- Home
- Conferences
- Conference Proceedings
- Conferences
3rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 12 Mar 1990 - 15 Mar 1990
- Location: Golden, Colorado, USA
- Published: 12 March 1990
31 results
-
-
Resistivity Mapping With Airborne Electromagnetic Induction Apparatus
By A. BeckerThe benefits of mapping the electrical conductivity of the earth's surficial layers in support of various engineering, geological and hydrological investigations are amply demonstrated in the scientific record that spans the last sixty years. Until quite recently all such surveys were done directly on the surface with the classical four electrode dc resistivity method. Although
the early practitioners of this technique (Lee, 1936) had to contend with poor instrumentation, lack of reliable data interpretation aids, and strong competition from water diviners, much progress was made and resistivity measurements are now used on a routine basis in all parts of the world. Most of the investigations on record were carried out with the aim of outlining
occurrences of groundwater and of determining its quality. Next we note engineering applications based on the definition of the lithology and thickness of soil cover which must be known for the proper planning of dam sites, road locations, pipeline routes and mining operations. All of these applications rely on the successful differentiation and mapping of surficial deposits. The
measurements are based on the fundamental precept that different geological formations have characteristic values of electrical conductivity.
-
-
-
Interpretation Of Data From Electrical Resistivity Measurements
More LessThe underlying purpose of any geophysical data-acquisition
program is the discerning of some aspect of sub-surface conditions.
The process of drawing inference from accumulated data is that
which we call "interpretation." With some justification and no
deprecation, the step of "making sense" of a set of geophysical
survey results is often viewed as more an art than a science. The
thesis of this presentation is that the interpretive art is most
productively pursued as an intuitive process guided by an
understanding of the controlling physics. The process is generally
assisted by consideration of the results expected from known
models. Accordingly, we shall review the governing physics of
electrical properties of earth materials and of the measurement
techniques commonly employed and then turn to consideration of some
of the computing methods available to assist the interpreter,
including both forward and inverse methods.
-
-
-
Gravity As A Tool To Delineate Buried Valleys
Authors Benjamin H. Richard and Paul J. WolfeThe gravity method with specific emphasis on its use in buried valley
studies is reviewed. The technique has been successfully applied in a
number of areas. Case studies are presented to illustrate results in two
parts of the United States. The Hanford Military Reservation near
Richland, Washington, has folded basalt flows and Pleistocene sediments.
A residual gravity map, produced by removing a third-order trend surface
from the data, allowed interpretation of a buried valley system which is
important in controlling groundwater flow. Subsequent studies have
supported the conclusions drawn from the gravity data. In southwestern
Ohio a number of gravity studies have been used to refine maps of the
preglacial drainage system. These gravity maps have located errors in
bedrock maps which were based on water well data. Detailed gravity
profiles have helped understand the configuration and nature of sediments
filling the valleys.
-
-
-
Applications Of The Self-Potential Method For Engineering And Environmental Investigations
More LessSelf-potential (SP) surveys detect surface voltage variations
caused by subsurface flows of fluid, heat, and ions. Therefore
the SP method can be useful in applications where such flows are
related to subsurface targets of engineering or environmental
interest. Examples of engineering and environmental applications
of the SP method discussed in this paper include studies of fluid
flow in the vicinity of dams, reservoirs, wells, and faults;
investigations of coal mine fires, steam injection, and nuclear
tests; and surveys for environmental contaminants.
Although the equipment and field procedures used for SP
surveys are relatively simple, considerable care must be taken to
ensure that data are reproducible, that sources of noise are
recognized, and that appropriate data reduction techniques are
used to correct for electrode drift and polarization.
Interpretation of SP data then may be carried out using
qualitative, geometric, or analytic methods. Qualitative
recognition of typical anomaly patterns is helpful for
determining source locations and selection of more quantitative
interpretation methods. Geometric source modeling, similar to
that done for other potential field methods such as gravity and
magnetics, is used to estimate source configuration and depth.
Analytical modeling, based on concepts of irreversible
thermodynamics and coupled flows, can provide information about
the nature, location, and intensity of SP anomaly sources.
