|
|
According to [DINENISO14688:2018], volcanic soil is defined as “magma that has been emitted into the atmosphere during intense volcanic eruptions and, over time, has formed deposits; e.g., pumice, scoria, ash.” (Table: Designation and description of volcanic types of soil [ENISO14688]) |
||||||
|
|
|
||||||
|
|
Fine soil particle shape depends solely on the type of mineral.
Coarse soil particle shape and roughness depend on the type of rock as well as the individual history of transportation and weathering.
|
||||||
|
|
The grain particle shape has an influence on the texture and isotropy of the soil, as well as on the structural characteristics of the subsoil, such as:
[Soos96] [Trian00]. (Image: Particle shape - well rounded) (Image: Particle shape - Rounded) (Image: Particle shape - Sub rounded) (Image: Particle shape - Angular) (Image: Particle shape - Very angular) |
||||||
|
|
|
||||||
|
|
The primary distinctive feature of mineral soil is the grain size of the individual particles. The determination of the grain size is the first step in the designation and classification process of a certain type of soil. (Image: Soil grain sizes from 0 – 4 mm) (Image: Soil grain sizes from 4 – 25 mm) |
||||||
|
|
An important factor in soil classification presented in the upcoming pages is the soil particle size (grain size). Two scales are used for classification purposes of soil grain size:
The table below presents the most common sieve mesh opening sizes for these two scales. (Table: US sieve mesh size) |
||||||
|
|
|
||||||
|
|
|
||||||
|
|
The cumulative frequency polygon of the mass percentages of the given soil sample is called a grading curve (or grain size curve), and is used for a definite designation of the soil. (Image: Grading curves of some characteristic types of soil [Neuma64]) |
||||||
|
|
(Image: Grain sizes classification) (Table: Soil characteristics) |
||||||
|
|
Example: The measured values of the sedimentation analysis resulted in the following mass percentages: (Formula: Aus den Messwerten der Siebanalyse folgten die Gewichtsanteile) With ∑m (D < d) as the percent passing (percentage by weight) through the screen with the mesh size d and ∑ m(D) as the total mass of the sample. Consequently: (Formula: Gewichtsanteil y(0,063)) (Formula: Gewichtsanteil y(0,125)) (Formula: Gewichtsanteil y(0,25)) Table: Dry screening … |
||||||
|
|
The following particle size distinctions are made when grading non-cohesive types of soil:
|
||||||
|
|
|
||||||
|
|
The grading curve results in essential curve parameters that require a prior determination of d10, d30 and d60.
By means of these details the curve parameters CU (coefficient of uniformity) and CC (coefficient of curvature) can be calculated to describe the |
||||||
|
|
The shape parameters of the grain size distribution curve are determined by the coefficient of uniformity CU (in [DINENISO14688:2018] and [[ASTM D6913]] ) and the coefficient of curvature CC. (Formula: Calculation of the coefficient of uniformity CU) The coefficient of uniformity CU specifies the average inclination (slope) of the grading curve that has been determined according to [[ASTM D422]] and/or [DIN18123], whereas the coefficient of curvature … |
||||||
|
|
A well-graded grain size distribution is present if CU ≥ 6 and 1 ≤ CC ≤ 3, whereas a poorly-graded or intermittent grain size distribution holds true for all other cases (see table). However, according to [Estermann (1994)], these determinations should be slightly limited, as both criteria can also apply to certain discontinuously running grading curves. (Table: Classification of coarse types of soil depending on the coefficient of uniformity and … |
||||||
|
|
The classification of very coarse types of soil according to the table requires very large samples. In that case, it is impossible to extract representative samples from borings [DINENISO14688:2018]. (Table: Classification of very coarse soil as per ISO 14688-2) |
||||||
|
|
(Image: Attention!) Using the grading curves and the coefficient of uniformity CU, a first essential conclusion can be derived on the compactness- or displacement capability, as well as water permeability of the soil. |
||||||
|
|
In any case of a specific application, it is essential to determine the site-specific grain size distribution of the soil. Using grain size data from other nearby sites could lead to distortions in understanding the soil properties. This concept is shown by the grain distribution curves of various soil samples collected from the German city of Hamburg. These curves clearly illustrate the variety in grain sizes and the soil uniformity even within a … |
||||||
|
|
|
||||||
|
|
The soil condition of coarse types of soil is characterised by the bedding density, whereas fine types of soil are characterised by their consistency. |
||||||
|
|
|
||||||
|
|
Why is it important to know the relative density of the soil? (Image: Attention!) The relative density helps to identify the arrangement of individual grains in coarse soils relative to each other. Using this information, we can make immediate conclusions about the soil stability, displacement capability, and water permeability of the soil within an excavation. |
||||||
|
|
Assuming an ideal single size grain, there are only two types of bedding:
In the case of loose bedding, individual soil grains can move relative to each other. Dense bedding is the natural formation for single-size grain soils. In this form, the soil is solid like a rock; the soil grains can only … |
11094 search results:
