US2678540A - Process for the production and sinking of caissons of any desired shape - Google Patents

Description

May 18, 1954 Filed March 8, 1951 H. LORENZ PROCESS FOR THE PRODUCTION AND SINKING OF' CAISSONS OF' ANY DESIRED SHAPE 4 Sheets-Sheet 1 May 1s, 1954 H. LORENZ 2,678,540

PROCESS FOR THE PRODUCTION AND SINKING' OF CAISSONS OF ANY DESIRED SHAPE Filed March 8., 1951 4 Sheets-Sheet 2 M/UJC- 2,678,540 SINKING SHAPE 4 Sheets-Sheet 5 May 18, 1954 H. LORENZ PROCESS FOR THE PRODUCTION AND n 0 OF CAISSONS OF ANY DESIRED Flled March 8, 1951 .ICCQC `0000000 0000000000000000000 00000000000000 0,0000000000000 000000000000 000000000000000000000000000 .0,00.90.90.30.99?. 0 0

000000000 90.000000000000000 .H00000000000N0N0000N0N0000000000000000@ 0 4 4 4 o .0.0`0.0.0.0.0.n.0.0 t4 f. v0000N0N00000000000000000000000000000`\ 0 .000000000N0N0n0n0n000000000000000000. v000nv 000. .0.90040000000000000003 May 18, 1954 H. LORENZ HE PRODUCTION AND SINKING OF' CAISSONS OF ANY DESIRED SHAPE PROCESS FOR T 4 Sheets-Sheet 4V Filed March 8, 1951 /n veror Ny M Patented May 18, i954 OFFICE PROCESS FOR THE PRODUCTION AND SINKING OF CAISSONS OF ANY DE- SIRED SHAPE Hans Lorenz, Berlin-Tempelhof, Germany application March 8, 1951, Serial No. 214,496

Claims priority, application Germany f March 11, 1950` 11 Claims.

This invention relates to a process for the production and sinkingof caissons of any desired shape and has for its object to permit the production of such caissons with minimum dimensions, weights and reinforcement.

The penetrationof a caisson into the soil is based upon a slide phenomenon and the loading i of the cutting edges of the caisson must therefore be sufficient toovercome both the stability of the soil within the working chamber from which the soil is removed, and also effect a breech therein, that is to `say `arching of the material. This process is unfavourably influenced by the friction of the soil against the outer surfaces of the caisson since this friction acts in opposition to, and therefore has the` eifect `of reducing, the weight acting on the cutting edges.

It has been proposed to avoidthisdisadvantage` by giving the caisson an upwardly tapered form. li-Iowever,` this expedient was abandoned since it caused considerable disturbances in the structure of the soil outside the caisson.

It has furthermore been proposed that` the caisi son should have, at the level of the cutting edge, somewhat larger dimensions than its side walls to reduce the friction against `the side Walls. Neither does this expedient produce the required results since, more especially at great depths, the cavity around theside Walls and above the knife edge, becomes iilled With soil forced therein.

Filling the cavity with certain materials, such as slag, has also been attempted without any appreciable success. Therefore, in all known caisson foundations sticking of the caisson is frequently unavoidable especially in the case of different soil strata, and it is necessary to provide, in addition to the caisson weight necessary for the final structure, ballast by means of which it `can be further sunk.

Even more undesirable results are produced by unequal friction at the same level, which unequal friction occurs more especially in the case of caissons of rectangular cross-section. `In `order to allow for bonding stresses thus produced, the wall of the caisson must be heavily reinforced. The same applies to tensile reinforcement `required when danger exists of the caisson sticking far above its cutting edge and of a great weight acting on this crosssection.

Consequently, the presence of the side wall friction unavoidable in caisson foundations results in a considerable over-dimensioning, additional reinforcement and consequently excessive cost, the expenditure of `which is unwarranted by the final structure.- l

According to the invention, the aforesaid disadvantages in the sinking of caissons of any desired form are completely avoided if there is introduced between the side wall of the caisson and the soil, a liquid having thixotropic properties which does .not penetrate into the voids of the soil but, by forming a fluid-tight film, sets up a liquid resistance to the soil pressure, which resistance may, in accordance `with the concentration of the liquid, be greater than the hydrostatic pressure, so that on the one hand it protects the earth wall against collapse and on the other hand exerts on the side wall of the caisson purely horizontal readily determinable forces and does not exert on the side Wall of the caisson any vertical components produced by friction.

