ENG – Pavement; LWD

Avaleht Foorumid ENG – Introduction ENG – Pavement; LWD


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    Pavement. This may be an area, where every country has its own rules.
    In Europe, we have ESAL – but seems that concept has very little common – only dual wheel and maybe 10 tons axle. Everyone has different tire pressure – thus the ESAL impact is different in every sense. But also, allowed load of 11,5 tons is more or less common.
    OK, we have some EN-standards, but seems that concerning asphalt, bitum quality – it does not help, as the chemists in oil sector have developed the standard for oil industry, not for road engineers.
    EN standards clarify how to prepare material specification. But as example, for pavement calculation we need some E-modules – and for the same material, different values are used in different countries. Someone is basing these on lab tests, some others state these are experience-based from times, we were unable to measure anything.
    But my main concern still is – whatever way we calculate the bearing capacity of road construction layers, these have to be measurable. And we expect that with LWD. Lightweight Deflectometer.

    AND – one more aspect – E-modulus depends on stress under which the modulus is measured. Therefore, IF or WHEN we measure bearing capacity, we have to use stress level, which will be normal for the current top layer of construction, while everything is completed. This is only way, which may enable comparison of calculated values with measured. AND also, only way to measure E-modules of materials for the calculations.

    There is some progress in UK, some in Italy. Probably also Denmark. Germany is sticking plate load test (fixed stress level) and maybe GDP (low stress level, suitable only for subground and sand layers (under crushed stone base layers).

    We may argue, but for research AND quality control, danish group suits better. Started in 2017 and now we use two Dynatest LWD 3032 devices. In Estonia there is at least one more, in Latvia-Lithuania together also three devices. Not much, comparing with over 300 Inspector devices in Estonia.

    Using LWD in different tasks.
    1) simple Quality Control – while the conversion between PLT (plate load test Ev2) and LWD is not linear and depends on materials, in Tallinn standard pavements we tried to compose the relevant table, integrating UK idea of moving average & minimal value into package. Also, as simplification, transformation between different stress levels within different LWD-s (all three generations) is required. We may argue, where the bearing capacity is the main key, where the compaction factor (how much E-value has raised or deflection reduced within the drop serie).
    And remark – if anybody else has similar finding – that, if geosynthetics are used, within the depth of impact of LWD (but also, PLT and FWD), result (bearing capacity) is lower than without geosynthetics, during construction process. We hope, that during traffic loading, the situation improves at least to equal with the level of w/o geosynthetics (this is valid for geotextiles AND geogrids both).
    2) cold stabilisation QC – based on Italian experience (thanks, Alessandro Marradi), to test within 4 hr after compaction, and within 24 hr – if the target bearing capacity values are achieved, next layers (asphalt) without laboratory tests of stabilized material required. Speeds up the process and also easier maintenance on drying/hardening period of stabilized layer.
    3) QC of pavement restoration after different pipe or cable works, we found that often in the middle of work area, new/restored pavement bearing capacity is okey (deflection equal or less than in untouched area of old pavement), but in transition area even twice lower. That means, instead of ca 20 years of pavement life, only 1-2 years. Reason is also simple – digging as small trench as possible, not extending it during backfill, there is no way to recompact the sides of trench during backfill. And solution is simple – during backfill, at every layer, the sides should be widened to compact together old and new material.

    the list has to grow as we are convinced, that technology is good and we need to use all it can.

    • This topic was modified 3 years, 7 months tagasi by Ain.
    • This topic was modified 3 years, 7 months tagasi by Ain.
    • This topic was modified 3 years, 7 months tagasi by Ain.
    • This topic was modified 3 years, 7 months tagasi by Ain.
    • This topic was modified 3 years, 7 months tagasi by Ain.
    Erwin Kohler

    Hello Ain. Another task that we are exploring with LWD is something for thin concrete pavements. We did a brief experiment to see if using LWDs with two geophones could determine Load Transfer Efficiency (LTE) across the joints. The initial results looked promising. We plan to expand the experiment, comparing LTE obtained from traditional FWD and from LWD. We hope to have and answer soon and we will report to this forum.


    Great, Erwin – I have just the task in one airfield with concrete pavement – not thin unfortunately, where Dyna DK should do the FWD (actually, HWD, with PCN and so on). What is “thin” in your dialect?

    • This reply was modified 3 years, 7 months tagasi by Ain.

    Some ideas to improve Dynatest LWD
    – external connectors needed only for external sensors – load cell and central deflection cell could be connected directly inside the electronic box, or from behind the box
    – connector type should be mechanically more reliable
    – on top of main block there is message, that do not use w/o foam buffers – better to state here, which buffers where – and, especially for research purposes, the relation is NOT with selected weights but applied loads (kN)
    – bluetooth connector stability still to be improved (somehow it works better than earlier, but would like to have easier reset functionality without need to restart LWD application
    – maybe, the transport wheels can be directly installed to main unit – this has already been done in some competitors devices, assembling the carriage is rather slow process
    – transport box to redesign, so the modified LWD (3032) fits into box w/o disconnecting the connectors
    I suppose, if client has several devices, it is possible to calibrate same set of external sensors to several LWD devices
    Question of calibration – it basically is check in controlled conditions, on fixed surface – is it possible to do the check by the client, sending result to office and if everything is fine, no need to transportation of device, certificate may be released electronically. However, there is need to assess conditions of buffers, when new buffers have to be ordered. On any mechanical or electronical problems, the maintenance is anyways required

    • This reply was modified 3 years, 6 months tagasi by Ain.
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