US2911795A

US2911795A - Mandrel for driving pile shells

Info

Publication number: US2911795A
Application number: US551678A
Authority: US
Inventors: Walter H Cobi
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-12-07
Filing date: 1955-12-07
Publication date: 1959-11-10
Anticipated expiration: 1976-11-10

Description

Nov. 10, 1959 w. H. COBI 2,911,795

MANDREL FOR DRIVING PILE SHELLS Filed Dec. '7, 1955 4 Sheets-Sheet 2 Nov. 10, 1959 w. H. coal MANDREL FOR DRIVING PILE SHELLS 4 Sheets-Sheet 4 Filed Dec. 7, 1955 United States Patent "ice MANDREL FOR DRIVING PILE SHELLS Walter H. Cobi, Port Chester, N.Y.

Application December 7, 1955, Serial No. 551,678

8 Claims. (Cl. 6179) The invention relates to expansible pile driving mandrels and particularly to expansible and contractable mandrels or cores capable of insertion into the empty shell or mold for a cast-in-place pile and of driving the shell into the ground under hammer blows. g

The invention in some of its aspects relates to mandrels of this type which have come to be known as pneumatic mandrels, in which the expansion is caused by the application of fluid pressure to tubular container means forming part of the mandrel.

It is a principal object of the invention to provide a mandrel which is simple in construction and operation and which is universally adapted for placing of piles in soils of different consistencies. I

i It is a further object to provide such a mandrel in which the number of moving mechanical parts is reduced to a minimum and to provide such a mandrel which is effective in driving a pile she'll into position and which will serve also as a funnel or conduit for introduction of core material, such as concrete, for the pile.

A further object is to provide such a mandrel wh ch is adapted for placing and forming cast-in-place piles of the type having a bulb or ball foundation.

It is also an object to provide a pile driving device which may be readily adapted to meet most of the many, greatly different ground conditions which are met with in this extensive and complex field without resort to machine shop changes.

In accordance with a principal feature of the invention the mandrel has fixed, rigid surface portions that lie closely to the interior surface of the pile shell for continuous effective rigid guidance or support of the pile shell under any operating conditions whether the mandrel is in expanded or contracted condition.

An additional feature is the provision in the surface of the mandrel of clamping means adapted to be extended beyond the said rigid surface portions for clamping contact with the pile shell in the expanded condition of the mandrel for locking of the pile shell to the mandrel under any installing and operating conditions.

More specifically the mandrel comprises a rigid driving structure which fits into a pile shell so that the rigid peripheral surfaces of the mandrel lie close to the interior surface of the shell throughout its length both while being inserted into or extracted from the shell and under driving conditions; the mandrel further including a plurality of clamping means disposed in spaced parallel relation along the surface of said driving structure, being imbedded therein during the contracted condition of the mandrel and projecting beyond it during the expanded condition.

In accordance with another important feature of the invention the rigid mandrel structure comprises a core in the form of a hollow tube or pipe of heavy steel which may be generally cylindrical or may have a plurality of flat sides, which is sturdy and rigid enough to serve I r 2,911,795 Patented Nov. '10, 1959 as a driving mandrel operating in medium dense soilbut which also is adapted for actual driving operation in conjunction with a driving ram lowered through themterior of the mandrel tube for combined driving actionin hard rocky soil, and which furthermore is effective as a conduit for passing core material for the pile, such as concrete, to the bottom end of the mandrel either for or for stagewise filling of the pile shell to near the surface of the ground. In one form the hollow core has a smooth inner surface and its outer surface is of generally cylindrical shape and is provided with suitable recesses or grooves running parallel along the structure for mounting of the said clamping means.

When the mandrel tube or hollow core is used alone for driving, the bottom end is closed by a heavy bottom plate which serves to distribute the driving force from the tube over the whole bottom area of the boot which closes the bottom end of the pile shell.

In accordance with a further feature of the invention the clamping of the rigid mandrel structure to the pile shell is effected by expansible tubular pressure container means inflatable in response to application of a fluid pressure. More particularly the clamping means comprises a plurality of longitudinally disposed pressure fluid containers attached externally of said rigid structure for direct clamping contact with the pile shell.

In an alternative arrangement each clamping means is in the form of a longitudinal metallic unit presenting an outer metallic clamping surface and operative in response to inflation and deflation of a longitudinal pressure fluid container to clamp the mandrel to the shell, the units being circumferentially spaced and alternating with the rigid guiding surfaces about the mandrel structure. v

In accordance with a more specific feature the pressure fluid containers may bemade of rubber, natural or synthetic and cured to have a flat shape with two opposed large flat sides for operating contacts with the mandrel structure and the pile shell.

In accordance with another specific feature the pressure container tubings are disposed in shallow grooves formed in the external surface of the mandrel structure for protection in deflating condition during handling of the mandrel in field or yard, as well as during insertion of the mandrel into a pile shell or removal therefrom.

