Patent Application
20080101873
In a principal aspect, the present invention relates to a method and apparatus for constructing a support pier comprised of one or more compacted lifts of aggregate material. The apparatus enables formation or construction of a single or multi-lift pier within a soil matrix while simultaneously reinforcing the soil adjacent the pier. The apparatus thus forms a cavity in the soil matrix by forcing a hollow tube device into the soil matrix followed by raising the tube device, releasing or injecting aggregate through the tube device into the cavity section beneath the raised tube device and then for multi-lift piers driving, pushing, lowering, and/or forcing, the tube device downward to compact the released aggregate material while simultaneously forcing the aggregate material vertically downward and laterally outward into the surrounding soil matrix.
In U.S. Pat. No. 5,249,892, incorporated herewith by reference, a method and apparatus are disclosed for constructing short aggregate piers in situ. The process includes drilling a cavity in a soil matrix and then introducing and compacting successive layers or lifts of aggregate material in the cavity to form a pier that can provide support for a structure. Such piers are made by first drilling a hole or cavity in a soil matrix, then removing the drill, then placing a relatively small, discrete layer of aggregate in the cavity, and then ramming or tamping the layer of aggregate in the cavity with a mechanical tamper. The mechanical tamper is typically removed after each layer is compacted, and additional aggregate is then placed in the cavity for forming the next compacted layer or lift. The lifts or layers of aggregate, which are compacted during the pier forming process, typically have a diameter of 2 to 3 feet and a vertical rise of about 12 inches.
This apparatus and process produce a stiff and effective stabilizing column or pier useful for the support of a structure. However this method of pier construction has a limitation in terms of the depth at which the pier forming process can be accomplished economically, and the speed with which the process can be conducted. Another limitation is that in certain types of soils, especially sand soils, cave-ins occur during the cavity drilling or forming process and may require the use of a temporary casing such as a steel pipe casing. Use of a temporary steel casing significantly slows pier production and therefore increases the cost of producing piers. Thus, typically the process described in U.S. Pat. No. 5,249,892 is limited to forming piers in limited types of soil at depths generally no greater than approximately 25 feet.
As a result, there has developed a need for a unique pier construction process and associated special mechanical apparatus which can be successfully and economically utilized to form or construct aggregate piers at greater depths, at greater speeds of installation, and in sands or other soils that collapse and are unstable when drilled, without the need for a temporary casing, yet having the attributes and benefits associated with the short aggregate pier method, apparatus, and construction disclosed in U.S. Pat. No. 5,249,892, as well as additional benefits.
Briefly, the present invention comprises a method for installation of a pier formed from one or more layers or formed lifts of aggregate material, with or without additives, and includes the steps of positioning or pushing or forcing an elongate hollow tube having a special shaped bottom head element and unique tube configuration into a soil matrix, filling the hollow tube including the bottom head element with an aggregate material, releasing a predetermined volume of aggregate material from the bottom head element as the hollow tube is lifted a predetermined incremental distance in the cavity formed in the soil matrix, and then imparting an axial, static vector force and optional dynamic vector forces onto the hollow tube and its special bottom head element to transfer energy via the lower end of the shaped bottom head element of the hollow tube to the top of the lift of released aggregate material thereby vertically compacting the lift of aggregate material and also, simultaneously forcing a portion of the released aggregate material laterally or transaxially into the sidewalls of the cavity. Lifting of the hollow tube having the special bottom head element followed by pushing down with an applied axial or vertical static vector force and optional dynamic vector forces impacts the aggregate material which is not shielded by the hollow tube from the sidewalls of the cavity at the time of impaction, thereby densifying and vertically compacting the aggregate material as well as forcing a portion of the aggregate material laterally outward into the soil matrix due to the shaped bottom of the bulbous bottom head element facilitating lateral forces on and within the released aggregate material and therefore imparting lateral stress on the adjacent soil matrix. The released, compacted, and partially displaced aggregate material thus defines a “lift” which generally has a lateral dimension or diameter greater than that of the cavity formed by the hollow tube and bulbous bottom head element resulting in a pier construction formed of one or more compacted lifts of aggregate material.
