Specifically, the first-class site soil refers to the site with uniform soil layer, no obvious change in allowable bearing capacity, convenient construction and no adverse geological effects. Class II site soil refers to all kinds of site soil except gravel soil, Class III site soil refers to gravel soil, and Class IV site soil refers to Grade I or II foundation soil of construction site.
Generally, it should be determined by the distance between the top surface of the soil layer with shear wave velocity greater than 500 m/s and the shear wave velocity of the underlying rock and soil layer not less than 500 m/s. When there is a soil layer with shear wave velocity less than 2.5 times that of the upper soil layer below 5m, and the shear wave velocity of this layer and its underlying layer is not less than 400 m/s, it can be determined according to the distance from the ground to the top surface of this soil layer.
Matters needing attention in site classification
One kind of site is called stable site, which is characterized by high foundation bearing capacity and low compressibility, and is not prone to liquefaction, landslide, earthquake subsidence and other problems, and has little impact on the safety and stability of buildings. The second kind of site is called unstable site, which is characterized by low bearing capacity, high compressibility of foundation, easy liquefaction and earthquake subsidence, and has certain influence on the safety and stability of buildings.
The three types of sites are called unstable sites, which are characterized by low bearing capacity of foundation, high compressibility, easy liquefaction, landslide, earthquake subsidence and other problems, and have a great impact on the safety and stability of buildings. It should be classified according to the actual situation and avoid blindly applying the theory. Natural conditions such as geology, hydrology and meteorology in the area where the site is located, as well as specific conditions such as the type, scale and structure of buildings should be considered.