Shots were fired at 25 cm intervals between the depths of 50 and 72 m. Direct energy from a source in one borehole is received by several geophones that are connected by a cable in the other borehole. D4428 d4428m14 standard test methods for crosshole seismic testing precision cross hole seismic test seismic crosshole method. The primary purpose of obtaining crosshole data is to obtain the most detailed in situ seismic wave velocity profile for sitespecific investigations. Crosshole seismic tomography outline borehole seismic tomography involves the measurement of the travel times of seismic ray paths between two or more boreholes in order to derive an image of seismic velocity in the intervening ground. Crosshole seismic tomography for engineering site investigation. Overview historical data and geologic maps surface geophysics borehole geophysics cross hole testing hydraulic measurements hydraulic testing, water levels, sampling, pumping tests. Crosshole ip imaging for engineering and environmental applications.
The resistance, r, of the circuit electrodes plus earth can be calculated from ohms law, r vi, where v is the measured voltage drop and i is the current through the circuit. D4428 d4428m14 standard test methods for crosshole seismic testing precision crosshole seismic test seismic crosshole method. Singlehole and crosshole geophysical imaging methods singlehole and crosshole geophysical imaging. The project site was located at the crossing of new atlantic lock complex of the panama canal. Overview historical data and geologic maps surface geophysics borehole geophysics crosshole testing hydraulic measurements hydraulic testing, water levels, sampling, pumping tests. Cross hole and down hole tests can be used to measure vs. Single hole and cross hole geophysical imaging methods single hole and crosshole geophysical imaging. The seismoelectric method is an active geophysical method that consists of measuring the electromagnetic excitations associated with the conversion of the mechanical energy of seismic waves into electromagnetic energy at macroscopic interfaces characterized by variation in the electrical, hydraulic, andor mechanical properties.
The conventional approach involves lowering a 3component borehole geophone down one hole while lowering a source down an adjacent hole s, firing the source at some prescribed depth interval. Seismic methods can provide detailed information about rock properties and geological structure between boreholes. Quantifying compressible groundwater storage by combining. Quantifying compressible groundwater storage by combining cross. The results of cross hole seismic tomography at sites where there is good geological control are presented. The seismic waves can be denoted as p v or p z for a downward propagating compression wave and as s vh or s zx for downward propagating and horizontally polarized shear wave.
It is shown that while the geological sections do not contain velocity information they have provided structural constraints which provided fresh. Measurement of seismic attenuation from highresolution. General crosshole procedures environmental geophysics. An atmospheric hole that is detected in two consecutive scan lines is shown near the.
It is shown that while the geological sections do not contain velocity information they have provided structural constraints which provided. This approximation is valid where the velocity does not vary greatly, but in many regions of interest velocity variations of 1020 percent or more are observed, causing significant ray curvature. Standard test methods for crosshole seismic testing. Introduction to geophysics lecture notes download book. It is then clamped at intervals, commonly five feet, and at each interval the board is hammered. A typical seismic crosshole tomographic geometry consists of sources and detectors located in separate boreholes as shown in figure 10. For down hole seismic surveys there are many different acquisition geometries, depending on how the energizing system and the receivers are arranged among themselves. We utilize the most advanced techniques for determining velocities and site characteristics. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Typically, geophysical borehole logging will be conducted in each drill hole for the purpose of defining lithologic and stratigraphic continuity of the deposits.
The results of crosshole seismic tomography at sites where there is good geological control are presented. Crosshole seismic overview a threeaxis geophone is lowered into a speciallyprepared, cased borehole and excited with a hammer source in a similar borehole nearby. Figure 1a shows the twodimensional model for the crosshole em tomography problem, and figure 1b is a conceptual configuration of the crosshole em tomography system. Cross hole surveys are conducted in 3 or 4 inch id pvc cased holes that are typically grouted in place to provide good coupling with the borehole walls. It is assumed that downhole and crosshole tests have similar results. Effective interpretation almost always involves looking at results from more than one log type. Multihole seismic modeling in 3d space and crosshole.