By thixotropy is understood the property oi certain colloidal suspensions which enables them to pass suddenly from the liquid aggregate condition into the solid aggregate condition. Such liquids do not penetrate into porous structure, such as coarseV grained soil, even under high external pressures. There is formed on the surface of contact of the liquid with the soil, a waterimpermeable nlm which prevents further penetration of material similarly to a rubber membrane. Experiments have shown that even with soil, such as gravel and rubble, having large voids between particles, this property is fully maintained.

Such a liquid may be produced, for example, by a suspension of pure bentonite in Water. Ex periments have shown that the thixotropic action of such a suspension collapses at a concentration of about grammes of bentonite per litre of water. The specific gravity of this suspension is at first only slightly greater than l gramme per cubic centimetre. If, for example, it is necessary in view of the existing soil conditions to increase the specific gravity, it is possible to add finely ground heavy spa, which does not separate from the suspension in the form of a sediment, since it is prevented from sinking by the thixotropic properties of the liquid even when left to stand for a long time. pension mixed with heavy spa is consequently maintained for a long time and can be increased to about 3 grammesper cubic centimetre.

The employment in deep boring and shaft sinking industries of thick washes or drilling muds for retaining open bore holes and circular shafts is already known. `These drilling muds, which consist generally of emulsions of argilaceous material present in situ, utilize the possibilities of thixotropic liquids consisting of bentonite, only The specific weight of the susto a small extent. Neither is this necessary for retaining open the bore holes and circular shafts with the existing circular cross-sections, since owing to the arching effect a small counter-pressure is sufficient to ensure stability of the earth wall. However, the static conditions are far less favourable in the case of overhanging walls of plane or any other form such as exist in the case of caissons of rectangular cross-section or upwardly tapered caissons. in such cases, stability of the earth walls can only be obtained if all properties of thixotropic liquids which do not act hydrostatically in the same way as water, are intentionally utilized. Again, in the case of caissons of round cross-section, the object of the invention, that is to reduce the dimensions and reinforcement to the extent statically necessary for the permanent structure, is only achieved if all the properties of the thixotropic liquid are intentionally utilized.

However, by introduction of a liquid having thixotropic properties between the side walls of the caisson and the soil, not only is collapsing of the soil intoA the cavity between the 'side walls of the caisson and the soil avoided, but in addition no friction is set up on the surface of the side walls so that the said surface has only to take up the hydrostatic pressure of the liquid introduced. This pressure can be readily calculated at any depth so that oVer-dimensioning of the caisson which has hitherto been necessary and usual both to overcome the frictional resistances and also to allow for the uncertainty in the estimates of the pressure of the soil, is eliminated. Moreover, the liquid pressure has equal values under all circumstances, as rneasLu-ed in horizontal section. The stresses on the side walls of the caisson are consequently annular stresses which can readily be taken up with minimum cross-sections. The lack of guiding of the caissons by the soil can be simply compensated by a roller guide system, for example, at ground level.

In the sinking of a caisson foundation in open water, the thixotropic liquid is not introduced until the horizontal curb above the cutting edge of the caisson has penetrated into the water bed, the higher specific gravity and the colloidal properties retaining the liquid in the space between the side Walls of the caisson and the soil thus preventing it from rising and separating and from penetrating into the soil.

To reduce further the friction, the lateral surfaces of the structural unit containing the working chamber are arranged to project rearwardly above the knife edge, and the space between these backwardly projecting lateral surfaces'and the soil may be lled with thixotropic liquid.

rEhe new process according to the invention may also be applied to a caisson having no side walls. In this case, the structure unit provided With knife edges and enclosing a working chamber is` sunk into the soil alone, the necessary pressure on the ceiling of the working chamber being produced by the weight of the thixotropic liquid bearing thereon. Uniform sinking is ensured by anadjustable suspension of the structural unit on bearers or floats. After nnal sinking, the space above the ceiling of the working chamber is completely or partially filled with concrete from below or another structural unit of any desired form may be mounted on the foundation created.

If the structural unit provided with knife edges and embracing a Working chamber has no side walls or has side walls projecting rearwardly to a considerable extent, it is furthermore proposed to fill the liquid-filled space above the ceiling of the working chamber with a thixotropic liquid, the concentration of which decreases in stages from the soil side to the centre, if necessary to zero.