-
-
-
Application Of Controlled Source Audio-Frequency Magnetotelluric Measurements To Engineering And Environmental Problems
More LessDuring the past decade, electrical geophysical techniques have
been gaining acceptance for investigating geotechnical problems,
particularly in the area of detecting and monitoring ground
water contamination. While much of this work can be done by
monitoring wells alone,. the cost of such programs is often
prohibitive. Electrical geophysics has proven to be helpful in
mapping contaminant plumes and in optimizing the placement of
monitoring wells.
-
-
-
Geophysical And Remote Sensing Techniques For Detection And Measurement Of Oil Slicks On Water
More LessA variety of remote sensing techniques are able to detect oil slicks on
water, including side-looking radar, passive microwave radiometers,
ultraviolet-infrared line scanners, laser fluorosensors and various visual
sensors. Each technique keys on some property of the oil which differs
from that of the open ocean (such as emissivity) or on some property of
the ocean which is altered by the presence of oil (such as the surface
roughness). Combinations of one or more of these sensors have been
installed on various aircraft and are in routine use around the world.
They are generally able to detect and map oil slicks reliably under most
weather conditions.
A more difficult problem is measurement of the thickness of an oil slick,
which can range over six orders of magnitude from less than a micrometre
to ten centimetres. The thickness of a spill varies spatially and over
time as a slick spreads. Clearly knowledge of the thickness is required
to estimate oil volumes and thereby plan efficient countermeasures.
-
-
-
Landfill Assessment Using Electrical Resistivity And Seismic Refraction Techniques
More LessGeophysical techniques offer an economical, noninvasive way of
determining buried structure and assessing integrity at certain types of
closed landfills. Such landfills often are plagued by cover and liner
defects and may accumulate dangerous volumes of highly polluted groundwater
(leachate) which can leak into surrounding aquifers. Also, as widespread
landfill gas production and mining of landfill materials for recycling
becomes a reality, geophysical techniques offer a low-cost alternative to
borings for mapping refuse thicknesses and variability at sites where
inadequate dumping records exist. In this experiment three landfills in
the suburban Chicago area were evaluated using electrical resistivity
sounding, azimuthal resistivity and seismic refraction techniques. Wenner
and Schlumberger array electrical soundings were inverted in a leastsquares
procedure to yield multilayer geoelectrical models. Wood, newspaper, cloth, glass, plastic and metal refuse interspersed with soil
exhibited resistivities ranging from 9-53 ohm-m (unsaturated) and 2-7 ohm-m
(leachate-saturated). Clay-till cover materials exhibited resistivities
typically ranging from 10 to 30 ohm-m. Depths of interfaces such as the
top of refuse, leachate level and the base of refuse were estimated from
soundings with errors averaging about 30%. Larger errors were encountered
over fractured or newly emplaced cover materials, areas where resistivity
contrasts with underlying refuse were small (< 10 ohm-m) or where refuse
resistivities exceed cover resistivities. Seismic refraction measurements
could not be used to determine cover thickness and deeper landfill
structure due to a velocity inversion and strong scattering and attenuation
of seismic energy in the refuse. Average direct P-wave velocity, however,
decreased in heavily fractured cover materials. Strong peaks on azimuthal
resistivity plots occurred in these same areas which suggests that seismic
velocity changes can be combined with azimuthal resistivity to delineate
areas of serious cover fracturing.
-
-
-
Digital Borehole Logging Instrumentation And Software, A Systems Approach To Design And Implementation
More LessWith the advent of small and powerful computers, new borehole geophysical logging
systems are being designed and manufactured. Many of these systems lack an
integrated approach of combining digital downhole probes, uphole instrumentation,
and acquisition and analysis software in an interactive, simple to use, and flexible system.
This case study describes the “systems approach” during the design of logging
hardware and software which allows for the equipment and support programs to be
altered and updated for a changing market demand without requiring massive engineering
or conceptual changes. This “systems approach” allows for a fully interactive
logging acquisition, presentation, and analysis system capable of supporting a variety
of geophysical downhole probes, and analysis routines.
The “systems approach” to the design of a fully-digital borehole logging system
incorporates a three-phase plan. The first phase consists of the design of fully digital
downhole instrumentation requiring no additional uphole electronics, other than a
universal probe interface board located in the surface instrumentation. The second
phase consists of a standard computer system used as a surface recording, analysis,
and output device for the log data. The third phase is an integrated software package
that monitors, controls, and allows input from the digital probes and the logging operator.
