cyclic triaxial nov 2007

Soil Mechanics Presentaion

Cyclic Triaxial System Nov 2007

The Wykeham Farrance

Cyclic Triaxial

System



The wykeham Farrance Cyclic Triaxial System was the first pneumatic system commercially produced

The cyclic triaxial system is used to investigate problems associated with liquefaction, blasting shear modulus and strength degradation. One of the benefits of the Wykeham Farrance cyclic triaxial system it can replicate any wave shape associated with these problems.

Frequency and wave shape can very from one investigation to another.



Cell bas showing exit port for the base bender element

Access ring for transducer cables

TRI-CELL plus



All the control and data acquisition functions are performed by the (IMACS) Integrated Management and Control System.

The IMACS has 3 control channels and 13 data acquisition channels.

Axis one is the axial stress

Axis two cell pressure

Axis three back pressure



The cyclic loading is delivered via a through rod double acting pneumatic actuator which is fixed to the crosshead of the standard Wykeham Farrance triaxial load frame.

The actuator has a +/- 5kN capacity but for monotonic shearing higher than 5kN we have a piston clamp that can be screwed up against the load frame crosshead which will lock the actuator in any position. Higher loads can be achieved using the load frame.

Piston Clamp



The feed back for load and waveshape control is from an internal submersible 5kN load cell.

The feed back must be from a submersible load cell to avoid problems caused by ram friction and changes in confining pressure. These are eliminated in the PID control



Suction top cap for connecting the load cell

To the sample

This part connects to the load cell base with a vacuum line passing through the triaxial cell top

Top cap with vacuum ring attached

Having a rigid connection between the sample and the loading mechanism is essential for all stages of the test. It allows the application of a seating load or zero load on the sample which will remain throughout the test.



A critical part of cyclic loading and waveshape control is the alignment of the actuator and the triaxial cell ram. The Wykeham Farrance system has two adjustments. One adjusts in the horizontal plane and the other a ball seat aligns in the vertical.



The system has two displacement Transducers. One is mounted in series with the pneumatic actuator. This is to indicate the ram position in the actuator. The second is mounted on the triaxial cell ram to measure sample displacement . Two are required because we zero the sample displacement transducer during the test



Cell and back pressure are controlled by digitally controlled valves with the transducers mounted adjacent to the valve. The valves are mounted on an auxiliary air receiver with air filter to ensure clean air is supplied to the valves



Pore water pressure is measured at the base of the triaxial cell using a pressure transducer and de-airing block. We have a valve either side of the pore water pressure block. The inner valve to allow water to be flushed through the de-airing block and to allow in situ calibration check of the pressure transducer.



The application of back pressure to the sample is controlled through a solenoid valve, open and close signal are sent via the IMACS. This is done automatically in saturation consolidation and for drained or undrained shear



Volume change is measured through a volume change transducer. This is positioned in the back pressure line giving a direct measurement of volume change. The volume change transducer is equipped with a change over valve which reverses the flow to increase the volume change range from 100cc upwards.



Test set up page for consolidation, stress path, shear and cyclic stages



Continuous Saturation



Consolidation Page



Stress Path page



Shear Page



Cyclic Graph



Charting Options



Playback file allows imported waveshapes to applied to the sample by selecting non standard test in the cyclic shear set up parameters



Playback Converter



0

10000

20000

30000

40000

50000

60000

70000

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520

Waveshape data displayed in Excel



Cyclic Cell Pressure



-40

-30

-20

-10

0

10

20

30

40

De

via

tor

str

es

s, q

(k

Pa

)

-15

-10

-5

0

5

10

15

Ax

ial s

tra

in,

a (%

)

-0.2

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30Number of cycles, N

Ex

ce

ss

po

re p

res

su

re r

ati

o,

u/p

' c

Test data showing the build up of excess pore water pressure and strain during cyclic loading



-50

-40

-30

-20

-10

0

10

20

30

40

50

0 20 40 60 80 100 120

Mean normal effective stress, p' (kPa)

De

via

tor

str

es

s, q

(k

Pa

)

PTL

Test start

p' c = 100 kPa

f = 0.1 Hz

q cyc = 30 kPa

’’h0h0

’’v0v0

’’hh

’’vvdddd

’’vv=0=0

’’hh=0=0



• Liquefaction

• Blasting

• Shear Modulus & Damping Ratio

• Strength Degradation

The cyclic triaxial system is used to investigate problems associated with liquefaction, blasting shear modulus and strength degradation. One of the benefits of the Wykeham Farrance cyclic triaxial system it can replicate any wave shape associated with these problems.

Frequency and wave shape can very from one investigation to another.



Earthquake

Rail track

Blasting

Waveshapes are different, they can be reproduced saved or imported from an outside source. Waveshapes can be manually inputted with a 40000 point description

cyclic triaxial nov 2007

Documents

test cyclic triaxial

valves cyclic triaxial

control system

cyclic shear

pneumatic system

cyclic loading

triaxial cell ram

parameters cyclic triaxial