(MODULE 10) SITE EXPLORATION AND CHARACTERIZATION

Question 1

___ efforts typically represent a very large share of the geotechnical engineering budget.

Answer 1

site characterization

Question 2

___ efforts typically represent a very large share of the geotechnical engineering budget.

Answer 2

site characterization

Question 3

we often spend more time and money ___ and ___ than we do performing analyses and developing designs

Answer 3

exploring the subsurface conditions; defining their engineering characteristics

Question 4

the objectives of a site exploration and characterization program include:
1. determining the location and thickness of ___ and ___
2. determining the location of the ___ along with other ___.
3. recovering ___ for testing and evaluation
4. conducting tests, either in the field or in the laboratory, to ___
5. defining special ___ and ___

Answer 4

1. soil and rock strata
2. groundwater table, important groundwater-related issues
3. samples
4. measure relevant engineering properties
5. special problems and concerns

Question 5

we can explore subsurface conditions using ___, and recover samples for testing and evaluation.

Answer 5

borings

Question 6

we do not know what soil conditions exist between borings and must rely on ___ combined with a knowledge of ___.

Answer 6

interpolation; soil deposition processes

Question 7

soil data gathered during site exploration:
1.
2.
3.

Answer 7

1. soil profile (layer thickness and soil identification)
2. index properties of soil (water content, Atterberg limits, etc)
3. strength & compressibility characteristics

Question 8

before planning a site exploration and characterization program, the geotechnical engineer must gather certain information on the proposed development.

Answer 8

Stage 1-1 Desk Study: Project Assessment

Question 9

information gathered during the project assessment would include matters such as:
1. the ___, ___, and ___ of the proposed improvements
2. the type of ___, ___, and ___
3. the existing ___ and any proposed ___
4. the presence of ___ on the site, if any.

Answer 9

1. types, locations, and approximate dimensions
2. construction, structural loads, and allowable settlements
3. topography; grading
4. previous development

Question 10

The first step in gathering information on a site often consists of reviewing published sources. Sometimes, these efforts reveal the results of extensive work already performed on the site, and very little additional exploration may be necessary.

Answer 10

literature search

Question 11

sources of relevant literature include:
1.
2.
3.
4.

Answer 11

1. geologic maps
2. soil survey reports
3. geotechnical investigation reports
4. historic groundwater data

Question 12

the process of detecting features on the earth’s surface from some remote location.

Answer 12

Remote sensing

Question 13

the ___ consists of walking the site and visually assessing the local conditions.

Answer 13

field reconnaissance

Question 14

which stage is site reconnaissance?

Answer 14

stage 2

Question 15

field reconnaissance also includes marking the ___.

Answer 15

locations of proposed exploratory borings and trenches.

Question 16

usually involves test pits and/or soil borings (boreholes)

Answer 16

subsurface exploration

Question 17

which stage is subsurface exploration?

Answer 17

Stage 3-1

Question 18

The most common method of exploring surface conditions; involves drilling a series of vertical holes in the ground

Answer 18

exploratory borings

Question 19

___ perform at least 90 percent of geotechnical drilling, and can drill to depths of 30m with little difficulty.

Answer 19

truck-mounted drill rigs

Question 20

For drilling in firm and dense soils, the simplest methods use a ___ or a ___ to produce an open hole.

Answer 20

flight auger or bucket auger

Question 21

How does drilling with an auger work?

Answer 21

as the auger is lowered into the hole and rotated to dig into the soil. it displaces soil with its spiral blades and is removed from the borehole before repeating the process.

Question 22

Drilling with a smaller auger can meet refusal (inability to progress further) when they encounter ___.

Answer 22

hard boulders or hard bedrock

Question 23

to combat a smaller auger’s inability to cut through hard rock, a ___ is used.

Answer 23

larger-diameter auger

Question 24

open hole methods encounter problems in soils prone to caving or squeezing. how is this prevented?

Answer 24

casing, a temporary lining made of steel pipe. this is installed after drilling with bentonite slurry which expands in the borehole. once the casing is sealed, the slurry is removed from the interior of the casing.

Question 25

another, more common method of drilling in soils prone to caving or squeezing is to use a hollow stem auger. how does it work?
1.
2.
3.

Answer 25

1. each auger section has a pipe core (stem) with a temporary plug on the bottom of the first section. the auger sections are drilled in, and the temporary plug is removed. 2. samplers are inserted through the stem and into the soils and are then recovered. 3. the plug is replaced, and drilling continues to the next sample depth.

Question 26

the third method of drilling in soils prone to caving or squeezing is to fill the boring with drilling mud or ___. how does it work? additionally, what method is used to place this drilling mud into the borings?

Answer 26

bentonite slurry; this material provides a hydrostatic pressure on the walls of the boring, preventing caving or squeezing.

this slurry is applied using the rotary wash method, which flushes the drill cuttings up to the ground surface by circulating the mud with a pump.

Question 27

___ simultaneously advances the hole and obtains nearly continuous undisturbed samples.

Answer 27

coring

Question 28

under ‘coring’

after each core run, the sample is brought to the ground surface and placed in a container for examination and storage. what is this container called?

Answer 28

core box

Question 29

the conditions encountered in an exploratory boring are recorded in a ___

Answer 29

boring log