Measurement of resistivity of unsaturated soils using van der Pauw method

The electrical resistivity method is the main non-destructive method for measuring compaction and moisture migration of the unsaturated soils. The van der Pauw method is a well established technique for measuring the resistivity of semiconductor materials with high accuracy and suitable for a wide range of materials. The present investigation is focused on the development of an apparatus to measure the electrical resistivity and sample properties of soils based on the van der Pauw method. The proposed device consists of four parts: (1) a sensor head, which includes four Ti electrodes, (2) an AC constant current source which sends current into soils, (3) dynamic strain indicator which detects the voltage between other two electrodes, and (4) data processing system. The device is evaluated through tests on clay samples. The factors which affect the measurement accuracy, such as depth of samples, size of electrodes, temperature, are tested. By using the proposed method, the relationship among the electrical resistivity, water content and compaction of samples is investigated. The main advantages of the proposed device are high accuracy, measurement stability and no disturbance.