SOIL STIFFNESS FOR JAKARTA SILTY AND CLAYEY SOILS Gouw Tjie-Liong Hiasinta Bina Nusantara University ABSTRACT

Transcription

1 SOIL STIFFESS FOR JAKARTA SILTY AD CLAYEY SOILS Gouw Tjie-Liong Hiasinta Bina usantara Uniersity ABSTRACT The upper layer of Jakarta soil is mostly silty and clayey types, which is ery compressible and ery sensitie to the loads applied that could caused damages to the building. These problems are usually not caused by the strength but more on the deformation properties of the soil. This research is aim to help the engineers in predicting the soil deformation modulus by getting the right E-alue from an empirical correlation. In this research, data are collected from the soil inestigation companies in Jakarta. The excel spreadsheet program was used in data processing and also to deelop the correlation to find the E-alue. At the end of the research the releant conclusion were drawn to get the proposed correlation between E s alue and E s. Keywords: Silty and Clayey Soils, Deformation Modulus, Empirical Correlation. 1. ITRODUCTIO There are many projects deeloped on clayey soil in Jakarta, ery often it is also built on soft clay layer, especially in north Jakarta. As ones may know that apart from shear strength, the compressibility properties of the clayey soils need to be studied prior to the construction of the intended structures, as the deformation of the structures will largely depends on how compressie the soil is. It can be seen that there are many damages in the building around Jakarta. For example, we could see the building cracking, the separation of the main building structure and soil around it, the waing road and the floor popping up inside buildings. These serious problems usually not caused by the strength but more on the deformation properties of the soil. Therefore, one should predict soil response to the anticipated loads before the building is built, so one could see how far the deformation will take place. To predict soil deformation to the applied loads, soil stiffness needs to be accessed in a reasonable way. Howeer, it is not easy to get the right stiffness parameter, which is also known as modulus of deformation, termed as E-alue. Many correlations to estimate the soil deformation modulus are aailable. Howeer, those correlations come from oersea soils, and, to the authors knowledge, none has been deelop for Indonesian local soil conditions. It will be beneficial if similar correlations can be deeloped for local soil conditions as this will be able to gie guidelines for engineers in estimating the local soil deformation modulus. This study was aimed to deelop such correlations. Howeer, due to the time limitation, the research was limited to: o o Clayey soils in Jakarta only, especially, Senayan, Sudirman, Pluit and some other areas. The correlation deeloped were based on oedometer, triaxial, pressuremeter, standard penetration test, and atterberg limit test. 2. DATA PROCESSIG 2.1 Deformation Modulus of Soil Deformation modulus of soil (E, a property of elastic material, is defined as a constant of proportionality between stress and strain as Δσ E =... (1 Δε This soil parameter is most commonly used in the estimation of settlement from static loads. It describes the tendency of an object to deform along an axis when forces are applied along that axes which is defined as the ratio of compressie stress to compressie strain. It is used to measure the stiffness of a material. ITERATIOAL FORUM FOR JUIOR CIVIL EGIEERS 1

2 2.2 Pressuremeter Test Deformation modulus from pressuremeter test (E PMT, is determined through the theory of expansion of an infinitely thick cylinder. Thus, E PMT where: = 2 Δp (2 s m ΔV V + Vf Vm = 2 Δ P = P f P Δ V = V f V μ = s Poisson's Ratio ~.33 for drained condition ( 1+ μ ( V + V 2.4 Triaxial Test Deformation modulus from the triaxial test (E 5, is deried by the stress-strain cure obtained from the laboratory testing as shown in Fig. 3 below: ε ε peak ε 5 E 5 σ 3 σ 5 σ peak σ Fig.3 Stress-Strain Cure for E 5 Fig.1 Plot of pressure s. total caity olume (After Das Oedometer Test Deformation modulus from oedometer test, (E oed, is determined by the following formulation: Where Δe m = (3 ΔP ( 1+ e1 1 E oed = (4 m Find the peak deiator stress, σ peak, from the test cure, diide the σ peak into two equal parts, to get σ 5. Then, read the corresponding strain alue, ε 5 along the cure from the σ 5. The Deformation modulus alue will be determined as σ5 E = (5 ε In the triaxial test, usually the tests are done by arying the confining pressure, σ 3. And it appears that the E alue aries with the confining pressure. The greater the confining pressure the greater the E. Therefore, it is necessary to take an E alue at a referenced confining pressure, which is usually taken at 1kPa. This referenced E alue is termed as E 5-ref, and it is determined as shown below: E 5 5 Δ P = P 2 P 1 Δ e = e 1 e 2 e Cc E 5-ref (P 2, e 2 (P 1,e 1 1 kpa Fig.4 Deriing E 5-ref σ 3 P (Log Scale Fig.2 Typical cure of oedometer test ITERATIOAL FORUM FOR JUIOR CIVIL EGIEERS 2

