Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.) Technical Chapter 5: Support 5.1 Rigid support in drifts and stopes 5.2 Single mechanical prop 5.3 Hydraulic prop support 5.4 Rock bolts, rods, rock stabilizers

Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)

Technical Chapter 5: Support

5.1 Rigid support in drifts and stopes

Deep Mining General
Underground Mining Support

germ.:	Starrer Ausbau in Strecke und Abbau
span.:	entibacion rigida en galeria y explotacion, enmaderacion

TECHNICAL DATA:
Dimensions:	dependent upon roadway cross-section
Extent of Mechanization:	not mechanized
Alternative Forms:	possibly pneumatic chain saw to adjust roof bars and props, gas welding units for steel supports (for example from old railroad rails), cutting torch.
Operating Materials:
Type:	wood, possibly impregnation agents, e.g. common salt, iron or copper vitriol, mercury or zinc chloride.
Quantity:	large quantities
ECONOMIC DATA:
Investment Costs:	vary greatly depending on location of mining operation, cost of wood, cost of transportation, quality of wood, etc.
Related Costs:	possibly pneumatic chain saw (e.g. from Spitznas) for wooden supports, welding torch for steel supports.

CONDITIONS OF APPLICATION:

Operatig Expenditure:	low |————|————| high
Maintance Expenditure:	low |————|————| high
Replaces other Equipment:	all other types of support
Regional Distribution:	worlwide
Operating Experience:	very good |————|————| bad
Environmental Impact:	low |————|————| very high
	damage to vegetation due to use of wooden supports
Suitability for Local Production:	very good |————|————| bad
Lifespan:	very long |————|————| very short
	steel frame-sets are reusable

OPERATING PRINCIPLE:

Framing or timbering support consists of two props and one roof bar made of wood or iron. Support capabilities vary depending upon the type of connection between the props and the roof bar.

The German framing method is characterized by the interlocking or scarfing of bars and props. The frame-set can then resist both shear forces as well as vertical compressive loading. Depending on the calculated ratio between these two loads, scarfing can be designed more for shearing forces or more for vertical compressive loading. To increase the compressive strength of the props, the props are installed with the thicker end toward the roof.

The Polish timbering method is characterized by a loose laying of the roof bar on top of the two grooved props. This method cannot counter shearing forces (lateral compression).

The 'Silesian' method includes a "soldier sprag" brace wedged between the props underneath the roof bar to reinforce the props against lateral compressive forces.

Frame-set supports are additionally braced by wedging struts between the props of adjacent sets to increase their stability. The spacing between sets ranges from a few centimeters up to 1,5 m depending on the compressive load. In Inclined formations, frame supports are installed with the props perpendicular to the stratification (dip).

REMARKS:

For mine support, a timber with a long fiber structure is always employed, such as spruce, fir, or other conifer wood, or eucalyptus. Timbers of these wood types shatter slowly when their loading capacity is exceeded and thus warn the miners through a definite creaking. Short-fibered timbers break without any prior, slowly-developing visible or audible indications. A dense, resinous, slow-growing wood type is always preferable for mine support purposes. For mining activities of longer duration, the timber should be cultivated by the mine operators themselves near the mine site.

Timber employed in moist or wet mines, especially for shaft construction in exhaust ventilation shafts or drifts in water-bearing strata, should be previously treated by a preservative. Timbers are impregnated by dipping them into special solutions, such as Roman-salt, copper sulphate, etc., either with or without pressure.

Timber support normally is not reuseable. The only exception is simple prop timbering for stoping which is sometimes recovered and the wood then reused for shorter props, head boards, breast timbers or wooden cribbing. In situations requiring excessive support, such as mining in incompetent rock, the cost off timbering becomes a significant factor in the economic analysis of the operation. Here the higher investment costs for friction prop support can result in a substantial savings In operation costs, since these support elements can be reused.

Timbering is the simplest roof support method in incompetent rock (e.g. in faulted zones) and contributes greatly to increasing mine safety. It is, however, disadvantageous for artificial mine ventilation in that it increases air resistance.

