Cutting (geotechnics)

“ The conditions under which the instrument is worked are obviously such that this edge will be rapidly worn down by attrition from the hard rock material, and by fracture. To withstand these destructive actions, two qualities are requisite in the material of which the instrument is composed, namely, hardness and toughness. Thus there are three important conditions concurring to determine the nature and the form of a cutting tool to be used in rock boring—1, a necessity for a cutting edge ”

“ Except in hard rock, the top width of a cutting, and therefore the amount of material to be excavated, increases rapidly with the depth; hence if a cutting exceeds a certain depth, which varies with the particular circumstances, it may be more economical, instead of forming the sides at the slope at which the material of which they are composed will stand, to make them nearly vertical and support the soil with a retaining wall, or to bore a tunnel. ”

“ To understand clearly the action of the rock drill, we must consider the nature of the substance which has to be perforated. He who has examined the mineral constitution of rocks will have recognised the impossibility of cutting them, using that term in its ordinary acceptation, inasmuch as the rock constituents are frequently harder than the material of the tools [2] employed to penetrate them. As a rock cannot be cut, the only way of removing portions of it is to fracture or to disintegrate it by a blow delivered through the medium of a suitable instrument. ”

“ With regard to the formation width, i.e., the width of the bottom of a cutting or the top of an embankment, and the prevention of slips in earthwork, ample breadth is necessary in cuttings for the purposes of drainage, although less in a rock cutting than in that of ordinary soil, and the extent of the top of an embankment has some influence in the promotion of stability. ”

“ Whatever may be the stone selected, it ought to be kept constantly moist during the operation. If not, the tools will soon get heated and their temper will be impaired. When a tool has for a certain time undergone the erosive action of the stone, the cutting angle becomes too acute, too thin, and bends over on itself, constituting what is called “the feather edge.” ”

“ All saturated or wet earth should, if practicable, be run to spoil, but it is not easily effected, as it cannot well be filled into one waggon of a set, for it may be present throughout the whole surface of a cutting, nor in variable weather can operations be conveniently suspended until the exposed faces of a cutting are dry, but means are generally available by which any serious deterioration may be lessened. ”

“ In dry and warm soils the cuttings may be from twelve to eighteen inches long, or even longer if it is desirable to bend them in a circular way in the holes in which they are to be planted, or if the soil is very warm and dry, when it is of importance that the cutting should reach the deeper moisture. A twelve or fourteen inch cutting is probably an average size cutting, and one that will answer most conditions, in case they are not previously known.
A nurseryman, or any one who can give his cuttings as much attention as they require, can use even the very tips of the vines and make them grow. ”

“ Side cuttings are a protection against slips in embankments when they are sufficiently far from the toe of the slope, as they form drainage channels, but the excavation being top soil is loose and porous, therefore, when the lower 158portion of an embankment is made from side cutting and the upper from a cutting, the firm material may be at the top and the more open earth at the base ”

“ As in excavating cuttings the surface is bared and vegetation removed from the soil, water has easier access, and unless the ground when excavated is immediately covered as before, its normal state is not preserved. One point of considerable importance is to ascertain whether in any cutting or embankment percolation is uniform and regular; some infiltration will necessarily take place, as water will gravitate from the top to the bottom and will find the easiest course or line of least resistance, which may not be at the lowest level. ”

“ Also in a cutting in sidelong ground if a stratified rock dips parallel, or nearly so, to the slope of a hill, slips are probable, as it may slide towards the cutting. Similarly, in a cutting in drift or alluvial soil, or any that will quickly weather, resting upon rock, especially should it have a smooth bed inclining towards the formation, the superimposed earth will usually be unstable, and even the act of penetrating the top stratum, or the erection of a retaining wall or the weight of a small embankment upon it, may cause it to move ”

“ Cuttings—may be from any wood you have to spare, and should be about a foot long, having two buds. Plant at an angle of forty-five degrees, one bud and two thirds of the cutting under the soil. A little shade and moisture will cause nearly all to grow. A little grafting-wax on the top will aid the growth, by preventing evaporation. The cutting, so buried as to have the top bud half an inch under fine mould, is said to be surer. Cuttings should be made late in fall, or early in winter, and preserved as scions for grafting. ”

“ The side of the roughing cutter A is ground to a slight angle c to provide clearance for the cutting edge, and the front has a backward slope s to give the tool keenness. This tool is a good form to use for roughing cuts in cast iron. The finishing tool at B has a broad flat edge e and it is intended for coarse feeds and light cuts in cast iron. If a round cutting edge is used for finishing, a comparatively fine feed is required in order to obtain a smooth surface. The corners of tool B are rounded and they should be ground to slope inward as shown in the plan view. ”

“ In excavating a cutting in soil likely to slip, care should be taken that the surfaces are not strained by lumps being left upon them which are only retained by reason of the cohesion of the earth, as they will cause weak places less able to bear any pressure brought upon the slopes through the sides being deprived of continuity of support. ”

“ When planted, a few sharp taps with the foot will sufficiently fix the cutting. When the flat bar is used, a hole is first made by the bar, the cutting is then inserted, and the hole filled up by again inserting the bar near the cutting, and by pressing it forward towards the latter. Neither of these tools can be used in dry or stony soils, but in moist and loamy soil, which has been previously well prepared, they are most excellent, as doing the work both quickly and well. ”

