As a core equipment in the field of geotechnical engineering, the complexity and high precision of the true triaxial tester determine that various faults may occur during use. The following is a systematic summary of common fault phenomena, cause analysis, and targeted troubleshooting methods:

1、 Abnormal pressure loading fault of true triaxial tester

Phenomenon 1: The uniaxial/biaxial directional pressure cannot reach the set value

Possible reasons

Hydraulic pump wear leads to insufficient output flow;

The aging of the proportional valve coil causes a decrease in electromagnetic torque;

Oil circuit blockage (such as excessive impurities in the filter);

Zero drift or calibration failure of pressure sensor.

Exclusion steps

Check if the liquid level in the hydraulic station's oil storage tank is normal and replenish anti-wear hydraulic oil that meets ISO VG46 standards;

Clean or replace the oil suction filter (recommended maintenance every 500 hours);

Use specialized testing tools to test the response curve of the proportional valve, and replace it with a spare valve of the same specification if necessary;

Re calibrate the pressure sensor (using standard weights for static calibration).

Phenomenon 2: Three directional pressure imbalance exceeds the allowable error range (>5%)

Fundamental inducement

Improper PID adjustment of servo control parameters causes dynamic lag;

Internal leakage caused by wear of the oil cylinder sealing ring;

Eccentricity during sample installation leads to lateral additional torque.

Solution

Enter the controller parameter mode to optimize the integral gain I value (typical adjustment range is 0.1~0.3);

Disassemble the oil cylinder and replace the imported polyurethane U-shaped sealing ring (hardness Shore 90 degrees);

Use a laser centering device to ensure that the concentricity error between the center of the sample and the pressure plate is less than 0.1mm.

2、 Inaccurate displacement control problem of true triaxial tester

Phenomenon 1: Frequent jumping of axial deformation measurement data

Potential root cause

LVDT displacement sensors generate noise signals due to electromagnetic interference;

Excessive clearance of the transmission screw leads to idle error;

Setting the sampling rate of the A/D acquisition card too low can cause aliasing effects.

Repair measures

Install a magnetic ring shielding cover at the cable joint of the displacement meter, and the grounding resistance should be less than 4 Ω;

Adjust the pre tightening nut of the ball screw to control the reverse clearance within 0.02mm;

Raise the data acquisition frequency to 1kHz or above and enable the digital filtering function.

Phenomenon 2: Lateral displacement exceeds the theoretical calculation result

Key investigation points

Insufficient lubrication of the lateral restraint device slide rail increases friction;

There is a tilt angle deviation between the sample cap and the contact surface of the indenter;

Insufficient stiffness of the frame leads to accumulated elastic deformation.

corrective action

Apply high-temperature fluorine grease to the linear guide rail before daily work;

Use a precision angle gauge to adjust the levelness of the indenter to a precision of 1/1000;

Verify the finite element model of the rack and increase the thickness of the locally reinforced rib plate by 20%.