The aggregate material is released from the special bottom head element of the hollow tube as the bulbous bottom head element is lifted, preferably in predetermined incremental steps, first above the bottom of the cavity and then above the top portion of each of the successive pier aggregate lifts that has been formed in the cavity and the adjacent soil matrix by the process. The aggregate material released from the hollow tube is compacted by the compacting forces delivered by the hollow tube and special bottom head element after the hollow tube has been lifted to expose a portion of the cavity while releasing aggregate material into that exposed portion. The hollow tube and bulbous bottom head element is next forced downward to vertically compact the aggregate and to push a portion of the aggregate laterally into the soil matrix. The aggregate material is thereby compacted and partially displaced in predetermined, sequential increments, or lifts. The process is continuously repeated along the length or depth of the cavity with the result that an aggregate pier or column of separately compacted lifts or layers is formed within the soil matrix. A vertically compacted aggregate pier having a length of fifty (50) feet or greater can be constructed in this manner in a relatively short period of time without removal of the hollow tube and special bottom head element from the soil. The resulting vertically compacted aggregate pier also generally has a formed cross sectional dimension consistently greater than that of the hollow tube.
A number of types of aggregate material can be utilized in the practice of the process including crushed stone of many types from quarries, or re-cycled, crushed concrete. Additives may include water, dry cement, or grout such as water-cement sand-grout, fly-ash, hydrated lime or quicklime, or any other additive may be utilized which may improve the load capacity or engineering characteristics of the formed aggregate pier. Combinations of these materials may also be utilized in the process.
The hollow tube with the bulbous bottom head element may be positioned within the soil matrix by pushing and/or vertically vibrating or vertically ramming the hollow tube having the leading end, bulbous bottom head element into the soil with an applied axial or vertical vector static force and optionally, with accompanying dynamic vector forces. The soil matrix, which is displaced by initial forcing, pushing and/or vibrating the hollow tube with the special bottom head element, is generally displaced and compacted laterally and vertically downward into the preexisting soil matrix. If a hard or dense layer of soil is encountered, the hard or dense layer may be penetrated by pre-drilling or pre-penetrating that layer to form a cavity or passage into which the hollow tube and special bottom head element may be placed and driven.
The hollow tube is typically constructed from a uniform diameter tube with a bulbous bottom head element and may include an internal valve mechanism near or within the bottom head element or a valve mechanism at the lower end of the head element, or it may not include an internal valve closing and opening mechanism. The hollow tube is generally cylindrical with a constant, uniform, lesser diameter along an upper section of the tube. The bulbous or larger external diameter lower end of the hollow tube (i.e. bulbous bottom head element) is integral with the lesser diameter hollow tube or may be separately formed and attached to the lower end of the lesser diameter hollow tube. That is, the bulbous bottom head element is also typically cylindrical, and has a greater external diameter or external cross sectional profile than the remainder of the hollow tube and is concentric about the center line axis of the hollow tube. The lead end of the bulbous bottom head element is shaped to facilitate penetration into the soil matrix and to transmit desired vector forces to the surrounding soil during penetration as well as to the aggregate material subsequently released from the hollow tube. The transition from the lesser external diameter hollow tube section to the special bottom head element may comprise a frustoconical shape. Similarly, the bottom of the head element may employ a frustoconical or conical shape to facilitate soil penetration and subsequent aggregate compaction. The leading end of the bulbous bottom head element may include a sacrificial cap member which is fixed to the bottom head element while penetrating the soil matrix upon initial placement of the hollow tube into the soil matrix, to prevent soil from entering the hollow tube. The sacrificial cap may then be released or disengaged from the end of the hollow tube to reveal an end passage when as the hollow tube is first lifted so that aggregate material may be released through the hollow tube and may flow into the cavity which results from lifting the hollow tube.