This case study describes the advantages to this “systems approach” of design in log
accuracy, ease-of-use, and integration of data for post-analysis using log data derived
from an actual field-proven system.
-
-
-
Expert Systems -- Their Role In Environmental Investigations
More LessToo many people confuse “expert system” with a machine that replaces humans in decisionmaking
situations. As a result, expert-system technology often is perceived as a threat to the professional
in the same way that factory workers are threatened by robotics. A more-realistic view is that of a tool
which encourages a structured approach to decision-making. The essence of an expert system is the
knowledge engineering upon which it is based, not the resulting computer program In this context,
expert systems offer advantages to the professional environmental geophysicist. They can be an effective
mechanism for meeting quality-assurance requirements, and they provide a framework within which to
justify adequate funding for geophysical surveys.
This paper is an unusual case history in that it deals with the exploration process itself rather than
a specific prospect. It reviews our efforts to analyze the seismic refraction process and develop guidelines
for making decisions, from initial survey design to fmal interpretation. It addresses three principle
elements of a refraction survey: survey design, field acquisition, and interpretation, and it presents
examples that demonstrate the advantages of a structured approach to decision-making.
-
-
-
Modern Data Interpretation Software And Its Role In Geophysical Investigations
By C.H. StoyerA geophysical investigation consists of six steps:
1. Defining the problem (target) and demonstrating the feasibility of achieving the required goals.
2. Designing the experiment, including method(s) to be used and the survey parameters.
3. Quality control/real time interpretation to insure that reliable data is being acquired and that the premises arising from experiment design are valid.
4. Interpreting the data in terms of the problem (target) which has been defined.
5. Estimating the range of alternative interpretations and their effect on the goal of the experiment.
6. Reinterpretation of the data at a later date when more information becomes available.
Computers and their associated software play an increasingly
important role in the efficient and precise execution of
geophysical experiments. Digital data acquisition and storage is
becoming more and more prevalent. This allows the geophysicist
to collect vast amounts of data with relative ease. The
increased data volume, coupled with the requirement for more
sophisticated data processing and analysis has resulted in the
development of more advanced software packages. Equally
important to the software's capability to handle sophisticated
analysis on large data sets is the human interface which enables
the geoscientist to access these tools in an productive manner.
Modern interpretation software enables the feasibility study
and survey design to be conducted in an efficient and accurate
manner. Real time data interpretation and quality control
requires on site use of such software. Finalizing the results
and evaluating the range of alternative interpretations requires
software if it is to be carried out thoroughly and cost
effectively. Some of the more sophisticated field techniques
cannot be interpreted at all without such software. The addition
of report ready displays and interfaces to powerful word and
drawing processors further improves quality, productivity and
cost effectiveness.
-
-
-
Dips And Chips -- Pc Programs For Analyzing Seismic Refraction Data
Authors James H. Scott and Richard D. MarkiewiczOver the past several years a number of programs have been written for analyzing
seismic refraction data on personal computers. Some of these programs are small
enough and fast enough to make on-site interpretation practical on a spread-by-spread,
or even shotpoint-by-shotpoint basis. The results can be used to plan and guide the
layout of additional shotpoints, spreads, and seismic lines to assure that sufficient data
have been collected before leaving the field site, and to avoid shooting unnecessary
spreads. Currently available public domain and commercial software packages can meet
the needs of a wide variety of objectives, ranging from simple forward and inverse
modeling to obtain approximate depths to refractors having uniform velocities, to
sophisticated techniques for determining depths to undulating refractors having lateral
changes in velocity. Each program has its specific area of applicability for solving
engineering and environmental problems, depending on the complexity of the geologic
setting, and on the level of detail desired in the resulting interpretation. This paper
compares characteristics and specifications of several refraction software packages, whose
capabilities are illustrated in examples of computer output for synthetic and real data sets.
