تأثیر زمان برظرفیت باربری محوری شمع‌های کوبشی در خاک رس نرم

نویسندگان
کمیل خاکپور 1
علی کمک پناه 2
1 دانشجو دکتری
2 دانشگاه تربیت مدرس
چکیده
در اغلب اوقات آزمایش بارگذاری شمع در فاصله زمانی کوتاه پس از اجرای آن انجام می‌شود. نتایج حاصله بعنوان ظرفیت باربری نهایی شمع در طراحی لحاظ می‌شود. کوبش شمع سبب تغییر شکل زیاد خاک اطراف شمع و بوجود آمدن اضافه فشار آب حفره‌ای در پیرامون آن می‌شود این امر سبب کاهش مقاومت برشی و ظرفیت باربری شمع می‌گردد. آزمایش استاتیک و دینامیک شمع بیانگر ظرفیت باربری شمع در زمان آزمایش می‌باشد برای بررسی تاثیر گیرش در ظرفیت باربری شمع، آزمایش‌ها باید در زمان‌های مختلف انجام شود که این امر زمان‌بر و غیراقتصادی می‌باشد. بنابراین باید راه حل‌های عددی و تجربی توسعه یابد تا بتوان با توجه به تعداد محدودی آزمایش‌های استاتیکی و دینامیکی تاثیر زمان در ظرفیت باربری شمع را بررسی کرد. محاسبه ظرفیت باربری شمع با زمان سبب کاهش قطر، طول و تعداد شمع و کاهش اندازه تجهیزات کوبش می‌شود که این موضوع از دیدگاه اقتصادی قابل توجه است. هدف از این تحقیق بررسی ظرفیت باربری شمع‌های کوبشی در خاک رسی نرم در زمان‌های مختلف پس از کوبش می‌باشد. آزمایش‌ها برای ارزیابی افزایش ظرفیت بابری شمع کوبشی در خاک رس نرم شمال ایران در نظر گرفته شده است. چندین آزمایش بارگذاری بر روی شمع‌های آلومینیومی کوبشی در خاک زسی نرم انجام شد. نتایج نشان می‌دهد 14روز پس از کوبش، ظرفیت باربری شمع نسب به زمان پایان کوبش تقریبا 80% افزایش داشته است. بخش عمده از افزایش ظزفیت باربری در سه روز پس از کوبش می‌باشد و پس از آن نرخ افزایش ظرفیت باربری شمع کاهش می‌یابد.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Time effect on the axial bearing capacity of driven pile in soft clay

نویسندگان English

Komeil Khakpour 1
Ali komakpanah 2
2 Associate Professor
چکیده English

Determination of ultimate pile capacity is important for proper design and construction of pile foundations. Most of the time, the pile load test is carried out shortly after the installation of pile. The pile capacity obtained from the load test is often assumed to be the ultimate pile capacity in most of design methods. However, during pile installation, the soil around the pile experiences large deformations and changes in excess pore water pressure, which in turn reduces the shear strength and pile bearing capacity. After the completion of pile driving, the pile capacity increases as the strength of the surrounding soil increases mainly by reconsolidation, manifested by the dissipation of excess pore pressure at the soil-pile interface zone. the ultimate pile capacity could be underestimated if pile load test was carried out while excess pore water pressure still remains, which may lead to a conservative pile design. It should be noted that a pile static load test (SLT) and a dynamic load test (DLT) only measure the pile load–displacement relation and ultimate load at the time of testing; they do not provide any information on pile capacity variations over time. Pile load tests must be repeated at different times to evaluate any set-up effects, which can be time-consuming and costly during pile construction. Therefore, it is essential to develop empirical and numerical solutions to enable analyzing and estimating long-term pile set-up effects on the basis of limited numbers of SLT and DLT tests. Accurate estimation of pile setup, rather than measuring directly in the field, may reduce the cost of piling and still provide the required performance for the pile. Prediction of pile capacity gain with time after driving would certainly be advantageous from an economic standpoint. Incorporating the effects of setup into pile design is expected to reduce the general cost of piling project by reducing pile diameter, pile length, size of driving equipment, and subsequently piling duration. The major reasons for set-up can be categorised into the following two groups: (1) the generation of excessive pore water pressure during pile driving and subsequent dissipationover time, leading to soil consolidation, and (2) the aging process. The purpose of this research is to conduct experimental research aimed at developing an understanding of pile capacity in soft clays and to develop relationship between the pile capacity and elapsed time after the end of initial driving for cohesive soils. An experimental program was developed to study the evolution of pile capacity increase with time for piles driven into a type of soft clay in northern Iran. results of a series of pile load tests conducted on small-scale Aluminum pile foundations driven into soft clay. The piles were tested instantly after driving to measure their initial bearing capacities, and were tested repeatedly over different elapsed times to study the evolution of pile capacity over time. Results show pile capacity increases approximately 80% of initial value, 14 days after initial pile driving. A large proportion of this pile capacity increase over time, also known as setup, was generated within the three days due to fast excess pore water pressure dissipation, and afterward, the pile capacity increased at a lower rate.

