AU641174B2 - Method and tool for producing a pile - Google Patents

Description

Method and Tool for Producing a Pile Field of the Invention The present invention re ates to the field of building and construction'or, more specifically, to pile moulding processes and tooling assbmblies and can be used to make pile fpundations in the process of constructing or reconstructinrg buildings and engineering structures.

i Prior Art There is known a process of pile fabrication (DE, C, 2651023), used to reinforce existing foundations and comprising the steps of drilling a hole by the use of churnand-rotary drilling rig and casing pipes as a means of protection, inserting the reinforcing bars, and introducing into the hole pipe to be used'to,pump in cement-andsand mortar.lAfter delivering the necessary mortar'and before its'setting, an injecti6n pipe ispassed therethrough, which pipe is used to pump in cement mortar at high pressure 'to achieve a spread at the fboting of the pile formed in the process.

This process is disadvantageous in that-the pile has :a low bearing capacity around its side surfaces, inasmuch as the hole for the pile is formed by soil excavation, and a layer of less dense soil is formed around its walls, which fails tr contribute to the functioning of the pile. It is for this reason that 'the pile'has to be made of greater length so that its lower end would rest against dense soil (rock or moraine).

Another disadvantage of this process is low efficiency due to having to carry out the operations comprised in the process in succession, sinking a hole, then inst'alling casing pipes, extracting the drilling tool, inserting into the hole a pipe to allow of pumping in cement-and-' sand mortar, filling the hole with this mortar, removing' the casing'pipes and the pipe used to pump in cement-andsand mortar, installing in the hole an injectionipipe, and feeding in cement mortar, with an 'interval to be maintained hr r 2in between ithe latter two of the listed operations, this being associated with the set'ting,of the pile material which acts as packer during the pumping-in at high pressure of cement mortar.

There is-known a pile fabrication assembly (US, A, 4060994) comprising a pipe designed to feed in setting material andiconnected to a mortar pump.. The pipe is sunk into a hold, and s tting material is fed into it to form the body of 4 pile, the pipe being extractedas the material fills:the hole.

The assembly in question is disadvantageous in thatthe pile it is capable of prpducing has a low bearing capacity because the assembly ban only provide for feeding imaterial into the hole, not* for compacting the surround- :ing soil. The low bearing capacity of the pile is further, due to the setting material being mixed with water or soil while it is fed into the hole. Besides, there may occur discontinuities in the pile material along the pile height owing to ground water or clay mortar breaking through inside the pipe.

Another disadvantage of this assembly is that the ipile frabrication time it is capable of providing is quite long, since apart from the hole sinking and the filling of the hole with setting material there are the operations that have to be carried out to prevent the walls of the hole from caving in, i.e. installing casing pipes inside S the hole or filling it with clay mortar.

Disclosure of the'Invention The invention is based upon the objective of providing a process and a tooling assembly f6r pile moulding such 'that would afford of forming around the pile a higher density soil zone contributing to the pile function and thereby increasing the bparing capacity of the pile,l as well as decreasing the pile moulding time on account of reduced number of operations.

r7 i A A 3 Therefore, the invention discloses a process of in situ moulding of an in-ground supporting pile comprising the steps of: introducing into the ground a feeding discharge pipe, to which is coupled high voltage electrical discharge means, and forming a pile formation zone therebeneath; concurrently causing electrical discharges from said discharge means while feeding self-hardening pile forming material from said feeding pipe to the pile formation zone, thereby to generate shock waves to compact the ground soil structure in the pile formation zone so as to allow in-feed of the self-hardening pile forming material, the electrical discharges being of pulsed energy controllable to provide a desired diameter of the pile formation zone at any depth; and displacing the discharge means in either an upward or downward direction to mould the supporting pile throughout its depth.

The increase in the bearing capacity of the pile afforded by the method of fabrication is due to the fact that, in the process of high-voltage discharges being induced in the setting material fed into the pile formation zone, there occur periodically discontinuous increases in pressure leading to this zone being widened, the soil 20 around it being compacted, free and pore-contained water being squeezed :off, and setting material infiltrating the freed soil pores. As a result, there is formed around the pile a zone of fixed soil, and a zone of packed soil around the zone of fixed soil. Also, the proposed process permits adjusting of the cross-sectional area of the pile with depth by adjusting the total energy of discharges with the depth of the pile formation zone, thereby controlling the bearing capacity of the pile in the process of moulding as a function of the soil type.

In the process there are no operations to protect the hole walls from caving in by any of the existing known methods (casing pipes, clay mortar), and the time requirement for pile fabrication is also reduced by integrating in the material supply, pile shaft formation, and soil compaction operations.

The setting material may be fed into a pioneer hole used ^UBF F/21 OK as pile formation zone.

