Site Exploration Flashcards
Aims to get more detailed information about the subsurface materials
site exploration
objectives of site exploration
nature of soil and its stratification
disturbed and undisturbed samples for visual identification and appropriate lab tests
depth and nature of bedrock
in situ field tests
drainage conditions from and into the site
special construction problems with existing structures nearby
position of water table
direct methods of site exploration
test pits or trenches
drillholes or boreholes
rock coring
soil sampling
augers
water-pressure testing
water table measurement
standard penetration test SPT
cone penetrometer test CPT
vane shear test
Typically the site exploration
technique for horizontal structures
which only requires a shallow layer of
foundation
test pits or trenches
Holes in the ground are drilled and
samples are taken. Holes commonly
reaches several meters in depth.
drillholes or boreholes
accomplished with a diamond tip
rock core barrel attached to a drill
rig. The coring recovers a
cylindrical core of rock by rotating
and advancing the hollow core
barrel.
rock coring
typically in percent, is the amount or length of material collected divided by the total length of the core run
core recovery
a modified core recovery percentage in which the lengths of all sound rock core pieces over
100 mm in length are summed and
divided by the length of the core run. The
lengths must be measures along the
centerline of the core.
rock quality designation
3 rock core tests
moisture content
point load index
unconfined compression test
degree of wetness/dryness of the rock
moisture content
measures the durability of a rock, can be
correlated to the compressive strength
point load index
to determine the compressive
strength
unconfined compression test
drilling devices/drilling bits to
excavate soil from a hole. Only used to
advance the depth of the hole.
augers
sampler in conjunction
with standard penetration testing.
Hollow tube with driving shoe at the
bottom. The tube can be split
longitudinally.
split spoon
also known as thin-walled tubes are usually used in obtaining undisturbed clay samples
Shelby tubes
lab tests for soils
soil density and specific gravity
moisture content
Atterberg limits
compaction tests
permeability
soil strength
water is pumped under pressure in drillholes
and the rate of resulting water flow is measured. The water loss coefficient, ratio of pressure to flow, indicates degree of openness of joints and the spacing of significant water conductors.
water-pressure testing
holes are typically left overnight for
groundwater to stabilize and the depth of water is measured.
water table measurement
indirect methods
geophysical methods
These are methods where soil is not directly
sampled, although, may still be disturbed in
some manner.
geophysical methods
artificial geophysical methods
seismic and resistivity (can be controlled to a certain degree)
natural geophysical methods
gravity and magnetic methods (forces are only observed and measured, can’t be controlled)
Uses the energy from an explosion or pounding/hammering in/on
the ground
seismic methods
wave travelling along the surface
direct wave
The point where refracted and direct waves come at the same time
critical distance
only works if the lower layer has higher velocity than the layer above. Usually works when it is a soil upper layer and rock lower layer.
seismic refraction
Used to locate faults, landslides,
and bedrock channels
Requires much deeper area
compared to the shot-to-detector-array distance – this makes sure that refracted
waves are not going to be a
problem in the measurement
seismic reflection
Dependent on porosity and fracturing of rock, salinity of pore water, ground temperature, and clay content
resistivity methods
Involves measurement of one or more magnetic or electric field components
electromagnetic methods
a device with transmitter and receiver
terrain conductivity meter
use radio transmitters and wider
in range (thousands of kilometers)
very low frequency VLF method
uses pulsed electromagnetic waves
and their time needed to be reflected (from surface to subsurface interface back to surface) and provides high resolution.
ground probing radar GPR
can be done on ground but can also be done using airplanes carrying magnetometers in what is called Aeromagnetic Surveying.
magnetic methods
Probes are sent down drill holes to measure certain properties of along the wall of the hole
drillhole logging techniques
Two holes are used with one hole having the
disturbance source (at a certain depth) and a
receiver is at the other hole (at same depth as
disturbance source) and receives seismic waves from the first hole.
cross hole technique
