Chapter 4 - Further properties of Soil Flashcards
(22 cards)
What do the particles that make up soil vary significantly in?
Size
What is a good way of classifying the soil being dealt with?
By looking at the size of particles
What does ‘PSD’ stand for?
Particle Size Distribution
What is the particle size distribution?
A graphical way of representing the range of particle sizes present in the soil.
How is a PSD plot obtained?
Sample of the soil is washed through a series of sieves, each one progressively having smaller holes, resulting in the smaller particles falling to the bottom and the larger particles staying at the top
What does Dxx stand for?
The particles size of which percentage the soil is smaller than, e.g D50 would be the particle size 50% of the particles are smaller than.
What does the Uniformity Coeffient tell us?
How steep are PSD curve is
What does a ‘well graded’ soil have?
Particles distributed across all sizes
What does a ‘poorly graded’ soil have?
Particles that are all similar in size
When is the term ‘uniform’ used?
When particles all have the same sizes
What does the amount of void space depend on?
The particle size distribution and the arrangement of particles
If the PSD has a high uniformity coefficent value, and the particles are arranged in an optimal fashion, what will occur?
There will be little void space and the soil will be very dense
What is the equation for relative density, Id?
Emax - e / Emax - Emin
How do we classify fine particles, such as silt and clay?
By using a plasticity index
Why do clay particles ‘stick’ to each other?
Due to the electro-static attraction between the surfaces of clay platelets
Do clay particles remain stuck to each other when in water?
Yes
How do silt particles ‘stick’ to each other?
Small quantities of water hold the particles together due to surface tension forces
What does the term ‘plastic’ mean?
When a soil can be deformed and keep its shape and does not crack when deformed
What is the liquid limit, WL?
Boundary in terms of water content between ‘plastic’ behaviour and ‘liquid’ behaviour
What is the plastic limit, Wp?
The boundary in terms of water content between ‘plastic’ and ‘brittle’ behaviour.
How do you determine the liquid limit of clay?
Find the water content at which a metal cone will penetrate to a certain depth into a sample of the clay ‘The fall cone test’
How do you determine the plastic limit of clay?
Roll a thread of the clay under your finger tips, the water content of the clay when it cracks is defined as the plastic limit. D = 3mm
