US1183352A - Building tunnels. - Google Patents

Description

E. DIEBITSCH.

BUILDING TUNNELS.

APPLICATION FILED mm, 1914.

1,1 88,852. Patented May 16, 1916.

SHEETI. TIM W M I HF E. DIEBITSCH.

BUILDING TUNNELS.

APPLICATION man APR.4. 1914.

1,1335%. Patented May16,1916.

6 SHEETS-SHEET 2.

WI T/VESSES:

THE COLUMBIA PLANOGRAPH (20.. WASHINGTON, D. c.

E. DIEBITSCH.

BUILDING TUNNELS. APPLICATION min APR.4. I914.

Patented May 16, 1916.

7 IILIIII F I M I I 1 H g I 1 I I WI 771/5885 S E. D IEBITSCH. BUILDING TUNNELS.

APPLICATION FILED APR. 4, 1914.

WI T/VESSES THE (IGLUMBIA PLANouILwH c0, WAsmNn'rc D. c-

E. DIEBITSCH BUILDING TUNNELS.

APPLICATION FILED APR. 4, 1914.

Patented May 16, 1916.

III-"- v llllllllll 7| WI TNESSES E. DIEBITSCH.

BUILDING TUNNELS.

APPLICATION FILED APR.4.1914.

Patented May16, 1916.

WITNESSES THE COLUMBIA PLANOGRAPH co., WASHINGTON, n. c.

EMIL DIEBITSGI-I, OFNUTLEY, NEW JERSEY.

BUILDING TUNNELS.

Specification of Letters Patent.

Patented May M5, rare.

Application filed April 4, 1914. Serial No. 829,445.

To all whom it may concern:

Be it known that I, EMIL DinBrrsci-i, a citizen of the United States, residing in Nutley, New Jersey, haveinvented certain new and useful Improvements in Building Tunnels, of which the following is a specification.

This invention aims to provide an economical and safe method of building tunnels, adapted especially for submarine tunnels, and especially for such tunnels as have to pass partly through earth and partly through rock, which are not located very far below the bottom of the river, like some of the tunnels built under the East river at the city of New York.

The accompanying drawings illustrate a complete process embodying several features of novelty which are defined .in the claims hereinafter and which are capable of separate application under various conditions.

The work is carried on by means of an apparatus or structure which I call a pneumatic caisson but which in its preferred form differs in several respects from the ordinary pneumatic caisson,-notably in that it extends for its full cross-section clear above the surface of the water and is adapted to carry on its own decks most or all of the machinery used so as to constitute a practically self-contained equipment, in that it has chambers for fixed ballast and for water ballast which can be pumped out to lift it and shift it to another point and then restored to sink it, and in that it forms no part of the finished structure.

Figure 1 is a longitudinal section through the caisson in place for the building of the first section of the tunnel, showing the eXcavation through mud, sand, gravel or other soft material to the bed upon which the tunnel is to rest, at the right hand of the figure, and showing the excavation down to the rock at the left hand; Fig. 2 is a similar view showing the caisson advanced to the end of a completed section of the tunnel in position to connnence work on the next section; Fig. 3 is a similar view showing the excavation completed, an invert of concrete built therein and a section of tunnel lining in place in the working chamber ready to be lowered upon the invert; Fig. 3 is'a horizontal section on the line 3-% of Fig. 3; Fig. t is a transverse section midway of the length showing the excavation partly through rock and partly through mud; Fig. 5 is a similar view showing the excavation where there is no rock, but only mud; Fig. 6 is a section on the line 6-6 (Fig. 3) showing the later stage of the operations in which the invert is completed ready to receive the tunnel lining, and showing the design of the gate at one end of the working chamber; Fig. 7 is a similar view showing the invert, lining and roof complete; Fig. 8 is a horizontal section through the working chamber approximately on the line 8-8 of Fig. 3; Fig. 9 is an enlarged plan view on the same plane showing the head of the sheet pilesafter driving; Fig. 10 is a plan, Fig. 11 a vertical section and Fig. 12 an enlarged detail in vertical section, illustrating another style of apparatus and method by which the tunnel lining can be intro duced.