In applying this process, a considerable proportion of bentonite may be saved, which is particularly important if the caissons to be produced have fairly large cross-sections. The invention is based upon the discovery that thixotropic liquid columns of different concentrations do not mix with one another. If, for example, the caisson hasv a cross-section of 30 x 20 metres, it is quite sufficient in order to achieve the object aimed at, to provide, above the ceiling of the structural element, an annular liquid column of a thickness of about 0.5 metres and a concentration of 200 grammes per litre, in contact with the soil wall. The adjoining liquid column in the inward direction may also beV annular and it preferably has a thickness of approximately l metre with a concentration of about grammes per litre, while the innermost layer, which lls .the entire free space, or which extends as far as the rearwardly projecting side wall of the caisson, may consist of pure water. n some cases it is sufficient to provide two liquid columns above the structural unit, in which case the outer liquid column in contact with the soil wall also has a high concentration. It will readily be seen that, especially in the case of caissons of large cross-section, considerable quantities of bentonite may be saved. provide on the soil side, a thin liquid column of highly concentrated bentonite suspension while the remaining liquid columns filling the large internal space, may consist of clay solution of lower concentration, the additions or which, for example clay or loam, may be produced in situ.

According to the invention, the liquid columns i of different concentrations are preferably introduced through pipe lines and nozzles arranged in or on the top of the structural unit and fed through delivery tubes during the sinking, for example from above or, if the working chamber in the structural unit is of sufficient dimensions, from the working chamber itself.

Preferably, short partitions are provided on the ceiling of the structural unit to iniiuence the direction of iiow of the liquids of different concentrations in the required manner.

The new process for the production and sinking of the caissons of any desired shape may also advantageously be employed for inclined sinking, in which case the caisson'is first sunk vertically to a certain depth and thereafter further sunk at a constant, or if desired, variable angle of rotation, for example by unequal excavation Y of soil in the working chamber.

Inclined sinking of a caisson is preferably effected when the structure to be built upon the caisson constantly undergoes considerable horizontal stresses, for example, due to the pressure of earth. By inclined sinking of a caisson it is possible to adapt the structuralunit in an improved manner to the supporting line, that is to say to the line connecting the points of application of the resultante in the individual crosssection. Y

In a known process for inclined sinking, the longitudinal section of the working chamber is constructed inthe form of a rhombus so that the caisson is guided obliquely downwards on one It is merely necessary toV lateral surfacepf thetlhombus bythe resistance of earth. Inthis process, the,caisson, travels,`

when sinking,l through a. horizontal distance which must be ,predeterminem This calculation, however, often causes diiiiculties since assumptions must be made for the purpose of simplication.` Nevertheless soil constants necessary for this purpose cannotbe ascertained with suicient accuracy.

While in the known inclined sinking method thebase of the `workingchamberalways remains horizontal, inthe new process the base can be adjusted to any angle` of `rotation in relation to the horizontal. `This aiords a great advantage in that fat eachsinkingdepth the resultant of the forces may be perpendicular to the base, so that if the sinking operationis ,correctly conducted, that` is to sayifthe angle ,of` rotation is correctly adjusted, the supporting line coincides with the centre axis of the structure, that is to say no moments are set up at any point,` and the structure thus only undergoes a compressive stress. A further advantage resides in that no accurate calculation as regards the positioning of the caisson need be made in advance, but corrections in the position of the caisson can readily be made during the sinking process.` Such corrections are citen necessary alsoj when caissons are sunk vertically. For this purpose, it is merely necessary to determine the momentary position of the caisson at ground level by means `of a simple measuring device. The space above the working chamber remains lled with thixotropic liquid, so that co1- lapse of overhanging soil walls `is rendered ,impossible.

The excavation of varying depths of soil at the transverse walls ofthe working chamber may be effected manually, that is to say by workmen operating under compressed air, or mechanically by installing automatic ilushing devices, for example with the aid of a mammoth pump. According to requirements, the caisson can be directed downwardly in the rotated position at a constant angle f rotation, or the angle olf rotation maybe constantly varied, so that the centre of gravity` of the working chamber describes a descending curve. The angle of rotation for "the caisson may be increased to 90 or more, so that from a certain Sinking depth the caisson moves horizontally or even rises again. In this vvay,` shafts or bores holes may be formed extending horizontally or at any desired angle.

Preferably, the space formed above the caisson is so lled with thixotropic liquids of dierent concentrations that liquids of higher concentration may be introduced in contact with the soil walls, more particularly at the overhanging soil walls than at the centre ofthe chamber.

When the caisson has reached the required depth, the chamber lled with thixotropic liquid is concreted from below, a reinforcing basket having been inserted in the liquid-filled open end beforehand. Since the thixotropic properties of the liquid prevent collapse of soil from the walls of the shaft even when these walls overhang, any disintegration of thewall or shuttering thereof for the purpose of concreting, is unnecessary.

If it is desired to give the foundation structure a particular economical form, it is also possible to providein the space lled with thixotropic liquid forms or `shuttering, the internal space of which is ooncreted, whereafter the shuttering is withdrawn and theremaining spaces filled with thixotropic liquid areiilled 'with earthor thin concrete.

