The word soil, when used in normal contents, just refers to that on which we all stand. However, engineers define (in construction) soil as any earth material that can be moved without blasting, while geologists define as rocks or sediments altered by weathering. Practicing engineers classified soils in to different types based on the grain (particle) size distribution of soil. According to this classification, the main soil types are boulders, gravel, sand, silt, and clay. Different ‘soil separate size limits’ have been developed by different institutions and organizations like Massachusetts Institute of Technology (MIT), US Department of Agriculture (USDA), American Association of State Highway and Transportation Officials (AASHO), Unified Soil Classification System, etc. However, currently the classification of Unified Soil Classification System is widely used all over the world.
Sand
Sand is one of the oldest materials used in the world of construction. Individual particles or grain of soil can be seen with our naked eye. Sand consist of coarse particles; according to unified soil classification system, particles sizes ranging from 0.075mm to 4.75mm are categorized as sand. Sand is cohesionless aggregate of coarse, sharp, angular particles. Sand is one of the raw material of concrete (as fine aggregates). When sand is used as the bedding material, it must be compacted before the commencement of construction, then the settlement will be low. Sand is seen in beaches, river beds, etc.
Gravel
Gravel is not only used for construction purposes, but also for a variety of purposes like gardening, etc. Gravel is an aggregate of rounded or angular fragment of rocks and minerals. According to unified classification system, particle sizes ranging from 4.75mm to 76.2mm are categorized as gravel. Gravels have a large bearing capacity. Bearing capacity means the safe load per unit area that the ground can carry. Further, gravels can carry huge structures without any sign of settlement. Settlement in construction means the settlement of structures in to the ground. In some rural areas, gravel is also used to surface the roads.
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What is the difference between Gravel and Sand? Though sand and gravels are construction materials, they have some different characteristics embedded on them. – Particle sizes of soil in gravel range from 4.75mm to 76.2mm, while particle sizes of soil in sand range from 0.075mm to 4.75mm. That means soil particles in gravel are larger than that of sand. – Bearing capacity of gravel is higher than that of soil. – When huge structures are considered, foundation cost in gravel is lower than constructing foundation in sand. – Settlement of structures in gravel is much smaller than settlements in sand, for a given large load. – Porosity in sand is relatively higher than in gravel. – Sand can be used as a raw material of concrete, while gravel is not used. – Water retention capacity of gravel is higher than that of soil.
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