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Soil mechanics

Axis translation method: configuration of test system

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General description
General description
Axis translation method with High Air Entry Stone (HAES). Operating principle.
One of the problems when a sample with high suction is to be tested, is to prevent the sample from sucking the water from the porous stone on the base pedestal and cause cavitation in the triaxial cell pore water measuring system.
To prevent this happening the porous disc has been replaced with a high air entry stone, cemented into the base pedestal. The high air entry stone will allow water to pass through but not air, at various values. For example, a 5 bar stone will not allow air under 5 bar pressure to pass through the stone. The stone is cemented into the base pedestal to prevent water passing around the outside of the stone. The saturated stone will then allow the passage of water but not air. This will make it very difficult for the water to be sucked out of the stone; it will stop air entering the stone but it will not stop cavitation under the stone. This requires another modification to our triaxial system. To stop cavitation happening and to enable the suction to be measured, an air pressure is applied to the pore space in the sample. Suction is caused by the surface tension forces providing a difference in pressure between the air and the water pressure. If the air pressure is zero (atmospheric) then the water pressures will be negative. If we increase the air pressure in the pore space, the water pressure will also increase, keeping the difference between the air and water pressure the same. The air pressure is increased until the water pressure becomes positive. The suction is still maintained because the water pressure is still lower than the air pressure. The air pressure is applied via the top cap (in the same way as a water back pressure in a saturated test) at about 200 kPa below the air entry value of the porous stone. This will raise the pressure inside the sample to a positive value and in turn will apply a positive pressure to the porous stone and the pore water transducer.
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Ordering info

Typical configuration of a system to perform triaxial tests on unsaturated samples 70 mm dia. with the axis translation method
 
Code Description Q.ty
28-WF4170 Double wall triaxial cell for 70 mm dia. specimens 1
28-WF4170/1 Pedestal with HAES for 70 mm dia. samples 1
28-WF4170/2 Top cap for 70 mm dia. samples 1
28-WF4005 Tritech triaxial testing machine, 50 kN cap. 1
86-D2015 Air compressor, 50 l 1
28-WF2016/2 Air filter/water trap for air compressor 1
28-WF4220/A De-airing tank, 7 l 1
28-WF2001 Vacuum pump 1
86-D2005 Air drying unit 1
86-D0819 Silica gel dessicant with indicator 1
28-WF4225 Valve panel for de-airing tank 1
28-WF4331 Pressure control panel, 3 lines 1
28-WF4330/2 Digital gauge for 28-WF4331 1
28-WF4320 Bladder air/water cylinder 2
28-WF4191 Nylon tubing 6x8 mm dia., 10 m 2
28-WF6353 Submersible load cell, 5 kN cap. 1
30-WF6208 Displacement transducer 25 mm travel 1
30-WF6221 Mounting bracket for 25 mm dia. cell ram 1
28-WF6300 Pressure transducers, 10 bar 2
28-WF6310 De-airing block 2
28-WF4410 Automatic volume change apparatus 2
30-WF6016 Geodatalog, 16 channels datalogger 1
30-WF6042 Transducer extension cables 6

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