Development of a Longwall Floor Sensor

This report describes the outcomes of this project which developed radar-based sensing for measuring the coal-to-stone seam interface depth on a longwall floor. The motivation was to advance the maturity of real-time geosensing to support the development of new geologically-responsive automated horizon control systems.

A major outcome for the project was the development, deployment and evaluation of a portable radar system on a fully operational longwall. It is believed this represented the most systematic ground penetrating radar evaluation performed on an Australian longwall. Encouraging results were obtained, with radar-based subsurface interface features regularly detected that were in good agreement with drill based ground truth validation. The evaluation also provided an important opportunity to gain greater awareness of practical factors that were relevant to operational performance.

The results achieved represent clear progress in the understanding and maturity of radar based sensing for longwall horizon control as well as roadway development.  

Seam based horizon control largely remains an open problem for the industry. The reason is that the longwall environment presents many practical challenges for the development of seam based sensing. Challenges include efficacy of candidate sensing, longwall accessibility issues, highly variable ground conditions, complex and uncertain geology, physical installation constraints, regulatory requirements, equipment survivability, and lack of existing validation methods.  In response to these challenges, this project focussed on three major development steps:

• Evaluate and validate radar technology in a Negligible Explosion Risk Zone with similar geology as likely found on an operating longwall face;
• Undertake engineering tasks to design and package the radar sensing system into a form that is suitable for an underground longwall evaluation; and
• Install the sensor on an operational longwall for a short term trial period and assess performance through systematic evaluation and ground truth validation.

In terms of system development, new radar hardware configurations were designed, built and evaluated which represented a major advance in the scope and maturity of radar technology applied to underground horizon sensing. Several different approaches were explored to address the issue of suitable radar housing, including a custom mimic flameproof enclosure, repurposing an existing flameproof enclosure, and a custom dielectric enclosure design. It was, however, the opportunity to deploy a custom radar package - housed in a Pelican case and operated under UPEE - that provided the breakthrough moment that enabled an on-face longwall radar evaluation.

In terms of validation, new ways to characterise the floor conditions and variability in subsurface strata layers needed to be developed to provide ground truth validation. This included a variety of inspection and measurement instruments, drilling and coring equipment, and chip monitoring methods for manual validation. Many of the methods developed to provide essential subsurface ground truth had not previously been attempted or deployed on an operational longwall face - these new methods thus represent practical steps forward in geological validation.