Controlling deep foundations by the transparency method
(also called sonic coring, sonic logging, or crosshole method).
NORME : NFP 94 - 160 - 1
 |
The
CS 97 replaces the CS 87. It is the most recently
developed pile integrity testing device among
those developed by CEBTP.
It
has been developed by laying the stress on the
precision of measurements, the simplicity of
use and above al the profitability of the tests.
The
length of piles can also be easily measured
by the parallel seismic method simply by adding
a few accessories : a specific software, a hammer,
a cable counter). |
The
core drilling method enables you to verify the continuity
of deep foundations, of piles, of moulded walls, or
of barrettes, by detecting possible cracks or anomalies
along the shaft or at the tip. You can estimate the
homogeneity and the quality of the concrete, and you
can position the defects precisely, at the tip of
the pile as well.
Theoretical
principle :
In
a homogeneous concrete, the velocity of sound is constant.
Its value is close to 4000 m/s. It rapidly decreases
in presence of anomalies such as soil inclusions,
cracks, segregations, etc...
Sonic
core drilling consists of a continuous measurement
of the sound velocity along the pile. The measurement
is performed between an emission and a reception probe.
Both
probes are taken down two tubes which are bound to
the steel reinforcement. The signal is transmitted
to the CS 97 unit, which keeps it in memory, processes
it and returns the diagraph onto the screen while
the probes are lifted.
The
diagraphs :
The
signals received by the reception probe are modulated
and they are converted into levels of grey. The image
thus obtained, which is called a diagraph, gives a
characteristical representation of the zone scanned
in the pile and of the quality of the concrete.
 |
-Small anomaly. |
 |
-Important anomaly |
 |
-Cut pile |
 |
-polluted concrete at the bottom of the pile. |
schematic
cross-section of a pile
the diagraph
The
technology of CS 97 takes advantage of the whole know-how
of CEBTP and of its experience of the hard conditions
of measurements on a site.
The
CS 97 equipement is delivered complete to you, and
ready for use.
The
equipement is comprised of :
| a
CS 97 unit.
an
laser A4 printer.
a
printer connection cable.
an
emission probe.
an
amplified reception probe.
a
cable winch (100 m) for the emission probe.
a
cable winch (100 m) for the reception probe.
a
pulse triggered lifting winch.
a
cable winch (50 m) for the lifting winch.
a
tripod for the lifting winchl.
three
connection cables with the CS 97 unit.
an
interlink connecting cable.
a
user's manual in English and in French.
|
 |
General
characteristics of the CS 97 equipment :
Power
supply :
Option 1 : AC 110 volt up to 320 volt automatical.
Option 2 : AC 110 volt up to 320 volt automatical,
or 12 volt.
Power
consumption : 40 Watt.
operation
temperature : From 0 to 50°C.
Probe diameter : 25 mm.
Screen :
LCD black and white 6 in screen.
keyboard :
Alphanumeric, waterproof IP 65, QWERTY keyboard.
Printer :
Laser A4 format printer.
Dimensions of the CS 97 unit : 43 x 20 x 51 cm.
Weight
of the CS 97 unit : 13.6 kg (for the mains
power supply version).
Sampling
frequencies : From 125 kHz up to 2 MHz.
Vertical
resolution :
can be selected between 1 measurement every 1.25,
2.5 or 5 cm.
Probe
lifting speed : can be selected between 20,
40 or 80 cm/s.
Time
base : 125 ms, 250 ms, 500 ms, 750 ms, or
1 ms.
Maximum control depth : 150 meters.
Maximum
width of concrete one can scan : 3 meters
(2.5 m are recommended).
Maximum
internal storage capacity : 80 000 meters if 1
measurement every 1.25 cm.
levels of grey : 8
3
diagraphs can be plotted on each printed page.
Language
of the software : English.
Langue
dimpression : English, French, Spanish or
Portuguese language.
(other alphabetical languages upon request
The
software can be used from the keyboard or from the
mouse.
Exploitation
system : Windows 95.
Total
weight of the equipment (CS 97 unit, cables, probes,
printer, etc...) : 66 kg
Operating
the CS 97 :
The
tubes have to be installed prior to casting the
concrete, and they have to reach the base of the
pile. These are metallic tubes filled with water
whose internal diameter is at least 35 mm. The number
of tubes varies with the pile diameter :
For
diameters < 0.60 m : 2 tubes.
For 0.60 m < diameters < 1.20
m : 3 tubes
For
1.20 m < diameters : at least 4 tubes.
 |
 |
 |
Possible paths :
1 2 |
1
2
2
3
3
1 |
1
2
2
3
3
4
4
1
1
3
2
4 |
In the case of moulded walls and barrettes, the
number of tubes is defined according to the dimensions,
by limiting the distance between tubes to 2.50 meters.
| Possible
paths : |
1
2
2 3
1 3
2 4
|
3
4
4 5
3 5 |
if
distances allow to do so : |
2
5
1 - 4 |
Some
shallow foundations can be fitted by a tube with
a larger diameter and shorter than the others. This
tube is meant to allow a drilling and an injection
in case of an anomaly at the base of the pile.
The
tube can be made of standard steel, even though
slightly stained, such as heating equipment tube,
and they can be assembled by muffs.
Plastic
tubes should not be used for their adherence to
concrete is low.
The
tubes have to be free of such inside debris as concrete
or earth, in order not to perturb the measurement.
The
base also has to be stopped by a strong stopper,
in order to retain the water and to avoid risks
of probe jamming.
The
printing :
The
CS 97 equipment is delivered along with a laser
printer.
The
user can therefore print at once on the site, right
after performing the measurements, or he can print
when back to his office, since the measurements
are stored in the CS 97 unit (80 000 meters of diagraphy
can be stored)..
It
only takes a small while to process the results
of a foundation.
After
he has entered a few pieces of information (file
number, pile number, remarks, etc...), the user
can launch the printing of the diagraphs of a foundation,
or of the whole site.
The
report can then be edited very quickly.
The
above figure shows an example of print which can
be obtained very quickly on the site or in the office
(the normal format is 21 x 29.7 cm). .
The
diagraphs shown as examples reveal anomalies at
the bottom of the pile, and on the central diagraph
particularly, two anomalies at 0.75 and 5 meter
depths.
The
user can also automatically print a summary table
of all the building site as shown in the example
above.
This document is directly integrable in the report.
The CS97 printing documents are printable in French,
English, Spanish, and Portuguese language.
Further
information :
All
the connectors of the CS 97 are Murphy-proofed,
in order to avoid switching errors.
The
user's manual clearly explains how to use the CS
97.
When
training on his own, a new user makes connections
according to the instructions of the manual, and
he simulates the measurement step by step as if
he were on a real site.
It takes less than an hour to get to know how to
use the CS 97.
A
training can be provided by CEBTP if the user
has a need of it.
A
control and maintenance service for the sensors
and the material can also be proposed by CEBTP
<Historical
overview of the foundation control by the transparency method>
<Parallel seismic
methods with the CS 97>
<The different means
of controlling a foundation>
