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- 2066 Magh (old course)
- 2065 Chaitra (old course) · 6 marks
Macadam versus Telford construction
Short answer
Telford used a heavy hand-packed stone foundation (400–450 mm) on a flat subgrade; Macadam used thinner (250 mm) compacted angular stone on a cambered, drained subgrade with no special foundation. Macadam is superior because it is cheaper, faster, and its principle of a dry subgrade carrying load remains fundamental today.
Compare the main features of Telford and Macadam construction (why is Macadam road superior to Telford construction?). Make sketches of those road sections.
Both are early-19th-century methods of road construction. Telford (Thomas Telford, 1757-1834) used a heavy stone foundation; Macadam (John McAdam, 1756-1836) used compacted broken stone laid directly on the subgrade.
Sketches
Telford section Macadam section
~~ 40 mm wearing coat ~~~~ ~~ 50 mm top: 20-25 mm stone ~~
== 100 mm broken stone === == 100 mm layer: 50 mm stone ==
== 100 mm broken stone === == 100 mm layer: 50 mm stone ==
## hand-set foundation ###
## stones 170-250 mm #####
---- flat subgrade ------- ---- cambered subgrade (kept dry) ----
(Typical thicknesses: Telford about 400-450 mm in total; Macadam about 250 mm.)
Comparison
| Basis | Telford | Macadam |
|---|---|---|
| Foundation | Large hand-packed stones, 170-250 mm | No special foundation; natural subgrade |
| Thickness | About 400-450 mm | About 250 mm |
| Subgrade | Flat (level) subgrade | Subgrade given a camber and drained |
| Cost | High | Much lower |
| Construction | Slow, needs skilled labour | Fast and simple |
| Surface | Two layers of broken stone with a wearing coat | Angular stones compacted, binding with their own dust |
| Principle | Load spread by a strong base | Load carried by a well-drained, dry subgrade |
Why Macadam is superior
- Needs much less material and labour, so it costs less.
- Quicker to build and easier to repair.
- Its principles (good drainage, camber, compacted angular aggregate) are still the basis of modern roads; Telford's heavy base is unnecessary when the subgrade is dry and well drained.
- It was easily improved to bituminous macadam by adding tar or bitumen.
✓ Answer checked by Claude Opus 5.5 (high effort)
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