کلیدواژه‌ها English

Driven pile
Soil set-up
Physical Modeling
[1] Attar IH, Fakharian K. Influence of soil setup on shaft resistance variations of driven piles: Case study. International Journal of Civil Engineering, Transaction B: Geotechnical Engineering. 2013 Nov 1;11(2):4-5.
[2] Chow FC, Jardine RJ, Brucy F, Nauroy JF. Effects of time on capacity of pipe piles in dense marine sand. Journal of Geotechnical and Geoenvironmental Engineering. 1998 Mar;124(3):254-64.
[3] Bullock PJ, Schmertmann JH, McVay MC, Townsend FC. Side shear setup. I: Test piles driven in Florida. Journal of Geotechnical and Geoenvironmental Engineering. 2005 Mar;131(3):292-300.
[4] Svinkin MR. Discussion of “Setup and Relaxation in Glacial Sand” by Mark R. Svinkin. Journal of Geotechnical Engineering. 1996 Apr;122(4):319-21.
[5] Seidel, J. and Kolinowski, M. “Pile set-up in sands”, Procedures of the 6thInt. Conf. on the Application of StressWave Measurements to Piles, Sao Paulo, Brazil, Balkema, 2000, 267- 274.
[6] Rausche F, Robinson B, Likins G. On the prediction of long term pile capacity from end-of-driving information. In Current Practices and Future Trends in Deep Foundations 2004 (pp. 77-95).
[7] Komurka VE, Wagner AB, Edil TB. Estimating soil/pile set-up. Wisconsin Highway Research Program; 2003 Sep.
[8] Axelsson G. Long-term set-up of driven piles in sand (Doctoral dissertation, Institutionen för anläggning och miljö).
[9] Karlsrud K, Haugen T. Axial static capacity of steel model piles in overconsolidated clay. Publikasjon-Norges Geotekniske Institutt. 1986(163).
[0] Randolph MF. Science and empiricism in pile foundation design. Geotechnique. 2003 Dec 1;53(10): 847-76.
[11] Samson L, Authier J. Change in pile capacity with time: case histories. Canadian Geotechnical Journal. 1986 May 1;23(2):174-80.
[12] Huang S. Application of dynamic measurement on long H-pile driven into soft ground in Shanghai. In Proc., 3rd International Conference on the Application of Stress-Wave Theory to Piles 1988 May 25 (pp. 635-643). Ottawa, Ontario, Canada.
[13] Tan SL, Cuthbertson J, Kimmerling RE. Prediction of pile set-up in non-cohesive soils. In Current practices and future trends in deep foundations 2004 (pp. 50-65).
[14] Bullock PJ. The easy button for driven pile setup: Dynamic testing. InFrom Research to Practice in Geotechnical Engineering 2008 (pp. 471-488).
[15] Schmertmann JH. The mechanical aging of soils. Journal of Geotechnical Engineering. 1991 Sep;117(9) :1288-330.
[16] Rausche F, Robinson B, Likins G. On the prediction of long term pile capacity from end-of-driving information. In Current Practices and Future Trends in Deep Foundations 2004 (pp. 77-95).
[17] Chow FC, Jardine RJ, Brucy F, Nauroy JF. Effects of time on capacity of pipe piles in dense marine sand. Journal of Geotechnical and Geoenvironmental Engineering. 1998 Mar;124(3) :254-64.
[18] Steward EJ, Wang X. Predicting pile setup (freeze): a new approach considering soil aging and pore pressure dissipation. InGeo-Frontiers 2011: Advances in Geotechnical Engineering 2011 (pp. 11-19).
[19] Ng KW, Roling M, AbdelSalam SS, Suleiman MT, Sritharan S. Pile setup in cohesive soil. I: experimental investigation. Journal of Geotechnical and Geoenvironmental Engineering. 2012 Apr 25;139(2):199-209.
[20]De Mello, V. F. B., Foundations of buildings on clay. State-of-the-Art report. Proc. 7th ICSMFE, 1969,49-136.
[21] Skov R, Denver H. Time-dependence of bearing capacity of piles. In Proc. Third International Conference on the Application of Stress-Wave Theory to Piles. Ottawa 1988 May 25 (pp. 25-27).
