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

Received: 5 January 2010 / Accepted: 21 May 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

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*Corresponding author; email: gdsbgoh@gmail.com