تعیین مدول برشی حداکثر محصور نشده خاک رس تثبیت شده با آهک بوسیله دستگاه المان خمشی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانش آموخته دکتری مهندسی ژئوتکنیک، گروه مهندسی عمران، واحد اراک، دانشگاه آزاد اسلامی، اراک، ایران

2 استادیار، گروه مهندسی عمران، واحد اراک، دانشگاه آزاد اسلامی، اراک، ایران

3 استادیار، گروه مهندسی عمران، دانشکده فنی مهندسی، دانشگاه رازی، کرمانشاه، ایران

4 استاد، پژوهشکده مهندسی ژئوتکنیک، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران، ایران

چکیده

تعیین مدول برشی حداکثر کرنش کوچک خاک‌های تثبیت شده از اهمیت ویژه‌ای برخوردار است و یکی از اساسی‌ترین ویژگی‌های خاک در زلزله و بارگذاری­های دینامیکی است. برآورد دقیق پارامترهای دینامیکی خاک از جمله مدول برشی حداکثر در تحلیل رفتار سازه‌ها نقش تعیین‌کننده‌ای دارد. در این مطالعه با استفاده از دستگاه المان خمشی، تأثیر مقادیر مختلف آهک (5%، 10%، 15% و 20%)  با میزان آب (45%، 65% و 85%)در زمان‌های عمل‌آوری 28 و 56 روزه بر مدول برشی حداکثر خاک رس نرم تثبیت شده با آهک ارزیابی گردیده است. مقدار آب در ترکیب خاک رس و آهک حدوداً به‌ترتیب 1، 5/1 و 2 برابر درصد رطوبت حد روانی خاک رس انتخاب شده است.  نتایج نشان می‌دهد که تغییرات مدول برشی حداکثر خاک رس نرم تثبیت شده، تابع مقادیر آهک و آب است، با افزایش میزان آب بیش از حد روانی خاک، مدول برشی حداکثر به‌طور قابل‌توجهی کاهش پیدا می­کند و افزایش میزان آهک تا سطح معینی باعث افزایش مدول برشی حداکثر می‌شود و پس از آن کاهش می­یابد. افزودن میزان آهک و آب بیشتر از مقادیر تعیین شده موجب ناکارآمدی فرایند تثبیت می‌گردد.
  

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Evaluation of the unconfined maximum shear modulus of lime-stabilized clay with bender element experiments

نویسندگان [English]

  • seyed hassan jafari 1
  • seyed hamid lajevardi 2
  • Mohammad Sharifipour 3
  • mohsen kamalian 4
1 Ph.D. Graduated, Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran
2 Assistant Professor, Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran
3 Assistant Professor, Department of Civil Engineering, Faculty of Engineering, Razi University, kermanshah, Iran
4 Professor, Geotechnical Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
چکیده [English]

