International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 6, June 2017, pp. 218 224, Article ID: IJCIET_08_06_025 Available online at http://www.ia aeme.com/ijciet/issues.asp?jtype=ijciet&vtyp pe=8&itype=6 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 IAEME Publication Scopus Indexed EXPERIMENTAL STUDY OF INCIPIENT MOTION CONDITION FOR NON-UNIFORM SEDIMENT Rakesh Kumar P.G Student, Civil Engineering Department, Bharati Vidyapeeth Deemed University College of Engineering Pune, Maharashtra, India Deepali R. Kulkarni Assistant Professor, Civil Engineering Department, Bharati Vidyapeeth Deemed University College of Engineering Pune, Maharashtra, India Vipin Chandra Assistant Professor, Department of Civil Engineering, Bharati Vidyapeeth Deemed University College of Engineering Pune, Maharashtra, India ABSTRACT Experiments on incipient motion condition and bed load transport of different fractions for non-uniform sediment are reported in this study. Analysis by this study and other investigators has shown some limitations of available relation for critical tractive stress (CTS) of sediment mixture. Study of hydraulic parameter such as velocity, discharge, sediment transport capacity, depth, critical tractive shear stress etc. is investigated with the help of experiments. Experiments were conducted in a 10 meter long, 0.30 meter wide and 0.45 meter deep tilting flume in P.G Hydraulic Lab of BVDU College of Engineering, Pune Key words: Non- Uniform Sediment, Critical tractive stress, Geometric standard deviation. Cite this Article: Rakesh Kumar, Deepali R. Kulkarni and Vipin Chandra. Experimental Study of Incipient Motion Condition for Non-Uniform Sediment. International Journal of Civil Engineering and Technology, 8(6), 2017, pp. 218 224. http://www.iaeme.com/ijci IET/issues.asp?JType=IJCIET&VType=8&ITy ype=5 1. INTRODUCTION In case of open channel flow having non- uniform sediment, for the low value of discharge the flow condition is similar to that of fixed bed condition but with the increase in discharge there is random motion of sediment particles on the bed. The condition of flow is such that the sediment particle of given characteristics at the bed just start their motion, this condition is the critical condition. The critical condition is also known as incipient motion condition of sediment particle. The stress corresponding to this critical condition is the Critical Tractive http://www.iaeme.com/ijciet/index.asp 218 editor@iaeme.com
Experimental Study of Incipient Motion Condition for Non-Uniform Sediment Stress (CTS). Designing the stablechannel and for the calculation of change in bed level for downstream and upstream of dams, critical tractive stress is an important parameter. For the understanding of sediment transport, the initiation of sediment motion is required. The critical tractive stress in case of uniform sediment is explained well by Garde and Ranga Raju, 1985, but for non- uniform sediment bed it becomes complex because of sheltering effect and exposure effect in non-uniform sediment. Several investigations have worked for the determination of Critical tractive stress of individual fractions in mixture of sediment. The calculation of Critical Tractive Stress is useful in Stable Channel Design Hydraulic design of various structures Scouring studies Erosion, Aggradation, Degradation studies 2. LITERATURE REVIEW The study of incipient motion condition is very important for many problems related to hydraulic engineering such as design of stable channel, bridges, canals, problems associated with degradation, aggradations, changes in plan form of river etc. Some investigators suggest that the critical tractive stress of particle having size d i depend on the size to arithmetic size d a i.e and the non- dimensional critical tractive stress of mean size i.e τ *ca. Whereas some other investigator such as Rakoczi (1975) and Naragaqa (1982) consider σ g ( Geometric standard deviation) to be a parameter affecting critical tractive stress including da and τ *ca. Bed slope is small in case of most open channel flow so slope component does not have an important significance but on steep slope, this slope component plays an important part. Many investigators have studied incipient motion condition for uniform as well as for non uniform sediment. To study incipient motion condition critical tractive stress approach is more rational. This systematic approach was first introduced by Shields (1936). He analyzed the equilibrium condition of a particle lying on bed, composed of uniform material. He emphasized that critical shear stress is mainly a function of a Reynold s number of a particle at initiation of motion. Further study was carried out by White (1940). Natural streams consist of non uniform sediment. This aspect of non uniformity was discussed by Einstein (1950), afterwards Egiazaroff (1965), Ashida and Michiue (1971), Hayashi et.al. (1980), Xie and Chen (1982), Parker et. al. (1982), Misri et al. (1984), Samaga et al. (1986a), Mittal et al. (1990), Bridge and Bennett (1992), Patel and Ranga Raju (1996), and Fang and Yu (1998) proposed several methods for calculating the fractional transport rate of non uniform bed-load. Hsu and Holly (1992) also proposed a method to predict the gradation of non uniform bed-load by considering the probability and availability of moving sediment. Samaga et al. (1986b) and Karim (1998) established empirical functions for estimating the fractional transport rates of suspended load and bed-material load. In the processes of non uniform sediment movement, the coarse particles on the bed are easier to be entrained than the uniform sediment of equivalent sizes, because they have higher chance of exposure to the flow. This aspect of shielding effect was studied by Wilberg and Smith (1987), Parker et.al. (1990), Many investigators have concluded that the critical shear stress is a function of sediment size but at the same time there is influence of bed slope as well. Few of them considered bed slope also such as Neill (1967) showed that critical shear stress increases as channel slope http://www.iaeme.com/ijciet/index.asp 219 editor@iaeme.com
Rakesh Kumar, Deepali R. Kulkarni and Vipin Chandra increases. Later experimental and field studies were carried out by Ashida and Bayazit (1973), Mueller et.al. (2005), Schvidchenko et.al. (2000-2001) and indicated that motion is slope dependant even on low slopes (S< 0.01) and for small size particles (R e < 10 2 ). Shield stress is applicable for lowland rivers as well as steep mountainous rivers. All the investigators till now presented the critical tractive stress as a function of sediment characteristics such as their mean diameter, its standard deviation etc. The present study is to compute the critical tractive stress for non uniform sediment for different standard deviation other than the previous study and to compare the results with the previous study. 3. EXPERIMENAL SETUP The experiments were carried out in Post Graduate Hydraulic Laboratory of BVDU College of Engineering, Pune. Experiment was conducted in 10 m long, 0.30 m wide and 0.45 m deep flume. The recirculating flow system was served by a 50 hp, variable-speed, centrifugal pump located at the downstream end of the flume. The flume used which is having the minimum slope of 0.015 and maximum slope of 0.0020. The average slope is considered from field studies e.g. Ganga, Yamuna, Bramhaputra, Kosi in their original form the sloop is about 0.0015 to 0.0020.The flume slope will be adjusted as per the requirement throughout the experiments. Test section of size 1.0 m long, 0.75 m wide and 0.10 m deep will be provided in the flume for laying the sediment sample. Two pointer gauges with Vernier, having precision of 0.1 mm was used to measure the water levels at upstream as well as downstream of the test section. To measure the point velocity, calibrated propeller type of current meter will be used. The V notch will be use dat downstream end of the tilting flume for measuring discharge. Sediment sample was prepared with non-cohesive non uniform soil having standard deviation more than two. Natural sand was sieved into different sizes and mixed according to the required proportions to achieve non uniformity. Different samples were prepared for conducting the experiments. Figure 2 Experimental Setup http://www.iaeme.com/ijciet/index.asp 220 editor@iaeme.com
Experimental Study of Incipient Motion Condition for Non-Uniform Sediment 4. EXPERIMENTAL PROCEDURE The flume was set to a pre-determined slope and filled with the required sediment mixture. Initially very low discharge was allowed into the flume, so that the sediment bed became fully saturated. The discharge was then increased in increments, maintaining uniform flow each time by adjustment of the tail gate. The discharge (Q) and corresponding uniform flow depth (d) was noted as soon as the critical condition as indicated by the movement of a small number of particles of required sediment size. The sample of moved sediment was collected at the end of the flume. The size distribution for the transported material will be carried out for all the cases. The experiments will be repeated for different discharges and at different slopes. The results was tabulated and analyzed accordingly. Conclusions were based on the analysis of experimental data by a 50 hp, variable-speed, centrifugal pump located at the downstream end of the flume. The experimental setup is given in Figure below. 