COMPARATION OF PC’ AND CV VALUE IN CLAY BY USING ALTERNATIVE METHODS Rico Cahyadii Gouw Tjie Liongii i
Universitas Bina Nusantara, E-mail:
[email protected] ii Universitas Bina Nusantara, Kode Dosen: D3183
ABSTRAK Parameter Pc’ dan juga Cv merupakan parameter yang penting untuk dapat memprediksi penurunan tanah dengan baik. Penurunan tanah yang tidak diprediksi dapat mengakibatkan kerusakan pada sebuah struktur bangunan. Oleh karena itu diperlukan nilai parameter yang tepat dan sesuai. Pada analisis kali ini akan dilakukan penelitian untuk mencari nilai parameter yang paling baik menggunakan beberapa metode alternatif yang merupakan penurunan dari metode konvensional yang sudah ada dan metode alternatif yang baru. Penelitian nilai Cv akan menggunakan metode Taylor dan dibandingkan dengan metode Asaoka. Penelitian Pc’ akan menggunakan metode baru yang disebut parallel rebound method dan dibandingkan dengan metode Cassagrande konvensional. Kemudian dilakukan survei untuk melihat konsisten/tidaknya hasil metode-metode tersebut. Hasil penelitian menunjukkan nilai Cv metode Asaoka terbukti lebih baik dan berbanding terbalik dengan beban yang digunakan. Sedangkan untuk nilai Pc’ hasil survei yang didapat menggunakan parallel rebound method bersifat lebih konsisten dibandingkan metode Cassagrande. Kata kunci: Cassagrande, Asaoka, Taylor, penurunan, tanah
ABSTRACT Pc’ and Cv are important parameters that must be used to predict the consolidation settlement of soil. Incorrect settlement parameters will cause wrong prediction of settlement magnitude and rate, as a consequence the differential settlement shall also be incorrectly predicted. Therefore the parameters has to be more or less precisely derived. In this study, existing method in defining the above two parameters shall be reviewed, and be compared with alternative methods to determine the value of Cv, Taylor and Asaoka Methods shall be compared. For Pc’, convetional Cassagrande method shall be compared to a new method called Parallel Rebound Method. All the methods are taught to 30 students and then statically compared to find out which method give the lowest standard deviation. The result show that the value of Cv by using Asaoka method proved to give a better value and inversely proportional with the pressure that’s being used. For Pc’ value, the result show that a new proposed parallel rebound method has a more constant value that the Cassagrande method. Keywords: Cassagrande, Asaoka, Taylor, settlement, soil. 1
PREFACE Background Whether a building can rise or not is depends on how that building construct and the quality level of the materials that’s used to build that building. But, the main thing from the rise/or not a building is the strength of the base structure of that building. The base structure is useful to hold the building’s weight. Therefore the soil characteristics need to be studied before the building is getting build. The density’s level, the soil’s type through the ground water level must be known before building so that the lower structure can functioned properly. For example, the soil’s composition around the lower structure with a high ground water level will differ from the soil’s composition made from sands and has a low ground water level. A settlement that isn’t properly predicted can be a major problem especially if the lower structure had been made. It can cause the whole building to settle lower. The worst case is if the differential settlement is occur, it can cause many cracks and the building can totally collapse due to the differential in settlement to that building.
Problem Identification Pc’ and Cv are the parameters needed to determine the value and the degree of the consolidation. But the parameters value by using a conventional method oftenly give an inconsistent value. Therefore, a differential method from the conventional method is needed in order to get a more consistent and better value. So far to determine the value of Pc’ the Cassagrande method is used. But that method is a graphical method therefore the result will differ according to each user’s eyes. Whereas to determine the value of Cv value, Square root of time method is commonly used, but an error(s) can occur in the process so that the value of the settlement and the time oftenly didn’t give the right result.
Purpose and Benefits This research has a goal to determine the value of preconsolidation pressure (Pc’) and Cv from clay soil around DKI Jakarta region. The value is to be expected to give a more constant value. The benefits from this research is to simplify the calculation for the consolidation value that occur in that soil by using parameters Pc’ and Cv.
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RESEARCH METHOD Data Collecting Technique Data needed in this research is the result of the consolidation test including dial reading and graphic plot between void ratio and pressure. Those data was acquaired from the soil laboratorium in Jakarta.
Data Processing Technique The data are numbered so that it won’t swapped while the data are input into the excel. The excel program itself is selfmade and has a function to calculate for the Asaoka and Taylor methods. This program then will presented the graphic’s result from the data that have been processed.
Data Display Data that has been processed before then presented in graphics form to simplify the research’s result. In each graphs, the data are differentiated so that the difference can be seen clearly.
