Advanced Geotechnical Engineering
ES4D8
Contaminated Land(Lecture 4)
Mohaddese Mousavi-Nezhad
Room: D211
Email:m.mousavi-nezhad@warwick.ac.uk
31/05/2016
The University of Warwick
1
Site Investigation
Phase II investigation: consist of a site characterisation phase
(phase IIa) and groundwater monitoring well installation
(Phase IIb).
• The extreme complexity and variability inherent to most
soils necessitates that a multitude of investigation and
monitoring approaches be incorporated into subsurface
investigations.
• Both field and laboratory tests are necessary to
comprehend the presence and behaviour of polluted soils.
• Field testing primarily provides information regarding soil
characteristics, groundwater flow conditions, and
pollutant migration.
• Laboratory testing supplies data on the type and quantity
of a pollutant present in the subsurface.
Basics & Terminology
A variety of investigative techniques are available for the collection
of data for the characterization of sites. The actual site
investigation will include direct and indirect methods.
Direct methods for site investigation:
• Boreholes
• Piezometers
• Geotechnical analysis of soil samples
Indirect methods:
• Aerial photography
• Ground penetrating radar
• Earth conductivity and resistivity geophysical studies.
Basics & Terminology
Geophysical Techniques
• Ground Penetration Radar (GPR)
• Electromagnetic conductivity (EM)
• Electrical resistivity surveys
• Seismic surveys
Ground Penetration Radar (GPR)
We measure
• Two way travel time
• Amplitude of the signal
We identify the depth of the layer or
objects underground.
Ground Penetration Radar (GPR)
Ground Penetration Radar (GPR)
Ground Penetration Radar (GPR)
Hyperbola
Basics & Terminology
Ground Penetration Radar (GPR)
Ground Penetration Radar (GPR)
1
2
3
Ground Penetration Radar (GPR)
• There are depth limits to this technique, with signal attenuation
becoming more important at depths where subsurface materials
have low electrical conductivities, i.e., where pore fluids are
present in quantity.
• Optimal conditions for this technique are sandy or rocky soils in
unsaturated (vadose) zones or bedrock with low hydraulic
conductivity where water is not permanently present.
• Clay-rich sediment, which by their nature retain more water
than most sediments, and other dump or saturated sediments
will generally yield poor results.
• However, reliable data are obtainable in settings where pore
fluids have a low specific conductance, e.g., where significant
amounts of petroleum products are present.
Electromagnetic conductivity (EM)
The system consists of a transmitter coil (TC), energized with
an alternating current at an audio frequency, and a receiver
coil (RC), located at a short distance away from the
transmitter.
• The transmitter coil (TC) creates a primary magnetic field
(Hp) that induces currents in the subsurface.
• These currents generate a secondary magnetic field Hs which is sensed, together
with the primary field, Hp, by the receiver coil (RC).
Electromagnetic conductivity (EM)
• In general, this secondary magnetic field is a complicated function of the intercoil spacing, s, the operating frequency, f and the ground conductivity, σ. In a
simplified form:
Hs is secondary magnetic field at the receiver coil,
Hp is primary magnetic field at the receiver coil,
ω = 2πf, f is frequency,
μ0 is permeability of free space,
σa is ground conductivity,
s is inter-coil spacing
Electromagnetic conductivity (EM)
Since the electromagnetic technique produces results in conductivity units, it
can be of immediate use at the site to:
• Determine the water quality: The recorded conductivity values provide an
indication of the relative difference in dissolved ion contents, hence provide
a measure of water quality, as shown in Table 2 (next slide).
• Quantify the soil salinity: Salinity classes, based on electrical conductivity of
a saturated extract, as defined by US EPA, are shown in Table 3 (next slide).
• Determine the concentration of cations and heavy metals: This can be
obtained with the use of the following relationships (Kayyal and Mohamed,
1997):
(a) For cations:
σ = 0.121249 + 0.003155xC 0.940930
(b) For heavy metals:
σ = 0.004773 + 0.001894xC 0.941766
σ is electrical conductivity in mmho/cm, and C is the equilibrium
concentration of the total heavy metals or cations in solution (ppm).
Electromagnetic conductivity (EM)
Table 2: Typical values of specific conductivities for various water types.
Table 3: Salinity classes of soils.
HYDROGEOLOGICAL INVESTIGATIONS
Well installation procedure depends on:
(1) the expected geology of the site,
(1) type of liquid waste and its anticipated effect on the drilling mud
and well materials
(3) the effect of the installation procedures on the reliability of the
water quality data.
Appropriate drilling methods for sampling and installing wells
should be selected.
