Chance Technical Design Manual

C. Calculation of Soil Resistivity

EQUATION A-2

R = R meter (M) (WSF)

where

R meter

= Meter resistance reading (ohms)

Water Table

Corrosion

M = Meter MULTIPLIER reading WSF = Wenner spacing factor = 191.5L (ft) = 628L (m) L = Pin spacing R = Soil resistivity (ohm-cm) D. Additional Resistivity Measurements 1. The soil resistivity (R) is the average value over the depth of soil equal to the spacing of the pins. Therefore, to get a profile of the soil resistivity one must repeat the procedures in paragraph B above with the pins spaced at 10, 15 and 20 feet on center. 2. Repeat the entire test at right angles to the original alignment. E. Documentation Record the field data and the calculations onto the Soil Resistivity Log. A sample log is presented below (See Fig ure A-12). F. Evaluate Results When the Soil Resistivity (R) has been determined, refer to Figure A-5 to determine an estimate of the loss of weight by corrosion over a 10-year period for underground bare steel structures. CORROSION CONTROL TECHNIQUES The amount and type of corrosion control is a function of structure type, service life, and the overall aggressiveness of the project soils. The following requirements are typical. The specifier should review and edit as appropriate for the project. • Structure Type: Temporary structures generally do not require corrosion protection. A temporary structure is defined within a specified time frame (i.e., months rather than years). In general, permanent structures have a service life greater than 24 months. • Service Life: A typical service life of 50 to 75 years should be used unless otherwise specified. If the service life of a temporary CHANCE ® Helical Pile/ Anchor or Atlas Resistance ® Pier is likely to be extended due to construction delays, it should be considered permanent. For a service life of less than 20 years in non-aggressive soil, corrosion protection is not recommended. • Soil: Soil can be classified as aggressive or non aggressive. See Guide to Model Specification-Helical Piles for Structural Support and Model Specification - Helical Tieback Anchors for Earth Retention found under the Resources tab on chancefoundationsolutions.

Soil

Extension Section

Helical Screw Foundation

CORROSION

CORROSION OF HELICAL PILE/ANCHOR AT THE WATERLINE FIGURE A-8

Concrete

Soil

Cathode

Anode

Corrosion

Extension Section

Helical Screw Foundation

Lead Section

4. Adjust the SENSITIVITY switch to HIGH position and adjust the OHMS dial to refine the reading. 5. Record the reading (R meter ) 6. Return the OHMS and MULTIPLIER to the maximum settings and repeat the test. 7. Repeat the test with the pins spaced at 10-feet on center, then at 15-feet and 20-feet on center. Record the readings CORROSION OF HELICAL PILE/ANCHOR FOUNDATION WITH A CONCRETE CAP FIGURE A-9

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