1.Technical principles and "non nuclear" advantages
Q: How does EDG measure soil density and moisture content without nuclear radiation?
High frequency radio technology (RF): The working principle of EDG is to use four metal steel nails (electrodes) inserted into the soil to form a high-frequency electromagnetic field.
Measurement of dielectric constant: Different soil densities and moisture contents result in vastly different dielectric constant and conductivity. The dielectric constant of water is very high, while the dielectric constant of air is very low. The instrument measures the electrical properties of the soil between steel nails, and through internal algorithms, can deduce the wet density, dry density, and moisture content of the soil.
Q: What are the advantages and disadvantages of EDG compared to traditional "nuclear density meters" and "sand filling methods"?
Advantages:
Safety and compliance: No nuclear radiation, no need to apply for a toxic/radioactive permit, transportation and storage are extremely simple.
Efficient and fast: Steel nails can be inserted on-site and tested with just one click. Typically, compaction and moisture content data can be obtained directly within 1-2 minutes.
Disadvantages:
Dependent on empirical models (calibration): EDG does not directly "count" density, but indirectly calculates it through electricity. If strict "Soil Model Calibration" is not performed on the soil samples on site before testing, the measured data will be completely distorted.
Boundary sensitivity: The measurement range is limited to the core area enclosed by four steel nails and is highly susceptible to interference from large surface particles of metal, cables, nearby large rocks, or severe uneven water accumulation.
2. Soil Modeling and Calibration
Q: Why is the data measured by EDG completely incorrect when arriving at a new construction site? What is' soil modeling '?
Answer: This is the most common mistake made by beginners. EDG cannot achieve "out of the box testing".
Before formal testing, you must establish a soil model on site:
Find 1-3 representative testing points on the construction site and use EDG to measure their basic electrical data.
Subsequently, traditional sand cone or ring knife method tests were conducted at exactly the same location, and soil samples were taken back to the laboratory for drying to accurately measure dry density and moisture content.
Input the real physical data obtained by sand filling and drying methods (as standard values) into the EDG software, allowing the instrument to "remember" the linear relationship between the electrical properties and density of this soil.
After establishing this model, the data measured by EDG will be accurate when encountering the same type of soil on this construction site in the future.
Q: Can a soil model be universal? When is it necessary to re model?
Cannot be used universally. Once the following situations occur, it is necessary to re model:
The type of soil has changed (for example, from clay to gravel soil, or from a different mining site).
The minerals or salts contained in the soil have undergone significant changes (salt will dramatically alter conductivity).
The grading undergoes a drastic change (sudden increase or decrease in the content of large particle crushed stones).
3.On site operation and error control
Q: What are the strict requirements for the penetration depth and spacing of four electrode steel nails (T-Bars)?
Depth consistency: The positioning template and conical hammer provided by the instrument must be used to ensure that the 4 steel nails are vertically driven into the soil, and the driving depth must be strictly consistent (usually around 150mm, depending on the instrument model). If the steel nails are tilted or driven too shallowly, it will cause deformation of the measured electromagnetic field geometry and deviation of the data.
Close contact: Steel nails must be tightly attached to the soil. If there are gaps (air layers) around the nail due to repeated shaking during nailing, the measured dielectric constant will be significantly lower (lower compaction degree).
Q: Why is the data unstable when measuring newly paved or rolled high-temperature asphalt pavement or swamp soil with extremely high moisture content?
Temperature effect: The electrical properties (dielectric constant) of soil and moisture are highly sensitive to temperature. Usually, EDG is equipped with temperature compensation probes, but if the temperature difference changes too much or the temperature of the newly compacted foundation is too high, it will exceed the conventional compensation range of the instrument.
Excessive free water: When the soil is in a completely supersaturated state and there is accumulated water on the surface, the conductivity will form a short-circuit surge, causing the calculated moisture content of the instrument to explode or the dry density to be abnormal.
4.Troubleshooting of common data anomalies
Q: What could be the reason why the measured moisture content does not match the laboratory drying method?
Scenario A (high EDG data): Check whether the soil contains high levels of salt (such as marine sedimentary soil, saline alkali land) or chemical additives (such as lime, cement stabilized crushed stone in the early stages). These components will significantly enhance conductivity, causing the instrument to mistakenly believe that the moisture content is high.
Scenario B (EDG data low): Check if there are pores around the steel nails; Or the soil belongs to pure large non cohesive sand and gravel, with extremely poor water storage capacity and poor electrical contact.
