Fragen Lern Cd 4.4 Crack
the soil surface may be smooth, rough, or irregular in structure. it may have a discernible horizon structure, or it may be homogeneous, with all the constituents mixing smoothly. the surface may be granular, paveable, or discontinuous.
the structure of a soil is important. soil structure can be defined in terms of its physical, chemical, and biological components. because of the variability of these components and their relationship to one another, the structure of a soil may be described in a number of ways, and a large number of terms are used to characterize them. the first of these is perhaps the most common. in general, structure refers to the spatial arrangement of the soil components and the way in which they are related to one another. the structure may be divided into two principal classes: geologic and hydrologic.
geologic structure is characterized by size, shape, and the relative abundance of the constituents. the constituents are usually in definite layers and are separated by definitive units. these may be layers of bedrock, stratified layers of one material, or layers of soil that contain one or more of the other components.
hydrologic structure is determined by the interactions of the components. there are three principal types of hydrologic structure: a matrix, a matrix with fractures, and matrix with filters. in matrix soils, the material has no distinct layers or layers that serve as barriers. in matrix with fractures, the materials are separated by barriers, usually layers of bedrock. in matrix with filters, the material is still continuous in all directions, but has local areas that are permeable.
the main factor limiting infiltration of water in the soil is its finite permeability. from the point of view of water infiltration into the soil profile, water enters the soil profile near the surface in a short distance and moves rapidly deeper as a result of the hydraulic gradient, which is greater near the surface. at a depth of about 0.5 meter, hydraulic conductivity drops to an amount that is on the order of 1% of that at the surface. at this depth, the rate of water infiltration is limited and it is at a rate that is less than 1% of the flux in the soil profile from the soil pore space to the atmosphere. many infiltration studies have estimated the rate of infiltration into the soil profile in terms of the infiltration rate of water in the soil profile from the soil pore space to the atmosphere.
soil is characterized as having a hydraulic conductivity equal to zero when the fluid head is lower than the hydraulic potential. the hydraulic potential is the theoretical pressure that would be exerted on a column of water in saturated soil or a column of air at the pressure head and the height of the column. under saturated conditions, the pressure head is equal to the water potential, which is the difference between the actual atmospheric pressure, and the vapor pressure of water (e.g., at the soil surface). the hydraulic conductivity is thus equal to the rate at which water flows in the column of water or air to the vapor pressure head. the hydraulic conductivity of the soil is the volume-flow rate per unit head, measured in cm/sec.
according to national standards, technical specifications, and research, soil is classified according to its physical properties, such as particle size, bulk density, and macroporosity. see table 4-3 for the basic classification of soils. note that one must be careful when making generalizations about soils from one region to another. for example, the soils of one region may be classified in the text or on a map with a general label, such as gravel, sand, loam, or clay. however, this label may not mean the same thing to everyone in a region. do not assume that soil type means the same thing to all experts in a region.