Referring now to the embodiment of the invention illustrated, the caisson has an upper deck A, a lower machinery deck 13 and a working chamber C, the deck or roof D of which is sufiiciently high above the cutting edge to provide a space free of cross bracing for the introduction of large built up portions of the tunnel as hereinafter described and to permit various other operations to be carried on easily. Any number of shafts E with air locks F 011 their upper ends are provided for giving access to men and mate rials to the working chamber. The usual or suitable ballast chambers are provided into and out of which water can be pumped to lower and raise the caisson. The usual air compressors and other machinery may be carried on the machinery deck 13 so that the whole apparatusis self-contained. In Fig. 1 iron ballast G is shown between the plates H, H of the double wall which sur rounds the working chamber. Besides the openings through. air locks and shafts for the passage of men and materials while working under air pressure, one or more special openings into the working chamber are provided for the admission of large sections of the tunnel or tunnel lining, with means for keeping these openings covered while working under air pressure. For example, in the construction of Figs. 1, 2 and 3 an opening is provided at one end of the chamber. The passage J is traversed by a gate or dam K of a style commonly used for closing the entrances of dry docks guided in sultable g ooves K and'l in th sides and bottom of the passage, which grooves" are lined with strips K of rubber or similar packing material backed by timbers K*. The gate fits loosely between the packing strips as shown in dotted lines, Fig. 3, except when an unbalanced pressure forces it against one or the other of the strips, when it makes a tight joint. In ordinary operation the air pressure forces the gate against the strips K at the outer sides of the grooves. By releasing the pressure the gate is permitted to move upward into a recess L in the upper part of the caisson. It is lifted and lowered by any suitable mechanism such for example as a hydraulic lift cylinder L extending above the upper deck and carrying a piston whose rod L is connected to the top of the gate. The lower edges of the recess L are also lined with packing strips L The character of the bottom is indicated in Fig. 1. It consists in part of mud, sand or gravel M and in part of rock N sloping off into the mud, sometimes entirely below the level of the bottom of the tunnel as at the right hand of Fig. 1, sometimes extending above the top of the intended tunnel as at the left hand of Fig. 1 and sometimes projecting only partly into the space to be occupied by the tunnel as in the right hand portion of Fig. 2. The roof of the tunnel, in the case assumed, is only a few feet below the bottom of the river. I propose,

4 therefore, by means of a dredge to excavate a trench roughly in the mud of the river bottom to an approximately level bearing for the edge of the caisson. The sides of such a trench are indicated at 0. See especially Fig. 7 When this has been done the caisson is lowered upon the bottom of the trench with one end at approximately the point where the rock N passes above the bottom of the trench as shown in Fig. 1. For the case of the East river, above referred to, extreme high water is indicated by the letters EHIV and mean low water by the letters MLW and the caisson extends at least forty-five feet below extreme low water, this being the distance permitted between the top of the tunnel and extreme low water. The working chamber must be large enough in length and breadth to build a substantial section of the tunnel at one operation, say one hundred feet long and forty feet wide where two tunnel tubes are to be built together. The working chamber must also be high enough to give head room for placing and driving piles. For a tunnel twenty-five feet from top to bottom the sheet piles must be at least the same length and the height of the working chamber must be slightly greater. Having sunk the caisson at the point indicated the air pressure is applied and the excavation is proceeded with in the usual way, excavated material being taken out through the shafts and locks In order to hold up the sides while the excavation is proceeding sheet piles P arev driven from within the working cham her, taking care to keep the sheeting below the excavation and bracing it wherever necessary. by cross braces P. The sheet piles aredriven to' or slightly below the level of the bottom of the tunnel, or to rock where the latter projects above such level. These piles are made as nearly air tight as possible.

In the case illustrated the tunnel is to be built entirely below the cutting edge or lower edge of the caisson. In other cases it may be preferable to locate the cutting edge at a level between the top and the bottom of the tunnel so that the latter when completed will project upward into the caisson. The excavation in the latter case will extend below the cutting edge for a distance equal to only a part of the height of the tunnel. l/Vhere the excavation below the cutting edge is of considerable depth it is impossible to balance the pressures upon the opposite faces of the piles. The pressure of air within the excavation is practically uniform from top to bottom, the weight of the air being negligible; but the pressure of water or mud against the outer faces of the piles varies by about fourtenths of a pound per square inch for each vertical foot of distance. For a twenty-five foot excavation for example there would be a difference of ten pounds per square inch between the pressure at the'top and that at the bottom. It is impossible, therefore, to have an evenly balanced pressure on both sides of the piles. I purpose to use a pressure of air equal to or slightly greater than the hydrostatic pressure-at the bottom. U1 der such circumstances there is tendency for the air to leak out wherever possible and especially in the upper part of the excavation. If there'shouldbe a large number 'of openings, even though each is small, the leakage wouldbe considerable. In such a case I propose to limit or prevent the loss of air by covering the small openings through which the leaks take place with sheets of paper, felt or other substantially impervious material. Such sheets are shown .at Q in Fig. 5 laid against the face of the piling. The sheets must be first pasted upon the face of the piling to hold them in place temporarily. The excess of internal pressure will hold them in place permanently. It. is not essential that the sheets cover all the openings and stop all possible leaks. The covering may be applied to a greater or less extent according to circumstances. WVhen the excavation has been carried to a greater depth at one end of the working chamber than at the other end similar impervious sheets may be laid directly upon the bottom at the points where it is higher or des1 gns.

