New Equipment Restores Open-cast Coal Sites
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FVE1s1 for men with long experience iof public-works contracting, the
demand made in connection with open-cast coal mining, that the land should be restored to its original state, involved a new technique. The task of re-forming the ground, achieving good contours and drainage grades, was quickly mastered, but to restore the land to its original condition has been a greater problem. The elimination of certain difficulties in this work is the object of a giant resoiling unit that has recently begun operations in Lancashire.
To the earthworks specialist, restoration by tractor is sound, because it tends to prevent subsidence, but the constant traversing of the ground by heavy machines is liable to form a " pan " in the subsoil which retains the water near the surface and involves considerable difficulties for the farmer. In certain areas the creation of is " slacker backfill was considered, but this introduces a new factor, as it obviously implies a risk of uneven settlement, with a probability of regrading being needed in two or three years' time
To improve conditions, separate storage and 'replacement of subsoil was introduced about two years ago, but this did not eliminate the troubles resulting from consolidation. To find a remedy for the problems caused by land "lying wet" after restoration, special study of the matter was made by Mr. S. Salt and Mr. T Green, of Wigan.
A plan was evolved for attaching a deep scarifier to the rear of a tractor, coupling a serarler direct and trailing a grader joist behind, so that no heavy weight should travel over the land after treatment by the triple unit had taken place. With the subsoil thus broken up by the scarifier and the top soil relaid, much of the natural drainage is restored.
To provide a powerful tractive unit a new Sherman Tank has been stripped of its armour and rebuilt to such an extent that the only original sections remaining are the tracks, driving shaft and power unit. To ensure maximum adhesion, the engines have been remounted high at the front, with the drive operating from the rear instead of from the front.
This machine is powered by two G.M. oil engines of 44)0 b.h.p. and, at 2,000 r.p.m. engine speed, has a drawbar pull of approximately 92,000 lb. in first gear.
As already indicated, the scarifier is fitted directly to the tractor and this unit carries four tines, set 2 ft. 6 ins. apart, which cut into the consolidated earth to an even depth of 2 ft, 3 ins. To make it a practical proposition to break up the subsoil in this manner, to spread the top soil over it, and to level out, all in one operation, it was essential to incorporate a scraper of exceptional size, as otherwise much of the advantage of the outfit would be defeated by the constant coming and going to bring small quantities of top soil to be rein Id as they were needed.
To achieye this object, Mr. Green acquired an American 30-ton scraper, of which only a few are available in this country, thus making what is believed to be the largest soilspreading unit operating anywhere in the world.
Every filling of the scraper bucket enables a 30-yd. run to be made when scarifying, spreading top soil to a depth of 9 ins, and grading; the outfit travel-. 14-15 m.p.h. while performing the three opera tions. An attachment for scrub clearance is being made.