Setting material may likewise be fed directly into the soil which in this case serves as pile formation zone., This enables further reduction of the pile moulding time 'by avoiding the hole sinking operation.

When moulding a pile having its radius changing with.

,height, the.number of discharges may be conveniently varied during the displacement of the material-supplyand discharge-induction zone in a manner such that at a given Oepth of the pile formation zone this number is directly related to the pile radius specified for this depth.

Then moulding a pile haying its radius changing with, height, the discharge frequency may be varied during the displacement of the material-supply and discharge-induction zone in a; manner such that at a given depth of the pile formation zone its value is directly related to the pile radius specified for this depth.

While moulding a pile lin a pioneer hole, it is advisable that the number of discharges, n, at a'given deuth of the pile formation zone be equal to: n exp 1 XK( fW- r 0 where: r is the pile radius specified for the given depth, m, r is the radius of the pioneer hole, m, W is the energy of one discharge at.the given Sdepth, K is a coefficient accounting for the int'ensity of accumulation of irreversible deformations in the soil, and Xis a coefficient accounting for the soil properties.

In one of the embodiments providing for pile fabrication directly in the soil, the material-supply and dis-

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(r 1: 5 charge-induction zone is displaced deeper down into the soil,'with the number of discharges, n, at a given depth being equal to in exp r V (2) where: r is the pile radiu specified for the given depth, m, W is the energy of one discharge at the given depth, J, K is a coefficient accounting for the intensity of accumulation of irreversible deformations in the soil, and X is a coefficient accounting for the soil properties.

According to another embodiment providing for pile fabrication directly in the soil, the material-supply and discharge-induction zone is displaced down into the soil depth, and, on reaching the depth corresponding to the specified pile height,'the material-supply 'and discharge-induction zone is displaced upwards, with the energy of the discharge, Wl, incident to the'downward displacement of the material-supply and discharge-induction zone, being determined from the relation d f

W

1 (3) 13' 12 where: d is the maximum cross-sectional size of the tooling assembly, providing for the supply of material and induction of discharges, mm, and f is the soil strength coefficient according to Protodyakonov's scale, while the'number of discharges, r, at the given depth during the upward displacement is determined from the relation 6 n exp (4) K (fW 0.5 d) where: W is the energy of one discharge at the given depth during the upward displacement of the material- -supply and discharge-induction zone, J, i r is the pyle radius.specified for the given depth, m, K is a coefficient accounting for the: intensity of; accumulation of irreversible deformations in the, soil, Xis a coefficient accounting for the soil proper-' ties, and d is the maximum cross-sectional size of the tooling assembly, providing for the supply of material and induction of discharges, m.

While moulding a tapered pile, it is advisable that material-supply and discharge-induction zone be displaced with a step increment A h derived from the relations.

4 h r' sin 2 arc tan tan t r'>r" and A h r' tg [2 arctg tg ]at r' r", where: b is the allowable relative deviation from the specified pile radius, c- is the specified angle of pile taper, and r' and r" are the specified pile radii for the preceding and subsequent increment, respectively.

'viding that the ing assembly designed for pile fabrication and comprising a pi to supply setting material, contains additionallyan electric arger complete with electrodes arranged coaxially and space rt, of which one has n annr form "nr- i. MTInn+r- 017pi. an -I rIII'M n -7- Therefore, the invention further discloses apparatus for the in situ moulding of an in-ground supporting pile comprising: a feeding discharge pipe for the feeding of self-hardening pile-forming material from a discharge opening thereof; and high voltage discharge means coupled to the discharge pipe forming a pile formation zone therebeneath, said discharge means comprising an electrical discharge generator coupled to first and second electrodes, a current carrying rod, an insulation rod and a coaxial connecting cable, said electrodes being arranged coaxially and spaced apart, and, of which, a first electrode has an annular form and is mounted over the insulation rod passing therethrough, the first electrode being rigidly connected to the discharge pipe promixate Ihe discharge opening thereof, the second electrode being secured on the lower end of the insulation rod and connected with the current carrying rod'arranged within the insulation rod, being connected to the central core of the coaxial cable, and the outer core of the coaxial cable being connected to the first electrode, the diameter of the second n .electrode being greater than that of the insulation rod, and the distance from the second electrode to the said discharge opening being 20 not less than the distance between the first and second electrodes; and whereby, the apparatus can be used to generate shock waves by electrical discharges between the first and second electrodes to compact the ground structure in the pile formation zone to allow replacement in-feed of the pile forming material, the electrical discharges being of pulsed energy controllable to provide a desired :diameter of the pile forming zone at any depth.

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BFD/210K 7A Owing to the presence of the electric discharger attached to the setting material supply pipe near its discharge opening, the proposed tooling assembly may be used to implement the process as described above, permitting of feeding the setting material while simultaneously inducing high-voltage discharges therein. Also, the tooling assembly is suitable for having a pile moulded in a borehole as well as directly in the soil.

