---
title: "USCS classification, 75 micron 62%"
subject: "Soil Mechanics"
chapter: 3
key: "semester_4/soil_mechanics:uscs-classify-75micron-62-percent"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/uscs-classify-75micron-62-percent
site: BCT Engineering
---

# USCS classification, 75 micron 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-75micron-62-percent
- 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 = 62%, liquid limit = 54%, plastic limit = 23%.

## Short answer

Since 62% passes 75µm sieve, it's fine-grained; with LL=54% (>50) and PI=31% above A-line (PI>0.73(LL-20)), the soil is inorganic clay of high plasticity, CH.

## Answer

#### Given
Passing 75 micron $= 62\%$; $w_L = 54\%$; $w_P = 23\%$.

$$
I_p = 54 - 23 = 31\%
$$

- 62% passes the 75 micron sieve (more than 50%), so the soil is **fine-grained**.
- $w_L = 54 > 50$: **high plasticity (H)**.
- A-line at $w_L = 54$: $I_p = 0.73(54 - 20) = 24.8\%$. Since $I_p = 31 > 24.8$, the soil is **above the A-line**: clay (C).

**Answer: CH, inorganic clay of high plasticity (fat clay).**

## Check yourself

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

1. Ip = 54 - 23 =
   A. 77%
   B. 31%
   C. 23%
   D. 54%
   Answer: B. Ip = wL - wP. (Key point: Plastic index)

2. A-line Ip at wL = 54 is
   A. 31%
   B. 19%
   C. 24.8%
   D. 39.4%
   Answer: C. 0.73 x 34 = 24.8. (Key point: A-line)

3. 62% passing, above A-line, wL > 50 gives
   A. MH
   B. CL
   C. OH
   D. CH
   Answer: D. Fat clay. (Key point: Result)

## Close variants set in other exams

- [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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- [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
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