1. Grontmij Pavement Consultants Kolding, Denmark
Poul-Erik Jakobsen
PRIMA100 LWD
A - Applications
B - Benefits

2. PRIMA-X Falling Weight Deflectometers
Since 1968
…up to present standard!
Three versions:
Up to 150 kN
Up to 250 kN
Up to 300 kN
© Grontmij | Carl Bro

3. FWD – simulates the passing of a truck wheel…
With the FWD –
Falling Weight Deflectometer -
we induce a deflection bowl
Measures:
Applied pressure!
Resulting deflection!
One truck causes wear
like cars
deflection bowl
Calculates:
#1 Material modules, Em
#2 Remaining service life
© Grontmij | Carl Bro

4. PRIMA100 LWD – Light Weight Deflectometer
The task is different from the big FWD!!
The main aim is NOT to calculate
modulus and service life.
The aim is to control
surface bearing capacity
during construction.
The surface bearing capacity
is known from the
design process.
PRIMA100 measures alone surface bearing capacity!

5. PRIMA100 LWD – Light Weight Deflectometer
Needed an equipment for unbound layers
Those available not sufficient
Did not record the stress/force,
but only deflection.
Therefore we developed the PRIMA100!!
f(1-ע2)*σ0*a
E0 = (MPa) d0
The stress applied changes with the soil!
Same energy can produce a force between eg. 8 and 12 kN!
Consequently it is essential to measure stress!!!

6. Applications for PRIMA100
Operate on unbound materials!!
subgrade – clay, sand, gravel
subbase – sand
base course - gravel
recycled concrete
recycled asphalt
slag
limestabilised soil …
Because you need to produce a sufficient deflection!!

7. Applications for PRIMA100
Applied stress LWD vs FWD
Force
Load Plate
Half falling height
(10 kg) (5 kN)
Full falling height
(10 kg) (10 kN)
(15 kg) (15 kN)
(20 kg) (20 kN)
100 mm - r = 0,05
637 kPa
1.273 kPa
1.910 kPa
2.546 kPa
200 mm - r = 0,10
159 kPa
318 kPa
477 kPa
300 mm - r = 0,15
71 kPa
141 kPa
212 kPa
283 kPa
Relate to the typical values of kN applied
with the FWD when used at road surveys:
50 kN => 707 kPa on a 30 cm load plate

8. PRIMA100 LWD measures the E0
You measure one figure - despite the number of layers!

9. PRIMA100 LWD – cone of influence
Using more geophones
gives you the chance to
get information from
deeper layers
Additional geophones are
only used in special cases
eg. research. E1 E2 E3 E4
More geophones = information from
more different depths
The longer the distance from the
center the smaller the deflection.

10. Applications for PRIMA100
You can regain your E0 at 110 MPa by adding
an extra half a meter of sand, which is
fairly expensive and hence nice to respond to on beforehand.
Your PRIMA100 helps you identifying the problem!!
Influence on the overall E0 caused by poor subsoil.
The only change is the Em value of the subgrade,
You see a substantial decrease of the E0 value.
Hence knowledge on the subgrade is essential!!
The only change is the Em value of the subgrade,
You see a substantial decrease of the E0 value.

11. Applications for PRIMA100
Optimise design… control your subsoil!
Perform detailed LWD measurements along the track eg. each 50m or 100m
Record E0 values.
Benefits:
is it as expected??
can you extend the lifetime of your road
can you optimise your design
can you optimise the use of raw materials (protect the environment)
save money – short term or long term

12. Applications for PRIMA100
Quality control – subbase, base course
Maybe extra benefit?
Can you save thickness
on the base course or
the asphalt layer?
Base course
Subbase
Subgrade
Measure E0 on top of the relevant layer.
E0 as prescribed?
Yes: Be happy and go on!
No: Be happy - that you found out at an early stage!

13. Applications for PRIMA100
Stress dependency of bearing capacity
The graph shows:
Future stress on subgrade approx. 105 kPa
you can use Em 20 MPa.
Future stress on subgrade approx. 50 kPa
you can use Em 40 MPa.
And it gives a significant difference in design!!
Hence utilising the PRIMA100 results you can
optimise your design!
Granular
Due to the fact that PRIMA100
is equipped with the load cell,
you are able to record the
stress dependency of the soil
Clay/clayey
Clay is often tricky and exact knowledge gives the chance to set up an exact design
Granular/friction materials are fairly simple
as there is no or a slightly positive dependency
Example: Subgrade

14. Applications for PRIMA100
Compaction software… calculate for different
subsoil modulus
Future stress ~50 kPa
Subsoil modulus 40 MPa
Future stress ~105 kPa
Subsoil modulus 20 MPa
Benefit: Save a lot of money on buying sand
Save the environment

15. Applications for PRIMA100
Lime Stabilisation
Pics by Danish Soilstabilisation
Measure the surface E modulus
before and after treatment
documentation
optimising
Surface E modulus
Substantial improvement

16. Applications for PRIMA100
PRIMA100 – material testing/potential raw material
explore the quality close to the trace E0
H1 E1? E2
Measure E(subsoil), E2
Build in and compact the unknown material
Measure E0 and H1
Wanted: E1
– modulus of the upper layer!
Use Compaction software
Know E2 – modulus of the subgrade
Know E0 – modulus of our construction
Know H1 – thickness of the upper layer

17. Applications for PRIMA100
Documentation Geogrid
Do you gain
something from
using a geogrid?
A minor non-scientific test
2,7MPa ,9MPa ,1MPa ,9MPa
Documenting the effect
of a grid
Documenting differences

18. Applications for PRIMA100
Keep an eye on the signal…
Perfect!
High water
content
Poor
compaction

19. PRIMA100 - Hints Verification: Choose a point, which is not disturbed.
Check the measured values from
time to time.
Calibration: Every 12 months – DO IT!
Deflection:
Deflections below μm
– increase falling height/smaller plate
Deflections exceeds 2200 μm
– decrease falling height/bigger plate
Force/stress: Nothing special to take care of.
Pulse time:
Preferable approx. 17 msec.
To long – mount buffers.
To short – dismount buffers.
Preparation measuring point:
Eventually level out with a little moist sand.
Falling height:
Use different falling heights
to check if stress dependent

20. Calibration and traceability PRIMA100
Correct calibration is essential for
collecting correct results
Calibration includes
load cell
geophone(s)
Calibration must be traceable
our equipment must be calibrated
by accredited institution
as prescribed by the manufacturer

21. Frequency response - original
Calibration geophone PRIMA100
Find the exact cut off
Find the exact slope
Frequency response - original
Want to do it better than factory specifications!

22. Corrected frequency response
Calibration geophone PRIMA100
Apply
amplifying
Corrected frequency response
Linear in the range where the information is collected!

23. Calibration load cell PRIMA100
Must be linear with slope 1
Must hit 0,0
Fit of the PRIMA100 versus the reference load cell