' laid on the top of the lining.

so as to limit or prevent the loss of air through the material at the bottom of such high points where it is unprotected by pilmg.

Supposing the excavation of mud completed as in Fig. l, I may make this a starting point for tunneling through the rock N, thus saving the large expense of previous operations in which the tunnel has been started from one of the ends, the excavated material being transported back to the starting point for the entire length of rock tunneling, and a shield being carried through the rock because of the necessity of using it where the rock disappears and mud is encountered. As shown in Fig. 1, I propose to first seal the 1o1nt between the rock and the cutting edge at one end of the caisson by dumping a clay filling It at this point. Then from within the caisson I first remove the portion of the rock which lies below the working chamber and then tunnel through the rock in any usual or suitable way, removing the rock as it is excavated through the working chamber and the air locks until the tunnel has been extended nearly through the rock to the next section in which mud is encountered, or entirely through the rock to the shore end, if the rock extends continuously. Having completed the excavation, as in Fig. 4t or in Fig. 5, the tunnel is to be built therein. The method of such building will depend largely upon the design of the tunnel. I have supposed a twin tunnel with alining of iron or steel tubing surrounded by a considerable thickness of concrete. Other constructions, however, may be used. For example, especially in the case of a single tunnel, the usual cast iron segments may be used to build up the lining. For building tunnels with a concrete shell and a metal lining the first step is to lay an invert S of concrete (Fig. 6) in the bottom of the excavation, constituting approximately the lower half of the shell. In advance of laying the invert S, piling S as indicated in Fig. 3 may be driven, the heads of the piles being cut off at such a point as to support the invert which is then laid thereon. Such a piling support is looked upon with favor by some engineers in soft material. Various other systems for supporting the tunnel may be carried on in the working chamber, my invention providing facilities for a great variety of systems Ordinarily, however, it would be sufficient to lay the invert directly on the mud. The lining is then laid on this invert and a roof or cover T of concrete (Fig. 7)

Where the tunnel lining is to be of cast segments these segments may be introduced through the air locks and shafts and assembled in place on the supporting invert. Similarly sheet steel or iron linings may be introduced in small sections through the air locks and riveted together into a built up lining in the working chamber. It may be preferable, however, where the sheet steel lining is to be used, to rivet the parts tofirst to the construction of Fig. 3 I take a suitable length of built up sheet steel tubing, say fifty or one hundred feet thereof, close the ends and sink such portion alongside the end of the caisson and parallel with the line of the tunnel, an indicated at U in dotted lines. The buoyancy of this lining section is ordinarily suflicient to float it. In case of necessity buoyant tanks or floats may be attached thereto to bring it to the correct weight. Thereafter by pumping water into and out of the lining section or the attached floats I can sink the same to the depth desired very accurately. This is a well understood operation and has been successfully employed in tunnel building. Having the lining section U at the desired location I let the air out of the caisson and allow the water to enter. This balances the pressures on opposite sides of the gate K at the end of the caisson and allows the latter to be lifted easily into its recess L, thus opening the gate. The lining section U is then shifted endwise into the working chamber after which the gate K is lowered and the air pressure again put on in the working chamber, closing the gate tightly. The lining section may be pushed into the working chamber from the outside or it may be pulled in by means of cables passing from the deck down into the working chamber and around guide pulleys and carried through the passage J by divers and attached to the forward end of the tunnel section. Or a combination of these two methods, or in fact various other methods, may be used for introducing the lining section into the working chamber. After closing the gate the compressed air is first introduced only sufficiently to force out part of the water to enable workmen to enter the chamber and secure the lining section to traveling blocks or cranes or slmilar supporting means fastened to the ceiling of the working chamber. The water can then be forced out entirely and the lining section carefully lowered into its proper place on the invert and its rear end bolted or otherwise attached to the forward end of the completed section II. In order to open the gate K promptly I may provide small flooding gates or valves by which the working chamber can be quickly filled with water when the air pressure is withdrawn so as to quickly counterbalance the pressures on opposite faces of the gate. When the gate is closed and the water is to be expelled I may assist the operation by centrifugal pumps of large capacity working in combination with the air pressure.

