US20120282038A1

US20120282038A1 - Electrokinetic conditioning of foundation piles

Info

Publication number: US20120282038A1
Application number: US13/307,794
Authority: US
Inventors: Lutful I. Khan
Original assignee: Cleveland State University
Current assignee: Cleveland State University
Priority date: 2010-11-30
Filing date: 2011-11-30
Publication date: 2012-11-08

Abstract

A method for increasing load capacity of a foundation pile installed in a ground material is described. At least one electrode is embedded in the ground material at a predetermined distance from the installed pile. A direct current power source is provided, with the power source including at least one cathode connection and at least one anode connection. One of the at least one cathode connection is secured to the foundation pile. One of the at least one anode connections is secured to each of the at least one electrodes. The direct current power source is activated to generate an electric gradient between the foundation pile and the at least one electrode, with the electric gradient being selected to direct charged soil particles in the ground material toward the foundation pile.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/417,980, entitled “INCREASING CAPACITY AND ENHANCEMENT SET-UP OF STEEL PILES IN CLAY SOIL BY ELECTROKINETIC METHOD” and filed Nov. 30, 2010, the entire disclosure of which is incorporated herein by reference, to the extent that it is not conflicting with the present application.

BACKGROUND

Pile foundations are used for the support of heavy structures, such as bridges, tall buildings, and the like. A significant increase in the load capacity of these piles is often observed over time after initial installation, and is generally attributed to consolidation of cohesive ground materials, such as clay and cohesive soils, around the pile after pile installation, and dissipation of water pressure around the piles. This time-dependent strength gain is commonly referred to as “set-up,” and may be tested by “re-strikes” of the piles, measuring the displacement of the pile as the result of application of a known force. While formulas have been developed to estimate pile capacity as a function of elapsed time after installation, these formulas may not be relied upon in subjecting the piles to loads during construction. As such, the construction of pile foundations often requires a waiting period after installation of the piles for a sufficient increase in load capacity. Further, the pile capacities are often not utilized to their full potential as construction often relies upon capacities that are measured, for practical reasons and safety considerations, after several days to a few weeks from installation when only a fraction of set-up has occurred, for example, to minimize construction delays.

SUMMARY

The present application describes systems and methods for accelerating or increasing set-up of an embedded structure (e.g., a steel foundation pile) by generating an electrical polarity at the embedded member that is opposite an inherent electrical polarity of a cohesive ground material into which the structure is embedded, such that the cohesive ground material is attracted to or adhered to the embedded structure. In one such exemplary embodiment, a positive electrical polarity is generated at a steel foundation pile to attract cohesive clay soil particles having a net negative surface charge.
The present application also describes systems and methods for facilitating removal of an embedded structure (e.g., a steel foundation pile) by generating an electric polarity at the embedded member that is the same as an inherent electrical polarity of a cohesive ground material into which the structure is embedded, such that the cohesive ground material is dispersed or repelled from the conductive member, thereby reducing ground material adhesion to the embedded conductive member for reduced resistance to pull-out.
Still other advantages, aspects, and features of the present application will become readily apparent to those skilled in the art from the following description, wherein there is shown and described an exemplary embodiment of the present application. As it will be realized, the present application is capable of other different embodiments, and its several details are capable of modifications in various aspects, all without departing from the scope of the present application. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from the following detailed description made with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a system for electrokinetic conditioning of an embedded structure, according to an exemplary embodiment;

FIG. 2A is an illustration of an exemplary mold for preparing a soil sample for bench scale pile set-up testing;

FIG. 2B is an illustration of an exemplary hammer arrangement for a bench scale pile set-up test;

FIG. 3 illustrates a graph of load required for a 3 mm penetration versus time, as tested in Example I below;

FIG. 4 illustrates a graph showing load versus electric gradient application duration, as tested in Example I below;

FIG. 5 is a schematic illustration of an exemplary pile driving arrangement;

FIG. 5A is an enlarged view of the pile from the pile driving arrangement of FIG. 5;

FIGS. 6-9 graphically illustrate the difference in pile capacities between electrokinetically conditioned soil samples exposed to an electric gradient of 30 Volts DC per foot and substantially identical soil samples not subjected to an electric gradient, as tested in Example II below; and

FIG. 10 graphically illustrates the difference in pile capacities between substantially identical clay soil samples exposed to different amounts of applied electric gradient, as tested in Example II below.