In addition to purely wooden supports, there are also systems which employ mixtures of wood and steel, as well as purely steel supports or arches and - also widely distributed - yielding arches made from steel channel sections.

An alternative method for supporting drifts is the construction of non-cemented or cemented brick arches. These are used to support longitudinal vault-like tunnels, requiring either expensive abutments on both sides (built into deep grooves in the floor or constructed as retaining walls) or as adjacent arches with span-widths of several meters which run along both sides of the vault parallel to its longitudinal axis. Bricked arch support is extremly expensive and is suitable only where galleries must remain open for longer durations. In areas of stoping activities, support is provided by individual props (see 5.2).

SUITABILITY FOR SMALL-SCALE MINING:

As an auxiliary support in stopes and drifts, timbering is a very sturdy support method which is quick and simple to install. The local availability of timber for the supports has a major effect on the costs. In areas of poor vegetation, timbering should not be employed In order to avoid destruction of forests.

Fig.: polish and Swedish timber sets. Source: Treptow.

Fig.: Timbering with individual props; left: a) simple prop, b) prop with head board and foot block; right: prop, wedged to counter lateral compression. Source: Treptow

Fig.: Joint between prop and roof bar of a Polish frame-set (left) and scarf joint between the prop and roof bar of a German frame-set (right). Source: Treptow

Fig.: Different types of simple timbering for various deposit and strata conditions. Source: Treprow

German frame-set timbering with breast timbers, typical roof lagging and latticed lagging of the stopes. Fig.: Laggin in German timbering support in a drift. Source: Treptow

5.2 Single mechanical prop

Deep Mining, General (Coal)
Underground Mining Support

germ.:	Einzelstempelausbau/mechanisch
span.:	estemple individual mecanico

TECHNICAL DATA:
Dimensions:	from 0,63 - 3,15 m
Weight:	approx. 10 - 50 kg
Extent of Mechanization:	not mechanized
Form of Driving Energy:	manual
Mode of Operation:	intermittent
ECONOMIC DATA:
Investment Costs:	dependent on material
Operating Costs:	low
Related Costs:	none, requires only hammers for installation; bars of wood or steel rails.

CONDITIONS OF APPLICATION:

Operating Expenditure:	low |————|————| high
Maintenance Expenditure:	low |————|————| high
Personnel Requirements:	low
Location Requirements:	suitable for areas of low timber availability
Replaces other Equipment:	wooden timbering, etc.
Operating Experience:	very good |————|————| bad
Environmental Impact:	low |————|————| very high
Suitability for Local Production:	very good |————|————| bad
Under What Conditions:	meetal workshop
Lifespan:	very long |————|————| very short

Bibliography, Source: Bansen, Fritzsche, Woodruff

OPERATING PRINCIPLE:

A single mechanical prop consists of encased prop sections which are mechanically telescoped outward for wedging the prop between the floor and the roof or roof bar. Rigid props are differentiated from yielding props according to the operating principle: rigid props, for example threaded and nonius-props, can only react to increased compressive loads when a wooden bar permits deformation, otherwise they collapse when the maximum load is exceeded. Yielding props, on the other hand, telescope together when the maximum load is exceeded. This can be achieved either by friction systems (friction prop) or by inserting compressible elements (e.g. peat prop).

REMARKS:

Flexible due to unlimited reapplication possibilities.

Different types:	- nonius-prop / temporary prop
	- friction prop
	- threaded prop / temporary prop

can possibly be made out of scrap, e.g. railroad rails.

A common problem is that single mechanical props can only be installed with a low setting load. Various mechanical setting devices make the setting process easier.

The less the props are extended, the better they can withstand loading without bending and will therefore last longer.

Problems arise in employing mechanical prop supports in mines which are characterized by highly fluctuating deposit thicknesses, in that a precise assessment is required in advance to determine the appropriate long-term prop length. This greatly limits their suitability for small-scale mining.

SUITABILITY FOR SMALL-SCALE MINING:

A mechanical prop support is a suitable reuseable support method in mining of deposit zones where relatively low compressive loads are encountered. The low setting load is a major disadvantage of this technique, which -- particularly when a large quantity of props are employed -- is technically inferior to hydraulic prods.

