ZORN Mini | Light Weight Deflectometer for narrow trenches

Too narrow for a Light Weight Deflectometer? Not for the ZORN Mini!

A narrow solution with proven quality. ZORN Light Weight Deflectometers are trusted by leading construction companies and supervisory authorities alike. For many years, they have also been used in broadband expansion projects. 

The reason is simple: the measurement is completed in just two minutes, no additional tools are required, and the results are reliable and safe.

The ZORN MINI allows you to cost-effectively test the compaction of backfill material even in confined and narrow trenches. This helps you prevent damage caused by later settlement - damage for which you, as the contractor, may be held liable by the client. Avoid these risks. Test quickly and safely. Even beginners can start immediately. The ZORN Mini works on the same principle as its “big brother LWD”. See how easy it is in our user videos.

Unique: Thanks to its specially developed oval load plate, the ZORN Mini reliably performs measurements directly inside fiber optic trenches. 

And with the unique bayonet locking system, you can effortlessly lift out the entire device including the load plate - an advantage that makes a decisive difference in everyday construction work.

Fast. Precise. Efficient.

A LWD for narrow trenches

A small device for a large task. Cable trenches for broadband fibre optic cable are often narrower and shallower than those for conventional supply cables. Nevertheless, the quality of the compaction must be correct during the filling of the trenches. Conventional falling weight deflectometers are too large for a test and therefore unsuitable.

With the ZORN MINI a Lightweight Deflectometer specially developed for this application is now available to construction companies and their contractors. Based on the proven test specification TP BF-StB, Part B 8.3, users can reliably test the compaction from a trench width of 120 mm using this device.

New challenges demand appropriate skills. The loading plate for the ZORN MINI has an oval shape and with a minimum width of 100 mm matches the geometry of a narrow fibre optic cable trench. The area of the plate is the same as that of a conventional Light Weight Deflectometer with a round loading plate of 150 mm diameter. The maximum normal stress under the loading plate of the ZORN MINI is 0.2 MN/m2.

Also while backfilling narrow fibre optic cable trenches, courses of material are generally applied in layers and compacted. The course thicknesses of 150–200 mm are less than during conventional road openings. The ZORN MINI is equipped with a 5 kg falling weight matched to these conditions. The impact force generated with this falling weight of 3.535 kN is optimal for testing these courses.

The most important information about the ZORN Mini is summarised in the flyer.

FAQs zum ZORN Mini

The ZORN Mini was developed specifically for compaction testing in narrow utility trenches and can be used in trenches as narrow as 120 mm. This makes the Light Weight Deflectometer particularly suitable for narrow fiber-optic trenches, fiber-optic network expansion, and trenching operations.

The oval load plate of the ZORN Mini is designed to fit the geometry of narrow trenches and has a minimum width of 110 mm. This allows the load plate to be positioned even in areas where conventional Light Weight Deflectometers with round load plates cannot be used due to their dimensions.

The test is conducted in accordance with Germany TP BF-StB, Part B 8.3.

Conventional Light Weight Deflectometers are primarily designed for sufficiently large test sites. In narrow cable trenches (such as those frequently encountered during fiber-optic installation and trenching) the standard load plate cannot be positioned due to its width.

The ZORN Mini was therefore developed specifically for this application. The oval load plate, with a minimum width of just 110 mm, fits into narrow fiber-optic cable trenches. At the same time, its base area corresponds to that of a conventional Light Weight Deflectometer with a round load plate 150 mm in diameter. The ZORN Mini operates with a 5-kg drop weight and an impact force of 3.535 kN. This makes it suitable for testing the comparatively thin, layer-by-layer compacted layers in narrow utility trenches.

Yes. The ZORN Mini was specifically developed for compaction testing in fiber-optic network deployment, in fiber-optic cable trenches, and in trenching operations.

When backfilling fiber-optic and broadband routes, the installed materials are typically compacted in layers. The layer thicknesses used in this process are often around 150 to 200 mm. The ZORN Mini, with its 5-kg drop weight and the resulting impact force of 3.535 kN, is precisely tailored to these operating conditions.

This Light Weight Deflectometer thus enables direct testing of compaction quality on the job site, especially when the cable trench is too narrow for a conventional LWD device.

Typical applications include:

  • Compaction verification in fiber-optic network expansion
  • Inspection of fiber-optic cable trenches
  • Self-inspection during trenching
  • Broadband and residential connection construction
  • Narrow urban routes
  • Other confined areas in utility and road construction 

The ZORN Mini is specifically designed for use in narrow utility trenches. When backfilling fiber-optic and broadband cable trenches, the materials are typically placed and compacted in layers with thicknesses of approximately 150 to 200 mm.

The load capacity of the ZORN Mini has been adjusted accordingly for this application. The device features a 5-kg drop weight that generates an impact force of 3.535 kN. The combination of a narrow oval load plate and reduced load capacity is tailored to the thinner layer thicknesses typical of fiber-optic network expansion projects.

As with any compaction test, the following applies: The assessment is determined not only by the layer thickness, but also by the type of soil or backfill material used, the required degree of compaction, and the respective contractual or technical specifications.

The ZORN Mini is used to determine the dynamic modulus of deformation (Evd) during the dynamic plate load test. The Evd value is expressed in MN/m² (or MPa) and provides a parameter for assessing the bearing capacity and compaction quality of the tested soil or the installed layer.

The ZORN Mini has a specified Evd measurement range of 15 to 70 MN/m². The measurement electronics automatically calculate the dynamic deformation modulus from the measured settlement. It is important to note that the Evd value determined with the ZORN Mini should not be equated across the board with a measurement value from a standard Light Weight Deflectometer. The ZORN Mini is designed for the specific geometric and structural conditions of narrow utility trenches. The specific evaluation of the Evd value is carried out in accordance with the respective technical specifications, tender documents, or contractual agreements. The underlying test method is the dynamic plate load test using the LWD in accordance with TP BF-StB Part B 8.3.

The ZORN Mini is ideal for any situation where a compaction test using a LWD must be performed in a very confined space. In addition to fiber-optic network expansion and the installation of fiber-optic broadband cables, the device is particularly well-suited for: 

  • Trenching and microtrenching
  • Narrow utility trenches
  • Service connections and broadband routes
  • Intra-municipal utility construction sites
  • Confined areas in road construction and civil engineering
  • On-site compaction self-inspections

The key advantage is the combination of a compact design and a narrow, oval load plate. This allows compaction tests to be performed even in locations where a conventional LWD cannot be used effectively due to the space required for setup.

The ZORN Mini was designed specifically for narrow utility trenches, not only in terms of its load plate but also for ease of handling on the job site.

A unique feature is the bayonet lock between the load plate and the loading mechanism. This allows the ZORN Mini to be inserted into the narrow trench as a single, complete unit and then lifted back out again.

With a conventional Light Weight Deflectometer, on the other hand, the load plate and the loading device are typically moved separately: First, the load plate is positioned in the trench, and then the loading device must be placed on top of it. This can be cumbersome, especially in narrow and deep trenches.

With the ZORN Mini, however, a single motion is all it takes to securely connect the loading device to the load plate via the bayonet lock. With a total weight of just 17 kg, the unit remains easy to handle and can be easily deployed and retrieved even in confined spaces. This means the ZORN Mini is consistently designed for practical use on construction sites: a narrow load plate, compact design, and handling that’s well-suited for narrow trenches.

In short: The ZORN Mini doesn’t need to be assembled in the trench - it goes in as a single unit and comes out as a single unit.

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