Incontrast to the relatively limited iield of applicationofrthe known ,inclined sinking method, the new inclined sinkingprocess can also be employed to produce, for example, a supporting wall or quay wall if the soil `on the `air side or Water side adjacent the4 supporting wall is not to be dredged away until later, as is the case, for example, in theproduction of new harbour basins or the like. In this case, the supporting wall or quay wall is lowered in the manner described and the harbour basis is dredged out after completion of the concrete work.` With such a construction of the supporting or quay wall, all reinforcing and shuttering steps are unnecessary,

It is also possible to adapt the form of the quay wall on the air side and on the water side to the configuration of hulls of ships. In the production of such a supportingor quay wall, a layer of thixotropic liquid preferably remains in the bottom of the soil side of the supporting wall. The object of the said layer is to distribute uniformly over the supporting wall, a soil pressure composed of periodically occurring loads at individual points or along sections of the land with the aid of the hydrostatic action `of this layer of liquid, so that it is unnecessary to dimension the supporting walls in accordance with the most unfavourable load which will occur, as is the case in normal practice. i

For a better understanding of the invention and to show how it may be carried into effect, the same will now be described with reference to the accompanying drawings, in which:

Figures l to 3 show in vertical section, a caisson in various sinking stages and Figure 4 is a horizontal section in the line IV-IV of Figure 3,

Figures 5 to '7 show in vertical section, a caisson foundation in open water and in different sinking stages, and Figure 8 is a horizontal section on the line VIII-VIII of Figure 7,.

Figures 9 to 11 show in vertical section, a caisson foundation in which the caisson has no side walls, again in different sinking stages, and Figure l2 is this caisson foundation in plan view,

Figure 13 is a caisson in horizontal section in different stages of an inclined sinking operation,

Figure 14 shows a supporting wall erected on an obliquely sunk caisson, and

Figure i5 shows the same supporting wall employed as a quay wall.

In the caisson foundation shown in Figures l to 4, a thixotropic liquid I of suitable concentration is introduced between the caisson. side wall of jacket 2 and the soil 3; The cutting edge of the caisson a comes into Contact with the soil and prevents penetration of the liquid l into the working chamber 5. By means of a roller guide system e at ground level, inclination of the caisson during sinking is prevented.

The cutting edge l is produced and sunk in the normal manner. As soon as the curb T provided above the cutting edge, sinks below ground level, the hollow space deiined between the caisson jacket 2 and the soil 3 is filled with thixotropie liquid. This lling is supplemented during the further sinking to such an extent that the liquid always reachesground level. When the caisson has beensunk to the required final depth, the thixotropic liquid introduced is no longer required. It is removed, and if desired recovered, by filling the space with concrete between the jacket and the soil through the medium of pipes introduced therein and simultaneously pumping off the liquid issuing at vthe top.

The ,Same Sinking ,memos is alsoY applicable, as`

Vconcrete from below.

shown in Figures 5 to 8, to foundations in open water when required to sink a body produced elsewhere, for example a floating caisson, which is first deposited on the water bed. Since the specific gravity of the thixotropic liquid I is always greater than that yof Water, the thixotropic liquid introduced remains in the cavity between the jacket 2 and the soil 3 and is not washed out, nor does it penetrate into the soil, owing to its thixotropicV properties.

The new sinking method is applicable to any caisson foundation irrespective of whether it is a question of open caissons or of compressed air foundations. Figures 1 to 4 show as an eX- ample a compressed air foundation, while Figures 5 to 8 show an open caisson.

The quantity of thixotropic liquid to be introduced is relatively small and since the cost of producing such a liquid is also low, considerable saving is effected by reducing the crossesection of the caisson side wall or jacket which only has to take up horizontal hydrostatic pressure. Furthermore the Walls and ceiling of the working chamber are substantially lighter, since the vertical hydrostatic pressure required for sinking acts directly above the cutting edges.

A further development of the new process is illustrated in Figures 9 to l2. In this case the cutting edge 4 and the working chamber 5 are again produced at ground level. By dredging out the soil in the working chamber 5, the cutting edge 1i is lowered so far that the curb l of the cutting edge lies below ground level. In the further sinking operation, the thixotropic liquid I is again introduced into the cavity. In contrast to Figures 1 to 8, the foundations shown in Figures 9 to 12 have no jacket provided above the ceiling of the working chamber, the connection to the Working chamber being established merely by an upwardly extended shaft tube 8. The entire space 9 above the ceiling of the working chamber is filled with thixotropic liquid I, and the hydrostatic pressure of this liquid both secures vthe shaft wall against collapse and affords the necessary pressure on the ceiling of the working chamber for further sinking. To ensure uniform sinking of the caisson and to prevent a sudden penetration, for example when soft strata are encountered, the caisson is suspended on cables 6 which, in the case of smaller constructions are secured to bearers laid over the shaft openings, or in the case of larger constructions are suspended from containers I floating in the liquid. When the caisson has reached theV required depth, first the working chamber and then the entire liquid filled space 9 is filled with Experiments have shown that, in contrast to concreting under water, concreting in the thixotropic liquid is as easy as in the air. Above all, washing out and separation of the fresh concrete is avoided.

