CA1090149A - Method of driving sheet piles into a rock substratum - Google Patents

Abstract

ABSTRACT

Problems arise when erecting a sheet pile on rock substratum and subsequently anchoring the piles. If a channel is blasted, this has the draw-back that the over burden has to be initially cleared prior to blasting and then replaced subsequently. In addition, the piles when secured in the blasted channel when refilled with concrete and the anchors in the rock substratum are not as securely supported as piles driven into normal substratum. A method of erecting sheet pile and a method of anchoring the sheet pile is disclosed where the substratum is shattered by blasting sufficiently to allow the piles and the anchors, which are also piles, to be driven into the rock substratum. Each method involves drilling bore holes and inserting a water tight charged container into these and determining the volume of charge relative to container volume such that the rock substratum surrounding a bore hole after detonation is not significantly damaged in its external form but has a shattered internal structure allowing pile driving.

Description

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BACKGROUND TO THE INVENTION
Thi3 invention relates to a method of driving sheet piles into a rock substratum, both for the purpose of producing a ~heet pile wall and also for subsequently anchoring the 6heet pile wall. The lnvention iB
particularly intended for use in marine and river works, but i8 al60 suitable for every other civil enginesrinB branch in which a 6heet pile wall mu6t be placed in a rock 6ubstratum.

In the engineering of inland and coastal ports or other waterways, provi6ion must frequently be made for great differences in water level and, because of the trend towards ever larger ships, for very large draft. For the ~erths, sheet pile walls are generally used, which are compo6ed of individual sheet pile6 adjoining one another and must be driven to a predetermined depth to provide a secure fixing. Frequently, however, thi6 required drlving depth cannot be achieved, because a rock substratum i6 present at quite shallow depth in the soil structure, preventing any driving beyond this depth.

Such a driving depth limited by a rock 6ubstratum is not harmful if the lower ends of the sheet piles can be fixed in the rock 6ubstratum sufficiently for the_pile6 to obtain adequate fixity even though the theoretically calculated driving depth based upon soft 60il conditions 20 i8 not reached. Because the pile6 have sharp bottom edges, the bottom end of the pile6 can usually be driven without great difficulty to a sufficient penetration for reliRble fixity, provided the rock sub-stratum is comparatively soft. With a harder rock substratum, however, . /this simple ,' ~' . . .,, ' -, ' ~ , ; ' ' ' ' :' "" '~ - :: ' .

109~ 9

-2-this simple driving is no longer pogsible, because the bottom ends of the plle~ become upset when driving is attempted, or they buckle sideway6.

For the~e difficult ~round conditions a process is known, in which the 6heet pile~ are no longer driven, but are 6et into a channel blasted in the rock and concreted in there using underwater concrete. This process i8 extraordinarily complicated and costly, since before the generally V-shaped channel can be blasted, all loose rubble and the like overlying the rock must be removed, it being necessary in fairly loose overburden to maintain an angle of slope of 3:1, in order reliably to prevent the channel from filling up after blasting. After placing of the sheet piles in the V-trench and the 6ubsequent concreting operation, it i6 frequently necessary to backfill the loose material that has been removed with 80 much trouble, in order to as6ure the final stability of the finished sheet pile wall. Apart from the extra work required, the real advantages of a 6heet pile wall, namely its firm fixing in the 60il resulting from the compaction of the substratum during drivingf are ;
completely lost, and instead the sheet pile wall is installed after the manner of a freestanding wall.

When a non-dri~able rock substratum is present, difficultias are eo encountered not only in the construction of the sheet pile wall, but also correspondin& difficulties exist in its subsequent lateral anchoring.
After the erection of a sheet pile wall, that is after the driving of the individual sheet piles, it can be necessary for the upper end of the sheet pile wall 'o be 6ecured against displacement, which i8 usually effected by means of anchors, which extend approximately at 45 obliquely downwards from the upper edge of the sheet pile wall. Such an anchorage is provided espeGially for those sheet pile walls that are sub~ected to /high soil ~ ., ,, . .. ~ , . . . .

