Dynamic formulae are best suited for Coarse grained soil.

Coarse grained soil refers to soil particles that are larger in size, such as sand and gravel. These types of soils have a relatively low water-holding capacity and less cohesion between particles compared to fine grained soils.

Dynamic formulae are empirical relationships used to estimate soil properties based on the results of dynamic tests, such as the Standard Penetration Test (SPT) or the Cone Penetration Test (CPT). These tests involve driving a metal rod or cone into the ground and measuring the resistance encountered. The results of these tests, combined with other factors such as the soil type and groundwater conditions, can be used to estimate various soil properties.

Coarse grained soils are typically more granular and have larger void spaces between particles compared to fine grained soils. This allows for better penetration of the dynamic testing tools and provides more accurate measurements of soil resistance. The dynamic formulae have been developed and calibrated based on the behavior of coarse grained soils, and therefore, they are best suited for this type of soil.

On the other hand, fine grained soils, such as clay and silt, have smaller particles and tend to be more cohesive. The cohesive nature of these soils can affect the results of dynamic tests, leading to less accurate estimations of soil properties using dynamic formulae. Furthermore, the small particle size and high water-holding capacity of fine grained soils can impede the penetration of dynamic testing tools, making it difficult to obtain reliable measurements.

In conclusion, dynamic formulae are best suited for coarse grained soils due to their granular nature, larger void spaces, and better penetration characteristics. These formulae provide a useful tool for estimating soil properties in this type of soil, which is commonly encountered in civil engineering projects.