Summary of the Drawings Embodiments of the invention will now be described with reference to the accompanying drawings, in which: FIG. 1 illustrates a pile moulding process according to one of the embodiments of the invention, FIG. 2 illustrates a pile moulding process according to another embodiment of the invention, 15 FIG. 3 illustrates the first stage of the pile moulding process according to the third embodiment of the invention.

FIG. 4 illustrates the second stage of the pie mould-

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*Sl S S BFD/210K 8 ind process according to! the third embodiment of the invention,:, illustratesa tooling assembly to use for pile fabrication, according to the invention, and FIG. 6 illustrates the change in the characteristics.

of the soil around the pile fabricated in accordance with the invention.

Best Modes to Carry out the Invention The ~pope ed process is carried out into effect as follows. Any..known method, thus rotary drilling, is used to sink a pioneer hole 1 (FIG. 1) of a diameter less than, that of the pile tolbe fabricated (in the case of a cylindrical pile) or equal to the minimum diameter of the pile to be fabricated (in the case of a pile with the diameter changing with height). Rein orcing bars are positioned in the hole 1, if so specified, and a tooling assembly 2 is lowered into the bottom par't of the hole 1, tooling assembly comprising a pipe 3 to supply a setting material and an electric discharger 4. The pipe 3 is connected to a mortar pump (not shown), and the electric discharger 4, to a current pulse generator 5. A setting material 6 based on cement of synthetic binders is fed under pressure, continuously or in portions, through the pipe 3 while current pulse are supplied from the.generator 5 to the electrodes *discharger 4 to produce high-voltage discharges of electricity within the mterial 6.,Thus, the zone 7 to be found underneath the bttom end of the tooling assembly 2 is a zone where material is supplied, and discharges are induced.

Each discharge produced within the hole 1 filled partially or completely with the material 6, causes a discontinuous increase in pressure. The resultant impact effects have the result of compacting the material 6 within the zone 7, widening the hole 1 in its lower part, squeezing free porecontained water away from the adjacent soil, and having the material 6 infiltrating soil pores freed from water to form

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9a fixed-soil zone 8 bf high strength, as also a compactedsoil zone 9 situated around the zone 8 and having improved building qualities (higher bearing capacity of the soil due to a lower voids ratio and a higher modulus of deformation). The free space formed as a result of material 6 being compacted, is gradualli filled by new portions of material so that each subsequent discharge occurs in a new volume of material.

The tptal.energy of disbharges their number in this case is selected so as to assure the lower part of the hole 1 being widened to match the pile diameter specified for the lower part of the pile. It is in this way that the pile footing'is formed.

As established experimentally by the inventors, the energy of ,each discharge must be at least 5 kJ while the pressure of 'the hydraulic stream within the -hole 1 may rise from 50 to 200 MPa. 'With discharge energies'below kJ, the pile formation time is longer thanthe'material; setting time, resulting in a lowerpile material strength.

Inducation of discharges with energies above 200 kJ is not recommended because increasing loads on the hole walls may lead to exceeding the permissible soil oscillation velocity and to a seismically harmful effect upon the neighbouring buildings and structures. Be'sides, the weight and size characteristics of the assembly designed to implement the proposed process will increase with increasing discharge energy.

Further, the tooling assembly 2 and, hence,, the material supply and discharge*'induction zone 7 thereunder are displaced upwards, as shown by arrow in FIG. 1, with a step increment- h, and the process as described'above is repeated, thus forming the subsequent pile shaft sec'tions. In the event when a pile is fabricated with a radius changing with height, the number of discharges at each subsequent step is indreased as against that at the 1 v< S-5 preceding step in case the pile radius is increased, and vice versa. 'The step increment A h is determined in relation tQ the principle specified, for the pile radius changing with height and to desired pile fabrication accuracy. Thus, for the fabrication of a cylindrical pile, the tep increment A h remains constant, its value being equal to Sh r-sin [arc cos (6) where: r is the specified pile radius, and b is'the allowable relative'deviation from the specified pile radius.

For the fabrication of a tapered pile, the step increment h is determined from the'relation h Sin 2 arctg tg at r' r" or' (7) h tg rct g ta-] at r' r" S. i L 2 where r' and r" are the specified pile radii at the 'preceding and subsequent steps, respectively, and oC(is the spe4 cified angle of the'pile taper.

With thisstep increment the number of discharges, n, per each step may be selected such that the radius of the pile section being moulded at each step be less than the specified radius r by the value of br. This is related to the fact that at each step 4here is a pile section moulded in the form of a spherical segment with a surface area exceeding that of a similar pile section of the specified radius.; Thus, the proposed process affords a pile of a somewhat smaller volume with no detriment to the bearing capacity, permitting material savings on this account.