-
-
-
Results Of Shear-Wave Measurements
More LessBecause seismic shear waves (S waves) propagate in earth materials differently than do
compressional waves (P waves), the addition of a shear-wave capability to the engineering
geophysicist’s shallow-depth seismic system markedly broadens its usefulness. In general, S waves
respond only to lithologic changes, whereas P wave are affected by both the lithology and the
fluids contained. In one area studied, both the saturated overburden and the bedrock had nearly
the same P-wave velocity, and therefore the boundary between them was undetectable by P-wave
methods; however, it was detectable by S-wave methods. Since the water table could be seen with
P-wave methods, the volume of the unconfined aquifer could be estimated--P waves for its top; S waves for its base.
The amplitude, frequency content, and arrival time of shear waves all change significantly
across a near-vertical boundary. I have used these S-wave characteristics to map earth fissures
and to locate the edge of a concealed high wall of a reclaimed surface mine.
Reflections of horizontal shear (SH) body waves are commonly masked by SH surface
waves, but these surface waves do not occur where the surface layer’s shear-wave velocity is close
to or higher than that of the lower layers. Because of this lack of surface-wave noise, and
because of the inherent simplicity of SH-wave propagation (for example, no wave-type conversion
at interfaces), studies have obtained usable SH reflections from a tar sand underlying a
limestone sequence, possible SH reflections from within an ignimbrite section, and excellent
shear-wave reflections interpreted as having come from lenticular clay bodies at depths of 12 and
32 m beneath the surface of an alluvial fan.
-
-
-
The Feasibility Of Shear Wave Reflection Profiling Of A Shallow Bedrock Surface Buried Under Alluvium
Authors Thomas T. Goforth and Chris HaywardA number of papers have been written in the last few years
concerning optimum techniques for adapting classical reflection
techniques to the shallow environment. However, despite an overall
successful evolution of shallow applications, two basic problems have
hindered the implementation in some geologic environments. One
problem has been the overwhelming of the weak reflection by the
multi-mode Rayleigh ground roll propagating along the free surface.
Another is that the water table forms such a great impedance
contrast that it is often difficult to illuminate reflectors below it.
Both of these problems are particularly bothersome when the
subsurface to be investigated involves the sequence dry
alluvium/wet alluvium/bedrock. The use of shear wave profiling
offers a possible solution to these problems. Love waves do not exist
on the free surface of a half-space, and if the thickness of the
alluvium is several times the wavelength of the Love wave, the
development of the shear “ground roll”. will be inhibited. Also, shear
waves are not sensitive to changes in type of pore fluid and do not
“see” the water table. Thus, we might expect to be able to propagate
shear energy through the water table and obtain reflections from
below it even though compressional waves cannot effectively
penetrate the air/water interface.
-
-
-
Application Of Seismic Refraction Survey To Investigation For Tunnel Construction
Authors Naomichi Yokoya and Takashi KanemoriThe seismic refraction method has been widely used in Japan for engineering purposes
such as investigations for tunnel and dam construction. The following features of the
seismic refraction survey are considered as reasons why it has been widely used.
(1) It is feasible to determine subsurface structure (in seismic velocity) with enough
resolution and accuracy even though at a site with complex topography and
subsurface structure.
(2) It is feasible to detect faults and fracture zones where careful design will be required.
(3) A lot of data relating with mechanical properties of rock, including seismic velocity,
have been gathered and are utilized as database. By using the database, mechanical
properties of rock can be evaluated with seismic velocity, so that results of the
seismic refraction survey bring useful information for designing and execution
management of construction.
This paper reviews practical technique of the seismic refraction method that is commonly
carried out in Japan, including survey planning, data acquisition technique and analysis
technique, necessary for getting reliable results. Also, a case study of the seismic refraction
survey with survey line 6.5 km long, carried out to investigate tunnel construction site is presented.
-
-
-
Influence Of Galvanic Currents On Electromagnetic Surveys
By J.D. McNeillIn this paper we differentiate the electromagnetic response from
various targets into two components. These are the vortex current
component, which is generated by the time-varying primary magnetic
field, and the galvanic current component, generated by the primary
electric field. Separation of the response into these two
components is an approximation, the accuracy of which is a function
of variables such as target conductivity contrast, background
conductivity, target size, distance from target to the transmitter,
transmitter type, frequency or time range of measurement, etc.
(McNeill, 1985). That it is an approximation, albeit useful,
should be kept in mind.
