US2233872A - Means and method for solidifying underground structures - Google Patents

Description

March 4, 194,1- R. R. PRocToR MEANS AND METHOD FOR SOLIDIFYING UNDERGROUND STRUCTURES Filed July 27, 1936 2 Sheets-Sheet l AY 1 focrofz, @im A c.. f

March 4, 1941. R. R. PRocToR MEANS AND METHOD FOR SOLIDIFYING UNDERGROUND STRUCTURES ,2 Sheets-Sheet 2 Filed July 27, 1956 1M... Q uEwEu/, .../u1..

Patented Mar. 4', 1941 PATNT oFFlcE MEANS AND METHQD FOR SOLIDIFYING UNDERGROUND STRUCTURES Ralph B.. Proctor, Glendale, Calif., assignor to California Talc Company, Los Angeles, Calif., a corporation of Delaware Application July 27, 1936, Serial No. 92,750

.6 Claims.

This invention pertains to a method and means for solidifyingunderground structures, such as porous or broken formations. Such solidiiication may be necessary or desirable in order to stop seepage ofv water or to render the ground formation solid so as to be able to support foundations for building structures or for any other purpose where porosity of the ground structure is objectionable.

It has been proposed to ll the pores as passages of the ground structure, for instance, adjacent to wells or the like by pumping into the ground a grout mixture sometimes containing cement with the purpose that upon setting the grout will close the passages. When a cement grout alone is used the process often fails of its purpose because the cement mixture in setting shrinks in volume. This is due to the fact that the cement settles somewhat before setting so that when set and dry an opening still remains in the structure.

It has also been proposed to ll such structures with a grout containing cement and a colloidal clay, such as bentonite, which has the property of preventing the settling out of the cement before setting and also of rendering the nal structure waterproof. In the method thus proposed, it has been the purpose to provide a grout which will form a solid concrete, quick-setting and of increased strength as compared with ordinary cement. In some methods the purpose has been to provide a grouting mixture of relatively high viscosity so that when forced into the ground crevices or passages, it will tend to plug the opening before penetrating into the passage to a great distance. These methods have the defect that on account of the quick-setting property of the grout used, the operation must be rapid and the mixture must frequently be renewed by wasting the old portion before it sets. It is also an objection to these methods that the mixture sets with extreme hardness so that if subsequent settling or movement of the ground should occur new passages may be opened up.

It is an object of the present invention to provde a method and a medium for grouting underground formations whereby the objections to former methods outlined above may be overcome.

Another object is to provide a method and a medium such that the grout may be caused to penetrate the porous formations to a great distance in order that the porous structure may be converted into a solid, practically continuous structure to a considerable distance from the point at which the operation takes place.

Another object is to provide a medium which will be slow setting so that it may remain liquid for a sumcient time to accomplish penetration of the porous structure to an increased distance. Another object is to provide a method whereby the grouting medium may be maintained in circulation, the consequent movement being effective ing ground formations in order that, if settling or movement of the ground should occur, the grouted portions may follow the movement in a manner similar to that of the natural parts of the formation. i

Further objects will appear from the following description taken in connection with the accompanying drawings, in which:

Figure 1 represents a vertical section of a portion of the earth illustrating the manner in which underground structures may be rendered solid by pumping a solidiflable medium thereunto, to-g gether with the apparatus for carrying out the method;

Figure .2 is a detail of the regulating valve of the apparatus of' Figure 1;`

Figure 3 is a plan view of aportion of the ground surface intended to illustrate the manner of carrying out the method of this invention in preparing for the construction of a dam or the like;

Figure 4 is a vertical section of. a tunnel showing the application of this method to such structures; and

Figure 5 is a diagrammatical view representing a vertical section similar to Figure 1 illustrating apparatus whereby this invention may be practiced by the use of compressed air instead of a pump for circulating the medium to the porous stratum.

In accordance with the present invention, earthy formations, whether composed of clay or rock, are grouted with a grout composed of cement, water, and a gel. The gel may be an' one, or a mixture of', a great variety of materials ,capable of forming a gel with water, for instance, colloidal clay, sodium silicate, starch, gum arabic, gum tragacanth, gelatin, agar,l soap and pectin. Sufficient of the gel is employed to prevent the water of the grout from -deserting the cement. therein until the grout is finally in position. Such a grouting mixture may be injected into the earthy formation in any suitable manner, for instance, under pressure suillcient to cause it to penetrate and illl the ssures and crevices of the formation.