“ If chalk beds incline across a valley, and have an impervious stratum of clay upon them, it has been found that the most water issues at or about the point where the impervious seam first overlies the chalk, i.e., at the edge of the basin, and the greater its depth, the less the flow; therefore, should a cutting be located at a place where this stratum is thinnest, more water from springs may be expected than at any point where the impervious layer is thicker. ”

“ A groove about 1/16 of an inch deep was cut encircling the bone, and it was shaped into two pieces. Apparently some preliminary smoothing had already been done, as suggested by additional scoring marks. The authors tested various tools to determine which might be most efficient in cutting such a groove. Flat sharp flakes or knives could be used, but usually not enough pressure could be brought to bear without breaking the tool. However, certain implements, called “gravers” in this paper, were rather well adapted for such work. The tool could be used as a plane for cutting. ”

“ There is no limit to the depth of a cutting except a due regard to economical construction, provided the slopes are sufficiently flat, and the lateral and upward fluid pressure in the slope, and formation and quantity of water not too great for the stability of the earth; but, in the case of embankments, the load upon the ground and the deposited material in great measure restricts the height, or necessitates an embankment being gradually spread out, so as to enlarge the bearing area as the weight is increased. ”

“ As in clay and all retentive soils, water is always present, and as the impervious nature of clay prevents water gravitating and being drained, and as owing to wet seasons the permeable portion of the clay may gradually become overcharged and be reduced to a muddy condition, slips may occur years after a clay cutting has been excavated or an embankment deposited. In clay embankments the greater weight upon the centre may gradually press water towards the slopes and cause them to slip; hence the value of covering the formation in order to lessen percolation. ”

“ The quality of the rubbing accomplished depends much upon the selection of the blocks of pumice stone. The blocks of light weight, open grain, tunneled with innumerable air cells, are to be preferred for good cutting properties. Immersed in water, they float instead of sinking. The buoyancy of a piece of lava determines its porosity and its cutting power. This kind of stone may be used until the surface is well reduced, when, preferably, the stone of closer texture and tighter grain may next be used and continued in use until the final dressing up has been concluded. ”

“ But the length of cutting edge in action, with a given tool and under a given depth of cut, increases as that edge is made longer to carry the coarse feed, and the long cutting edge produces a strain that tends to spring or bend the work, and that causes the tool to dip into seams or soft spots, or into spongy or other places, where the cutting strain is reduced, and also to spring away from hard spots or seams, where the cutting strain is increased. ”

“ The strength of a cutting forms to a great extent a guide as to the quality of the tool, since the stronger the cutting the less it has become disintegrated, and therefore less power has been expended in removing it from the work.
The cutting speed for wrought iron should be sufficiently great that water being allowed to fall upon the work in a quick succession of drops as, say, three per second, the cuttings will leave the work so hot as to be almost unbearable in the hands, if the cut is a heavy one, as, say, reducing the work diameter 1⁄2 inch at a cut. ”

“ In sidelong ground the formation is frequently partly in cutting and partly in embankment, if so, and the drain is impermeable and can be thoroughly relied upon, it may be advisable to make the formation incline towards the hill, so as to drain it, lessen, and perhaps prevent percolation into the semi-embankment or under its seat, for the soil being loosened by the process of excavation and deposition is in the mass more porous than in a cutting. ”

“ Consequent upon cohesion, a cutting may stand for some time almost vertically; nevertheless stability cannot be considered as solely regulated by the cohesion of earth, for an embankment of gravel, sand, or broken rock with a proper slope and protected from erosion will usually safely bear more load than an embankment of clay, although the former material may be said to have no cohesion ”

“ The reason for decreasing the slope and thus increasing the lip angle for harder metals is to give the necessary increased strength to the cutting edge to prevent it from crumbling under the pressure of the cut. The tool illustrated at A, Fig. 13, is much stronger than it would be if ground as shown at B, as the former is more blunt. If a tool ground as at A, however, were used for cutting very soft steel, there would be a greater chip pressure on the top and, consequently, a greater resistance to cutting, than if a keener tool had been employed ”

“ One reason why the cutting process is so popular in shipyards is because in making steel ships, holes are cut in the plates, ribs, and beams, wherever possible without lessening the strength, to lighten the frame.
Probably the most picturesque use of the cutting device is by wreckers of steel structures. Nowadays whenever there is a bad fire the building is left a tangled mass of steel pipes and girders that can only be cleared away with the greatest risk of life, and the greatest difficulty. The process always was a long, tedious one until the oxy-acetylene cutting came into use. ”

“ If this process can be indefinitely continued, the cuttings must become smaller and smaller, for the following reason. Suppose, at the outset, the boundary point nearest to the intersection of the axes is distant from that intersection by, say four inches; it is clear that we cannot, after any number of cuttings, have a part of the boundary at less than four inches from the intersection. For there never is, after any cutting, any approach to the intersection except what there already was on the other side of the axis employed, before that cutting was made. ”

“ Clay underlying gravel often contains numerous pockets and seams filled with running sand, and should there be a permanent head of water the discharge will be in large quantities and at a considerable velocity. A cutting in wet sandy clay is generally treacherous and difficult to manage. ”

“ An inclined water-bearing stratum between rock loosely bedded and inclined towards a cutting, unless drained and supported, will probably cause a slip consequent upon the action of water or frost; on the other hand, veins may alone hold the masses together, and, therefore, when they are affected the cementing medium is destroyed; however, inclined water seams are a frequent cause of slips, for where any water-bearing earth meets a closer and consequently less pervious stratum, damp surfaces are produced, and an unstable condition ”