Sonic Method For Installing A Pile Jacket, Casing Member Or The Like In An Earthen Formation

Abstract

A jacket member is placed over a bar which forms a mandrel and is acoustically coupled thereto by means of adjustable couplers at a plurality of points therealong. A sonic oscillator of the orbiting mass type is coupled to the mandrel and driven at a frequency such as to set up resonant standing wave vibration of the mandrel. Sonic energy is thus coupled to the jacket and in turn into the earth formation into which the jacket is to be installed, thereby fluidizing the earthen material and causing the jacket to be driven into the ground.

Parent Case Text

This application is a division of my application Ser. No. 873,298, filed Nov. 3, 1969 and now U.S. Pat. No. 3,624,760.

Description

This invention relates to the driving of jacket or casing members into the ground and more particularly to the use of sonic energy for implementing such driving action.

In the prior art, apparatus is utilized for forming piles in which a mandrel, which may be tapered or stepped, has a thin steel jacket placed thereover, the two members then being driven into the ground together by means of a hammer drive. When the mandrel and jacket are in position, the mandrel is then removed, leaving the steel jacket in the ground, this jacket then being filled with concrete to form a "cast-in-place" pile. The use of a tapered or stepped construction has an advantage in this type of prior art device in that it provides an optimum use of the steel in that the smaller diameter lower sections of the jacket are held in the solider, lower down portions of the earthen formation, while a larger diameter portion is provided closer to the surface where the earthen formation is generally not quite as dense.

A considerable improvement in the efficiency of the driving action of this type of device can be achieved by utilizing sonic energy to fluidize the earthen formation and thus implement the driving action. This type of sonic driving is described, for example, in my U.S. Pat. Nos. 2,975,846 and 3,379,263.

This invention is concerned with an improved technique for coupling the sonic energy to the earthen formation by transferring such energy from the mandrel to the jacket at a plurality of optimum coupling points therealong, and in an optimum manner, so as to provide higher efficiency in the utilization of the sonic energy in driving the jacket member into position. Further, in one embodiment of my invention, a stepped mandrel and a correspondingly stepped jacket is utilized, the mandrel providing heavy mass at one end for good impedance coupling to a relatively large orbiting mass oscillator and a much lower mass at the opposite driving end which thus has a high vibrational output for optimum driving action. The technique of the invention further utilizes sonic rectification of the energy at its coupling between the mandrel and the jacket to increase the efficiency of the driving operation to assure its maximum utilization.

It is therefore the principal object of this invention to improve the efficiency of the driving of a jacket or casing member into an earthen formation.

Other objects of the invention will become apparent as the description proceeds in connection with the accompanying drawings, of which:

FIG. 1 is an elevational drawing indicating the general operation of one embodiment of the device of the invention,

FIG. 2 is an elevational view in cross section illustrating the details of construction of this first embodiment,

FIG. 3 is an elevational view with partial cutaway section illustrating a coupling bushing member which may be used in the embodiment of FIG. 1,

FIG. 4 is an elevational view with partial cutaway section illustrating a removable tip portion which may be used in the embodiment of FIG. 1,

FIG. 5 is an elevational view in cross section of a second embodiment of the device of the invention, and

FIG. 6 is a cross sectional view taken along the plane indicated by 6--6 in FIG. 5.

Briefly described, the technique of the invention comprises the use of a mandrel member over which is placed a relatively thin wall elastic jacket member. The jacket member is coupled to the mandrel member at several spaced points therealong. An orbiting mass oscillator is coupled to one end of the mandrel member and driven at a frequency such as to set up standing wave resonant vibration therein, the coupler points between the mandrel and the jacket preferably being spaced to provide optimum overall energy utilization. The jacket and mandrel are placed in the ground, the sonic energy causing these members to be driven therein. In one embodiment of the device of the invention, the mandrel and jacket have a stepped configuration, the driving end having a much smaller diameter than the end being driven by the oscillator, thus providing optimum coupling between the oscillator and the mandrel with an impedance transformation being provided at the driving end to provide optimum coupling of the sonic energy from the driving tip to the ground. The coupler members for coupling the sonic energy from the mandrel to the jacket are adjustable so that they can be positioned for optimum transfer of energy from the jacket to such mandrel. A special tip attachment is provided to adapt the mandrel to various lengths of jacket in the field. In addition, the couplers are arranged so that they provide sonic rectification in the transfer of the sonic energy from the mandrel to the jacket for optimum utilization of this energy.

