AS 1289.4.4.1:2017 – Methods of testing soils for engineeringpurposes Method 4.4.1: Soil chemical tests— Determination of the electrical resistivity of asoil—Method for fine granular materials .
AS 1289.4.4.1 sets out a procedure for the measurement of electrical resistivity of fine granular materials with a maximum particle size of 2.36 mm. This test is used for the quality control of bedding and backfilling materials for cast iron and steel pipe, buried metallic structures and reinforcement. This test does not indicate the corrosion hazards to buried metals as these are largely controlled by the nature of the groundwater.
The compacted density, moisture content and water type all influence the final value. The results obtained using this test method are specific to the conditions created within the method.
The following documents are referred to in this Standard:
AS 1289 Methods of testing soils for engineering purposes
1289.0 Part 0: Definitions and general requirements
1289.2.1.1 Method 2.1.1: Soil moisture content tests—Determination of the moisture content of a soil—Oven drying method (standard method)
ISO 3310 Test sieves—Technical requirements and testing (series)
The following apparatus is required:
(a) A plastic soil box.
NOTE: See Figure 1.
The box shall be approximately 220 mm long with internal dimensions of 40 mm wide x 30 mm deep. It shall be fitted with plate electrodes at each end and potential measurement pins on one side spaced so that the distance between their axes in centimetres is numerically equal to the cross-sectional area of the box in square centimetres. Potential measuring pins shall span the full width of the box.
(b) A suitable rectangular tamping tool.
(c) An instrument for measuring soil resistance readable and accurate to 1 Q.
(d) A balance of sufficient capacity with a limit of performance not exceeding 0.5 g.
(i) Fill the remainder of the soil box with material and lightly tamp the surface with the tamping tool.
Add water to the final layer saturating the material.
NOTE: If the soil box is not completely full, further material may be added to create a level surface. A final addition of water is required to saturate the sample expelling as much air as possible from the material.
(k) Connect the four terminals on the soil box to the appropriate terminals on the measuring instrument.
(1) Record the soil resistance 1 mm after connection.
(m) Weigh the soil box and material after test and record as M2 to the nearest 0.1 g.
(n) Remove all the material from the soil box and dry at 105—110°C to constant mass. Determine the mass of dry material (M3) to the nearest 0. 1 g.
(o) Repeat Steps (e) to (n) for remaining sub-samples.
(p) Calculate the mean of the four resistance values obtained (R). If any value departs from the mean by more than 10%, obtain another sub-sample and repeat the procedure.
(q) Fill the soil box with distilled water or the water used for the test, as appropriate.
(r) Connect the four terminals on the soil box to the appropriate terminals on the measuring instrument.
(s) Record the water resistance 1 mm after connection.
The following shall be calculated:
(a) Calculate the resistivity using the following formula:
p = resistivity (Q m)
R = resistance of the soil
A = cross-sectional area of soil box (mm2)
L = length between potential measurement pins (mm)
(b) Calculate the dry density of all four sub-samples tested using the following formula:
(c) Calculate the moisture content of all four sub-samples tested in accordance with AS 1289.2.1.1 using the following formula:
(d) Calculate the mean dry density and moisture content values for the four sub-samples. © Standards Australia