Fig.: (above): Simple yielding props with compressible insets. (right, of peat; left. of wood). Source: Bansen

Fig.: Types of props with compressible elements made of wood. Source: Bansen

Fig.: Nonius-prop, in which the nonius serves to increase the setting load of the otherwise rigid prop. Source: Bansen

Fig.: Friction elements of modern friction props. Source: Woodruff

Fig.: Cross-section of a duplex prop, the top part with threads and the bootom part with friction element.Source: Reuther

Fig.: Profile (left) and section view (right) of a wedged prop. Source: Reuther

Fig.: Various types of German-made friction props. Source: Woodruff

5.3 Hydraulic prop support

Deep Mining General
Underground Mining Support

germ.:	Einzelstempelausbau/hydraulisch
span.:	estemple individual hidraulico
Producer:	Salzgitter, DeBeSa

TECHNICAL DATA:
Dimensions:	650 - 3600 mm collapsed, 675 - 5000 mm extended
Weight.	steel: 42 - 240 kg/prop + 4 - 18 kg extension pieces, light alloy: 25 - 65 kg
Extent of Mechanization:	fully-mechanized when serviced by a central pumping and distribution system for hydraulic fluid; not mechanized when serviced by a manual pumping system (internal or external)
Form of Driving Energy:	electric or pneumatic pump for producing hydraulic pressure
Throughput/Performance:	10 - 15 sec. setting time Operating Materials:
Type:	oil in water-emulsion pure water (DeBeSa)
Quantity:	2 - 4 % oil in H2O, pH 5 - 8, dH up to 15
ECONOMIC DATA:
Investment Costs:	approx. 1.2 - 4 times the cost of friction props (see 5.2)
Operating Costs:	approx. 50 % of the costs for traditional timbering
Related Costs:	hydraulic high-pressure pump (approx. 200 bar) with setting gun, roof bars.

CONDITIONS OF APPLICATION:

Operating Expenditure:	low |————|————| high
Maintenance Expenditure:	low |————|————| high
Mining Requirements:	hydraulic props are primarily employed in slightly or partly mechanized coal mines, but are also found in ore mines, industrial mineral mines, etc.Even in fully-mechanized mines hydraulic props are still in use for special support, for example in areas of geological faults, at the ends of the face, face-roadway intersections, etc. due to their flexibility and versatility.
Replaces other Equipment:	timbering, friction props
Regional Distribution:	worldwide, especially in coal mining
Operating Experience:	very |————|————| good bad
Environmental Impact:	low |————————| very high
	With conventional props, high pollution of mine water and drainage ways due to use of oil-in-water emulsion for hydraulic fluid. Glued - joint steel pipe props from DeBeSa use pure water as hydraulic fluid and thereby contribute to environmental protection.
Suitability for Local Production:	very good |————|————| bad
Under What Conditions:	Assembly and repair of the glueable DeBeSa hydraulic props is possible in comparably simple manufacturing workshops.
Lifespan:	very long |————|————| very short
	The long lifespan and suitability for reuse, in conjuction with the capability to replace defective components, ensure longlasting employment.

Bibliography, Source: Salzgitter Company information, DeBeSa Company information, Fritzsche,
Woodruff

OPERATING PRINCIPLE:

Hydraulic props consist of a sealed working cylinder with two valves, one for intake (setting valve) and the other for discharge (release valve, working valve) of hydraulic fluid. For increased stability the hydraulic props are equipped with a claw at the upper head-end and a base at the bottom. The function of the props is to stabilize incompetent roof or hanging wall. The positioned prop is telescopically extended by highly-pressurized hydraulic fluid injected by means of a setting gun and wedged into place with a specific setting load adjusted according to the respective compressive rock load. When the rated load is reached during installation or by subsequent strata movement, the working valve engages and opens the cylinder. This yielding prevents damage to the support from increasing compressive loading. The optimal support is attained when the props are installed in combination with articulated bars which distribute the forces over a wider hanging-wall or roof surface. During prop recovery, the release valve is opened with a key, allowing the hydraulic fluid to escape and the prop, equipped with a spring, to recede. The prop is then available for reuse.

