Difficulty: Medium
Correct Answer: All the above.
Explanation:
Introduction / Context:
External soil loads on buried or embankment pipes are classically estimated using Marston–Spangler theory. The proportionality of load to geometric parameters depends on the installation condition (embankment vs. trench) and on whether the pipe behaves flexibly (soil carries part of the load) or rigidly (pipe carries most of the load).
Given Data / Assumptions:
Concept / Approach:
Marston’s formulas express earth load per unit length as W = C * γ * (geometric term). For embankment conditions, the governing geometric term scales with the square of the outside width (for circular pipe, the external diameter). In narrow trenches, load trends depend on trench width and the relative flexibility/rigidity of the pipe–soil system, yielding proportionalities to width*diameter (flexible) or to width squared (rigid).
Step-by-Step Solution:
Verification / Alternative check:
These are the well-known proportionality forms presented in buried pipeline design texts and codes for preliminary comparisons, prior to inserting site-specific coefficients and depth terms for final design.
Why Other Options Are Wrong:
Common Pitfalls:
Final Answer:
All the above.
Discussion & Comments