Application Cases

Experimental Title: Study on the Acoustic Characteristics of Saline Artificially Frozen Soil

Research Focus: The artificial freezing method utilizes refrigeration technology to freeze water within the ground layer, forming frozen soil to isolate groundwater from underground engineering structures, allowing construction to proceed under the protection of a frozen wall. Typically, a low-temperature coolant (often calcium chloride solution in freezing method construction) is circulated through freezing pipes to convert natural soil into artificially frozen soil. However, incidents of freezing pipe fracture occur occasionally due to ground conditions, freezing hole deviation, freezing techniques, and excavation methods. The resulting brine leakage compromises frozen wall stability. Current assessment methods for frozen wall development include the diagram multiplication method, empirical formula method, and numerical simulation method. The drawback of these methods is their high reliance on temperature measurement data from temperature monitoring holes, leading to inaccuracies at locations distant from these holes and potential oversight of critical issues like local frozen wall "windows" or insufficient strength. For artificial ground freezing under saline conditions, changes in the temperature field are complexly influenced by salt content, making anomaly detection even more challenging with existing methods. For instance, uneven salt distribution can lead to irregular frozen wall formation or uncertain risks of "windows" due to brine leakage. Understanding the development status and engineering performance of the frozen wall is crucial for the safe construction using the artificial freezing method under these specific saline conditions.

The propagation of acoustic waves in soil and rock media is closely related to their physical and mechanical properties. Understanding the acoustic characteristics of saline artificially frozen soil and establishing the relationship between acoustic parameters and the physical-mechanical properties of saline artificially frozen soil in artificial ground freezing projects can provide a necessary basis for acoustic detection of anomalies in brine-infiltrated frozen walls. Acoustic testing, as a convenient and rapid non-destructive testing technique, shows promise for achieving this goal. When acoustic waves propagate through frozen soil, their characteristics serve as a comprehensive indicator of factors such as soil temperature, water content, density, fissure conditions, and stress state. Simultaneously, frozen soil strength is also a comprehensive reflection of these factors. Through the relationship between the two, rapid in-situ determination of acoustic parameters can enable the estimation of the mechanical properties of the frozen soil on site.

Experimental Objective: To verify the acoustic characteristics of saline artificially frozen soil.

Test Equipment: Signal generator, ATA-2021B high-voltage amplifier, oscilloscope, charge amplifier, piezoelectric ceramic sensors, etc.

Experimental Process: First, a single-cycle sine wave is generated by the function generator. The excitation signal is then amplified by the ATA-2021B high-voltage amplifier and split into two paths. One path is directly output to the digital oscilloscope as the excitation waveform signal. The other path is used to drive the piezoelectric ceramic transmitter to generate vibrations and excite acoustic waves. These waves propagate through the test specimen. On the other end, the signal received by the piezoelectric ceramic receiver is filtered by the charge amplifier, amplified again, and transmitted to the digital oscilloscope as the received waveform signal. Finally, the oscilloscope's storage function is used to import the waveform data into a computer for determination of the propagation time. The experimental system setup is shown in Figure 1-1.

Figure 1-1: Experimental System Diagram

Experimental Results:

Figure 1-2: Diagram of Wave Velocity Ratio Variation Pattern

From Figure 1-2(a), it can be observed that under unconfined conditions, the wave velocity ratio slightly decreases with increasing salt content, with a variation range of 1.82~2.41. This indicates that the wave velocity ratio is not sensitive to changes in salt content under unconfined conditions. The wave velocity ratio of fully saturated frozen soil is greater than that of unsaturated frozen soil, suggesting that the wave velocity ratio is related not only to soil type but also to the degree of saturation. Under low confining pressures (4MPa, 6MPa), the wave velocity ratio increases with increasing salt content. Under high confining pressure (8MPa), the wave velocity ratio decreases with increasing salt content. From Figure 1-2(b), it can be seen that for frozen silt with the same salt content, the wave velocity ratio generally increases with increasing confining pressure.

Voltage Amplifier Recommendation:

Figure: ATA-2021B High-Voltage Amplifier Specifications and Parameters

The experimental materials in this document were compiled and released by Xi'an Aigtek Electronics. To learn more about experimental solutions, please continue to follow the Aigtek website. Aigtek is a high-tech enterprise in China specializing in the R&D, production, and sales of measurement instruments. It has consistently focused on the R&D and manufacturing of test instrument products such as high-voltage amplifiers, voltage amplifiers, power amplifier modules, and high-precision current sources.