitaran dan Sumber Alam

Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor D.E., Malaysia

Diserahkan: 5 Januari 2010 / Diterima: 21 Mei 2010

ABSTRAK

Parameter mekanik seperti nisbah Poisson merupakan parameter input kejuruteraan batuan terutamanya dalam perisian komputer model berangka. Kaedah seismos digunakan untuk menentukan nisbah Poisson jasad batuan segar (gred I), terluluhawa sedikit (gred II), terluluhawa sederhana (gred III) dan tinggi (gred IV). Nisbah Poisson setiap lapisan jasad batuan dikira berdasarkan nilai purata halaju gelombang mampatan (Vp) dan gelombang ricih (Vs) pada kedalaman tertentu. Halaju gelombang mampatan (Vp) diperoleh daripada survei seismos biasan dan halaju gelombang ricih (Vs) diperoleh daripada survei analisis spektral gelombang permukaan (SASW) atau analisis gelombang permukaan berbilang saluran (MASW). Sebanyak 66 ujian seismos telah dijalankan pada 9 cerun jasad batuan iaitu 6 ujian di atas 1 cerun jasad batuan granit di JKR kuari Bukit Penggorak, Kuantan, Pahang; 26 ujian di atas 4 cerun jasad batuan granit di Kuari Kajang Rock, Semenyih, Ulu Langat, Selangor; 12 ujian di atas 1 cerun jasad batuan granit di Lebuhraya Silk Kajang (km 14.6) Selangor; 14 ujian di atas 2 cerun jasad batuan syis di Jalan Kuala Kubu Baru-Bukit Fraser (km 15), Selangor dan 8 ujian di atas 1 cerun jasad batuan kuarzit di Section U10, Bukit Cherakah, Shah Alam, Selangor. Daripada ujian seismos, nilai maksimum nisbah Poisson jasad batuan yang bergred I, II, III dan IV ialah 0.295, 0.335, 0.355 dan 0.364. Nilai minimum nisbah Poisson jasad batuan yang mempunyai gred I, II, III dan IV ialah 0.215, 0.299, 0.334 dan 0.337. Nilai purata nisbah Poisson untuk jasad batuan bergred I, II, III dan IV ialah 0.274, 0.320, 0.345 dan 0.345. Nilai nisbah Poisson jasad batuan menjadi semakin besar apabila gred terluluhawa menjadi semakin besar. Nilai purata nisbah Poisson jasad batuan gred II, III dan IV bertambah sebanyak 16.8%, 25.9% dan 25.9% jika dibandingkan dengan jasad batuan gred I. Keadaan ini berlaku kerana perubahan retakan pada jasad batuan gred I adalah lebih besar apabila mengalami proses terluluhawa. Perubahan retakan menjadi semakin kecil apabila mengalami proses terluluhawa seterusnya. Tiada perubahan retakan berlaku pada jasad batuan gred III apabila menjadi jasad batuan gred IV.

Kata kunci: Analisis gelombang permukaan berbilang saluran; analisis spektral gelombang permukaan; nisbah Poisson; seismos biasan

ABSTRACT

The mechanical parameters such as Poisson ratio are input parameter for rock engineering especially in numerical modeling computer software. Seismic methods were utilized to determine Poisson’s ratio for fresh (grade I), slightly weathered (grade II), moderately weathered (grade III) and highly weathered (grade IV) rock masses. Poisson’s ratio for each layer of rock mass was determined based on average value of compressive wave (Vp) and shear wave (Vs) velocities at respective depth. Compressive wave velocities (Vp) were determined by seismic refraction method and shear wave velocities (Vs) were determined by spectral analysis of surface wave (SASW) method or multichannel analysis of surface wave (MASW) method. A total of 66 seismic tests were carried out on 9 rock mass slopes comprising 6 tests on 1 granitic rock mass slope at Quarry JKR, Bukit Penggorak, Kuantan, Pahang; 26 tests on 4 granitic rock mass slopes at Kuari Kajang Rock, Semenyih, Ulu Langat, Selangor; 12 tests on 1 granitic rock mass slope at Lebuhraya Silk Kajang (km 14.6) Selangor; 14 tests on 2 schistose rock mass slopes at Jalan Kuala Kubu Baru-Bukit Fraser (km 15), Selangor and 8 tests on 1 quartzitic rock mass slope at Section U10, Bukit Cherakah, Shah Alam, Selangor. From the seismic tests, the maximum values of Poisson’s ratio for grade I, II, III and IV rock masses were 0.295, 0.335, 0.355 and 0.364. The minimum values of Poisson’s ratio for grade I, II, III and IV rock masses were 0.215, 0.299, 0.334 and 0.337. The average values of Poisson’s ratio for grade I, II, III and IV rock masses were 0.274, 0.320, 0.345 and 0.345. The values of Poisson’s ratio for rock masses were increased when the weathering grade increased. The average values of Poisson’s ratio for grade II, III and IV rock masses increased 16.8%, 25.9% and 25.9% if compare to grade I rock mass. This scenario occurred because fracture changes on grade I rock mass were bigger when experienced weathering processes. The fracture changes became smaller when experienced weathering processes further on. No fracture change occurred on grade III rock mass when became grade IV rock mass.

