Spherical
Ball Penetrometer
 BPT
Specifications |
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Click
here to
get a 573Kb summary of the Technical Specifications
of the Spherical Ball Penetrometer in a PDF format. |
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The
Spherical Ball Penetrometer , 'BPT', is a specialist
in situ tool that can be deployed as an alternative to Benthic
Geotech's standard piezocone system.
The
BPT comprises a large, relatively smooth spherical ball
that is attached to a smaller diameter, high tensile
steel shaft. The steel shaft is screwed to the 'tip load
cell' of Benthic Geotech's standard piezocone, and is
used to measure the penetration resistance of the ball
as it is pushed into the ground. Monitoring of pore water
pressure at the midpoint of the ball is also possible.
The
performance of the BPT as an in situ strength profiling
tool has been described by several authors, both in field
and in laboratory. An exact solution for undrained shear
strength as a function of ball resistance was derived
by Randolph et al (2000).
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BPT is a particularly useful device where an accurate definition
of the shear strength profile of very soft to firm, fine
grained soils is required. The BPT can measure a range
of shear strengths comparable to an in situ vane. However,
unlike vane testing, the BPT has the capability to undertake
continuous strength profiling.
Compared
to the standard piezocone, the larger bearing area of the
BPT mobilises significantly higher pushing forces on the
cone tip load cell, enhancing the resolution of the measuring
system. In addition, the closed form solution for undrained
shear strength greatly reduces uncertainty in selection
of appropriate coefficients for the calculation of true
in situ shear strength.
Though
not required in the calculation for undrained shear strength,
the capability to measure excess pore water pressure enables
dissipation testing to be undertaken at any point during the
course of sounding, at the discretion of the client.
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Penetrometer
is thrust into ground using PROD drill string
Instrumentation,
data storage and transmission assembly
Push rod and anti-friction sleeve
Spherical ball
Pore water pressure filter
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The
BPT is a very useful addition to Benthic Geotech's suite
of integrated down hole geotechnical tools.
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BPT
PERFORMANCE SPECIFICATIONS
| Penetrometer
Assembly |
60
mm diameter, hardened, smooth steel sphere attached to a 200
mm long x 20 mm diameter, high tensile push rod |
| Ball
Bearing Pressure, qbc |
Maximum
5 MPa (bearing area = 28 cm2) |
| In
situ shear strength resolution, Dsu |
<0.6
kPa (real time data), <0.1 kPa (memory data) |
| Ball
Pullout Pressure, qbt |
Maximum
4 MPa (monitored), maximum 10 tonne pullout capacity |
| Water
Pressure, Ub |
Total
25 MPa (Hydrostatic + Excess) |
| Penetration
rate |
Nominal
20 mm/sec |
| Real
time data transmission |
Acoustic
transmission (up to 100m drill string length) |
| Internal
backup memory |
Minimum
24 hours, 1 reading/sec, non volatile |
| Battery
life |
>24
hours per probe (expended whilst down the hole) |
| Max No.
of probes per deployment |
Typically
3 |
| Depth
control relative to PROD |
PROD
carriage position system, resolution 1 mm |
| Depth
control relative to mudline |
PROD
baseplate monitored relative to mudline, resolution 25mm |
Click
here to
get a 573Kb summary of the Technical Specifications of the Spherical
Ball Penetrometer in a PDF format.
Benthic
Geotech's Spherical Ball Penetrometer is the subject of current
patent applications.
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