DETAILED DESCRIPTION

The Detailed Description merely describes exemplary embodiments of the invention and is not intended to limit the scope of the claims in any way. Indeed, the invention is broader than and unlimited by the exemplary embodiments, and the terms used in the claims have their full ordinary meaning
Also, while the exemplary embodiments described in the specification and illustrated in the drawings relate to installation and removal of steel foundation piles, it should be understood that many of the inventive features described herein may be applied to installation and removal of other ground embedded structures, such as posts, spikes, and plates.
Installation or driving of foundation piles into cohesive soil, such as clay-based soil, generally causes the soil around the driven pile to undergo plastic deformation and to develop increased pore water pressure around the driven pile, both of which may contribute to an initial reduced or limited load capacity of the pile. After the pile driving or installation is completed, excess pore pressure around the driven pile tends to dissipate, and the cohesive soil tends to re-consolidate around the driven pile, resulting in increases in the load capacity of the driven pile over time. However, due to variations in soil conditions, both between the locations of multiple piles employed in a single construction product, and across multiple soil strata into which a single pile is driven, set-up of a conventionally installed pile may vary, and in some cases, little or no set-up may occur, or even a relaxation or loss of load capacity may occur over time. This variability in set-up has conventionally required significant waiting periods to verify sufficient load capacity of the driven piles, and to determine the number of piles required to support the eventual load. Further, due to the long periods of time over which natural set-up may occur, and the prohibitive costs and inconveniences of substantial construction delays, construction projects are often unable to take advantage of this long-term strength gain, and redundant piles are driven during construction to satisfy load capacity requirements after only a minimal waiting period.
The present application contemplates methods and systems of improving load capacity or set-up of a ground embedded structure, such as a steel foundation pile, by applying an electric gradient between the embedded structure and the surrounding soil. Without being bound by theory, applicant believes that this application of an electrical gradient between the embedded structure and a clay-based surrounding soil generates an electrochemical attraction between charged soil particles surrounding the embedded structure and the oppositely charged embedded structure. In the case of clay-based soils, the inherent negative surface charge of the clay particles facilitates electrochemical attraction to a positively charged structure. In some applications, moisture collected in the soil around the embedded structure allows for a phenomenon known as electrophoresis, in which an electrical field applied to the water creates an electric gradient between the soil and the embedded structure, causing charged clay particles to migrate through the water and toward the embedded structure. Adherence of these clay particles to the embedded foundation pile creates a clay plug surrounding the pile, increasing the effective diameter of the pile, resulting in an increased shaft resistance of the pile.
While many different arrangements may be utilized to apply an electric gradient between an embedded structure (e.g., an installed foundation pile) and the surrounding soil, in one embodiment, as shown schematically in FIG. 1, one or more electrodes 20 may installed or embedded into the soil S around the embedded structure 10, and an electrical potential gradient may be generated between the embedded structure and each of the one or more installed electrodes. In one such embodiment, a direct current power source 30 includes an adjustable direct current power supply (e.g., an Acopian AC to DC Power Supply, model no. U24Y2300), for example, to allow for a user selected voltage. A positive terminal 31 of the direct current power source 30 may be connected directly to the embedded structure (for example, using a conductive clamp, such as a mini-clip or gator clip), and one or more negative terminals 32 (e.g., branched terminals) of the direct current power source 30 may be connected directly to each of the embedded electrodes 20. The direct current power source 30 may then be activated and adjusted to apply a constant selected direct current voltage, thereby generating the desired electrokinetic field between the embedded structure 10 and the surrounding soil S. In other embodiments, for example, where the embedded structure is not itself conductive, additional electrodes may be embedded in the surrounding soil in contact with or in close proximity with the embedded structure, such that attachment of positive terminals to these proximate electrodes may serve to attract clay (or other negatively charged) cohesive soil particles toward the embedded structure, and to repel water molecules from the embedded structure.
While not intending to be bound by theory, applicant believes that the application of a low-intensity direct current through the water-saturated soil surrounding an installed foundation pile mobilizes negatively charged clay particles or colloids C (e.g., kaolinite, illite, montmorillonite, and chlorite clays) to cause the clay colloids to move toward the positively charged pile (or toward positively charged electrodes proximate the pile), a phenomenon referred to as electrophoresis. At the same time, neutral or net positive charged water molecules W are mobilized to disperse from the surface of the pile and flow toward the surrounding negative electrodes, a phenomenon referred to as electroosmosis. The effects of these two simultaneous phenomena include an increase in soil density around the pile, a decrease in water content and pore pressure around the pile, the formation of a clay plug around the pile, effectively increasing the effective diameter of the pile, and an increase in shaft resistance due to this increased effective diameter. All of these effects are believed to increase or accelerate set-up of the installed pile, as compared to the natural expected set-up of the pile in the absence of an applied electrokinetic field.
Many factors involving an installed foundation pile and the conditions of the surrounding soil may affect the amount of set-up experienced by the pile, including, for example, pile length, pile diameter, soil conditions (including materials, cohesiveness, and moisture content), elapsed time, and vibrations during pile driving (which may produce capacity impairing cracks in clay or other cohesive soil materials)
In an exemplary steel foundation pile installation and conditioning application, a stainless steel foundation pile having a diameter of approximately 12-24 inches and a length of approximately 40-150 ft. is embedded in clay based ground soil. Three electrodes (e.g., stainless steel rods) having a diameter of approximately 1-2 inches and a length of approximately 25 ft. (or at least about half the length of the pile) are embedded in the surrounding soil at a distance from the pile of approximately 3-6 feet and evenly spaced from each other. An adjustable direct current power source is provided, with a positive terminal connected to the pile, and branched negative terminals connected to each of the electrodes. The power source is operated to deliver a voltage of approximately 100-300 V DC, to provide a gradient of approximately 1-30 V/ft between the pile and the electrodes. This voltage is maintained for a predetermined period, for example, at least 24-48 hours, before a static or dynamic load capacity test is employed to verify that sufficient set-up has occurred to support the structure to be built on the pile or piles.
According to another aspect of the present application, electrokinetic conditioning of an embedded structure, such as a foundation pile, may be utilized to loosen the embedded structure, for example, to remove or reposition the embedded structure. In such an application, an electric gradient opposite of the electric gradient described above may be applied, with a negative charge applied to the embedded structure and a positive charge applied to one or more embedded electrodes surrounding the embedded structure. While not intending to be bound by theory, applicant believes that the application of a low-intensity direct current through the water saturated soil surrounding an installed steel foundation pile, with a negative charge applied to the pile, mobilizes negatively charged clay colloids to cause the clay colloids to move away from the negatively charged pile and toward the positively charged electrodes. At the same time, neutral or net positive charged water molecules are mobilized to migrate toward the surface of the pile further reducing the shaft resistance of the pile. The effects of these two simultaneous phenomena are believed to include a reduction in soil density around the pile, an increase in water content and pore pressure around the pile, and a resulting decrease in pile shaft resistance. All of these effects are believed to loosen the installed pile, thereby facilitating removal or repositioning of the pile within the ground soil.