In consequence of these features, the invention provides the further feature of a rigid mandrel core structure, having surface portions longitudinal thereof and disposed between the said grooves with an overall dimension to fit closely to the inner surface of the pile shell. This provision has the important advantage that during driving, the pile shell will not be dependent only, on the resilient backing of the expanded pressure tubings but will be further backed against buckling and bending by the closely fitting rigid surface portions. A further very significant advantage resides in the fact that the rigid mandrel parts do not undergo any change in mechanical dimensions on account of the expansion and contraction functions, but retain a relatively close fit in the pile shellwhich thus receives continuous support. In fact, the mandrel, when in contracted condition, may be raised or lowered within the pile shell in the ground without danger of the pile shell buckling under the ground pressure. Moreover, when the mandrel is used with corrugated shells the inflated flexible tubings bulge at least partway into the corrugations and serve as projections from the rigid surface of the mandrel structure for definite for the deflated or contracted condition, it is not necessary to reduce the size of the mandrel core structure to permitsuch projections to clear the corrugations for raising of the mandrel which might result in partial collapse of the pile shell under the ground pressure. It is only the projections from the mandrel core surface, in the form of bulges in the fiat sides of the pressure tubings, that are withdrawn inwardly toward the. axis of the mandrel, leaving; the intermediate rigid surface portions in close proximity to the pile shell for rigid supportagainst ground pressure even while the mandrel is being raised.

The various features enumerated, present other distinct advantages. Thus the placing of pressure container tubings along the exterior of the mandrel shell has the very important effect of applying a non-skidding driving force to the whole length of the pile shell, thereby obviating any danger that the boot, which is attached to the bottom of the pile shell, might be unintentionally driven off or loosened or deformed atnd thereby permit water to enter into the pile shell during driving operation. The pile shell, boot and mandrel will act as a unit. This efiect becomes even more significant in the driving of pile shells and boots which are-intentionally weakened inv some manner near the bottom end of the pile shell, coincident to the formation of a concrete bulb or ball foundation for the pile. During the driving operation of mandrel and ram the weakened portion will 'not be subject to strain, since pile shell and mandrel act as a unit together with the central ram. Furthermore, when the bottom end of the pile shell is ultimately andintentionally to be knocked off by the ram, the pile shell is still locked in unit with the mandrel which may be held locked to the shell.

Although the novel features which are believed to be characteristic of the invention are pointed out in the annexed claims, the invention itself as to its objects and advantages and the manner in which it may be carried out may be better understood by reference to the following description taken in connection with the accompanying drawings, forming a part hereof, in which:

-Figs. 1 to are simplified views showing mandrels with some main features, provided in accordance with the invention, and surrounded by a pile shell,

Fig. 1 showing a cross-section of a mandrel with three clamping means in contracted condition;

Fig. 2 showing the same mandrel in expanded condition;

Fig. 3 showing a cross-section of a hollow mandrel with four clamping means and a central ram;

Fig. 4 being a lengthwise section along line 4-4 in Fig. 1 showing the bottom end of the mandrel in Fig. l; and

Fig. 4A being a lengthwise partial section showing a corrugated shell and attached boot;

Fig. 5 being a lengthwise section along line 55 in Fig. 3 showing the bottom end of the mandrel in Fig. 3;

Fig. 6 is a simplified detail view cut across a pressure container and adjacent portions of a hollow mandrel;

Fig. 7 shows a lengthwise section of a preferred form of a mandrel of the general type shown in Figs. 3 and 5;

Figs. 8 and 9 show crosswise and lengthwise sections of preferred details of a wall portion and pressure tubing for the mandrel in Fig. 7 in relation to a wall portion of the surrounding corrugated pile shell, the tubing being in deflated or contracted condition;

Figs. 10 and 11 show similar views of the same parts, but with the tubing in inflated or expanded conditions;

Figs. 12 and 13 are lengthwise and crosswise sectional views of a junction section applicable to mandrels of the type shown in Fig. 7;

Fig. 14 is a lengthwise section through the bottom part of the mandrel shown in Fig. 7 with the central ram removed and a bottom plate attached;

Fig. 15 is a sectional view of a circumferential portion of a mandrel of the type shown in Fig. 7, showing a clamping unit having a metallic clamping surface;

Fig. 16 is a simplified cross-sectional view of a tubular mandrel with only one lengthwise expansion tubing; and

. clearance or very slightly more.

Fig. 17 is a view similar to Fig. 16 of a tubular mandrel. with a plurality of expansion tubings differently spaced about the surface of the mandrel.

Referring to the drawings in which like reference characters represent similar parts throughout the several views, Fig. 1 shows in simplified form a cross-section of a pile shell 20 having a uniform, internal radius r throughout its length and a mandrel core 22 having a uniform external and fixed radius R throughout its length only slightly smaller than the shell radius. In accordance with the invention the mandrel comprises the rigid steel driving structure 24, which has three or more shallow grooves 28; for mounting of longitudinal clamping means 26. Under idle or retracted condition the clamping means 26 are withdrawn into the grooves 28 so that they will be positively confined within the surface circle of the core structure.

Between the grooves 28, the core structure 24 presents smooth arcuate-shaped surface portions 30 of the radius R. The clearance r-R will depend primarily on the size of the pile shell. Thus for comparatively small shells, say of l0."-14" diameter, a clearance of about /s will sufiice for the intended purpose of permitting ready insertion and extraction of the mandrel when the clamping means 26 are in retracted position. For larger size shells it will rarely be necessary to provide more than a A" or Hence, the mandrel surfaces 30 lie close to the interior surface of the pile shell 20 and it will be understood that in using the expression closely fitting herein it is intended to, mean with tolerances within the dimensions mentioned above or of that order; the significant point being that sufficient clearance is provided between the shell and the mandrel core so that the mandrel in contracted condition may be inserted and withdrawn from the shell, but when in the shell the surfaces of the peripheral surfaces of the man-. drel core are close enough to the inner surface of the shell to provide a backing support to prevent undue buckling of the shell during driving operations.