Alternatively, or in addition, the leading end of the bulbous bottom head element may include an internal mechanical valve that is closed during initial penetration of the soil matrix by the hollow tube and bulbous bottom head element, but which may be opened during lifting to release aggregate material. Other types of leading end valve mechanisms and shapes may be utilized to facilitate initial matrix soil penetration, prevent soil entrance into the hollow tube, permit release of aggregate material when the hollow tube is lifted, and to transmit vector forces in combination with the leading end of the special bottom head element to compact the successive aggregate lifts.
Further, the apparatus may include means for positioning one or more vertical uplift members within the formed pier for subsequent use as a vertical uplift anchor force resistance member, as well as for a tell-tale member within the formed pier for measuring the movement of the bottom of the formed pier upon loading, such as during load testing. Such ancillary features or means may be introduced through the interior of the hollow tube during formation of the pier.
Alternatively, uplift anchor rods or a tell-tale rod or rods may be placed on the outside of the hollow tube and the bulbous bottom head element. Such rods would run longitudinally along the length of the hollow tube and head element and thus be positioned at the side of the cavity formed thereby. One, or two or more rods may be placed in such a manner. The rods placed on the outside of the hollow tube and head element may be employed alone or in combination with such rods initially positioned on the inside of the hollow tube.
As yet another feature of the invention, vibration dampers may be employed in combination with a hopper that feeds aggregate or other material into the hollow tube. Thus, two or more dampers may be used and thus, employed in combination with the driving mechanism.
In another aspect of the invention, the diameter of the hollow tube along its longitudinal length between the hopper or top end of the hollow tube and the bulbous bottom head element may be varied. The largest diameter hollow tube section may be positioned at the top of the hollow tube, with progressively smaller diameter sections below the largest diameter section, the smallest of which is joined to the bottom head element. This arrangement can effect reduction in total weight of the hollow tube, while increasing the strength in those portions of the hollow tube where greater strength is required. The hollow tube may be assembled in multiple sections which are bolted, welded or otherwise fastened together. The outer configuration of adjacent sections may also be varied, for example, they may have various geometrical cross sectional shapes such as circular, elliptical, hexagonal, etc. The sections may be pre-assembled or assembled by connecting them seriatim during soil penetration.
In the practice of the method of the invention, it may be advantageous to utilize crushed stone which has angular facets or faces rather than rounded or river stone which is more commonly used with other soil improvement methods. The ability to use crushed stone in the practice of the method enables the use of a material not commonly employed for building such piers and, as such, provides the capability to construct a pier having certain practical advantages such as a higher density and a greater stiffness. Nonetheless, rounded or river stone may also be used. Combinations of such stone including crushed stone and rounded or river stone may also be used.
As another feature of the invention, the hollow tube and bulbous bottom head element may be appropriately guided in movement into the soil matrix by means of an alignment guide. The alignment guide provides an additional function of preventing the hollow tube and special bottom head element from displacing laterally (“kicking out”) during initial penetration into the soil matrix. One example of a special alignment guide is a toroidal guide member encircling the hollow tube and fastened to the drive machine to provide for guidance thereof for the hollow tube and bulbous bottom head element. Other forms of special alignment guides can be utilized and more than one alignment guide may be utilized.
As yet another feature, the hollow tube and bulbous bottom head element may be forced or driven into a soil matrix by means of a vibratory hammer which is fastened thereto by means of a lock plate construction. The lock plate is held in position by bolts or rods which are retained by special lock washers, for example, the special lock washers having the commercial name “Northlock Washers”. This arrangement reduces the electricity created between the driving apparatus and the hollow tube with bulbous bottom head element.
The typical exterior diameter of a circular cross section embodiment of the special bottom head element is in the range of about 14 inches. Other typical sizes in terms of the diameter of the head element include a head element having a diameter of anywhere from 12 to 16 inches and the range of the practicable diameters of a head element may be from about 10 to about 20 inches. This differs from other tubular apparatus for soil improvement which typically are larger, from 24 to 36 inches in diameter. The shape of the head element in cross section is typically cylindrical, although other shapes may be utilized to provide the relative bulbous shape of the bulbous bottom head element when contrasted with the cross sectional area of the hollow tube section attached thereto.
