The cost of underground haulage is lessened by the use of cars of large capacity.
As the mine is opened the deposit is subdivided into blocks of convenient size by parallel passages, which form later the main haulage roads, and by transverse openings for ventilation.
In steeply inclined beds the working-place can be so arranged that the mineral will fall or slide from the place where it is broken down to the main haulage road.
As already noted large pillars must always be left to protect shafts, adits and the more important mine-passages necessary for drainage, ventilation and the haulage of mineral.
The main haulage tracks are laid at the bottom of the stope, which thus forms the level.
The working-floors are connected by winzes with the main haulage roads below.
Haulage roads are driven in the ore so as to divide the floor into areas of convenient size.
In this manner one floor after another is worked until the floor containing the main haulage roads of the level below is reached.
The floor containing these old haulage roads now becomes the top slice of the one hundred-foot block of ground below and is mined out as described.
The subdrift system requires a smaller amount of narrow work in excavating the necessary haulage roads, and is therefore better adapted to hard ores in which such narrow work is expensive.
Each floor is opened up by subsidiary haulage roads and worked out in small rooms which are timbered and filled with broken rock when completed.
Drainage channels are provided, usually along the main haulage roads, by which the water flows to a sump excavated at the pump shaft.
Only a very small proportion of the decline in the price of wheat since 1880 is due to cheapened transport rates; for while the mileage rate has been falling, the length of haulage has been extending, until in 1900 the principal wheat fields of America were 2000 m.
A towing chain, laid in the bed of the river, extends from Hamburg to Aussig, and by this means, as by paddle-tug haulage, large barges are brought from the port of Hamburg into the heart of Bohemia.
The latter includes not only the actual excavation of the mineral, but also haulage and hoisting by which it is brought to the surface, timbering and other means of supporting the excavations, and the drainage and ventilation of mines.
Work is then started on the floor above, the upper floors being connected with the main haulage roads by winzes which are maintained through the filled ground.
The use of the heavy timbers and continuous framing which characterize this system facilitates greatly the work of mining and maintaining the haulage roads on the different floors, and gives more rigid support to the unmined portions of the block of ground above.
For deep workings the milling method is usually employed, in which the ore is excavated in funnel-shaped pits, each of which connects with underground haulage roads by a shaft.
Before the bottom of these pits reaches the level of the haulage roads below, a new set of roads will have been driven at a lower level and connected with the excavations above by the shafts.
For hand tramming, animal and rope haulage, the rails weigh from 8 to 24 lb per yard, for locomotive haulage 30 to 40 lb.
In metal mines, where, as a rule, mechanical haulage is inapplicable, the cars are moved by men (trammers).
Animal haulage is employed chiefly in collieries and large metal mines; sometimes for main haulage lines, but oftener for distributing empty cars and making up trains for mechanical haulage.
Trolley haulage lacks the flexibility of steam or compressed air haulage, and is limited to main lines because the wires must be strung throughout the length of the line.
For heavy gradients rope haulage has no rival, though for moderate grades it is often advantageously replaced by electric and compressed air haulage.
In the tail-rope system of haulage, best adapted for single track roads, there are two ropes - a main and a " tail " rope - winding on a pair of drums operated by an engine.
(For details see Hughes, Text-book of Coal Mining, pp. 236-272; Hildenbrand, Underground Haulage by Wire Rope.) Rope haulage is widely used in collieries, and sometimes in other mines having large lateral extent and heavy traffic. With the tail-rope system, cars are run in long trains at high speed, curves and branches are easily worked, and gradients may be steep, though undulating gradients are somewhat disadvantageous.
High prices of materials and of haulage and freight rates added difficulty to the task of rebuilding, which was accomplished with remarkable energy and speed.
Square sunk into the blue ground; the diamantiferous rock was hoisted by bucket and windlass, and roadways were left across the pit to provide access to the claims. But the roadways soon fell in, and ultimately haulage from the claims could only be provided by means of a vast system of wire ropes extending from a triple staging of windlasses erected round the entire edge of the mine, which had by this time become a huge open pit; the ropes from the upper windlasses extended to the centre, and those from the lower tier to the sides of the pit; covering the whole mass like a gigantic cobweb.
In the meantime a new level and a system of haulage roads have been driven a hundred feet below, and winzes have been driven upward to connect with the old level which is to be abandoned.
Backof ore above are then mined in retreating back towards the haulage road.
This occasions much added expense in the maintenance and retimbering of the haulage roads on the upper floors.
Locomotive haulage is applicable to large mines, where trains of cars are hauled long distances on flat or undulating roads of moderate gradients.