When, as shown in simplified form in Fig. 2, the longitudinal clamping means 26 are expanded, as for driving operation, they extend radially outward from the grooves 28 and beyond the surfaces 30 until they come in gripping contact with the inner surface of the pile shell 20. They thus become clamped between the pile shell and the bottoms of the grooves for firmly locking the shell to the driving core 24. When again contracted they withdraw to within the surface radius R, as shown in Fig. 1. Thus the retracted clamping means 26 will not obstruct the insertion of the mandrel into the shell, or removal of it from the shell.

The close proximity of the arcuate surface portionsv 30 conforming to the shape of the interior surface of the pile shell, has the important advantage that the straightline driving of the shell to a predetermined position and in a predetermined direction is not dependent on the resilient backing of the shell by the clamping means as in prior practice. When the earth pressure, particularly encountered when driving shells in clay or in sandy or watery strata, tends to force the shell wall inwardly during driving, the slight, yet fixed clearance rR will, in any case, permit only a slight deformation of the shell so that, for all practical purposes, the shell will retain its original shape both transversely and longitudinally.

This is particularly important for driving piles under exacting conditions. Furthermore, in the presence of shift, ing heavy rocks, dents might readily be forced into the side of the shell, thereby unduly reducing the cross-sectional area of the pile and reducing its calculated strength. This difiiculty is also overcome by the relatively close fit of the rigid core structure in the shell, as provided in accordance with the invention.

When the mandrel is used for driving a pile shell of corrugated sheet, as shown in simplified form in Fig. 4A, the contact of each expanding means 26 with the shell s 20 may under expanded condition be increased along the whole length of the mandrel by means of a series of spaced projecting points or bulges 27 extending outwardly beyond the groove 28 into the corrugation valleys of the shell, the spacing of the projections generally corresponding to that of the corrugations. Thus, the clamping contact may include not only a friction component but also a structural locking eifect with the transverse corrugations. The withdrawal of such projections back into the groove 28 for clearing of the inner corrugation ridges of the shell during lengthwise shifting of the mandrel, does not change the diameter of the rigid driving core structure 24, as in prior practice. The shell thus is supported by the structure 24 to prevent undue deformation of the shell wall by earth pressure exerted against the outside of the shell wall.

In accordance with a further feature of the invention, and as shown in simplified form in the cross-sectional view in Fig. 3, the rigid structure corresponding to core 24 shown in Figs. 1 and 2 is in the form of a rigid hollow core 44, in the form of a tube or pipe, which fits closely in the pile shell 40, as does that of the solid core 24. The mandrel 42 thus comprises the hollow core structure 44 with a plurality of clamping means 46 disposed in groove 48, similar to grooves 28 shown in Fig. 1, four such grooves being shown in this instance. The wall of the hollow mandrel core 44 is designed to be heavy enough to accommodate the grooves 48. Between the grooves are the rigid guide surfaces 50. Thus, the hollow core has a central passageway or conduit 47 down through its entire length, which is completely closed all around its periphery and, preferably, it is provided with a smooth inner surface. The conduit 47 may be cylindrical as shown or may' have a plurality of flat sides, some of which may provide extra wall thickness for accommodation of clamping means 46.

In general practice the driving mandrel for a pile shell is inserted into the shell, and the clamping means are expanded for clamping shell and mandrel together for the driving. The shell is then driven into the ground under hammer blows directed against the driving head at the top end of the mandrel. The bottom end of the shell is closed Watertight by a boot secured to the shell and against which the driving force is directed. Thus while the bottom end of the mandrel engages the boot which forces a hole in the ground, the whole shell is forced downwardly into the earth along with the boot because the mandrel is clamped against the interior surface of the shell all along its length. After the shell has been driven to its intended depth, or as far as it can be driven due to ground conditions, the clamping means are contracted and the mandrel may be withdrawn from the shell, which then may be filled with concrete to form the pile core.

As shown in simplified form in Fig. 4 a driving mandrel 22 of the type shown in Fig. 1 may be terminated at the bottom end with a large flat surface 29 for driving contact with the boot 32 at the foot end of the pile shell 20, so that the boot will be subjected to a uniform force from the mandrel. Thus the boot may be in the simple form of a disc which, if desired, may have a collar 34 for watertight welding at 36 to the outside of the bottom end of the pile shell 20. Furthermore, the disc may be of comparatively thin sheet iron. The boot thus may be made at comparatively low cost and, being fully backed by the mandrel, it will be protected against breaking or undue deformation during driving.

The mandrel core structure may for driving purposes be solid, as shown in Fig. 1, thus ending at the bottom in a solid driving end, as referred to with respect to Fig. 4, or the mandrel core structure may be hollow, as shown in Fig. 3, in which case it may be terminated at its lower end in a solid end block fastened thereto and presenting a solid driving end to the boot. An arrangement of this type is shown in Fig. 14.

As shown in Figs. 1 and 4, the rigid solid driving core 24 is of uniform cross-section throughout its length so that the bottom end contacts the whole driving area of the boot 32, and by virtue of the slight clearance r-R, as referred to before, the whole length of the shell 20, the bottom end portion of the shell 20 and the collar 34 are solidly backed or supported by the rigid surface portions 30 of the driving core structure 24. Consequently slight deformation of the shell which might be brought about will be of little or no consequence.