Keywords: Multichannel analysis of surface wave; poisson’s ratio; seismic refraction; spectral analysis of surface wave

RUJUKAN

Arnie Salfarina Arshad. 2005. Pengelasan dan pencirian geologi kejuruteraan batuan di kuari JKR Bukit Penggorak Kuantan, Pahang Darul Makmur. Tesis Sarjana Muda Sains, Universiti Kebangsaan Malaysia. (Tidak diterbitkan)

Baizura Yunus, N., Ghani Rafek, A., Goh, T.L. & Hariri Arifin, M. 2009. Quantification of granite rock material weathering grades employing the Schmidt hammer rebound testing: Malaysian examples. Proceeding of Regional Conference on Environmental and Earth Resources: 169-174.

Bignell, J.D. & Snelling, N.J. 1977. Geochronology of Malayan granites. Overseas Geology and Mineral Resources 47: 77.

Gobbett, D.J. & Hutchison, C.S. 1973. Geology of the Malay Peninsular. New York: John Wiley & Sons.

Goh, T.L. 2008. Pencirian jasad batuan menggunakan kaedah SASW di Kuari JKR Bukit Penggorak, Kuantan, Pahang dan Bukit Tampoi, Dengkil, Selangor. Tesis Sarjana Sains, Universiti Kebangsaan Malaysia. (––do––)

Goodman, R.E. 1989. Introduction to Rock Mechanics. Ed. Ke-2. New York: John Wiley & Sons.

Hariri Arifin, M. Ghani Rafek, A. Goh, T.L. & Baizura Yunus, N. 2009. The use of Schmidt rebound hammer as a method to estimate the degree of weathering for metamorphic rocks from Malaysia. Proceeding of Regional Conference on Environmental and Earth Resources: 175-180.

Hutchison, C.S. 1972. Metamorphism. Dlm. Geology of the Malay Peninsular, disunting oleh Gobbett, D.J. & Hutchison, C.S. Hlm. 150-178. New York: John Wiley & Sons.

ISRM. 1981. Rock characterization, testing and monitoring. Dlm ISRM suggested Methods, disunting oleh Brown, E.T. Oxford: Pergamon Press.

Kansas Geological Survey 2007. http://www.kgs.ku.edu, [29, November 2007].

Lee, C.P. 1996. Probable reasons for paucity of the fossil record in the Kenny Hill formation. Warta Geology 22(2): 84-85.

Mohd Khairul Azmi. 2007. Anistoropi seismos batuan granit sebagai penunjuk kualitatif orientasi ketakselanjaran utama. Tesis Sarjana Sains, Universiti Kebangsaan Malaysia. (––do––)

Park, C.B. 2006. SurfSeis - Active and Passive MASW. User’s Manual V2.0. Kansas: Kansas Geological Survey.

Roe, F.W. 1951. The geology and mineral resources of the Fraser Hill area Selangor, Perak and Pahang, Federation of Melaya with account of mineral resources. Geological Survey Department Federation of Malaya. Kuala Lumpur: Caxton Press LTD.

Ser, K.Y. 2007. Pencirian geomekanik jasad batuan granit, Kuari Kajang Rock di Mukim Semenih, Hulu Langat, Selangor. Tesis Sarjana Muda Sains, Universiti Kebangsaan Malaysia. (––do––)

Sjogren, B., Ofsthus, A. & Sandberg, J. 1979. Seismic classification of rock mass qualities. Geophysical Prospecting 27(2): 409-442.

Suharsono & Abdul Rahim Samsudin. 2003. The attenuation effects of surface wave propagations on rock mass using SASW method. Bulletin Geological Society Malaysia 46: 475-478.

Tjia, H.D. 1976. Overturned structures in Kenny Hill formation, Selangor. Warta Geologi2(4): 63-65.

*Pengarang untuk surat-menyurat; email: gdsbgoh@gmail.com