A sensor device may be attached to the bulbous bottom head element to measure the vertical force over time as encountered by the bulbous bottom head element during the vertical compaction and lateral displacement of aggregate process. The sensor device enables measurement of the vertical force and the duration of vertical force being placed thereon. The sensor device can be attached to the bulbous bottom head element, for example, just above the lower shaped portion thereof to provide axial and transaxial readings.
As another feature, the apparatus of the invention may be used in combination with aggregate, with cementations grout in combination with aggregate, or with concrete, as well as other pier forming materials.
As another feature, the apparatus and method of the invention may be utilized in stiff, very stiff, medium dense or hard soils. In certain circumstances, one may pre-drill at least in part the soil at a pier location. Alternatively, it is possible to pre-penetrate the soil at a pier location with a special designed penetration head element fastened to a shaft. The cross sectional area of the shaft is typically less than the maximum cross sectional area of the penetration head element. The maximum diameter of the penetration head element is typically less than the diameter of the bulbous bottom head element attached to the elongate hollow tube. A conical penetration head on a shaft is an effective shape for the special designed penetration head element, although other configurations may be used. The operation of the pre-penetration step is prior to and typically separate from the steps of installing the pier by means of the hollow tube and bulbous bottom head element.
As another feature of the invention, aggregate piers made in accord with the apparatus and method of the invention may be installed at a depth beneath a soil surface. The aggregate pier may then serve as a base or support for an alternative type of pier construction. Thus, two or more different types of pier segments, one of which is the system described herein, may be joined or coupled or stacked to form a single pier.
The discharge opening at the extreme distal end of the bulbous bottom head element may vary in size. Typically, since the bottom head element is utilized to discharge aggregate or other similar material from an opening, then a portion of the extreme distal end of the bulbous bottom head element will comprise a generally horizontal structure coupled with a conical or generally conical surface. The bottom opening will typically comprise less than fifty percent of the surface area of the generally horizontal portion or section and the generally conical surface portion. The horizontal bottom portion and the generally conical portion impart forces directly onto aggregate released or discharged from the bottom opening.
Thus, it is an object of this invention to provide a hollow tube apparatus with a special design, larger effective diameter than the hollow tube, bulbous bottom head element useful to create a compacted aggregate pier, with or without additives, that extend to a greater depth and to provide an improved method for creating a pier which extends to a greater depth than typically enabled or practiced by known, existing short aggregate pier technology.
Yet another object of the invention is to provide an improved method and apparatus for forming a pier of compacted aggregate material that does not require the use of temporary steel casing during the pier formation process, particularly in soils susceptible to caving in such as sandy soils and soils below the ground water table.
Yet another object of the invention is to provide an improved method and apparatus for forming a pier of compacted aggregate material that may include a multiplicity of optional additives, including a mix of aggregate, the addition of water, the addition of dry cement, the addition of cementitious grout, the addition of water-cement-sand, the addition of fly-ash, the addition of hydrated lime or quicklime, and the addition of other types of additives, including the use of concrete, to improve the engineering properties of the matrix soil, of the aggregate materials and of the formed pier.
Yet a further object of the invention is to provide an aggregate material pier construction which is capable of being installed in many types of soil and which is further capable of being formed at greater depths and at greater speeds of construction than known prior aggregate pier constructions.
Yet a further object of the invention is to provide an improved method and apparatus for forming a pier of compacted aggregate material within a softened or loosened aggregate pier previously formed by different pier construction process and with different apparatus than that described herein in order to stabilize and stiffen the previously formed pier.
Another object of the invention is to provide a pier forming apparatus useful for quickly and efficiently constructing compacted multi-lift aggregate piers and/or aggregate piers comprised of as few as a single lift.
These and other objects, advantages and features of the invention will be set forth in the detailed description which follows.