As shown in Fig. 4 the expansible clamping members 26 may be terminated in the groove 28 a short distance above the lower end of the mandrel. In such case it is preferable to fill in the lower part of the groove by a filler block which may be welded in position, and flush with the bottom surface 29 so that the entire area at the bottom of the mandrel may engage the driving boot at the bottom of the shell.

Referring now to the mandrel 42 with a hollow core structure 44, as described in connection with Fig. 3 and further illustrated in the simplified view in Fig. 5, the hollow conduit 44 may of course serve to reduce the weight of the mandrel, as compared with the solid structure in Fig. 4. However the hollow space 47 may be put to effective use with important advantages. The holloW space may be occupied by a ram 51 having a flat end portion 58 in alignment with the bottom edge 49 of the hollow core structure 44. The ram, when driven in unison with the driving structure 44 thus completes the driving contact with the boot 52 attached to the bottom end of the pile shell 40. 1 When the shell has been driven to a desired depth, the operations may proceed as follows. The ram is lifted out of the mandrel if it has been used in the shell driving operation. Then the mandrel is contracted by contraction of the clamping means 46 which may be withdrawn fully into the grooves 48, and the mandrel then is lifted a short distance inside the shell, say 6 to 8 feet. When the clamping means are in contracted position there is no danger of the pile shell collapsing under the earth pressure or becoming unduly deformed, since it is supported by the closely fitting core structure 44, except for the short distance through which the mandrel was raised. This distance may by proper judgment of ground conditions be safely determined so that little or no deformation will take place there. The clamping elements 46 are then again expanded to engage the shell 40 to lock it to the shell. A quantity of concrete is then poured from the top through the hollow space 47 to fill the empty distance of the shell. This concrete may then be tamped by inserting the ram 51 for that purpose. The remainder of the shell is thereafter filled by successive steps of raising the mandrel a few feet and locking it and additional quantities of concrete are added and tamped. It will thus be noted that during these filling operations the pile shell is not left alone to support the earth pressure, but is backed by the mandrel whether the latter is contracted or expanded.

For locations where the pile is to be driven into and terminated in silt or soft Watery strata, the pile'shell with its boot may be constructed to have a line of weakness all around near the bottom end thereof, as at line AA in Fig. 5. The shell is driven to position. Then when the first pouring of concrete is made, the ram is inserted and driven against the concrete. This'causes the bottom end of the shell below the line of weakening to be driven oil with the boot into the soft stratum and concrete passes out to form an enlarged concrete ball foundation. In the meantime, the pile shell is locked in position by the expanded mandrel. This procedure may be repeated until a secure footing of concrete has been made in the soft stratum. Under these particular conditions the soil in the ground is likely to be very mobile and under increasing fluid or plastic pressure as the depth is increased. The continuous rigid support by a rigid closely fitting driving mandrel as provided by the invention is highly desirable for efiective and accurate pile driving operations.

Longitudinal clamping means for mounting in the grooves of the rigid driving core structure in accordance with the invention may be made in different forms. In accordance with a preferred form the clamping means comprises a long tubular container, inflatable by fluid pressure to expand it and deflatable to contract it. simplified, form of pressure container 60, is shown in Fig. 6; there being one in each groove 48 of the rigid mandrel core 42. The tubular container 60 is of the generally flat type, presenting two wide clamping surfaces 61 to contact mandrel core 42 and the pile shell 40. The tubing 60 is of a rubber or rubber-like material or of similar nature which has been cured to assume the contracted flat shape when deflated, so that it will normally remain withdrawn within the mandrel surface of radius R. The flat sides may, if desired, be cured to conform accurately to the opposite surfaces of pile shell 40 and mandrel core.

The pressure container tubing 60 is preferably made of strong and tough material with relatively thick, textile reinforced, substantially non-elastic, 'or non-stretchable wall because it must be capable, when inflated, of locking the mandrel to the pile shell during the driving operation, so that the downwardly directed hammer blows on the mandrel are transmitted to the shell, and these blows must be of sulficient intensity to overcome the frictional resistance to downward movement of the shell imposed by the surrounding earth on the outside of the shell.

With the tubing 60 clearing the inner surface of the pile shell 40 by slightly more than the distance rR in contracted condition it may readily be expanded into contact with the pile shell. The surface of the wall material of the tubing serves to effect sufficient friction between the contacted metal surfaces of the shell to prevent undue slippage of the tubing during driving. Any convenient means may be provided to retain the tubing in the groove 48 when the mandrel is not in the shell, as during handling in the yard or in the field. The flat type tubing permits reduction to a practical minimum of the wall thickness of the mandrel pipe 44, so that a large hollow conduit may be provided for passing of concrete to the bottom of the mandrel. It may further be noted that the wide fiat surfaces 61 of the tubing 60 will retain substantially their full width in the expanded condition and that therefore a total required contact pressure may be obtained by a comparatively low specific fluid pressure within the tubing.

Referring now to Figs. 7-11 which show in some detail a driving mandrel embodying the invention which is particularly adapted for driving corrugated pile shells, the mandrel 100 comprises a full length rigid driving mandrel core 120 in tubular form which mounts four fluid pressure containers 140, circumferentially spaced 90 apart, only two being visible in Fig. 7; a centrally positioned full-length ram 160; and a drive head 170 for driving the mandrel core 120 and the ,ram 160.

The driving core structure 120 comprises a long continuous steel tube extending from the drive head 170 to the bottom end of the corrugated pile shell or casing 200. The upper end of the tube extends a short distance above the upper edge of the pile casing 200 for mounting of a reinforcing head ring 150 and fittings for the pressure containers 140.

