Where construction work of the type described is carried out, it is customary to excavate the ground to form a groove therein, to lay a pipe in the groove and thereafter to fill the groove back to the ground level with a re-filling material. In a case where the excavated ground material i. e., a soil and sand material, contains plenty of water or moisture, or pebbles, rocks, concrete pieces and so forth with a resultant deteriorated soil quality, the material cannot properly be utilized as a groove refilling material.
Where the excavated ground material is thus of very bad quality as described, it has hitherto been a customary requirement for a proper re-filling material of acceptable soil quality to be specifically called for and carried on a truck or the like transportation vehicle to re-fill the excavated groove therewith back to the ground level or, on the other hand, for the excavated ground material to be designated for disposal as waste earth and sand material. Not only has this rendered pipe laying construction work very costly but also has resulted in an undesirably extended period of time required for each such individual installation job.
There has also hitherto been known a machine for refining an earth and sand material of very deteriorated quality as described above into an improved soil quality. A typical example of such a machine has been disclosed, e. g., in Japanese Unexamined Utility Model Publication No. Sho 62-39827.
The typical soil refining machine is constructed of a hopper for an earth and sand material whose soil quality is to be improved, an earth and sand material transporting belt conveyer, a hopper for a soil refining material, a soil refining material transporting mechanism, a crushing and mixing device and so forth which are together mounted upon a frame. The machine is designed to operate in such a manner that earth and sand material of very bad quality stored in the earth and sand material hopper may be carried by the earth and sand material transporting belt conveyer into the crushing and mixing device whereas a soil refining material stored in the soil refining material hopper may be carried into the crushing and mixing device by the soil refining material transporting mechanism whereupon the earth and sand material and the soil refining material may be crushed, stirred and uniformly mixed together in the crushing and mixing device to give rise to earth and sand material of acceptable soil quality.
Where the soil quality is being thus upgraded from a very bad level to a highly satisfactory level with a soil refining machine as described above, it has been found to be critical to bring the CBR (i. e., an index that is used to evaluate the ability to support a load) of the soil quality refined earth and sand material to an appropriate level.
As with a soil refining machine as described above in which both the earth and sand material and the soil refining material are designed to be each fed invariably by a given amount, however, it has also been found that if the nature (including the kind, percentage of water content, etc.) of the earth and sand material varies, the proportion of the soil refining material to the earth and sand material for supply would remain constant, thus causing the CBR value of the soil quality refined earth and sand material to largely vary.
It has further been observed that the earth and sand material delivered into the crushing and mixing device may vary in amount, depending on the amount of the earth and sand material stored in the earth and sand material hopper. Then, too, the CBR value of the soil quality refined earth and sand material would vary, given a constant amount of supply of the soil refining material.
Accordingly, with the above mentioned problems in the prior art taken into account, it is an object of the present invention to provide control apparatus for a soil refining machine whereby a soil quality refined earth and sand material is always given an appropriate value of CBR.