mine support for a long stoping excavation (longwall), whose installation, load relief, and movement behind the advancing face are accomplished by mechanical means, without dismantling the support. Powered support is mainly used in coal mines (about 800 units were in operation in the USSR in 1973); together with a cutter-loader, face conveyor, and supports for connecting the longwall with drifts, powered support forms stoping complexes or units, which provide mechanization of all the basic mining operations at the working face (stope). The modern types of powered support in use today were first designed in the mid-1950’s.
Powered support is classified according to functions of interaction with surrounding rock (load-bearing, barrier, load bearing-barrier, and barrier-load-bearing types) and according to the design arrangement for interaction of the sections (sectional, set, and unitized types).
Load-bearing support is designed to prevent collapse of the roof within the working space of the excavation (stoping) area. The support sections consist of a roof, two to six hydraulic bearing props, a base, and one or two hydraulic jacks for advancing. The zone at the face of the longwall is supported by the section roofing, which acts as a cantilever. The roofing is continuous along its length or consists of two or more hinged links, thus providing better contact with the uneven surface of the hanging wall. Load-bearing powered support is used mainly in seams up to 2 m thick (and sometimes up to 3.5 m thick).
Barrier support is subjected only to the load transmitted by caved-in rock and protect the working space by means of enclosing overhead covers (roofs). Such support is not widely used.
Barrier-load-bearing and load-bearing-barrier supports have elements that support the hanging wall and protect the working space from collapsing rock. Support of the load-bearing-barrier type supports the hanging wall over a greater width of working space than does support of the barrier-load-bearing type; the section has two to three hydraulic props, which makes possible its use in longwalls with a strong main roof but a weak nether roof. The barrier part is in the form of a strong sloping covering. Such support is used mainly in seams 1.6 to 2.5 m thick; as of 1974, designs were being developed for seams up to 3.5 m thick. The sections of the barrier-load-bearing type of support have a strong, sloping enclosing covering and a relatively short baffle plate (deflector), which supports the hanging wall over a small width at the face by means of a single prop. This type of support is used in seams 2.0-3.5 m thick in the case of readily collapsible main rock and weak rock in the nether roof.
Powered support whose sections do not have continuous kinematic linkages with one another and with other longwall equipment is called sectional support. Sectional support is not widely used because of the great time and labor involved in moving and setting it.
Set-type support consists of sets of two or more kinematieally interconnected sections. The support sets are not interconnected.
The sections of unitized support are continuously kinematieally linked to the base element of the stoping complex (the base of the conveyor), the guide frame of the stoping machine, or a special base element. All or part of the sections of unitized support are equipped with hydraulic jacks for advancing. The existence of a permanent (continuous) connection with the base and, as a rule, the directed movement are favorable prerequisites for remote and automatic control of the entire working face (stoping) equipment complex. Unitized support is regarded as the most promising type. The hydraulic drive and hydraulic system of powered support are controlled from pushbutton stations installed in the longwall every 5–8 m or from a central control panel located in the drift.
In the USSR, M-87 and M-97 load-bearing support, MK and M-81 load-bearing-barrier support, OKP and OMKT-M barrier-load-bearing support, and KTU barrier support are used for gently sloping seams. Powered support for inclined seams (M-87DN and KM-127) and steep seams (AShch, KGD-2, ANShch, and AKD) is being introduced. Support of the load-bearing type exists in the greatest number of versions.
In other countries, development of powered support is directed mainly toward the design and improvement of support of the load-bearing type, both in the unitized arrangement and the set arrangement.
Improvements are being made in the development of powered support to reduce its metal content and cost, increase the reliability of all components, optimize parameters, and create designs that, together with cutting and loading equipment, provide full automation of the processes of excavation and transportation of coal and of the support of mine workings, as well as control of rock pressure at the working face and at its juncture with the development workings.
REFERENCESpravochnik po krepleniiu gornykh vyrabotok. Moscow, 1972.
V. V. ZHUKOV