A colloidal clay, such as bentonite, is particularly useful as the gel ingredient of the grout constituted in accordance with the present invention. While .the employment of small quantities of bentonite together with cement has heretofore been found to expedite the setting of cement, the present invention contemplates the employment of 5% or more of bentonite based upon the dry weight of the solid constituents in the grout, that is to say, for instance, in a grout composed of cement, bentonite and w-ater without sand, one part of bentonite to nineteen parts of cement maybe employed, or greater bentonite to cement ratios may be employed in order to meet xthe conditions desired and to cause the grouted formation to approximate the character of the original formation.

In the practice of the present invention, the gel, while to some extent increasing the viscosity of the grout, nevertheless, facilitates the injection of the grout into the formation on account of the lubricating property of a gel. A very advantageous feature of the present invention, however, resides in the fact that greater proportions of water may be employed per given weight of cement than is possible without .the use of the gel in the grout. The employment of the gel, such, for instance,as bentonite, prevents the Water from 'being forced away or deserting the particles of cement as the grout mixture is being forced into a ilssured formation, and consequently, not only is a substantially greater volume of grout obtainable from a given quantity of cement, but, when a gel is employed with the cement, the user may be assured that the cement 4particles have been forced to the extremity of the fissure and not deposited close to the point of injection as is frequently the case when the ordinary water-cement grout is employed.

In making the grouting mixture in accordance with the present invention the cement and gel, such as bentonite, may be mixed together dry in the desired proportions and thereafter hydrated with the desired amount of water, or, as is frequently the more convenient Iprocedure when fthe grout is compounded upon the site of application, the bentonite may rst be hydrated with the desired amount of water so as to produce a gel and the dry cement added to the gel in the vclesired proportion. As an illustrative example of a grout which may be employed with advantage in the grouting of earthy formations, such as clay or ordinary soil and where the set grout will have substantially the same hardness as the natural earth, the grout may be composed of as follows: to each sack of cement (94 pounds) add 62.6 pounds of bentonite and incorporate with 60 gallons of water. This results in a volume of 8.90 cubic feet for each sack of cement, the bentonite present constituting 9.5% of the total weight, the cement 14.3% of the total weight and the water 76.2% of the total weight. A grout constituted in this manner required two lweeks for itsinitial set and was not nally setat the expiration of lthirty days.

As another example in which the grout is so constituted as to have somewhat greater compressive strength than in the previous example but still usuable for grou-ting such formations as clay or soil because the strength thereof is as great and not substantially greater than the natural formations, the grout may .be constituted as follows: use one sack of cement (94 pounds) incorporated with 40 pounds of bentonite and 40 gallons of water. The resultant mixture will have a. volume of approximately 6.07 cubic feet and will be composed of 20.0% cement, 8.5% bentonite and 71.5% water. Such a grout had taken its initial set in six days but at the expiration of one month the nal set had not taken place.

As illustratingv a grout which is adaptable for use in grouting either clay or rock formations, the following proportions may be employed. One sack of cement (94 pounds) is incorporated with 30 pounds of obentonite in 30 gallons of water. This results in a grout having a volume of 4.68 cubic feet, the bentonite constituting 8%, the cement 25% and the water 67% 0f the groult. This grout took on its initial set in three days and had finally set at the end of one month.

The present example may be regarded as suitable for an all-purpose grout, while 4for the grouting of panticular types of formations, some of the other examples may be superior in some respect over the others.

As illustrating a grout which is particularly useful in .the grouting of rock and stone formations, it may be constituted as follows: one sack of cement incorporated with `1'7 pounds of bentonite and 20 gallons of water. Such a mixture produces 3.26 cubic feet ofgrout and is composed of 6.1% bentonite, 33.9% cement and 60% Water. The grout of this example had taken on its initial set in three days and its final set in two weeks.