Number and depth of boreholes
• Number of Boreholes
– Depends on site conditions
– Should enable the basic geological structure of the site to
be determined
– Typically one borehole for 200-400 m2
• Borehole Depth
– Must include all strata that was affected by contaminants
or have the potential to be affected
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Drilling Methods
 Percussion (or Cable Tool) Drilling
 Auger Drilling
– Hand Auger
– Mechanical Augers
 Flight Augers
 Bucket Auger
 Hollow Stem Augers
 Rotary Drilling
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Percussion Drilling
(after Craig 2004)
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Percussion Drilling (contd.)
 Perhaps the commonest technique
 Reasonably cheap
 Can reach to large depths
 Suitable in almost all soils
 The rig is versatile
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Auger Drilling
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Hand Augers
•
•
•
•
Borehole diameter up to 200mm
Depths of around 5m
Very cheap
Used in self-supporting strata
without hard obstructions or
gravel-sized particles
• Auger must be withdrawn at
frequent intervals for the removal
of soil
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Mechanical Augers
(after Craig 2004)
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Flight Augers
• Typical diameters between 75 mm and
300mm
• Borehole depths up to 30-50 m
• Suitable for cohesive soils
• Require considerable mechanical power and
weight
• Give only a very rough indication of the
levels and character of the strata
• Continuous-flight augers (b) more efficient
than short-flight augers (a)
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Flight Augers (contd.)
Continuous flight auger drilling
(http://www.machibroda.com)
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Bucket Auger
• Consists of a steel cylinder, open at
the top but fitted with a base plate on
which cutters are mounted
• Typical diameters between 300 and
900mm
• When the bucket is full it is raised to
the surface to be emptied
• Allows downhole logging
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Bucket Auger (contd.)
Hollow Stem Auger
– Casing with outer spiral
– Inner rod with plug/or pilot
assembly
– For sampling, remove pilot
assembly and insert sampler
– Typically 1.5m sections, keyed,
box & pin connections
– Maximum depth 30‐50m
– Internal diameter 50‐300 mm
Hollow Stem Auger
• No drilling fluids are used and disturbance of
the geologic materials penetrated is minimal.
• In formation where the borehole will not stand
open, the monitoring well can be constructed
inside the hollow-stem auger prior
to its removal from the hole.
• The hollow stem auger has an added advantage
in offering the ability to collect continuous in-situ
geologic samples without removal of the auger
sections.
Hollow Stem Augers (contd.)
Rotary Drilling
• The fastest drilling method
• Although primarily intended for
investigation in rock, the method is
also used in soils
• Bit at the en of drill rod is rotated
and advanced
• Soil/rock cuttings removed by
circulating drilling fluid (e.g.
bentonite mud)
• Typical core diameters of 41, 54,
and 76 mm
Sampling
Sampling Process
Type of Soil Samples
1) “Undisturbed” Sample
– Minimizes effects from
potential disturbance
– Needed for determination of
in-situ density, in-situ
permeability, soil shear strength
and compressibility
2) Disturbed Sample
– No attempt to retain the in-situ
structure of the soil
– Suitable for classification and
compaction tests
Well Installation Techniques
• After the test bore hole is
drilled and the subsurface
material is sampled, a
monitoring well device can
be installed in the bore hole
for groundwater sampling
and measuring piezometric
levels.
• Water samples can be taken
to determine the water
chemistry
Drive Point Wells
The most common techniques for monitoring well installations are:
• Drive Point Wells
• Individual Wells
Well Installation Techniques
The simplest and least expensive
technique to install a monitoring
well is to drive the well screen
and casing down to the desired
depth with a hammering device.
• Drive point monitoring wells
commonly range in diameter
from 15 to 30 mm.
• They have been successfully
installed in soft soils up to 30
m.
• The length of the screen
commonly ranges between
0.2 and 1.0 m.
Individual Wells
• The most common type of
monitoring well is the
individual well installed in a
drilled borehole.
• These types of monitoring
wells commonly range from
0.02 to 0.1 m in diameter.
• They are typically constructed
of steel, stainless steel, PVC,
or Teflon, depending upon
the requirements for
chemical sampling.
• The screen and filter pack
should ensure that formation
water can pass easily into the
monitoring well.
Individual Wells
• The placement technique is as
follow:
(1) Place the selected well screen
and casing down into the borehole
to the required depth,
(2) Install permeable filter pack
material around and slightly above
the well screen to allow
groundwater from the adjacent
formation to flow freely to the well
screen,
(3) Place a sealing material above
the filter pack to isolate the well
Screen from the rest of the
borehole,
(4) Backfill the annulus above the seal with a grouting material,
(5) Install a protective cover over the well casing at ground level for
Security and to prevent precipitation from entering the well.