US3100381A - Methods of producing caissons - Google Patents

Description

1963 s. E. CASE ETAL 3,100,381

METHODS OF PRODUCING CAISSONS Filed March 22, 1960 4 Sheets-Sheet 1 Aug. 13, 1963 s. E. CASE ETAL METHODS OF PRODUCING CAISSONS fi w E M H mm v e m I a? m w IZ Filed March 22, 1960 3, 1963 s. E. CASE ETAL 3,100,381

METHODS OF PRODUCING CAISSONS Filed March 22, 1960 4 Sheets-Sheet 3 Aug. 13, 1963 s. E. CASE ETAL METHODS OF PRODUCING CAISSONS 4 Sheets-Sheet 4 Filed March 22, 1960 United States Patent 3,100,381 METHGDd 6F PRODUCING QAESONS Stanford E. Case, Glen Ellyn, and James P. Walton, Bartlett, liL, assignors to Case Foundation (Iompany, Roselle, 1th, a corporation of California Filed Mar. 22, 196i Ser. No. 16,722 12 Claims. (Cl. 6135) This invention relates to methods of producing caissons.

In the past most structures have been supported by pilings driven into the earth, by spread footings, or by other conventional types of foundations. Foundations of these conventional types have proven unsatisfactory in many instances. In recent years, it has been found that a greatly improved foundation is achieved by use of caissons which are concrete columns, reinforced if required, extending to suitable depths into the earth for secure support by a load bearing stratum of material, such as bed rock, dense sand, gravel, firm clay or hardpan. Such caissons have been found to be superior to other foundations for many reasons, among which are the elimination of:

(1) Heave and displacement.

(2) Damaging vibrations.

(3) Uncertainties as to load bearing ability.

(4) Danger from impact eccentricity, overturning and settlement.

(5) Out of plumb foundations.

(6) Pile caps.

(7) Back fill and compaction.

(8) Drift of foundation.

(9) Uneven grade of foundation.

(10) Loss of surrounding ground.

Caissons also greatly minimize problems of:

(l) Dewatering in substructure construction. (2) Objectionable noise in construction.

(3) Substructure shoring and bracing.

(4) Variations of water table.

In addition, caissons are substantially cheaper, can be installed much quicker for early completion dates, and are more accurately designed by applied soil mechanics than other foundations. 1

However, prior to the development of the method of our invention, it has been extremely costly and difficult to provide caissons in soil having a layer of sand, sand and gravel or other granular material. In addition, when the water table is present in this pervious material extreme difiiculty is encountered by past used methods. Also, caissons have a low cut-off, i.e., having a top below the surface of the granular material and/ or water table, have presented formidable problems. When it is borne in mind that these conditions are frequently met, it will be appreciated that use of the superior foundation achieved by caissons has been materially limited.

We have developed a novel method which enables caissons to be used economically in granular soil and/ or water bearing soil even with low cut-offs. Caissons constructed in accordance with our method, under such adverse conditions, are less costly, less subject to defects due to caveins and water problems, produced with relatively economical equipment and require less time to produce than previously possible. The method of our invention enables the caisson to be universally used as an economical, safe and sure foundation.

In general, our method of producing caissons is as follows:

A column of earthextending downwardly from the surface is agitated, mixed or stirred to place the earth and granular material in the column in a fluid or viscous state. When necessary, water is added to produce a column of material with the sand and granular material in suspension ice as a slurry. Bentonite or other material having similar properties is mixed into the column of material when and as required to produce a suspension of material having the desired consistency. A column of suspended material is produced to a depth penetrating into a layer of clay or other impervious material. A structural casing is then lowered into the slurry column which easily penetrates the same without use of excessive force due to the lack of resistance of the slurry. This casing is placed in a sealing engagement with the impervious material. The column of material within the casing is then readily removed by any convenient method to produce a water-free and material-free shaft.

When required, a shaft is drilled continuing downwardly through the impervious material until clay, hard pan or rock having sufficient bearing strength is reached. The bottom of the shaft is then belied and cleaned out, if and as required.