AREAS OF APPLICATION:

Use of hydraulic single prop supports is only practical and economic where incompetent roof or hanging wall require a support method which can be adjusted to meet rapidly changing conditions. Hydraulic prop supports are appropriate for short-term installations involving frequent changes of location due to rapid face advance, or where high prop-setting loads are desireable. Such conditions arise in coal mining with roof caving or backfilling, in longwall mining, in room and pillar mining, as well as in ore mining by overhand stoping. In addition, single hydraulic props are suitable for support of all special mining activites such as support of fault-zones or roof-fall areas, machine rooms, and face-roadway intersections.

REMARKS:

The use of single hydraulic props in the situations listed above can contribute significantly to protecting valuable natural resources by substituting for traditional timbering methods. Replacing the normally non-reuseable support timbers (e.g. in Turkey, totalling more than 1 m³/20 t of useable output) with re-usable props can also result in decreased operating costs.

The limited working length of the hydraulic prop, like mechanical friction props, is disadvantageous in mines with fluctuating seam or vein thickness.
Due to the high setting load achievable with hydraulic props, capable of supporting areas 5 to 10 times larger than mechanical props, the prop density can be reduced.

The DeBeSa Company is striving to adapt their products (individual props and articulated bars) to meet the demands of small-scale mining in developing countries:

- assembly and repair can be performed by local labor. The costs for an assembly and repair shop amount to only around 10 % of the costs of commonly manufactured parts.

- the approx. 30 % net product arising from local production preserves the country's foreign exchange position.

- cost savings of more than 50 % can be realized compared to the widely-used wood timbering.

- the capital investment for a highly developed and complex support system is not required.

- the use of glueable Joints in this modular system permits the replacement of damaged parts, therefore increasing the lifespan of the remaining components.

- storage costs are reduced by around 70 % as inventory can be limited to only a few standardized parts.

Disadvantages of hydraulic props include high consequential or related costs for producing and distributing high-pressure fluids (pneumatic or electric high-pressure pump, liquid storage tank, high-pressure hoses, setting guns, etc.).

This disadvantage can be overcome by employing props which are set with manually-operated pumps. Such props were employed earlier in Germany, and are still used today in Anglo-Saxon countries. They function by using a hand pump to force the hydraulic fluid from the upper cylinder (storage cylinder) into the lower cylinder (working cylinder), analogous to a hydraulic automobile jack.

SUITABILITY FOR SMALL-SCALE MINING:

The type of prop system employed affects the consequential costs. Simple manually-operated props offer an alternative to timbering in small-scale mines. The investment for single hydraulic props with an external pump system can only be recovered when large quantities are employed to offset the higher costs for the necessary auxiliary installation devices.

Fig.: Telescoping, setting and drawing (recovery) of hydraulic individual props with manual pump (left, from top to bottom) and cross-section of a hydraulic prop. Source: Woodruff

Fig.: Sketch of a hydraulic prop, supplied externally with hydraulic fluid. Source: Manufacturer's information, Salzgitter

5.4 Rock bolts, rods, rock stabilizers

Deep Mining in Competent Rock
Underground Mining Support

germ.:	Felsanker
span.:	barras, pernos de anclaje, pernos pare hormigon
Producer:	Atlas Copco, Grauvogel, Lenoir et merrier, GHH, Becorit, Gebr. Windgassen, Ingersoll-Rand

TECHNICAL DATA:
Dimensions:	800 mm - 4,000 mm length, 16 - 42 mm for drilling hole 32 - 76 mm
Weight:	1 - 25 kg
Extent of Mechanization:	not/partly mechanized
Mode of Operation:	intermittent
Capacity/Throughput:	5 - 100 t pulling force
Technical Efficiency:	30 - 40 min/bolt inserting time in low mechanized mines, density of bolts up to 1 per m²
ECONOMICAL DATA:
Investment Cost:	approx. 20 DM/piece
Consequential Cost
through Coupling Effects:	jack-hammer with drill steel of same length as bolt, spanner or roof bolting drilling and setting machine

