Sampling

Question 1

Sampling frequencies for sand?

Answer 1

top of each new stratum, then 1m intervals. (SPT)

1.5m if distrubed.

Question 2

Sampling frequencies for Clay?

Answer 2

Top of each new stratum, after 1.5m intervals (U100)

each 1m if disturbed.

Rock - continous core sampling

Question 3

types of samples

Answer 3

disturbed

undistrubed

Question 4

disturbed soil meaning

Answer 4

wash boring cutting, shell and augur material.

Mixed up and contaminated w/ other layers

Question 5

Types of classes and information contained

Answer 5

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)

Question 6

Soil sensitivity equation?

Answer 6

St = shear peak/shear remoulded

Question 7

Causes of soil disturbance

Answer 7

changes in stress;

b) mechanical disturbance;
(c) changes in water content (e
(d) chemical changes

Question 8

Cause of change in stress conditions

Answer 8

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

Question 9

reducing side friction

Answer 9

inside smoothness

inside clearance

internal sliding liners

self explanitory

Question 10

How disturbance effects shear strength?

Answer 10

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

Question 11

Disturbance effect of stiffness and compressibility?

Answer 11

small strain stiffness proprtioanl to mean effective stress

changes in stress changes stiffness

60% stiffness change atleast

Question 12

methods of sampling

Answer 12

Block samples

Open drive samples

Piston samples or “push in” samples

Continuous samplers

Question 13

what is Open drive (u100) and how is it used

Answer 13

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.

Question 14

Open drive (u100)

Answer 14

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.

Question 15

u100 sampler, what class does it give?

Answer 15

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.

Question 16

disatavantge of split spoon

Answer 16

very high mechanical disturbance

Question 17

thin walled

Answer 17

pushed in (u100 is driven)

Ar = <15

only suitable for fine soils.

give class 1.

Question 18

Piston sampler advantages

Answer 18

high quality samples when used with thin walled tube

expensive, not suitable for very stiff soils of granular.

Question 19

How to use piston sampler

Answer 19

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

Question 20

Foil sampler used for and how to set up

Answer 20

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.

Question 21

sand sampling, how to sample?

Answer 21

in situ tests

using sampling tools (bishops sampler)

can be frozen to contain structure.