Patent Description:
The cost of constructing a foundation pile depends on, among other things, the amount of material needed to construct the pile. Two practices for reducing the amount of material required are: (<NUM>) constructing a pile with an enlarged base; and (<NUM>) preloading the pile base.

Foundation piles with enlarged bases may achieve a similar or greater loading and/or pull out capacity than foundation piles without enlarged bases while using similar or even less material (material such as concrete or grout).

Existing tools and methods for constructing foundation piles with enlarged bases typically require underreaming of a pile shaft to form a bulb at a base thereof. Such tools and methods often require temporary hole support in the form of steel casings or the like, and the use of several different tools.

Preloading (or prestressing) the base of a pile can enhance pile performance by inducing settlements prior to actual use of the foundation pile. This can better inform material usage, drilling depth and/or pile diameter.

However, existing methods for preloading the base of a pile typically require the use of grout under high pressure and various types of expanding sleeves or bags. To preload a pile base using pressure grouting, a hollow section or grout tubes and an expansion body have to be preinstalled in an underground void. Moreover, before pressure grouting can be performed, the pile shaft has to be formed and be of sufficient strength, and a secondary mobilisation to site is often required.

Existing tools and methods for forming piles with enlarged bases and for preloading piles can be relatively time, labour, and material-intensive, and thus costly.

Additionally, it can be difficult to determine the actual loading capacity of a foundation pile using existing piling tools and methods. As such, foundation piles are often excessively overengineered with design safety factors of three or more. This results in piling contractors digging deeper and installing wider and/or deeper foundation piles than are actually necessary, thereby increasing material and labour costs.

<CIT> discloses a hollow auger for making piles. The auger comprises a hollow support tube with a helical external blade which extends along the length of the support tube.

<CIT> discloses a drilling auger. The auger comprises two concentric tubes, with helical screws extending along the lengths of the two concentric tubes.

<CIT> discloses a cutting head for making a threaded continuous flight auger pile. The cutting head comprises an inner hollow tubular member, with a helical flight which extends along the length of the tubular member.

<CIT> discloses a drilling auger for making enlarged base piles having two concentric tubes.

It is desired to overcome or alleviate one or more difficulties associated with existing piling tools and/or methods, or to at least provide a useful alternative.

According to a first aspect of the present invention, there is provided a tool for forming an underground cast-in-situ pile having an enlarged base, the tool comprising:.

In embodiments of the invention, the jack screw means is threadingly engaged with the first pile-forming member such that rotation of the jack screw means in one direction moves the pile-forming members into the digging state, and rotation of the jack screw means in the opposite direction moves the pile-forming members into the base-forming state. This power screw mechanism for moving the pile-forming members relative to one another is simple to operate and can be fitted to and used by existing excavators and piling rigs which are often already equipped with rotary heads which can be used to drive the jack screw means.

In embodiments of the invention, the jack screw means and the second pile-forming member are rotatable, but not longitudinally movable, relative to one another. To this end, the second pile-forming member may comprise a collar via which the jack screw means is secured to restrict relative longitudinal movement therebetween. A thrust bearing may be disposed between the jack screw and the second pile-forming member to enable relative rotation therebetween. In this way, rotation of the jack screw in a direction which drives the base-forming members towards the base-forming state results in either one pile-forming member being driven deeper into the ground, or the other pile-forming member being raised, depending on whether the former or the latter movement requires less torque. This will be influenced by the composition of the ground in which the pile-forming members are in.

In embodiments of the invention, the tool also comprises limiting means for limiting the extent to which the base-forming members can be spaced from one another. The limiting means may take the form of a collar extending from the jack screw means. In this way, when the pile-forming members are moved into the base-forming state, the first pile-forming member is brought into contact with and engages the collar, thereby restricting further longitudinal movement between the pile-forming members which would further increase the space between the base-forming members.

In embodiments of the invention, the pile-forming members are telescopically arranged and configured such that one pile-forming member cannot be rotated independently of the other pile-forming member.

In embodiments of the invention, the first pile-forming member is a first screw pile; the second pile-forming member is a second screw pile; the first base-forming member is a first helix; and the second base-forming member is a second helix. As such, the present tool may be realised by known screw/helical pile arrangements.

In embodiments of the invention, the first pile-forming member is a first blade pile; the second pile-forming member is a second blade pile; the first base-forming member is a first blade; and the second base-forming member is a second blade. As such, the present tool may be realised by known blade pile arrangements.

According to a second aspect of the present invention, there is provided a method of forming an underground cast-in-situ pile having a shaft and an enlarged base, the method using a tool of the first aspect of the invention and comprising:.