Instead of making an end of the working chamber open I may provide one or more passages directly from the working chamber to the outside through the roof, such .for example, as the passage 7), Fig. 11, which is cut through the deck D of the working chamber and through the machinery deck B, and which is provided at the level of the main deck A with a removable cover 0. This passage 1) is shown as extending through the full width of the working chamber and extending lengthwise between deep girders (Z adjacent to two of the smaller air locked passages E. The cover, indicated as a whole by the letter 0, consists, as shown in detail in Fig. 12, of a heavy plate 6 stiffened or braced by longitudinal I-beams f. The plate rests on gaskets g on the tops of the girders (Z and is held down by bolts h at intervals hooked under or otherwise fastened to the girders d, extending upward between a pair of the I-beams f and carrying at its upper end a washer 11 large enough to rest firmly on the two I-beams, and a heavy nut j by which the cover can be clamped down on the girders. The nuts j may be provided with large enough wings to operate them directly or may be operated by means of wrenches or other tools. One or more openings like I) with covers 0 may be provided. Ordinarily one would be all that is needed and the cover may be made in sections or in .a unit as illustrated. When the cover a is removed, the air being first let out of the caisson, a portion of the tunnel or a built up section of the tunnel lining equal in width to the working chamber and in length to a substantial part thereof may be let down and slung in the working chamber in the manner of the lining section U of Fig. 3. Or the length of the lining section and the location of the cross braces P may be such as to permit the lining section to be lowered clear down to position on the invert. Or the cross braces P may be re moved, the lower ends of thepiles being supported on their inner faces by means of the completed invert and the upper ends being never subjected for any length of time to severe inward pressure and being held by their guides in the working chamber; in which case, of course, the section of the tunnel lining may be lowered without chance of interference from the cross braces.

-After the tunnel lining section is lowered into the working chamber the cover 0 will be replaced, air pressure applied and water removed and the workmen will reenter the chamber and set the tunnel lining. exactly in place and fasten it to the previously completed section. This operation may be repeated several times without shifting the caisson where the length of completed lining section introduced is only a fraction the length of the working chamber, or the caisson may be shifted between each of the successive operations of introducing a section of the lining; the concrete arch, of course, being laid over the lining before shifting the caisson. The lining being in place and the concrete arch or roof being completed over it the next step is to shift the caisson. For this purpose a portion of the ballast is removed so that the caisson is lightened and is lifted by its buoyancy slightly above the top of the completed portion of the tunnel. Where the tunnelis entirely below the cutting elge, as in the case illustrated, the caisson needs to be lifted only a few inches. Where the tunnel is built partly below the caisson and partly within the working chamber, the caisson, of course, must be lifted a corresponding height. It is then transported lengthwise along the preliminary excavation O. Va-

rious known means may be used for guiding the caisson during such movement and for shifting it. The completed end of the tunnel may provide a suitable fixed abutment for securing a purchase to shift the caisson longitudinally, such. a shifting scheme being indicated diagrammatically in Fig. 2 by a cable V attached 'to the completed end of the tunnel and running over a block fastened to the inner face of the rear end of the tunnel. the same sort may be used. Or where it is undesirable to put any such strains on the tunnel tow boats or the like may be applied on the outside to draw the caisson along. When the rear end of the caisson is located over the completed end of the tunnel more ballast is introduced and the caisson is again sunk to a bearing, when the previous operations are repeated. Before shifting the caisson from one section of the work to the next the sheet piles will generally be withdrawn and held in the working chamber at a suitable elevation to clear the cutting edge and ready for the operation on the next section. Or the sheet piling can be cut off at a point above the excavation where the difiiculty of pulling it out is too great.