The procedure as described above is continued until a pile shaft ofheight h is'fully formed. This done, the tooling assembly 2 is extracted. While feeding in the material 6,iits flow"rate is o .controlled that its level in the hole i should be at the elevation of the hole mouth.

o9 I I 11 It has been established experimatelly that the effect bf the first discharge is to increase .the radius r of the ,o pioneer hole 1 to the value of r1 equal to r V W m, (8) .where: Xis a coefficient accounting for the soil properties, and W is the energy of one discharge, J.

After n discharges the increase of Z r r-r d in the radius of the hole 1 can be determined from the empirical irelation z rn r i (K:ln n 1) (9) where: r r -r is the hole radius increment 'due to 1 o the effect of the f jrst discharge, and K is a coefficient accounting for the intensity of a:ccumulation of irreversible deformations in the soil.

It follows, from the equations and that the number' of discharges, n, required to form a pile section of radius, r,.is equal to n =exp K The coefficient K/and are determined empirically. The coefficient(K depends onthe state of the .sbil, and its values lie within the range'of 0.2 to; 0.7. The coefficient i depends on the soil type and increases with increasing soil density. For sand, the;coefficient L is 6qual to 0.00163 while for loam it ib 0.0021.

In the case under consideration, wherein the pile is fabricated with the radius changing with height, the total energy of,discharges is varied with the advance of the tooling assembly 2 by way of varying the number of discharges proportionate to the required change in the pile radius, 12 as follows from equation The tooling assembly in this case is advanced discretely, with a step increment of h, while the discharge frequency in this case is constant, being, selected on 4he basis of the specified pi-.

Ie moulding time, with due consideration of the properties of the settihg material used but not'less than, 0.05 Hz.

The tdtal energy of discharges may also be adjusted in relation to the height of the pile being formed by way of varyingithe discharge frequency in accordance with the variation of the pile radius. Obviously, the greater the required pile radius at the given depth, the higher the discharge frequency must be at this:depth, and vice versa. In this case the tooling assembly 2 is advancedcontinuously at a constant speed. Selecting disaharge frequency values must take into account the fact that the, pile formation process (includes widening the hole 1 and compacting the soil around it.

This process can take different dourses depending on the relation between the discha 9 ge frequency and the pressure fall velocity in the material-filled hole. If the discharge frequency is no greaterthan 0.1 Hz, then every next tdischarge will occur after the pressure drops completely,, arid the soil consolidation is complete, the soil increasing in density as discharges~are induced. With thefrequen-.

cy increasing above o.1 Hz,'the soil structure degradation processes and, the soil compaction processes coincide in time, and this leads to faster pile shaft formation. On the one hand, in this case, increasing discharge frequency will allow of decreasing the energy of eadh discharge,while providing for tneir total energy to be sufficient for degrading the structure of the soil and, for compacting it. On, the other hand, with a high frequency'of discharges, each subsequent discharge occurs unser the conditions of. an ''incomplete soil consolidation process dependent upon the' filtration'properties of the soil, which properties detert Si r I S' 13 mine the water yield velocity. Owing to this fact, the effectiveness' of each discharge is reduced, while the energy spent in pile formation is increased. Thus, with the initial soil voids ratio value of 0.690, increasing the frequency bf discbarges from,0.09 Hz to 6Hz will.reduce the effect of compaction due to the discharg'e by a factor of 9. Varying the discharge frequency swill allow 'of adjusting the pile formation speed,within, very wide limits. De-' creasing the discharge frequency below 0.05 Hz is not recommended because the pile body formation time in this case becomes commensurable .with the material setting time.

In this case, discharges produce an unfavourable effect upon the formation of material structure in the setting process, leading!to lower bearing capacity of the pile.

The upper discharge frequency limit is set by the capability of the current pulse generator.

In the embodiment under discussion, the pioneer hole 1 is the pile formation zone. In another pile fabrication [embodiment the pile formation zone,is the soil, i.e. the pile is moulded directly in the soil, without having to sihk a hole. In this case, the toling assembly 2 (FIG. .2) is introduced into the' soil to a depth of 0.3-0.5 m by any known method, thus by rotary drilling or by pressing-in, Sand the setting material 6 is fed in, just as previously described, to wet the respective soil zone and have highvoltage discharges of electricity induced within'this zone in a number such that the formatioh of the top pile section of the specified diameter would be assured. Following this, the tooling assembly 2 is advanced deeper into the soil by a step increment h defined by equation ior equation (7)'depending on the form of the pile being made. Since the material 6 is fed into the soil, the number of discharges, i, at this depth is greater than that used when the material is supplied into a pioneer jole, being determined from the relation I 7 14 n exp (11) where r is the pile radius, specified for the given depth.