In embodiments of the method, step (b) further comprises:.

In embodiments of the method, the force relates to a torque force applied to the jack screw means to move the pile-forming members towards the base-forming state.

Therefore, the torque required to be applied to the jack screw means to move the pile-forming members towards the base-forming state can be indicative of a load bearing capacity of a foundation pile constructed at a certain depth underground.

In embodiments of the method, the force relates to an axial load carried by one or both of the pile-forming members. This axial load can be measured by one or more strain gauges fitted to the or each pile-forming member. The axial load and thus reading from the strain gauge(s) can also be indicative of the load bearing capacity of a foundation pile constructed at a certain depth underground.

<FIG> shows a piling rig <NUM> to which is fitted a tool <NUM> embodying the present invention.

The tool <NUM> comprises longitudinally extending pile-forming members and a jack screw means <NUM>. A rotary head <NUM> of the piling rig <NUM> can be used to selectively drive the jack screw means <NUM> and the pile-forming members.

<FIG> shows the tool <NUM> in greater detail. The tool <NUM> can be used to form an underground cast-in-situ pile having an enlarged base. The tool <NUM> comprises a first pile-forming member which is depicted in the Figures as an external screw pile <NUM>. The external screw pile <NUM> has a first base-forming member which is depicted in the Figures as an upper helix <NUM>. The tool <NUM> also comprises a second pile-forming member which is depicted in the Figures as an internal screw pile <NUM>. The internal screw pile <NUM> has a second base-forming member which is depicted in the Figures as a lower helix <NUM>.

The two piles <NUM> and <NUM> extend collinearly with one another and are telescopically arranged such that one can move in a longitudinal direction relative to the other. The tool <NUM> also comprises a jack screw means <NUM>, henceforth referred to as a jack screw <NUM>. Rotation of the jack screw <NUM> is configured to cause relative longitudinal translation between the two screw piles <NUM> and <NUM>.

The internal screw pile <NUM> is tubular and comprises a longitudinally extending inner channel <NUM> through which a flowable fill, such as mortar, cement or grout, can be supplied from above. To form the shaft portion of a cast-in-situ pile, the flowable fill can exit through an outlet <NUM> at a lower end of the internal screw pile <NUM> as the tool is driven out of the ground. A lower end of the internal screw pile <NUM> carries the lower helix <NUM>. In certain embodiments of the tool <NUM>, the outlet <NUM> is closed by a sacrificial cap while the tool penetrates underground, not dissimilar to those used in respect of continuous flight auger piles. Of course the outlet <NUM> may be closed by other means to prevent soil from entering into the channel <NUM> of the internal pile <NUM> as the piles <NUM> and <NUM> are driven underground.

The external screw pile <NUM> extends in the longitudinal direction and defines a channel <NUM> through which the internal pile <NUM> passes through. The external pile <NUM> comprises a lower shaft section <NUM>, which carries the upper helix <NUM>, and an upper threaded section <NUM>.

The upper threaded section <NUM> has an external diameter that is larger than that of the lower shaft section <NUM>. The threaded section <NUM> comprises a tubular cavity having an internal thread <NUM> which allows the external pile <NUM> to form a power screw engagement with the jack screw <NUM>.

The jack screw <NUM> comprises a tubular body <NUM> through which the internal screw pile <NUM> extends in the longitudinal direction. An upper end of the tubular body <NUM> is releasably secured to the internal pile <NUM>. To this end, the jack screw <NUM> comprises an upper rim <NUM>, and the internal pile comprises a corresponding collar <NUM> whose diameter is greater than the inner diameter of the tubular body <NUM> of the jack screw <NUM>. As such, if the internal pile <NUM> were to be inserted into the jack screw <NUM> from above, the collar <NUM> of the internal pile <NUM> would abut against the rim <NUM> of the jack screw <NUM>, thereby preventing the internal pile <NUM> from traveling further through the jack screw <NUM>.

In the depicted embodiment of the tool <NUM>, a thrust bearing <NUM> is disposed between the rim <NUM> of the jack screw <NUM> and the collar <NUM>. The thrust bearing <NUM> is contained within an annular side wall <NUM> of the jack screw <NUM> which projects upwardly from the rim <NUM>. A second thrust bearing <NUM> fits over and around the internal pile <NUM> and sits upon the collar <NUM>. An upper plate <NUM> through which the internal pile <NUM> passes is fitted over the second thrust bearing <NUM> and is secured to the rim <NUM> of the jack screw <NUM> via bolts <NUM>. This thrust bearing <NUM> and <NUM> engagement between the internal pile <NUM> and the jack screw <NUM> enables rotation and restricts longitudinal translation therebetween.

