10th Asian Regional Conference of IAEG (2015)

Shear Strength Reduction of Tertiary Jatiluhur-Subang
Claystones Due to Swelling Processes
Imam A. SADISUN(1), Rendy D. KARTIKO(1), Arif KESUMANINGTYAS(1),Tri E. UTAMI(2) and Eddy SUCIPTA(1)(1) Geological Engineering Study Program, Faculty of Sciences and Technology, Institut Teknologi Bandung,Jl. Ganesha No.10, Bandung 40132, Indonesia
E-mail: imam@gc.itb.ac.id(2) Center for Groundwater Resources and Environmental Geology, Geological Agency, Indonesia

Abstract
Swelling processes of Tertiary Jatiluhur-Subang claystones have been received an extensive
attention since numerous engineering problems were found recently, such as along the Cipularang
toll road and in the development area of Sport Training Facility and Education Centre (P3SON)
Hambalang, West Java, Indonesia. Accordingly, this research was carried out to deal with theswelling characterization of these claystones by means of an unconfined swelling test. A series ofmineralogical analysis using X-ray diffraction (XRD) were also performed. Furthermore, in orderto know how the swelling processes give effects to the decrease in shear strength of the claystones,
a series of direct shear test was done for some samples having different immersion time. The
claystone commonly has a greenish gray to dark gray color, non-calcareous and massive/monotone(not showing layering structures). The unconfined swelling test indicates unrestricted swelling inall directions and results indicate a swelling strain magnitude as a function of time. The results forselected representative specimens of the claystone show nonlinear relationships between axial
swelling strain buildups and time during immersion. The swelling strain magnitude seemedsignificantly close relations to the occurrence of montmorillonite and the ratio of clay/non-clayminerals. The shear strength reductions of the claystones after 25 days immersion which occurs
along with the changes in swelling strain are quite varied, reaching up to 57%.
Keywords: Tertiary claystones, swelling, strain, montmorillonite, shear strength

This research was carried out to deal with thedetailed characterization of swelling by means of an
unconfined swelling test (Fig. 1), while doing visualobservation of slaking process that occurs during thetest (Table 1). As a case study, some claystones werecollected from some areas of the northern part ofWest Java Province, Indonesia. A series of laboratory
test of physical properties, including mineralogicalanalysis using X-ray diffraction (XRD) were also
performed. Furthermore, how the swelling andslaking processes give effects to the decrease in shear
strength of the claystones, a series of direct shear test
was done for some samples having different
immersion time. In general, the results of thisresearch will be very useful for determining theappropriate solution to anticipate problems dealingwith swelling and slaking processes.

1. Introduction
Swelling and slaking processes of claystones are
generally strongly influenced by changes in naturalconditions, such as changes in water content and/orin-situ stress conditions (Sadisun et al., 2002; Sadisun
et al., 2005; Czerewko and Cripps, 2006). Thesechanges will result in further rock deteriorations, ofwhich mostly characterized by strength degradation
and/or fracturing. Accordingly, swelling and slaking
processes have been received an extensive attention
since numerous engineering problems were foundrecently, such as along the Cipularang toll road, in thedevelopment area of Sport Training Facility andEducation Centre (P3SON) Hambalang and along theSemarang-Bawen toll road.

1

10th Asian Regional Conference of IAEG (2015)

Fig. 1 A schematic device of unconfined swelling test andstructural coordinate of dial gauge position
Table 1 Criteria for visually classifying claystones to slaking (Sadisun et al., 2005).

The unconfined swelling test indicates unrestricted
swelling in all directions and results indicate aswelling strain magnitude as a function of time. The
results for selected representative specimens ofSubang claystone are presented in the graphs showing
the axial swelling strain buildup versus time
relationships in two different plotting methods (Fig.
2). The relationships between axial swelling strain
buildups versus time exhibited the non-linear swellingstrain process during immersion. The swelling strains
seemed significantly influenced by occurrence ofmontmorillonite (widely known as expansive clay
mineral) and the ratio of clay/non-clay minerals.
Swelling strains in the vertical direction were most
likely to be higher than in the horizontal direction,
therefore it can be inferred that swelling strains of theclaystones are anisotropy.
It was also evident that swelling strain could be
generally divided into three distinct stages
representing the instantaneous, primary andsecondary swelling processes. The distinction on thestage of swelling strain also indicated that there was
likewise distinction in rate of swelling strain. The
increasing rate in swelling strain was commonly
somewhat rapid in the beginning, becoming slower ata moment and then faster until it eventually slows
down to a relatively steady state.

