Scholarly article on topic 'Using the Schmidt Hammer on Rock Mass Characteristic in Sedimentary Rock at Tutupan Coal Mine'

Using the Schmidt Hammer on Rock Mass Characteristic in Sedimentary Rock at Tutupan Coal Mine Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Singgih Saptono, Suseno Kramadibrata, Budi Sulistianto

Abstract The uniaxial compressive strength is one of important parameter to determine the shear strength of rock mass by the rock classification method. To determine uniaxial compressive strength used by a testing on laboratory or in practically can use t he index method, in this research, alternatively is to use Schmidt Hammer. A method used Schmidt Hammer to determine the uniaxial compressive strength of rock is to calibrate between Schmidt Hammer Rebound (R) and uniaxial compressive strength test of laboratory and its the results are an empirical equation. The advantage of this method can practically to assess the strength of rocks in the field. At this paper is one of the alternative uses of the uniaxial compressive strength determining in sedim entary rocks in Warukin Formation at Tutupan open pit coal, South Kalimantan, Indonesia. And the next research is going to process towards another formation.

Academic research paper on topic "Using the Schmidt Hammer on Rock Mass Characteristic in Sedimentary Rock at Tutupan Coal Mine"

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Procedía Earth and Planetary Science 6 (2013) 390 - 395

International Symposium on Earth Science and Technology, CINEST 2012

Using the Schmidt Hammer on Rock Mass Characteristic in Sedimentary Rock at Tutupan Coal Mine

Singgih Saptono , Suseno Kramadibrata , Budi Sulistianto a*

a Universitas Pembangunan Nasional "Veteran " Yogyakarta, Yogyakarta 55283, Indonesia b Institut Teknologi Bandung, Bandung 40191, Indonesia

Abstract

The uniaxial compressive strength is one of important parameter to determine the shear strength of rock mass by the rock classification method. To determine uniaxial compressive strength used by a testing on laboratory or in practically can use the index method, in this research, alternatively is to use Schmidt Hammer. A method used Schmidt Hammer to determine the uniaxial compressive strength of rock is to calibrate between Schmidt Hammer Rebound (R) and uniaxial compressive strength test of laboratory and its the results are an empirical equation. The advantage of this method can practically to assess the strength of rocks in the field. At this paper is one of the alternative uses of the uniaxial compressive strength determining in sedimentary rocks in Warukin Formation at Tutupan open pit coal, South Kalimantan, Indonesia. And the next research is going to process towards another formation.

1. Introduction

The management of Open Pit Adaro coal mine is very concerned with keeping slopes stable because the pit is currently being mined at a very deep level, about 190 m below the original surface, some areas are very steep and it stretches 17 km from south to north east. The coal bearing strata is dominated by weak and friable to medium strong sandstone and mudstone of young formation (Warukin Formation) and in particular the mine experiences high rainfall. Having learned the local environmental condition, it is apparent that the most influence factor to the potential slope failure is the strength deterioration of the coal bearing strata. Currently, the coal mining in Tutupan mine PT. Adaro Indonesia has reached a depth of more than 190 m with elevations as low as -98 mRL and this will get deeper to a depth of -204 mRL in order to fulfill the world coal demand. One of method determine uniaxial compressive strength is index method the Schmidt Hammer (SH).

The SH originally designed for testing the hardness of concrete in 1948 was first used in a geomorphological context in the 1960s. The SH have become the advantages and disadvantages of the device for measuring rock characteristics and has been used for an increasing range of purposes, including the study of various weathering phenomena a range.

* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address: author@institute.xxx .

1878-5220 © 2013 The Authors. Published by Elsevier B.V.

Selection and/or peer review under responsibilty of Institut Teknologi Bandung and Kyushu University. doi:10.1016/j.proeps.2013.01.051

2. Previous Studies

The instrument measures the distance of rebound of a controlled impact on a rock surface. There are now several version of the hammer. The 'N' type it can provide data on a range of the rock types from weak to very strong with compressive strengths that range from 20 to 250 MPa. The 'L' type hammer has an impact tress time lower than the'N' type and the 'P' type is a pendulum hammer for testing materials of very low hardness, with compressive strength of less than 70 kPa. When the SH is pressed against a surface, its piston is automatically released onto the plunger. Part of the piston's impact energy is consumed by absorption and is transformed into hear and sound. The remaining energy represents the impact penetration resistance of the surface. This enables the piston to rebound. The distance traveled by the piston after it rebounds is called the rebound value (R). Harder rocks have higher R values (Gaudie, 2006). Rebound values are influenced by gravitational forces to varying degrees so that non-horizontal rebound values must be normalized with reference to the horizontal direction (Day &Gaudie, 1977). The R Value is shown by a pointer on a scale on the side of the instrument (range 10 - 100). It us therefore important that the Schmidt Hammer is used with care and that it is properly calibrated (McCarroll, 1987).