EXAMPLE I

Preliminary Testing

Preliminary bench scale tests were conducted on two pile-clay specimens. The material specifications for the preliminary tests are given in Table 1.

TABLE 1

Specifications of Materials used during Preliminary Tests

Item	Material	Dimensions/Weight	Manufacturer

Pile	Stainless	Hollow pipe	Spee-D-Metals,
	Steel	Length = 9 in., Thk = 0.42 in.	Cleveland, OH.
		OD is 1 in. for a length of 3 in.
		and 0.5 in. for the remaining
		6 in.
Soil	Kaolinite		50 lb bag	Feldspar
	Clay		Corporation,
			Atlanta, GA
Electrode	Stainless	Solid ¼ inch dia. rods	Machine
	Steel		Shop, CSU

The procedure followed in preparing the kaolinite sample was similar to the one for Standard Proctor Test, ASTM D-698. The soil was compacted in a mold with a diameter of 4 inches and a height of 6.5 inches (including the collar). The soil was mixed with 34% by weight water and then compacted in four equal layers by a hammer that delivered 25 blows to each layer. The hammer had a mass of 2.5 kg (5.5 lb) and a drop of 12 inches. FIGS. 2A and 2B illustrates the exemplary mold 40 and hammer 50, respectively, that were used. The 1 inch diameter stainless steel pile was then driven into the center of the clay sample by lightly tapping the sample.
Care was taken during pile driving to avoid the formation of vibration cracks in clay. The mold was then covered with a rubber pad to prevent moisture loss due to evaporation. The specimen was then kept in a covered tub partially filled with water. This arrangement was helpful in maintaining the moisture content of the soil sample throughout the testing period.
The two specimen to be tested were statically loaded using a tri-axial testing machine (model #, supplier) on Days 0, 1, 3, 8, 16, 22, 31 and 46 after the end of initial driving. A rapid moisture content test (e.g., OHAUS, MB 200) was conducted prior to each static load test. An electric gradient of 30 Volts DC/ft was applied to Specimen A, between static load tests, Day 3 onwards.
Two kaolinite clay-steel pile specimen were prepared in accordance with the method explained above. Laboratory testing was then performed using a preliminary test program. The two specimens to be tested were statically loaded using the tri-axial testing machine on Days 0, 1, 3, 8, 16, 22, 31 and 46 after the end of initial driving. A rapid moisture content test was conducted prior to each static load test. An electric gradient of 30 Volts DC/ft was applied to Specimen A, between static load tests, from Day 3 onwards. Static load test results are presented in tabular and graphical form below.
Load versus penetration data taken on all test days is presented in Table 2. Specimen A was subjected to an electric gradient of the order of 30 Volts DC/ft between test days, starting from Day 3. Because specimen B was not connected to any voltage source, it was allowed to achieve set-up as a natural process.
As shown in Table 2, at day 3, pile capacities of both specimens were almost identical (239 N for Spec A and 244 N for Spec B). It can be seen from these graphs that from Day 3 onwards, there were substantial increases in the pile static capacity values of Specimen A as compared to Specimen B. An electric gradient of 30 Volts DC/ft was applied to Specimen A for a duration of 100 hours between Day 3 and Day 8. The resulting pile capacity values at the end of Day 8 were 693 N and 293 N for Specimens A and B, respectively. Further application of the electric gradient to Specimen A for a cumulative duration of 443 hours resulted in capacities of 1937 N for Specimen A (compared to 419 N for Specimen B) at the end of Day 31. FIG. 3 shows a graph of load required for a 3 mm penetration versus time. A graph showing load versus electric gradient application duration is shown in FIG. 4.
The moisture contents of both specimens were approximately 34% at the beginning of the testing sequence, and showed a variation of approximately ±5% during the course of the testing period.
Results obtained from preliminary tests confirmed the feasibility of the research proposal and paved the way for more extensive research. Specimen A, after being subjected to an electric gradient of 30 V DC/ft for a duration of 100 hours, gained pile capacity 9 times greater than the pile capacity of Specimen B, which was allowed to achieve natural set-up. Moisture contents of Specimens A and B did not alter substantially during the course of the testing period.