In the detailed description which follows, reference will be made to the drawing comprised of the following figures:
General Construction:
As a first step of the method, a hollow tube or hollow shaft 30 having a longitudinal axis 35 including or with a special bottom head element 32, is pushed by a static, axial vector force driving apparatus 37 in
Typically, the hollow tube 30 has a uniform cylindrical external shape, although other shapes may be utilized. Though the external diameter of the hollow tube 30 is typically 6 to 14 inches, other diameters may be utilized in the practice of the invention. Also, typically, the hollow tube 30 will be extended or pushed into the soil matrix 36 to the ultimate depth of the aggregate pier, for example, up to 50 feet or more. The hollow tube 30 will normally fasten to an upper end drive extension 42 which may be gripped by a drive apparatus or mechanism 37 to push and optionally vibrate or ram, the hollow tube 30 into the soil matrix 36. Alternately, as shown in
The hopper 34, which contains a reservoir 43 for aggregate materials, when located at the top of the hollow tube 30, will typically be isolated by the isolation dampers 46, 48 from extension 42. The vibrating or ramming device 37 which is fastened to extension 42 may be supported from a cable or excavator arm or crane. The weight of the hopper 34, ramming or vibrating device 37 (with optional additional weight) and the hollow tube 30 may be sufficient in some matrix soil conditions to provide a static force vector without requiring use of a separate static force drive mechanism. The static force vector may optionally be augmented by a vertically vibrating and/or ramming dynamic force mechanism. Also, the hopper 34 may be separate from the hollow tube 30 and extension 42. For example, a separate hopper not mounted on the top of the hollow tube 30 (not shown) may feed aggregate or other material into the hollow tube 30 along the side of the tube.
Typically, the internal diameter of the hollow tube 30 and head element 32 are uniform or equal, though the external diameter of the bulbous bottom head element 32 is greater than that of hollow tube 30. Alternatively, when a valve mechanism 54 is utilized, the internal diameter of the head element 32 may be greater than the internal diameter of the hollow tube 30. Bulbous bottom head element 32 may be integral with hollow tube 30 or formed separately and bolted or welded onto hollow tube 30. Typically, the inside diameter of the hollow tube 30 is between 6 to 10 inches and the external diameter of the special bottom head element 32 is about typically 12 to 18 inches. The opening diameter 53 in
Also the plate or valve 54 may be configured to facilitate closure when the hollow tube 30 is pushed downward into the soil matrix 36 or against aggregate material 44 in the formed cavity. For example, the diameter of member 54 may exceed that of opening 52 as shown in
The lower bulbous bottom head element 32 of hollow tube 30 typically has a length in the range of one to three times its diameter or maximum lateral dimension. The bulbous bottom head element 32 provides enhanced lateral compaction forces on the soil matrix 36 as tube 30 penetrates or is forced into the soil and thus renders easier the subsequent passage of the lesser diameter section 33 of the hollow tube 30. The frustoconical or inclined leading and trailing edges 50, 63 of the head element 32 facilitate lowering or driving penetration and lateral compaction of the soil 36 because of their profile design. The trailing inclined section or edge 63 in
Method of Operation:
Raising of the hollow tube in the range of two (2) to four (4) feet is typical followed by lowering (as described below) to form an aggregate pier lift 72, having a one (1) foot vertical dimension is typical for pier forming materials as described herein. The axial dimension of the lift 72 may thus be in the range of ¾ to ⅕ of the distance 91 the hollow tube 30 is raised. However, the embodiment depicted in
Upon reaching the desired penetration into the matrix soil 36 (
Optionally, additive materials are discharged into the annular space 104 defined between the upper section 33 of hollow tube 30 and the interior walls of the formed cavity 102. The additive materials may flow through ancillary lateral passages 108 or supplemental conduits 110 in the hollow tube 30. As the hollow tube 30 is raised, the cavity 102 is filled with aggregate and optionally, additive materials. Also, additive materials in the annular space 104 may be forced outwardly into the soil matrix 36 by and due to the configuration of the bulbous bottom head element 32 as it is raised.