-
-
-
Selection Of Antennas For Gpr System
Authors C.M. Lepper and R.S. DennenThe antennas are a significant component of the underground radar
tomography system developed for in-seam hazard detection. Several antenna
configurations were tested above ground to select those which might be best
for underground use. The relative forward gain of each antenna was determined
in a series of experiments. The antennas were tested both alone and with
reflection shields spaced from fractional to several wavelengths behind the
antennas. Antennas included triangular (bow-tie), linear dipoles and
monopoles and a series of horn antennas. The results indicate few significant
differences in agreement with laboratory modeling tests and place the emphases
on operational features i.e. the ease of use as a chief factor in antenna
selection.
-
-
-
Enduser Quality Assurance Requirements For Geophysical Surveys: A Case Study Provided By A Dc Grid At The Waste Isolation Pilot Plant
Authors David J. Borns and Susan PickeringQA requirements may fill many pages and may appear overwhelming. But the reguirements
are largely met by adherence to field and other scientific methods already practiced
by geophysicists and geologists. The step required is to document these existjng
practices. Once these methods are documented as procedures, the development of a
quality assurance plan will be relatively painless. The simple approach toward these
goals, especially for small contractors, is the maintenance of project and software
notebooks.
-
-
-
Application Of Gpr And Seismic Techniques To Investigation Of Bridge Abutments
Authors Gene Simmons, George Fields, Jutta Hager and Darren ConboyA combination of ground penetrating radar (GPR) and seismic
transmission delay was used to determine the thickness of stone
blocks making up the abutments of a bridge crossing trolley track
of the Massachusetts Bay Transit Authority's (MBTA) Red Line in
Dorchester, Massachusetts. The work was performed for Barnes and
Jarnis, Inc. and the MBTA to assess the adequacy of the bearing
strength of the abutments for a planned new bridge deck.
GPR data were obtained on both abutments with a 500 MHz system
on horizontal traverses at 3 to 5 foot intervals, on vertical
traverses at 5 foot intervals, and on single blocks. The GPR
survey encountered three types of complications: (1)
interpreting multiple reflections of the radar signal from the
backs of irregular blocks; (2) differentiating signals reflected
from the sides of blocks from signals reflected from the backs of
blocks; and (3) limited penetration of the radar signal in the
central portions of the abutments due to infiltration of salty
water from the roadway above.
These difficulties were resolved with a second, independent
survey method. A 12-channel seismograph was used to obtain
seismic data for one of the abutments. The geophones were
attached to the face of the abutment and seismic signals were
generated by a source 30 to 80 feet behind the wall. Two seismic
profiles were obtained with geophones attached in horizontal
lines and four profiles with geophones attached in vertical
lines. Differences in transmission times were used to estimate
total thickness of the stone blocks.
Using the combination of GPR and seismic transmission delay
techniques, we found the thickness of the stones near the top of
each abutment to be approximately 5 to 6 feet, increasing toward
the bottom to a thickness of approximately 10 to 12 feet.
-
-
-
Permanent Dc-Resistivity Arrays To Monitor The Development Of A Disturbed Rock Zone Around Underground Excavations.
Authors Mary Catherine Pfeifer, Henrik T. Andersen and Catherine K. SkokanPermanently installed DC-resistivity electrode arrays offer
the opportunity to accurately monitor very small changes in bulk
resistivity with time. A set of two arrays were installed
underground at the WIPP site in southeastern New Mexico, to
monitor the development of the Disturbed Rock Zone and migration
of fluids around an underground excavation in bedded salt.
-
-
-
Detection Of Conductive Fracture Zones By Underground Multicomponent Dc-Resistivity Surveying
Authors E.M. Williams, C.K. Skokan and H.T. AndersenUnderground multicomponent DC-resistivity can be used to locate
conductive zones in the vicinity of underground excavations.
The method was used at the Waste Isolation Pilot Plant in
southeast New Mexico to locate fluid saturated fracture zones
within the Salado evaporite formation. Two deep cased drill
holes north of the facility were used as a bipole current source.
A two-meter dipole was used to observe the three orthogonal
components of the potential difference along profiles in the
underground excavations. Fracture zones were located in several
areas and later verified by hydrological tests and subsequent drilling.
The method can.be readily adapted to other applications such as
road- and water-tunnel testing, and underground mining.