TABLE 2

Load versus penetration data obtained on all tests days
Load in ‘N’

DAY

Dis

0

1

3

8

16

22

31

46

‘mm’

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
1	85	151	143	176	197	210	702	229	1126	265	1218	303	1521	387	819	429
2	108	171	185	199	218	228	713	243	1164	279	1201	315	1933	405	1558	466
3	127	185	203	210	227	235	693	249	1155	286	1226	324	1918	412	1789	489
4	143	195	216	218	235	239		251		293			1937	419	2029	508
5	157	206	225	223	239	244
6	169	216	231	227
7	179	223	237	231
8	190	231

EXAMPLE II

Extended Testing

Further, expanded bench scale testing was also performed, using twenty soil samples, designated P1 through P20, of varying clay content, moisture content, and electrokinetic field conditions, as shown in Table 3 below:

TABLE 3

Test program details

	Clay	Moisture	D.C. Voltage
Specimen	Content (%)	Content (%)	(Volts)

P1	50	35	0
P2	50	35	0
P3	50	35	30
P4	50	35	30
P5	25	12	0
P6	25	12	30
P7	25	17	0
P8	25	17	30
P9	100	40	0
P10	100	40	0
P11	100	40	1
P12	100	40	1
P13	100	40	10
P14	100	40	30
P15	100	40	30
P16	100	40	10
P17	100	35	0
P18	100	35	0
P19	100	35	30
P20	100	35	30

Static load tests were scheduled to be conducted on days 0, 1, 3, 7, 14, 21, 35, 42, 49, 56 and 63. Specimens P1-P8 constituted soil samples containing a mixture of sand and kaolinite clay having the clay content identified in Table 3, while specimens P9-P20 were formed entirely from kaolinite clay. DC voltages applied to the respective samples between static load tests, as identified in Table 3, began on day 3 of the test. The test program was developed to compare the pile capacity values between: (a) specimens subjected to electric gradient versus those that are not; (b) specimens subjected to different DC potential values; (c) specimens with different clay content; and (d) specimens with different moisture content.
The specifications for all other materials used in the testing are given in Table 4.

TABLE 4

Specifications of Materials

Item	Material	Dimensions/Weight	Manufacturer

Pile	Stainless	Solid pipe	Spee-D-Metals,
	Steel	Length = 14.65 in.	Cleveland, OH.
		Top 8 inches: ½ dia.
		Middle 6 inches: ¾ dia.
		Bottom solid cone: ¾ dia.,
		0.65 ht
Soil	Kaolinite
	50 lb bag	Feldspar
	Clay		Corporation,
			Atlanta, GA
	Sand
	50 lb bag	Silica sand #1
Electrode	Stainless	Solid 14 inch long, ¼ inch dia.	Machine
	Steel	rods	Shop, CSU

