---
title: "USCS classification, coarse fraction 62%"
subject: "Soil Mechanics"
chapter: 3
key: "semester_4/soil_mechanics:uscs-classify-coarse-fraction-62"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/uscs-classify-coarse-fraction-62
site: BCT Engineering
---

# USCS classification, coarse fraction 62%

Soil Mechanics · Chapter 3: Soil Identifications and Classification

- Asked in: 2073 Bhadra, 3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/uscs-classify-coarse-fraction-62
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-3

## Question

Classify the following soil as per the unified soil classification system: soil passing from 75 µ sieve = 4%, soil passing from 4.75 mm sieve (coarse fraction) = 62%, coefficient of uniformity = 5, coefficient of curvature = 2.6.

## Short answer

Only 4% fines, so coarse-grained. Gravel=38%, sand=58%, so sand dominates; with Cu=5 (<6) and Cc=2.6, it is poorly graded sand with gravel, SP.

## Answer

#### Given
Passing 75 micron $= 4\%$; passing 4.75 mm $= 62\%$; $C_u = 5$; $C_c = 2.6$.

- Fines are only 4%, so the soil is **coarse-grained**.
- Gravel (retained on 4.75 mm) $= 100 - 62 = 38\%$; sand $= 62 - 4 = 58\%$. Sand is more than half of the coarse fraction (58/96 = 60%), so it is **sand (S)**.
- Fines are < 5%, so grading decides: well-graded sand needs $C_u \ge 6$ and $1 \le C_c \le 3$. Here $C_c = 2.6$ passes, but $C_u = 5 < 6$ fails.

**Answer: SP, poorly graded sand (with gravel).**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Passing 4.75 mm = 62%, fines 4%: sand is 58% of the 96% coarse part, so the soil is
   A. gravel (G)
   B. fine-grained
   C. sand (S)
   D. silt (M)
   Answer: C. 58/96 = 60% > 50%. (Key point: Sand)

2. With fines under 5%, the symbol is decided by
   A. Atterberg limits
   B. dual symbols
   C. the plasticity chart
   D. grading only (W or P)
   Answer: D. No fines-type check needed. (Key point: Fines < 5%)

3. Cu = 5, Cc = 2.6 gives
   A. SW
   B. SP, since Cu < 6
   C. SC
   D. GP
   Answer: B. Cc passes but Cu fails. (Key point: Result)

## Related in Soil Mechanics

- [USCS classification, 75 micron 62%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Auscs-classify-75micron-62-percent) — Soil Mechanics, chapter 3
- [USCS classification, 75 micron 8%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Auscs-classify-75micron-8-percent) — Soil Mechanics, chapter 3
- [USCS classification, 75 micron 4%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Auscs-classify-sieve-four-percent) — Soil Mechanics, chapter 3
- [USCS classification, 75 micron 39%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Auscs-classify-75micron-39-percent) — Soil Mechanics, chapter 3
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