-
-
-
Geographic Information System Analysis Applied To Mapping Subsurface Brine, Brookhaven Oil Field, Mississippi
Authors Bruce D. Smith, Joseph L. Plesha and Robert J. BisdorfOil and brine production from deep horizons (1 km) in the Brookhaven oil field in southern Mississippi
has caused brine contamination of shallow (400 m) ground water. In order to evaluate the use of airborne
geophysical methods to map the extent of subsurface brine contamination, the U.S.Geological Survey, with
research funding from the Environmental Protection Agency, contracted a helicopter electromagnetic (HEM)
survey of the oil field area. The speciiic objectives of this research are to (1) evaluate the application of
airborne geophysical methods in an area of many cultural features that can interfere with these measurements,
and (2) interpret the subsurface distriiution of brine and fresh water. We applied a particular Geographic
Information System (GIS) can be to address these objectives.
The GRASS (Geographical Resource Analysis Support System) program developed and distriiuted
in the public domain by the Army Corps of Engineers Research Laboratory (CERL) has been adapted by the
USGS for use on a networked system of Hewlett Packard 9000 series 300 computers. Many other GIS software
packages available both commercially and in the public domain could be used to perform tasks similar to those
described here.
-
-
-
Transient Electromawetic Imaginq Of A Basin Margin Underneath The Savannah River Site, Aiken, South Canolina
Authors Bryan James, Van Price and Jim HildAn experimental transient electromagnetic (TEM) survey was performed at
the Savannah River Site (SRS) near Alken, South Carolina, to assess the
viability of a subsurface imaging method. The goal of the survey was to
improve resolution of mapping the margln of a buried Triassic basin partially
underlying SRS. A high data density survey was conducted utiiizing multiple
large loop transmitters with overlapping profiles of measurements from each
transmitter. Any attempt to image subsurface structure requires such data density.
A gap in interpretation tools exists in all electrical methods between
layered earth inversion and numerical modeling of two-dimensional (20) or
three-dimensional (3D) structures. Recent TEM research has focused on
development of methods to image subsurface geoelectric structure without
resorting to numerical modeling. The method described here constructs a
subsurface geoeiectric image by a novel means of stacking TEM data in both
time and space.
The stacking procedure is based on knowledge of where currents are
flowing in the subsurface of an approximate background model. Weights for
stacking of the TEM data into estimates of anomalous current flow on a
subsurface grid are calculated from these known current flow patterns as a
function of time, measurement position and subsurface grid element position
using Biot-Savart’s Law.
Thus, for the SRS survey, a 2D structure is imaged built on knowledge
of the fleids of an approximate one-dimensional (1D) model. The basin margin
under SRS is successfully resolved by the imaging method. The imaging
result provldes better resolution than obtained by splicing together layered
earth inversion models.
Various pros and cons of this imaging method are discussed to indicate
future directions for TEM imaging.
-
-
-
We Don't Get No Respect / Perceptions Of Engineering And Environmental Geophysics
More LessThe lament in the title is familiar to every geophysicist in this audience. For at least the last
twenty-five years that I have been in the business, geophysicists in every industry except oil have been
complaining that our clients neither understand what we do nor appreciate what we have to offer. For the
most part we have blamed everyone but ourselves:
Geologists call us “geomagicians”; they don’t comprehend our technology.
Engineers want answers with too many significant figures; they don’t understand the uncertainties
in our measurements. Environmental geoscientists won’t listen; they need to learn how we can help them.
Mining engineers don’t trust us. Clients never want to pay what it takes for good results; they don’t appreciate the complexities of
our business. Regulators have unrealistic qualitycontrol expectations; they don’t realize that every project is
inherently research. Politicians want to register us. Charlatans give us a bad name. SAGEEP was one of the first serious attempts to admit that we have a responsibility to
communicate with and sell ourselves to industries such as mining, groundwater, civil/geotechnlcal
engineering, and environmental management. The attendance at these symposia and the national
recognition they’ve received are testimony to the insight, hard work and success of a small group of
geophysicists who conceived and organized SAGEEP. Now it is time to recognize that all of us have a
responsibility to build on their beginning.
-
-
-
Application Of Geotomography To Rock Investigations
Authors Hideki Saito, Hiromasa Shima and Tetsuma ToshiokaThree types of geotomography, namely, seismic, radar and resistivity tomographies were
developed and applied to investigating the rock foundation for a planned bridge pier.