Four spaced longitudinal channel strips 122 of steel, of a curved cross-section (see Fig. 8) are fastened against the outer surface of the tube 120 as by welding. The strips (which, for convenience of description, are herein referred to as peripheral surface plates) are mounted to provide spacings between them to form grooves 124 for the location of the four pressure fluid containers or tubings 140. The four outside peripheral curved surfaces 126 of these, plates 122 form the guide or backing surfaces for the pile shell. The circle defined by these curved surfaces has a radius R slightlysmaller than theradius. r of the circle definedby the inner surface of the pile shell. Consequently the surfaces 126 lie closely to the inner surface of the shell irrespective of whether the pressure tubings 140 are in inflated (expanded) or deflated (contracted) condition.

As shown in detail in Figs. 8 and 9, each pressure tubing 140 is of a generally flat shape with two wide parallel flat wall portions 142 throughout its length, these portions being joined by curved portions 143 of a comparatively short radius. The flat walls 142 may have a curvature conforming to the surfaces 126 of radius R but they are normally disposed slightly within the radius R when in deflated condition and are held in position by cross-pieces 128 at suitable intervals along the groove 124. The pressure container tubings are preferably of textile reinforced rubber-like material, the material being cured to retain the indicated shape in relaxed or deflated condition and to quickly return to that shape upon deflation after the tubing has been inflated or expanded.

The inner flat side 142 of the tubing normally bears against short transverse ridges 130 in the bottom of the groove, being held there by the cross-pieces 128. By this means the flat sides 142 may be held in an intermediate position within the groove 124 so that they may expand outwardly into contact with the corrugations and inwardly between the ridges 130. The expanded condition is illustrated in Figs. 10 and 11. For this purpose the ridges 130 may be spaced longitudinally about the same as the ridges in the corrugations of the pile casing 200, thereby causing both fiat sides 142 to be slightly distorted under expansion, thus greatly reducing warping strains in the tubing wall. The ridges 130 may be short bars, and they and the straps or cross-pieces 128 may be welded in position.

Whereas the nature of the surface of the rubber-like material of the tubings is such that it tends to cling to the metal surfaces and thus provides a good locking action between pile shell and mandrel, the fact that the outer wall 142 projects itself into the corrugations and the inner wall lays itself around the cross bars 130, insures that a positive mechanical locking effect distributed uniformly over the entire length of each tubing 140 is provided. By this effect the bottom edges of pile shell and mandrel core may be kept in accurate alignment despite the impacts during the driving, so that there will be no disturbance at the boot, and no stretching of the shell and also so that a weakened bottom end may be knocked off, when the mandrel is held stationary and only the ram is driven.

At the bottom end, the pressure container tubings 140 are closed tight to retain the fluid pressure. The ends may be vulcanized flat and clamped tight by clamps 144 which are fastened to the bottom of the grooves 124 (see Fig. 7). Below these clamps the plates 122 forming the grooves 124 may be cut short and terminate against a solid base ring 145 welded to the driving core 120 flush with its bottom edge for the purpose of completing the driving surface against the boot 210 and of providing an. outer backing surface for the collar 212 of the boot for full protection of the vulnerable edge of the boot.

The top end of each pressure container tubing 140 terminates in a circular shape and is fitted with suitable end cap 146 having a nipple 147 for attachment to:

to the upper end of the mandrel by screws. It may be removed for access to the tubing terminations when desired. The plates 122, forming the grooves 124, terminate:

at their upper ends in contact with the reinforcing, head.

ring 150;

The reinforcing ring 150 for the driving tube 120 is in the form of aheavy steel cylinder which fits down over the tube 120 and is securely welded thereto. The top edge 155 is flush with the end of tube 120 to present a large circular driving surface. The wall thickness of this reinforcement ring 150 is tapered downwardly toward the brackets 151, where it engages the four plates 122.

. Thus the bottom edge 156 of the head ring 150 will transmit the driving force to the plates 122, and through them to the boot 210 of the pile shell.

Two lugs 157 extend radially from the ring 158. These have suitable holes 157a for cables from the leads. Two or more other lugs 158 extend upwardly from the ring 150. They have holes 158a for bolting the lugs to the drive head 170.

Thus the common drive head 170 may be bolted to both the reinforced hollow mandrel core 120 and the ram 160 for raising or lowering both in unison and for driving on both simultaneously. The driving head may be unbolted from the mandrel core 120 by removing the bolts from holes 158a for raising or lowering the ram 160. Meanwhile, if desired, the shell may be held in position by clamping it to the core 120 which in turn may be anchored. The head may also be attached to the core for raising or lowering it within the pile shell and for driving on the core structure alone.

For the latter operation the mandrel core structure may be provided with a detachable bottom plate 180, as shown in Fig. 14. This plate has a foot portion 181 with a large bottom surface 182 for engagement with substantially the whole area of the boot 210 of the shell and with an upper shoulder surface 183 for receiving the thrusts from the mandrel core 120 and from the plates 122 acting through the ring 145. The bottom plate has a raised boss portion 184 fitting into the mandrel core pipe 120 and bolted thereto for withdrawal therewith when the driving has been completed. The ring 145 may be welded to the mandrel core 120, as already described, or it may be detachable with the bottom plate 180.