The sheet piling can be of various con- Structions as well as the means for guiding and driving them. A specially strong construction, to enable them to withstand great pressure and to make them as nearly air tight as possible, is illustrated in Fig. 9. Each pile in this construction comprises a pair of Other schemes of timbers W fastened by means of bolts X to opposite faces of an I-beam Y of considerable depth. The flanges Z of the I-beams are exposed, the timber being cut away around such flanges, and are embraced by steel guides a which are fastened to the inner wall plate H of the working chamber.

In tunneling from the caisson into the rock, as soon as the heading has been sufiiciently advanced toward the shore to determine that the tunnel can be driven without the use of compressed air it will probably be more economical to close the tunnel end with a bulkhead and to drive the balance of the tunnel from a shaft on the shore by known methods. If either shore end of the tunnel is not in rock, but in mud, sand or gravel the portion built in accordance with this invention under the river may be continued under the shore by means of shields. Such shields can be set up in the working chamber, located as nearly as expedient to the bulkhead line and advanced under the land, using the caisson as a shaft for the passage of men and materials.

In operating my improved apparatus it is advisable that, after transportation to a given point, sufficient water ballast be introduced to sink it to the desired level and a certain additional amount of ballast to hold it firmly on the river bottom under the heaviest air pressure needed for the conduct of the work. The operations of moving and sinking the caisson should be conducted during periods of slack water when there is little or no current. In the case of ordinary currents there will be no substantial difficulty in controlling the caisson by means of hawsers leading to anchors placed up stream.

The sheet piling acts chiefly as a diaphragm between the air pressure within and the hydrostatic pressure without, serving to distribute the comparatively small inequalities of pressure between the two opposing forces. It should be made stiff enough andstrong enough to take the calculated pressure per square inch over the space of from six to ten square feet in order to take care of soft spots in the mud, or blow holes or cavities caused by dredging which may exist in the banks against which the sheeting bears. When the caisson is located over a rock bottom the sheeting is driven to the rock so as to make a tight connection therewith and is braced across. This will practically exclude water, or will cut the inflow of water down to a point where it can be taken care of by pumps and the air pressure in the trench may be reduced to atmospheric pressure. In such circumstances the air locks may be removed or covers such as shown at 0 may be lifted and the work carried on as in an open cofferdam with great expedition. The style of apparatus with its large working chamber from Which the driving of piles and various other operations can be carried on as described lends itself in fact to a great variety of operations and to the adopting of very useful expedients in accordance with the character of the bottom and other conditions which may be encountered and which may differ from point to point along the length of the tunnel.

As compared with the ordinary shield method, especially where the shield is covered by a comparatively shallow layer of mud, the present process is very much safer for workmen. Tn shields with vertical working faces the unbalanced pressures at the top and bottom frequently result in blow-outs with loss of air and danger to the work and sometimes with death to the workmen. The present invention permits also of constructing the work from the outside as well as from the inside so that the resulting structure of steel lining and surrounding concrete is better in every respect than the ordinary construction built by the shield method of thousands of cast iron plates with acorresponding number of joints and bolts, the whole laid directly on the mud of the river bottom. With my improved method the bottom can be inspected and reinforced with piling or otherwise if necessary before the actual tunnel is constructed. Every step of construction can be done under complete inspection and with comparative ease and accuracy. For reasons above stated a certain amount of cover is necessary to operate shields, and tunnels built by means of shields must be located comparatively deeply below the river bed; whereas with this invention the tunnel can be built at the minimum depth allowable by harbor regulations below the surface of the river. Also with this invention the labor and handling of materials can be accomplished more economically. There is a'saving in the total cost of plant and operation. The apparatus resting on the river bed provides a stable deck equipped with derrick and practically all the necessary machinery for the handling of materials excavatedand for the transferring of materials to or from the apparatus. By providing a large uncovered area for the work a large number of men can be em ployed and the work completed quickly and economically. The progress of the work is not liable to the interruptions from blowouts and other accidents which often occur with shields. The advantages of the invention are especially noticeable, as compared with the shield method, where the tunnel is located with a shallow over-burden of soil and where the tunnel is to penetrate alternately sand and gravel and then rock and then partly rock and partly sand.

Though I have described with great particularity of detail a certain specific embodiment of my invention yet it is not to be understood therefrom that the invention is restricted to the particular embodiment described. Various modifications thereof in the individual steps of the process and in the combination of steps employed and the order of such steps may be made by those skilled in the art Without departing from the invention.