An inner form having the dimensions of the finished caisson is then lowered within the structural casing. As hereinafter explained this form may be releasable. The lower end of the form is placed in sealing engagement with the impervious clay. The form is then aligned and secured within the structural casing. Where required, reinforcing steel is placed within the form and lower shaft. Concrete is then poured into the lower shaft and form until filled to desired cut-off level. After the concrete is set suificiently to be self-sustaining, the form, if releasable, is released from engagement with the concrete column and removed, and if not releasable is left in place. After the concrete is completely set and can no longer be damaged by surrounding earth and water, even with a low cut-01f, the structural casing is withdrawn. When necessary, the space between the form and casing is backfilled before the casing is removed.

As will be hereinafter explained, certain of the steps of the above described method are not always needed and various combinations of the individual steps are used, depending on the requirements and conditions.

Among the objects of our invention is to provide a method of producing caissons:

( 1) which enables caissons to be produced in granular (2) which enables caissons to be produced in water or water bearing soil;

(3) which allows use of low cut-ofi in adverse soil conditions;

(4) which enables accurate placing of reinforcing steel, dowels or anchor bolts and maintains these in place after the casing and/ or form are removed;

e (5) which prevents damage to the caisson after the concrete is poured;

( 6) which produces caissons freefrom faults and defects;

( 7) which does not require the use of extremely expensive equipment;

(8) which allows caissons to be produced faster and cheaper than heretofore possible;

(9) which produces caissons that are free from defects due to damage produced by water and loose soil;

(10) which allows all forms and casings to be recovered for re-use;

(11) which allows all operations to be performed from the surface; (12.) which allows universal use of caissons in almost all soil conditions; and (13) which allows a structural, sealing casing to be lowered through granular material with a minimum of force. These and other objects and advantages will become more readily apparent as the description proceeds and is read in conjunction with the accompanying drawings in V which:

FIG. 1 is an elevational view showing a typical cross section of the earths surface;

FIG. 2 is similar to FIG. 1 but shows a column of suspended material which has been agitated and to which bentonite and water have been added;

FIG. 3 shows a structural casing lowered into place; FIG. 4 shows the suspended earth removed from the I structural casing and the lower portion of the shaft comcaisson completed.

Referring to FIG. 1, a cross sectional view of the earths surface is shown, and it should be appreciated that many variations in the stratum occur., The particular terrain of FIG. 1 is merely illustrative. The earth formation shown olfers serious problems to the use of caissons because of the presence of sand and water above the impervious stratum.

In FIG. 1, the surface layer is designated at it and generally comprises surface clay, black dirt, sand fill and other materials. The surface layer is usually quite thin. Below the surface layer is a stratum of granular material, such as sand and gravel and various mixtures of dirt, silt, sand, rocks, etc, hereinafter referred to as sand layer 12. An impervious soft to firm clay layer 16 is next encountered and this clay becomes more dense as the depth increases until a stratum of hardpan 18 results. Hardpan is a compact firm material having excellent bearing propertieson which a caisson may be supported. Water is frequently present in sand 12' 'and, for purposes of illustration, we have indicated the level of the water table by dotted line 20. V 7

As an example only, in Chicago, Illinois, near Lake Michigan, the various layers may have the following depths: Surface layer 10 from 1 to 10 feet; sand layer 12 from to 30 feet; clay layer 16 from to 60 feet; and hardpan 18 will extend down to bed rock. The depth of the completed caissons of the type we contemplate will usually vary from 20 to over 100 feet.

If an open excavation is made in sand layer 12, cavein continually occurs. In addition, the presence of water in the sand will cause any excavation to fill with water and sand. The situation is likened to digging a hole in a sand beach near the edge of the water.

Sand 12 has'no cohesion but offers substantial resistance to driving a casing or any other'member through the sand due to compaction of the sand and friction against the driven member. Very powerful and expensive driving equipment would thus berequired. To overcome this problem and allow easy placement of a casing, layers 10 and 12 are placed in suspension.

Producing Suspended Column able on the job site. For purposes of illustration, we have shown an auger bit 28 in FIG. 2.