Thus, as shown in Figs. 7 and 8 the mandrel in con tracted condition fits closely to the corrugated pile shell 200 but it may readily be inserted therein until its bottom edge touches the boot 210 which is welded to the pile shell. The upper end of the mandrel core extends some distance above the upper edge of the pile shell to provide space for the pressure tubing terminations.

The ram 160 comprises a long steel tube 162 which when inserted, extends through the whole length of the mandrel core, and passes loosely inside the tube. At the bottom end, the ram, as shown in Fig. 7, has a solid foot 163 welded thereto to provide a driving surface against the boot 210 and to supplement the driving surface of the hollow mandrel core.

' The ram 160 is detachably mounted, at its upper end, to the mandrel head 170. As shown in Fig. 7, the hollow ram tube 162 is fastened at its top end, as by a bolt 165, to the drive head 170 which is common to the mandrel and the ram so that the ram may be detached. The drive head 170 is of solid construction and comprises a heavy circular driving plate 172 for engagement with the top edge 155 of the reinforced mandrel core. From the bottom of the plate 172 a shouldered boss 174 extends downward to fit inside the hollow mandrel core 120 and inside the ram tube 162 to which it is removably bolted by the bolt 165. The plate 172 has two or more slots 176 in its periphery to receive the lugs 158 for bolting the reinforcing ring 150, and hence the hollow core 120, to the head 170 during driving operations. An upstanding annular flange portion 177 serves to form a pocket to accommodate a hammer cushion 172a on the top surface of the plate 172. Suitable holes 178 are provided in plate 172 to lash the head to the base of the hammer for lifting the ram with or without the mandrel core.

When the mandrel core and drive head are joined at the lugs 158 and slots 176 the core and ram form a unit capable of driving the pile shell and its boot into the ground. By means of the bulging pressure fluid containers substantially non-slipping and non-elastic driving contact is established throughout the entire length of the pile shell. The corrugated surface of the pile shell is furthermore backed up both by the pressure tubings and, even more rigidly, by the closely fitting mandrel surfaces between the tubings, so that formation of dents or buckles in the shell are practically completely prevented. Also, the boot is well backed by the bottom surfaces of driving core and ram and the edge of boot and shell by the outer surface of the core, thereby simplifying the boot construction.

If desired, the mandrel may be made in sections which may be joined together by junction sections. Thus, as shown in simplified form in Figs. 12 and 13, two

core sections

231 and 232 of the mandrel are connected together to form a unitary structure by means of a junction section 235.

The two mandrel sections will be assumed to be of Y the same general design as that shown in Fig. 7, thus comprising the tubular driving structure with a plurality of expansion tubings 140 lodged in grooves 124 with cross-bars between longitudinal plates 122.

Whereas the mandrel core sections conveniently are hollow, the junction section 235 is not. It comprises a solid connector element 236 of generally cylindrical shape with an outer radius slightly less than the radius R of the plates 122, allowing for the thickness of an outer thin cylindrical shield 237 protecting the fittings at the ends of the tubings 140. The connector 236 which may be in the form of a steel casting has a recess 238 for each pair of terminations 240 with two shelves 241 for mounting the termination fittings. The casting has two shouldered neck portions 239 fitting snugly into the ends of the driving tubes 120 and is welded thereto.

The tubings are terminated in cylindrical caps 246 with nipples 247, the same as shown in Fig. 7 and the nipples in each recess are interconnected by a piece of hose 247a. The cylindrical shield 237 of thin plate is divided in half lengthwise and is fastened in position when the interconnections have been completed.

The top and bottom ends of the joined mandrel core sections may, if desired, be provided with recessed castings similar to the casting 236 except that each such casting will accommodate only one set of terminations for the tubings 140. The top casting may be shaped to fit a drive head such as and the bottom casting may be extended into a rigid driving foot or plate practically closing the bottom end of the driving tube 120.

This sectional type of mandrel is expanded and con? tracted in the same manner as that shown in Fig. 7 and is as effective in supporting the pile shell during driving.

A modified form of clamping means for clamping the mandrel to the shell is illustrated in Fig. 15, which shows in cross-section a fragment of a hollow core mandrel. The mandrel core 300 is in many respects like the construction of the mandrel core shown in Fig. 7. It comprises a rigid core structure, having a hollow steel tube.

320 on which are mounted a plurality of circumferentially spaced curved steel plates 322, spaced from tube 320 by spacer blocks 322a, and secured by welding. The plates 322 are mounted to provide spacings between them forming grooves 324, in which are mounted the clamping means 340. Grooves 324 extend longitudinally along the core, as do the grooves 124 in the embodiment illustrated in Fig. 7, and the driving tube 320 is provided with a reinforcing head ring, similar to ring 150 shown in Fig. 7 and a reinforcing foot ring similar to ring 145 shown in Fig. 7. The driving head is also constructed like driving head 170 (see Fig. 7) and the entire structure may be the same as shown in Fig. 7 except for the modifications described in more detail in connection with Fig. 15.

It will be observed that the surface plates 322 overhang the filler blocks 322a to form spring retainerflanges 323, one on each side of the groove 324. It will be understood that Fig. 15 illustrates a typical clamping unit and that like plates forming grooves and clamping units are mounted in spaced relation around the entire periphery of the mandrel core 300. The number of clamping units will depend upon the diameter of the pile shell which the mandrel is intended to drive. The smaller the diameter of the shell, the smaller will be the number of clamping units required. In the embodi ment shown in Fig. 15, the outside curved surfaces 326 of the plates 322 form the guiding and back up surfaces for the pile shell and correspond generally to the surfaces 126 in the embodiment illustrated in Fig. 7. As in the embodiment shown in Fig. 7, the radius R of the circle defined by the surface plates 322 in the embodiment shown in Fig. 15 is slightly less than the radius r of the circle defined by the interior suiface of the shell 200a.