It has been found most helpful in analyzing the method of this invention to analogize the acoustically vibrating circuit utilized to an equivalent electrical circuit. This sort of approach to analysis is well known to those skilled in the art and is described, for example, in Chapter 2 of "Sonics" by Hueter and Bolt, published in 1955 by John Wiley and Sons. In making such an analogy, force F is equated with electrical voltage E, velocity of vibration u is equated with electrical current i, mechanical compliance C.sub.m is equated with electrical capacitance C.sub.e, mass M is equated with electrical inductance L, mechanical resistance (friction) R.sub.m is equated with electrical resistance R and mechanical impedance Z.sub.m is equated with electrical impedance Z.sub.e.

Thus, it can be shown that if a member is elastically vibrated by means of an acoustical sinusoidal force F.sub.o sin.omega.t (.intg. being equal to 2.pi.times the frequency of vibration), that

Where .omega.M is equal to 1/.omega.C.sub.m, a resonant condition exists, and the effective mechanical impedance Z.sub.m is equal to the mechanical resistance R.sub.m, the reactive impedance components .omega.M and 1/.omega.C.sub.m cancelling each other out. Under such a resonant condition, velocity of vibration u is at a maximum, power factor is unity, and energy is more efficiently delivered to a load to which the resonant system may be coupled.

It is important to note the significance of the attainment of high acoustical "Q" in the resonant system being driven, to increase the efficiency of the vibration thereof and to provide a maximum amount of power. As for an equivalent electrical circuit, the "Q" of an acoustically vibrating circuit is defined as the sharpness of resonance thereof and is indicative of the ratio of the energy stored in each vibration cycle to the energy used in each such cycle. "Q" is mathematically equated to the ratio between .omega.M and R.sub.m. Thus, the effective "Q" of the vibrating circuit can be maximized to make for highly efficient, high-amplitude vibration by minimizing the effect of friction in the circuit and/or maximizing the effect of mass in such circuit. The heavy, tapered pile gives good Q. Moreover, the rectifier action also increases the energy retention in the mandrel.

In considering the significance of the parameters described in connection with equation (1), it should be kept in mind that the total effective resistance, mass, and compliance in the acoustically vibrating circuit are represented in the equation and that these parameters may be distributed throughout the system rather than being lumped in any one component or portion thereof.

It is also to be noted that orbiting-mass oscillators are utilized in the implementation of the invention that automatically adjust their output frequency and phase to maintain resonance with changes in the characteristics of the load. Thus, in the face of changes in the effective mass and compliance presented by the load with changes in the conditions of the work material as it is sonically excited, the system automatically is maintained in optimum resonant operation by virtue of the "lock-in" characteristic of applicant's unique orbiting mass oscillators. Furthermore in this connection the orbiting mass oscillator automatically changes not only its frequency but its phase angle and therefore its power factor with changes in the resistive impedance load, to assure optimum efficiency of operation at all times. This automatic adjustment to load impedance works particularly well with the rectifier feature of this invention. The vibrational output from such orbiting mass oscillators also tends to be constrained by the resonator to be generated along a controlled predetermined coherent path to provide maximum output along a desired axis.

