Light Weight Deflectometer Measuring Dynamic Modulus and CBR on-site Immediately

Transcription

1 Light Weight Deflectometer Measuring Dynamic Modulus and CBR on-site Immediately Dynamic Plate Load Test 12 Oct 2011

2 Overview What is the Light Weight Deflectometer What does it do? Where did the Light Weight Deflectometer come from? What does it simulate? What results do you get? Explanation of results graphs. Range limitations. How is it part of an integrated compaction control system Relationship with other devices What is the CBR Extension? What is the relationship between the Dynamic Modulus and CBR? What results do you get? Explanation of results graphs. Range limitations. What are the influences on the results? How do you calibrate the equipment? Technical standards How is the device used? Advantages and limitations 2

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4 What does it do? The Light Weight Deflectometer can be used for: measuring the bearing capacity (deflection) degree of compaction insitu and laboratory dynamic CBR of subgrade/subsoils, unbound base layers, granular layers, backfilling materials, soil stabilisation with lime, cold recycling materials and pavements, cycle tracks and footpaths. 4

5 What does it simulate? The Light Weight Deflectometer is developed from the idea that a truck with 10 tons axle weight moves at 80 km per hour on the road. Soil pressure of 10 tons / m² = 0.1 MN / m² along a time of 18ms Sizes of the test device: Diameter of the loading plate 300mm Force of load device 7.07kN Soil pressure under the load plate 0.1 MN/m² during a load time of about 18 ms The measuring time of 18 ms is created with the plate springs. This dynamic load plate test simulates and these conditions.

6 Principles of Operation The soil receives an impact of maximum force Fs transmitted through the fall of the drop weight onto a circular plate of radius r, which is assumed to be rigid. When the device is calibrated, the force is selected such that the maximum normal stress σ under the load plate is 0.1MN/m 2. To calculate Evd, the deformability of the soil under a vertical load, as described above, with a settlement amplitude s (in mm) and the duration of impact t s : Evd (MN/m 2 ) = 1.5 x r x σ /s For the 10kg drop weight and 300mm diameter plate Evd = 22.5/s For the 15kg drop weight and 300mm diameter plate Evd = 33.75/s 6

7 How does it work A weight of 10 kg drops from a height of 72 cm on a load plate with a diameter of 300 mm. On the load plate, an acceleration sensor is arranged. From this acceleration signal will be calculated the dynamic deformation modulus Evd kg loading device (Evd 5-70 MN/m²) - 15kg loading device ( MN/m²) The easy-to-operate ZFG 3000 GPS enables the user to enjoy short test times (approx. 2 minutes), precise repeatable measurements, on-site printouts complete with all information and simple data transmission to the PC with SD-Card. The measured result is available after only 4 steps.

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13 Degree of Compaction The ZFG 3000 has an acceleration sensor attached to the base plate. The first integration of acceleration shows the velocity of the plate. And the second integration gives the deflection. The degree of compaction is based solely on experience and provide the examiner with an immediate statement about the likely effectiveness of compaction, enabling you to take a decision about soil improvement or soil replacement. The value of s / v = 3.5 is relevant here. In case of compacted soil is valid: s / v < The compacted soil can be compacted further. s / v > 3.5 If compacted, the soil is unsuitable for further compaction! Soil improvement or a soil exchange is necessary. s / v > 3.5 If it is in-situ soil, it can be compressed further.

14 Integrated compaction control system Handheld testing devices, e.g. nuclear-density gauge, can only measure a limited amount of space at a time covering only a small percentage of the project s footprint. Compaction Uniformity to specification An Intelligent Compaction (IC) roller can test the entire range of the project, and its sensors can penetrate deeper into the fill. 14

15 Measuring Compaction: Fundamental Changes From Density to Stiffness Density Stiffness is the basis for calculating an even more fundamental material property, "modulus," which experts agree is the most accurate and independent means for judging deformation and, thus, a material's level of compaction. Stiffness* * Stiffness is loosely defined as a measure of a material's ability to resist deformation under load 15

16 Compaction Method Old Method Compaction Control Measurement Unit & When In-situ test methods Density After Compaction is Complete New Method Provides little or no on the fly feedback Stiffness Ongoing measurement & feedback to operator Nuclear Gauge Verified using a compaction control device (inc DCP, GeoGauge and Light Weight Deflectometer eg Zorn ZFG3000) Intelligent Compaction 16

17 Measuring Compaction: Fundamental Changes from Density to Stiffness Density Stiffness* * Stiffness is loosely defined as a measure of a material's ability to resist deformation under load 17

18 Relationship with Static Plate Evd and Ev2 relationship - the relationship between the static deflection modulus Ev2, measured by the static plate bearing test, and the dynamic deflection modulus Evd depends on the kind of soil and the degree of compaction. Experience shows that the ratio Ev2/Evd lies in the range 1.0 to 4. For densely compacted soils Ev2/Evd ~ 2.3 On average the following relation between the dynamic deflection modulus Evd, and the static deflection modulus Ev2, can be used: This relation does not hold for limiting values. 18

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20 CBR Extensions The dynamic CBR test, in particular, the in-situ field test, is a material test on compacted samples, with which one can judge what level of compaction can be achieved on the tested soil. All readings and analysis can be done in the field and the results are immediately available at the construction site. The CBR stamp has a diameter of 50 mm and a corresponding pressure amplitude of 3.6 MN/m2. The Dynamic CBR Extensions measure in-situ the dynamic California Bearing Ratio (CBR) value CBRd within a range of 20% CBRd 150%. The CBR-value is calculated as follows: CBR d = 87.3 / s 0.59 % (s [mm]) where s is the settlement amplitude (in mm) of the CBR stamp 20

21 Advantages Immediate evaluation of measurement possible on site Direct deflection readings: accelerometer directly connected to the base plate Time saving in testing (a maximum of 3 minutes per measuring point) Accurate repeatable results One-man use: designed for field testing No additional loading vehicle or support is required Testing on sites with difficult accessibility possible Readings captured on SD-card for data memory (10,000 data sets) allowing immediate on-site results printing and data transfer to PC Data interpretation software allows data storage, analysis and manipulation and easy inclusion into reports GPS-System for immediate determination of test position integrated with Google Maps Using extensions to the ZFG 3000, dynamic CBR (California Bearing Ratio) can be measured in-situ in the field and also laboratory CBR in a cylinder can be simulated.

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23 Technical Standards ASTM E Standard Test Method for Measuring Deflections using a Portable Impulse Plate Load Test Device Technical Test Progrom for soil and rock in the road TP BF - StB Part B Federal Highway Research Institute (BAST) 1992 In this test procedure, it governs, for example the device structure (material, size, weight) but also Experimental parameters (impact force = 7.07 kn, load time 18ms) and calibration cycles

24 Thank You Self Control by Contractors / Geotech Companies CBR recognised e.g. rail Used for acceptance where Ausroads / VicRoads standards don t apply e.g. remote regions, mines, construction sites etc 24