TRIAXIAL TEST SYSTEMS

UNCONSOLIDATED UNDRAINED (UU) TEST
The soil is set to be in unconsolidated state, only when the volume of soil remains the same without the air replacement. This soil is loose in the natural state. In case of undrained conditions, the pore water is not allowed to drain out of soil. The undrained and unconsolidated conditions is maintained during the triaxial test. Triaxial test is usually done in a small cell, where the sample is placed in the cylinder whose length to the diameter ratio is 2. In total, three number of principal stresses are applied to soil sample. One is axial stress plus the confining stress. Other two principal stresses are equal, as it is the pressure applied to the soil through water confining all over the sides.
There is a rubber sheath which is completely sealed at top and bottom, acting as an impermeable membrane. Pressure transducers are made to measure the pore pressure of the specimen.
This test is performed in two stages as below.
Stage 1: The vertical stress which is applied, forms the major principal stress. The perpendicular confining pressure forms the minor principal stress.
Stage 2: The axial deviator stress is applied to the sample, which brings shear stresses. This deviator stress is applied along axial direction till the failure happens in soil. Limiting shear stress value in which the soil fails along a plane is called as shear strength of soil.
S4700 Triaxial Test System for UU Test supplied complete with:
• Multi Speed Electromechanic Load Frame (S4630/01)
• Load Cell, 5 kN (G345/S5)
• Triaxial Cell for 38 and 50 mm Samples (S4710)
• Triaxial Cell for 70 and 100 mm Samples (S4712)
• Block for Pressure Measurement and De-Airing (S4715)
• Pressure Transducer - 2000 kPa (G360)
• Oil and Water Constant Pressure System (S4714)
• De-Airing Water Tank, 7 L. and Hose (S4717)
• TCM Readout Unit Featuring Software to Perform UU Triaxial Tests (S4708)
CONSOLITADED UNDRAINED (CU) TEST
This Consolidated Undrained (CU) Test is carried out on a cylindrical specimen of undisturbed soil sample with the measurement of pore water pressures in a triaxial cell and multi speed electromechanic compression machine. The specimen is alloved to saturate and consolidated under the aplied confining and back pressures prior to the start of the test. The volume change is monitored by measuring the water and air expelled during the saturation to consolidation stage. Once consolidation is completed, the sample is then isolated from the back pressure and no drainage is permitted during the shearing test. The calculated rate of strain can be as slow as 0.032 mm/min to measure the pore water pressures and stresses. From a set of tests on 3 specimens, Mohr circles of effective stress and total stress at failure can be plotted.
The efective cohesion and efective shear angle values can also be determined. The common specimen sizes are diameter: 72 mm x 144 mm height, diameter: 50 mm x 100 mm height and diameter: 38 mm x 76 mm height.
CONSOLIDATED DRAINED (CD) TEST:
CD tests can be performed on all types of soils. Drainage is allowed in both phases of triaxial testing; isotropic consolidation & shearing. Soil is consolidated under a chosen confining pressure; and after completion of consolidation it is tested for shear by applying deviator stress gradually at slow strain rate while allowing full drainage. It takes more time to complete a test as compared to CU test, and commonly known as "slow" test, which is seldom conducted except for research interest.
The consolidated drained triaxial compression test, with volume change measurement during shear is carried out in a similar sequence to the consolidated undrained test, but during shear the back pressure remains connected to the specimen which is loaded sufficiently slowly to avoid the development of excess pore pressures.
S4705 Triaxial Test System for UU, CU, CD Test supplied complete with:
• Multi Speed Electromechanic Load Frame (S4630/01)
• Load Cell, 5 kN (G345/S5)
• Triaxial Cell for 38 and 50 mm Samples (S4710)
• Triaxial Cell for 70 and 100 mm Samples (S4712)
• Block for Pressure Measurement and De-Airing (S4715) (3 Pcs)
• Pressure Transducer - 2000 kPa (G360) (3 Pcs)
• Oil and Water Constant Pressure System (S4714) (2 Pcs)
• Automatic Volume Change Unit (S4716)
• De-Airing Water Tank, 7 L. and Hose (S4717)
• Data Logger, 4 Channel Data Acquisition Unit (G285/4)
• TCM Readout Unit Featuring Software to Perform UU Triaxial Tests (S4708)
• TCM Readout Unit Featuring Software to Perform CU - CD Triaxial Tests (S4709)
Data Acquisition & PC Software
The CU-CD triaxial test is a complicated test needs load data, diplacement data 3 pressure data from triaxial cell and volume change data. Load data and displacement data are transfered and recorded through TCM304 Unit to the software. 3 pressure data from triaxial cell and volume change data transfered and recorded through the unilogger to the software.
The software for CD-CU tests is compatible with G285/4 datalogger and TCM304 unit. Datalogger can be connected to PC by RS232 port. All channel gains can be set manually and accuracy of the reading can be increased.
Triaxial Software is a modular software that when a new test wanted to do, it directs the user step by step. First the software wants to input initial measurements such as diameter, heigth, sample weigth etc. On this stage the user decides CU or CD test will be done and enters cell pressure increment steps, back pressure differential pressure and effective stress that will be used on consolidation.
After the initialization is completed, the user goes to Saturation Cell Pressure increment stage. Cell presure must be incremented to the pressure entered at initialization stage. During this stage the software calculates B and pore pressure and submits their graph respect to time. When B value saturates this stage must be ended. Generally value of B would not reach to 0.95, therefore a back presuure increment stage must be implemented. On the saturation back pressure increment stage, prior to the start of this stage software commands what back pressure must be applied respect to initial settings. The software draws volume change and pore pressure data during this stage.
Saturation stages can be done recursively at most of 10 cycles. The relevant data of each stage is written to respective files for further investigation and report facilities. When the saturation is completed the consolidation stage can be implemented. On this stage the software commands to adjust both cell and back pressure to apply effective stress. On the consolidation stage Volume change, pore pressure and pore pressure disssipation percent is drawn as graphs. When the stage is completed, the next stage will be shear stage of CU or CD. The software suggest the shear speed respect to the results found on consolidation stage. Axial displacement and force must be tared prior to the start of shearing.
On the shear stage deviator stress, pore pressure, ơ’ versus ơ’3 and s’ versus t’ graphs are drawn. 4 different test specimen can be configured in same file. All the results are used for drawing mohr circles. The data is evaluated with respect to specimen shear end condition. This condition can be selected as constant pore pressure, constant volume change effective prime deviator ratio etc. With the final measurements one set of data is closed. The raw data can be exported to Microsoft Excel. Without using Microsoft Excel environment all reports can be printout which includes summary of each stage with relevant graphs.