A very substantial number of R value has been obtained from many different rock types in many parts of the world (Gaudie, 2006). At one end of the scale 'weak' rocks such as chalk, aeolianite and marls have low compressive strength. At the other end, silicates, very hard limestones, quarzites, and various igneous rocks many have values that exceed 60, and very occasionally 70.

Goudie (2006) made conclusion of used of the SH that the SH is a convenient means of establishing rock hardness in the field, providing that certain precautions are taken in the light of its known limitations. Portable, cheap, free from operator variance, simple and easy calibrated and free from any noticeable temperature effects, it can with due care produce rock hardness values that correlate well with such parameters as uniaxial compressive strength or Young's Modulus of Elasticity.

The SH tests are increasingly quantitative. The latter is recommended for obtaining estimates of wall strength for subsequent calculation of shear strength, when utilizing the wall roughness coefficient (JRC) described under roughness.

Selby (1993) has divided rocks up into 6 classes (Table 1). This provides a useful basis for classifying rocks and forgiving a clear indication of a rock's character.

Because of its speed, simplicity, portability, low cost and non-destructiveness, the SH has been used as a means of estimating other rock properties, such as compressive strength (Sendir, 2002). Various researchers have studied the relationship between rock compressive strength and SH R values as shown Table 2. The R2 value has range between 0.7 and 0.99 (Yasar&Erdogan, 2004). The regressions vary greatly between different rock type, however (Dincer et al., 2004) and so should be used only for particular lithologies (Sachpazis, 1990). Nonetheless, as Hack and Huisman (2002) point out, a large number of simple test in the filed, using the SH, will tend to give a better estimate of the intact rock strength at various location than a limited number of more complex test.

3. Proposed Equation

As mentioned before that the equation of SH (Goudie, 2006) include the UCS of varied rock that is obtained from non-tropical countries. The samples are obtained from coal bearing strata that is located in the tropical country so that rock strength deterioration due to weathering is taken into account. The weathering process is simulated through slake durability tests. It is expected that the proposed equation will be more representative than the previous one in the application for estimate for uniaxial compressive strength in Indonesian open pit coal mine.

Rock mass characterization studies produce empirical equation relationship between the uniaxial compressive strength and the SH Rebound (R) shown the power function (Figure 1).

The previous researchers gave the R value for mudstone and sandstone that varies is between 10 and 38.6 for the mudstone and 10 to 44.7 for sandstone (Table 3). While the value of R for the mudstone and sandstone of the cover turned out to be among the respective 10 - 26 and 10 - 28.

The previous researchers provide empirical equation of the relationship uniaxial compressive strength and Schmidt Hammer Rebound with varied functions, logarithmic functions, exponential, power, and linear (Table 4). The purposed empirical equation for estimate UCS to weak rock on the coal bearing strata in Warukin Formation, is:

UCS = 0.308R1327

where: UCS= uniaxial compressive strength (MPa), R = Schmidt hammerrebound

Table 1. Approximate strength classification of rocks (Selby, 1993)

Description Uniaxial Point load Schmidt Characteristic rocks

compressive strength Hammer N-

strength, IS(50), MPa Type, 'R'

Very weak rock - 1-25 0.04-1.0 10-35 Weathered weakly

Crumbles under shrap blows Compacted sedimentary

with geological pick point, rocks-chalk, rock salt

can be cut with pocket knife.

Weak rock - shallow 25-50 1.0-1.5 35-40 Weakly cemented

Cuts or scraping with pocket Sedimentary rocks - coal

knife with difficulty, pick siltstone, also schist

point indents deeply with

firm blow

Moderately strong 50-100 1.5-4.0 40-50 Competent sedimentary

rock - knife cannot be used to Rocks - sandstone shale, slate

scrape or peel surface,

shallow indentation under

firm blow from pick point

Strong rock - hand-held 100-200 4.0-10.0 50-60 Competent igneous and

sample breaks with one m Metamorphic rocks - marble,

firm blow from hammer end granite, gneiss

of geological pick

Very strong rock - >200 >10 >60 Dense fine-grained igneous

requires many blows a snd metamorphic rocks -

from geological pick to quartzite, dolerite, gabbro,

break intact sample basalt.