The aspect ratio, or the ratio of length of the pile to the diameter of the pile, was increased by increasing the test length of the pile from 3 inches to 6 inches and reducing its diameter from 1 in. to ¾ in. A solid stainless steel pipe section with a solid conical bottom as was preferred over the earlier hollow pipe to eliminate plugging effect or end face resistance of the soil sample. The conical shape of the base of the pile was selected to minimize the effect of the end face resistance of the pile. Additionally, the use of a solid pile in place of a hollow pile was intended to eliminate the effects of resistance against an inner surface of a hollow pile. Twenty such pile segments were manufactured at Spee-D-Metals in Cleveland, Ohio.
The procedure followed to prepare the soil sample was similar to the one for Standard Proctor Test, ASTM D-698. The soil was compacted in a PVC mold with a diameter of 6 inches and a height of 12 inches. Due to the additional height of the mold, the specimens could be tested over a longer period of time resulting in more experimental data.
Twenty soil samples with different sand-clay proportions and moisture contents were prepared on the basis of the test plan, as discussed above and shown in Table 3. The soil was mixed with the appropriate percentage by weight of water and then compacted in four equal layers by a hammer that delivered 25 blows to each layer. The hammer had a mass of 2.5 kg (5.5 lb) and a drop of 12 inches.
During preliminary testing, piles were driven into the soil sample by lightly tapping the pile head. To make the driving sequence more uniform for the extended testing, a pile driving arrangement was constructed. FIG. 5 shows a schematic diagram of the manually operated pile driving arrangement 100, which includes a solid platform base 120 and a hammer 130 and collar assembly. The platform functioned to hold the soil sample in place during the event of driving. The hammer and collar assembly was arranged to achieve correct pile alignment and uniform pile driving.
During the design and construction of the pile driving arrangement, an appropriate weight, size and length for the hammer ram were determined by a trial and error method. The design of the collar was dependant on the size and weight of the ram. The purpose of the collar was to avoid simultaneous movement of the ram and the pile, while the ram was raised to a known drop height. So it had to act like a separator between the ram and the pile. At the same time, the collar had to be always in contact with the pile and move with it during the entire event of driving. The soil specimen, the pile, and the hammer and collar arrangement had to maintain individual as well as relative positions during the driving sequence to obtain an accurate pile alignment and uniform driving. This was achieved by constructing a support frame structure fabricated from solid steel rods and metal plates.
In installing the piles, the hammer ram was manually raised to a fixed drop height using a rope and pulley assembly, and released so that it fell under the influence of gravity. Several blows were needed to drive the pile six inches into the ground. The amount of energy needed to drive the pile was recorded, in the form of the hammer weight, number of blows and the drop height. The weight of the hammer ram was constant and approximately equal to 1.7 kg (3.75 lbs). Accordingly, a drop height of 3 inches induced an energy in the amount of 0.94 lb-ft for each hammer blow.
In preparing for the test, twenty ¾ inch diameter stainless steel piles 110 (as shown in FIG. 5A) were driven into the center of soil samples prepared earlier, thus creating twenty soil-pile specimens ready for testing. The day on which the piles were driven was termed as Day 0 on the time log. Day 0 can also be defined as the day that marks the completion of the end of initial drive (EOID) event, a term which is a widely used in pile driving. Three ¼ inch diameter solid stainless steel rods with an approximate length of 14 inches were driven into those specimens which were going to be subjected to an electric gradient. These rods were equally spaced around the pile and at approximately 1.5 inches from the pile surface, or about 2 inches from the center of the mold.
These steel pile-clay specimens were covered with plastic secured by a rubber band at all times to minimize the effect of loss of moisture content due to evaporation. The specimens were stored in an aluminum water tank between testing events to reduce moisture losses due to evaporation. The tank was partially filled with water and covered with a thick polythene cover.
A rapid moisture content test was conducted on every specimen on all test days before performing a static load test, using an OHAUS MB 200 moisture analyzer. The rapid moisture content detector oven dried a soil sample in approximately 15 minutes (as compared to a 16 to 24 hour drying time in case of a regular moisture content determination test), and displayed the absolute value of the moisture content in terms of a percentage on a LCD screen. The moisture content test was performed in accordance with ASTM D4959.
The specimens to be tested were statically loaded using a tri-axial testing machine (e.g., an ELE Tri-axial Testing System). The tri-axial machine includes a hydraulic loading platform to which a load cell and penetrometer are attached. The load cell and penetrometer are connected to a computer which is programmed to dynamically read, tabulate and plot the load versus penetration graph for each specimen.
The static load test was performed in accordance with ASTM D-1143 with a minor variations to account for use of a tri-axial testing machine instead of a conventional axial compressive loading device.
To generate an electrokinetic field between the piles and the surrounding electrodes, a positive terminal of a direct current voltage source was connected to the pile, and negative terminals of the voltage source were connected to each of the three electrodes. The DC voltage source applied a constant voltage across the specimen for the duration of the test period. The test program requirement made it mandatory that at least three voltage sources, which could apply 1V, 10 V and 30 V on different specimens, be used simultaneously. A log was maintained to record the durations of application of electric gradient.
The temperature of each of the specimens was monitored on a regular basis, including during the application of electric gradient. A lab thermometer was used to record temperatures.
The twenty soil-pile specimens of varying clay content, moisture content, and eletrokinetic field exposure were subjected to static load testing on days 0, 1, 3, 7, 14, 21, 28, 252, and 256, as measured from the end of initial driving. (Static load testing was terminated during testing on Day 42 due to technical problems with the load cell used in the tri-axial testing machine). The application of electrokinetic fields to the specimens was carried out from Day 3 to Day 42, with only brief termination of the electrokinetic fields during static load testing.
Test data taken on Days 0, 1, 3, 7, 14, 21, 28, 42 (partial), 252 and 256 are presented in Tables 6-15 respectively. Static load tests were terminated at the point when the specimens shows no further signs of increase in load for two or three consecutive increments of pile penetration. The maximum stable load attained by each specimen on all test days is tabulated in Table 16.

