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Rock Protodyakonov Strength Classification
2026-09-10Rock Protodyakonov Strength Classification (Method for Identifying Rock Hardness)
Rock Protodyakonov Strength Classification Table
| Rock Grade | Strength Degree | Representative Rocks | Protodyakonov Coefficient f |
| Ⅰ | Most solid | Densest and highly‑tough quartzite, basalt and other extra‑hard rocks | 20 |
| Ⅱ | Very solid | Hard granite, quartz porphyry, siliceous schist; relatively hard quartzite, high‑strength sandstone and limestone | 15 |
| Ⅲ | Solid | Dense granite, hard sandstone & limestone, quartz vein, solid conglomerate, high‑hardness iron ore | 10 |
| Ⅲa | Solid | Solid sandstone, limestone, marble, dolomite, pyrite; low‑strength granite | 8 |
| Ⅳ | Moderately solid | Ordinary sandstone, iron ore | 6 |
| Ⅳa | Moderately solid | Sandy shale, shaly sandstone | 5 |
| Ⅴ | Medium‑solid | Hard argillaceous shale, low‑strength sandstone & limestone, soft conglomerate | 4 |
| Ⅴa | Medium‑solid | Various low‑strength shales, dense marl | 3 |
| Ⅵ | Relatively soft | Weak shale, very‑soft limestone, chalk, rock salt, gypsum, anthracite, fractured sandstone, stony soil | 2 |
| Ⅵa | Relatively soft | Gravelly soil, fractured shale, agglomerated gravel & broken stone, hard coal seam, hardened clay | 1.5 |
| Ⅶ | Soft | Dense soft clay, relatively soft bituminous coal, compact compacted soil, clay‑based soil | 1 |
| Ⅶa | Soft | Soft sandy clay, gravel, loess | 0.8 |
| Ⅷ | Soil‑like | Humus soil, peat, soft sandy soil, wet sand | 0.6 |
| Ⅸ | Loose | Sand, hillside gravel deposits, fine gravel, loose soil, mined coal | 0.5 |
| Ⅹ | Quick‑sand‑like | Quick‑sand, swamp soil, water‑bearing loess and other high‑moisture soils | 0.3 |
Explanation of Protodyakonov Strength Coefficient
Rock strength is a quantitative index indicating how easy or difficult it is to break ore and rock.
In practical mining practice, some rocks are hard to destroy and fragment. Such rocks are also difficult for drilling and blasting, which indicates high hardness, namely high solidity. In engineering, the concept of rock solidity (Protodyakonov hardness coefficient, value f) is adopted to describe the difficulty level of rock fragmentation under external force.
Calculation Formula
| R: Uniaxial ultimate compressive strength of standard rock specimen, Unit: |
The Protodyakonov rock‑classification system classifies rocks according to this strength coefficient. Reference ranges for common rock types:
- Extra‑solid rock: f = 15～20, e.g. hard granite, limestone, quartzite;
- Solid rock: f = 8～10, e.g. ordinary granite, solid sandstone;
- Medium‑solid rock: f = 4～6, e.g. ordinary sandstone, iron ore;
- Weak rock: f = 0.8～3, e.g. loess (f = 0.3).
| ⚠️Concept distinction: Rock strength: Capacity to resist unidirectional external loads such as compression, tension, bending and shear. Rock solidity: Capacity to resist combined external forces (composite loads from pick‑shovel excavation, mechanical crushing, blasting impact, etc.). These are two different engineering concepts and shall not be confused.  Multifunctional All-in-one Machine for Underground Mine Roadway & Tunnel Non-blasting Excavation  This all-in-one machine integrates rock milling crushing and material conveying. The front milling head breaks surrounding rock, while the collection structure feeds debris to rear belt conveyor for transportation. Crawler chassis adapts to rough underground roads, widely applied for tunnel/mining roadway excavation and soft rock mucking.  This unit integrates scaling and mucking functions on one crawler base. The upper hydraulic boom removes unstable rock after excavation, while the front hopper and built-in conveyor transport debris out of work zone. It cuts logistics work of deploying separate machines, ideal for confined roadway worksites.  Wheel chassis delivers flexible cross-site travel, paired with hydraulic breaker and front dozer for breaking and ground leveling |