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crack meters
The JMDL-32XXAT Smart Single-Point Bedrock Displacement Meter extends Kingmach crack meters into embedded rock and foundation monitoring. It is designed for tunnel rock mass deformation, dam bedrock deformation, slope sliding, and foundation pit face movement. The assembly includes a flange, electrical displacement sensor, tie rod, anchor head, and PVC pipe, forming a practical embedded instrument for single-depth displacement. Listed models include 50 mm, 100 mm, and 200 mm ranges, each with 0.01 mm resolution. Product information lists displacement accuracy of 0.5%FS, temperature accuracy of plus or minus 0.5 degrees Celsius, and an operating temperature range from -30 degrees Celsius to +80 degrees Celsius. This product is useful where the monitoring point needs to be anchored into a known layer rather than mounted only on a visible surface. In tunnels, dams, slopes, and deep excavations, that embedded layout helps link surface observations with movement inside the rock or foundation body. During project setup, the measuring point should be matched with the expected travel direction, available mounting space, cable route, and required acquisition interval. This prevents a short-range joint instrument from being used on a long-travel point, or an exposed sensor from being placed where an embedded anchor is needed. It also helps the monitoring team set a baseline that can be defended during acceptance and later maintenance review.
Application of crack meters
In tunnel engineering, crack meters help monitor surrounding rock deformation, lining movement, tunnel portal displacement, clearance change, and crack opening after excavation. Tunnel sites often have wet air, dust, restricted access, and changing support stages, so the instrument must hold a stable baseline through construction disturbance. Kingmach JMDL-31XXAT multipoint displacement meters use drilling and grouting with anchor heads at different depths, allowing engineers to compare the movement of separate rock layers. The series lists 50 mm, 100 mm, and 200 mm ranges with 0.01 mm resolution. JMDL-32XXAT single-point bedrock meters can be embedded with a flange, tie rod, anchor head, and PVC pipe assembly. JMLS-22XXADT wire rope sensors can watch longer displacement paths or tunnel wall clearances. These readings help site teams decide whether deformation is responding to excavation sequence, groundwater, lining timing, nearby blasting, or long-term ground pressure. During operation, the monitoring team should keep the baseline, temperature, inspection notes, and nearby sensor behavior in the same review file. This makes it easier to tell whether a movement trend comes from normal service, a repair event, changing load, water influence, or developing structural risk. Clear records also help owners decide when a field inspection is needed instead of waiting for visible damage.
The future of crack meters
Longer service life will be a major future requirement for crack meters. Infrastructure owners want monitoring systems that remain useful beyond the construction phase and into operation, inspection, repair, and renewal. Kingmach lists 30-year designed service life on selected products such as the JMDL-24XXAT flexible displacement meter and JMDL-49XXAT formwork displacement meter, while models such as JMCW-21XXADT use non-contact sensing to avoid mechanical wear. Future specifications will likely ask more directly about waterproof rating, connector durability, cable route protection, sensor replacement access, and data continuity after maintenance. For dams, bridges, railways, slopes, and tunnels, a displacement record over several years is often more useful than a short burst of high-frequency data. This long view supports asset management and helps distinguish slow structural change from normal seasonal movement. The next improvement will be planned service records: expected inspection intervals, spare part notes, replacement dates, and clear links between old and new baselines after a sensor is changed.
Care & Maintenance of crack meters
For flexible geogrid crack meters, installation care is more important than later access because the product may be buried inside reinforced soil. Kingmach JMDL-24XXAT uses a bendable measuring rod, 30 mm and 50 mm ranges, 0.01 mm sensitivity, 0.5%FS accuracy, 20-point curve fitting, and a designed service life up to 30 years. Both ends of the geogrid should be clamped with the flexible sensor sections using mounting brackets so deformation transfers reliably. Avoid sharp bending, cable tension, bracket slippage, and damage during filling or compaction. Record the geogrid layer, chainage, depth, sensor direction, zero value, and backfill date. During operation, compare displacement with settlement and rainfall records. If the trend changes after heavy rain, traffic loading, or nearby excavation, inspect accessible cabinets and cables before deciding whether the buried geogrid movement itself has changed. Keep the installation photo, point number, zero value, and expected movement direction with the commissioning record for later review. If a reading changes after maintenance work, inspect the base, anchor, cable, and cabinet before assuming the structure itself has moved.
Kingmach crack meters
crack meters are often the quiet part of a monitoring system, but they decide whether deformation is understood as a trend or discovered as damage. Kingmach displacement products can be placed at expansion joints, cracks, foundation pits, slope faces, tunnel surrounding rock, dam bedrock, railway subgrades, high-formwork supports, and equipment stroke positions. Many models support digital transmission, anti-interference performance, waterproof sealing, and connection to automatic acquisition systems. The JMDL-21XXAT general-purpose meter records relative displacement and expansion joint movement with 50 mm or 100 mm ranges and 0.01 mm resolution. The JMDL-31XXAT multipoint meter can be installed by drilling and grouting, with anchor heads at different depths. When readings are reviewed with settlement, tilt, rainfall, pore pressure, or construction logs, engineers can see whether movement is seasonal, load-related, excavation-driven, or moving toward a control limit. The point should be named on the drawing, linked with its cable route, and checked against the expected movement direction before the first automatic reading is accepted. For daily review, the reading should be compared with nearby points, recent weather, site operations, and any loading event that could explain the movement.
FAQ
Q: Which crack meters are used for rock layers or bedrock?
A: JMDL-31XXAT multipoint meters are used for different surrounding rock layers, while JMDL-32XXAT single-point bedrock meters are used for tunnel rock mass, dam bedrock, slope, or foundation pit movement.
Q: How many points can the multipoint meter support?
A: The multipoint installation kit supports three to five monitoring points, with anchor heads fixed at different depths by drilling and grouting.
Q: What ranges are listed for these models?
A: Both JMDL-31XXAT and JMDL-32XXAT list 50 mm, 100 mm, and 200 mm models with 0.01 mm resolution.
Q: Why monitor several depths?
A: Different layers may move differently. Separating shallow and deep movement helps engineers judge whether the problem is surface creep, deeper rock slip, or overall mass movement.
Q: What records should be kept?
A: Keep drilling depth, anchor location, grouting date, channel name, zero value, cable route, and first stable reading.
Reviews
Michael Anderson
The strain gauges and load cells are extremely accurate and stable. They performed very well in our bridge monitoring project. Highly recommended!
James Thompson
The tiltmeters and accelerometers are very sensitive and provide precise data. Perfect for our structural health monitoring system.
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