TABLE 5

Specimen Information
PILE SET-UP EXPERIMENTAL DATA
PILE SET-UP EXPERIMENTAL DATA

P1

P2

P3

P4P

5P

6P

7P

8

P9

10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

Mois. Con.	35	35	35	35	12	12	17	17	40	40	40	40	40	40	40	40	35	35	35	35
DC Volt	0	0	30	30	0	30	0	30	0	0	1	1	10	30	30	10	0	0	30	30
% Sand	50	50	50	50	75	75	75	75	0	0	0	0	0	0	0	0	0	0	0	0
# Blows	0	0	0	10	10	65	0	8	63	102	80	123	177	110	110	147	438	300	336	325

TABLE 6

Load versus penetration data taken on Day 0
Day 0

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	10	11	21	27	24	130	2	6	67	132	74	99	128	128	116	105	326	282	244	242
2	11	11	23	31	41	147	2	6	74	137	85	104	128	129	127	120	330	291	250	258
3	11	11	23	32	47	155	2	6	78	141	90	104	128	128	130	128	332	296	250	267
4				32	50	160	2	8	82	141	92	111			132	132	333	296	250	274
5					55	164		10	82	142	95	111			136	134	334	300		279
6					55	167		11			97				137	137		300		288
7						172		11			99					137				292
8						176		11			99									300
9								11												307
10																				313
Day 0	11	11	23	32	55	176	2	11	82	142	99	111	128	128	137	137	334	300	250	313

TABLE 7

Load versus penetration data taken on Day 1
Day 1

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	10	11	21	27	24	130	2	6	67	132	74	99	128	128	116	105	326	282	244	242
2	11	11	23	31	41	147	2	6	74	137	85	104	128	129	127	120	330	291	250	258
3	11	11	23	32	47	155	2	6	78	141	90	104	128	128	130	128	332	296	250	267
4				32	50	160	2	8	82	141	92	111			132	132	333	296	250	274
5					55	164		10	82	142	95	111			136	134	334	300		279
6					55	167		11			97				137	137		300		288
7						172		11			99					137				292
8						176		11			99									300
9								11												307
10																				313
Day 1	11	11	23	32	55	176	2	11	82	142	99	111	128	128	137	137	334	300	250	313

TABLE 8

Load versus penetration data taken on Day 3
Day 3

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	25	29	43	48	84	200	4	20	113	168	126	134	139	148	164	176	324	345	284	408
2	25	29	42	46	89	206	5	21	113	168	130	134	139	147	164	176	329	345	284	416
3	25	29	42	46	92	210	6	21	113		130	134	139	147	162	176	332	345	284	420
4					92	210	6										334			426
5							6										335			433
6																				438
7
8
9
10
Day 3	25	29	42	46	92	210	6	21	113	168	130	134	139	147	162	176	335	345	284	438

TABLE 9

Load versus penetration data taken on Day 7
Day 7

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	25	31	252	231	115	1244	4	355	126	178	138	143	139	307	345	190	292	357	521	647
2	25	29	244	235	118	1611	4	349	126	176	134	143	139	287	340	190	328	357	584	660
3	25	29	244	239	118	1773	4	345	126	176	134	143	141	274	336	190	332	357	562	649
4				234		1800	6	345					142				333		542	641
5							8						142				334		534
6							8
7
8
9
10
Day 7	25	29	244	234	118	1800	8	345	126	176	134	143	142	274	336	190	334	357	534	641

TABLE 10

Load versus penetration data taken on Day 14
Day 14

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	26	34	265	227	142	2515	4	328	139	197	160	163	155	248	370	214	345	378	498	613
2	25	34	263	218	143	2521	4	336	139	193	159	160	155	248	366	210	349	374	504	618
3	25	34	263	212	146		4	333	139	193	157	160	155	248	357	207	352	371	504	617
4				206	148		5	340			155				353	206	353	370
5				205	151		6				155				349
6					155		8								345
7					160		8
8					164
9					168
10					172
Day 14	25	34	263	205	172	2521	8	340	139	193	155	160	155	248	345	206	353	370	504	617

