tailieunhanh - SOIL MECHANICS - CHAPTER 3

Hạt, nước, không khí 3,1 độ xốp Đất thường bao gồm nước, các hạt và không khí. Để mô tả một đất thông số khác nhau được sử dụng để mô tả sự phân bố của ba thành phần này, và đóng góp tương đối của họ với khối lượng đất. Đây là những cũng rất hữu ích để xác định các thông số khác, chẳng hạn như trọng lượng của đất. Họ được xác định trong chương này. Một thông số cơ bản quan trọng là n độ xốp, được định nghĩa là tỷ lệ khối lượng của không gian. | Chapter 3 PARTICLES WATER AIR Porosity Soils usually consist of particles water and air. In order to describe a soil various parameters are used to describe the distribution of these three components and their relative contribution to the volume of a soil. These are also useful to determine other parameters such as the weight of the soil. They are defined in this chapter. An important basic parameter is the porosity n defined as the ratio of the volume of the pore space and the total volume of the soil n Vp Vt. X Figure Cubic array. For most soils the porosity is a number between and or as it is usually expressed as a percentage between 30 and 45 . When the porosity is small the soil is called densely packed when the porosity is large it is loosely packed. It may be interesting to calculate the porosities for two particular cases. The first case is a very loose packing of spherical particles in which the contacts between the spheres occur in three mutually orthogonal directions only. This is called a cubic array of particles see Figure . If the diameter of the spheres is D each sphere occupies a volume nD3 6 in space. The ratio of the volume of the solids to the total volume then is Vp Vt n 6 and the porosity of this assembly thus is n . This is the loosest packing of spherical particles that seems possible. Of course it is not stable any small disturbance will make the assembly collapse. A very dense packing of spheres can be constructed by starting from layers in which the spheres form a pattern of equilateral triangles see Figure . The packing is constructed by packing such layers such that the spheres of the next layer just fit in the hollow space between three spheres of the previous layer. The axial lines from a sphere with the three spheres that support it from below form an regular tetrahedron having sides of magnitude D. The height of each tetrahedron is Dạ 2 3. Each sphere of the assembly with its neighboring part