Which of the following statements regarding the soil mechanics and operational behavior of subsoilers and deep chisel tines is/are CORRECT?
Options:
(A) The 'critical depth' is the transition depth below which soil failure changes from crescent upward shearing to lateral plastic compaction
(B) Working below the critical depth dramatically increases specific draught with minimal incremental soil shattering
(C) Adding a pair of lateral wings to the subsoiler foot increases the disturbed soil cross-sectional area with only a moderate increase in draft
(D) Operating a subsoiler above the plastic limit of soil produces extensive friable shattering and high structural porosity
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
Soil mechanics of deep tines (Spoor & Godwin / McKyes):
- **Statement A is correct:** Above critical depth, soil fails in an upward expanding crescent with open shear planes. Below critical depth, confining overburden pressure causes lateral flow and plastic compression without loosening.
- **Statement B is correct:** Working deeper than critical depth results in compaction and rapid surge in specific energy ($J/m^3$).
- **Statement C is correct:** Winged subsoiler feet widen the failure crescent by $2\text{--}3\times$ while increasing draft by only $20\text{--}30\%$, improving energy efficiency.
- **Statement D is incorrect:** When soil moisture is above the plastic limit, tines induce smeared surfaces, puddling, and deep rutting rather than friable shattering.