Soil dynamic properties play fundamental roles in the analysis and design of various earth structures. Shear modulus and damping ratio are two important dynamic properties. In particular, shear modulus, especially at the level of very small strains typically denoted as Gmax, is a dynamic property of great significance, which is frequently implemented in the seismic design of geo-structures against the destructive earthquakes. The shear modulus reveals the resistance of geo-structure to the deformations imposed by the external loading. On the other hand, one of the commonly used methods to increase the strength and stiffness properties of soft soils is to stabilize them using either cement or lime. Addition of these stabilizing agents to the parent soil strengthens the bonding among particles, thus resulting in the overall increase in the shear stiffness of the mixture. Therefore, the stabilization technique is always considered as an efficient method of soil improvement. In the current study, the small strain shear modulus of soft clay stabilized with various lime contents is thoroughly evaluated using the results of a comprehensive series of bender elements tests under isotropic stress states. Bender element is a nondestructive experiment commonly used to estimate the velocity of shear waves propagating through the soil samples. Using the shear wave velocity obtained, the small strain shear modulus of the specimens could be easily evaluated with a simple equation in soil dynamics. The applicability of the bender element test to measure the shear wave velocity for the stiff stabilized samples in this study was extended using a new innovative method. The influence of input frequency on the shear wave velocity measurements was also rigorously examined and it was concluded that it barely affects the received signals. Based on the bender elements experimental results, the influence of lime inclusion (5%, 10%, 15% and 20%), water content (45%, 65% and 85%) and curing time (28 and 56 days) on the small strain shear modulus is thoroughly investigated. The amount of water in the soft clay-lime mixture was selected to be about 1, 1.5 and 2 times of the liquid limit moisture of the parent clay. According to the experimental results, it is observed that the small strain shear modulus decreases dramatically with the increase in the water content over the liquid limit. The addition of lime to the clay, up to a particular level, leads to a considerable increase in the small strain shear modulus. However, beyond this optimum value, the shear modulus shows a declining trend with the increase in the lime content, which is an indicative of the inefficiency of the stabilization process. Thus, it is a common practice to limit the lime content to a specific percentage so as to obtain the maximum possible value of shear stiffness. The general trends of shear modulus variation for the samples stabilized at different curing periods are also observed to be quite similar. In general, the small strain shear modulus increases with the increase in the curing time, as more chemical reactions could occur within the mixture. Finally, a microstructural analysis was also conducted using the scanning electron microscopy (SEM) images of the treated specimens so as to somehow justify the trends of variation in small strain shear modulus obtained from the bender element experiments. Utilizing the results obtained in the course of this study, useful information is provided for the prediction of the small strain shear modulus of the clays stabilized with lime using deep mixing or grouting methods.
Indeed, the results of this study could be effectively used in different geotechnical construction projects to improve the parent soil strength and stiffness properties and ensure about the serviceability and efficient performance of the underlying soil deposit.

کلیدواژه‌ها [English]