In connection with the foregoing examples it will be observed that if the amount of bentonite in the respective mixtures is decreased, .the quantity of water employed is likewise decreased. It will be understood, however, that fthe higher the percentage of bentonite in the grout, the lower the strength of the resultant grout, but the higher the percentage of bentonite, the greater the volume of Ithe grout obtainable from one sack of cement. In any case, enough bentonite and enough Water will be employed to grout the fory tem and readily pumpable.

While in the foregoing descriptions reference has been made specically to the use of a grout composed of various proportions of cement, bentonite and water, it is to be understood that sand or other fine aggregate may be incorporated with the grout in either of the cases in order to extend the grout or to achieve characteristics desired in the set grout.

As illustrating the manner of employing the grout of the present invention, reference may be had to Figure 1 in which I represents the surface level of the ground and 2 represents fissures or passages in the ground structure along which seepage of water may occur. A hole 3 may be a well drilling, or it may be sunk simply for the purpose of reaching the fissures 2. The upper portion of the hole may be enlarged to receive a casing 4 which 'is preferably cemented in by means of cement 5 according to any well known procedure. This is in order to seal the casing into the ground at the surface level. An inlet pipe 6 is lowered within the casing 4 to near the bottom of the hole 3 and at its upper end is connected to a pump 'l whereby the grouting material may be pumped into the pipe 6. The

8 for delivery to a storage tank 9 connected by a supply pipe I to the pump 1. n

On account of the freely flowable nature of the grout mixture a pressureof 30 to 50 pounds .per square inch is ordinarily sufiicient to obtain satisfactory results. With such low pressures there is less danger of lifting the ground formation and thereby producing more cracks, as may be the case with more viscous mixtures requiring high pressures to force them into the fissures.

When the system is started in operation the pump 7 delivers the group mixture from the storage tank 9 by way of pipe 6 to the bottom of hole 3. The liquid rises in this hole and passes into the passages 2. A sumcient amount of liquid is provided so as to i'lll the hole 3 and the casing 4 and to flow out through a return pipe II back to the storage tank 9. Arranged in the pipe II is a pressure regulating valve I2 of any suitable design adapted to maintain the pressure substantially constant. A pressure gage I3 may be connected in the pipe II so as tol indicate the pressure maintained. The system is maintained in operation so as to keep the liquid circulating through the pipe 6 and up through the casing 4 back to the storage tank 9. This action maintains the entire body of liquid in movement or agitation upto the point where it enters the crevices 2. Such movement tends to `prevent the setting of the material and keeps it always properly mixed so that it may iiow readily into the crevices so long as the same remain open to receive a flow. After the material has penetrated to a considerable distance along the passage 2 under the pressure maintained on the system, the distant portion thereof will begin to set. 'Ihe setting will take place at different portions successively along the passages 2 toward the hole 3. Accordingly, a pressure of new material is maintained on the grout so that the passages 2 are maintained completely filled under pressure until setting actually takes place. Accordingly, the grout material will be supplied in suilicient quantity to completely ll the passages, Which material swells upon setting so that such passages will be effectively plugged, seepage of Water entirely eliminated, and the ground formation solidied so as to counteract any tendency to settle.

Arrangements are provided whereby indications may be obtained to tell when the ground ssures have been completely closed. As shown in Figure 1, a pressure gage 45 is connected to the inlet pipe 6 to indicate the pressure of grouting fluid as it enters that pipe. As stated before, the fluid, however, circulating through the hole returns to the storage tank 9 by way of the pipe II. A' shut-off valve 46 in the pipe Il may be closed after a certain period of operation in order to determine whether or not the ground fissures have been completely plugged. With the valve 46 closed, and the pump I operating. a pressure is maintanled on rthe grouting liquid in the hole, the excess liquid being returned to the tank 9 by way of a bypass 41 controlled by a relief valve 48 similar to the valve I2. With the pressure thus maintained on the grouting liquid in the hole, the pressure at the entrance is indicated by the gage45. The pressure of the grouting liquid after rising in the casing 4 is indicated by the gage I3. If there is a difference in pressure indicated by these two gages 45 and I3 it will be evident that there is a ilow of material into the hole. The amount of the excess pressure indicated by the valve 45 over that of the valve I3 will be an indication of the rapidity of flow of the material. A rapid ow will indicate that the passages are still wide open,

lwhile a slow flow will indicate that they are final plugging is attained. In order to maintain the operation under such a slow flow for an extended period a modified arrangement of apparatus may be employed which arrangement will now be described.