These techniques made it possible to reconstruct distribution images of seismic wave velocity,
electromagnetic ( EM ) wave velocity and resistivity, respectively. Therefore, if we want to
know the rock conditions totally, it is very effective to apply these three kinds of geotomography
jointly, and to interpret the results consistently.
In this paper, the methods of these tomography techniques developed by the authors were
reviewed briefly and a field example of applications of these techniques to site investigations
was demonstrated. We obtained three kinds of tomograms and identified fracture zones as
the low seismic velocity, low EM wave velocity and low resistivity zones. In addition, from
the interpretation results of these tomograms, we could not only map the fracture zones, but
could also estimate the rock conditions in detail. The results were confirmed by geological and
geotechnical investigations conducted after the excavation for the construction of the bridge pier.
-
-
-
A Case Study Of Rock Investigation Using Resistivity Image Profiling
Authors Hiromasa Shima and Hideki KamiyaThe authors have developed an electrical exploration
technology, called "Resistivity Image Profiling", which has
since been applied to many sites in Japan. In this method, a
two-dimensional or a three-dimensional underground resitivity
distribution is analyzed. This method combines an accurate
in-situ measurement technique and automatic computer analysis to
obtain more detailed and reliable results than conventional
electrical methods. The analyzed results are displayed as a
color profile which shows the resistivity structures more clearly.
2-D "Resistivity Image Profiling" was applied in a mountainous area where construction of a highway tunnel was
planned. The final analysis results show a complicated
resistivity distribution having a range from less than 50 Ω ·m
to more than 5000 Ω ·m. Using the resistivity values, we
classified the rock properties into four general categories:
fresh rock, relatively fresh rock that includes many joints,
weathered or altered rock, and fracture zone with clayey
materials. Further, we estimated both underground water levels
and locations of faults to identify the most likely area where
water burst out could occur. The tunnel is now under construction and the excavation
results are confirming our interpretations of fault locations
and rock properties. The actual locations of water burst out
also have shown good agreement with our predictions.
-
-
-
Delineation Of Buried Valleys Using Integrated Geophysical Techniques
Authors Steven R. Becker, Benjamin H. Richard and Paul J. WolfeIn northeastern Greene County, Ohio, Beaver Creek (a very small
stream) flows through a valley whose width exceeds a mile in some places.
Orton (1874) recognized that this valley was once the site of a much
larger river. Kulibert (1979) established that during early Wisconsin
glaciation the valley was occupied by the much larger Mad River. The
valley is also partly superimposed on the preglacial Hamilton River Valley
(Norris et al., 1950). Both valleys, the ancestral Beaver Creek and
Hamilton River, are currently filled with sediments. This study is a
detailed multi-faceted geophysical profile study of the ancestral Beaver
Creek Valley where it exists cut into the west side of the Hamilton River
Valley (Figure 1).
-
-
-
The Use Of Geophysics In Preacquisition Site Assessments (Psa’S) A Case History
Authors Don Kleinfelder, Todd Croft, Rich Fink and Bill GatesEnvironmental consultants must occasionally perform environmental audits on parcels that
have little or no known historic records. In such cases, the accurate evaluation of
geophysical data can be invaluable.
This paper presents a case study in which a magnetometer survey was used to evaluate a
vacant parcel that formerly contained six military helicopter pads and gotentiallg still
contained associated underground storage tanks. An in-depth records searc reveale little
-about the site, but evaluation of proton magnetometer data indicated a dense, potentially
vertical object approximately 15 to 20 feet below the surface near the pad locations.
Excavation of the anomaly revealed a concrete vault and a redwood vault connected by a
10’ long, 6” diameter metal pipe. The pad and vault were both filled with an assortment of
military porcelain, glassware and scrap metal. Unconvinced that such debris caused the
anomaly, we scanned the excavation with a metal detector and located an object beneath
the concrete pad. Further dewatering and excavation uncovered an 8-inch diameter, 40-
foot deep irrigation well remnant of pre-military ranching operations. We concluded that
this casing produced the magnetometer anomaly.
This study provides a lesson on the necessity of carefully evaluating excavated objects based
on the geophysical data before assuming that the objects represent the target anomaly.
