(MODULE 10) SITE EXPLORATION AND CHARACTERIZATION Flashcards
___ efforts typically represent a very large share of the geotechnical engineering budget.
site characterization
___ efforts typically represent a very large share of the geotechnical engineering budget.
site characterization
we often spend more time and money ___ and ___ than we do performing analyses and developing designs
exploring the subsurface conditions; defining their engineering characteristics
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 ___
- soil and rock strata
- groundwater table, important groundwater-related issues
- samples
- measure relevant engineering properties
- special problems and concerns
we can explore subsurface conditions using ___, and recover samples for testing and evaluation.
borings
we do not know what soil conditions exist between borings and must rely on ___ combined with a knowledge of ___.
interpolation; soil deposition processes
soil data gathered during site exploration:
1.
2.
3.
- soil profile (layer thickness and soil identification)
- index properties of soil (water content, Atterberg limits, etc)
- strength & compressibility characteristics
before planning a site exploration and characterization program, the geotechnical engineer must gather certain information on the proposed development.
Stage 1-1 Desk Study: Project Assessment
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.
- types, locations, and approximate dimensions
- construction, structural loads, and allowable settlements
- topography; grading
- previous development
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.
literature search
sources of relevant literature include:
1.
2.
3.
4.
- geologic maps
- soil survey reports
- geotechnical investigation reports
- historic groundwater data
the process of detecting features on the earth’s surface from some remote location.
Remote sensing
the ___ consists of walking the site and visually assessing the local conditions.
field reconnaissance
which stage is site reconnaissance?
stage 2
field reconnaissance also includes marking the ___.
locations of proposed exploratory borings and trenches.
usually involves test pits and/or soil borings (boreholes)
subsurface exploration
which stage is subsurface exploration?
Stage 3-1
The most common method of exploring surface conditions; involves drilling a series of vertical holes in the ground
exploratory borings
___ perform at least 90 percent of geotechnical drilling, and can drill to depths of 30m with little difficulty.
truck-mounted drill rigs
For drilling in firm and dense soils, the simplest methods use a ___ or a ___ to produce an open hole.
flight auger or bucket auger
How does drilling with an auger work?
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.
Drilling with a smaller auger can meet refusal (inability to progress further) when they encounter ___.
hard boulders or hard bedrock
to combat a smaller auger’s inability to cut through hard rock, a ___ is used.
larger-diameter auger
open hole methods encounter problems in soils prone to caving or squeezing. how is this prevented?
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.
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.
- 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.
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?
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.
___ simultaneously advances the hole and obtains nearly continuous undisturbed samples.
coring
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?
core box
the conditions encountered in an exploratory boring are recorded in a ___
boring log
