Utilizing High-Density Electrical And Audio Frequency Magnetotelluric Methods in Engineering Investigations

Utilizing High-Density Electrical and Audio Frequency Magnetotelluric Methods in Engineering Investigations

SUMMARY

High-density electrical method and audio frequency magnetotelluric method are commonly used geophysical exploration techniques in engineering investigations. The high-density electrical method provides shallow depth exploration with high precision, while the audio frequency magnetotelluric method offers deeper exploration with slightly lower accuracy. Both methods focus on detecting the resistivity of rock and soil formations, and through inverting subsurface information and cross-verification, they are effectively applied in detecting concealed faults underground. This study takes a project site in Pingtan as the research subject, utilizing data from high-density electrical and audio frequency magnetotelluric surveys to determine the thickness of the overburden layer in the work area and the geological conditions of the underground space.

CONCEPT

The high-density electrical method is a DC resistivity method. Its principle is the same as the traditional DC resistivity method, but its device uses a combined cross-section device. They are all geophysical exploration methods based on the difference in electrical conductivity of underground media (rock formations).

RESULT

The bedrock in the work area is mainly granite, with some areas consisting of andesite. The resistivity of the bedrock is relatively high, showing significant physical property differences compared to the anomalous areas.

High-density electrical inversion diagram

Results graph of geodesmic visual titry

By comparing the two methods, it is evident that each has its own advantages and disadvantages. The high-density electrical method excels in high precision, capable of detecting even small anomalies. Additionally, it is efficient, as one data collection setup can provide an entire profile of information. However, its drawback lies in its limited exploration depth, typically less than 150 meters, and it is sensitive to terrain conditions.

On the other hand, the magnetotelluric method's strength lies in its ability to explore greater depths, reaching depths exceeding 500 meters, and its adaptability to complex terrain conditions. Nevertheless, its weaknesses include poorer shallow signal quality, susceptibility to electromagnetic interference, lower precision compared to the high-density electrical method, and difficulty in distinguishing small anom.