A lower end of the tubular body <NUM> of the jack screw <NUM> carries an external thread <NUM> which is threadingly engageable with the threaded upper section <NUM> of the external pile <NUM>. In this way, rotation of the jack screw <NUM> in a first direction causes longitudinal translation of the screw piles <NUM> and <NUM> relative to one another. In other words, rotational force (i.e. torque) applied to the jack screw <NUM> is converted into linear motion of the screw piles <NUM> and <NUM> relative to one another.

<FIG> shows the tool <NUM> in a digging state. In the digging state, the upper helix <NUM> of the external pile <NUM> physically engages the lower helix <NUM> from above. This physical engagement between the helices <NUM> and <NUM> prevents both the jack screw <NUM> and the external pile <NUM> from being rotated in a manner that would lead to the unscrewing of the jack screw <NUM> and external pile <NUM> from one another. In other words, the external pile <NUM> is prevented from being unscrewed from the jack screw <NUM> by virtue of the lower helix <NUM> blocking movement of the upper helix <NUM> and thus the external pile <NUM>.

Both screw piles <NUM> and <NUM> are rotationally locked to one another. Referring to <FIG>, the piles <NUM> and <NUM> are engaged with one another in a slot and key arrangement <NUM> such that neither screw pile <NUM> and <NUM> can be rotated independently of the other. In other words, rotation of one pile causes rotation of the other. Of course, the number of slots and keys can vary and the male and female locking relationship between the piles <NUM> and <NUM> can be the inverse of what is depicted in <FIG>.

Referring back to <FIG>, when the tool <NUM> is in the digging state, the screw piles <NUM> and <NUM> can be driven into the ground to a predetermined depth. To this end, torque is applied to the jack screw <NUM> (e.g. from the rotary head <NUM> of a piling rig <NUM>) so as to rotate it in a first direction which would notionally unscrew the jack screw <NUM> and external pile <NUM> from one another. Since the physical engagement between the helices <NUM> and <NUM> prevents such unscrewing (as discussed above), rotation of the jack screw <NUM> in the first direction simply rotates both screw piles <NUM> and <NUM> so that they can be driven into the ground to a predetermined depth. With the helix <NUM> and <NUM> of each pile <NUM> and <NUM> engaged with one another, the screw piles <NUM> and <NUM> can be screwed into the ground as shown in <FIG>.

Once the screw piles <NUM> and <NUM> have been driven to a predetermined depth, the piling rig operator can start forming the notional void in which the enlarged base is to be constructed. Referring to <FIG>, the direction of the torque applied to the jack screw <NUM> is reversed so as to rotate the jack screw <NUM> in a second direction. This causes the jack screw <NUM> and the external pile <NUM> to screw towards one another. Consequently, the helices <NUM> and <NUM> are driven apart from one another so that they are spaced from one another in the longitudinal direction, as indicated by reference numeral LI. The separation of the helices <NUM> and <NUM> from one another creates a notional underground void with a diameter that approximates the diameter of the helices <NUM> and <NUM>, and a height that approximates the longitudinal distance LI between the upper helix <NUM> and the lower helix <NUM>. As this notional void is formed, the flowable fill is supplied through the tool <NUM> and exits side outlets <NUM> (shown in <FIG>) thereof so as to fill the void and form the enlarged base.

Referring to <FIG>, continued rotation of the jack screw <NUM> in the second direction moves the screw piles <NUM> and <NUM> into a base-forming state wherein the helices <NUM> and <NUM> are maximally spaced from one another, as indicated by reference numeral L2. The tool <NUM> may comprise limiting means which restrict further separation between the helices <NUM> and <NUM>. In the embodiment shown in <FIG>, the jack screw <NUM> comprises limiting means in the form of an externally projecting collar <NUM>. The collar <NUM> defines a surface against which an upper rim <NUM> of the external pile <NUM> abuts if the jack screw <NUM> continues to be rotated in the second direction. By virtue of the external pile <NUM> physically abutting against the collar <NUM>, further rotation of the jack screw <NUM> in the second direction does not act to further separate the helices <NUM> and <NUM> from one another. As such, the limiting means acts to define the maximum distance L2 the helices <NUM> and <NUM> can be spaced from one another in the longitudinal direction.

