Environmental Engineering Reference
In-Depth Information
Figure 11.36 Pressure-volume controller manufactured by GDS
Instruments. (Courtesy of GDS Instruments, London.)
the high-air-entry disk and appear as water volume change
on the water volume change indicator.
Several soil-testing equipment manufacturers have devel-
oped controlled-pressure piston- and cylinder-type appara-
tuses for measuring the flow of water in or out of soil
specimens. The separation between air and water is still
maintained through a high-air-entry disk at the base of the
soil specimen. Figure 11.36 shows one such device (i.e.,
pressure/volume controller) manufactured by GDS Instru-
ments, London. The controller can be used either in a pres-
sure control mode or a volume change mode. Measurements
of water volume change can be made when the controller is
operated in a pressure control mode. Details of operation of
the controller are illustrated in Fig. 11.37.
Air can also diffuse through high-air-entry disks, and it is
necessary to have a device that can measure diffused air. Air
diffusion should be taken into consideration whenever the
Figure 11.34 Direction of water movement for flow out from
specimen with three-way valves opened to left.
and diffused air leakage in the triaxial test are given by
Poulos (1964). Figure 11.35 shows the overall layout of the
apparatus components associated with water volume change
and the measurement of diffused air. Water volume changes
must be corrected for the volume of air that diffuses through
Figure 11.35 Schematic of control board and plumbing layout for modified triaxial apparatus.
 
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