ON THE QUESTION OF FROZEN SOIL DESTRUCTION BY A COMBINED METHOD

B. I. Yuzhakov, I. G. Basov

(Presented by the Department of Mining Machines)

One of the principal methods of excavating frozen soil is cutting the ground with slotting—bar-type and disk-milling—machines. The productivity of slotting machines depends to a considerable degree both on their technical parameters and on the scheme used to prepare the frozen soil for excavation. In addition, the productivity of slotting machines is limited by the technical capabilities of the excavating machine (a single-bucket excavator, crane, bulldozer). In most cases, excavation of frozen soil after slots have been cut by bar or disk-milling installations is carried out by single-bucket excavators with bucket capacities of \(0.5\)—\(0.65\ \text{m}^3\). Moreover, when the soil is frozen to only a slight depth (up to \(0.8\)—\(1.0\ \text{m}\)), its excavation is carried out without additional destruction of the blocks of frozen soil between parallel slots. But in most cases the operation of a single-bucket excavator is possible only when mutually perpendicular slots are cut, outlining prismatic blocks of definite dimensions, or when the blocks between parallel slots are destroyed by means of plow-type installations or wedge and ball hammers. All this substantially increases the cost of earthwork operations in winter.

An analysis of the factors affecting the productivity of earth-cutting machines shows that the latter can be substantially increased by reducing the number of square meters of slot area per \(1\ \text{m}^3\) of prepared frozen soil (the value \(S_{\text{sh}}\)). To reduce the value of \(S_{\text{sh}}\) without impairing the quality of preparing frozen soil for excavation (the lumpiness of the soil), it is necessary to change not only the preparation technology but also the very method of destroying frozen soil.

This can be accomplished by using additional devices that ensure destruction of the inter-slot block simultaneously with the cutting of parallel slots. In this case there is no need to pass transverse slots, and the value \(S_{\text{sh}}\) will depend only on the distance between the longitudinal slots \(l_1\) and the width \(L_{\text{pop}}\) of the area being worked:

\[ S_{\text{sh}}=\frac{1}{l_1}+\frac{1}{L_{\text{pop}}},\ \frac{\text{m}^2}{\text{m}^3}. \]

For destroying the inter-slot block in this case, the most suitable method is destruction by tearing-off, which has found its ...

application in mining. The prospects of this method are due to the low energy consumption of the destruction process, amounting to \(0.02\text{–}0.04\ \mathrm{kW\cdot h/m^3}\) in coal destruction, which is 50–100 times less than the energy consumption of destruction by existing working tools of mining machines. This is explained by the fact that destruction by the breakaway method is carried out mainly through tensile deformations, while the temporary tensile strength of rocks and frozen soils is 4–60 times lower than their compressive strength.

In mining, the borehole and slot methods of breakaway have found application.

In the first case, breakaway of the rock is accomplished with the aid of various devices placed in a borehole, toward the exposed surface.

In the slot method of breakaway, destruction is carried out with the aid of devices mounted in the working member, which cuts a slot or slots. Attempts to implement this method of destruction were undertaken by engineer A. K. Serdyuk as early as 1933. However, his working members for coal combines did not find practical application because of the complication of the machine. In addition, in order to chip off the coal layer it was necessary to stop the combine, which reduced its productivity.

In addition to hydraulic devices for coal destruction by the breakaway method, attempts were made to use mechanical jaws, pressure cams, wedging and breaking wedges.

A significant contribution to the study of the method of destroying coals and rocks by breakaway in recent years has been made by the staff of the Department of Mining Machines of the Karaganda Polytechnic Institute. Experimental relationships have been established for the breakaway force of coals and rocks as a function of the width of the target, the breakaway step, and the destruction scheme; new actuating members have been created (pos. 3, Fig. 1). Studies show the possibility of significantly reducing the specific energy consumption of rock destruction by the combined method in comparison with generally accepted methods.

Work on creating devices for destroying inter-slot targets of rocky soils was carried out by I. M. Iskenderov, and of frozen soils—at the Tomsk Polytechnic Institute. The experiments showed that such a method of destruction (pos. 4, Fig. 1) can be used for an inter-slot target of soil of seasonal freezing (up to \(2\ m\)) with a thickness of up to \(1\ m\). In this case, productivity increases and the cost of loosening decreases by more than a factor of 2.

Thus, the application of the new method of destroying frozen soil will make it possible to considerably expand the field of application of slotting machines.

An analysis of the operating conditions of breakaway devices for bar machines as applied to the excavation of a frozen soil layer shows that the principal type of breakaway is partially blocked breakaway of the soil, since after the very first destruction a third exposed surface appears, characteristic of these breakaway conditions (pos. 4, Fig. 1). The semi-blocked and semi-free breakaway encountered in the combined method of soil destruction are only special cases of this type of destruction (pos. 4, Fig. 1).

The studies on breakaway currently available do not provide the necessary recommendations for substantiated design of devices that destroy frozen soil by breakaway. It is therefore necessary to conduct studies whose aim is to determine rational breakaway parameters not only from the point of view of destroying frozen soil, but also from the point of view of the manufacturability of preparing it for excavation. These studies include determining the rational

Fig. 1

the pitch of frozen-soil breakaway, the breakaway arm, the depth at which the breakaway device is set in the slot, and, finally, the thickness of the rib between slots, as functions of the strength of the frozen soil layer, the depth of freezing, and the depth of the slot being cut.

In addition, the investigations include studying the process of rib destruction as a function of the breakaway conditions arising under the selected technology for excavating the frozen soil layer, and as a function of the nature and point of application of the destructive load.

Studies of the energy relationships in the process of destroying frozen soil by breakaway, and the identification of analytical relationships for this process, will make it possible to provide the necessary recommendations for the design and manufacture of means for destroying frozen soil by the combined method—cutting with simultaneous breakaway of the rib between slots.