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~3--high 60il pressur~ on one 6ide, and which are 6upported in the driven 6tate at the lower end only, as u congequence of the exi6ting ~oil 6tructure. Very frequently, these conditions occur in the securing of banks and in the con6truction ofquay6tructure6 for waterway~
where a rock ~ubstratum i~ proscnt ~t the placc wh~re lnnd mects wutcr.

The usual method of installing the anchors on the landward side of the sheet pile wall for a non-drivable rock substratum consists in drilling boreholes obliquely downwards from the seaward side from the upper edge of the wall, and then positioning simple anchors in the form of steel flat6 or angles loosely in the boreholes. The boreholes together with the anchors in them are then completely filled with concrete, which after hardening produoe6 retaining forces predominantly due to frictional bond between the concrete and the wall of the borehole.
Due to a lack of compaction of the ground material, 6uch as is produced in driving, these retaining forces are not especially high per unit area, 80 that the frictional area between the concrete and the borehole wall must be designed to be correspondingly large. For this reason the anchors must frequently be made very long, resulting in a steep increase in the drilling co6ts.

A further disadvantage of this anchoring method lie6 in the fact that, if the bond friction i8 temporarily 106t for example due to a blow or a shock, only sllding friction remains effective, which, as i~ well-known, provides much lower retaining forces than bonding friction. Such impacts can arise, for example, from carele6s berthing of a ship along-- 25 side the sheet pile wall or from other vibrations, for example from a road in the vicinity. Vibrations arising from blasting which must be carried out in ~he vioinity of the sheet pile wall are especially /dangerous .
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dangerous. This i8 alway6 the case when the useful draft of the water-way ad~acent to the wall must be increased and, on account of a rock 6ubstratum, blastlng is unavoidable. There is then a ri6k that the 6heet pile wall will lose the holding power of its anchors over a very large length immediately after blasting, and will be forced away by the soil pressure.

Considered overall, it has therefore hitherto not been possible, where a non-drivable rock substratum is present, to construct sheet pile walls by simple driving of the lower ends of the piles and to anchor them laterally where necessary by 6imple driving of anchors. Instead, it has hitherto been necessary to adopt other measures, in which no driving operations were involved and in which, apart from oth~r disadvantages, it was also necessary to accept that the very high retaining forces which arise from driving piles due to the resultant compaction of the sub6tratum couldnot be achieved.
SUMMARY OF THl~ INVENTION ~r It is an object of the invention to create a method which enables stable 6heet pile walls to be constructed by driving the lower ends of 6heet piles evan where a hard, intrinsically non-drivable rock substratum is present, and to fix the lateral anchors for such sheet pile walls by driving.

For the erecting of sheet pile wall6, the invention provides that holes are bored through any overlay present into the rock substratum at predetermined spacings along the intended wall, that a watertight ~ ~ container containing an explosive charge is inserted into each hole, ;~ 25 the volume of the explosive charge being small by comparison with the ~ ~ volume of the container, that the explosive charges of at least two - ~ adjacent holes are simultaneously detonated, and that then the sheet /piles . '' . , ~

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--` 1090149 1. , piles are dri~en into the rock substratum of shattered internal structure but still almost undamaged external form between the hole6.

The principle of this lnvention therefore consists in makine po~sible the driving of the individual sheet piles forming part of a sheet pile wall into an intrinsically non-drivable rock substratum, as R result of the fact that the rock substratum is made drivable by means of an explosion. Tbis explosion is not a blasting-away in the usual sense, but a type of 6hattering blasting, which is carried out by ~eans of an explosive charge prepared according to this invention and which to a certain extend "soften6" the rock 6ubstratum. The individual sheet piles can then be driven successively into a rock substratum prepared in this manner, without especial difficulty and especially without the risk of an upsetting or buckling of the lo~Jer ends of the piles, the rock material displaced in the driving of the piles causing a compaction of 1~ the stratum "softened" by the explosion, which results in a firm and secure fixing of the sheet pile wall in the sub6tratum.