Figure 1. The relationship between uniaxial compres- sive strength and the Schmidt Hammer Rebound (R)

Table 2.Correlation between Schmidt hammer rebound and uniaxial compressive strength and Young's modulus (Gaudie, 2006)

Equation R2 Reseacher Lithology

UCS = 6.9 x 10(00087^R + 016) 0.94 Deere and Miller (1966) varied

UCS = 6.9 x 10(L348^R " 1325) - Aufmuth (1973) varied

UCS = 0.447exp(0.045(R + 3.5) + y) - Kidybinski (1980) Coal, Shale, mudstone

UCS = 2R 0.72 Singh et al. (1983) Sandstone, siltstone

UCS = 0.4RLM - 3.6 0.94 Sheorey et al. (1984) Coal

UCS = 0.994R - 0.383 0.70 Haramy and De Marco (1985) Coal

UCS = 702R - 1104 0.77 O'Rourke (1989) Sandstone

UCS = 2.208e0.067R 0.96 Katz et al. (2000) Limestone, sandstone

UCS = exp(0.818 + 0.059R) 0.98 Yilmaz and Sendir (2002) Gypsum

UCS = 2.75R - 36.83 - Dincer et al (2004) Andesite, basalts, tuffs

UCS = 2.22R - 47.67 E - Aggistalls et al (1996) Gabbros, basalts

i, E = 6.95y2R - 1.14 x 106 0.88 Deere and Miller (1966) Varied

E = 6 9 x 10°06 l^R) + 186) - Aufmuth (1973) varied

E = 0.00013R3 09074 0.99 Katz et al. (2000) Syenite, granite

E = exp(1.146 + 0.054R) 0.91 Yimaz and Sendir (2002) gypsum

UCS = Uniaxial compressive strength (MPa), E = Young's modulus (MPa), R = Schmidt hammer rebound number, y = rock density (gr/cm3) (Yasar&Erdogan (2004)

Table 3. Schmidt Hammer rebound (R) of sandstone and mudstone

No Lithology Country Schmidt hammer 'R' researchers

1 Mudstone Jepang 10.5 - 32 Hayakawa &Matsukara (2003)

2 Mudstone Ankara, Turkey 27.1 - 38.6 Gokceogal&Aksoy (2000)

3 Mudstone Kaikoura, New Zealand 32 - 35 Stephenson & Kirk (2000)

4 Mudstone Tutupan, Indonesia 10 - 26 Saptono&Kramadibrata

5 Sandstone Ankara, Turkey 18.3 - 33.6 Gokceogal&Aksoy (2000)

7 Sandstone South East, Jordan 41 - 44.7 Goudie, et al (2002)

8 Sandstone Tutupan, Indonesia 10 - 28 Saptono&Kramadibrata

Table 4. Proposed equation correlation between Schmidt hammer rebound and uniaxial compressive strength

Equation R2 Researcher Lithology

UCS = 6.9 x 10l00087vR + 0161 0.94 Deere & Miller (1966) varied

UCS = 6.9 x 10[1348 W - 13251 - Aufmuth (1973) varied

UCS = 0.447exp[0045(R + 3'5) + 1,1 - Kidybinski (1980) coal, shale, mudstone

UCS =0.308 R1327 0.90 Saptono&Kramadibra ta sandstone, mudstone

UCS = 2R 0.72 Singh et al (1983) sandstone, mudstone

UCS = 2.75R - 36.83 - Dincer et al (2004) Andesite, basalt, tuff

UCS = 702R - 1104 0.77 O'Rourke (1989) sandstone

4. Concluding Remarks

Determination of measurement the weak rock strength in the field we need a method that is fast, easy and precise so one of method is to use the index measuring device, which use Schmidt Hammer Rebound. Its result is a function empirical equation of relationship between uniaxial compressive strength and Schmidt hammer rebound (R). This research would be to replace qualitative geological hammer in sedimentary rock in coal bearing strata in Warukin Formation. This research is going to process towards another formation in tropical country as Indonesia.

Acknowledgements

Thanks to the Management of PT. Adaro Indonesia which continues to support the research of rock mass characterization and would you like to thank the students, laboratory staff and technicians involved in this research.

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