On reaching the depth h'equal to the pile height, the tooling assembly is extracted; and reinforcing bars are mounted in the pile if so required. In the process of pile fabrication, the flow rate of the material 6 is so controlled as to have its level at the elevation of the top section of the pile.

I

In contrast to the embodiment providing for pile, fabricati'on in a pioneer hole, an additiohal increase is assured in the bearing capacity of the pile in this case, because there is no soil excavation incident to the hole'sinking, and the.pile formation is effected by way of opening up the soil "from zero" to the specified pile radius. Besides, an.

indubitable advantage of the embodiment providing for pile fabrication in the soil lies in material and time savings associated with the exclusion of the hole sinking 'operation.

Just as' in the case where a pile with a radius changing with height is moulded in a pioneer hole, the displacement of the tooling assembly 2 may; be accompanied by varying the pulse frequency in adcordance with the principle specified for pile radius chahging with height, rather than the number of pulses, The considerations set forth previously in connection with the selection of the energy of one discharge and the discharge frequency hold good also in the case where a pile is fabricated directly ilh the soil.

Fabrication of a pile in the soil in the direction "from top tb bottom" is a convenient procedure when reinforcing foundations of existithg buildings and structures where there are voids and cavitie under the foundation, due to the action of ground waters.'Tehre is another method of pile fabrication in the soil that is possible and may be preferable while putting up intermediate supports in the basements of buildings and structures to be reconstructed S 35 or when laying down tiew foundations for buildings and 1 t 15 structures to be constructed. In accordance with this embodiment of the invention, theiitooling assembly 2 (FIG.3) is likewise sunk into the 'soil,:and the electrically conductive setting material 6 is fed in, with high-voltage d ischarges being induced within,the soil. However the energy.

"of discharges is selected such that each of them will give rise to the formation of a funnel or cone under the lower' 'end of the tooling assembly 2, with a radius approximately equal to half the diameter of the tooling assembly 2. The formation of a funnel under the tooling assembly 2 facilitates its passage through the soil, the toolinglassembly 2 sinking into the soil on its own or being pressed into :it with a slight effort. To provide for the self-sinking 'of the toolihg assembly 2 in;to the soil, the energy of one discharge, must be equall to d 3 f W- 4 ,L (12) 13.12 where: d' is the maximum cross-sectional size of the tooling assembly, mm, and f is the soil strength coefficient according to Protodyakonov's scale The discharge frequency is selected so as to provide for the d( jired tooling assembly sinkin speed V: (Hz) (13) 5.9 \W/f The speed V in equation 813) is measured in m/h On reaching the depth corresponding to the pile base' 'elevation in the soil, pile!moulding is effected as described above but in the direciton from bottom to top, .raising the tooling assembly 2 (FIG.4) with a step increment i h, the number of discharges, n, at each step being defined by the relation r (14) n exp o.K(V W 0.5 d) 16 where W is the energy of one discharge at this step, J.

Thus, in this case pile'moulding'is, carried out from -sole to top while material supply and discharge inductions incident to the delivery of rhe tooling assembly to the S pile sole formation,location are effected solely for the purpose of lowering the soillresistance to the downward displacement of the tooling assembly.

The tpoling assembly designed for pile fabrication 'comprises a pile 3 (FIG.5) to supply the setting material and an electric discharger complete with electrodes 10 and 11 arranged coaxially and spaced apart along their axis.

The pipe 3 consists of sever.al sections added up as the tooling assembly is sunk deeper into the hole or soil, showing the end of the bottom section ofthe pipe 3.

The electrode 10 -the upper, one with the tooling assembly in the working position has the form of aring screwed over a metal bush 12, while ,the lower electrode 'i has the form of a cone with a large angle of taper and with ;the vertex facing downwards.i This form of the lower electrode 11 will facilitate sinking of the tooling asembly into the soil, but it is not indispensible, i.e.,the lower electrode may be in the form of a flat disc or a ring.

Integral with the lower electrode 11 is a current-carrying rod 13 passing along the discharger axis inside the bush 12 and connected with the central core of a coaxial cable' 14 connected to one of the leads of the current pulse generator (not shown). The length of the cable 14 should be sufficient to provide for the sinking of the tooling assembly to the specified depth corresponding to the height of the pile to be fabricated. The space within the ,bush 12, Sthe current-carrying rod 13,;down to the lower electrode 11, and that section of the cable ,14 connected to the rod 13, are filled with insulating material, e.g. polyethylene, forming an insulation rod 15, whose diameter is less than that of the electrode 11 by, 8 to 10 mm, the space -17betweeh the lower end surface of the electrode 10 and the annular peripheral area of tle top surface of the electrode.

11, extending beyond the rod ,15, forming an interelectrode space 16.