;, By contrast to the usual introduction of a charge for blasting away rock for example, in the invention the explosive charge is housed inside an exFansion chamber formed by the container, which 6erves as a first expansion 6pace after the detonation. It has been found that pressure .
~ waves 6pread out from the peripheral zones of this expansion chamber, .
these waves being well capable of shattering the internal structure even of a very hard rock, but not causing any noticeable change in position.

This effect takes place in all directions around the source of pressure waves, and is purpo6efully amplified in a preferred direction by the .1 ~ , . ~ , . . .
fact that a second gimilar pressure wave source, that is an explosive oharge prepared aocording to this invention, i6 installed at a predetermined 1 /distance.

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diRtance. If the distance i8 correctly ~elected - it is about ten time~ the borehole diameter, usually 60 to 150 cm - the entire rock 6tructure situated between the two boreholes is then shattered to a width of at least three times the borehole diameter to such an extent that a sheet pile wall can be driven ln with about 25 to 40 blows per 10 Gm.
The container eerving for forming the expansion chamber in the environment of the explosive charge should preferably be of plastics material, but in any case must not be of metal. If parts of the container remain behind after detonating of the charge in the region into which the sheet pile walls are later to be driven, then any plastic6 ~ residue will never interfere with spatial movement, whereas metal pieces ; could constitute a considerable hindrance. The 6implest procedure i6 to make the containers from cutting lengths from continuous PYC tubes, ~ ;
and then closing the ends of the length with appropriate caps. Tubes of this type are commercially available as drainage pipes at a favourable ~ -price.

In general, no special measure6 are necessary for centering the charge inside the container, since it i6 not of importance for the 20 described effect of pre-expansion whether the explosive charge, usually `~
in the form of cords, rests against the wall of the container or is in the middle. If for any reason, however, centering is desired, suitable spacers may be used. The only important thing is that a 6ufficiently large gas space shall be available inside the contalner to serve as the ~expanRion volume. The smaller this expansion volume i6, the more the charge will have a tendency to displacement, that is to change the position of the rock, and if the expan6ion volume is completely absent, thi6 displacement effect is the only one that occurs.
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1090~9 ID regard to the further aspect of fixing lateral Qnchorage6 for a sheet pile wall, the invention starts from the known measure of pro-viding a boring extending obliquely downwards from the upper edge of the wall into the rock eub6tratum. According to the invention, s 5 pro~ision i8 also made for a sheet pile to be used as anchor, for the diameter of the borehole to be made smaller than the maximum width of the sheet pile, for a watertight container containing an explosive charge to be inserted into each borehole, for the volume of the explosive charge to be 80 chosen in relation to the volume of the container that, 1o after the charge has been detonated, the rock 6tructure in the vicinity of each borehole is drivable for the associated sheet pile due to a shattering and the borehole i6 widened out slightly to a hole, and that the sheet pile is driven approximately with it6 central axi6 along the axis of the hole.

In an important further embodiment of the basic concept of the - invention, therefore, use is again made of the principle of "softening"
; the previously non-drivable rock 6ubstratum by means of a shattering bla~t, for the fixing of the lateral anchor6 of sheet pile walls.
Here again, the explosive charge is hou6ed inside a container constitu-2~ ting an expansion space, from the peripheral zones of which the pressure waves which 6hatter the rock 6tructure spread out, without producing any ~ notable change in position. A slight change in position, which consist6 ; ; in the 61ight expanding of the original borehole to a hole, can be ; easily regulated by an appropriate design of the size of the expansion -~
-~ 25 chamber. The blasting iB therefore 80 carried out that both a de~struc-' .
tion of the rock ctructure of the surrounding rock occurs and also the preli=lnary 6tages of a bla6ting for di6placement comes into effect, Out /the latter , , ,~ , , , . . -. ::
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10901~9 the latter in 60 mild a form that the result i~ a widening out of the borehole to a hole, but not ye~ a dlsplacement of the wall forming the hole. In this connection, the volumetri~ ratio between the explosive ch~rge and the container cannot be determined firmly in advance, but will depend in each case upon the type of rock in which the anchor i6 to be formed. It is obvious that for a fairly soft rock Aubstratu~, the preliminary stages of the blasting for displacement must be smaller in their effect than for an especially hard rock.

