Sains Malaysiana 39(6)(2010): 989–997

Micro-structure and Engineering Behaviour of Weakly Bonded Soil

(Mikro-struktur dan Sifat Kejuruteraan Tanah Berikatan Lemah)

Z. Ali Rahman*

Faculty of Sciences and Technology, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor, Malaysia

D.G. Toll

School of Engineering, University of Durham, South Road Durham DH1 3LE

England, United Kingdom

D. Gallipoli

Department of Civil Engineering, University of Glasgow

Glasgow G12 8LT, Scotland, United Kingdom

M.R. Taha

Faculty of Engineering and Architecture

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Diserahkan: 5 Oktober 2009 / Diterima: 30 April 2010

ABSTRACT

This study was carried out to investigate the undrained behaviour of weakly bonded soil. Artificial specimens were used and were prepared from a mixture of sand and kaolin. The mixture was fired at 500¡C for 5 h to create uniform strength of artificial weakly bonding between sand particles. Based on microscopic observation of the specimens revealed that the fired kaolin formed bridges between the sand particles and most of the sand particles were entirely coated by kaolin. It was observed that very few sand grains made a direct grain to grain contact. The occurrences of inter-particle voids either isolated or connected to form larger voids. Fissures found in between the bonding and the grains were due to high temperature firing. A series of consolidated undrained tests (CU) were performed using conventional triaxial compression test. The stress ratio curves for the bonded specimens showed a significant peak at early strain and the values of maximum stress ratios dropped with increasing applied confining stresses. For the destructured (or unbounded) specimens, no apparent peaks were observed and the stress values were slightly lower compared to that of bonded specimens. The bounding surface for the destructured specimens is represented by a straight line equivalent to stress ratio of 1.24. This line is equivalent to strength parameters of internal friction angle, φ’ and cohesion intercept, c’ of 31o and 21 kPa, respectively. Meanwhile, the bounding surface for the bonded specimens is indicated by some curvature at low stress (p′<150 kPa) and high stresses (p′>1100 kPa). The study clearly suggested the role of bonding on the engineering behaviour of residual soils in undrained conditions.

Keywords: Bonded soil; residual soil; undrained tests; void ratio

ABSTRAK

Kajian telah dilakukan bagi menyiasat sifat tidak bersalir bagi tanah berikatan lemah. Spesimen buatan telah digunakan dan disediakan daripada campuran pasir dan kaolin. Campuran tersebut dibakar pada suhu 500¡C selama 5 jam untuk menghasilkan ikatan lemah buatan dengan berkekuatan sekata antara butiran pasir. Pemerhatian mikroskop terhadap spesimen mendedahkan pembentukan jejambat kaolin di antara butiran pasir dan kebanyakan partikel pasir disaluti oleh kaolin. Sedikit persentuhan terus antara butiran ke butiran diperhatikan. Kehadiran reruang antara butiran sama ada terasing atau berhubungan membentuk reruang yang lebih besar. Rekahan-rekahan yang ditemui di antara pengikatan dan butiran adalah disebabkan oleh kesan pembakaran pada suhu yang tinggi. Siri ujian terkukuh tidak bersalir (CU) telah dilakukan menggunakan ujian konvensional mampatan tiga paksi. Lengkok-lengkok nisbah tegasan bagi spesimen berikatan menunjukkan puncak yang ketara pada awal terikan dan nilai-nilai maksima nisbah tegasan menyusut dengan peningkatan tegasan mengurung yang digunakan. Bagi spesimen tak berstruktur (tidak berikatan), tiada puncak yang jelas diperhatikan dan nilai-nilai tegasan adalah lebih rendah berbanding spesimen berikatan. Permukaan sempadan bagi spesimen tidak berikatan diwakili oleh garis lurus setara dengan nisbah tegasan 1.24. Garisan ini setara dengan parameter kekuatan bagi sudut geseran dalam, φ’ dan pintasan jelekit, c’ masing-masing sebanyak 31o dan 21 kPa. Manakala permukaan sempadan bagi spesimen berikatan pula ditunjukkan oleh sedikit lengkungan pada tegasan rendah (p′<150 kPa) dan tegasan tinggi (p′>1100 kPa). Kajian ini jelas mencadangkan peranan pengikatan di dalam lakuan kejuruteraan tanah baki dalam keadaan tidak bersalir.

Kata kunci: Nisbah liang; tanah baki; tanah berikatan; ujian tidak bersalir

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*Pengarang untuk surat-menyurat; email: zarah1970@ukm.my