---
title: "USCS classification using D10, D30, D60"
subject: "Soil Mechanics"
chapter: 3
key: "semester_4/soil_mechanics:uscs-classify-d-values"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/uscs-classify-d-values
site: BCT Engineering
---

# USCS classification using D10, D30, D60

Soil Mechanics · Chapter 3: Soil Identifications and Classification

- Asked in: 2078 Poush, 4 marks
- Video: [Sieve Analysis and Classification of Soil using Unified Soil Classification (USCS) and AASHTO system](https://www.youtube.com/watch?v=vd6UqJMYVmY) — Master Civil Engineering
- 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-d-values
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-3

## Question

Classify the given soil according to the USCS classification system.
% of soil passing through sieve no. 200 (0.075 mm) = 40%
% of soil retained in sieve no. 4 (4.75 mm sieve) = 55%
The grading characteristics of soil were: $D_{10}$ = 1.2 mm, $D_{60}$ = 3.8 mm, $D_{30}$ = 2.6 mm

## Short answer

Gravel with fines, symbol GM or GC depending on fines plasticity. With 40% fines (>12%), grading symbols are not used; gravel is 55% and sand only 5%, so gravel dominates. Coarse fraction is poorly graded: Cu=3.17, Cc=1.48.

## Answer

#### Given
Passing 75 micron (No. 200) $= 40\%$; retained on 4.75 mm (No. 4) $= 55\%$; $D_{10} = 1.2$ mm, $D_{30} = 2.6$ mm, $D_{60} = 3.8$ mm.

#### Step 1: Coarse or fine?
60% is retained on the 75 micron sieve, so the soil is **coarse-grained**.

#### Step 2: Gravel or sand?
- Gravel $= 55\%$
- Sand $= 100 - 55 - 40 = 5\%$

Gravel is more than half of the coarse fraction, so the soil is **gravel (G)**.

#### Step 3: Grading parameters
$$
C_u = \frac{D_{60}}{D_{10}} = \frac{3.8}{1.2} = 3.17, \qquad C_c = \frac{D_{30}^2}{D_{10}D_{60}} = \frac{2.6^2}{1.2 \times 3.8} = 1.48
$$
The gravel fraction is poorly graded ($C_u < 4$), but $C_c$ is in the range 1 - 3.

#### Step 4: Fines content
The fines are 40%, which is more than 12%. So the grading is **not used**; the symbol depends on the type of fines (GM or GC) found from $w_L$ and $I_p$ using the A-line. The plasticity data are not given.

**Answer: a gravel with fines, GM or GC (silty or clayey gravel).** If the fines are silty the symbol is GM; if the fines plot above the A-line with $I_p > 7$ it is GC. The grading ($C_u = 3.17$, $C_c = 1.48$) of the coarse fraction is poor.

## Check yourself

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

1. Passing 75 micron 40%, retained on 4.75 mm 55%: sand is 5%, so soil is
   A. gravel
   B. sand
   C. fine-grained
   D. silt
   Answer: A. Gravel dominates. (Key point: Gravel or sand)

2. Cu = D60/D10 =
   A. 3.17
   B. 1.48
   C. 4.6
   D. 2.17
   Answer: A. 3.8/1.2. (Key point: Cu)

3. Cc = D30^2/(D10 D60) =
   A. 3.17
   B. 1.48
   C. 0.67
   D. 2.6
   Answer: B. 6.76/4.56. (Key point: Cc)

4. Because fines are 40%, symbol is decided by
   A. grading, GW or GP
   B. gravel content only
   C. type of fines (wL, Ip, A-line), giving GM or GC
   D. Cu alone
   Answer: C. Grading not used. (Key point: Fines > 12%)

## Related in Soil Mechanics

- [ISSCS classification, 55% passing 200](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aissc-classify-passing-55) — Soil Mechanics, chapter 3
- [Classify soil, No. 4 70%, No. 200 30%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aclassify-soil-no4-no200-ll33) — 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 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 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 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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