Coke Breeze Backfill Quantity
Computes carbonaceous backfill volume, weight, and bags for an anode bed.
Example
You enter
- Augered hole diameter (in) 8
- Hole depth (ft) 10
- Anode diameter (in) 2
- Anode length (ft) 5
- Number of anodes 10
- Backfill density as placed (lb/cu ft) 70
- Bag weight (lb) 50
- Waste allowance (%) 10
- Soil resistivity (ohm-cm) 5000
You get
- Column (ft³) 3.49066
- Anode (ft³) 0.109083
- Backfill per anode 3.38158
- Backfill lb per anode 236.71
- Bed backfill (lb) 2367.1
- Bags to order 48 bags, or 53 with the 10% allowance
- Bag count with waste 53
- One anode column to earth 9.87 ohms
- Narrower resistance (ohm) 10.6158
- Wider resistance (ohm) 9.28513
- Doubling the depth 5.84 ohms (-41%) -- drill deeper
Checked against published worked examples from: US Department of Defense.
Details, formula, and sources
ScopeComputes carbonaceous backfill volume, weight, and bags for an anode bed, and the resistance effect of the column geometry. Widening an 8 in hole to 10 in buys 6%; doubling its depth buys 41%. Voids are where the anode is consumed, so the waste allowance is not padding.
Formula or tablebackfill = column volume - anode volume per anode; weight = volume x density as placed; column resistance by Dwight R = 0.00521 rho / L x [ln(8L/d) - 1].
Source and editionThe backfill supplier's data and the CP designer govern.
Free accessPublic geometry and Dwight's relation.
What governsEstimate. AHJ and licensed professional govern.
API field nameshole_diameter_in, hole_depth_ft, anode_diameter_in, anode_length_ft, anode_count, backfill_density_pcf, bag_weight_lb, waste_pct, soil_resistivity_ohm_cm, column_ft3, anode_ft3, backfill_ft3_per_anode, backfill_lb_per_anode, bed_backfill_lb, bag_count, bag_count_with_waste, base_resistance_ohm, narrower_resistance_ohm, wider_resistance_ohm, deeper_resistance_ohm
- Density as placed, which varies with product and tampingsupplier data
- Column the backfill column is treated as the effective anode for resistanceCP practice