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Hydrogeology > Soils 1 > Flashcards

Soils 1 Flashcards

(61 cards)

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1
Q

Poorly Graded

A

Most of the soil particles are the same size

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2
Q

Well Graded

A

the particles sizes are distributed over a wide range

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3
Q

Gap Graded

A

soil with two or more uniformly graded parts

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4
Q

Hydrometer Analysis

A

Hydrometer analysis calculates the diameter of particles based on their settling times

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5
Q

What sizes of particles are used in a sieve analysis?

A

used for particle sizes > 0.075 mm in diameter

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6
Q

What sizes of particles are used in a hydrometer analysis?

A

used for particles sizes < 0.075 mm in diameter

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7
Q

What is a grain size analysis useful for?

A 
very useful for cohesionless soils
 Estimate permeability
 Filter design (gradation criteria)
 Soil classification
 Pavement construction (gradation suitability)
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8
Q

When is grain size info of limited usefulness?

A

limited usefulness for cohesive soils
 Size of “individual particles” may depend on degree of disaggregation
 Accuracy of GSD curve questionable for fine soils
 Cohesive soil behavior depends more on other factors (i.e., clay mineral
type, w%, stress history, etc.)

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9
Q

What does stokes law allow for?

A

allows us to find the velocity of the particles and this is related to diameter. : Thus settling time and particle diameter

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10
Q

What charge does clay carry?

A

Clay carries a net negative charge.

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11
Q

What is soil a combination of?

A

Air, water, and solids

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12
Q

What do the atterberg limits describe?

A

The consistency of fine-grained soils with varying moisture contents.

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13
Q

How is the liquid limit determined?

A

1.) Soil is placed in cup. 2) Groove is cut in soil 3) Cup is then lifted and dropped until a distance of 12.7 mm of the groove closes

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14
Q

Liquid Limit

A

The moisture content in percent that takes 25 blows to close a groove of 12.7mm.

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15
Q

What can a flow curve be used for?

A

can be used to estimate the LL when it is difficult to meet the required closure at 25 blows.

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16
Q

What is the one point method

A

estimates the liquid limit based on a single trial, and is generally valid for LL=Wn(N/25)^(tanb)

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17
Q

Plastic Limit

A

The moisture content in which the soil crumbles when rolled into 3.2mm diameter threads.

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18
Q

What is the Plasticity Index useful for?

A

Usefull for classification and soil property estimation.

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19
Q

Shrinkage Limit

A

The point at which a soil no longer loses any moisture.

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20
Q

Liquidity index

A

a measure of the relative consistency of a natural soil

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21
Q

If LI>1, (if w>LL)

A

soil can be sensitive to disturbance and behave like liquid when disturbed

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22
Q

If Li<0, (if w

A

Soil deposits are heavily over overconsolidated

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23
Q

What is the Consistency Index at the LL

A

0

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24
Q

What is the Consistency Index at the PL

A

1

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25
What is activity?
A measure of the swelling potential of clay soils
26
What are three types of soil activities?
Inactive clay, Normally active clay, Active clay
27
What is the A-line?
A line on a PI vs LL chart that separates inorganic clays from inorganic silts
28
Where are inorganic clays in a plasticity chart?
Above the A-line
29
Where are inorganic silts in a plasticity chart?
Below the A-line
30
What is the U-line
The upper limit of the relationship b/w PI and LL of any known soils
31
What are the particle limits in the USDA system?
Sand size, silt size, and clay size,
32
In what classification system do you have to account for gravel size?
USDA
33
What is the relationship between cu and grading.
As Cu goes down, uniformity goes up.
34
When is a soil well graded (Cu)
Cu>10
35
When is a soil poorly graded?
Cu<5
36
Compaction
The densification of soil by removal of air
37
What are some advantages of compaction?
qx
38
What happens to the dry unit weight initial as water is added?
In initially increases because water acts as a softening agent
39
After a certain point, what happens to the dry unit weight as water is added?
At some point (w=w2), the dry unit weight decreases as water is added.
40
Optimum moisture content
The moisture content at max dry unit weight
41
How is a proctor test done?
Soil compacted in 3 layers and 25 blows/layer. Wt hammer = 2.5 kg at height of 12 in.
42
Other then water content, what two major factors affect compaction?
Soil Type and compaction effort.
43
What type of soil exhibits a compaction curve other then a single-peaked bell shaped curve.
Some sands
44
As compaction effort increases....
The maximum dry unit weight increases, and the optimum moisture content decreases.
45
How many layers are used in a modified proctor test?
5
46
How many blows are delivered to each layer in a modified proctor?
25
47
What is the weight of hammer for each compaction test?
Standard = 2.5, modified = 4.5
48
What is the height for each compaction test?
12 for standard, 18 for modified
49
When a smooth wheeled rollers suitable?
Sandy and clayey soils
50
To what depth are smooth wheeled rollers effective?
20 to 30 cm, so place soil in shallow layers.
51
When are pneumatic rubber tired rollers useful.
Sandy and clayey soils, only 70 to 80% coverage
52
When are sheepsfoot rollers usefull?
Usefull for compacting clayey soils.
53
When are vibratory rollers useful?
Efficient in compacting granular soils.
54
In most earthwork, what percent of specified dry unit weight is necessary in the field?
90-95%
55
When are GW and GP soils useful?
Good material as base of pavement
56
Are GM and GC good for pavement?
No
57
What are some strengths of gravel?
High stregnth, low compressibility, easily compacted
58
Sands (General)
Good fills, easily compacted
59
What happens to sands if wetted?
SW and SP retain stregnth. SM and SC loose some strength but still good.
60
Low Plasticity Silts and Clays
Usually acceptable fills.. Lose more strength when wetted. Prone to frost heave problems
61
High Plasticity Silts and Clays
Generally poor choice for retaining wall backfill. - Difficult to compact - Expansive and low wet strength - Low k and best choice when need low k like landfill caps and liners

Hydrogeology (6 decks)

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