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33 TABLE 5.1 Geotechnical properties of the Porcelain clay 35 Property Test 1 Test 2 30 1 Liquid Limit, % 40.23 37.7 Erosion Rate (mm/hr) 2 Plastic Limit, % 19.17 14.4 25 3 Plastic Index (PI), % 21.06 23.3 4 Bulk Unit Weight ( KN / m 3 ) 19.65 24.99 5 Water Content, % 27.35 30.5 20 6 Shear Strength, KPa 10.7 18.1 15 bed was prepared, but before the experiment started; the aver- 10 Sample A age value is shown in the Table. The erosion properties of the Sample B 5 Porcelain were tested by Cao (2001) in the EFA. Two sam- ples were tested separately using tap water. The erosion rate 0 versus shear stress curve is shown in Figure 5.6. 0 10 20 30 40 50 Gudavalli (1997) used three types of clays for his experi- Shear Stress (Pa) ments: Porcelain, Armstone, and Bentonite. The properties of these clays are presented here because Gudavalli's tests Figure 5.6. Erosion function for the Porcelain clay. were the basis of the original SRICOS Method and because these tests are used in this study as well. The geotechnical properties of these soils were measured according to ASTM vated portion. It was critical to remove all the soft film and any standards and are given in Table 5.2. The erosion properties excess water on the old soil surface; otherwise, the old soil and of the Porcelain clay were measured in the 0.45-m-wide flume. new soil would not stick tightly together and the new soil could The bed shear stress was varied from 0.118 Pa to 7.92 Pa by be flushed away in lumps. This requirement was particularly changing the flow velocity. The water depth was maintained important for the contraction scour tests. constant during the experiments. Each test was conducted for a few hours. The bed shear stress was computed by Prandtl's equation for the velocity versus depth profile obtained by 5.6 FLUME TESTS: PROCEDURE ADV measurements very close to the soil bed. These exper- AND MEASUREMENT iments amounted to running a large-scale EFA test. The rela- tionship between erosion rate and shear stress is shown in Complex pier scour tests were conducted in the 1.5-m-wide Figure 5.7. flume and all of the tests were done according to the following The Porcelain clay was delivered in blocks of 250 mm × procedure: 180 mm × 180 mm. Each block was in a sealed bag. The clay was installed block by block in the soil tank, as shown in Fig- 1. Prepare soil bed and pier installation; ure 5.8. After the completion of one layer, kneading with a 2. Perform vane shear measurements; 20-lb concrete block was used to minimize the voids and 3. Take initial readings of the soil surface elevation around holes between blocks. The next layer was placed on top of the piers; the first one, and so on. Once the soil tank was full, the soil 4. Install the ADV; surface was leveled by using a straight-edged spatula. 5. Perform calculations of water volume in the flume and After each test, the excess water was pumped out, a zone of pump rate to get the expected water depth and velocity; clay was removed around the scour hole until undisturbed clay 6. Take measurements of the velocity profile and water was reached, and fresh Porcelain clay was placed in the exca- surface elevation; TABLE 5.2 Properties of the soils used in Gudavalli's research (Gudavalli, 1997) S. No. Property Porcelain Armstone Bentonite 1 Liquid Limit, % 34.40 44.20 67.00 2 Plastic Limit, % 20.25 18.39 27.22 3 Plastic Index (PI), % 14.15 25.81 39.78 4 Specific Gravity 2.61 2.59 2.55 5 Water Content, % 28.51 26.18 39.28 6 Sand Content, % ------ 25(grog) ------ 7 Clay Content, % 100 75 100 8 Shear Strength, KPa 12.51 16.57 39.56 9 CEC, (meg/100g) 8.3 10.0 16.1 10 SAR 5.0 2.0 21.0 11 PH 6.0 5.2 8.5 12 Electrical Conductivity (mmhos/cm) 1.2 1.1 1.1 13 Bulk Unit Weight ( KN / m 3 ) 18.0 17.89 17.45