The upper elec ode 10 i.s welded to the end of the pipe 3, the distaAce from the discharge opening.17 of the pipe 3 to the .lower electrode 11 being not less than the'interelectrode space 16. Other ty es of connection between the pipe 3 and the electrode 10 are possible, thsu the pipe 3 may be screwed into this electrode, in which case adjustmeht bf the interelectrode space'16 by shifting the electrode along the bush 12 may be effected on disconnecting the pipe 3 from the electrode 10, thip facilitating the preparation of the tooling assembly for operation.

The pipe 3 is electrically connected with the screen braiding of the coaxial cable 14, Which is in turn connected to the other lead of the current pulse generator, connected to its enclosure. The current-carrying rod 13 has circular projections 18 whose purpose is to prevent the stresses active between the electrodes. 10 an'd ?1 during discharges from disturbing 1he rigidity' of fastening of the current- -carrying rod 13 within the insulation rod In the lower part of the pipe 3, near its discharge opening 17, there is installed a non-return valve 19 whose purpose is to prevent ingress of soil into the pipe 3.

Instead of a valve 19 this function can be served by a deflector to be attached to the pipe 3 under its discharge opening.

The electrodes 10 and 11 and the current-carrying rod 13 are fabricated from tough"(viscous) steel, with the surface'layer hardened to reduce metal erosion from the electrode surface during discharges.

The tooling assembly i installed vertically in, e.g., a drilling rig (not shown), with the pipe 3 mounted within the swivel head of the rig. The electrode 10 is displaced rli I i 18 ;along the bush 12 to adjust the interelectrode space 16 tothe desired value such that would assure conversion of.

discharge energy into mechanical work at maximum efficiency.

Where a pile is to be moulded in a pioneer hole, the tooling .assembly is lowered to the hole bottom, and sections are .added up to the pipe 3 as it is being lowered. The hole bottom reached, the cable 14 is connected to the input of' the current pulse generator,i and the pipe 3 to,the mortar' :pump (not shown). The setting material is fed via'the pipe '3 under pressure to the hole. bottom, and the current pulse generator is put on at,the same time to feed current pulses 'to the electrodes 10 and 11. High-voltage discharges arise in the interelectrode space 16, leading to the lower sec- I ,,tion of the.hole being widened and filled with the setting material and to the soil around this section being fixed and compacted, As the pile is being formed section by pection, the tooling assembly is bding gradually raised upwards. The displacement of the tooling assembly'iq controlled by, observing .the marks traced upon the side surface of the pipe!or the feed rack of the drilling rig swivel head.

Where a pile is to be moulded directly in the soil, the tooling assembly is pre sed into the soil to a depth of 0.3-0.5 m and is used to mould the pile in a similar manner while sinking the tooling aosembly deeper and deeper into the spil.

FIG.61 presents experimental data showing the change in the strength of the soil ardund the pile 20 fabricated according to the invention. Plotted on the horizontal of the graph is the distance v from the pile axis in metres, and on the vertical the depth h in metres. As may be seen' from FIG.6, around the pile' 20 are formed a fixed-soil *zone 8 with a compressive strength R of 0.4 to 1 MPa and a compacted-soil z2 e consisting of three subzones 21, 22, .and 23 having va3ues of deformation modulus:E, equal to 480 MPa, 330 MPa, and 810 MPa, respectively. Left of the s 19 graph illustrating the pile 20 with,the'adjoining soil is a geological section of the site where. this pile has been moulded. The soil layer 24 is medium-sited sand with a voids ratio e equal to 0.75, the layer 25:is fine water- -saturated sand (e 0.72, 190 MPa), the layer 26 is dusty sand (e 0,67, E 150 MPa, the soil angle of internal friction P 280, cohesion!C 0.04 kPa), and the layer 27 is fine water-saturated sand with the same characteristi'cs as those of the layer 25. Underlying the layer 27 is, moraine. Comparing the characteristics of the initial soil with those of the soil adjoining'the pile 20, it can be seen that the bearing capacity of the soil around the pile and under its sole is 1 5 to 3 times higher.

The following are specific examples of embodiment of the proposed process.

Example 1 Fabrication of a pile section of 0.3 m diameter and 1 m height'in a water-saturated sand soil, with the tooling, assembly displaced from top to bottom as described in connection with FIG.2.

Setting material: cement mortar Coefficient K accounting for', the intensity of accomulation of irreversible deformations in the soil: 0.54' Coefficient L acco nting for the soil properties. 0.00163 Maximum cross-sectional size of the tooling/assembly: 0.09 m Cement mortalr flow rate: 2.3 m3/h Energy of one discharge: 50 J 'Discharge frequency: 1 Hz Number of steps: 14 Step increment value: 0.071 m (Number or discharges per step: 16 Pile section formation time per step: 0.0044 h Formation time for a 1 m long pile section: 0.062 h Example 2 Fabrication of a tapered pile'section with a minimum diameter of 0.3 a height of i m, and an angle of taper of 14° in a dense loamy soil., with the tooling assembly displaced from bottom to top as described in connection with FIGS. 3 and 4.