Other methods of passing the grouting mixture to the porous stratum may, of course, be used. In Figure 5 is illustrated an arrangement whereby compressed air or similar medium is employed to pass the mixture down to the porous stratum. In this gure 26 represents a pressure tank adapted to contain a supply of the grouting medium and connected by a conduit 26 to the pipe 6. An air supply connection 21 controlled by a valve 2B is arranged to introduce air pressure on the surface of the medium in the tank 25 so as to force thesame down the pipe 6. A second tank 29 similar in all respects to the tank 25 is connected by a conduit 30 to the casing 4. This tank is also connected by a conduit 3I controlled by a valve 32 to a source of compressed air supply indicated at 33. The tanks 25 and 29 may be equipped with air relief valves 34 and 35, respectively. Similarly the conduits 26 and 30 may be provided with control valves 36 and 31. The ca sing l may be provided with a valve controlled waste outlet 38. The pipe 6 is preferably connected with a valve controlled water inlet 39.

In operating this embodiment the air pressure is admitted to the tank 25 so as to force the grouting medium from said tank down the pipe 6 and into the hole. The circulating medium passes up the casing 4 and through the conduit 30 and into the tank 29, the air valve 35 beingopen and the air valve 32 being closed during this part of the operation. This circulation continues until nearly all of the grou-ting fluid has been expelled from the tank 25.- The operation is then interrupted sufficiently to close the valves and 28 and to open the valves 34 and 32. This permits air to exhaust from a tank 25 and supplies air pressure to the -tank 29. As a result the direction of circulation is now reversed, the medium passing from the tank 29 through the conduit 3Q and down the casing 4 to thebottom of the hol`e,then up the pipe 6 and back .to the tank 25., This operation may be continued as long as necessary, the direction of circulation being reversedlVr periodically whenever the liquid is nearly all expelled from one tank or the other. Additional grout mixture can be introduced through valves 34 or 35, if required.

The procedure just described is of advantage where the grouting operation must extend through a long period. It has been desirable to continue the grouting operation so long as there is any indication that the ground passages have not all been l closed. In order to determine whether or not any passages are open, the operation may be interrupted and the hole washed out by admitting vwater at the connection 3l, the valves 36 and 31 being closed and the waste water being discharged at the connection 38. After a thorough washing the connection 38 may be closed by its valve, while the water pressure is maintained.r A pressure gage is connected to the pipe 6 and a second gage 4| is connected to, the `casing 4. Comparison of these gages while the water pressure is maintained will indicate whether or not the passages are all closed. If the gage 4i reads less than .the gage 40, it indicates a seepage, the difference in pressure being due to the resistance to flow in the pipe 8. This test may be made at any desired interval during the operation untia complete closure is finally indicated.

Figure 3 represents a plan view of a portion of the ground where a dam is to be constructed. The lines I4 represent contour lines indicating a valley at the center of the `figure. In this valley a dam is indicated at i5. In preparation for .the building ofa dam the present method may be applied by sinking a series of holes l at suitable` intervals along the broken line A-A. It will be seen that this line of holes is extended from such a level on each side of the valley as will be above the crest of the proposed dam. downwardly to the bottom of the valley and up on the other side to a similar level. The grout may then be pumped into the ground at each one of these holes in the manner described in Figures 1 or 5. In this manner it may be insured that all seepage passages within the reach of the operations carried out, as determined by the number and depth of Ithe holes 3, will be suitably filled with grout and effectively plugged so as to prevent any possibility of water seep'ing therethrough past the dam.

.This method may also be Aused in order to insure that the dam structure is positively bonded with the ground formations upon which itl rests by applying the grout so as to ll any cavities which may possibly appear between the two. 'I'his applies tothe foundation as well as to the side abutments of a dam where such are used. In fact by this grouting method a substantially monolithic structure may be formed of the dam and its supports and abutments.