Figure 13 shows a caisson in different stages of an inclined sinking operation taking place along the curve R. The caisson is constructed in the form usually adopted for straight sinking and is provided at its lower end with cutting edges II. Above the cutting edges I I, the lateral surfaces I2 of the caisson are arranged to project rearwardly, so that the space I3 between these rearwardly projecting lateral surfaces and the soil, and'also the space M' above the ceiling of the caisson, may be filled with thixotropic liquid. When the caisson has been vertically sunk to a predetermined depth, depending upon the loading conditions and the soil conditions, the caisson is inclined owing to the fact that a greater excavation of soil takes place below the cutting edge.y

shown to the right in the drawings than on the opposite side. According to requirements the caisson may be sunk to the required depth at a constant or variable angle of rotation. Preferably, the inclined sinking takes place in such a manner that the line connecting the center points of the individual cross-sections'coincides with the supporting line R of the subsequent structure.

Figure 14 shows a finished supporting wall erected on the obliquely sunk caisson I5. This supporting wall I E, which has an upwardly tapering cross-section, is formed with the aid of forms or shuttering positioned inside the shaft filled with thixotropic liquid. After withdrawal of the shuttering, the remaining spaces I1 and I8 filled with thixotropic liquid are filled with soil or thin concrete.

Figure 15 shows a supporting wall I5 corresponding in its dimensions to the supporting wallY shown in Figure 14. The supporting wall I6 here serves asa quay wall when the soil has been dredged out after completion of the wall. The form I9 of the quay wall on-the air side and water side is adapted to the configuration of the hull skin of a ship. The space 2G on the soil side between vthe quay wall I6 and the soil is filled with thixotropic liquid.

I claim: Y

1. A process` for producing a foundation by sinking a caisson which comprises the step of introducing into a cavity dened between the caisson and the surrounding soil a liquid having thixotropic properties capable of preventing the liquid from penetrating into the voids of the surrounding soil and of causing the liquid to form a fiuid-tight nlm, Vwhereby the liquidiopposes hydraulic resistance to the pressure of the soil.

2. A process according to claim 1 wherein the resistance opposed by the liquid isV so conditioned by the concentration thereof as to support the soil wall of the cavity against collapse by exerting purely horizontal forces thereon and as to lubricate the caisson `and soil wall to eliminate vertical components due to friction as the caisson is lowered.

3. A process according to claim. lfor producing a foundation beneath a body of water which cornprises first sinking the caisson into the soil bed underlying the water until the upper surface of the caisson has penetrated beyond the surface of the bed, providing a hollow shaft above the caisson having a lesser periphery than the caisson thereby to denne a cavity between the shaft and the soil bed, and thereafter introducing into said cavity a thiXotrop-ic liquid having a higher specic gravity than water and colloidal properties sumcient to prevent said liquid from rising out of said cavity and separating off and from penetrating into the soil.

4. A process according to claim l wherein the concentration of thethixotropic liquid decreases from a maximum adjacent the surrounding soil Y to a minimum remote from the soil.

5. A process according to claim 4 wherein the thixotropic liquid of highest concentration comprises a thin layer of a highly concentrated benson to cause lowering thereof at an angle to the vertical.

7. A process according to claim 6- wherein a line connecting the center points of successive positions of the caisson as it is lowered at an angle to the vertical coincides with the pressure line of the foundation to be produced.

8. A process according to claim 6 wherein the angle to the vertical is progressively increased up to at least 90 as the caisson is lowered.

9. A process according to claim 6 for producing a supporting Wall which comprises removing the soil from one side of the wall to expose said side.

10. A process according to claim 9 wherein a film of thxotropic liquid is retained between the 15 adjacent soil and the side of the wall opposite to said exposed side, thereby to distribute soil pressures evenly over the whole surface of said opposite side.

11. A process according to claim 9 wherein said exposed side is substantially complementary in configuration to the hull of a ship.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 961,788 Moran June 21, 1910 2,213,169 Ouchi Aug. 27, 1940

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