The following is a comprehensive explanation of the core influencing factors of the rock elastic modulus tester:
1、 Core performance parameters of instruments and equipment
Sensor accuracy and stability
Load sensor: Nonlinear error needs to be ± 2%, and failure under quasi-static loading conditions. The typical fault is that the pressure ring that is not regularly calibrated is prone to produce hysteresis loops, causing the unloading curve to deviate from the theoretical path and artificially increasing the residual deformation ratio.
2、 Preparation and pretreatment process of specimens
Geometric dimension control
End face flatness: When the parallelism deviation of the upper and lower surfaces of the specimen is greater than 0.02mm, eccentric compression will occur, causing secondary bending moments to change the true stress distribution.
Quality density difference: For every 1% increase in internal porosity caused by insufficient compaction, the measured elastic modulus can decrease by 3% -5%.
Moisture state and maintenance conditions
The higher the moisture content, the lower the elastic modulus of the rock. This is because the presence of water reduces the bonding force between mineral particles inside the rock, resulting in a decrease in overall stiffness and deformation resistance. The fluctuation of standard curing room temperature and humidity (Δ T>2 ℃/Δ RH>5%) can cause a difference of up to 8% in cement hydration degree, significantly affecting the early development of elastic modulus. The optimization plan is to use an intelligent vibration system to control the forming density, and apply release agent on the inner wall of the trial mold to reduce friction resistance.
3、 Key control nodes in the testing process
Alignment and preloading treatment
Physical alignment accuracy: When the deviation between the axis of the specimen and the center of the pressure plate is greater than 1mm, the local pressure bearing area of the contact surface decreases, resulting in shear component interference with axial deformation.
Pre load elimination gap: Without applying initial load (about 5% of the ultimate load), entering the formal loading stage directly, the false deformation caused by the machine's idle stroke can account for up to 15% of the total deformation.
Loading system execution
Graded loading strategy: Load in 4-5 levels according to the requirements of GB/T 50081, and creep deformation cannot be released if the holding time is less than 60 seconds.
Cycle number control: After repeated preloading three times, formal testing can effectively close microcracks and stabilize the contact state.
4、 Disturbance effects of environmental conditions
Temperature humidity coupling effect
Temperature sensitivity: For every 1 ℃ increase in temperature, the rock volume expansion coefficient is about 1 × 10 ⁻⁵, which is equivalent to introducing additional strain.
Humidity dependence: The dry environment promotes the escape of moisture, causing the specimen to self shrink. During the testing period, the relative humidity should be controlled at 60% ± 5%.
Vibration isolation requirements
Basic vibration reduction configuration: When the ground vibration acceleration in the laboratory is greater than 0.05g, an airbag isolation platform needs to be set up, otherwise the environmental vibration will be captured by the displacement meter as a pseudo deformation signal.
Only by comprehensively controlling the above factors, establishing standardized operating procedures (SOP), and implementing equipment preventive maintenance (PM), can the testing accuracy of the rock elastic modulus tester be effectively improved, providing reliable data support for fields such as geotechnical engineering and geological exploration.