2. Petrographical characteristics of the claystones
The claystone samples used in this study were thencalled as Jatiluhur-Subang Claystones; a soft rockformation of Miocene to Pliocene ages within theBogor-Kendeng trough in the northern West Java area.
There were six samples used in this study, whichtaken by cutting blocks of rock outcrops. In this case,sample 1 was in the most weathered condition, on thecontrary to the sample 6 having the freshest condition.
Generally, the claystone has a greenish gray to darkgray color, non-calcareous, massive/monotone (notshowing layering structures), and is relatively
impermeable, with some thin intercalations of finegrained sandstone. The results from XRD analysis
have shown the composition of plagioclase, quartz,
montmorillonite, Illite and kaolinite with someoccasional muscovite and siderite. Porosity and watercontent were tend to increase in weathered claystones
than in fresh claystones, however unit weight wastend to decrease. Atterberg limits analyses showedthat all claystones can be categorized as CH (clayhigh plasticity).
3. Results and discussions: Swelling processes andshear strength reductions

210th Asian Regional Conference of IAEG (2015)

Fig. 2 Volumetric swelling strain indexes of Subang claystones for each different sampel

The rapid rate of strain at early stages of swelling
process revealed that rapid increase of specimen
volume was occurs at the first minutes after
immersion of the specimen into water, which wasvisually indicated by the initial development ofhairline cracks or visible traces of fissility (slaking
class 1). This process was might be caused byentrapped air pressure, which existed on dependent ofinitial rock water content, wetting or water uptakerates, and air thrust. The rate of water uptake wasaccelerated by the occurrence of capillary effect inwhere the water was forcedly moved towards
capillary paths.
The rate of swelling strain turned into slower at a
moment usually showing very low gradual increase ofstrain magnitude which was considered as theabsorption process of water into hairline cracks andspecimen itself without much increase of volume.
After the absorbed water began to open the hairline
cracks, it was then initially generated reaction
between the water and any expandable clay minerals
present, which in turn gave the highest rate of volume
increase. In this case, the highest rates of swellingstrain take place at 2-8 hours from the time thespecimen was immersed. Since it is widely known
that smectite is the main expandable clay mineral, it isinteresting to evaluate the variation of swelling strain
as a function of smectite content (Yevnin andZaslavsky, 1970; Moghal and Al-Shamrani, 2011).
At the latest stage and after most cracks had been
opened and filled with water (slaking class 3), the rateof displacement due to swelling strain slowed down
gradually until it reached a relatively steady state at
which no change in axial swelling strain could beobserved by the dial gauges. Based on these results, it
was important to be noted that owing to the surface (<3 m) and more weathered condition of claystones,
volume changes due to swelling process had atendency to decrease.
The decrease in shear strength of the claystones
after immersion occurs along with the changes inswelling strain and its accompanying slaking
processes. The relationship between the magnitude of
decrease in shear strength and increase in swellingstrain after 25 days immersion quite varied (Fig. 3).
Experimental results showed important reduction inboth cohesion and internal friction angle, but atdifferent rates, with the application of different lengthof immersion time. In general, the decreases in shear
strengths of the claystone are entirely ranging from45 % to 57 %.

Fig. 3 The relationship between swelling strain and shear strength for each different sampel3

10th Asian Regional Conference of IAEG (2015)

Sadisun, I. A., Shimada, H., Ichinose, M. and Matsui,
K. (2002): An experimental study of swellingstrain in some argillaceous rocks by means of an
improved unconfined swelling test. Proc. ISRM
Regional Symposium on Rock Engineering
Problems and Approaches in UndergroundConstruction, Seoul, Korea, pp. 227-234.

Acknowledgments
This research was supported by Research andInnovation Programs for Research Group 2014 ITB.
The authors would like to gratefully thank toArlangga V. Baskara, Misbahudin, Satrio Dwijayanto
and Teguh Winari who have involved in field survey.
References

Sadisun, I. A., Shimada, H., Ichinose, M. and Matsui,
K. (2005): Study on the physical disintegration
characteristics of Subang claystone subjected to amodified slaking index test. Geotechnical andGeological Engineering, Vol. 23, No. 3, pp. 199218.

Czerewko, M. A. and Cripps, J. C. (2006): The
implications of diagenetic history and weatheringon the engineering behaviour of mudrocks. Proc.
IAEG2006, Paper No. 424. The GeologicalSociety of London.

Yevnin, A. and Zaslavsky, D. (1970). Some factors
affecting compacted clay swelling. Canadian
Geotechnical Journal, Vol. 7, No. 1, pp. 79–91.

Moghal, A. A. B. and Al-Shamrani, M. A. (2011): On
the swelling characteristics of semi arid and arid
soils of Saudi Arabia. Proc. Indian GeotechnicalConference. Dec. 15-17, 2011, Kochi (Paper No.
B-026).

4