CONDITIONS DE APPLICATION:

Operating Expenditures:	low |————|————| high
Maintenance Experience:	low |————|————| high
Mining Requirements	bolts have to be preloaded whose intensity is difficult to assess manually. Pneumatic impact wrench or setting winch is therefore preferred.
Replaceable Equipment:	other support methods in solid rock excavations
Regional Distribution:	worldwide
Experience of Operators:	very good |————|————| bad
Environmental Impacts:	low |————|————| very high
	deecreasing demand for wood in mines
Suitability for Local Production:	rod anchor	very good |————|————| bad
Under what Conditions:	metal manufacture
Lifespan:	very long |————|————| very short

Bibliography, Source: Fritzsche, Company Info, Woodruff, Ruther

OPERATING PRINCIPLE:

Bolt support is being applied to fix rock strata which are slacking off due to a decreasing pressure of strata in the area of mining excavations at the stable rock mass. This is being done by inserting a bolt into a drilling hole that is then either wedged mechanically or along the whole length or sections cemented or pasted together with the adjoining rock. The anchor bolt transmits the tension to the screwed roof-bolt head.

AREAS OF APPLICATION:

To support mining excavations and roadways of underground mines. Bolt support can be an alternative to timbering which is what is commonly used in the developing countries.

In hard rock mining, bolts are used where larger excavations in stable rock are supposed to last long, e.g., storage bunkers, crushers, chambers, draw points.

Various types of bolts that are used can be classified as follows:

Mechanical bolts:	- slot-and-wedge bolt*
	- expansion anchor as expansion shell bolt*
	- expansion wedge bolt* and wedge shell bolt*
	- split set and folding bolt
Mortar bolts:	- cement bolts
	- resin-based mortar bolts
Combination bolts:	- end-cemented expansion bolt or split set
	- cemented press bolt

*such types of anchors need the lowest extension of mechanical equipment

REMARKS:

Bolted support shall be applied, where nonrelaxed rock is stable. Bolted support would be the wrong method in faulted zones.

Advantages of bolted support are the fast insertion and that no space requirements are needed.

Blasting tremors can affect the bracing of mechanical bolts.

Different bolts for mechanical bracing in stable and semi-stable rock are available. Semi-stable and loose rock necessitates cemented bolts. Expansion bolts are usually braced with half its yield stress.

Besides washers and bolting plates with or without angular compensation, bolted support is being applied by lagging screen wire, steel belts etc. The lagging keeps back the broken rock and directs stress to the bolts.

For the optimal functioning of bolted support, it is necessary to insert the bolt in the direction of the expected pulling force. Specific geological knowledge (stratification, foliated structure) is therefore necessary.

Besides metallic bolts, wooden slot-and-wedge anchors were applied in the U.S.A. mainly in places with soft hanging such as argillaceous and quarzitic shalestone. Its dimensions were 5 cm, 125 cm length, 6 × 6 cm head, turned on a lathe with fresh, wet pine or spruce wood, two wedges 1 7/8 × 1 × 16" and one 30" in anchor plate. The cost approx. 0.5 US$/plece. The advantages were, high retaining force in loose adjoining rock, the possible production at the mine site, and high corrosion resistance. Such anchors have been produced locally with output of some 500 pieces/man-shift and setting capacity of some 100 pieces/ms.

SUITABILITY FOR SMALL-SCALE MINING:

Bolted support is advisable only for pneumatic mechanized mines with semi-stable adjoining rock as roof support.

Figs.: Different types of expansion bolts, Reuther.

Fig.: Wooden bolted support in Dayrock Mine, USE, by Woodruff

mechanic bolts
expanding anchors	friction pipe bolts
Figure

mortar bolt
cement mortar bolt	synthetic resin-based mortar bolt
Figure

combinations of mechanic and mortar bolt partely filled at bottom with mortar
completly filled with mortar	expanding anchor with resin-based mortar
Figure

Fig.: Different types of bolt systems, Reuther