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As per IS classification SM soil is known as
Silty clay
Silty gravel
Sandy gravel
Silty sand
Silty sand
According to the Indian Standard Classification System (ISCS) defined in IS: 1498, soil symbols are represented by two letters ┬╖ The first letter denotes the primary grain size (S for Sand, M for Silt, C for Clay, G for Gravel) and the second letter denotes the plasticity or gradation characteristics (M for Silt, C for Clay, W for Well-graded, P for Poorly-graded) ┬╖ Thus, 'SM' denotes Silty Sand.
According to the Indian Standard Classification System (ISCS) defined in IS: 1498, soil symbols are represented by two letters ┬╖ The first letter denotes the primary grain size (S for Sand, M for Silt, C for Clay, G for Gravel) and the second letter denotes the plasticity or gradation characteristics (M for Silt, C for Clay, W for Well-graded, P for Poorly-graded) ┬╖ Thus, 'SM' denotes Silty Sand.
CuтАЛ=D10тАЛD60тАЛтАЛ тАФ Coefficient of Uniformity (used for grading)
CcтАЛ=D10тАЛ├ЧD60тАЛ(D30тАЛ)2тАЛ тАФ Coefficient of Curvature
The ISCS system uses a binary coding method where the primary constituent is placed first and the secondary property is placed second ┬╖ For 'SM', 'S' represents the coarse fraction (sand-sized particles) and 'M' (from the Swedish word 'mo') indicates that the fine-grained fraction is predominantly silty in nature, exhibiting low plasticity.
S stands for Sand (particles passing 4.75 mm IS sieve and retained on 75 micron IS sieve).
M stands for Silt (particles passing 75 micron IS sieve with low to medium plasticity).
IS classification is based on grain size distribution and Atterberg limits.
SM is a coarse-grained soil where more than 50% of the coarse fraction passes the 4.75 mm sieve.
Uniform system for engineering communication.
Predicts soil performance in construction projects.
Does not explicitly account for particle shape.
Requires laboratory testing (sieve analysis and Atterberg limits).
Foundation engineering.
Pavement subgrade design.
Option A (Silty clay) would be classified as 'ML' or 'MH' depending on plasticity.
Option B (Silty gravel) is represented by 'GM'.
Option C (Sandy gravel) is represented by 'GW' or 'GP'.
D is correct тАФ The symbol SM represents a coarse-grained soil that is predominantly sand (S) with a silty (M) fines content.
Remember that 'M' stands for silt (Swedish 'mo') and 'C' stands for clay ┬╖ Always pair the primary texture first and the secondary behavior modifier second.