The de6truction of rock structure produced by the blasting and thus the loGsening i6 basically neces6ary in order that dri~ing can be carried out at all into the rock. It is also, however, necessary that for the lateral anchoring of the 6heet pile wall a 5teel flat or angle- `~
section which fits into the borehole shall no longer be used, but instead a usual sheet pile, which exceeds in its dimensions the dimensions of the borehole, which is to be expanded to form a hole. In the subsequent introduction of the sheet pile, the borehole then serves as a displace-ment chamber for the material displaCed by the 8heet pile. This dis-¦- ~- placement volume formed by the borehole is smaller than the displacement ~olume necessary for the volume of the sheet pile, which in turn has the result that a compacting of the surrounding rock substratum 1006ened by the blasting results from the introduction of the sheet pile. This leads to very high retaining forces for the driven anchor and thus to a firm and reliable fixity of the anchor.

Before blasting, the holes have a diameter of about 32 - 65 mm.
After detonation of the charges? the dimensions of which will depend upon ": . .
` ~ the experience gained from preliminary trlal blasting, a region of approximately 500 mm diameter around the hole and along its axis is i .':: ,- : ' ~ -/usually 1;~:: :' ~: .

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10901'1'3 g usually altered by the blasting, th~t i~ in particular ls destroyed in its structure. From the external diameter of the hole to the edge of the altered region, the compacting of the rock wheu pile6 are driven decreases progre~sively. The 6heet pile6 are driven in such a way that thelr central region is approximately i~ the centre of the hole, and thus the two longitudinal edges are driven into the rock substratum loosened by the blasting. For fairly large sheet piles or for appropriate soil conditions, it is also possible for two holes 6ituated alongside each other to be drilled for one and the same sheet pile, in which case when driving the centres of the holes are situated apprbxi-mately in the region of the outer edges of the sheet piles.

When anohoring a 6heet pile wall according to the method of this invention, either fewer anchors or shorter an¢hor6 may be used for ~:
attaining the same stability of the sheet pile wall. The preparatory work i8 correspondingly cheaper, 80 that the method according to thi6 invention makes possible not only a reliable but also a cheaper anchorage - than hitherto;

Where the demands upon the anchor in respect of it6 holding forces are unusually high, a somewhat longer anchor and thus a greater length ~-of borehole is necessary for correspondingly unfavourable soil conditions.
It may then be of advantage, instead of a single container, to arrange several~one after the other, 80 that approximately the same alteration to the rock occurs at every depth along the axis of the borehole. Alter-natively, a single, long container may be used, in which a plurality of explo6ive charges, adapted in respect of volume to the conditions, are disposed one after the other. Independently of the arrangement, all explo8ive charges associated with one borehole are always simultaneously /detonated.
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` 1090149 detonated.
Regardless of whether a 6heet pile wall is being constructed or lateral ~nchors a~e being fixed for a 6heet pile wall, the method according to the present invention i8 suitable both for rock in the dry and al6c for rock underwater, and any drivable overburden which may be pre6ent above the rock substratum is not a further disadvantage.
The introduction of the containers into the boreholes is most easily done by means of tubes, which are introduced to'follow up the' drilling tool during the drilling of the borehole, and thus prevent the new borehole from becoming filled up. After the containers have been' inserted through these tubes, the tubes c~n immediately be removed.
Even if the borehole then becomes filled up, this is in no way harmful ~ to the effects of the bla6t.
`, : BRIEF DESCRIPTION OF EMBODIMENTS
Th- further objects and advantages of the invention will be explained in more detail below with reference to the two non-limiting embodiments illustrated in the drawing.
The drawings show: ' j .
Fig. l a diagrammatic plan on a row of bore holçs ' for the construction of a 6heet pile wall, Fig, 2 a diagrammatic eide view in section of the ' row of borehole6 of Fig. l, ~' .
Fig. 3 a diagrammatic'cross-sectional ~iew through a sheet pile wall with an associated anchor, and , Fig. 4 A and B in two somewhat different forms of embodiment, a diagrammatic plan on the anchor in the ' direction of dri~ing.
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Fig. 1 and 2 show diagrammatically the procedure when constructing a ~heet pile wall. The ~heet pile wall itself i8 not showD, its position being indicated by the dot-and-dash line l in Fig. l. Along this broken line l, a plurality of boreholes are sunk, the depth of the boreholes 2 - 5 and the water level 3 being visible in Fig. 2. Each borehole 2 extends through a possibly present overburden 4 into the upper layer of a rock sub6tratum 6. For anchoring the sheet pile wall, its sheet piles should be driven into the rock substratu~ 6 for anchoring purposes to a depth which i6 approximately equal to the depth of the boreholes 2 within the gubgtratum 6 (e.~., 30 cm).

