The Stoneblower

The pneumatic ballast injection machine was developed in the late 1970's as part of the mechanisation of track maintenance. Here is the text of a contemporary internal R&D article about the prototype which became known as the 'Stoneblower'. 


Ballast Injection technique for railway track maintenance

Track maintenance is a major item of expenditure by railways throughout the world representing in most cases the largest single maintenance cost incurred in any railway's operations.

As a result of a fundamental re-appraisal of current mechanised track maintenance methods a new technique has been identified which offers a number of advantages.

The technique, automated pneumatic ballast injection, has been tested experimentally including trials on the Eastern Region in the York area and has shown significant improvements compared with existing methods particularly so far as long term maintenance of the required track geometry is concerned.

The original experiments, carried out using simple, mainly manual methods, demonstrated the potential of the technique and resulted in a decision to build a pre-production prototype machine. This would provide a test bed on which to develop the automatic systems required and also to give practical demonstrations of the advantages of the technique to potential users and customers.

Current Methods

Railway track constructed using rail and sleepers supported on a bed of stone ballast suffers a progressive loss of geometrical quality due to traffic loadings. The change in geometry is primarily produced by the displacement of the stone ballast adjacent to the sleepers.

The machines currently used to restore track geometry are tampers and the principle of operation is to lift the track to the required level, insert tines into the ballast, which are then vibrated and squeezed together to bring the stones back under the sleeper.

Measurements show that whilst a good initial geometry is achieved the effect is relatively short lived. Quite often the track returns to its pre-tamping position within three months.

Pneumatic Ballast Injection

Work by the Soil Mechanics Section has shown that much more permanent improvements to track geometry can be achieved by injecting a volume of new ballast under the sleeper. The required amount of stone is forced by compressed air into a void created by raising the sleeper. Pilot experiments have shown that this process gives a much improved permanence to the track geometry corrections.

Pre-Production Machine

A pre-production prototype track maintenance machine has been designed and constructed to include all the functions that would be required for a mechanised ballast injection process. To save time an experimental unit has been constructed by extensively modifying an existing type of tamping machine.

The machine includes a track lifting unit to raise the track; a stone placing unit which allows the delivery tubes to be positioned and driven into the ballast; stone supply unit which feeds the required volume of stone to the delivery tubes.

The pre-production machine has been commissioned and a carefully planned series of development tests and trials is to be carried out during 1981.

The project is being carried out in conjunction with the BRB Chief Civil Engineer and a major presentation has been given at Derby to leading engineering companies to try to interest British industry in building machines for world railway markets.

Pre-production stoneblower

The pre-production Stoneblower 

Author's collection

Stoneblower The Stoneblower pictured at the south end of Stanton Tunnel

Author's collection

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