Field Estimates for Measuring Rock Fragment Content Marc Crouch, SSDQS, MO14 Professional Development Workshop Ocean City, MD October 23-26, 2000

2 Methods for Measuring Rock Fragment Content Weighing Water displacement

Objective is... “The percent by weight of the horizon occupied by rock fragments >10 inch and 3-10 inch in size” “Soil fraction passing a number 10 sieve as a weight percentage of the less than 3 inch fraction” (2-76 mm)

Materials Need some stuff to do the job right

Materials Container (bucket and/or coffee can) Weight scale Tape measure sampling scoop Water

Sample the horizon Get a good representative sample from the horizon Use scoop, spade ??

Weighing Method Direct way of measuring weight and calculating as a percent of the whole horizon (> 3 inch) and the soil material less than 3 inch fraction (sieves)

Weighing Method -Step #1 Place material in container If bucket, need not fill completely Just make sure that you have a sample representative of the horizon

Weighing Method-Step #2 Weight the bucket + soil note weight as: W (soil) = ----example---- W (soil) = 7kg

Weighing Method-Step #3 Sieve the soil with 75mm sieve to retain >3 inch (if have one)-set this aside Note that this is for spherical or equiaxial shapes; not for flat fragments-see SSM Table 3-11, page 143

Weighing Method-Step #3 If do not have the 3 inch sieve, measure for fragments greater than 3 inches

Weighing Method - Step #4 Weigh the > 3 inch. Note weight as: W (>3-measured) = ----example---- W (>3-measured) = 1kg

Weighing Method -Step #5 Subtract weight of >3 inch from weight of whole sample Note this as weight of <3 inch fraction of the horizon example---- W (soil2) = 6kg

Weighing Method-Step #6 Sieve the < 3 inch fraction with #10 sieve to retain 2-76 mm -set this aside

Weighing Method - Step #7 Weigh the 2-76 mm Note weight as: W (2-76mm-measured.) = ----example---- W (2-76mm-measured.) = 3kg

Weight Summary Soil w/ >3” = 7 kg >3 inch = 1 kg Soil w/o >3” = 6 kg 2-76 mm = 3 kg

Weighing Method - Step #7 Calculate weight % of > 3 inch W (>3) % = W (>3-meas.) / W (soil w/>3”) X example---- W (>3) % = 1/7 X 100 = 14%

Weighing Method - Step #8 Calculate weight % of mm W (2-76mm) % = W (2-76mm-meas.) / W (soil w/o >3”) X example---- W (2-76 mm) % = 3/6 X 100 = 50%

Water Displacement Method An indirect method of calculating weight as a percent of the whole horizon. Calculation equals volume Will need further calculations or conversion charts to estimate weight

Water Displacement-Step # 1 Place material in container. Have several sizes of containers so that can fill the container Tamp the soil in the bucket to better approximate the bulk density, accounting for void space

Water Displacement-Step # 2 Sieve the soil with 75mm sieve (if have one) to retain >3 inch- Set this aside Note again SSM Table 3-11, page 143 for flat fragments

Water Displacement-Step # 2 If do not have the 3 inch sieve, measure for fragments greater than 3 inches

Water Displacement-Step # 3 Replace the soil in the bucket, tamp again, and add,3 inch sample so that container is again filled This is for volume of the less than 3-inch part of the horizon H w/o

Water Displacement-Step # 4 Sieve with #10 sieve to retain 2-76 mm or the 2mm-3 inch fraction, set this aside

Water Displacement-Step # 5 Measure bucket height from bottom to the top Note height: ----example---- H (bucket) = 10 cm

Water Displacement-Step # 6 Add water to the bucket Enough to anticipate covering rock fragments when they are added

Water Displacement-Step # 7 Measure from the top of the water to top of the container Note height as: ----example---- H (w) = 7 cm

Water Displacement-Step # 8 Return the > 3 inch rock fragments to the bucket measure from top of water to the top of the container record: ----example---- H (>3) = 7.5 cm

Water Displacement-Step # 8 This is measurement of volume of the > 3- inch as part of the whole horizon remove the > 3-inch rock fragments

Water Displacement-Step # 9 Check height of water in container again Return the 2-76 mm rock fragments to the bucket Measure again from the top of water to top of container record

Water Displacement Measurement Examples Height of bucket = 25 cm from top of water to top of container w/o fragments = 15 cm from top of water to top of container with >3 inch only = 10 cm from top of water to top of container with 2- 75mm only = 5 cm

Water Displacement-Step # 10 Calculate the volume of the rock fragment >3 inch in size Subtracting the value derived with >3 inch from value derived w/o rock fragments = 5 cm (amount displaced by >3 inch fraction) 5 divided by 25 =.20 X 100 = 20% of container which represents the whole horizon in this case.

Water Displacement-Step # 11 Calculate the volume of the rock fragments 2-75 mm Subtracting the value derived with 2-75 mm from value derived w/o rock fragments = 10 cm (amount displaced by mm fraction) 10 divided by 25 =.40 X 100 = 40% of container which represents the <3 inch part of the horizon in this case.

Why do this? Our visual efforts to estimate volume are usually high Complete a certain number of actual measurements in order to calibrate your observations with actual measurements.

Where is this used? Where else… NASIS

And how do we get there? Conversion charts, for now NASIS will have a sieve calculator in the future