نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشد، دانشکده مهندسی عمران، دانشگاه صنعتی جندی شاپور دزفول. ایران

2 استادیار دانشکده مهندسی عمران دانشگاه صنعتی جندی شاپور دزفول

3 استادیار گروه مهندسی عمران دانشگاه صنعتی جندی شاپور – دزفول ، ایران.

چکیده

    ورود جریان غلیظ به مخزن و رسوب­گذاری در مجاورت بدنه سد و تأسیسات وابسته به آن می­تواند مشکلات متعددی از جمله انسداد دریچه‌های تخلیه کننده تحتانی را به­همراه داشته باشد. هم­چنین ورود رسوبات به لوله پنوستاک به­هنگام آبگیری نیروگاه در شرایط نامساعد مخزن می‌تواند منجر به خوردگی پروانه توربین شود. آگاهی و شناخت از سرعت ترسیب رسوبات وارده به مخزن می‌تواند در راستای تهیه منحنی فرمان برای بهره برداری از نیروگاه سدهای مخزنی نقش به­سزایی بازی نماید. در این مقاله به ارزیابی سرعت سقوط رسوبات چسبنده وارده به دریاچهسد کرخه در حالت سکون پرداخته شده است. برای این منظور از روش استوانه‌ی ته نشینی استفاده گردید. نمونه­برداری رسوبات از هفت منطقه‌ی مختلف دریاچه سد کرخه انجام شد و خصوصیات فیزیکی آن­ها تعیین گردید. آزمایش‌ ته نشینی با غلظت‌های اولیه 4، 6 ، 8، 10، 15، 20 و 25 گرم بر لیتر صورت پذیرفت. نمونه گیری از استوانه‌ی ته نشینی در فواصل عمقی 20 سانتی­متر انجام شد. فاصله‌ی زمانی نمونه‌گیری از استوانه­ ی  ته­ نشینی بسته به میزان غلظت از 5 دقیقه تا 240 دقیقه تنظیم گردید. در این تحقیق سرعت سقوط ذرات، از حل عددی معادله دیفرانسیل مک لافلین به روش عددی تفاضل محدود محاسبه شده‌اند. نتایج حاکی از آن است که بیشترین سرعت سقوط در زمان 10 الی 15 دقیقه در ابتدای فرآیند ته­نشینی اتفاق می‌افتد. هم­چنین نتایج نشان داد که افزایش غلظت اولیه رسوبات منجر به کاهش سرعت سقوط خواهد شد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Assessment of the Cohesive Sediments Fall Velocity in Karkheh Dam Reservoir

نویسندگان [English]

  • Mahnaz Shadorvan 1
  • Babak Lashkar-Ara 2
  • Hesam Seyed kaboli 3

1 M.Sc. Student, Department of Civil Engineering, Jundi-Shapur University of Technology, Dezful, Iran.

2 Assistant Professor, Department of Civil Engineering, Jundi-Shapur University of Technology, Dezful, Iran

3 Assistant Professor, Department of Civil Engineering, Jundi-Shapur University of Technology, Dezful, Iran

چکیده [English]

In reservoir of dams, especially near the dam body, the cohesive fine sediments are deposited mainly. The mechanical behavior of these sediments is largely controlled by the interparticle attraction caused by electrostatic and physiochemical forces. these properties cause the stickiness and accumulation of clay particles and formation of dense masses called flocs, which is sometimes referred to as flocculation. flocculation is influenced by several factors including salinity, flow regime, sediment concentration and organic matter. Flocculation is the most important factor that makes the settling, fall velocity and transfer of cohesive sediment considerably more complex and dynamic than non-cohesive sediments. In order to determine the relations governing cohesive sediments, the physical characteristics and behavior of these sediments should be identified. The terminal settling velocity of sedimentary particles in liquids, called particle fall velocity, is one of the most important properties in determining the physical properties of sediments caused transfer, deposition and consolidation. The fall velocity of cohesive sediments is influenced by many factors, including salinity, initial particle size, turbulence, temperature of water, and suspended sediment concentration.
McLaughlin (1959) provided a method for measuring the fall velocity of particle (ω) in stillwater, using a settling cylinder with 10 cm diameter and less than 1 meter height and established a differential formula based on its research as follows:

d(wC)/dz+dC/dt=0                                                                                                                                       (1)

Fathi Moghadam et al (2011) studied the settling properties of the cohesive sediments in the Dez Dam reservoir. They concluded that particles for all concentrated samples and in all depths reached to their maximum fall velocity approximately at the same time (15 minutes after starting the test). The lower concentration samples appeared to have higher maximum fall velocities than the higher concentration samples, but for a shorter duration.

کلیدواژه‌ها [English]

  • Settling Column
  • Flocculation Reaction
  • Fall Velocity
  • Cohesive sediment

1-    Arman, A., Fathi-Moghadam, M., Emamgholizadeh, S. and Alikhani, A., 2007. Effect of Flocculating and Dispersing Material on Concentration and Fall Velocity of Cohesive Sediments. 7th International River Engineering Conference Shahid, Chamran University. (In Persian).