TABLE 11

Load versus penetration data taken on Day 21
Day 21

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	34	42	261	286	8	500	151	206	191	197	239	454	737	500	340	378	728	1052
2	29	38	265	264	8	479	147	202	189	192	227	454	765	384	342	378	739	1064
3	29	38	269	252	12	471	147	199	188	189	223	445	739	370	345	378	705	1038
4			265	253	12	458		197	185	189	218	436	708	358	345		689	1000
5				250	10	478		193	185		218	432	674	352			695	963
6						479		193				429	648	345			697	947
7												424	628	344				929
8												420						914
9
10
Day 21	29	38	265	250	10	479	147	193	185	189	218	420	628	344	345	378	697	914

TABLE 12

Load versus penetration data taken on Day 28
Day 28

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	29	41	374	563	202	2596	8	643	164	214	239	235	345	412	571	416	353	395	685	1014
2	29	38	387	450	207	2550	8	622	160	212	234	231	328	416	601	419	355	395	653	1017
3	29	38	369	352	210	2555	8	626	160	209	231	227	315	429	606	416	357	395	647	1029
4			366	334	211	2550	12	643		206	227	227	315	437	606		357		651	1038
5				333	214			647		206	227			434					639	1021
6					218									437					639	1017
7					218														639	1017
8
9
10
Day 28	29	38	366	333	218	2550	12	647	160	206	227	227	315	437	606	416	357	395	638	1017

TABLE 13

Load versus penetration data taken on Day 42
Day 42

Load in ‘N’

Disp ‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	42	46	626	782	8
2	42	46	647	739	8
3	42	46	647	706	11
4				660	13
5				660	13
6					14
7					17
8
9
10
Day 42	42	46	647	660	17

TABLE 14

Load versus penetration data taken on Day 252
Day 252

Disp	Load in ‘N’

‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	126	108	717	754	940	3627	45	1176	369	462	524	571	866	811	960	564	580	567	874	991
2	121	105	730	743	876	3693	47	1199	362	440	534	588	856	839	903	700	574	556	977	1174
3	121	100	717	736	850	3744	50	1212	359	420	565	588	854	861	886	721	570	545	992	1241
4		99	703	728	823	3777	53	1223	357	401	570		852	875	886	735	566	540	1041	1200
5		99	690	700	824	3832	53	1271	357	389	580		850	882		742	566	537	1071	1200
6			690	700		3854		1310		378	580		848	900		740		537	1112
7						3927		1341		368			847	900					1163
8						3954		1341		359			847						1192
9						4000				351									1212
10						4069				351									1212
Day	121	99	690	700	824	4517	53	1341	357	351	580	588	847	900	886	740	566	537	1212	1200
252

TABLE 15

Load versus penetration data taken on Day 256
Day 256

Disp	Load in ‘N’

‘mm’

P1

P2

P3

P4

P5

P6

P7

P8

P9

P10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

1	131	105	646	720	1013	3076	50	1348	386	402	686	645	647	697	782	582	563	550	1054	1053
2	126	101	683	728	998	3775	57	1481	386	393	694	646	700	753	869	869	569	557	1144	1134
3	126	100	693	741	982	3854	59	1535		378	669	643	730	807	928	703	570	557	11367	1154
4		100	693	708	977	3917	63	1587		372	650	643	752	845	987	760	575	557	1196	1180
5				708	965	3929	66	1586		364	650		767	873	1000	760	578		1239	1209
6					956	4003	68	1586		361			782	903	1000		583		1264	1225
7					945	4001	72			360			801	924			588		1264	1221
8					945	4006	74			357			817	943			588			1222
9						4060	84			361			851	960
10						4100	84			361			851	960
Day	126	100	693	708	945	4620	84	1596	386	361	650	643	851	960	1000	760	588	557	1264	1222
256

TABLE 16

Summary of Maximum Stable Loads on all Test Days

Maximum Stable Load in ‘N’

Day

P1

P2

P3

P4P

5P

6P

7P

8

P9

10

P11

P12

P13

P14

P15

P16

P17

P18

P19

P20

0	11	11	23	32	55	176	2	11	82	142	99	111	128	128	137	137	334	300	250	313
1	15	19	32	37	71	193	2	15	95	153	107	117	128	132	145	153	334	326	276	397
3	25	29	42	46	92	210	6	21	113	168	130	134	139	147	162	176	335	345	284	438
7	25	29	244	234	118	1800	8	345	126	176	134	143	142	274	336	190	334	357	534	641
14	25	34	263	205	172	2521	8	340	139	193	155	160	155	248	345	206	353	370	504	617
21	29	38	265	250			10	479	147	193	185	189	218	420	628	344	345	378	697	914
28	29	38	366	333	218	2550	12	647	160	206	227	227	315	437	606	416	357	395	638	1017
42	42	46	647	660			17
252	121	99	690	700	824	4517	53	1341	357	351	580	588	847	900	886	740	566	537	1212	1200
256	126	100	693	708	945	4620	84	1596	386	361	650	643	851	960	1000	760	588	557	1264	1222