The hollow tube 30 is thus typically raised substantially the full length of the initially formed cavity 102 and then, as depicted by
After completion of the second downward movement, the hollow tube 30 is raised typically the full length of the cavity 102, again discharging aggregate and optionally additive materials during the raising, and again filling, the newly created cavity 102A (
Alternatively, after completion of a single lift, the resulting aggregate pier with or without optional additive materials, further steps of re-entry of hollow tube 30 and bulbous bottom head element 32 into the formed single lift aggregate pier, may be eliminated. In other words, the apparatus may be used to form a single elongate pier within the soil matrix extending the vertical length of soil penetration. The single lift aggregate pier with densified adjacent matrix soils may be effective without further strengthening or stiffening. One situation in which a single lift aggregate pier will typically be effective is in liquefaction mitigate during seismic events when the matrix soils are liquefiable.
Summary Considerations:
Water or grout or other liquid may be utilized to facilitate flow and feeding of aggregate material 44 through hollow tube 30. The water may be fed directly into the hollow tube 30 or through the hopper 34. It may be under pressure or a head may be provided by using the hopper 34 as a reservoir. The water, grout or other liquid thus enables efficient flow of aggregate, particularly in the small diameter hollow tube 30, i.e. 5 to 10 inches tube 30 diameter. Typically the size of the tube 30 internal passage and/or discharge opening is at least 4.0 times the maximum aggregate size for all the described embodiments. With each lift 72 being about 12 inches in vertical height and the internal diameter of tube 30 being about 6 to 10 inches, use of water as a lubricant is especially desirable.
It is noted that the diameter of the cavity 102 formed in the matrix soil 36 is relatively less than many alternative pier forming techniques. The method of utilizing a relatively small diameter cavity 102 or a small dimension opening into the soil matrix 36, enables forcing or driving a tube 30 to a significant depth and subsequent formation of a pier having horizontal dimensions measurably greater than the external dimensions of the tube 30. Utilization of aggregate 44 with or without additives including fluid materials, to form one or more lifts by compaction and horizontal displacement is thus enabled by the hollow tube 30 and special bottom head element 32 as described. Lifts 72 are compacted vertically and aggregate 44 forced transaxially with the result of a highly coherent pier construction and production of a stiffer and stronger aggregate pier with a larger diameter than its original cavity diameter.
Test Results:
A hole or cavity of approximately 8-inches in diameter was drilled to a depth of 20 feet and filled with concrete to form a drilled concrete pier (test D). A steel reinforcing bar was placed in the center of the drilled concrete pier to provide structural integrity. A cardboard cylindrical form 12 inches in diameter was placed in the upper portion of the pier to facilitate subsequent compressive load testing. The matrix soil for all four tests was a fine to medium sand of medium density with standard Penetration Blow Counts (SPT's) ranging from 3 to 17 blows per foot. Groundwater was located at a depth of approximately 10 feet below the ground surface.
The aggregate piers of the invention, reported as in tests A, B, and C, were made with a hollow tube 30, six (6) inches in external diameter and with a special bottom head element 32 with an external diameter of 10 inches. Tests A and B utilized aggregate only. Test C utilized aggregate and cementatious grout. Test A utilized predetermined lifting movements of two feet and predetermined downward pushing movements of one foot resulting in a plurality of one foot lifts. Test B utilized predetermined upward movements of three feet and predetermined downward pushing movements of two feet, again resulting in one foot lifts. Test C utilized predetermined upward movements of two feet and predetermined downward pushing movements of one foot, and included addition of cementatious grout.
