| Electrical prospecting is one of the most important geophysics survey methods, which was extensively used in engineering geology, environmental geology, hydrologic geology and some mineral survey and exploration. The theoretical foundation of electrical prospecting is that the resistivity of different rocks and minerals are different, and different fields have different responses to telluric current structure. So we can inverse telluric current structure of medium according to the response, that is, the resistivity and distribution of underground rock and mineral. The response of the electrical prospecting has volume affection characteristics, so what the electric law studied and used for a long time is the structure "block " model, and it is less likely to consider the influence of the perfect conductor fracture. The fracture that is a common structure in the rock will form a perfect pass way for electric current after filling water. There is less theory analysis and experiment about how perfect conductor fracture system influences the distribution of the electric current and the ground response of that field. This thesis simulates the fracture with aluminium slice, and preliminarily researches the response of the point current source field through water gullet and out-door experiments. Experiment conditions and results are as follows:(1) Indoor water gullet experiment. The measure of the gullet is 98cmx56.3cmx56.5cm. The supply power is DC power with the type of JD-73, APS-1501. FLUKE 45 dual display multi-meter is used to read experiment result. Supply and receive electrode are common copper poles. The source electrode and measure electrode are adopted with two-pole method. Supply power and measure proceed on the water surface. Observation is within the range of 50cmx50cm with the center of supply electrode. The interval of points is 1 cm or 2cm. First we do the experiment with uniform distributed field, the apparent resistivity of water is 35.15Ωm. Then we simulate fracture with aluminium slices of 30cm×20cm×0.02cm and 10cm×10cm×0.02cm, the apparent resistivity of water is2.67×10-5Ωm. The aluminium slice should be parallel to or 1cm higher than the water surface, etc., and the aluminium slice is lcm or 8.5cm away from the positive current electrode. Through comparison of simulative field with fracture and common filed, we find there are great changes in the electric field distribution after the simulative fracture was placed, and the amplitude comes up to 58 mV, when the supply voltage was 15V.(2) Outdoor on-the-spot experiments. On the open-air level land, the dry cell, APS-1501 direct current steady voltage power etc. were used to supply power, and FLUKE45 type high-accuracy multi-purpose meter and WDDS-1 digital resistivity meter were adopted to observe. The ordinary copper is used for supply and receive electrodes. The source electrode and measure electrode are adopted with the two-pole method. Power supply and measure are proceeding only on the ground, and observation is within the range of 2m×2m with the center of the positive electrode. The interval of measure points is 10cm. Foremost the distribution of uniform clay field whose resistivity is 16.78Ωm was measured. Then the whole 30cm×20cm×0.02cm aluminium slice was vertically...
|
PDF Full Text Request