In Figure 4 a tunnel is illustrated in which I6 represents the concrete lining and Il the temporary lining supported by [blocks I8 against the rock structure. A seepage passage 2 .is shown which may be reached by pipe 6 to which the pressure apparatus, shown in Figure 1', may be attached where it enters the lining of the tunnel. In this case the grout may be pumped in directly or it may be circulated, as described, in connection with Figure 1, an enlarged hole and casing 60 being provided surrounding the pipe 8 as indicated in dotted lines. The space between the vlining I6 and the rock may be filled with grout I9 .b'y means of passages 20 and a vent opening 2i.

It will be seen that this invention provides means for controlling the now of ground water in a simple and effective manner. By the addition of a suitable proportion of bentonite, a grout mixture 'is obtained which remains uid for a Agreatly extended time. This'enables a full quantity of the material Y.to be pumped into the crevices before it tendsto set and greatly increased penetration is thereby obtained. 'I'he material is circulated so as to keep it in agitation throughout that' portion whichvhas not yet entered the ground formation, the liquid being fluid a moderate pressure is sufficient to cause it to penetrate a suilicient distance.

This invention also provides an eii'ective method whereby porous or imperfect ground structures may be rendered solid for the purpose of supporting foundations and such foundations may be solidly connected with the supporting formation by the use of this grouting method. Not only in new structures but in situations where the ground has settled away from the vfoundation of an old structure, the same may be rendered safe and, if necessary, waterproofed by the use of this method. f

Another use wherein this invention nds application is in solidifying ground structures which are broken up through theirstructure as distinguishedfrom structures which simply contain fissures or the like. For instance in certain types of very sandy soil or where the structure consists of decomposed rock in more or less finely divided form the use of the present method is of considerable advantage in which in treating such structures a mixture of bentonite and cement in substantially equal proportions may be pumped into the structure in accordance with this invention. The operation may be carried out in such a manneras to iill the voids as completely as possible with the bentonite. This mixture upon -final setting will then render the ground structure practically solid and suitable for foundations or other purposes. This method may be applied for instance in rolled filled dams and in other types of fill where it is desirable to solidify the entire structure.

Ihe material which has entered the ground formation does not shrink or settle upon setting but swells sumciently to force itself rmly against the bounding walls of the crevices so as to completelyilll the same. This is effective in obtaining av complete seal-immediatelyv or upon the first application of the grout.

y The nature of the grout is such that upon setting it forms a material closely resembling the surrounding clay in its strength and texture, the proportion of bentonite being properly adjusted for this purpose. In harder formations a different proportion of bentonite may be used such as to provide a harder structure uponsetting. As a result the structure left in the ground after grouting may be nearly homogeneous, or at least, of a substantially uniform strength. Accordingly, in settling, the presence of grout does not interfere with the shifting movements.

It will be understood, of course, that various changes in the methods of precedure as well as in the particular proportions of the material may be made within the'scope of the appended claims andlwithout departing from the spirit of this invention; it is to be understood, therefore, that ythis invention is not limited to the specific details shown and/or described.

Having thus described the invention, what is 'claimed is: y s

1. In the art of solidifying porous strata, the process comprising, subjecting a porous stratum to an initially freely owable but nally settable hydraulic cement mixture while agitating. that part of the mixture extraneous of the stratum.

2. In the art of solidifying porous strata, the process comprising, subjecting a porous stratum to an initially freely flowable and slowly but flnally settable hydraulic cement bentonite mixture while the mixtureA is maintained under pres- 5. ln the art of solidiiying porous strata, the' sure in excess of the head of the mixture in order to flow said mixture an extended distance into the porous straturn, and permitting the mix- `ture to set.

3. In the art of solidifying porous strata, the process comprising7 subjecting a porous stratum to an initially freely flowable but finally settable hydraulic cement mixture While the mixture is circulated down to the stratum and up to the l0 surface.

l5 is circulated down to the stratum and up to the surface under a pressure in excess of tne head of the mixture.

process comprising, subjecting a porous stratum to an initially freely iiowable and slowly but nally settaole hydraulic cementmentonite grout in which the bentonite is in excess of 6% and the hydraulic cement not over 46% of the weight of the grout, and permitting the grout to set. l

6. In the art of solidifying porous strata, the process comprising, subjecting a porous stratum to an initially freely ilowable and slowly but nally settable hydraulic cement-bentonite grout, applying pressure to the grout to new the same an extended distance into the porous stratum, and permitting the grout to set.

RALPH R. PROCTOB.

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