ELECTRICAL MEASUREMENT BASED LABORATORY TESTING METHOD OF PHYSICAL PROPERTIES OF SUBGRADE SOIL

The performance of subgrade soil can decay during long-term service. The moisture content and compaction degree are important control indicators for subgrade construction. Therefore,soil moisture content control and compaction quality are the key factors in the performance evaluation of subgrade. The research results can provide a theoretical basis for the detection and evaluation of the engineering properties of subgrade soil. In order to make up for the deficiencies of the existing detection methods,we developed a rapid indoor test device for soil physical parameters based on the quadrupole electric measurement method,while we changed the water content between the different compactions. We carried out a series of laboratory tests on the resistivity and polarizability of soil samples and obtained the correlation and change trend. We analyzed the influence of water content and compaction on electrical parameters and proposed the soil moisture content and compaction degree. We calculated the calculation formula of resistivity and polarizability and discussed the feasibility of the test method. The results show that the resistivity of soil in different regions decreases with the increase of water content and compaction. The polarizability of soil increases with the increase of water content and compaction. Under different compaction degrees,the resistivity and polarity of soil shows a similar index and logarithmic characteristics with the change of water content. For the loam of Wangqingtuo area in Tianjin,when the compaction degree ranged from 84.47% to 94.41% and the water content changed from 15% to 20%,the resistivity falls to original 1/3~1/2 times and the polarizability falls to 1.4~2.3 times. And we obtain the indoor fitting formula. In practical engineering,the resistivity method is more suitable for soil moisture detection,and the polarizability method is more suitable for soil compaction detection. The comprehensive resistivity and polarizability index have good prospects for roadbed engineering. The research results can provide a theoretical basis for the detection and evaluation of the engineering properties of subgrade soil.