SOIL TYPE

Soil types generally include topsoil, clay, silt, sand and gravel. The type of soil to be remedied will determine the preparation technique necessary to prepare the soil prior to application to the machine. Sand, silt and coarse soil can utilize a screen type device to separate large rocks and other debris from the material. The most effective screens consist of (a) a ‘grizzly bar’ pre-separator for removal of larger material and (b) a ‘shaker head’ screen which uses an oscillating vibratory stroke to grate and sift the material to a predetermined size. (Size classification is determined by the coarseness of the screen used on the shaker head assembly. In general, material should be classified to a size no greater than 1½ inches, and preferably ¾ inch. It is NOT advisable however to classify material to an extremely fine state, where the material is reduced to a powder.) Some screeners may include a belt feeder, which will move the ‘pre-classified’ material up to the feed system of the thermal machine at an adjustable rate.

Clays and topsoils require a different approach to classification. Wet clay materials will not allow the use of a shaker head screen due to its tendency to remain in a ‘mass’ form. These clay-type materials will typically lay on top of the screen or fill the cavities of the screen so that material cannot pass through. A different type of device called a ‘shredder’ is necessary in dealing with this material. There are several types of shredders available, although the type found to be the most effective consists of a hopper with a belt drive that feeds a second ‘cutter’ belt which tears up the material and throws it outwards from the shredder. It is very important that this material be fed into the machine at a uniform rate of speed and volume while still in this shredded condition. If allowed to stand, it will tend to resolidify into it s previous state. Large clumps of clay should NOT be fed into a thermal system. They will generally remain in a clump form inside the drum without allowing the internal material to remediate.