TERRATEST® App from now on in Google® Playstore

Our Light Weight Deflectometer TERRATEST5000 BLU is worldwide the first instrument in its class to be controlled via tablet or smartphone. For that purpose, TERRATEST^® has developed an app from now on available in Google^® playstore. This app proves to be useful also when used with the TERRATEST^® 4000 STREAM model, as it enables measuring results directly to be transferred from the measuring electronics ROBUSTA to a smartphone. This feature considerably speeds up order handling, as the results still on the construction site can be processed, and logs in form of a .pdf file can be sent to the office or to the customer without delay. Analysis of a dynamical load plate test by means of a light falling weight this way is performed in no time. The quality of the logs transmitted by app exactly corresponds to the documentation prepared by means of the TERRATEST^® 2.0 software, and offer even the additional benefit of automatically integrating photos of the measuring position captured on site within the file. “We are very proud of being able to offer this comfortable control method for our falling weight deflectometers to the clientele”, declares Frank Georg Schulz, CEO of TERRAEST^® GmbH Berlin. The possibility of using this app also for our new cable instrument TERRATEST^® 4000 STRAM demonstrates our innovative power and the continuous progress of our product portfolio.” App versions loaded from the Google^® playstore automatically create an update message, so that the user is instantaneously informed about the new version available - so he can profit from the new functions, which permanently extend the scope of the instrument corresponding to the current state of further development.

New Delivery to Kuwait

In the beginning of February, two Light Weight Deflectometers of the 4000 Voice Series were delivered to the South Al Mutlaa site in Kuwait. They are intended to be used for dynamical load plate tests, to be executed in the course of development work taking place under the responsibility of the Turkish Kolin group. “For our purchase decision, the essential criterion was the dust-tight ROBUSTA box housing the electronics”, explains project coordinator Mr. Mustafa Hakan. “When working in desert, safe protection of internal components is imperative, that’s easy to understand. I have been using TERRATEST® equipment in Turkey already for a long time, and it turned out to be absolutely reliable.” South Al Mutlaa currently represents the largest construction site in Kuwait and will be the core of a new Mega City with 30,000 houses, comprising a project volume of 1 billion US$.

Calibration of Light and Medium Weight Deflectometers

Calibration System “CS01” for Light and Medium Weight Deflectometers, presented by Dr. Bernhard Korsch, head of the calibration office and Frank G. Schulz, CEO of TERRATEST®. Both of them proudly show the admission documents just received from the German Federal Highway Research Institute (BASt). Only four of seven applicants have obtained the authorization for calibrating also Medium Weight Deflectometers.

Legal Basis: Acc. to Engineering Code for Soil and Rock in Road Construction TP VF-StB Part B8.3, Light Weight Deflectometers for dynamic load plate test have to be recalibrated once within 12 months. Regular calibration ensures precise measurement on the site and validity of measuring results when analyzing compaction quality of the soil acc. to ZTV E and ZTV A. Results originating from instruments not calibrated should not be used as compaction proof. The validity of the calibration becomes obvious by the test label attached to the components of the device.

Calibration of the New Medium Weight Models: Seven offices admitted for Calibration of Light Weight Deflectometers acc. to technical test regulation TP BF-StB Part B8.4 (2016), have applied to the German Federal Highway Research Institute (Bundesanstalt für Straßenwesen BASt in Bergisch Gladbach) for supplementary authorization of calibrating the new Medium Weight Deflectometer, but only four of the applicants obtained approval.

“We are very proud of having instantaneously met the stringent requirements of the BASt for Medium Weight Deflectometers”, declares Dr. Bernhard Korsch, head of the calibration office of TERRATEST® Berlin. “We had to transform the calibration system worked out in-house, with respect to the parameters of Medium Weight instruments. It was a particular challenge to adapt the software, due to the new settlement measuring ranges of the Light Weight Deflectometer and the Medium Weight Deflectometer – and we obtained the success we have earned. The development of the device itself and a corresponding calibration system was a quite complex task.”

In the beginning of October 2016, seven calibration offices were examined by the BASt, but the admission was granted only to three of them (apart from TERRATEST®). The Medium Weight Deflectometer, acc. to directive TP Stone-Road Construction, Part 8.2.1, disposes of the double impact force compared to a Light Weight model. This value is achieved by a falling weight with a mass of 15 kg and corresponding disk springs. This configuration is particularly useful for assessment of bearing capacity for layers without binders acc. to ZTV SoB-StB (anti-freezing and gravel-bearing layers, surfacing without binders). The same is valid for other applications with comparable bearing capacity, e.g. for qualified ground improvement in traffic routes construction.

Until now, TERRATEST besides the light weight models with usual impact force produces a version with force factor 1.5, used in North Rhine – Westphalia (Western Germany). In this region, a corresponding testing directive is in force. Increased force was put into practice by means of a falling weight with a mass of 15 kg and corresponding disk springs (as mentioned above). This instrument type was supplied with a so-called factory calibration based upon the requirements of TP BF-StB Part B8.3.

