🔭 Soil Classification মাটির শ্রেণিবিভাগ 😱
USCS, AASHTO, IS Classification | Group Index (GI) Calculator | Grain Size Classification
🏗️ Soil Classification (মাটির শ্রেণিবিভাগ)
Soil classification মূলত index properties এর উপর ভিত্তি করে করা হয়: Grain size distribution ও Plasticity characteristics
📚 মাটির শ্রেণিবিভাগ পদ্ধতি
🔶 1. Unified Soil Classification System (USCS)
Developed by Arthur Casagrande (1948)
Classification Basis:
Coarse grained soil → Grain size distribution
Fine grained soil → Plasticity (Atterberg limits)
Major Groups: Coarse Grained Soil, Fine Grained Soil, Organic Soil, Peat
🔶 2. AASHTO Soil Classification
Developed by American Association of State Highway and Transportation Officials
Groups: A1 → A7 (Engineering soils), A8 → Peat / Muck
Group Index (GI): Subgrade quality নির্ধারণের জন্য ব্যবহার হয়
🔶 3. Indian Standard Soil Classification System (IS)
Based on grain size + plasticity
Fine soil → 3 ভাগ: Low compressibility, Medium compressibility, High compressibility
✔ USCS-এ শুধু Low & High থাকে
📏 Grain Size Based Classification
| Size (mm) | Soil Type |
|---|---|
| >300 | Boulder |
| 300–80 | Cobble |
| 80–4.75 | Gravel |
| 4.75–0.075 | Sand |
| 0.075–0.002 | Silt |
| <0.002 | Clay |
✔ Note: Fine sand is still coarse grained soil
🪨 Coarse Grained Soil Classification (USCS)
Case 1: Fines < 5%
Clean soil
GW, GP, SW, SP
Case 2: Fines = 5–12% (Dual Symbol)
Example: SP-SC, GW-GM
Borderline case
Case 3: Fines > 12%
Based on Plasticity Index (Ip):
Ip < 4 → Silty (M)
Ip > 7 → Clayey (C)
Ip = 4–7 → Dual symbol
Examples: GM, GC, SM, SC
🧪 Fine Grained Soil Classification (Plasticity Chart)
Based on: Liquid Limit (LL) & Plasticity Index (PI)
Important Lines:
A-line → Clay boundary
U-line → Upper limit
Classification:
CL → Low plastic clay
CH → High plastic clay
ML → Silt
MH → Elastic silt
OL / OH → Organic soil
🏖️ Sand (বালু)
Composition: Mostly Silica (SiO₂)
🔸 Types of Sand (Source Based)
1. Pit Sand
Angular particles, Depth: 1–2 m, Best for concrete/mortar (if salt free)
2. River Sand
Rounded particles, White color, Good quality
3. Sea Sand
Contains salts ❌ Not suitable for construction
✔ Nala sand → Impure (avoid)
🔸 Sand Size Classification
| Type | Size | Use |
|---|---|---|
| Fine Sand | 1.587 mm | Plastering |
| Coarse Sand | 3.175 mm | Masonry |
| Gravelly Sand | 7.62 mm | Concrete |
📊 Group Index (GI) Calculator
Group Index (GI) Calculator
🔸 Group Index (GI) Formula
GI = 0.2a + 0.005ac + 0.01bd
Where:
a = (% passing 75µ sieve – 35)
b = (% passing 75µ sieve – 15)
c = (Liquid limit – 40)
d = (Plasticity index – 10)
✔ Negative হলে → GI = 0 ধরা হয়
✔ GI = 0 → Best soil
✔ GI = 20 → Worst soil
| GI Value | Subgrade Quality |
|---|---|
| 0 – 1 | Good |
| 2 – 4 | Fair |
| 5 – 9 | Poor |
| 10 – 20 | Very Poor |
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