Setting material: ,ement-sand mortar Coefficient K accounting fo' the intensity of accumulation of irreversible deformations in the soil: 0.7 Coefficient accounting for the soil properties. 0.00302 Maximum cross-sectional size of the tooling'assembly: 0.09.

A. While sinking the tooling assembly into the soil to a depth of 1 m Energy of one discharge: 33.34 kJ Discharge frequency: 0.18 Hi Effort to ;be applied to the tooling assembly to provide for its sinking: 17 kN Sinking speed of the tooling assembly: 40 m/h Sinking time of the tooling ;assembly:t0.025 h B. While moving the tooling assembly from bottom to top 2 Energy 'of one discharge: 'Discharge frequency: 1 Hz iNumber of steps: 6 The remaining data are cited in the Table below.

Step Pile dia- Increment Number of Pile section for- No. meter at gi- per step, discharges mation time per ,,ven depth, m per step step, h m 0 0.30 0.13 3 8.3 x S1. 0..33 0.14 4 1.1 x 10 3 2 0.36 0.16 5 1.4 x 10 3 3 0.40 0.17 1.94 x 10 3 4 0.44 0.19 11 3.1 x 10 3 0.49 0.21 18 5.0 x 10 3 6 0.54 31 8.6 x 10-3 6 0.54 3l 8.6 x 21 Example 3 Fabrication of a cylindrical pile section of 0.4 m diameter and 1.0'm height in a pioneer hole of 0.13 m diameter and 1.0 m depth sunk in a clay soil. Pile fabricated as described in connection with FIG.1. Setting material: cement sand mortar Coefficient K accounting for the'intensity of accumulation of irreversible deformations in the soil:' 0.7 Coefficient accounting for the soil properties: 0.00302, Maximum cross-sectionalsize of the tooling assembly: 0.09 m Cement-sand mortar flow rate: 2.02 m 3 /h Energy of one discharge: 50 ,kJ Discharge frequency: 1 Hz Number of steps: 12 Step increment value: 0.087 Number of discharges per step: 16 Pile section formation time per step: 0.0044 h Pile section'formation time 'for 1 m length: 0.062 h.

Although the embodiments of the invention as described abpve apply to the fabricat on of cylindrical and tapered piles, it will be understood that the proposed invention can also be used for other forms of piles, e.g. of graded ,(stepped) profile consisting of several cylindrical Ssections varying in diameter), which can be conviniently used in a soil, one or several layers of which have a dras- ,tically reduced strength. Another possible type is cylindri- ,cal-tapered piles. Besides, pile radius variation with height is obtainable not only by adjusting the number of'discharges or the discharge frequency as the tooling assembly is displaced, but also by controlling the energy of individual discharges. Also, changing the discharge energy may be combined with varying the number of discharges or the discharge frequency.

The possibility of using piles of any profile, as applicable to the specific construction conditions, affords i i, 22 control. of the bearing capacity of the pile in the process 'of fabricatipn in relation to the physical properties of the soil. Owing to the soil around the pile being fixed and compacted, the bearing capacity of the pile proves to be 5 to 6 times as great as that of a filling (cast- -in-situ) pile produced by alknown method.

The invention also proyides for lowering or,- :in case the pile is moulded directly,in the sqil exclusing the !costs involved in drilling a hole ahd permits of dispensing with the use of casing pipes and,clay mortar, i.e.

of reducing the number of operations and reducil.g the pile fabrication time.

Industrial Applicability SThe invention can be used inlmaking pile foundations in the process of constructing or reconstructing ;(rehabilitating) buildings and engineering qtructures.

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Claims (5)