A method of using the tool <NUM> will now be described. Referring to <FIG>, the tool <NUM> is positioned above the ground and the screw piles <NUM> and <NUM> are moved (e.g. via the jack screw <NUM>) so that they assume the digging state wherein the helices <NUM> and <NUM> are proximate to and preferably engaged with one another. In other words, the helices <NUM> and <NUM> are substantially not spaced from one another in the longitudinal direction, as shown in <FIG>. The screw piles <NUM> and <NUM> can then be drilled underground to a predetermined depth, as shown in <FIG>.

With reference to <FIG>, once the screw piles <NUM> and <NUM> have been drilled to the predetermined depth, the piling rig operator can apply torque to the jack screw <NUM> (or external pile <NUM>) via the rotary head <NUM> in a direction which screws the jack screw <NUM> and external pile <NUM> toward one another, so as to begin separating the helices <NUM> and <NUM> from one another.

The torque required to separate the helices <NUM> and <NUM> can be indicative of ground composition and thus ground quality and stability. The magnitude of this torque can be used to estimate a loading capacity of an enlarged base should an enlarged base be formed at the predetermined depth. As such, as the piling operator separates the two helices <NUM> and <NUM> from one another, the operator may note the magnitude of the torque applied. If the torque is below a threshold amount which is indicative of a sufficiently strong enlarged base, then the operator can cease separation of the helices <NUM> and <NUM>, and instead, move the screw piles <NUM> and <NUM> back into the digging state and continue drilling deeper to a second predetermined depth, where the operator can again commence separation of the helices and determine if the applied torque is equal to or greater than the threshold amount. In this way, the depth at which the foundation pile should be installed can be quickly and easily estimated simply by considering the torque that is required to separate the helices <NUM> and <NUM>. This obviates the alternative of excessively overengineering the foundation pile due to load bearing uncertainty (e.g. digging far deeper than is necessary and constructing foundation piles with diameters far greater than necessary).

It should be noted that forces other than the torque applied to the jack screw can be used to predict the loading capacity of a foundation pile. For example, one or more strain gauges can be fitted to one or both piles <NUM> and <NUM> to measure the axial loading thereof as the piles <NUM> and <NUM> are moved away from one another. In this way, axial forces in the or each pile <NUM> and <NUM> can also be used to predict the load bearing capacity of a foundation pile.

Once the piling rig operator determines that the magnitude of the torque or axial force required to separate the helices <NUM> and <NUM> is equal to or greater than a threshold amount which is indicative of a sufficiently strong enlarged base, the operator can continue separating the helices <NUM> and <NUM> while supplying the flowable fill through the tool <NUM> channel <NUM> and out the side outlets <NUM> of the internal pile <NUM>. The flowable fill thus gradually fills up the notional void created by the separation of the helices <NUM> and <NUM>, thereby forming the enlarged base of the foundation pile.

The screw piles <NUM> and <NUM> can then be gradually withdrawn (e.g. by backscrewing) from the ground. As the piles <NUM> and <NUM> are withdrawn, the flowable fill is supplied through the tool <NUM> channel <NUM> and out the outlet <NUM> so as to fill in the notional void created by the length of the tool <NUM>, thereby forming the shaft of the cast-in-situ pile. The diameter of the shaft approximates the smaller diameter of the tubular bodies of the screw piles <NUM> and <NUM>, rather than the larger diameter of the helices <NUM> and <NUM>. In this way, a cast-in- situ foundation pile can be formed with an enlarged base, and the loading capacity of the foundation pile can be known with greater accuracy.

Tools <NUM> embodying the present invention may also be fitted to and used with other machines, such as an excavator <NUM>. An example is shown in <FIG>.

Claim 1:
A tool (<NUM>) for forming an underground cast-in-situ pile having an enlarged base, the tool (<NUM>) comprising:
a first pile-forming member (<NUM>) having a first base-forming member (<NUM>);
a second pile-forming member (<NUM>) having a second base-forming member (<NUM>), the pile-forming members (<NUM>, <NUM>) extending collinearly and being movable in a longitudinal direction relative to one another between:
a digging state wherein the base-forming members (<NUM>, <NUM>) are proximate to one another so that together, they define a leading helix of the tool (<NUM>) such that the pile-forming members (<NUM>, <NUM>) can be driven underground to form an elongate hole underground having a first diameter; and
a base-forming state wherein the base-forming members (<NUM>, <NUM>) are spaced from one another in the longitudinal direction so as to form an underground void between the first and second base-forming members (<NUM>, <NUM>) at a depth of the elongate hole, the void having a second diameter that is greater than the first diameter and being fillable with a flowable fill to form the enlarged base of the underground cast-in-situ pile; and
jack screw means (<NUM>), rotation of which causes relative longitudinal movement between the pile-forming members (<NUM>, <NUM>).