Sampling Flashcards
Sampling frequencies for sand?
top of each new stratum, then 1m intervals. (SPT)
1.5m if distrubed.
Sampling frequencies for Clay?
Top of each new stratum, after 1.5m intervals (U100)
each 1m if disturbed.
Rock - continous core sampling
types of samples
disturbed
undistrubed
disturbed soil meaning
wash boring cutting, shell and augur material.
Mixed up and contaminated w/ other layers
Types of classes and information contained
class 1: classification, moisture content, density, strength, deformation and consolidation
Class 2: classification, moisture content, desnity
Class 3: classification, moisture content
Class 4: classification
Class 5: None (just strata data)
Soil sensitivity equation?
St = shear peak/shear remoulded
Causes of soil disturbance
changes in stress;
b) mechanical disturbance;
(c) changes in water content (e
(d) chemical changes
Cause of change in stress conditions
reduction of total stress due to sampling.
Borehole will reduce stress at base.
swelling of sample as stress relief
effective stress and moisture content will change
reducing side friction
inside smoothness
inside clearance
internal sliding liners
self explanitory
How disturbance effects shear strength?
destructures real soils
higher pore pressure generated during shearing.
heavily OC clays mean effective strength can cause increase in intact strength.
hammer tube can fracture along fissure strength reduces
Disturbance effect of stiffness and compressibility?
small strain stiffness proprtioanl to mean effective stress
changes in stress changes stiffness
60% stiffness change atleast
methods of sampling
Block samples
Open drive samples
Piston samples or “push in” samples
Continuous samplers
what is Open drive (u100) and how is it used
driving tube into ground (cheap)
causes some disturbances to samples.
thick walls u100 can be - solid barreled or split barreled. Ar>20%
Split easier of soil can be used SPT
Thin walled (shelby) more fragile than u100, but cause less disturbance. driven in.
Open drive (u100)
driving tube into ground (cheap)
causes some disturbances to samples.
thick walls u100 can be - solid barreled or split barreled. Ar>20%
Split easier of soil can be used SPT
Thin walled (shelby) more fragile than u100, but cause less disturbance. pushed in.
u100 sampler, what class does it give?
area ratio < 30%
driven in w/ hammer
in fine soils, the standard open tube may be giving class 2 samples, but more often class 3.
in brittle fissured materials, class 3 often 4 if water is present.
disatavantge of split spoon
very high mechanical disturbance
thin walled
pushed in (u100 is driven)
Ar = <15
only suitable for fine soils.
give class 1.
Piston sampler advantages
high quality samples when used with thin walled tube
expensive, not suitable for very stiff soils of granular.
How to use piston sampler
piston positoned at top of tube and lowered while outer tube contiunes downwards.
air tight seal maintained by piston locked in position
piston prevents soil for enter tube
Foil sampler used for and how to set up
very long samples
overcomes internal fricton
sampler goes into soil and piston held in position, foils are unrolled w/ sampler tube as it decends, to enclose it.
sand sampling, how to sample?
in situ tests
using sampling tools (bishops sampler)
can be frozen to contain structure.