[22] Guang-Yu Z. Wave equation applications for piles in soft ground. InProc., 3rd International Conference on the Application of Stress-Wave Theory to Piles (BH Fellenius, ed.), Ottawa, Ontario, Canada 1988 May 25 (pp. 831-836).
[23] Bogard JD, Matlock H. Application of model pile tests to axial pile design. In Offshore Technology Conference 1990 Jan 1. Offshore Technology Conference.
[24] Long J, Bozkurt D, Kerrigan J, Wysockey M. Value of methods for predicting axial pile capacity. Transportation Research Record: Journal of the Transportation Research Board. 1999 Jan 1(1663):57-63.
[25] Svinkin MR, Skov R. Set-up effect of cohesive soils in pile capacity. InProceedings, 6th international conference on application of stress waves to piles 2000 Sep 11 (pp. 107-111).
[26] Karlsrud K, Clausen CJ, Aas PM. Bearing capacity of driven piles in clay, the NGI approach. In Proceedings of Int. Symp. on Frontiters in Offshore Geotehcnics, Perth 2005 Sep (pp. 775-782).
[27] Zhang LM, Wang H. Development of residual forces in long driven piles in weathered soils. Journal of Geotechnical and Geoenvironmental Engineering. 2007 Oct;133(10):1216-28.
[28] Deng TF, Zhao ZF, Gui Y. Time Effect on Bearing Capacity of Jacked Piles Using the Back-Analysis Method. In Pavement and Geotechnical Engineering for Transportation 2013 (pp. 175-182).
[29] Ng KW, Suleiman MT, Sritharan S. Pile setup in cohesive soil. II: Analytical quantifications and design recommendations. Journal of Geotechnical and Geoenvironmental Engineering. 2012 Apr 25;139(2) :210-22.
[30] Reddy SC, Stuedlein AW. Time-dependent capacity increase of piles driven in the Puget Sound Lowlands. In From Soil Behavior Fundamentals to Innovations in Geotechnical Engineering: Honoring Roy E. Olson 2014 (pp. 464-474).
[31] Haque, MdN, Abu-Farsakh, M.Y., Zhang, Z., Okeil, A.: Developing a model to estimate pile set-up for individual soil layers on the basis of PCPT data. J. Transp. Res. Board 2579, 17–31 (2016a).
[32] Haque, M.N., Abu-Farsakh, M.Y., Tsai, C., Zhang, Z.: Load testing program to evaluate pile set-up behavior for individual soil layers and correlation of set-up with soil properties. J. Geotech. Geoenviron. Eng. (ASCE) (2016b).
[33] Wood DM. Geotechnical modelling. CRC Press; 2004 App 2.
[34] ASTM D 422. 2008. Standard test method for particle size analysis of soils, ASTM Standard 0408, 10–17, West Conshohocken, PA, USA, ASTM.
[35] ASTM D 4318. 2008. Standard test method for liquid limit, plastic limit, and plasticity index of soils, ASTM Standard 04 08, 1–13, West Conshohocken, PA, USA, ASTM.
[36] Standard AS. D854,“Standard test methods for specific gravity of soil solids by water pycnometer method”. Annual Book of ASTM Standards.;4.

[37] Standard AS. D2435/D2435M-11, 2011. Standard test method for one-dimensional consolidation properties of soils using incremental loading. Annual Book of ASTM (American Society of Testing Material) Standards, 04.08. ASTM International, West Conshohocken, PA.
[38] ASTM 4648 2000. Standard Test Methods for Laboratory Miniature Vane Shear Test for Saturated Fine-Grained Clayey Soil.
[39] ASTM, D. (1994). 1143. D 1143M-07 Standard Test Methods for Deep Foundations Under Static Axial Compressive Load.
[40] Afshin A, Rayhani MT. Evaluation of bearing capacity with time for small-scale piles driven into Leda clay. International Journal of Geotechnical Engineering. 2015 Jun 5;9(3):307-15.
مهندسی عمران مدرس
دوره 18، شماره 2
خرداد و تیر 1397
صفحه 61-73