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

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

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 10000-40000 cars deflection bowl Calculates: #1 Material modules, Em #2 Remaining service life © Grontmij | Carl Bro

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!

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!!!

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!!

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 50-150 kN applied with the FWD when used at road surveys: 50 kN => 707 kPa on a 30 cm load plate

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

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.

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.

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

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!

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

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

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

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

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

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

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 100-150 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

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

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!

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

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