What I claim is- 1. In the building of a submarine tunnel the method which consists in sinking a pneumatic caisson, excavating under compressed air to a level below the edge of said caisson, and laying in the excavation so formed a tunnel with its top below said edge of the caisson.

2. In the building of a submarine tunnel the method which consists in sinking a pneu matic caisson, excavating under compressed air to a level below the edge of saidcaisson and laying in theexcavation s0 formeda tunnel with its top below said edge of the caisson, raising and transporting said caissonto the end of the completed portionof the tunnel and laying an extension of such portion by the same method.

3. In the building of a submarine tunnel partly through earth and partly through rock the method which consists in sinking a pneumatic caisson with one end locatedapproximately or substantially at the point where the tunnel is to pass from earth .to rock, excavating under compressed air from the working chamber of said caisson downward to a level below the edge of said caisson, and extending said excavation horizontally into the rock.

4. In the building of a submarine ltunnel the method which consists in sinking a pneumatic caisson, excavating under compressed air to a level below the edge of said caisson, driving sheet piling from within the working chamber of said caisson to protect the sides of the excavation so formed, and laying a tunnel in said excavation.

5. In the building of a submarine tunnel the method which consists in sinking .a pneumatic caisson, excavating under compressed air to a level below the edge of saidcaisson, forming a foundation below said level and building on said foundation a tunnel with its top below said edge of the caisson.

6. In the building of a submarine itumiel the method which consists in .sinkingapneumatic caisson, excavating under compressed air to a level below the edge of said caisson, laying a supporting invert of concrete ,on the bottom of the excavation so formed, laying a tunnel lining of metal on said invert, and laying over said lining a concrete arch, the top of which is below said edge of the caisson.

7. In the building of a submarine tunnel the method which consists in sinking a .pneumatic caisson, excavating ,under compressed air from the working chamber of said caisson, laying a portion of a tunnel in the excavation, raising and transporting the caisson .to the end of said portion of the tunnel, opening a large passage from said working chamber directly to the outside, and moving a large built-up portion of the tunnel through said passage into the working chamber While the latter is stationary at the end of said completed portion.

8. In the building of a submarine tunnel the method which consists in sinking a .pneumatic caisson, excavating under compressed air from the working chamberof said caisson, laying a portion of a'tunnel in the excavation, raising and transporting the caisson to the end of said portion of .the tunnel, opening a large passage from said working chamber directly to the outside,and moving a large built-up portion of the tunnel through said passage .into the working chamber while the latter is stationary at the end of said completed portion, and zthere after closing said working chamber, applying air pressure and connecting said builtup .portion of .the .tunnel tosaid completed portion lunder compressed air.

.9. In the building of a submarine tunnel the method which consists insinkinga pneumatic caisson, laying a supporting invert of concrete from within the working chamber of said caisson, opening a large passage from .said working chamber directly to the outsideand moving a large built-up portion of a tunnel lining through such passage into the working chamber while the latter is stationary over said invert, closing the working chamber and applying air pressure and placing such portion of the lining in position onsaid invert under compressed air.

10. In the building of a submarine tunnel themethod which consists in sinking a pneumatic caisson, excavating under compressed air to a level below the edge of said caisson, opening a large passage from said working chamber directly to the outside, introducing a large built-up portion of the tunnel through said working chamber, closing .the working chamber, applying air pressure, and laying said portion of the tunnel in said excavation .under compressed air.

11. In the building of a submarine tunnel the method which consists in sinking a pneumatic caisson, excavating under compressed air to a level below theedgeofsaid caisson, laying a supporting invert of concrete in the excavation so formed, opening a large passage from said working chamber directly to the outside, introducing a large built-up portion of a tunnel lining through such passage ;into the working chamber, closing the Working chamber, and applying air pressure and laying said portion vof tunnel lining on said invert and a said lining.

concrete archover 12. In the building of a submarine tunnel the method which consists in sinking a pneumatic caisson, excavating under compressed air to a level below the edge 01": said caisson,

5 and covering apertures through which air might leak with sheets of fabric which are practically impervious to air.

13. In the building of a submarine tunnel the method which consists in sinking in the 10 river a caisson of sufficient size to permit the introduction of a shield and then tunneling into the shore with such shield, using EMIL DIEBITSGH.

Witnesses:

D. ANTHONY USINA, LULU STnBENvoLL.

tlopiea of this patent may be obtained for five cents each, by addressing the Commissioner of latents, Washington, D. G.

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