Inasmuch as each of the clamping assemblies 340, spaced around the periphery of core 300, are the same, it will suflice to describe a typical assembly or unit as shown in Fig. 15. It comprises a longitudinal steel gripper element 342, a seating element 341, having mounted therebetween the fluid pressure container tubing 345, which, as shown in Fig. 15, is in deflated or contracted condition. The gripper and

seating members

342 and 341 have a length corresponding to the length of the groove 324. The seating member 341 is of generally U-shape, and has laterally extending flanges 341a which abut and rest against the side wall of the core tube 320 and has a cross member 341b providing a seat against which the inner wall of the fluid pressure tubing 345 rests. The gripper element 342 is of the same length and general shape as the seating element 341. It has laterally extending flanges 344a, which may abut flanges 341a when the tubing 345 is in deflated condition. The outside or gripper surface of the gripper element 342 has fixed thereon ridge or bar members 343 which are mounted crosswise and spaced at intervals along its length to register with the corrugations of the shell 200a. The gripper element 342 is spring biased toward the axis of the mandrel by means of two rows of compression springs 350, one row on each side of the groove 324, which urge the grippers 342 in an inward direction. The springs, in each row, are held in place by a pair of oppositely disposed retainer bars 351, having a length corresponding to grippers 342, and each having oppositely disposed recesses in which the ends of the springs are seated, thus retaining the springs in spaced parallel relation. One of each pair of spring retainer bars rests upon flange 344a of gripper 342 and the other retainer bar abuts and rests against flange 323 of plate 322. Both rows of springs 350 are mounted in the same manner.

When the tubing 345 is in deflated condition, as shown in Fig. 15, the springs 350 urge the grippers 342 inwardly so that the gripper surface and ridge bars 343 do not extend outwardly beyond the circle defined by the surface plates 322. Hence, when the clamping units .340 are in normal contracted condition the mandrel may be inserted 12 into and withdrawn from the shell 200a, in substantially the same way .as the embodiment shown in Fig. 7 when it is in contracted condition; the two embodiments being constructed in substantially the same way except for the clamping means 340 and surface plates 322.

When the mandrel is inserted in the shell 200a and it is desired to clamp it to the shell for driving or other purposes, fluid pressure is introduced into the pressure tubings 345 to inflate (expand) them. This causes the gripper elements 342 to move radially outward, against the opposing force of the springs 350, into gripping contact with the interior surface of the shell 200a, to lock the mandrel to the shell and the mandrel otherwise may be constructed and operated as the embodiments illustrated in Figs. 7 and 12 and described above.

Although the embodiments hereinabove described employ a plurality of pressure containers circumferentially spaced around the periphery of the mandrel core, the number employed may be different in different designs. In some instances, for example, in the design of mandrels for the smallest sizes of pile shells, a single clamping device may be used, as diagrammatically illustrated in Fig. 16, wherein one pressure tubing 440 along one side of the mandrel driving core 420 is employed. Fig. 17 diagrammatically illustrates still another spacing of the clamping devices 449 around the periphery of the mandrel core 420.

It will be seen from the foregoing that the invention provides a mandrel capable of various modifications and embodying many features of construction which are advantageous. Inasmuch as the mandrel core fits within the pile shell with its peripheral rigid surfaces lying in close proximity to the interior cylindrical surface of the shell to form a backing up support for the shell wall, buckling of the shell and formation of dents in its wall during driving, are elimiated or at least reduced to minimum.

The various features lend themselves to construction of a mandrel which may not only be used for driving but also, the separate driving tube and ram may be employed in such a way that after the shell is driven into place, the driving tube may be raised in successive steps, and locked each time to the shell to hold it in place, while concrete is introduced into the shell in batches through the hollow tube and then tamped by means of the ram which itself is adapted also for exerting driving impacts on the boot, if desired, during the driving operation. The mandrel also may be employed to drive a pile shell closed at its lower end with a so-called discardable boot, which may be knocked off after the pile shell has been driven to desired depth, so that concrete may be introduced and tamped to form a pile having an enlarged base in the form of a concrete bulb or ball foundation; this type of pile being particularly desirable where the footing of the pile rests in soft silt or like earth formation. From the foregoing description, other features and advantages will be apparent to those skilled in the art.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalent of the features shown and described or portions thereof, but it is recognized and to be understood that various modifications are possible within the scope of the invention claimed.