1. 2. A process as claimed in claim 1, comprising the further step of firstly forming a pioneer hole in the ground which starts the 4 "0 pile formation zone. *o 3. A process as claimed In claim 2, wherein in the event of a 0 pile to be moulded with a diameter changing with depth, the number of discharges is varied during the displacement of the discharge means in a manner such that at a given depth of the pile formation zone this number is directly related to the pile radius specified for this depth.
2. 4. A process as claimed in claiim 2, wherein in the event of a pile to be moulded with a diameter changing with depth, the discharge "frequency is varied during the displacement of the discharge means in a ~manner such that its value at a given depth of the pile formation zone is directly related to the pile radius specified for the given depth. A process as claimed in claim 1, wherein the number of discharges, n, at a given depth of the pile formation zone is equal to r n exp B /x K (X r o BFD/210K 24 where: r is the pile radius specified for the given depth, in metres, r is the radius of the pioneer hole, in metres, N is the energy of one discharge at the given depth, in Joules, K is an empirical coefficient as herein described accounting for the intensity of accumulation of irreversible deformations in the ground soil, and is an empirical coefficient as herein described accoiinting for the ground soil properties.
3. 6. A process as claimed in claim 1, wherein the discharge means is displaced down into the ground soil, with the number of cischarges, n, at a given depth being equal to r n exp K where: r is the pile radius specified for the given depth, in metres, W is the energy of one discharge at the given depth, in Joules, K is an empirical coefficient as herein described accounting for the intensity of accumulation of irreversible deformations in the soil, and is an empirical coefficient as herein described accounting for the soil properties.
4. 7. A process as claimed in claim 1, comprising the further steps of the discharge means being displaced down into the ground soil, :and, on reaching the depth corresponding to the specified pile height, is displaced upwards, the energy of one discharge, NI, during the downward displacement of the pile formation zone being determined from the relation *3 1 (in Joules)
5. 13.12 where: d is the maximum cross-sectional size of the tooling assembly assuring material supply and discharge Induction, in mi limetres, and BFt/210K 25 f is the soil strength coefficient according to Protodyakonov's scale, and the number of discharges, n, at a given depth during the upward displacement of said pile formation zone being determined from the relation r X n exp K X\Y 0.5 d) where: W is the energy of one discharge at the given depth during the upward displacement of the material-supply and discharge-induction zone, in Joules, r is the pile radius specified for the given depth, in metres, K is an empirical coefficient as herein described accounting for the intensity of accumulation of irreversible deformations in the soil, is an empirical coefficient as herein described accounting for the soil properties, and d is the maximum cross-sectional size of the tooling assembly o:o: assuring material supply and discharge induction, in metres. 8. A process as claimed in claim 3, wherein in the event of moulding a tapered pile the pile formation zone is displaced with a step increment of Ah determined from the relations 'a A h r' (l-b).sin {2 arc tanE(l-b).tan at r'>r" and Ah r' (l-b).tan {2 arc tan[(l-b).tn at r'<r" where: b is the permissible relative deviation from the specified pile radius; a is the specified angle of taper of the pile, and r' and r" are the specified pile radii for the preceding and subsequent steps, respectively. 9. Apparatus for the in situ moulding of an in-ground supporting pile comprising: a feeding discharge pipe for the feeding of self-hardening pile-forming material from a discharge opening thereof; and FD/210K ik 26 high voltage discharge means coupled to the discharge pipe forming a pile formation zone therebeneath, said discharge means comprising an electrical discharge generator coupled to first and second electrodes, a current carrying rod, an insulation rod and a coaxial connecting cable, said electrodes being arranged coaxially and spaced apart, and, of which, a first electrode has an annular form and is mounted over the insulation rod passing therethrough, the first electrode being rigidly connected to the discharge pipe promixate the discharge opening thereof, the second electrode being secured on the lower end of the insulation rod and connected with the current carrying rod arranged within the insulation rod, being connected to the'central core of the coaxial cable, and the outer core of the coaxial cabl6 being connected to the first electrode, the diameter of the second electrode being greater than that of the insulation rod, and the distance from the second electrode to the said discharge opening being not less than the distance between the first and second electrodes; and whereby, the apparatus can be used to generate shock waves S* •by electrical discharges between the first and second electrodes to i compact the ground structure in the pile formation zone to allow .i in-feed of the pile forming material, the electrical discharges being of pulsed energy controllable to provide a desired diameter of the pile forming zone at any depth. "See: DATED this TWENTY FIRST day of JUNE 1993 o. SO Alexei Leonidovich Egorov and Gennady Nikolaevich Gavrilov Patent Attorneys for the Applicants SPRUSON FERGUSON 'L8FD/21OK 27 PILE MOULDING PROCESS AND TOOLING ASSEMBLY FOR IMPLEMENTING THE SAME Abstract A pile moulding process compripes feeding a setting material into a pioneer hole or into the soil, with high-voltage discharges of electricity induced in the mate- rial fed in, and displacing the material-supply and discharge-induction zone along the height of the pile being moulded. The total energy of discharges at a given depth is such that the respective seciton of the hole (1) or of the soil is widened to match the pile diameter spe- cified for the given depth. The effect of discharges is to create around the pile beinglmoulded a fixed-soil zone (8) of higher strength and a compacted-soil zone featuring improved construction properties. The tooling assembly for pile moulding comprises a pipe to supply material and an electric discharger complete with electrodes (10and 11) arranged copxially, spaced apart, and mounted over an insulation rod (15) passed through the first electrode The first electrode (10) is con- nected with that end of the pipe 83) which contains its discharge opening so that its axis is parallel with that of th pipe and the distance between the second electrode (11) and the discharge opening (17) of ,the pipe; is not less than the interelectrode space (16). FIG.1 C* i v x~