civil engineering - Soil swelling and mass/volume relationships - Engineering Stack Exchange
Soils with a bulk density higher than g/cm3 tend to restrict root growth. The total soil volume is the combined volume of solids and pores which may contain. SOIL MECHANICS. Soil Composition. Main Variables: V = Volume. W = Weight m = Mass. Subscripts: a = air v = voids w = water s = solids t = total (or. Volume Mass Relationship of Soils. 7. Bulk Mass Density of Soil. The bulk mass density (?) is defined as the total mass (M) per unit volume (V)?=M/V.
Notation and Units
The average values of air, water and solid in soil are easily measured and are a useful indication of a soils physical condition. Soil BD and porosity the number of pore spaces reflects the size, shape and arrangement of particles and voids soil structure. Both BD and porosity Vpores give a good indication of the suitability for root growth and soil permeability and are vitally important for the soil-plant-atmosphere system Cresswell and Hamilton, ; McKenzie et al.
Structural composition of soil, containing soil fraction Vsolids and pore space for air Vair and water Vwater. Measuring bulk density Bulk density measurements can be done if you suspect your soil is compacted or as part of fertiliser or irrigation management plans see Bulk Density — On Farm Use factsheet.
To account for variability, it is useful to take several measurements at the same location over time and at different depths in the soil, for example at 10, 30 and 50 cm depths to look at both the surface soil and subsoil.
It is also useful to measure the bulk density of when comparing management practices e. The most common method of measuring soil BD is by collecting a known volume of soil using a metal ring pressed into the soil intact coreand determining the weight after drying McKenzie et al.
Sampling the soil This method works best for moist soils without gravel. If sampling during summer, it is possible to wet the soil manually to keep bulk density core intact. To do this, place bottomless drum on the soil and fill with water, allowing to wet naturally for 24 hours. Using the appropriate tools see information boxprepare an undisturbed flat horizontal surface in the soil with a spade at the depth you wish to sample.
Push or gently hammer the steel ring into the soil.
Soil Phase Relationships
A block of wood may be used to protect the ring. Macropores are most prevalent in sandy soils and well-aggregated soils, but can be converted to micropores by compaction. Medium-textured soils have an abundance of mesopores.
Clays promote aggregation but can also be readily compacted.
Soil Phase Relationships - zolyblog.info
Clays also increase water storage by providing an abundance of micropores. Thus, texture and structure, plus the level of induced compaction, are the main properties governing amount and type of pore space in the soil. Organic matter affects porosity through its enhancement of soil aggregation. Porosity can be calculated if bulk density and particle density are known.
Bulk density is soil mass divided by unit volume. In its natural state, a soil's volume includes solids and pores, therefore, a sample must be taken without compaction or crumbling to correctly determine bulk density. It increases with depth and tends to be high in sands and compacted pan horizons, and tends to be low in soils with abundant organic matter.
Tillage operations looen soils and temporarily lower bulk density, while compaction processes raise bulk density. High bulk densities correspond to low porosity. Natural soil-forming processes that increase aggregation reduce bulk density, but excessive tillage and raindrop impact on bare soil destory aggregation and increase bulk density. Particle density is the volumetric mass of the solid soil.Phase Relations
It differs from bulk density because the volume used does not include pore spaces. For most soils, this value is very near 2. Particle density varies little between minerals and has little practical significance except in the calculation of pore space.
Porosity is that portion of the soil volume occupied by pore spaces.
- Soil Phase Relationships
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- Bulk Density – Measurement
This property does not have to be measured directly since it can be calculated using values determined for bulk density and particle density. A cm3 cylindrical container was used to collect an undisturbed soil sample.