SOIL RESISTIVITY-MEASUREMENT AND ANALYSIS

AN EXTENSIVE RESISTIVITY SURVEY WAS UNDERTAKEN IN SOUTH CENTRAL ONTARIO TO DEVELOP CORRELATIONS OF SOIL CONDITION WITH THE CONDITION OF BURIED GAS PIPELINES. BOTH THE WENNER 4-PIN METHOD AT GRADE AND SOIL BOX WITH SAMPLES AUGERED FROM THE PIPE DITCH WERE USED. COMPARISON OF THE DATA SHOWED THE READINGS OBTAINED FROM THE SOIL BOX MEASUREMENTS TO BE CONSISTENTLY LOWER THAN THOSE PROVIDED FROM THE AT-GRADE SURVEY. READINGS WERE ANALYZED VISUALLY AND STATISTICALLY. READINGS OBTAINED WITH THE SOIL BOX PROVED MORE RELIABLE. DETAILS ARE GIVEN OF THE INVESTIGATION PROCEDURE. MEASUREMENTS WERE MADE IN OPEN SPACES. SOIL SAMPLES WERE OBTAINED FROM GAS COMPANY ROUTINE EXCAVATIONS. IF GROUND WATER WAS PRESENT, THE SAMPLE WAS FULLY MOISTENED WITH IT. IF NO GROUNDWATER WAS PRESENT, THE SAMPLE WAS SATURATED WITH LOCAL TAP WATER. THE SURVEY IN METRO TORONTO IS ALSO DESCRIBED. THE ANALYTICAL PROCEDURES BEST SUITED FOR ANALYSIS OF THE LARGE VOLUME OF DATA IS DESCRIBED. THESE PROCEDURES REQUIRED THAT THE MEASUREMENTS BE RANKED IN ASCENDING ORDER AND ASSIGNED PROBABILITES (ILLUSTRATED IN FIGURE). WHERE POSSIBLE, SOIL BOX DATA WERE COMPARED WITH DATA FROM AT GRADE SURVEYS. RESULTS OF SUCH COMPARISON ARE TABULATED. RECOMMENDATIONS ARE MADE REGARDING THE PERFORMANCE OF RESISTIVITY SURVEYS. SUCH SURVEYS INTENDED TO DETERMINE THE CORROSIVITY OF SOIL IN CONTACT WITH PIPELINES SHOULD BE CARRIED OUT BY RANDOMLY AUGERING SOIL SAMPLES FROM THE PIPE DITCH AT PIPE DEPTH. SOIL MEASUREMENTS SHOULD BE MADE ON FULLY MOISTENED SAMPLES COMPACTED IN A SOIL BOX INCORPORATING SEPARATE ELECTRODES FOR CURRENT AND POTENTIAL MEASUREMENT. WHEN EVALUATION OF SOIL CONDITIONS IS NECESSARY FOR A FUTURE PIPELINE AND RELIABLE DATA FOR THE LOCATION IS NOT AVAILABLE, SOIL TYPES SHOULD BE IDENTIFIED USING A SOIL MAP. WHEN RESISTIVITY DATA IS REPORTED, THE MANNER OF TESTING SHOULD BE SUFFICIENTLY DESCRIBED, PARTICULARY IF SOIL BOX MEASUREMENTS ARE INVOLVED.