What Is a Porosimeter?

Porosity refers to the percentage of pore volume in the bulk material to the total volume of the material in its natural state. Porosity includes true porosity, closed porosity, and prior porosity.

(1) Porosity of materials <br The porosity of materials refers to the percentage of the volume of pores in the bulk material and the total volume of the material in its natural state, which is expressed by P. The calculation formula of the porosity P is:

Porosity can be divided into two types:

Porosity is an important factor affecting soil permeability. The pores in the soil are divided into effective pores and ineffective pores. Only effective pores can produce seepage, and ineffective pores have no effect on the size of the seepage. The so-called invalid pores are mainly divided into three categories: non-connected pores, semi-connected pores, and pores that are connected but cannot penetrate through the flow of permeated water. The third type of pores mainly refers to the pores occupied by the water film around the soil particles. For coarse-grained soil, inactive pores are mainly disconnected and semi-connected pores, and the proportion of pores combined with water film is very small. But for cohesive soils, because the particles are very small, the proportion of disconnected and semi-connected pores is small, while the proportion of pores occupied by the combined water film is large.

It is generally believed that the permeability coefficient of coarse-grained soil is much larger than that of cohesive soil, because the porosity ratio of coarse-grained soil is much larger than that of clay, which is actually a wrong understanding. In fact, the relative density of soil particles is almost the same, and the bulk density of coarse-grained soil is much larger than that of cohesive soil, indicating that the porosity of coarse-grained soil is much smaller than that of clay. The permeability coefficient formula is directly related to the porosity ratio. The above analysis shows that the porosity ratio of the clayey soil is large, but its permeability coefficient is small. Therefore, it is necessary to discuss the reason for the difference between the permeability coefficient of coarse-grained soil and clayey soil from the perspective of analytical theory.

In a square area of 1 m2, the total area of the soil particles and the total pore area are constant and do not change with the particle size; however, the pore area occupied by the combined water film increases as the particle size decreases. The ineffective pores in the clay account for almost 85% of the total pores, and less than 0.18% of the pumice stones with the largest particle size. This fully proves that compared with coarse-grained soil, most of the pores in the clayey soil are occupied by the combined water film. The existence of a large number of invalid pores in this clayey soil has a large porosity ratio and its permeability coefficient. Rather the small root cause. Therefore, simply applying the empirical formula for calculating the permeability coefficient of coarse-grained soil to cohesive soil, the calculation result will inevitably have a large error. Only by correcting them and excluding the influence of invalid pores occupied by the water film, can the unified empirical formula for the permeability coefficient of coarse-grained soil and cohesive soil be achieved ^[2] .