MODULE 1

Question 1

Saturated soils

Answer 1

voids are filled completely with water

Question 2

Dry soil

Answer 2

voids are filled completely with air

Question 3

Fines

Answer 3

Clay and Silt

Question 4

Sand

Answer 4

0.06 - 2 mm

Question 5

Gravel

Answer 5

2 - 60 mm

Question 6

Cobbles

Answer 6

60 - 200 mm

Question 7

Boulders

Answer 7

> 200mm

Question 8

Coefficient of Angularity

Answer 8

Fu = 4πA/l^2
where A = cross-sectional area
and l = perimeter

Question 9

Roundness Coefficient

Answer 9

R = r/x

Question 10

Plastic Limit

Answer 10

wPL: water content below which fine soil behaves brittle and crumbly

Question 11

To determine wPL

Answer 11

• roll out threads of clay (3mm diameter)

- wPL is defined as the moisture content w when threads become brittle

Question 12

Liquid Limit

Answer 12

wLL: water content above which fine soil behaves as a liquid

Question 13

To determine wLL

Answer 13

BS: standard fall-cone tests
- usually carry out several tests at different w and draw a straight line between w and fall distance

US: use a Casagrande apparatus, cut V-shape in soil - count number of standard taps to cause the cut to disappear
- test requires more “judgement” than the fall - cone

Question 14

Clays

Answer 14

• have a plate-like structure

- the higher the wLL, wPL and PL, the more plastic the clay (i.e. the more it will shrink, swell and change volume)

Question 15

Non-plastic silts

Answer 15

• are like extremely fine sand

-

Question 16

Soil Classification

Answer 16

35% fines = “fine”

Question 17

Static Compaction

Answer 17

• sheepsfoot roller: shallow compaction
• smooth-wheel roller: shallow compaction
• pneumatic (multi-tired) roller: shallow compaction

Question 18

Dynamic Compaction

Answer 18

• vibratory roller: shallow compaction
• High Energy Impact Compaction (HEIC): deep compaction
• Impact Load (weight dropping): very deep compaction

Question 19

Vibro-compaction

Answer 19

very deep compaction

Question 20

Proctor Compaction Tests

Answer 20

laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density

Question 21

Standard Proctor Test Method

Answer 21

• cylindrical 1-litre mould (H=12.7cm and D=10cm)
• standard hammer (M = 2.5kg; dropping height 300cm)
• build 3 equal-volume layers and apply 27 blows per layer: compaction energy = 600kJ/m^3

Question 22

Modified Proctor Test Method

Answer 22

• cylindrical 1-litre mould (H=12.7cm and D = 10cm)
• standard hammer (M = 2.5kg; dropping height 450cm)
• build 5 equal-volume layers and apply 25 blows per layer: compaction energy = 2700 kJ/m^3

Question 23

Compaction

Answer 23

densification of soil by expulsion of air and the rearrangement of particles

Question 24

Benefits of compaction

Answer 24

• increases strength
• reduces permeability
• decreases compressibility (settlement)

Question 25

Effects of compactive effort

Answer 25

• increase the dry unit weight (density)

- decrease the optimum water content

Question 26

Effects of gradation

Answer 26

(uniformity coefficient): poorly graded and gap graded granular soils are easy to compact

Question 27

effective stress, unsaturated soils

Answer 27

σ’ = (σ - Ua) + X(Ua - Uw)
where X depends on the degree of saturation
Ua = pore air pressure
Uw = pore water pressure

Question 28

C(u)

Answer 28

Coefficient of Uniformity

• C(u) less than or equal to 10 “uniformly graded”
• C(u) greater than 10 “well graded

Question 29

C(z)

Answer 29

Coefficient of Curvature

• C(z) between1 and 3 = “well graded”
• C(z) less than 1 or greater than 3 = “gap graded”

Question 30

Clay size

Answer 30

less than 0.002 mm

Question 31

Silt size

Answer 31

0.002 to 0.06 mm

Question 32

amount of fines for “coarse” soil

Answer 32

less than 35%

Question 33

amount of fines for “fine” soil

Answer 33

more than 35%

Question 34

very dense

Answer 34

D(r) more than 85%

Question 35

dense

Answer 35

D(r) 65 - 85%

Question 36

med. dense

Answer 36

D(r) 35-65%

Question 37

loose

Answer 37

D(r) 15 - 35%

Question 38

very loose

Answer 38

D(r) less than 15%

Question 39

Dense soils have superior engineering properties

Answer 39

• higher stiffness (less deformability

- higher strength (improved stability)