Analyses of the data can be related to stiffness or modulus of the piers constructed. At a deflection of 0.5 inches, test A corresponded to a load of 27 tons, test B corresponded to a load of 35 tons, test C corresponded to a load of 47 tons and test D corresponded to a load of 16 tons. Thus at this amount of deflection (0.5 inches) and using test B as the standard test and basis for comparison, ratios of relative stiffness for test B is 1.0, test A is 0.77, Test C is 1.34, and Test D is 0.46. The standard, Test B, is 2.19 times stiffer than the control test pier, Test D. The standard Test B is 1.30 times stiffer than Test A, whereas the Test C with grout additive is 2.94 times stiffer than the prior art concrete pier (Test D). This illustrates that the modulus of the piers formed by the invention are substantially superior to the modulus of the drilled, steel-reinforced concrete pier (Test D). These tests also illustrate that the process of three feet lifting movement with two feet downward pushing movement was superior to the process of two feet lifting movement and one foot downward pushing movement. The tests also illustrate that use of cementations grout additive substantially improved the stiffness of the formed pier for deflections less than about 0.75 inches, but did not substantially improve the stiffness of the formed pier compared with Test B for deflections greater than about 0.9 inches.
In the embodiment disclosed, because the bulbous bottom head element 32 of the hollow tube or hollow shaft 30 has a greater cross sectional area, various advantages result. First the configuration of the apparatus, when using a bottom valve mechanism 54, reduces the chance that aggregate material will become clogged in the apparatus during the formation of the cavity 102 in the soil matrix 36 as well as when the hollow tube 30 is withdrawn partially from the soil matrix 36 to expose or form a cavity 85 within the soil matrix 36. Further, the configuration allows additional energy from static force vectors and dynamic force vectors to be imparted through the bottom head element 32 of the apparatus and impinge upon aggregate 44 in the cavity 70. Another advantage is that the friction of the hollow tube 30 on the side of the formed cavity 102 in the ground is reduced due to the effective diameter of the hollow tube 30 being less than the effective diameter of the bottom head element 32 and therefore being less than the initial diameter of the formed cavity. This permits quicker pushing into the soil and allows pushing through formations that might be considered to be more firm or rigid. The larger cross sectional area head element 32 also enhances the ability to provide a cavity section 102 sized for receipt of aggregate 44 which has a larger volume than would be associated with the remainder of the hollow shaft 30 thus providing for additional material for receipt of both longitudinal (or axial) and transverse (or transaxial) forces when forming the lift 72. The reduced friction of the hollow tube 30 on the side of the formed cavity 102 in the soil 36 also provides the advantage of more easily raising the hollow tube 30 during pier formation and prevention of the hollow tube 30 becoming stuck within the soil matrix.
In the process of the invention, the lowest lift 72 may be formed with a larger effective diameter and have a different amount of aggregate provided therein. Thus the lower lift 72 or lowest lift in the pier 76 may be configured to have a larger transverse cross section as well as a greater depth when forming a base for the pier 76. By way of example the lowest portion or lowest lift 72 may be created by lifting of the hollow shaft 30 four feet and then lowering the hollow tube 30 three feet, thus reducing the height of the lift 72 to one foot, whereas subsequent lifts 72 may be created by raising the hollow shaft 30 three feet and then lowering the hollow tube 30 two feet, thus reducing the thickness of the lift 72 to one foot.
The completed aggregate pier 76 may, as mentioned heretofore, be preloaded after it has been formed by applying a static load or a dynamic load 75 at the top of the pier 76 for a set period of time (see
The aggregate material 44 which is utilized in the making of the pier 76 may be varied. That is, clean aggregate stone may be placed into a cavity 85. Such stone may have a nominal size of 40 mm diameter with fewer than 5% having a nominal diameter of less than 2 mm. Subsequently a grout may be introduced into the formed material as described above. The grout may be introduced simultaneous with the introduction of the aggregate 44 or prior or subsequent thereto.
When a vibration frequency is utilized to impart a dynamic force, the vibration frequency of the force imparted upon the hollow shaft or hollow tube 30 is preferably in a range between 300 and 3000 cycles per minute. The ratio of the various diameters of the hollow tube or shaft 30 to the bulbous bottom head element 32 is typically in the range of 0.92 to 0.50. As previously mentioned, the angle of the bottom bevel may typically be between 30° and 60° relative to a longitudinal axis 35.
