Soil Classification

18 important questions on Soil Classification

What is heterogeneity in soil?

The spatial variability of soils, particularly evident in the deltaic soil deposits of the Netherlands

What is the spatial heterogeneity of the ground a function of?

The way of deposition, whether it is from natural deposition or from an engineered construction

How can we explain differential settlements like a bumpy road?

Soft soils that are highly compressible and because of the high heterogeneity of the soil
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What do we know about how our geotechnical design will behave from heterogeneity?

We are unsure and can represent it as a normal probability density function. And by finding our more and more about the soil we can reduce the uncertainty (i.e. Variance)

How does the process work for a geotechnical design?

1) Site investigation 2) Sampling or In-situ Tests 3) Laboratory 4) Soil Classification and Mechanical Tests 5) Material Properties & Behaviour 6) Geotechnical Analysis 7) Geotechnical Design

What are is the international classification according to grain size (diameter) of soil?

Clay < 0.002 mm, 0.002mm < silt < 0.063mm, 0.063 < sand < 2mm, 2mm < gravel < 63mm

How do soil types, based on grain sizes, differ from behavior?

Mechanical behavior can be very different, clay is much less permeable than sand and usually much softer, and peat is usually very light and strongly anisotropic & compressible

Why is grain size not very useful sometimes for classification?

It is only a first indicator and does not say much about the mechanical properties, e.g. Shape also plays an important role

What forms or shape can grains have?

Round and angular, angular grains have more friction and are thus stronger

What does a Sieve analysis do?

Gradation; you can find out what portion of the soil is which grain size.

How does as grain size distribution curve work?

You can draw lines at the mm-borders for the different types of grains and then you can read the %'s for each type

What caused the sinkholes in the Bennett Dam and how did they solve it?

They filled them with concrete but this was not a localized problem so it did not help. The whole Dam is likely built on poorly graded soil causing internal erosion (suffusion)

How do the chemical compositions of sand and gravel compare?

They usually have the same minerals as the original rock which they were created from e.g. Quartz

What is notable about the chemical composition of clays?

They can lead to creep and swelling characteristics with minerals created by chemical erosion

What is the chemical composition of peat?

Decayed trees and plants, consists of carbon compounds

What do we mean with the consistency of a soil?

For fine grained soils (silt and clay) it determined whether a soil can be easily handled. This is often dependent on water content, low content makes it solid like and high liquid like, intermediate plastic like

What is the plasticity index?

The difference between the liquid and plastic limits; PI = w_L - w_P which is often important to have a high value for in dikes

How does the International Classification System work?

Character 1 can be G S M(silt) C O(organic) Pt (Peat) and Character 2 can be W (well graded) P (poorly graded) M (silty) C (clayey) L (low plasticity) or H (high plasticity)

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