3 2.5 SPT test The SPT alues ary and largely depend on the deices and the execution method. Therefore, to deelop a good correlation the SPT field alues were corrected to a standard effectie SPT energy of 6%. Below is the correction formula: E r = α β γ 6 (6 field E 6 E oed (kpa E oed - 1(6 Eoed (kpa = (6 R 2 = Data (6 Where: 6 = ormalized -SPT alue to an effectie hammering energy of 6% α = Rod length correction β γ = Standard sampler correction = Borehole diameter correction (see Table 1 for α, β, γ field = Field SPT blow count ( alue E r = SPT effectie energy E 5-ref (kpa Fig.5 E oed - 1(6 E 5-ref - 1(6 E 5-ref (kpa = (6 R 2 = Data Table 1. Correction Factors for Field alue 5 Rod length: (α > 1m m m m.75 Standard Sampler (β 1. US sampler without liners (β 1.2 Borehole diameter: (γ mm mm mm 1.15 The -alue is further normalized to an effectie oerburden pressure of 1 kg/cm 2 (1 kpa as follow: E 5' (kpa ( Fig.6 E 5-ref - 1(6 E 5' - 1(6 E 5' (kpa = 128 1(6 R 2 = Data 1 C (6 (6 = ( (6 Where C = 1 σ (8 1 Fig.7 E 5-ref - 1(6 E PMT - ( E PMT (kpa = 89 (6 R 2 = Data 3. RESULTS The results of the research are presented below: E PMT (6 Fig. 8 E PMT (6 ITERATIOAL FORUM FOR JUIOR CIVIL EGIEERS 3

4 E oed - Eoed (kpa = 11 R 2 = Data o E PMT (kpa = 89 (6 (12 (< (6 <48, R 2 =.84 E oed (kpa Correlation to 1(6 o E oed (kpa = 135 1(6... (13 ( < 1(6 < 2, R 2 =.78 E 5-ref (kpa Fig. 9 E oed s. E 5-ref - 35 E 5-ref = R 2 = Data Fig. 1 E 5-ref - o E 5 (kpa = 128 1(6 (14 (< 1(6 <1, R 2 =.77 o E 5-ref (kpa = (6 (15 (< 1(6 <17, R 2 =.64 Correlation to o E oed (kpa = 11 (16 (< <128, R 2 =.63 o E 5 (kpa = 124 (17 (<<69, R 2 =.75 o E 5-ref (kpa = 122 (18 (<<128, R 2 =.67 E 5' (kpa E5' - E 5' (kpa = 124 R 2 = Data From the correlation coefficient, it can be seen the correlations which are deeloped by correcting the (6 to 1 (6 gie the better results, as shown by the higher alue of R 2. This is due to the consideration of the effectie oerburden pressure of the soil COCLUSIO Fig.11 E 5 - After all the data that are carefully analyzed, below are the resulting correlations: Correlation to (6 o E oed (kpa = 33 (6... (9 (< (6 <46, R 2 =.64 o E 5 (kpa = 354 (6 (1 (< (6 <41, R 2 =.64 o E 5-ref (kpa = 292 (6 (11 (< (6 <5, R 2 = RECOMMEDATIOS 1. Further data collection is suggested to improe the reliability of the correlation. 2. Further research is recommended to deelop other corelation for Jakarta soils, and other localities in Indonesia. This will be ery useful for local engineering practice. 3. A Proper soil inestigation procedure is recommended in order to get a better data, therefore, the extracted correlation can be more reliable. 4. One must be ery careful in using the the correlation for the geotechnical engineering job as the correlation may depends on the local soil condition. 5. The proposed correlation shall only be used as a guideline only. It is suggested to carry out the releant test to determine the right soil stiffness, especially in a project that hae high degree of importance. ITERATIOAL FORUM FOR JUIOR CIVIL EGIEERS 4

5 REFERECES Al-Khafaji, A. W., & Andersland, O. B. (1992. Geotechnical Engineering and Soil Testing. Saunders College Publising, Florida. Bowles, J. E. (1979. Physical and Geotechnical Properties of Soils. McGraw-Hill, Inc., USA. Bowles, J. E. (1986. Engineering Properties of Soils and Their Measurement. McGraw-Hill, Inc., USA. Carter, M. (1983. Geotechnical Engineering Handbook. Pentech Pressed Limited. London. United Kingdom. Clayton, C. R. I., Matthews, M. C., & Simon,. E. (1995.Site Inestigation A Handbook for Engineers. Second Edition. Blackwell Science, Oxford, United Kingdom. Das, B. M. (28. Fundamentals of Geotechnical Engineering. Third Edition. Cengage Learning, USA. Gouw, T. L. (1995. Sudah Standardkah Standard Penetretion Test Kita. Jakarta. Holtz, R. D., & Koacs, W. D. (1981. An Introduction to Geotechnical Engineering. Prentice-Hall. ew Jersey. Terzaghi, K., Peck, R. B., & Mesri, G. (1996. Soil Mechanics in Engineering Practice. Third Edition. John Wiley & Sons, Inc., USA. ITERATIOAL FORUM FOR JUIOR CIVIL EGIEERS 5