Warta Geologi, Vol. 47, No. 3, December 2021, pp. 217–225
Soil moisture retention characteristics of saprock from
the weathering profile over a biotite-muscovite granite in Peninsular Malaysia
John Kuna Raj
No. 83, Jalan Burhanuddin Helmi 2, Taman Tun Dr. Ismail,
60000 Kuala Lumpur, Malaysia
Email address: jkr.ttdi.tmc@gmail.com
Abstract:
The weathering profile at the slope cut near Km 16 of the Kuala Lumpur – Ipoh
trunk road can be differentiated into an upper, 11.8 m thick pedological soil
(zone I) and a lower, 31.9 m thick saprock (zone II) comprising silty sandy
gravels that distinctly preserve the minerals, textures and structures of the
original granite. In order to investigate the influence of particle size
distributions on soil moisture retention characteristics, saprock samples were
collected at depths of 26.53 m (Sample A), 31.29 m (Sample B) and 41.93 m
(Sample C). Samples A and B, with porosities of 37%, comprise 33% gravel, 27%
sand, 22% silt and 18% clay, and 31% gravel, 24% sand, 25% silt and 22% clay,
respectively. Sample C with a porosity of 44% consists of 24% gravel, 28% sand,
38% silt and 10% clay. Tests with the pressure plate method show increasing
suctions from 0 kPa through 0.98 kPa and 9.8 kPa to 33 kPa and 1,500 kPa to
result in gravimetric soil moisture retentions of 31.9% through 28.6% and 23.3%
to 16.9% and 6.8% in sample A, of 32.1% through 24.9% and 21.5% to 17.8% and
7.4% in sample B, and of 31.5% through 30.3% and 27.30% to 23.5% and 9.5% in
sample C. Regression analyses of gravel, sand and clay contents plotted against
moisture contents retained at high suctions (33 kPa and 1,500 kPa) yield
negative trends with variable correlation coefficients (R2), though
plots involving silt contents yield positive trends with large correlation
coefficients (R2 >0.9966). It is concluded that adsorption of
water on surfaces of silt sized particles (of mainly sericite derived from
weathering of feldspars) that gives rise to the retention of soil moisture in
saprock.
Keywords:
Biotite-muscovite granite, saprock, soil moisture retention, silt content
DOI :
https://doi.org/10.7186/wg473202104
ISSN
0126–5539; e-ISSN 2682-7549