In order to produce suspended column 22, auger bit -28 is placed in position and rotated while being fed up can be added from source 24..

in many soils, the addition of WHitl and agitation will not produce sufiicient suspension of the granular material. For example, in pure sand, a mixture will be created by agitation in the presence of water, but very rapid settlement of the sand follows when agitation stops and sufiicient time is not available to allow placement of a structural casing. In these conditions, bentonite or other similar product isxadded to produce material that will remain in suspension for ample periods of time.

Bentoniite'is the general term used to identify montmorill'onite clays or acid treated natural or activated clays, which are very hygroscopic. Thus bentonite has the ability to absorb large quantities of water and swells and enlarges on such absorption. Small amounts of bentonite mixed with water will produce a mass having the consistency of grease, and smaller amounts of bentonite added to Water will produce a viscous slurry. Bentonite is a type of montmorillonite clay. There are three main classificaitions'of clay with several main variations each. Many of these will suspend sand and can be successfully employed. Bentonite is thiotropic (gels and urigels without fatigue).

Bentonite when mixed with water and sand forces the faces of granular material away from each other and reduces the angle of cohesion and removes the shear resistance from the formation. This enables a casing to pass readily because the friction in the material has been minimized. In some cases, the clay that is present on the job site may be used to produce the suspension. The terms bentonite, thixotropic compounds aud/ or absorbent compounds are used herein to generically mean all materials having the necessary properties for use in our process.

When bentonite and water are stirred into layers 10' and 12, the sand and other material are suspended in the slurry. After complete mixing, the drilling can be stopped for considerable time before the sand will settle out of suspension. It should be appreciated that materials ther than bentonite may be used to produce the desired Referring to FIG. 2', we have shown a column of suspended material, generally designated 22. This column of suspended material is' produced by mixing, stirring tor agitating the material in the column. Generally the addition of water is required and we have schematically indicated a water source at 24. Also it is generally required that bentonite or other material of required properties be added to the formation and a source of bentonite is indicated at 26. 7

While many methods can be used to agitate the earth, the most convenient method is to use a conventional auger bit. As will hereinafterappear, these bits and operating equipment may be used to complete the excavation of the caisson through the lower clay layers and thus are availr viscous mass.

- The bentonite and water may be added at the surface and are worked downwardly into the soil by combined rotary :and vertical movement of the bit. Also, the bentonite could be added below the surface by pumping it through the hollow core of a kelly to the bit. By these methods, columns up to 40 feet or more deep can be suspended in about an hours time, and ths column will remain in proper suspension to receive casings for a sufiicient period of time. The column of suspended material will exert sulficient pressure against the surrounding said to prevent its collapse into the mixture and this is enhanced by keeping the level of the mixture in the shaft quite high.

It is quite important, as will hereafter appear, to extend the suspended column a short distance, such as one 1) foobinto impervious clay layer 16, and the reaching of the impervious clay layer is evidenced by the presence of solid clay on bit 23 when it is surfaced.

The diameter of column 22 is greater than the diameter of the finished caisson and greater than the diameter of the structural casing, and this is of course controlled by selecting a proper size for bit 28. Usually the diameter of column'22 is about one 1) foot larger than the structural casing allowing a six (6) inch clearance on each side.

7 Positioning Structural Casing Referring to FIG. 3, a structural casing 3% is shown in place. Casing 3b is lowered into column 22 from the top. Since the earth is suspended, there is no :appreciable compaction of the earth below the bottom edge of the casing, due to the viscous nature of column 22 which is simply displaced by the casing. In addition, no appreciable drag or frictional forces will be exerted by the slurry against the faces of casing 30. Only relatively small force is required to push the casing into place and the force is suffi ciently small to not exceed the force that can be exerted by the crowd mechanism of the standard drilling rig. When casing 30 reaches the bottom of column 22, the casing is pushed from the top until bottom edge 32 of the casing penetrates a short Way into unagitated impervious clay 16 to provide sealing engagement in the clay. If the impervious stratum below is rock, the casing may have teeth on the lower end and can then be rotated and ground into sealing engagement with the rock.