Geologists use dems to accurately locate the elevation of drillhole collars. This ensures that the crosssections are vertically accurate. Geophysical methods can be used for costeffective site characterization and monitoring by observing variations in the electrical, magnetic, and seismic properties of subsurface materials. Geophysics at the borehole and cross borehole scale carole johnson, john lane and john williams ogwbranch of geophysics. The surveys were done from the underground workings at aecls underground research laboratory curl in june, 1993.
The seismic cross hole method consists of measuring the travel time of seismic waves propagating from a seismic energy source downhole hammer located in one borehole, to detectors downhole geophones placed at the same depth in adjacent boreholes. First it is hammered on one of its ends and a record is made. Subsurface surveys extensive education and experience. The attached chart next page shows specific applications for logging services which princeton geoscience can provide, indicating which tools are useful for particular applications and the borehole conditions required. The potential of seismic crosshole tomography for geotechnical site. Highresolution crosshole seismic data have been acquired at the imperial college borehole test site in northumberland, england. Geophysical methods commonly employed for geotechnical. We propose a cross hole imaging approach based on seismoelectric conversions sc associated with the transmission of seismic waves from seismic sources located in a borehole to receivers electrodes located in a second borehole. According to the literature, the seismic piezocone test has proven to be a fast, economical and reliable method to determine go. This is particularly important when constructing geological crosssections from data obtained from drillhole logs.
The transportation research board is one of six major divisions of the national research council, which serves as an independent adviser to the federal government and others on scientific and technical questions of national importance. The 5 chapters presented here started off as a set of rough lecture notes and are updated every year. First, there must be measurable contrast in a geophysical property between the target of interest and the background. Geophysical methods for characterization and monitoring. Airborne geophysical methods geology for investors. Our senior personnel have performed geophysical surveys for more than 30 years each, and can design a survey that is costeffective and accurate.
Gravimetry, newtons law of gravitation, gravity effect of selected bodies, magnetometry, magnetism of rocks and minerals, magnetic measurements for an archaeological prospection, geoelectrical methods, resistivities of. Crosshole seismic tomography geophysics geoscienceworld. Seismic crosshole method norcal geophysical consultants inc. Probes that measure different properties are lowered into the borehole to collect continuous or point data that is graphically displayed as a geophysical log. Hole seismic surveys and head response to atmospheric tides. Photograph 7 setup for crosshole seismic shear wave measurements. Normally 2 to 4 holes spaced 15 to 25 feet apart are used with the casings capped at the bottom and all water removed from the holes. This procedure is covered by an astm guideline but has several variants.
The s vh or s zx is also referred to as an s h wave. As part of the crosshole procedure borehole deviation logs are also run to accurately determine the attitudes of the boreholes in the suite. Invariant are requirements to measure both p and s waves and to use a reversible source to aid in. Application of crosshole tomography for assessment of. Pdf the role of downhole measurements in marine geology and. For geophysics to be effective in addressing a site remediation problem, two conditions must be met. The improved algorithm was employed to invert cross. Common data collection approaches include borehole, surface, and cross borehole geophysics. Mlni for volume integral equations, and use it to make calculations for forward and inverse problems of 3. Crosshole testing takes advantage of generating and recording seismic body waves, both the p and s.
Chinese journal of geophysics 20002018 earth interactions. They describe the concept of crosshole and downhole geophysics for the measurement of shear wave velocity in the field. Geophysical methods commonly employed for geotechnical site. View the article pdf and any associated supplements and figures for a period of 48 hours. The pwave and swave velocities are directly related to the important geotechnical elastic constants of poissons ratio, shear modulus, bulk modulus, and youngs modulus. Model i is a simple model with a highvelocity sphere placed inside homogeneous medium in order to simulate the boulder in the quaternary weathered layer as shown in fig. Downhole survey a sturdy hardwood board is laid beside the wellhead, and a downhole seismic, three component, clamping geophone is lowered into the hole. The geophysical survey called crosshole consists in the determination of horizontally travelling compression p and shear s seismic waves at test. Timelapse crosshole electrical resistivity tomography monitoring effects of an urban tunnel f. Crosshole geophysical testing determines the shear wave velocity of soils which provides an indication of its stiffness. This page includes two powerpoint pages created by professor paul w. A course in geophysics should appeal to geology majors as well as physics majors. Inventory and risk assessment manual aumira section 3. This book explains the following topics in geophysics.
Emc has over 20 years of seismic acquisition and processing experience. First, the crosshole seismic tomography method eliminates depthrelated restrictions during observations compared to the surface methods. The earth model considered here is set to be invariant in conductivity. Image of earths ultraviolet dayglow, primarily in the atomic oxygen emissions at. Crosshole and downhole tests can be used to measure vs. Downhole crosshole geophysics earth measurement corp. To precisely determine and analyze the nature of crosshole seismic wave propagation, a geological model having boulder is shown in fig. The simulated traces of the final model obtained by the full. It is assumed that down hole and cross hole tests have similar results. Comparisons have been made between the tomograms and the geological cross sections in order to assess the technique under in situ conditions.
To precisely determine and analyze the nature of cross hole seismic wave propagation, a geological model having boulder is shown in fig. Common pitfalls in crosshole seismic testing are 1 the use of sourcereceiver borehole spacings too. May 31, 20 numerical results indicate that mlni is an efficient method to compute the scattering fields of large. In this way the seismic wave travel path distances can be determined at every measurement depth. Application to the interpretation of a field survey d.
A seismic crosshole test was performed by generating both compressional waves and shear waves into the ground. An introduction to electrical resistivity in geophysics. Geotechnical geophysics is the application of geophysics to geotechnical engineering problems. Mayne, school of civil and environmental engineering in georgia tech. Cross borehole electrical resistivity tomography ert measurements introduction resistivity imaging at the surface may be used for applications such as cavity detection, geotechnical investigation, site characterization, monitoring of groundwater recharge, detection of lnapls and dnapls. However, crosshole geophysical testing may show that the ground has been suitably improved in some cases where cone penetration tests are unable to demonstrate an equivalent level of improvement. Fracture imaging within a granitic rock aquifer using. Weve been involved in many engineering studies and can collect the necessary information. Our geophysical staff has combined experience of over 200 years. Crosshole seismic testing has the definitive advantage of assessing a complex layered velocity structure with alternating high and low relative velocities. Traditionally, cs testing has been considered the most accurate method in determining vs, because it is a direct measurement of the wave speed. Collier geophysics offers a broad range of nearsurface geophysical exploration methods.
The resistance of a circuit is determined by the conductors size, shape, and resistivity, p, an intrinsic. Borehole seismic methods largely fall into two categories, namely, crosshole seismics and seismic tomography. Raypaths between source and receiver were horizontal and parallel to plane layered beds of sandstone, mudstone, and limestone. Pdf crosshole seismic testing is a valuable technique for determining seismic velocity profiles for critical structure siting investigations. Cross borehole electrical resistivity tomography ert. Fewer boreholes are needed to achieve a continuous picture of the subsurface thereby reducing overall costs and the risk of missing target features.
Borehole geophysics is the science of recording and analyzing measurements of physical properties made in wells or test holes. Lecture notes essentials of geophysics earth, atmospheric. Many tomographic interpretations of crosshole seismic traveltimes have approximated the raypaths with straight lines connecting the source and receiver. Geology majors will have expectations of such a course that are different from the expectations. Geophysics at the borehole and crossborehole scale carole johnson, john lane and john williams ogwbranch of geophysics.
Atmospheric holes and small comets university of iowa. Crosshole survey consists in the direct measurements of horizontally travelling compression p and shear s seismic waves at test sites consisting primarily of. Often used as part of a comprehensive geotechnical investigation, the crosshole seismic survey yields valuable information as to the strength and cohesiveness of the underlying sediment and bedrock, information that is critical to any engineering endeavor. This website beta version contains information on geophysical methods, references to geophysical citations, and a glossary of geophysical terms related to environmental applications. General crosshole procedures environmental geophysics us epa.
192 1190 590 191 957 571 362 409 1540 729 282 900 1343 1068 616 942 180 1536 1450 1452 320 1104 1314 574 1114 1342 617 1286 1042 1300 804 560 1058 72 813 734 1431 640 1253 1154