As a further feature of the invention, the method for forming a pier may be performed by inserting the hollow tube 30 with the bulbous bottom head element 32 to the total depth 81 of the intended pier. Subsequently, the hollow tube 30 and bulbous bottom head element 32 will be raised the full length of the intended pier in a continuous motion as aggregate and/or grout or other liquid are being released or injected into the cavity as the hollow tube 30 and special bottom head element 32 are lifted. Subsequently, upon reaching the top of the intended pier, the hollow tube 30 and special bottom head element 32 can again be statically pushed and optionally augmented by vertically vibrating and/or ramming dynamic force mechanism downward toward or to the bottom of the pier in formation. The aggregate 44 and/or grout or other material filling the cavity as previously discharged will be moved transaxially into the soil matrix as it is displaced by the downwardly moving hollow tube 30 and special bottom head element 32. The process may then be repeated with the hollow tube 30 and special bottom head element 32 raised either to the remaining length or depth of the intended pier or a lesser length in each instance with aggregate and/or liquid material filling in the newly created cavity as the hollow tube 30 is lifted. In this manner, the material forming the pier may comprise one lift or a series of lifts with extra aggregate material and optional grout and/or other additives transferred laterally to the sides of the hollow cavity into the soil matrix. Alternatively, the last sequence can be the same or similar to the “typical” aggregate pier forming method of this invention, whereas thin lifts are formed by raising and lowering the hollow tube 30.
It is noted that the mechanism for implementing the aforesaid procedures and methods may operate in an accelerated manner. Driving the hollow tube 30 and bulbous bottom head element 32 downwardly may be effected rather quickly, for example, in a matter of two minutes or less. Raising the hollow tube 30 and bulbous bottom head element 32 incrementally a partial or full distance within the formed cavity may take even less time, depending upon the distance of the lifting movement and rate of lifting. Thus, the aggregate pier is formed from the soil matrix 36 within a few minutes. The rate of production associated with the methodology and the apparatus of the invention is therefore significantly faster.
Additional Features:
Numerous variations of the multiple section hollow tube may be practiced, although the typical sequence is for sections to decrease in cross sectional area from top to bottom. Example variations include sections that increase in traverse cross sectional area toward the top end of the hollow tube. The sections may increase in traverse cross sectional area and then decrease. They may have the same traverse cross sectional area but distinct cross sectional configurations. They may be integrally connected or detachable sections. Combinations of these described features may be used. The separate sections may be pre-assembled or they may be assembled seriatim at a work site as soil penetration occurs. Typically, they are pre-assembled.
Referring to
The embodiment of
Various modifications and alterations may thus be made to the methodology as well as the apparatus to be within the scope of the invention. Thus, it is possible to vary the construction and method of operation of the invention without departing from the spirit and scope thereof. Alternative hollow tube configurations, sizes, cross sectional profiles and lengths of tube may be utilized. The bulbous bottom head element 32 may be varied in its configuration and use. The bottom valve 54 may be varied in its configuration and use, or may be eliminated by adoption of a sacrificial cap. The leading end of the bulbous bottom head element 32 may have any suitable shape. For example, it may be pointed, cone shaped, blunt, angled, screw shaped, or any shape that will facilitate penetration of a matrix soil and compaction of discharged aggregate material. The enlarged or bulbous bottom head element 32 may be utilized in combination with one or more differing external diameter sections of the hollow tube 30 having various shapes or configurations. Therefore the invention is to be limited only by the following claims and equivalents thereof.
This application is a continuation in part application of Ser. No. 11/747,271 filed May 11, 2007 which is a continuation of Ser. No. 10/728,405 filed Feb. 12, 2004 which is a utility application based upon provisional application Ser. No. 60/513,755 filed Oct. 23, 2003, all of which are incorporated herein by reference and for which priority is claimed.
| Number | Date | Country | |
|---|---|---|---|
| 60513755 | Oct 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10728405 | Feb 2004 | US |
| Child | 11747271 | May 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11747271 | May 2007 | US |
| Child | 11876556 | Oct 2007 | US |