TERRATEST® from now on offers a low cost possibility of modifying load assemblies of these instruments, to configure a Medium Weight Deflectometer acc. to TP Stone-StB Part 8.2.1. Calibration takes place acc. to TP BF-StB part B8.4. At the same time, the measuring electronics are completed by new firmware, thus simplifying switching between Light Weight and Medium Weight applications. For this reason, on the construction site the exchange between different load assemblies required is easy to realize. It is sufficient to select command “MFG” in the menu of the TERRATEST® measuring electronics, to exchange the load assembly and then to start measurement. Simplified handling is a clear benefit of the arrangement. The advantage of a retrofit is obvious: Also former models this way can be used in conformity with ZTV SoB-StB. Of course it is possible to equip all existing Light Weight deflectometers with a Medium Falling Weight. “This enables our clients to examine also layers with comparatively high bearing capacity acc. to ZTV SoB-StB, without the need of purchasing new instrumentation”, announces Frank G. Schulz, CEO of TERATEST®. Until now, Light Weight Deflectometers could only be used for a maximum Ev₂ value of 120 MN/m². In between, numerous clients profit from the available option and convert their 15 kg load assembly to the new configuration with double impact force.”

Under laboratory conditions, light or medium weight deflectometers are calibrated on a rigid basis consisting of a concrete cube with dimensions (LxWxH) = 80 x 80 x 80 cm. The procedure itself is composed of two distinct measures:

1)    First the force of the load assembly is calibrated on the basis of a special load cell. The result must amount to 7070 (light weight) resp. 14140 N (medium weight models), at a tolerance of 1%. The force value can be modified by varying the height of fall, by means of the unlatching device installed at the top. The pulse time of impact is defined to 17 ms + 1.5 ms resp. + 1.0 ms for medium weight models, to be adjusted by the initial stress of disk springs. After precise setting of height of fall and initial stress of disk springs, three measuring sequences with 10 impacts each are carried out. Calibration is acceptable in the case of deviations for force and pulse time < 1% between distinct impacts, runaways are not tolerated.

2)    The procedure for the load assembly is now complete. The next step is calibrating the settlement measuring assembly in three different ranges: Soft, medium and hard. For that purpose, the load plate is clamped on a steel plate (thickness: 30 mm, diameter: 340 mm, mass: 30 kg), intended to symbolize the half-space below the load plate.

a)    Preparation: Below the steel plate, different polypropylene mats (for the calibrating ranges mentioned above) will have to be inserted in turn. For the hard mat, a settlement of 0.3 mm is expected, corresponding to soil relatively well compacted with an Ev_D value of 75 MN/m², usual in road construction. The soft mat with a settlement of 1.6 mm reflects properties of soft uncompressed, e.g. naturally grown soil with an Ev_D value of 14 MN/m². This defines the calibrated range of the light weight deflectometer, on the basis of the mats prescribed by BASt, to the zone between 15 and 75 MN/m².

For the Medium Weight configuration on the other hand, another set of mats has to be used, corresponding to a settlement of 0.3, 0.5 and 1.2 mm. As the stress below the load plate in the course of the impact achieves the double value compared to the trial described above, the calibrated range comprises the zone between 30 < Ev_D < 150 MN/m². This range corresponds to Ev₂ values even above 200 MN/m², so that reliable measurement on layers with particularly high rigidity is ensured.

b)    Procedure: As to the maximum settlement, the method consists in comparing the result of the TERRATEST® sensor to the results of three distance sensors. With the mats in place, these sensors are placed onto the load plate, intended to record its displacement in the course of the impact – this delivers an accurate reference value for maximum settlement. As this measurement represents a dynamical process at an extremely short pulse time (17 ms), accurate determination of maximum settlement by an acceleration meter is by no means trivial. “We are really impressed by the measuring accuracy of our instruments”, confirms Sven Krone, test coordinator for calibration of Light and Medium Weight Deflectometers at TERRATEST®. “The results are extremely repeatable; our devices are able to capture a nearly identical result during each single impact. Deviations are restricted to an absolute minimum. The scattering of the results for 10 impacts amounted to 3 µm. Relate this to the thickness of human hair of 50 µm!”

c)    Result: The average of maximum settlement determined by the three distance sensors is compared with the maximum settlement measured by the TERRATEST® sensor. The calibration is accepted only, if the deviation within all of the three ranges is sufficiently low (in the µ zone). Results of the TERRATEST® sensor and values issuing from the three distance sensors are mutually converted by means of a calibrating factor. After completion, reliable measurement on construction sites is ensured. All TERRATEST® instruments feature an internal counter, informing the user in time, before the end of cycle is reached. Calibration is then carried out at the factory service; a simple phone call is enough. The measure in all will take approximately one week.

“This way, the widespread acceptance of dynamical load plate test for light weight deflectometers can be expected for Medium Weight models as well. The new calibration directive is a great progress, as it enlarges the practical applicability of the measuring principle also to layers with an extremely high rigidity”, declares Frank G. Schulz. “The alternative of a static load plate test with a counter weight, e.g. a loaded truck, consumes too much time and cost, and is often nearly impossible to perform, especially in pipeline construction or places difficult to reach. For this reason, the demand for our instruments is continuously increasing, also originating from public institutions like communities or electricity, gas and water suppliers. We are sure that this development in future will hold on.”