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OCR for page 32
32
61x61
Diameter =61mm
61x122
Diameter =160mm 61x244
61x366
61x488
Diameter =273mm 61x732
Figure 5.3. Pier models used in the complex pier scour tests.
undisturbed by the presence of the probe. An ADV with a the water surface elevation, the water depth, and the change
velocity range of ±2.5 m/s and a resolution of 0.1 mm/s was in scour depth. The point gage is designed based on the fact
used to measure the velocity during the tests. The primary use that air, water, and soil have different electrical conductivity.
of the ADV was to measure the vertical velocity profile along The point gage system forms a closed circuit with one node
the water depth around piers and contractions. The upstream in the soil or water and the other one in the air. Once the point
mean depth velocity was the basic velocity recorded for the gage, which contains a needle attached to a vertical ruler,
pier tests. For the contraction tests, the ADV was used to mea- touches the interface between water and air or water and soil,
sure the velocity distribution along the centerline of the con- there is a sudden conductivity change that can be read easily
tracted channel at certain water depths before the scour on a voltmeter. When the water is dirty, the maximum scour
started and after the scour stopped. In some tests, more exten- location can be searched point by point using the point gage.
sive velocity measurements were conducted at specific loca- As shown in Figure 5.2, the point gage and ADV are
tions. These included the corners of contraction abutments installed in a hanging measurement cage riding on a carriage
and rectangular piers. that moves along the longitudinal direction of the flume. In the
A point gage with a new design was used in this study. flume tests, it was found that the presence of piers or contrac-
Without interrupting the experiments, it was used to measure tion abutments had almost no influence on the flow at a dis-
tance of one channel width upstream of the obstacle. There-
fore, the velocity and water depth were determined at this
location for each test. In addition, a digital camera was used to
record important phenomena during the tests.
5.5 SOILS AND SOIL BED PREPARATION
A Porcelain clay was used as the primary soil; for compar-
ison purposes, sands also were used in several tests. The pre-
dominant mineral of this commercially available Porcelain
(a) (b) (c) (d) (e) clay is Kaolinite. Geotechnical tests were conducted accord-
ing to ASTM standards. The geotechnical properties of the
Porcelain clay determined at two different times are summa-
rized in Table 5.1. Vane shear tests were conducted at three
different locations around the future scour hole after the soil
Response Distance
50mm
U
(f) (g) (h) (i)
V
(a, b, c-Contraction Width; a, d, e, f-transition angle, a, g, h, i-contraction
Flow Particle
length)
Figure 5.4. Abutment models for contraction scour tests. Figure 5.5. Diagram of the ADV.