The wall thickness of casing 38 will depend upon ground conditions as will the length of the casing. Normally, at least a /2" steel casing will be used. The diameter of the casing is normally 1 foot larger than the desired diameter of the finished caisson. The length of the casing will be sufficient to reach the impervious founda tion, and the top of the casing will usually be at ground level or above.

Removing Suspended Material From Casing After casing 30' is in place, the suspended material within the casing is removed in any convenient manner. This may be done by bailing buckets, drilling buckets, pumps, jets, auger bits, etc. Usually we prefer to bail out the material with a sand bail that fits within casing 39. In FIG. 4, the slurry within the casing has been removed.

Producing Lower Shaft With casing 30 emptied, the remainder of the shaft may be formed without any water or cave-in problems, since lower end 32 of the casing is sealed in clay 16. Since the lower part of the shaft will be formed through self-sustaining impervious formations, an auger bit, drilling bucket or the like will be used of a size the same as the final caisson. When the shaft reaches material having proper load-bearing characteristics, the drilling is terminated. The lower shaft is designated at 34 in FIG. 4.

It is the usual practice in hardpan to hell the bottom of the shaft since this gives a larger bearing area and increases the load that can be carried by the caisson. In addition, the bottom of the shaft should be cleared of loose material. A 60 bell as is shown in FIG. 4.

.With improved belling equipment, it is possible to complete the cleaning and belling of the bottom without sending men down into the shaft. However, if it is necessary to send a man into the shaft, the method we use affords protection against cave-ins and greatly minimizes the danger. V I

It should be clearly understood that in some instances casing 39 extends to the bottom of the caisson. If, for example, clay 16 has adequate bearing properties or if rock lay beneath sand 12, no lower shaft would be needed. In these conditions, the remainder of the process still applies.

Placing Form As seen in FIG. 5, a form 38 is next placed within structural casing 36. Form 38 may be of thin metal or other material and is of the same diameter as the completed caisson. For example Ms or less steel may be used on the form. The lower end 41? of the form extends down below the end 32 of structural casing 30, for example, 1 foot will usually sufiice. Since the lower shaft and form 38 are of the same diameter, a seal will be pro vided between the clay 16 and form 38 at the lower end. In some instances, it may be. necessary to flare the bottom of the form or pack around the form. The upper end 42 of the form is at or above the desired top elevation of the completed caisson. This top elevation of the caisson is called the cut-off and, as shown in the drawings, the caisson is to be provided with a low out-off, i.e., below the surface. In particular, the cut-off is in the sand layer 12 and below Water table 20. It should be understood that form 38 can extend up beyond the cut-off without interfering.

Form 38 may be a one-piece form which remains in place on the caisson after it is completed, or as shown in the drawings, it may be a releasable form that can be recovered for re-use. economy dictates that we prefer to recover the form for re-use, and this constitutes one of the several important features of our new process. Our new method allows recovery of the forms as will be hereinafter explained.

Form 38 is substantially less in diameter than casing 39 so a space is provided therebetween. This allows space for the form release operating mechanism and also allows space to plumb or align form 33, even if casing 35 is out of alignment. Normally form 38 is about 1 foot less in diameter than the structural casing.

The use of an inner form constitutes a very important feature of our invention with resultant advantages, as will hereinafter appear. It is necessary that form 38 be properly aligned to conform to the desired position of the finished caisson. In the illustrated case, since the caisson is to be vertical, form 38 is plumbed in place. Also form 33 must be securely held in place; otherwise, an unsatisfactory caisson would result. Even though casing 3i} may be out of plumb it offers a very good support for form 38, and enables both proper alignment and support of the form.

As shown in FIG. 5, form 38 has its lower end held in place by engagement with the impervious material.

Placing Reinforcing Steel The specifications for most caissons require the use of reinforcing steel, dowels or anchor bolts. In FIG. 5, we have shown reinforcing steel 44- placed within form 39 and lower shaft 34. This reinforcing steel 44 is held in place by conventional means within form 38 to reinforce the caisson when completed. Reinforcing steel 44 is easily placed from the surface and the casing 31} and form 38 do not interfere with their placement.

