The 'group action' of piles in a pile group is analysed using the Feld rule or Converse-Labarre formula. The group efficiency is relevant when:
Choose the correct answer
Every pile group has efficiency = 1 always
When pile spacing is small, overlapping stress zones cause the group to carry less than n × individual pile capacity
Only for single piles
When piles are in rock
Correct Answer
B. When pile spacing is small, overlapping stress zones cause the group to carry less than n × individual pile capacity
AI Detailed Explanation & IS Code Reference
Unlock the reasoning, formula path and code-linked notes inside your student dashboard.
Group efficiency < 1 when piles are closely spaced (< 3D c/c) in clay — stress zones overlap; group acts as a block failing on the perimeter. In sand, driving piles densifies sand → group efficiency can exceed 1.0. Converse-Labarre: η = 1 − θ[(n-1)m + (m-1)n]/(90mn) where θ = arctan(d/s), m = rows, n = cols.
ScoreCardAI links this solution with subject, topic and difficulty signals so your scorecard can identify weak areas after a full mock test.
Practice more Civil Engineering questions
This MCQ belongs to JE Level Premium Test Series. Full tests include timed attempts, rank comparison and subject-wise analysis.