Referring now to FIG. 1, a first embodiment of the device of the invention is illustrated. Mandrel 11 includes stepped sections 11a, 11b and 11c, which are fixedly joined together by suitable means such as welding, or interference fit, to form a one-piece integral unit. Mandrel 11 may be formed of cylindrical, thick walled pipe of a highly elastic material such as steel. Placed over the mandrel sections 11a, 11b and 11c are thin wall steel corrugated tubing sections 12a, 12b and 12c, which form a jacket around the mandrel. The jacket sections are coupled to each other by corrugated couplings 14 and 15, as to be described in connection with FIG. 2. The mandrel is coupled to the jacket, with rectifier action, by means of adjustable or selected bushings 17 and 18, as shown in FIG. 2 and later to be described in connection therewith. Suffice it to say at this point that the couplings may be adjusted to provide the rectified coupling (unidirectional portion of the elastic displacement cycle) of sonic energy in an optimum manner from the mandrel to the jacket.

An orbiting mass oscillator 16 has its casing attached to the top end of mandrel 11 and is rotatably driven by drive means (not shown) coupled to the oscillator through drive shaft 20. Oscillator 16 may be of the type described in my U.S. Pat. No. 3,379,263, which utilizes a pair of eccentric rotors which are rotated in opposite directions so that they produce vibration of mandrel 11 along the longitudinal axis thereof. The speed of rotation of oscillator 16 is adjusted to a frequency whereat resonant standing wave vibration of the mandrel occurs. The resonant energy is coupled from the mandrel through jacket 12 to earthen formation 25 to fluidize the formation thereby causing the mandrel and the jacket to be driven therein.

Referring now to FIGS. 2-4, the details of construction of a first embodiment of the device of the invention are illustrated. As already noted, cylindrical corrugated steel jackets 12a-12c fit over associated mandrel sections 11a-11c respectively. Jacket section 12a is joined to jacket section 12b by means of cylindrical corrugated coupler 14, which matingly engages the ends of these sections in the manner of screw threads. Jacket section 12b is similarly coupled to section 12c by means of coupler 15. Acoustical coupling is provided between mandrel section 11a and jacket section 12a by means of adjustable or selected bushing coupler member 17, the details of which are illustrated in FIG. 3. Bushing 17 includes a cylindrical tapered spacer member 17a. The bushing may be held to the mandrel in a desired position opposite shoulder portion 14a of coupler 14 by means of the wedge action provided by collet 17b with the tightening of screws 17d. Further holding action for retaining the bushing to the mandrel is provided by set screw 17c. Prior to the time that jacket section 12a is placed over mandrel section 11a, bushing 17 is placed in the desired position for coupling energy therebetween and attached to the mandrel in this position by means of collet 17b and set screw 17c. This adjustment should be made to provide a small "rectifier" gap 19 between the jacket and the mandrel so that only unidirectional pulses of sonic energy are transferred to the jacket (i.e., the half-cycle of the sonic energy which provides a downward pulse), the mandrel being substantially uncoupled from the jacket on the upward vibratory excursion. The device thus functions as a sonic rectifier, downward driving pulses of sonic energy being provided from the mandrel to the jacket. Bushing 17 should be positioned in place or dimensioned so that gap 19 is such as to afford optimum transfer of downward pulsating energy. This gap has to be less than the longitudinal distance traversed by the mandrel in an elastic half cycle. Coupler bushing 18 is similarly adjusted in position for optimum coupling of unidirectional sonic energy between mandrel section 11b and the shoulder portion 15a of jacket coupler 15.

The frequency of oscillator 16 is adjusted to provide a standing wave pattern in the mandrel as indicated by graph lines 30. The resonant vibration as shown should be at a frequency whereby any two of the coupling points, i.e., in this instance those at coupler bushings 17 and 18, are spaced within a quarter wave length of the standing wave pattern so that the sonic drives on the jacket at these various points are in unison, thereby minimizing the stress on jacket. A removable tip portion 37 is utilized, various lengths of these tip portions being available for installation at the end of the mandrel to match various lengths of jackets so as to provide rectifier action as the need may arise in the field. Tip portion 37, or any of the other joints in the mandrel, may have a tongue 37a thereon which fits into cavity 38 in the center portion of the adjoining portion of the mandrel, joinder between the two members being attained by means of a tapered key 40 which fits through apertures in tongue 37a and mandrel 11c and is held to the mandrel by means of bolt 42 and nut 43.