5. RESULTS The properties of the different mixtures used in this study and their grain size distribution of the mixture is shown in table 1. Following geometric parameters were computed in this study for the research workd a = Δ p i d i log d g = Δ p ilogd i σ g = d σ = d g * σ g where d a ~ arithmetic mean size d g ~ geometric mean size d 50 ~ median size of sediment mixture σ g ~ geometric std. deviation Δ p i ~ percentage of weight corresponding to size d i d 84 ~ particle size such that 84% of particles are finer than this size d 16 ~ particle size such that 16% of particles are finer than this size Table 1 Properties of Sediment Designation of d a (mm) d 50 (mm) σ g d σ (mm) Reference Mixture Mix 1 2.633 0.62 2.3 2.7071 Writer Mix 2 2.53 0.96 2.5 3.8175 Writer Mix 3 2.60 0.90 3.1 4.4392 Writer M 1 3.16 2.35 1.79 8.45 Patel and Ranga Raju M 2 3.10 2.15 1.50 7.85 Patel and Ranga Raju M 3 3.18 2.47 1.90 8.91 Patel and Ranga Raju http://www.iaeme.com/ijciet/index.asp 221 editor@iaeme.com
Rakesh Kumar, Deepali R. Kulkarni and Vipin Chandra The depth of flow, mean velocity, slope is shown in table 2 Table 2 Designation of Flow Depth (mm) Mean Velocity (m/s) Slope Mixture Mix 1 100 0.07 0.0015 Mix 2 120 0.08 0.0020 Mix 3 150 0.11 Critical Tractive Stress- According to Egiazar off the dimensionless critical shear stress for any size d i viz τ *ci, isτ *ci = τ *ci =. According to Hayashi et. al. the value of τ *ca is computed as follows =, for d i/d a <1.0 = / 2, for d i /d a >1.0 Table 3 Present Study d i d a d i/ d a τ *ci Egiazaroff τ *ca (Hayashi et. al.) τ *ci / τ *ca 4.75 2.633 1.80 0.01887 0.0339 0.556637 2 2.53 1.87 0.04159 0.0777 0.535264 1.50 2.60 1.82 0.0422 0.0768 0.549479 0.759 0.0744 0.0564 1.31914 0.791 0.07219 0.0519 1.390944 0.769 0.0859 0.066 1.301515 0.669 0.0936 0.0532 1.759398 0.693 0.08 0.0554 1.444043 0.577 0.0962 0.0555 1.733333 Table 4 Study by Patel and Ranga Raju d i d a d i/ d a τ *ci (Patel and τ *ca (Patel and τ *ci / τ *ca Ranga Raju) Ranga Raju) 4.36 3.16 1.379 0.01777 0.0342 0.519591 1.84 3.10 1.406 0.04368 0.0812 0.537931 1.54 3.18 1.37 0.0432 0.0834 0.517986 0.582 0.0655 0.0672 0.974702 0.593 0.06318 0.0623 1.014125 0.578 0.0769 0.0732 1.050546 0.487 0.0878 0.0612 1.434641 0.496 0.0721 0.0643 1.121306 0.484 0.0899 0.0656 1.370427 http://www.iaeme.com/ijciet/index.asp 222 editor@iaeme.com
Experimental Study of Incipient Motion Condition for Non-Uniform Sediment 10 Present Study τ*ci/ τ*ca 1 Study (Patel and Ranga raju) Present Study 0.1 0.1 1 10 di/da Patel and Ranga Raju Figure 1 Comparison of Present Study with Patel and Ranga Raju study 1 Present study τ*ci 0.1 0.01 0.1 di/d 50 1 Figure 2 Graph between τ *ci and d i/ d 50 6. CONCLUSIONS Experiments were conducted for non-uniform sediment. Critical shear stress for the nonuniform sediment was calculated. Results were compared with previous data of Patel and Ranga Raju having similar values of d i and d a. The graph between the non-uniform parameters di/da and τ *ci / τ *ca was plotted for the present study as well as past study. The graph shows the similar trend lines. From results, it is concluded that the method of Egiazaroff and Hayashi et.al. gave good results to calculate critical shear stress for nonuniform sediment. It has been concluded from chart 2 that, increase in individual particle size increases the value of τ *ci. REFERENCES [1] Patel and Ranga Raju, 1999, Critical tractive stress on nonuniform sediment, J. Hydr. Research, volume 37 1999, ISSN 1814-2079, Page. 38-58 [2] Kuhnle 1994, Incipient motion of sand-gravel sediment mixtures, J. Hydr. Engg., ASCE, Volume 119, No. 12, page 1400-1415. http://www.iaeme.com/ijciet/index.asp 223 editor@iaeme.com
Rakesh Kumar, Deepali R. Kulkarni and Vipin Chandra [3] Patel, and Ranga Raju, 1996 Fraction wise calculation of bld. transport, J. Hydraulic Research, Volume 34, No. 3, page 362-378. [4] D Dadoria, H L Tiwari and R K Jaiswal, Assessment of Reservoir Sedimentation In Chhattisgarh State Using Remote Sensing and GIS. International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 526 534. [5] Wllcock, P.R. (1993), Critical shear stress of natural sediments, J. Hydr. Engrg., ASCE, Volume 119, No. 4, page. 490-504. [6] Maloba Joseck Joab, Alex Khaemba, Njenga Mburu and Akali Ngaywa Moses, Effects of Increased Land Use Changes on Runoff and Sediment Yield In The Upper River Nzoia Catchment, International Journal of Civil Engineering and Technology, 7(2), 2016, pp. 76 94. [7] GARDE, R.J. and RANGA RAJU, KG. (1985), Mechanics of sediment transportation and alluvial stream problems, Second edition, Wiley Eastern Limited, New Delhi, India. [8] PATEL, P.L. (1995), Initiation of motion and bed load transport of non-uniform sediments, Ph.D. Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, University of Roorkee, Roorkee, India. [9] S. Narasimhan and Dr. S. Arivalagan, Reprocess of Dredged Sedimented Particles from Coastal Areas as Partial Replacement With River Sand in Concrete A Review. International Journal of Civil Engineering and Technology, 8(3), 2017, pp. 1138 1140. http://www.iaeme.com/ijciet/index.asp 224 editor@iaeme.com