Soil and Water Relationships
My superficial answer is porosity describes the spaces between other crustal solids that 'could' be occupied by water. (They could be occupied. tion of compressible sediments, the theory is not indicated to describe the relationships between porosity, pressure on the solids, and permeability of the. In a soil or rock the porosity (empty space) exists between the grains of minerals. Figure 3. Video showing how connected pores have high permeability and can A relationship does not necessarily exist between the water-bearing capacity.
Soil structure refers to the arrangement of soil particles sand, silt, and clay into stable units called aggregates, which give soil its structure. Aggregates can be loose and friable, or they can form distinct, uniform patterns. For example, granular structure is loose and friable, blocky structure is six-sided and can have angled or rounded sides, and platelike structure is layered and may indicate compaction problems.
Soil porosity refers to the space between soil particles, which consists of various amounts of water and air. Porosity depends on both soil texture and structure. For example, a fine soil has smaller but more numerous pores than a coarse soil.
A coarse soil has bigger particles than a fine soil, but it has less porosity, or overall pore space. Water can be held tighter in small pores than in large ones, so fine soils can hold more water than coarse soils.
Water infiltration is the movement of water from the soil surface into the soil profile. Soil texture, soil structure, and slope have the largest impact on infiltration rate. Water moves by gravity into the open pore spaces in the soil, and the size of the soil particles and their spacing determines how much water can flow in. Wide pore spacing at the soil surface increases the rate of water infiltration, so coarse soils have a higher infiltration rate than fine soils.
Permeability refers to the movement of air and water through the soil, which is important because it affects the supply of root-zone air, moisture, and nutrients available for plant uptake. A soil's permeability is determined by the relative rate of moisture and air movement through the most restrictive layer within the upper 40 inches of the effective root zone.
Log in to your subscription
Water and air rapidly permeate coarse soils with granular subsoils, which tend to be loose when moist and don't restrict water or air movement. Slow permeability is characteristic of a moderately fine subsoil with angular to subangular blocky structure.
It is firm when moist and hard when dry. Water-holding capacity is controlled primarily by soil texture and organic matter. Soils with smaller particles silt and clay have a larger surface area than those with larger sand particles, and a large surface area allows a soil to hold more water.
- Technical Questions
In other words, a soil with a high percentage of silt and clay particles, which describes fine soil, has a higher water-holding capacity.
The table illustrates water-holding-capacity differences as influenced by texture. Organic matter percentage also influences water-holding capacity.
The relationship between porosity and permeability of concrete
Samples in which kaolinite and illite occur as clay coatings fall within the boundaries of the three upper fields in Fig. However, fibrous illite can form within the pore space in the Rotliegend sandstones lower two fields in Fig. Under the scanning electron microscope, the appearance of numerous fine strands of illite within pores makes it obvious why permeability is so impaired.
At any given porosity, samples with the larger dolomite crystal sizes have the highest permeability Fig. At a given crystal size, an important control on porosity is the amount of calcite, which is believed to be recrystallized lime mud.
Different productive zones in the same field may have different dolomite textures,  suggesting that original sediment texture and chemistry were the main factors determining the distribution of crystal sizes. From measurements of specific surface area, the equivalent grain diameter is computed to range from 1.
Rock type influence on permeability
As indicated in Fig. The addition of pore space produces modest gains in permeability low slopes for the two data sets in Fig. To obtain petrophysically viable groupings, Lucia grouped all dolomitized grainstones with mud-dominated samples having large dolomite crystals and grouped dolomitized packstones with mud-dominated samples having medium-sized dolomite crystals key in Fig.
He suggests that the plot can be used to estimate permeability of a nonvuggy carbonate rock if the porosity and particle size are known.
He points out that the effect of vugs is to increase porosity but not alter permeability much.
It appears that the fundamental controls observed in the sandstones are also present in these selected carbonates, if care is exercised in categorizing the carbonates in terms of grain or crystal size.