Several significant features of this first embodiment should be noted at this point. First, the stepped mandrel structure provides a heavy mass at one end for optimum coupling to a large massive oscillator, and a much lower mass at the opposite end to provide an effective step-up transformation of the vibration resulting in high amplitude vibration at the driving end, where it is most needed. Secondly, the adjustable or selected bushings 17 and 18 provide means for adjusting the coupling between the mandrel and the corrugated jacket to optimum rectifier advantage for each particular installation requirement. Likewise, the use of a removable driving tip enables the use of a tip member which provides optimum driving. Further, the adjustment of the coupling between the mandrel and the jacket through the adjustable bushings to provide sonic rectification, i.e., vibrational drive only in the downward direction, provides the advantages of minimizing the stress placed on the jacket and further makes for better utilization of the sonic energy in that it is not dissipated in an upward loaded excursion, which provides no useful effect in the driving action. The sonic vibrational system by virtue of the sonic rectifier action is made to have a higher effective "Q" in view of the fact that the ratio between the energy stored to the energy dissipated in each vibrational cycle is thereby increased.

When the jacket has been installed in the desired position, the mandrel is lifted out therefrom and the jacket filled wit concrete to form the piling.

Referring now to FIGS. 5 and 6, a second embodiment of the device of the invention is illustrated. In this embodiment, the tapered mandrel and jacket of the first embodiment are not used, the mandrel being coupled to the corrugated jacket by means of a plurality of specially designed coupler devices.

Mandrel 51 has a plurality of coupler units 53 installed therein at spaced intervals therealong. Each coupler unit 53 may include three piston units 54, slidably supported in radial cylinders 56 formed in the mandrel. Pistons 54 are hydraulically actuated by pressurized fluid fed through line 58 to channel 59 formed in the center of the mandrel. With the pistons 54 unactuated, jacket member 60 is placed over the mandrel. The pistons 54 are then hydraulically actuated to drive them to the position indicated by the dotted lines in FIG. 6, the radial travel of the pistons being arrested by the abutment of piston shoulder 54a against shoulder 66a of retainer plate 66, which is fixedly retained in the mandrel. The travel of piston 54 is thereby arrested as shown by the dotted lines, in a position whereat there is a small gap between piston head 54b and the inner wall of corrugated jacket 60 both radially and longitudinally. This gap provides the "rectifier gap" necessary to achieve the desired sonic rectification. Thus, with the excitation of oscillator 16 at a frequency such as to cause longitudinal resonant standing wave vibration of mandrel 51, and with pistons 54 in their extended position, unidirectional sonic pulses are coupled from the mandrel to the corrugated jacket at the longitudinal gaps formed between the piston heads and the adjacent jacket corrugations. This second embodiment thus provides another way of transferring unidirectional sonic downward driving pulses to the jacket at several points therealong.

The method of this invention thus provides improved means for acoustically driving a pile jacket in which unidirectional sonic driving pulses are applied to the jacket in the driving direction at several points therealong.

Claims

I claim:

1. A method for installing a jacket in the ground comprising the steps of:

placing said jacket over an elastic mandrel member,

placing one end of said mandrel member and jacket member in the ground,

resonantly elastically vibrating said mandrel member so as to set up standing wave vibration therealong, and

coupling unidirectional pulses of said vibrational energy from said mandrel member to said jacket at a plurality of predetermined points spaced therealong to drive said mandrel member and jacket into the ground.

2. The method of claim 1 wherein the pulses of energy coupled at said predetermined points are applied in unison.

3. The method of claim 1 and further including the step of applying an extension to the end of the mandrel member to match its length to that of the jacket member.