It should be appreciated that form 38 serves an im: portant function in that it provides a solid support to enable accurate placement and support of the reinforcing steel. As will hereinafter more fully appear, the re inforcing steel is never subject to displacement with the method of our invention.

Pouring Concrete The caisson can now be completed by pouring concrete and FIG. 5 shows the shaft ready for such pouring. The completely poured caisson is shown in FIG. 6 and the concrete designated at 46. This concrete is poured in from the surface by the free-fall method Since forms 33 are expensive,-

, removal, of the casing.

the form 38 to prevent or make dillicult its removal.

' In addition, the concrete must not penetrate or push itself into, the area outside structural casing 3% which I would foul its removal. This latter is prevented by first the seal between form 38 and shaft Sid-and then by the seal between clay is and lower end 32 or casing 3d.

The pouring is completed when the level of concrete reaches the cut-off, which in this case is shown to be the top of form 38.

As shown in H6. 6, dowels 45', or anchor bots, are

now inserted in the concrete. Accurate placement is assured by the use of a template which is placed by precise measurements.

7 Removal of Form After concrete 46 has set sufficiently to have the caisson self-sustaining, which will usually require about 24 hours, when desh'ed, form 38 can now be removed. .Due to the fact that casing 30 remains in place, deleterious material will not contaminate the fresh concrete and no damage from cave-ins or water will result to the partially set caisson'by removal of the form.

As seen'in FIGS. and 6, the release mechanism of form 38 is operable from the top and the space between casing 39 and form 38 allows room for the release mechanism. Form 33 is made in two semi-circular pieces which are held together by locking pins 27 that pass through overlapping pin sockets 4i Sockets 49 are spaced along form 38 andr'o'r each pair of overlapping sockets ,one is attached to'e ach'of the form halves. ,Pins 47 vmay be pulled from material. This backfill usually extends to the surface of the ground within casing 3% and is generally indicated at 48 in FIG. 7. The bacltfill operation is doneonly after sufficient time has elapsed to prevent damage tothe caisson. 1 The importance of the use of a casing and form can now be appreciated :Eully. When the form is removed or lefit in place, the casing completely protects the caisson against any damage until the concrete sufficiently sets. In the" past this has always been a serious problem. In

;addition, if cart-h or water is allowed to cave in' against the unhardened concrete in the caisson the reinforcing steel and dowels are frequently displaced and these must be maintained in proper position. Furthermore" earth or water contact may weaken the caisson. Also the concrete never has an opportunity to drop in level by entering voids around the caisson because :form 38 pro- 1 V tects against this until the concrete is sufiiciently set and because casing 3t) remains in place. Any serious disturbance in the concrete will cause damaging displacement of the reinforcing steel and dowels.

Removal of Structural Casing IAfter concrete 46 has set sufficien-tly not to be damaged by contact with deleterious material, which may require from 1' to 4 days, casing 30 can now be removed Since there isonly loose fill material contacting the inner lace of'casing 36, the irictionalresistance to withdrawal is substantially lessened. In addition, the surrounding even after several days so no great resistance is ofiered to It should the appreciated that the suspended-material. is thixotropic and returns to a viscous state on vibration and impact. The casing is simply pulled up by readily available lifting equipment. In FIG. 8, we have shown the casinglltl removed. It

p and removing the form are eliminated.

will be noted that the surrounding earth will not cave in and. subside due to the backfill. In some areas subsidence of the surrounding earth does not matter and in this condition the backfill can be eliminated. The earth will later be excavated below the cut-olf level for other substructure work and the caisson will be exposed.

When form 38 is to remain in situ, the steps of releasing In this case, concrete 46 is allowed to set sufficiently so that it will not be damaged by deleterious material nor will the reinforcing steel and dowels be displaced. Then casing 3t? is removed as previously explained and the caisson is completed, with the form remaining in place about the caisson.

