Abstract—Land subsidence is a phenomenon that we often see in

the big cities that stood above the sediment layer, one of them is Jakarta. Land subsidence can occur due to many factors, including excessive extraction of ground water without offset by the inclusion of ground water through the watershed, loads exerted by the buildings, contents of clay minerals in the area consisting of expansive soils, or may also occur because of natural consolidation of soil. Atterberg limits of the test results with analytical methods of Casagrande (1948) in general, soil types in the study area have low to very high plasticity, including MH( high plasticity silt), CL( low plasticity clay), and CH( high plasticity clay). With the results of the analytical methods of Gillot (1962) and Seed et. al. (1968) showed that clay soils in the study area had the lowest activity number of 0.74 and a maximum of 1.35 which is the soil with high to very high activity, while the method of Williams and Donaldson (1980), in Hunt (2007), is the potential for the expanding (swelling)is very high. Based on the analysis of grain size, the research area can be grouped into 4(four) sediment texture units, namely: clay, silt, fine sand and medium sand. From the analysis of SEM (Scanning Electron Micrograph) and X-RD (X-ray diffraction), cay minerals in the investigation area showed that the Montmorillonite and Kaolinite minerals are dominant. Based on the graphs, the relation between activity number and the number of collisions on the SPT can be seen that the withdrawal of a linear line between the point spread that reflects the higher number of collisions, lower activity numbers. Where, the percentage of clay fraction is quite instrumental in this, so the magnitude of the percentage of the amount of the clay fraction contributed to greater number of collisions and inversely proportional to the activity which means the low number of activities, and vice-versa.

Keywords—clay minerals, land subsidence, Atterberg limits,

SEM. X-RD, SPT.

I. INTRODUCTION Background of the study:

AND is a material that cannot be separated from the lives of the early formation of the Earth until now. However, behind its use of land can also be turned into a disaster for

us. Md. Anisuzzaman 1, Dicky Muslim2, Nabila Shadrina4 are with Faculty of Geological Engineering, University of Padjadjaran; West Java; Indonesia; Arifuzzaman3, with Department of Civil Engineering, UITS, Dhaka, Bangladesh: (e-mail: anisuzzaman.ru@gmail.com).

Soil in the sense of engineering can be defined as an aggregate composed of mineral grains (with or without organic matter), structure and texture that can be easily separated, due to weathering, water and wind power. Soil also plays an important role in development because it can serve as a foundation and as a supporter of building construction materials. [4] Sediment layers in the Jakarta area is younger sediments derived from sedimentation - sedimentation of streams that are generally composed of alluvium. In alluvium soils typically contain clay minerals whose type depends on the parent rock, climate, and other factors. Proportion of clay minerals containing significant expansive clays, such as Montmorillonite, will respond to changes in water content as it expands (swelling) and shrink (shrinking). This kind of expansive soil behavior can cause problems in civil construction including geotechnical (roads, bridges, buildings, etc.) marked symptoms cracked the structure. [6]. The authors examine land subsidence in Jakarta Special Capital Region as it is an ongoing problem in the city and can result not only in damage to infrastructure, can also expand the area of flood inundation in the city. Thus, research needs to determine the exact cause of land subsidence in Jakarta to resolve the problems caused by land subsidence, as well as reduce risks that will occur in buildings that stood on the expansive ground.

Fig. 1 Map of land subsidence in Jakarta period 1982-1997(Centre for Environmental Geology, Geological Agency, ESDM)

The Role of Clay Minerals on Land Subsidence: A Case Study in Jakarta, Indonesia

Md. Anisuzzaman 1, Dicky Muslim2, Arifuzzaman3, and Nabila Shadrina4

L

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II. METHODOLOGY The methodology used in this study is to observe the surface and the subsurface. Investigations include mapping the distribution of surface soil and rocks, forms of the landscape and the subsurface structures. In this evaluation qualitative and semi-quantitative methods are used. Qualitative methods include processing and interpretation of aspects of the landscape, the local color, the texture of the soil, and so on to get information interpretive lithology and geological structure. Furthermore, qualitative methods are supported by field observations and laboratory tests of soil mechanics and physical/ engineering properties of the sol and rocks to get a picture of the end of the engineering geological conditions of the area. To identify the mineral content of clay in the area of research, conducted mineralogical testing are:

1. Scanning Electron Micrograph (SEM): Tests carried out using the Scanning Electron Microscope JEOL JSM-6360LA are equipped with energy dispersive spectrometer (EDS).The test is performed to obtain the images of the object minerals. This tool can magnify objects up to 300,000 times and determine the level of chemical element is semi-quantitative.

Fig. 2 Scanning Electron Micrograph (SEM)

2. X-ray diffraction (XRD): Testing using X-ray diffraction equipment PANalytical X'Pert PRO PW3040/x0. Testing was conducted to identify the types of minerals contained in the rock, either in total or specific clay minerals.

Fig. 3 X - ray diffraction (XRD) equipment.

III. RESULTS AND DISCUSSION Results of Laboratory analysis:- To know more details about the physical and engineering

properties of the soil samples, some laboratory tests are performed, such as:

A. Physical Properties of the soil: TABLE I

PHYSICAL PROPERTIES OF THE SOIL No.

