Residual shear strength of shales from the Gemas Formation based on ring shear tests

Warta Geologi, Vol. 46, No. 3
Author : J. K. Raj
Publication : Warta Geologi
Page : 179 - 185
Volume Number : 46
Year : 2020
DOI : doi.org/10.7186/wg463202001

Warta Geologi, Vol. 46, No. 3, December 2020, pp. 179–185

 

Residual shear strength of shales from the Gemas
Formation based on ring shear tests

 

J. K. Raj

83, Jalan Burhanuddin Helmi 2, Taman Tun Dr. Ismail, 60000
Kuala Lumpur, Malaysia

Email address: jkr.ttdi.tmc@gmail.com

 

Abstract:
Fresh, dark grey to black, shales with minor sandstones of the Triassic Gemas
Formation outcrop at the slope cut between Km 81.30 and 81.05 (southbound) of
the North-South Expressway near Ayer Hitam in Johore State. The beds strike 165°
with eastward dips of 35° to 43° and have thickness of between 0.2 and 1.5 m.
Over-lying the fresh bedrock along an irregular boundary is a bleached zone,
some 14 to 18 m thick, comprising light grey to white, in situ oxidized shales
and sandstones. Three samples were collected from a thick shale bed; fresh
samples A and B at 18 m and 15 m depth, respectively, and a bleached shale
sample C at 11 m depth. All samples were air dried, finely ground, and then
passed through a wire mesh sieve with 180 μm aperture sieve. The remoulded
samples were tested with the Bromhead ring shear apparatus, employing the
pre-shearing test procedure with multi-stage loading. Plots of shear stress
versus cumulative horizontal shear displacement under low normal stresses
(<150 kPa) yield failure envelopes with residual friction angles of 27.4°,
27.4° and 27.9° for samples A, B, and C, respectively. Under moderate to large
normal stresses (150-350 kPa), plots of shear stress versus linear displacement
sometimes slope upward due to increased friction as a result of sample
extrusion and settlement of the top platen. It is concluded that the
pre-shearing test procedure with multi-stage loading is best suited for low to
moderate, effective normal stresses (<250 kPa). Based on the test results,
the residual friction angle for shales from the Gemas Formation is between 27°
and 28°.

 

Keywords:
Gemas Formation, shale, ring shear tests, residual friction angle

 

DOI :
https://doi.org/10.7186/wg463202001

 

ISSN
0126–5539; e-ISSN 2682-7549


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