It should be appreciated that we have described preferred ways of practicing our methods as required by statute, but changes and modifications may be made in the methods, and certain steps added or deleted without'departiug from the scope of the appended claims. The particular conditions that are encountered will determine what exact steps are necessary.- For example, our novel method is applicable to work done in rivers, lakes or other bodies of water. Under such water conditions, the structural casing may be placed without the necessity of producing a suspension, since water offers no resistance to positioning the structural casing.

Having described our invention, we claim:

1 The method of producing a caisson comprising the steps of mixing a'column of earth in situ and in the presence of water, adding thixotropic compound to the mixed earth and water to produce a suspension that will remain in suspension a substantial periord of. time and which is of suificient density to support surrounding earth, said suspension being extended to impervious material, placing a casing into the suspension to the impervious material, removing the suspension from within the casing, digging a shaft downwardly in the im pervious materialcbelow the casing to bearing earth material, placing a form in said casing extending to said shaft, and placing-concrete insaid shaft and form.

2. The method of claim 1 including the steps of sealing the lower end of said casing into said impervious material, and providing sealing engagement between the lower .end of said form and said impervious material.

3. The method of claim 1 including the stepsof first releasing saidform lfrom said concrete and removing said form from said casing when said concrete has 4. The method of claim 1 including the step of removing said casin" after said concrete has set. 5. The method of claim 1 including the step of sealing the lower end of said casing into said impervious material. 7 o

6. The method of claim 1 including the steps of placing reinforcing steel in said form and removing said casing after said concrete is set so that said steel remains in propel-placement.

. 7. The method of claim 1 including the step of positionin'g and holding said rein-forcing steel within said 7 form.

.8. The method of claim 1 including the steps of placing the thixotropic compound on the'surface of the earth and moving this compound downwardly into the column.

9. The method of producing a caisson in earth having a sand layer above an impervious layer and wat er within the sand, comprising the steps of mixing the sand 7 material will readily lbecome viscous on being disturbed in situ and in the presence of water, adding thixotropic compound to the mixed sand and water to produce a suspension that will remain in suspension a substantial period of time and which is of sufiicient density to support surrounding sand, said suspension extending down to said impervious material, lowering a casing through said suspension to said impervious layer, emptying the suspension from the casing, digging a shaft into said impervious layerbelow said casing, placing a form in set, and removing said casingafter said concrete has .set.

said casing aligned with said shaft and the lower end being in engagement with said impervious layer, pouring concrete into said shaft and form to the height desired, releasing said form from said concrete when said concrete is self-sustaining, removing said form from said casing, and removing said casing from the earth when said concrete has sufliciently set.

10. The method of claim 9 and including the steps 0 sealing the lower ends of said form and easing with said impervious layer, fbelling the ibOttOl'Il of said shazflt after it is dug, cleaning the bottom of said shaft, and placing reinforcing steel in said form and shaft before said concrete is poured.

11. The method of producing a caisson in earth having a sand layer above an impervious layer, comprising the step of mixing the said in situ and in the presence of water and thixotropic compound to produce a suspension that will remain in suspension of substantial period of time and which is of suflicient density to support surrounding sand, said suspension extending to said impervious layer, lowering a casing through said suspension to said impervious layer, sealing the lower end of said easing into said impervious layer, emptying the suspension from the casing, digging a shaft into said impervious layer below said casing, placing a form in said casing aligned with said shaft, said form being in sealing en- 10 gagement with said impervious layer, pouring concrete into said shaft and form to the height desired, and removing said casing when said concrete has sufficiently set.

12. The method of claim 11 and including the step of placing reinforcing steel in said form and shaft before said concrete is poured.

References Cited in the file of this patent OTHER REFERENCES Engineering News-Record of Sept. 9, 1937, pp. 434 and 436.

Volclay, American Colloid -Co., Chicago, Ill. Data No. 229Supp. A, page 1. Received in Patent Oflice Nov. 6, 1941.

Claims (1)

1. THE METHOD OF PRODUCING A CAISSON COMPRISING THE STEPS OF MIXING A COLUMN OF EARTH IN SITU AND IN THE

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