RESULT AND ANALYSIS Data Analysis Result Berikut adalah hasil dari pengolahan secara grafis dari data yang telah didapat:
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Gambar 1 Perbandingan Metode Taylor, Metode Asaoka dan hasil dari lab P.T. Solefound - Data no5 (atas) - Data no 6 (bawah)
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Gambar 2 Perbandingan Metode Taylor, Metode Asaoka dan hasil dari lab P.T. Solefound - Data no 7 (atas) - Data no 8 (bawah)
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Gambar 3 Perbandingan Metode Taylor, Metode Asaoka dan hasil dari lab P.T. Solefound - Data no 9 (atas) - Data no 10 (bawah)
From the graphic, the comparation of Cv value from the research and the value from P.T. Solefound Sakti can be seen. From the comparation, can be seen that Asaoka method give a much closer result to the P.T. Solefound Sakti compared with Taylor method. From this, it can be concluded that Taylor method needs an experienced user in order to get a better result. The increase at the beginning of the graph resulting the graph result to go high first then gradualy becoming lower depends on the pressure value that’s being used. This is caused by the lost of overburden pressure in that soil. Overburden pressure is value of the pressure that happenned to the soil caused by the weight that load the soil from the surface. In this case, because the soil sample was taken from the natural soil, it lost the natural pressure from the top of its up-side therefore causing the lost of overburden pressure. It can be seen in this next scheme:
Sample Tube ϒ’H
ϒ’H
Sample Extraction
Due to the pressure-loss, the surface will encounter heave equal ϒ’H which lead to the increase of the soil surface
Image 4 Overburden pressure loss scheme
Therefore it can be hypothesized that the increase in Cv value at the early pressure is caused by the loss of overburden pressure in that soil sample and it need a certain amount of pressure to negate the overburden pressure loss. These are the results for the Pc’ value: 6
Gambar 5 Consolidation Graphic Data no 1
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Gambar 6 Consolidation Graphic Data no 2
Gambar 7 Consolidation Graphic Data no 3 From these graphics, there will be a survey for 2 methods which are Casagrande and Parallel Rebound Method. The results are:
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Gambar 8 1st Consolidation Data Survey Result Dengan Nilai: Cassagrande Average : 5,36 kgf/cm2 Standard Deviation Parallel Rebound Method Average : 3,06 kgf/cm2 Standard Deviation
: 1,61
: 0,51
Gambar 9 2nd Consolidation Data Survey Result
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The values are : Cassagrande Average : 8,71 kgf/cm2 Standard Deviation
: 1,63
Parallel Rebound Method Average Standard Deviation
: 5,41 kgf/cm2 : 0,74
Gambar 10 3rd Consolidation Data Survey Result Which value are: Cassagrande Average : 6,12 kgf/cm2 Standard Deviation Parallel Rebound Method Average : 3,19 kgf/cm2 Standard Deviation
: 1,47
: 0,82
The verification itself was made from the survey result done by Mr. Gouw Tjie Liong M.Eng. ChFC. Data 1 Cassagrande : 3,5 kgf/cm2 Parallel Rebound Method : 2,6 kgf/cm2 Data 2 Cassagrande : 5,8 kgf/cm2 Parallel Rebound Method : 6,0 kgf/cm2 Data 3 Cassagrande : 2,4 kgf/cm2 Parallel Rebound Method : 3,9 kgf/cm2 From the data acquaired and compared to the survey result done by Mr. Gouw Tjie Liong M.Eng. ChFC prove that the result of Parallel Rebound Method which surveyed to 30 students has a closer result than the Cassagrande method surveyed to the same partisipants.
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CONCLUSION AND SUGGESTION Conclusion From this research, the conclusions are : • Taylor Method needs experienced users in order to get a good Cv value • Asaoke method can be used to determine the value of t90 • Asaoka method give a result which doesn’t depend on the user’s eyes because it’s directly processed and counted by microsoft excel program. • Cassagrande method gives an inconstant value, this can be seen from the survey’s result to the 30 partisipants. This method really depends on the user’s eyes. • Parallel Rebound Method created by Ir. Gouw Tjie Liong M.Eng, ChFC., provides a more constant value, this can be seen from the survey’s result from 30 participants.
Suggestion • •
These are the suggestions for further research according this matter : A more advanced research for Parallel rebound Method is needed and using much more data. Need to do more surveys to determine the better result
REFERENCE Gunawan, A. 2010http://andrieasgunawan.blogspot.com/2013/03/mekanika-tanah-2-konsolidasidan.html Herman.2015.http://sisfo.itp.ac.id/bahanajar/BahanAjar/Herman/Konsolidasi%20lanjutan.pdf Novianto,D.,dkk.(2012).Pengaruh Perubahan Tegangan Prakonsolidasi Efektif (Pc’) Pada Penambahan Kapur Terhadap Tanah Lempung. Media Teknik Sipil Volume 10, Nomor 2, Agustus 2012: 95 – 101 Syarifudin,A,dkk.(2013). Perubahan Parameter Konsolidasi Tanah Lempung Tanon yang Dicampur Abu Ampas Tebu. E-jurnal Matriks Teknik Sipil Vol. 1 No 4. Surakarta, Indonesia Wardana,I.,G.,N.(2010).Korelasi Strain Rate dengan Kadar Organik Pada Test Konsolidasi Metode Constant Rate Of Strain. Jurnal Ilmiah Teknik Sipil Vol. 14. Denpasar,Indonesia .
BIOGRAPHY Rico Cahyadi born in Jakarta in May 7th 1993. He finished his bachelor degree at Universitas Bina Nusantara in Civil Engineering Major in 2015.
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