-
-
-
Case Eistory Of The Removal Of Lead Contaminated Soil Prom A Residential Area
More LessThe operation of a former battery processing facility from 1963
thru 1980 resulted in surface soil contamination of eighty homes
and nearby drainageways. Engineering plans were developed to
remove lead contaminated soil from the residential areas. The
plans defined area1 removal limits and depths based on a 500 parts
per million action level.
Soil removal plans were developed on a block by block basis.
Preliminary removal limits were established using the soil sampling
results performed an extent of contamination study. Removal limits
were verified with additional sampling prior to excavation.
Excavation sequences and methods were developed by the contractor
and engineers prior to removal activities to minimize unnecessary
inconveniences for the residents. Confirmatory samples taken after
the designed removal of contaminated soil were used to indicate the
need for additional excavation or the beginning of restoration.
A community relations program was instituted to provide residents
with a communication link to the client and engineers. The
community relations program promoted an atmosphere of open
communication which helped lead to a successful completion of the -
project. Periodic meetings between the residents and engineers
were set up during various project phases. These meetings often
provided valuable information explaining contamination patterns and
also allowed residents to express concerns and/or problems. This
program gave the residents a first hand knowledge of the project
and helped alleviate concern and worry.
This case history documents the procedures used to safely remove
lead contaminated soil from a residential area. Problems arising
from the removal action and restoration of properties were handled
on an individual basis. The open communications between the
engineers, the regulatory agency, and the residents resulted in a
successful remediation project.
-
-
-
Use Of The Seismo-Electric Effect In Engineering Problems
Authors Catherine K. Skokan and Dong ChiThe seismo-electric effect is observed as the development of
potential between two points in a rock subjected to elastic
deformation. This effect is a function of physical properties
which are parameters desired in the collection of geotechnical
data relevant to the estimation of the effects of geologic site
conditions on the level of ground shaking. Standard, high
resolution reflection or refraction seismic measurement of both
shear and compressional waves provide values of elastic moduli.
Borehole information can be added to supplement these data.
These measurements, by their nature, are directionally dependent.
Of interest to the geotechnical engineer evaluating geologic site
conditions are also values of porosity, permeability, fluid
saturation, and fluid salinity. Seismo-electric measurements
could yield this information in situ and at the same time as the
standard seismic measurement. The seismo-electric effect is not
directionally dependent and will, therefore, yield information on
the bulk properties of the rock.
-
-
-
Monitor Well Completion Evaluation With Geophysical Density Logging
Authors E.N. Yearsley, R.E. Crowder and L.A. IronsThe competency of monitor well completions with regard to grout
continuity and the presence of the bentonite seal and sand pack can be
uniquely evaluated with geophysical density logging. This method relies on
density contrasts among various completion conditions. The presence or lack
of particular completion materials results In differences measurable with
geophysical density probes.
Empirical measurements made in the laboratory with density probes
provide information on depths of investigation and probe response to specific
completion conditions. These measurements support interpretations made for
two geophysical log examples presented herein. The examples indicate
discontinuous grout Intermittent with alluvium and air voids.
The economics of the density evaluation method are advantageous,
particularly with respect to the implications of a poorly constructed monitor
well, which include possible contaminant cross-flow and misspent monitoring
expenses.
-
-
-
Multi-Mode Seismic Imaging Of Forward And Back Scattered Seismic Waves In A Cross-Borehole Physical Model
Authors A.H. Balch, H. Chang, Gregg Hofland and Kurt RanzingerSeismic cross-borehole data are extremely complex because they usually
contain compressional, shear, and converted mode body waves, plus tube waves.
The complexity is compounded by the fact that many of the seismic events are
forward-reflected and forward-scattered, while conventional seismic
interpretation usually assumes back reflection.
At Colorado School of Mines, we have developed a cross-borehole
processing and interpretation system which: 1. Separates p-waves from swaves,
2, Compensates for travel time errors due to phase distortion, and then,
3. Converts the recorded data into images of the subsurface reflectors and
scatterers. Four image outputs are obtained, one each for p-p, p-s, s-p, and s-s
reflections/diffractions.
The examples shown will demonstrate that imaged cross-borehole data are
vastly easier to understand and interpret geologically than the original recordings.
-