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Geotechnical Engineering > Section 1 > Flashcards

Section 1 Flashcards

1
Q

How are soils made?

A

Soils are formed over time as a consequence of climate, mineral, and biological processes

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2
Q

Types of Rock

A

Igneous, sedimentary, metamorphic

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3
Q

Types of weathering

A

mechanical weathering
chemical weathering

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4
Q

What are some examples of mechanical weathering?

A

moving water, glacial movement, thermal expansion and contraction, stress relief, plant roots, wave action, wind, freezing and thawing of water in cracks

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5
Q

What is meant by ‘particle’?

A

layers of silca + layers of alumina + the interlayer (how the layers of silica and alumina are bonded) = particle

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6
Q

examples of chemical weathering

A

oxidation, hydration, reduction, carbonation, solution, hydrolysis, leaching, cation exchange

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7
Q

What is colluvium?

A

colluvium is soil transported by gravity

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8
Q

what is alluvium?

A

alluvium is soil transported by running water

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9
Q

what is lacustrine or marine transportation?

A

Lacustrine or marine transportation is soil transported via still water

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10
Q

what is till?

A

Till or glacial till is soil that has been transported via glacier(s)

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11
Q

What is Diagenesis?

A

The process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock (lithification)

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12
Q

What is cementation?

A

Cementation involves ions carried by groundwater chemically precipitating to form new crystalline material within sediment pores

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13
Q

What is pedogenesis?

A

soil formation

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14
Q

What are soil profiles?

A

Soil profiles are tools that geotechnical engineers use to map out the strata of soil that will be encountered during an engineering project.

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15
Q

What is the boundary in grain size between fine grain (silt and clay) and course grain (sand) soils?

A

0.075mm which corresponds to the Sieve No. 200 is the grain size boundary between fine grain and course grain soils

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16
Q

What is the boundary in grain size between course grain soils and gravel?

A

4.75mm (which corresponds to the sieve number 4) is the grain size that determines course grains from gravel

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17
Q

What are silica tetrahedrons composed of?

A

silicon and oxygen

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18
Q

What are the two clay microstructures?

A
  • silica (tetrahedral) sheet
  • alumina (octahedral) sheet
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19
Q

What are alumina octahedrons composed of?

A

alumuna and either oxygen or hydroxyl

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20
Q

What is the microstructure of Kaolinite?

A

kaolinite is a 1 to 1 alumina to silica sheet held together by hydrogen bonds
Note
- kaolinite is the largest clay microstructure

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21
Q

What is the microstructure of Illite?

A

Illite is a 2 to 1 silica to alumina sheet, so two silica sheets sandwiching the alumina sheet
- this microstructure is held together by potassium ions (medium strength bond)
- medium size clay microstructure

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22
Q

What is the microstructure of montmorillonite?

A

Montmorillonite is a a 2 to one sillica to alumina sheet, so two silica sheets sandwiching the alumina sheet
- this microstructure is held together by Van der Waals forces (weak bond) so these bonds can be easily infiltrated by water
- smallest clay structure

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23
Q

What’s the big idea with specific surface?

A

The more surface area (smaller particles) the more opportunity for water to stick to the surface

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24
Q

What is adsorbed water? (pg. 12)

A

The surface charges on fine-grained soils are negative (anions). These negative surface charges attract cations and the positively charged side of water molecules from the surrounding water. This thin film/layer of water bonded to the mineral surface is known as adsorbed water.

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25
Q

What are some of the grain size descriptors associated with the grain size distribution graph?

A

median grain size (D50), effective grain size (D10), coefficient of uniformity (Cu), coefficient of curvature (Cc)

26
Q

What are some values you can assume in solving for phase relationships?

A

V (total volume) = 1
or
Vs (Volume of solids) = 1
or
Gs (specific gravity of solids) = 2.7

27
Q

What is the purpose of subsurface characterization?

A
  • to evaluate the general suitability of a site for a proposed project
  • to enable for an adequate and economical design
  • to disclose and make provisions for difficulties that may arise during construction due to subsurface conditions
28
Q

What are some items that should be included in the subsurface characterization?

A
  • nature of the deposits including geologic origin and subsequent deposition, erosion, weathering etc.
  • depth, thickness, lateral extent, elevations, and composition of each soil and rock stratum
  • ground water elevations, their differences across the site and changes with time and environmental conditions
  • engineering properties of the soil and rock strata that affect the performance of the structure
29
Q

What should you reference in conducting reconnaissance for subssurface characterization?

A
  • results of previous site investigations
  • geologic maps
  • topographical maps
  • soils maps
  • water well logs
  • google earth
  • aerial photographs
  • remote sensing data
  • utility locations
30
Q

In a site visit to classify the subsurface characteristics what are you looking for?

A
  • checking out previous grading and development
  • performance of nearby structures
    o the effect of new construction on existing
    structures
  • surface drainage conditions
  • exposed soil and rock types
  • site access
31
Q

What is involved in a detailed site investigation for subsurface characterization?

A
  • geophysical methods
  • soil borings and sampling
    o number, location, depth, and type
  • in situ tests
  • laboratory tests
  • groundwater monitoring
32
Q

What are some drilling methods used in geotechnical engineering?

A
  • test pits
  • augering (solid and hollow stem)
  • rotary drilling
  • percussion drilling
33
Q

How do you know how many boreholes to make at a site?

A

there is a standard for the number of boreholes to make based on the building type (building v. subdivision)

34
Q

What are some items to know about borehole depth?

A
  • minimum depth of 6 meters unless rock or very dense material is encountered
  • must penetrate below soft or compressible layers (e.g., fill)
  • at least 3m into rock
  • stress increase due to foundation load is less than 10% of geostatic stress
35
Q

What are some drilling methods involved in geotechnical engineering?