  • Maximum shear modulus
  • Small strain
  • bender elements
  • Stabilized soft clay
  • lime
1. Croft, J. (1967) The influence of soil mineralogical composition on cement stabilization. Geotechnique, 17(2), 119-135.
2. Bell, F. (1996) Lime stabilization of clay minerals and soils. Engineering Geology, 42(4), 223-237.
3. Basma, A.A. and Tuncer, E.R. (1991) Effect of lime on volume change and compressibility of expansive clays. Transportation Research Record (1295).
4. Xiao, H., Lee, F.H., and Chin, K.G. (2014) Yielding of cement-treated marine clay. Soils and Foundations, 54(3), 488-501.
5. Lee, F.H., Lee, Y., Chew, S.H., and Yong, K.Y. (2005) Strength and modulus of marine clay-cement mixes. Journal of Geotechnical and Geoenvironmental Engineering, 131(2), 178-186.
6. Gallavresi, F. (1992) Grouting Improvement of Foundation Soils, Grouting, Soil Improvement and Geosynthetics. ASCE, 1-38.
7. Kauschinger, J., Perry, E., and Hankour, R. (1992) Jet Grouting: State-of-the-Practice, Grouting, Soil Improvement and Geosynthetics, ASCE. 169-181.
8. Chia, B. and Tan, T. (1993) The use of jet grouting in the construction of drains in soft soils, Innovation in infrastructure development. Proc., 11th Conf. of ASEAN Fed. of Eng. Organisations, 20-26.
9. Yong, D., Hayashi, K., and Chia, B. (1996) Jet grouting for the construction of a RC canal in soft marine clay. Grouting and Deep Mixing: Proc. IS Tokyo, 96, 375-380.
10. Sugawara, S., Shigenawa, S., Gotoh, H., and Hosoi, T. (1996) Large-scale jet grouting for pre-strutting in soft clay. Proceedings of the 2nd International Conference on Ground Improvement Geosystems: Grouting and Deep Mixing. AA Balkema, Rotterdam, The Netherlands, 353-356.
11. Yahiro, T. and Yoshida, H. (1973) Induction grouting method utilizing high speed water jet. Proceedings of the Eighth International Conference on Soil Mechanics and Foundation Engineering, 359-362.
12. Kawasaki, T., Niina, A., Saitoh, S., Suzuki, Y., and Honjo, Y. (1981) Deep mixing method using cement hardening agent. Proceedings of the 10th International Conference on Soil Mechanics and Foundation Engineering, 721-724.
13. Saitoh, S., Suzuki, Y., Nishioka, S., and Okumura, R. (1996) Required strength of cement improved ground. Grouting and Deep Mixing, Balkema, 557-562.
14. Liao, H., Kao, T., Chen, M., and Wu, Z. (1992) Grouting for retaining wall movement control of a deep excavation in soft clay, Grouting in the ground. Proceedings of the Conference Organized by the Institution of Civil Engineers, Thomas Telford Publishing, 1994, 403-416.
15. Bergado, D., Ruenkrairergsa, T., Taesiri, Y., and Balasubramaniam, A. (1999) Deep soil mixing used to reduce embankment settlement. Proceedings of the Institution of Civil Engineers-Ground Improvement, 3(4), 145-162.
16. Horpibulsuk, S., Miura, N., and Bergado, D. (2004) Undrained shear behavior of cement admixed clay at high water content. Journal of Geotechnical and Geoenvironmental Engineering, 130(10), 1096-1105.
17. Atkinson, J. (2000) Non-linear soil stiffness in routine design. Géotechnique, 50(5), 487-508.
18. Clayton, C. and Heymann, G. (2001) Stiffness of geomaterials at very small strains. Géotechnique, 51(3), 245-255.
19. Atkinson, J. and Sallfors, G. (1991) Experimental determination of soil properties (stress-stiain-time). Proc. 10th Eur. Conf: Soil Mech., Florence, p. 915.
20. Chiang, Y.C. and Chae, Y.S. (1972) Dynamic properties of cement treated soils. Highway Research Record, 379, 39-51.
21. Fam, M. and Santamarina, J. (1996) Study of clay-cement slurries with mechanical and electromagnetic waves. Journal of Geotechnical Engineering, 122(5), 365-373.
22. Fatahi, B., Le, T., and Khabbaz, H. (2013) Small-strain properties of soft clay treated with fibre and cement. Geosynthetics International.
23. Kai, Y. (2017) Small Strain Behaviour of Cement Treated Singapore Marine Clay. Ph.D. Thesis, Department of Civil and Environmental Engineering, National University of Singapore.
24. Yang, L. (2008) Shear Stiffness Modeling of Cemented Sand and Cemented Clay. Ph.D. Thesis, Department of University of Notre Dame, United States of America.
25. Hoyos, L.R., Puppala, A.J., and Chainuwat, P. (2004) Dynamic properties of chemically stabilized sulfate rich clay. Journal of Geotechnical and Geoenvironmental Engineering, 130(2), 153-162.
26. Puppala, A.J., Kadam, R., Madhyannapu, R.S., and Hoyos, L.R. (2006) Small-strain shear moduli of chemically stabilized sulfate-bearing cohesive soils. Journal of Geotechnical and Geoenvironmental Engineering, 132(3), 322-336.
27. Bengt, B. (1993) Ground Improvement. John Wiley and Sons Publishing Company.
28. Oates, J. (1998) Lime and Limestone. John Wiley and Sons Publishing Company.
29. Christensen, A. (1969) Cement modification of clay soils. Portland Cement Assoc. R & D Lab Bull.
30. Trhlíková, J., BOHáč, J., and MAšíN, D. (2012) Small-strain behaviour of cemented soils. Géotechnique, 62(10), 943.
31. Viggiani, G. and Atkinson, J. (1995) Interpretation of bender element tests. International Journal of Rock Mechanics and Mining Sciences and Geomechanics, Abstracts, p. 373A.
32. Rajabi, H. and Sharifipour, M. (2017) An Experimental Characterization of Shear Wave Velocity (Vs) in Clean and Hydrocarbon-Contaminated Sand. Geotechnical and Geological Engineering, 35(6), 2727-2745.
33. Rajabi, H. and Sharifipour, M. (2018) Influence of weathering process on small-strain shear modulus (Gmax) of hydrocarbon-contaminated sand. Soil Dynamics and Earthquake Engineering, 107, 129-140.
34. Leong, E.C., Cahyadi, J., and Rahardjo, H. (2009) Measuring shear and compression wave velocities of soil using bender–extender elements. Canadian Geotechnical Journal, 46(7), 792-812.
35. Arroyo, M., Muir Wood, D., and Greening, P. (2003) Source near-field effects and pulse tests in soil samples. Géotechnique, 53(3), 337-345.