Sample

Moisture

of soil

(ω, %)

Unit weight

(γ, gr/cm3),

Specific

Gravity

(SG)

TS – 1 47,99 1,708 2,640

TS – 2 42,22 1,759 2,615

TS – 8 73,09 1,540 2,560

TS – 9 33,00 1,826 2,569

TS – 10 50,35 1,626 2,524

TS – 12 48,89 1,581 2,719

TS – 14 46,81 1,610 2,492

B. Atterberg Limit Tests:

This test is intended to determine the physical behavior of fine-grained soil (silt and clay) when the water level is changed. Parameters obtained from this test are liquid limit (LL), plastic limit (PL) and plastic index (PI). By knowing these parameters then a general soil properties can be known.

TABLE II

TEST RESULTS OF ATTERBERG LIMIT OF THE SAMPLES No.

Sample

Laboratory test results

Moisture of

soil

(%)

Liquid

limit (%)

Plasticity

limit (%)

Plastic

index (%)

TS-1 47,99 77,54 25,80 51,74

TS-2 42,22 49,90 21,02 28,88

TS-8 73,09 87,72 38,42 49,30

TS-9 33,00 107,60 37,43 70,16

TS-10 50,35 65,82 27,96 37,85

TS-12 48,89 102,34 34,60 67,75

TS-14 46,81 98,60 36,09 62,51

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C. Casagrande Method(1948): From the results of laboratory tests using Casagrande method (1948) [2] there are three (3) properties of the soil, namely MH (organic silt or diatomic fine sand, elastic silt), CH (high plasticity inorganic clay) and CL (inorganic clay with low to medium plasticity).

Fig. 3 Diagram of Casagrande method (1948)

D. Gillot Method (1968) and Method of Seed, et. al.,

(1962): From the results of laboratory tests based on the analysis of

Atterberg Limits and grain size analysis of the soil samples in the study area has a number of activities ranging from medium to very high [1]. According to the diagram of Gillot method (1968) [3] and the method of Seed et al (1962) [5] each soil sample showed mixed results, namely:

TABLE III

TEST RESULTS OF ACTIVITY NUMBER OF THE SAMPLES No. Sample Activity number Activity

TS – 1 0,74 High activity

TS – 2 1,06 High activity

TS – 8 1,33 Very high activity

TS – 9 1,07 Very high activity

TS – 10 1,26 Very high activity

TS – 12 1,35 Very high activity

TS – 14 0,96 High activity

Fig. 4 Diagram of Gillot method (1948)

E. Method of Williams and Donaldson, 1980, in Hunt, 2007): From the results of laboratory analysis by method of Williams and Donaldson, 1980, in Hunt, 2007) [7] each sample has a number of diverse activities are very high that indicates the potential for expanding (swelling) of land along the North Coast of Jakarta is quite high.

F. Grain size analysis: Based on the grain size analysis, the investigation area can

be grouped into four units of sediment texture are clay, silt, fine sand, medium sand.

G. Scanning Electron Micrograph (SEM) analysis: SEM analysis indicating the type of clay minerals with magnification 10 μm – 50 μm was performed on seven samples taken throughout the study area

Fig. 5 Diagram of Seed et. al., method (1962)

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Fig. 6 Diagram of Williams and Donaldson method, (1980, in

Hunt, 2007)

Fig.7 showing the mineral Kaolinite (Nacrite) and Montmorillonite.

H. X-RD (X-ray diffraction) analysis: The results of the analysis of X-RD (X-ray diffraction) showed

that the types of minerals that generally exist in the study area are Kaolinite and Montmorillonite.

The relationship between the activity number and the number of collisions (N) in the SPT:- From the following graph, it can be seen that the withdrawal of a linear line between the point spread that reflects the higher number of collisions, the number of smaller activities. Where, % of total clay fraction is quite a role in this, so the amount % of clay fraction has the higher number of collisions and inversely proportional to the activity which means that the low number of events, and vice versa.

Fig. 8 Relationship between number of impact(N) and activity

number(A).

IV. CONCLUSION The test results of the SEM (Scanning Electron Micrograph) showed that the dominant minerals in the study area are a kind of clay minerals with very high plasticity. Being the analysis of X-RD (X - ray diffraction) also showed that the dominant mineral types are clay minerals namely Montmorillonite and Kaolinite. Based on the analytical methods each of the clays in the study area has a number of high to very high activity suggesting that the potential for expanding (swelling) in the soil around the North Coast of Jakarta is very high.

REFERENCES [1] Bowles, J.E., 1989. Sifat-sifat Fisis dan Geoteknis Tanah (Mekanika

Tanah), Penerbit Erlangga, Jakarta, pp-562. [2] Casagrande, 1948. Sistem Klasifikasi Unified Soil Clasification System

(USCS), The U.S. Army Corps of Engineer and .The U.S. Bureau of Reclamation.

[3] Gillot, 1968. Clay in Engineering Geology. Elsevier Publishing Company, pp-234.

[4] Hirnawan, R.F., 1999, Modul: Geoteknik. Program Studi Teknik Geologi, Universitas Padjadjaran. Bandung.Not published.

[5] Seed, H.B., Wood Ward, R.J. and Lundgren, R.,1962, Prediction of Swelling Potential of Compacted Clays, Highway res. Board Bull:pp12-39.

[6] Tohari, Soebowo, Anwar, Ruslan, Siswandi, 2002. Pemetaan dan Perlindungan Lingkungan Daerah Perbukitan Serta Sifat Keteknikan Lempung Ekspansif Untuk Mendukung Perencanaan Tata Ruang. LIPI. Bandung

[7] Williams, A. A. B. and Donaldson, G., 1980. Building on expansive soils in South Africa. In Proceedings 4th International Conference on Expansive Soils, Denver, 2, 834–840.

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