Each borehole 2 is initially lined with a tube 8, so that no loo6e material can fall back from the overburden 4 into the new borehole.
After drilling i6 completed, a container lO i6 pushed through the tube ~;~
8 approximately to the bottom of the borehole. This container preferably con6iæt~ of a piece of PVC tube, closed at each end with a cap. In one of these caps there is a watertight passage, not shown, for the detonating of an explosive charge 12, shown dia~rammatically and housed inside the container. At the bottom end of each container lO, an antiflotation brake 14 1s mounted, which bears against the container lO when the latter is pushed into the borehole 2 and splays outwards if a movement occurs towards the mouth of the borehole, thus jamming the container inside the borehole.

A Mer each container has been introduced, the tube 8 is pulled out of the borehole 2, the loose material Or the overburden then again cover-~ ~ .
ing over the borehole together with the container. Thi6 of cour6e applies ; ~ only for the ca6e in which the overburden 4 consi6t6 of a loose material , which forms a conical slope. Where the overburden 4 con6ist6 of ~ firmer /material, ` ~ ' ' ~:
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~0901~9 material, the borehole remains substantially unaltered, which i6 not of importance for the carrying out of the method according to this invention.
As a departure from the view 6ho~Zn in Fig. 2, loose material from the overburden 4 may without disadvantage flow back also into the intermediate space between the borehole 2 and the outer face of the container 10. In each case, a sufficiently large expansion volume remains inside the contain-er 10 for the preliminary expansion after the detonation of the explosive charee 12.

Depending upon the tolerance level of the 6urrounding6 and the length of the sheet pile wall to be constructed, the charges 12 are then detonated by section6 or all 6imultaneously, causing shattering of the rock structure between the boreholes 2 to the desired extent. The effect of the blasts and the borehole depth have previously been determined empirically by trial bore6 and trial explosions, for which usually two to three tests ~5 are sufficient, so that the result of the blasting achieveg an extremely high 6uccess rate.

The pressure waves emitted from a borehole 2 give rise to the most inten6e shattering of the rock 6ubstratum 6 particularly within the cone 6hown in Fig. 1 diagrammatically in dot-and-dash lines 5, which is predominantly attributable to the fact that the pr~ssure waves from two boreholes 2 meeting each other with a speed of approximately 6,000 m/sec are reflected from one another and from freshly formed fissures within the rock sub6tratum 6, amplify and deflect each other, without however blasting away the rock. A portion of the overburden is here upweraly . : :
accelerated, but then sinks substantially vertically downwards, 6ince it i8 retarded by the overlying water.

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0901~9 After the blasting of a 6ection or of all the charees 12, hardly any change ha6 occurred to the ~oil structure. As previously, the overburden overlies with a pos6ibly highly va~iable thickness the rock 6ubstratum 6, which externally has hardly changed but is now drivable.
Any residue of containers remaining within the rock substratum 6 has no adver6e effect upon later pile driving, 6ince they are cut up or forced to one side by the lower edge of a sheet pile. Moreover, it has been found that usual sheet piles can be driven with a number of blows from 25 to 40, wi*h a ~aximum value of 50, for 10 cm penetration into the rock substratum 6 with it6 shattered structure.

