Tahmoor Coal Mine, a large underground coal mining operation, located in the Southern Highlands, required SOTO Consulting Engineers’ industry-specific expertise in order to register a new mine shaft for operation. Specifically, a structural design review was required on an outmoded overwind safety system, which resulted in the design, drafting and analysis of an advanced Fall Back Safety Catch assembly.

Initial Scope:

SOTO Consulting Engineers were approached to perform a design review of an outmoded overwind safety system, which is a critical piece of equipment in modern mines. Overwind and speed control devices are deployed to govern over-hoisting or speed of hoisting to better ensure safety of conveyance (usually a man & materials cage) that travels in a vertical shaft. Overwind, in mining engineering parlance, is the unintentional travel of such a conveyance beyond its normal operating limits.

A well-engineered overwind safety catch system includes devices mounted in the headframe, as well as on the conveyance itself, to prevent the conveyance from falling too far after it has been brought to rest subsequent to being overwound.


SOTO Consulting Engineers carried out detailed study of the site, which had an above-average shaft depth of 430m. The conveyance, which travelled through the 7m diameter shaft, had the capacity to carry 80 men. A fully-loaded conveyance, including ropes and sheaves, came to ~32 tonnes.

The SOTO team designed a precision system that could absorb the impact forces in situ on the head frame and cage resulting from an emergency arrest. The carefully engineered Fall Back Safety Catch assembly incorporated spring elements to reduce shock on structure and cage. This brought improved protection in the event of rope failure and the consequent fall of the cage down the shaft. When operational, the SOTO-designed system deployed these two main functions to prevent the cage from progressing beyond the upper limit of travel, with a similar system put in place for the counterweight. In the lead up to the system going live, the SOTO team subjected the materials and structure to rigorous testing, including Failure Effects Analysis (FEA), dynamic simulation, chemical analysis, tensile testing, and Charpy notch impact testing. Professional engineering thoroughness included third-party verification of design calculations and documentation.


The upgraded overwind catch systems was deployed on schedule and delivered fully on the project brief, providing the mine with an advanced system that will be used for many years to come. The systems were verified and operate in accordance with the requirements of AS3785.1-2005 – Underground Mining Shaft Equipment – Shaft Overwind Safety Catch System.

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