A
  • test pits
  • augering (solid stem and hollow stem)
  • rotary drilling
  • percussion drilling
36
Q

What determines the number of boreholes that will be made at a site?

A

Guidelines for the minimum number of boreholes are based on whether the construction is for a building or for subdivisions and are provided in an ASTM standard in a table

37
Q

How deep should boreholes be?

A
  • minimum depth of 6m unless rock or very dense material is encountered
  • must penetrate below soft or compressible layers (e.g., fill)
  • at least 3m into rock
  • 1 to 3 times maximum foundation width
  • stress increase due to foundation load is less than 10% of geostatic stress
38
Q

What are augers?

A

Augers are truck mounted and equipped with continuous-flight augeres that bore a hole 100mm to 250mm in diameter. Augers can have a solid or hollow stem.

39
Q

What are some advantages of hollow stem augers?

A
  • fast
  • inexpensive
  • equipment readily available
  • samples easily obtained
  • drilling fluids not required
  • groundwater levels easily obtained
40
Q

What are some disadvantages of hollow stem augers?

A
  • depths limited to 15 to 45m
  • cannot be used in Rock
41
Q

What is Rotary Drilling/Wash Borings?

A

Rotary drilling or wash boring is a drill bit advanced by the weight of the drill string and down-force of the drilling rig and rotated by a motor. Drilling fluids are used to remove the cuttings and maintain the stability of the borehole

42
Q

What are some advantages of rotary drilling/wash borings?

A
  • fast
  • drills into Soil and Rock
  • large depths possible
  • casing not required
43
Q

What are some disadvantages of rotary drilling/wash borings?

A
  • drilling fluid required with associated time and cost
  • difficulty in identifying groundwater level during drilling
  • sampling not possible during drilling
44
Q

What types of samples can we obtain in geotechnical engineering?

A
  • disturbed samples
  • and “undisturbed” samples
45
Q

Which samples are disturbed samples?

A
  • bulk samples
  • split-barrel (split-spoon) samples
46
Q

Which samples are “undisturbed” samples?

A
  • Hand Trimmed samples
  • thin-walled samples
  • piston samples
  • Denison samples
  • Coring
47
Q

How does taking split-barrel samples work?

A
  • sampler is driven into the soil at the bottom of the boring using repeated blows of a 140lb hammer falling 30in.
  • used in both coarse-grained and fine-grained soils
  • samples obtained as part of the Standard Penetration Test (SPT)
48
Q

How do thin-walled Shelby Tube Samples work?

A
  • sampler is pushed into the soil at the bottom of the boring using the hydraulic system on a drilling rig
  • most often used in fine-grained soils
  • amount of disturbance related to inside clearance ratio
49
Q

What is the Standard Penetration Test (SPT)?

A
  • the standard penetration test is the most common in situ test worldwide
  • Method: Drive a split-barrel sampler into the ground and measure the number of blows required to advance it 1ft.
50
Q

What does ASTM D1586 (SPT Standard) specify about this test?

A

That you should record the number of blows required for each 6inch. of penetration or fraction thereof:
- the first 6in. is considered to be a seating drive
- the “standard penetration resistance”, “blow count”, or “N-value” is the sum of the blows for the second and third 6-in. increments and is expressed as “blows per foot (bpf)”
- if the sampler is driven less than 18in. the number of blows for each 6in. increments and fractions thereof should be recorded (e.g. 50/4in.)

51
Q

What are some components/calculations involved in calculation for SPT?

A
  • theoretical free-fall energy of the SPT hammer: E(theo) = (weight of hammer) * (height the hammer falls) = 140lb * (30in) = 4200in.-lbs
  • friction and eccentric loading case losses: E(actual) = ER(r) * E(theo)
  • standard rod energy ratios of 60%
    NOTE: ER(r) obtained via calibration or assumed based on typical values
52
Q

What are the advantages and disadvantages of SPT?

A

Advantages
- obtain a sample and a number
- simple and rugged
- suitable in many soil types

Disadvantages
- obtain a sample and a number (and that’s it??)
- disturbed sample suitable for index tests only
- crude number for analysis

53
Q

What is the Cone Penetration Test (CPT)?

A
  • the cone penetration test involves a steel probe with a 60 degree apex tip and internal strain gages or load cells to measure tip stress, sleeve friction, resistance, and (optionally) pore pressure.
  • hydraulically pushed at a rate of 2cm/sec
  • no boring, no samples, no cuttings, no spoil
  • continuous readings of tip stress, sleeve friction, resistance, and (optionally) pore pressure, and other parameters
  • ASTM D 5778
54
Q

What are the advantages and disadvantages of Cone Penetration Tests?

A

Advantages
- fast and continuous profiling
- results not operator dependent

Disadvantages
- no sample is obtained
- high capital investment
- requires skilled operator and calibration
- may not work in all soils types

55
Q

What do the index properties of COARSE GRAIN soils tell us?

A

Index properties of coarse grain soils tell us the relative density of the soil

56
Q

What factors affect the engineering behavior of FINE GRAINED soils

A

Factors that affect the engineering behavior of fine grain soils include:
- clay mineralogy
- chemical and electrical bonds between clay particles
- interaction between clay particles and water

57
Q

How can we identify the index properties of fine grained soils?

A

Atterberg Limits

58
Q

What is the purpose of the Atterberg limits?

A

Atterberg limits are simple, arbitrary tests to quantify the complex interaction between clay particles and water. They are ‘low-tech’ tests that provide useful indicators of engineering behavior of fine-grained soils such as strength and compressibility.

59
Q

What are the Atterberg limits?

A
  • Liquid limit (LL)
  • Plastic limit (PL)
  • Plasticity Index (PI)
60
Q
A

Geotechnical Engineering (3 decks)

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