The method according to this invention for driving the sheet piles has been described with reference to a soil 6ituation, in which an overburden 4 with water above it is present above the rock substratum 6.
~he method according to this invention can, of course, also be used for making a rock substratum 6 drivable, which is exposed without any such overburden 4. Such very simple ground conditions are, however, seldom encountered, 80 that an overburden can be regarded as the normal ~ case. The method according to thi~ invention for the driving of sheet - piles can be used with particular advantage and cost saving under these oonditions.
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An explanation will now be given with reference to Fig. 3 and 4 of ~ how, according to this invention, the fixing of the anchors for a sheet ;~ pile wall in a rock stratum below water is carried out. Fig. 3 shoNs dia~rammatically in cro8s-section the portion of a typical bank land-scape, whioh has been stabilised and levelled with the help of the sheet pile wall 11. The individual piles 16 of the wall 11 are driven through the drivable overburden 4 into the rocky stratum 6, using the method /deccribed . - '.

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10901~9 deRcribed abo~e. The upper end of the indi~idual sheet pile6 16 of the wall 11 are joined together by a waling 8 as an upper closure.

The region to the right of the ~heet pile wall 11, which in the 6ituation shown is ~tlll filled with water, i~ backfilled after the fini6hing, stabilising and levelling of the bank area, 80 th~t an earth pressure acting towards the left on the sheet pile wall 11 is present. This exerts on the wall 11 a bending moment and a shearing force, which cannot be resisted by the sheet pile wall 11 itself.
An anchorage must therefore be provided, preferably at uniform inter-vals along the wall 11, this anchorage being usually installed in theform of anchors 20 on the shore side extending downwards at approxi-mately 45 from the top of the sheet pile wall into the ground.
Whereas previously these anchors 20 had the form of an angle or a flat section, the invention now provides that a sheet pile wall of the same type as the piles 16 is also used as the anchor. For the installing of these anchor sheet piles 20, at least one borehole 22 with a diameter of 32 - 65 mm i8 6USlk through the overburden 4 into the rock substratum 6 at the angle at which the anchors 20 will sub-sequently lie. Simultaneously with tbe progress of drilling, a tube (not 6hown) is introduced, so that the borehole 22, after the drill bas been removed, will not fall in. One or more watertight containers, containing an explosive charge, are then introduced through this tube into the borehole 22 and secured against flotation. The tube can then be withdrawn, and complete or partial 6ubsequent collAp~e of mater~al into the borehole 22 is not of importance.
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Depending upon the 80il conditions present, a sin~le borehole Z2 , may be surricient for each anchorage sheet pile 20, but it may also be :., /necessary ~, .
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necessary to sink two boreholes 22 alongside each other and to supply them with appropriate charges inside watertight container6. In general, one charge-container per borehole i6 6ufficient, but when in the case of particularly long boreholes with a 6ingle container and the charge situated therein, an adequately uniform alteration of the rock structure 6urrounding the boreholes cannot be achieved along the borehole axis in the de~ired manner, the provision of several container6 one behind the other may be more favourable. Re~ardless of the number of boreholes and containers chosen, all the charges associated wibh the anchor sheet pile 20 to be sub6equently driven are simultaneou61y detonated, the stren6th of the charges and the a6sociated expansion chambers within the containers being so adapted that the surroundings of the boreholes are shattered in their structure, and also each borehole is modified to an irregular hole 22', slightly increased in diameter.
This is shown in Fig. ~A for the case of one borehole and in Fig. 4B
for the case of two boreholes alongside each other for the anchor sheet pile 20. When driving the anchor sheet pile 20 into the hole (or hole6) 22', a compaction of the surrounding rock occur6, which i6 re6ponsible after the sheet pile has been driven for an especially firm ~eating, in partioulur for an extraordinarily hi~h retaining force.

The alteration in the surroundings to the borehole 22' i6 approxi-mately 500 mm in diameter and is 6hown diagrammatically in Fig. 3 in the form of broken lines 24. The anchor sheet pile 20 remains, during ~; the entire driving operation, within this region, so that the capability for driving~depends solely upon the increase in length of the frictional 6urfaces between the pile 20 and the rock 6 as driving proeresses. At the completion of the driving operation, the sheet pile 20 is therefore , /firmly ~ .

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10901~9 firmly clamped along lt6 entire driven length in the rock stub6tratum 6, the hole (or holes) 22' being once again densely filled in the manner initlally described by the displacement of material produced by the ~heet pile 20.

In the anchors previously commonly used, no clamping in this sense iB present, but the anchor pushed into the borehole obtains contact with the rock with the help of the filler material ~e.g., concrete) injected into the remaining intermediate spaces in the borehole, no prestressing between the two parts being present, but only a 61ight bearing pressure resulting from gravity. The high instability of the previously known anchor~ is therefore virtually excluded by the anchorage process accord-ing to the present invention. Later vibrations therefore have no effect - upon the stability of the anchorage, whether these vibrations are caused by lmpacts against the sheet pile wall 11 or by vibrations of the environ-ment, ~or oxample by blasting in the waterway. -,. ..
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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of driving the lower ends of sheet piles into a rock substratum for the purpose of constructing a sheet pile wall, comprising the steps of boring bore holes in the rock substratum and any over burden present at predetermined intervals along the intended sheet pile wall, inserting a water-tight container containing an explosive charge into each bore hole, selecting a small volume of the explosive charge relative to the volume of the container, detonating, simultaneously the explosive charges of at least two adjacent bore holes to shatter the rock substratum in its internal structure but leave the substratum almost undamaged in its external form between the bore holes, and, subsequently driving sheet piles into the rock substratum.

2. A method according to Claim 1, wherein the water-tight container is formed of plastics material and is provided with antiflotation means to secure the container against flotation in the bore hole.

3. A method according to Claim 2, wherein each container is made by cutting a length from a continuous tube and fitting end caps on the ends of the cut length of tube.

4. A method according to Claim 2, wherein the plastics material is polyvinylchloride (PVC).

5. A method of achoring a sheet pile wall in a rock substratum comprising the steps of selecting sheet pile for use as anchors for the sheet pile wall, drilling bore holes in the rock substratum at intervals on one side of the sheet pile wall and arranging the inclination of the bore holes to be at a predetermined angle obliquely downwards relative to an upper edge of the sheet pile in the line of the intended inclination of the anchors, selecting a diameter for each bore hole which is a lesser dimension than the maximum thickness of the sheet pile to be anchored therein, inserting a water-tight container containing an explosive charge into each bore hole, selecting the volume of explosive charge relative to the volume of the container such that, after the explosive charge has been detonated, the sheet pile to be anchored therein is drivable into the rock substratum in consequence of shattering of the rock substratum surrounding said bore hole and such that the bore hole dimensions are not significantly increased, and driving the sheet piles into the rock substratum to provide anchors with the driven direction of each sheet pile such that its inclination is parallel to that of the respective bore hole.

6. A method according to Claim 5, wherein two adjacent bore holes are formed for each sheet pile such that the sheet pile may be driven into the rock substratum with its external edges approximately in the region of each hole.

7. A method according to Claim 5, wherein at least two containers, each containing an explosive charge, are disposed one after another in a single bore hole and are simultaneously detonated.

8. A method according to Claim 2, wherein a said container is furnished with a plurality of explosive charges, each of which are simultaneously detonated.

9. A method according to Claim 5, wherein the containers are formed of plastics material and are secured by antiflotation means against flotation in the respective bore hole.

10. A method according to Claim 8, wherein each container is made by cutting a length from a continuous tube and fitting end caps on the ends of the length of tube.