一、Summary
"Intelligent true triaxial tester" is composed of a cubic soil sample, under the action of the surrounding pressure, namely, large principal stress, medium principal stress and small principal stress, through a variety of sensors (force sensor, displacement sensor, back pressure volume change sensor, pore pressure sensor, etc.), using the computer to collect information, And according to the relevant mathematical model for data processing of a special geotechnical test instrument. The instrument can be used for UU, CU, CD triaxial tests under the conditions of isotropic consolidation, K0 consolidation and different principal stress ratios.
The intelligent true triaxial tester applies loads in different principal stress directions on the basis of ordinary triaxial and obtains strains in three directions at the same time. In this case, the stress-strain relationship and the corresponding modulus and strength indexes of the three directions can be sorted out.
Intelligent true triaxial test instrument "can be divided into instrument (hardware) and software two parts.
二、Instrument part
1.1 Main technical indicators
1) Sample size: 70mm×70mm×120mm;
2) Maximum principal stress: 0~3Mpa;
3) Medium principal stress: 0~2Mpa;
4) Small principal stress: 0~1Mpa;
5) Pore pressure U: 0~1Mpa;
6) Back pressure: 0~ 0.6mpa
7) Displacement: large principal stress direction 0~30mm, small principal stress direction 0~8mm
8) Body changes: 0~200ml
9) Loading rate: 0.001~20mm/min (CNC stepless transmission)
10) Sensor accuracy: the system error is less than 0.3%
1.2 Components
1) True triaxial pressure chamber
True triaxial pressure chamber is the main core part of the test, it is composed of soil sample, soil sample base, soil sample cap, hydraulic chamber, direction of the displacement sensor, and wrapped in the soil sample outside the latex film; Pressure outside shell is made of organic glass of resistance to high pressure cylinder, aluminum alloy base, roof, mass pressure piston, piston, principal stress in the input set of hydraulic loading system and small primary stress loading device, the pore pressure sensor mounted at the bottom of the pressure chamber, at the same time equipped with a variety of displacement meter, principal stress, the pressure and consolidation, pore pressure, such as pipes, And various sensor cable related fastener interfaces and valves.
2) Axial pressure loading control system
It is composed of a set of variable speed mechanical devices dragged by a stepping motor and a computer, and the axial load is applied to the triaxial pressure chamber through the precise ball screw propulsion loading platform, and the triaxial stress and strain tests can be carried out under open and closed loop control. The loading rate of the system (0.001~20 mm/min) is composed of stepping motor, driver, switching power supply, touch screen of MCU control system and load sensor.
3) medium principal stress control system
The system has a set of independently controlled hydraulic loading devices. The device is equipped with a pressure sensor for closed-loop control of the size of the main stress, and a single chip microcomputer to drive a stepper motor, and through the flow control of the stress type hydraulic cylinder, connected in the pressure chamber water sac pressure device. The medium principal stress can be applied to the specimen, and the volume change of the flow can be measured at the same time, and the average displacement in the direction can also be calculated.
4) Small principal stress control device
The device can be controlled either by air pressure or hydraulic pressure. Air pressure control is supplied by an inlet proportional valve. Pressure range: 0~900Kpa This method is convenient to operate.
5) Back pressure body change system
The application of back pressure is mainly to solve the problem of soil sample saturation, of course, there are many methods to solve the saturation: vacuum air saturation, head saturation, back pressure saturation and other methods.
For general viscous soil permeability coefficient: greater than N *10-7cm/s, the back pressure volume change system, namely the hydraulic controller, can be used to apply back pressure to the internal end of the soil sample, but the other end of the soil sample let it drain, so that the air bubbles of the soil sample can be eliminated under the action of circulating water and the volume change can be measured.
6) Related sensors
Related sensors mainly refer to load sensor (10KN/3KN) (axial pressure sensor), pore pressure sensor, back pressure sensor, medium principal stress sensor has 4 LVDT displacement sensors, etc.
1 axial pressure sensor: used to measure the main stress, mounted on the lower end of the upper beam;
One pore pressure sensor: one is installed under the soil sample base in the pressure chamber to measure the pore water pressure of the soil sample base, namely U, and the vertical displacement is calculated by the system.