 

2-       Camp, T.R., 1936. A study of the rational design of settling tanks. Sewage Works Journal, pp.742-758.

 

3-       Fathi-Moghadam, M., Arman, A., Emamgholizadeh, S. and Alikhani, A., 2010. Settling properties of cohesive sediments in lakes and reservoirs. Journal of Waterway, Port, Coastal, and Ocean Engineering, 137(4), pp.204-209. (In Persian).

 

4-       Floyd, I.E., Smith, S.J., Scott, S.H. and Brown, G.L., 2016. Flocculation and Settling Velocity Estimates for Reservoir Sedimentation Analysis. Engineer Research and Development Center Vicksburg ms Vicksburg United States.

 

5-       Krishnappan, B.G., 2000. In situ size distribution of suspended particles in the Fraser River. Journal of Hydraulic Engineering, 126(8), pp.561-569.

 

6-       McLaughlin Jr, R.T., 1959. The settling properties of suspensions. Journal of the Hydraulics Division, 85(HY12), pp.9-41.

 

7-       Mehta, A.J., Parchure, T.M., Dixit, J.G. and Ariathurai, R., 1982. Resuspension potential of deposited cohesive sediment beds. In Estuarine Comparisons (pp. 591-609).

 

8-       Ou, Y., Li, R. and Liang, R., 2016. Experimental study on the impact of NaCl concentration on the Flocculating Settling of Fine Sediment in Static Water. Procedia Engineering, 154, pp.529-535.

 

9-       Ross, M.A. and Mehta, A.J., 1989. On the mechanics of lutoclines and fluid mud. Journal of Coastal Research, pp.51-62.

 

10-   Samadi-Boroujeni, H., Naderi-Boldaji, M., 2009. Investigate of fall  velocity of cohesive sediments using laboratory studies. Irrigation Science and Engineering, Scientific Journal of Agriculture,34(2), pp.31-41. (In Persian).

 

11-   Samadi-Boroujeni, H., Naghshbandi, S.A., 2014. Effect of Flocculation of Adhesive Sediments on Calculating the Fall of Sticky Sediments. 2nd International Congress on Structure , Architecture and Urban Development. (In Persian).

 

12-   Sanford, L.P., Dickhudt, P.J., Rubiano-Gomez, L., Yates, M., Suttles, S.E., Friedrichs, C.T., Fugate, D.D. and Romine, H., 2005. Variability of suspended particle concentrations, sizes, and settling velocities in the Chesapeake Bay turbidity maximum. Flocculation in Natural and Engineered Environmental Systems, pp.211-236.

 

13-   Scully, R.W., Schiffman, R.L., Olsen, H.W. and Ko, H.Y., 1984. Validation of consolidation properties of phosphatic clay at very high void ratios. In Sedimentation Consolidation Models—Predictions and Validation (pp. 158-181). ASCE.

 

14-   Shin, H.J., Son, M. and Lee, G.H., 2015. Stochastic flocculation model for cohesive sediment suspended in water. Water, 7(5), pp.2527-2541.

 

15-   Spicer, P.T., Pratsinis, S.E., Raper, J., Amal, R., Bushell, G. and Meesters, G., 1998. Effect of shear schedule on particle size, density, and structure during flocculation in stirred tanks. Powder Technology, 97(1), pp.26-34.

 

16-   Toorman, E., 1992. Modelling of Fluid mud Flow and Consolidation.

 

17-   Van Leussen, W., 1988. Aggregation of particles, settling velocity of mud flocs a review. In Physical Processes in Estuaries (pp. 347-403). Springer, Berlin, Heidelberg.

 

18-   Van Leussen, W., 1999. The variability of settling velocities of suspended fine-grained sediment in the Ems estuary. Journal of Sea Research, 41(1-2), pp.109-118.

 

19-   Wan, Y., Wu, H., Roelvink, D. and Gu, F., 2015. Experimental study on fall velocity of fine sediment in the Yangtze Estuary, China. Ocean Engineering, 103, pp.180-187.

 

20-   Wang, D., Liu, X., Ji, Z., Dong, Z. and Hu, H., 2016. Influence of flocculation on sediment deposition process at the Three Gorges Reservoir. Water Science and Technology, 73(4), pp.873-880. ‏

 

21-   Yamagami T., Ueno K. and Sakai, S., 2000. Back analysis for determination of sedimentation and consolidation properties, Coastal Geotechnical Engineering in Practice, Nakase and Tsuchida (eds) Balkema, Rotterdam, ISBN.

 

22-   Yang, C.T., 1996. Sediment transport: theory and practice.

 

23- ‏ You, Z.J., 2004. The effect of suspended sediment concentration on the settling velocity of cohesive
  sediment in quiescent water. Ocean Engineering, 31(16), pp.1955-1965.‏