What is'claimed is:

1. An expansible driving mandrel for a pile shell of generally cylindrical shape which mandrel comprises driving core structure of generally cylindrical shape of fixed diameter and having a plurality of lengthwise rigid peripheral surface portions of arcuate shape in horizontal section dimensioned to fit closely Within the interior surface of said shell the radius of curvature of said arcuate surface portions being equal to the radius of said core,

and the longitudinal edges of said arcuate portions defining longitudinal channels therebetween, and having a plurality of lengthwise disposed expansible and contractable clamping means mounted within said channels between said rigid peripheral surface portions, said clamping means when in contracted condition lying within said radius of curvature of said arcuate surface portions and being operable to project beyond said peripheral surfaces and to engage the interior surface of said shell with gripping contact when in expanded condition,

2. A mandrel for driving a pile shell which comprises a core portion of generally elongate cylindrical shape having a fixed diameter and having peripheral surfaces of arcuate shape which closely fit within the shell when the mandrel is inserted in the shell for the driving operation, the arcuate surface of each of said peripheral surfaces having a radius of curvature equal to one-half said diameter, means at the edges of said arcuate surfaces defining a channel between each adjacent pair of arcuate surfaces, a plurality of cross bars secured to said core at the bottoms of said channels and spaced apart along the length of said channels, and pneumatic expansible and contractable pressure container clamping means mounted on said core portion adjacent said surfaces and within said channels and lying between said core and the interior surface of said shell when the mandrel is inserted in said shell for the driving operation, said pressure containers when in expanded condition contacting and positively gripping said shell and said cross bars and locking the mandrel thereto and when in contracted condition not positively gripping said shell and when in contracted condition permitting removal of said mandrel from said shell.

3. A mandrel for driving a pile shell which comprises an elongate hollow driving core of generally cylindrical shape having a plurality of peripheral arcuate surface plates secured thereto, said plates having outer arcuate shaped surfaces, whose radius of curvature corresponds to the radius of said cylindrical core and mounted to provide elongate channels between adjacent plates, said arcuate surface plates serving as back up means to prevent buckling of a shell into which said core is inserted for driving, clamping devices, including hollow inflatable and deflatable pressure containers mounted in each of said channels, a reinforcing head ring at the top of said core, a driving head, means removably mounting said driving head on said driving core, an elongate ram removably secured at its top end to said driving head and extending downwardly through said hollow core the full length of said core and terminating in a driving plate, said pressure containers when in deflated condition being retracted into said radius of said arcuate surfaces and when in inflated condition extending beyond said outer arcuate surfaces for clamping said core to said shell.

4. A mandrel for driving a pile shell which comprises an elongate rigid driving core of substantially cylindrical shape having a plurality of arcuate surface portions which closely fits into the pile shell for guiding thereof during the pile shell driving operation, said arcuate surface portions having a radius of curvature equal to the radius of said cylindrical core and spaced apart to provide channels between each pair of adjacent arcuate surfaces, said core having a plurality of expansible and contractable clamping devices mounted lengthwise at its periphery within said channels and operable when in expanded condition to grip the interior surface of said shell and clamp said driving core and shell together for the pile shell driving operation, said clamping devices comprising a gripper element, a seating element and an inflatable and deflatable flexible pressure container mounted between said elements, said gripper element being operable to press against the interior surface of the pile shell with a gripping force and the seating element operable to press against the periphery of said core when said pressure container is inflated and spring biasing means to return said gripper element to non-gripping position when said pressure con tainer is deflated.

5. A mandrel for driving a pile shell of a given diameter which comprises at least two elongate core portions of generally cylindrical shape and having a fixed diameter and having peripheral arcuate surfaces which closely fit within the pile shell to be driven when the mandrel is inserted therein for the driving operation, said arcuate surfaces having a radius of curvature equal to the radius of said core and spaced apart to provide longitudinal channels therebetween, a removable junction section secured to the bottom end of one of said core portions and to the top end of the other of said core portions, said longitudinal channels being at the periphery of said core portions, expansible and contractable clamping devices mounted in said channels, said clamping devices when in contracted condition lying within said radius of curvature of said arcuate surfaces and when in expanded condition extending beyond said arcuate surfaces to grip the interior surface of the shell when inserted in the shell for the driving operation.

6. A mandrel constructed according to claim 5 in which the clamping devices include elongate flexible inflatable and deflatable fluid pressure containers mounted in said channels.

7. An expansible mandrel adapted for placing a pile shell and a bulb pile in position in soft ground, said mandrel comprising an open bottom hollow rigid cylindrical driving core closely fitting into the pile shell, said core having a plurality of peripheral arcuate surface portions spaced apart to produce longitudinal external grooves therebetween at the periphery of said core, the radius of curvature of said arcuate surfaces being equal to the radius of said core, a plurality of expansion means disposed in said external grooves at the periphery of said core for clamping said core to the shell, said expansion means when deflated being withdrawn into said radius of curvature of said arcuate surfaces, a full-length rigid ram disposed inside said core and a driving head having securing means for attachment separately to said core and said ram for simultaneous driving on the pile shell by said core and ram into the ground and for separate driving on said ram against a charge of concrete poured to the bottom of said core.

8. A mandrel according to claim 7 in which each of said expansion means comprises a tubular pressure fluid container constructed of reinforced rubberlike material adapted for locking action with corrugations in the pile shell when expanded.

References Cited in the file of this patent UNITED STATES PATENTS 452,854 Smith May 26, 1891 777,351 Raymond Dec. 13, 1904 845,120 Raymond Feb. 26, 1907 1,654,644 Goldsborough Jan. 3, 1928 2,050,215 Watt Aug. 4, 1936 2,062,421 Lindbom Dec. 1, 1936 1 2,334,386 Cortella Nov. 16, 1943 2,421,666 Upson et a1 June 3, 1947 2,558,689 Miller June 26, 1951 2,741,093 Riker Apr. 10, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,911,795 November 10, 19.59

Walter HQ Gobi It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line '7, after "mandrel either for" insert m forming a bulb foundation at the lower end of the pile column 8, line 61 after "with" insert a column 12, line 36, for "elimieted. reed eliminated Signed and sealed this 3rd day of May 19660 Attest:

KARL H. AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents