activities having civil works and military responsibilities .

3 . Background . Borehole television and camera systems provide an extra

dimension in obtaining borehole information and determining in situ rock

conditions . Advantages for television systems are direct viewing,

immediate analysis, variable focusing, and concurrent records . Borehole

camera surveys can provide color photography, 360 degree viewing area,

portable equipment, and high resolution images . The Corps of Engineers

pioneered development and use of the NX borehole camera and is currently

believed to be the only source for the 360 degree radial-view camera .

Television cameras and other systems are more recent developments .

4. Description of Equipment . Characteristics of different viewing

systems are listed in Table 1 for comparison of critical features and

possible limitations .

a . Television Systems . The television system uses a closed circuit

television camera and the image of the borehole sidewall is viewed on a

television monitor . Most borehole television systems are composed of a

probe containing television electronics or camera equipment, a

combination lowering device and cable drum, and a control console .

Television systems currently available for FOA's use are listed in

paragraph 8 . Features of most television systems include the alternative

use of an axial (downhole) or radial (sidewall) lens . Some systems have

the capability of direct viewing, on the monitor, of a compass-clinometer . Views may be transferred to a videotape for future

interpretations . The videotape can also be used to record voice comments

as the boring walls are viewed . In addition, a depth indicator located

on the console may be programmed to appear on tape, providing continuous

location of the probe in the borehole .
N

* Some systems have an effective dist

** Requires centering device .

SYSTEM

PROBE HOLE DIA

DIAMETER LENGTH MINIMUM 

TV Systems

3"

	

3"

1 - - 4

4

-

4

12"-32" 2"-5"

NX Camera - 30" 3" 

Borescope 2" -

1"

22 

Televiewer 2" 22" 3" **
c

b . CameraSystems . The Republic NX camera is designed to provide

continuous, overlapping, 360 degree coverage (radial view) of the

borehole walls . The camera is contained in a stainless steel, waterproof

cylinder . A magazine containing 25 feet of film will permit photographing about 75 feet of the boring . A photograph can be taken every 3/4

inch, thereby producing continuous pictures of the borehole sidewall . A

conical mirror located at the quartz window is truncated at the top to

expose the hollow interior of the cone . The opening permits the camera

to photograph, on each exposure, the orientation of a floating magnetic

compass and tilt indicator . By this means, a departure from vertical of

any section of the borehole is photographed simultaneously with the

compass orientation of the photograph . Film interpretation of the NX

system can be otained by two methods with the use of a special

projector . One method recreates (by means of a conical mirror) the

cylindrical geometry of the borehole . The mirror projects each

photograph onto the interior surface of a frosted glass cylinder . From

outside this cylindrical glass screen, the interpreter sees a projection

that resembles a rock core in true perspective, permitting a continuous

borehole log to be developed . The second method projects, by means of a

plain mirror, a distorted, flat, doughnut-shaped image onto the

projector's screen . The image is then analyzed and interpreted with the

aid of various types of overlays, depending upon the information

desired . At the present time, there is no known supplier of new NX

camera equipment .

c . Borescope . The borescope is basically a tubular periscope with

optical magnification and a light source . The equipment is sectional,

and is lowered into the boring by hand, or by use of a simple lowering

mechanism on a tripod . Optical fittings on the ends of the tube can be

selected for either radial or axial viewing and a camera attachment for

photographing the borehole can be fitted . The depth to which the

borescope may be used is limited by the ability of the system to transmit

adequate light to the hole . Not all borescope systems are waterproof .

d . Televiewer or Seisviewer . The borehole televiewer is a cablemounted downhole tool which transmits acoustic pulses to the borehole

wall and records the reflected energy . This energy is converted and

displayed on an oscilloscope, and can be photographed . The transmitter

of the acoustic signal sweeps the hole in a 360 degree arc oriented to

magnetic north . Because fractures, soft seams, cavities, and other

discontinuities will attenuate the acoustic reflection, these features

will be distinguished on the oscilloscope image . Changes in lithology

and porosity may also be distinguished by changes in the image

intensity . A major advantage to this system is that the log image does

not require clear fluid in the borehole, and therefore it can be

conducted in a mud filled boring . It does require use of a fluid to

transmit the acoustic pulse . Usual logging speed is 15 feet per minute .

3
EP 1110-1-10

21 May 82

e . ImpressionPacker . The impression packer can be used to obtain

fracture and "washout" data for limited sections of borehole . The

procedure for use consists of coating an inflatable formation packer with

a slow curing rubber compound, inserting it into the boring to the depth

of interest, and inflating the packer . When the rubber has cured, the

packer is deflated and withdrawn . The rubber membrane will contain an

impression of the fracture traces .

5 . Applications . Borehole television and camera systems provide easy to

reproduce records for future reference, are easily portable, can provide

360 degree borehole sidewall photographs, and produce good pictures

either in clear water-filled or dry holes . Also, the systems may be used

in well screen condition surveys, to ascertain grout distribution and

effectiveness in boreholes, and in borehole casing assessments . Borehole

drift angle and direction can be determined with the NX borehole camera

and with the use of a directional gyroscope in conjunction with certain

television systems . Specific applications of borehole viewing systems

for geotechnical data collection include :

a . Location of zones of core loss or "washout" .

b. Assessment of zones of core losses due to badly fractured zones

and very soft zones .

c . Determine geometry, spacing, and dimensions of rock joints,

fractures, bedding, and other discontinuities .

d . Determine dip direction of bedding, foliation, and shear and

fault zones .

e . Determine condition of rock-concrete contacts .

f . Evaluate openings along joints, fractures, and bedding .

g . Evaluate cavities .

h . For drill holes where no core has been obtained, viewing systems

may be able to provide data on :

(1) lithologic characteristics

(2) stratigraphic sequence

(3) bed thickness

(4) establishing horizon markers

(5) zones of oxidation and deterioration

(6) joints and. rock cleavage

(7) fractures--width of shear zone--strike

(8) fault clay and gouge

(9) brecciated and crushed zones

(10) stylolites

(11) cross bedding

(12) unconformities

4

and dip
6 . Discussion . The television camera is easy to use and provides an

immediate- image which can be stored on videotape . The resolution of the

TV image is not as good as that of a film camera . The television system

can record an entire hole' in one operation, whereas the film camera can

only record about 75 feet of the hole before it must be withdrawn and the

film changed . The borehole camera can take color or black and white

photographs, but color may not be available for TV images in the smaller

sizes . The film camera images cannot be evaluated until the film is

processed and projected . Holes must be free of mud or muddy water to

provide optimum results . The borehole can be flushed and/or "wiped", and

flocculants added to settle suspended sediments . The seisviewer can be

used in holes filled with drilling mud . Special uses of viewing systems

could be to obtain additional data on the extent of solution cavities or

mines and to assess the success of mine and cavity backfilling . The

camera can also be used to examine well screens and casings or to monitor

holes specially drilled for the` purpose of observing cracks in concrete

or stress relief in foundations or excavations . Where hydrofracturing is

performed to determine in-situ stress, cameras can be used to measure the

fracture orientation (stress direction) . They may also be used for

orientation purposes where obtaining oriented core is not possible or

feasible . Borehole viewing systems should not be used as a substitute

for obtaining cores . However, these systems can provide valuable data in

holes where coring has not been done, such as drains, NX grout holes,

wells, instrument borings, etc .

8 . Availability . Corps of Engineers owned viewing equipment and

services are available as listed below : (Point of contact in parentheses)

a. Waterways Experiment Station

Mechanics Division) .

- NX camera

- TV cameras ;

- televiewer

- borescope

for NX hole, for

(Engineering Geology and Rock

5 inch hole

b . US Army Engineer Division Laboratory, Southwestern (Director,

SWD Laboratory) .

- NX camera

c . US Army Engineer District, Walla Walla (Foundation and Materials

Branch) .

NX camera

TV camera, for 4-1/2 inch hole

d . US Army Engineer District, Mobile (Geotechnical Branch) .

- TV camera, for 3 inch hole

5

21 May 82
EP 1110-1-10

21 May 82

e . Other government agencies have developed their own camera and TV

systems for special uses . For special or limited purposes, consideration

may be given to fabrication of an inexpensive camera system such as

described in "Development of System for Photography of Underground

Openings Through Drilled Holes," Missouri Highway and Transportation

Department, Report No . 80-2, March 1981 .

FOR THE COMMANDER:

W. RAY

olonel, Corps of Engineers

/Chief of Staf

6