FIGS. 6-9 graphically illustrate the difference in pile capacities between electrokinetically conditioned soil samples exposed to an electric gradient of 30 Volts DC/ft and substantially identical soil samples (i.e., same composition and moisture content) not subjected to an electric gradient. As shown in FIG. 6, electrokinetically conditioned soil samples having a 50% clay content and 35% moisture content experienced a 1043% greater pile capacity on average after 28 days, and a 620% greater pile capacity on average at the conclusion of the 256 day test. As shown in FIG. 7, an electrokinetically conditioned soil sample having a 75% clay content and 12% moisture content experienced a 1170% greater pile capacity after 28 days, and a 489% greater pile capacity at the conclusion of the 256 day test. As shown in FIG. 8, an electrokinetically conditioned soil sample having a 75% clay content and 17% moisture content experienced a 5392% greater pile capacity after 28 days, and a 1900% greater pile capacity at the conclusion of the 256 day test. As shown in FIG. 9, electrokinetically conditioned soil samples having a 100% clay content and 35% moisture content experienced a 220% greater pile capacity on average after 28 days, and a 217% greater pile capacity on average at the conclusion of the 256 day test.
FIG. 10 graphically illustrates the difference in pile capacities between substantially identical soil samples (i.e., 100% clay content and 40% moisture content) exposed to different amounts of applied electric gradient (0 V, 1 V, 10 V, and 30 V/ft). Using the naturally set-up (i.e., no applied electric gradient) samples as a baseline, the samples exposed to a 1 V DC/ft electric gradient experienced a 24% greater pile capacity on average after 28 days, and a 73% greater pile capacity on average at the conclusion of the 256 day test. The samples exposed to a 10 V DC/ft electric gradient experienced a 100% greater pile capacity on average after 28 days, and a 240% greater pile capacity on average at the conclusion of the 256 day test. The samples exposed to a 30 V DC/ft electric gradient experienced a 285% greater pile capacity on average after 28 days, and a 262% greater pile capacity on average at the conclusion of the 256 day test.
A rapid moisture content test was conducted on every specimen on all test days before performing a static load test. Table 17 shows a moisture content log at the beginning and the end of the testing period, in which slight reductions in the moisture contents of these specimen during the course of the testing period are noted.

TABLE 17

Moisture Content Log

Moisture content (%)

Day	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10

0	35	35	35	35	12	12	17	17	40	40
252	34	35	33	32	11	12	15	15	38	38
256	34	34	32	31	12	11	15	15	38	38

Day	P11	P12	P13	P14	P15	P16	P17	P18	P19	P20

0	40	40	40	40	40	40	35	35	35	35
252	37	36	38	37	36	38	34	34	32	32
256	36	36	38	37	36	33	33	34	32	32

The temperature of the specimens was monitored on a regular basis, especially during the period over which the electric gradient was applied. Table 18 shows a log of temperatures that was maintained during the testing period, in which the temperatures of the specimens were observed to be close to the ambient temperatures on the respective test days, and not substantially affected by the application of the electric gradient.

TABLE 18

Temperature Log

Temperature (° F.)

Day	P1	P2	P3	P4	P5	P6	P7	P8	P9	P10

14	73	74	72	73	72	73	72	73	72	73
18	74	74	76	75	73	72	73	77	74	73
22	73	72	74	74	73	75	73	75	72	72
28	72	72	72	73	73	73	72	72	73	72
30	69	69	69	69	69	69	69	69	69	69
42	72	73	72	72	73	72	71	71	72	72

Day	P11	P12	P13	P14	P15	P16	P17	P18	P19	P20

14	71	71	72	83	87	72	78	79	80	82
18	72	73	74	79	77	74	79	79	80	79
22	72	72	73	75	74	73	78	78	78	77
28	69	70	70	75	73	69	78	78	75	74
30	69	69	69	69	69	69	69	69	69	69
42	72	72	73	72	72	71	71	70	71	71

While various inventive aspects, concepts and features of the inventions may be described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects, concepts and features may be used in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present inventions. Still further, while various alternative embodiments as to the various aspects, concepts and features of the inventions--such as alternative materials, structures, configurations, methods, circuits, devices and components, software, hardware, control logic, alternatives as to form, fit and function, and so on--may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the inventive aspects, concepts or features into additional embodiments and uses within the scope of the present inventions even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the inventions may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present disclosure; however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. Moreover, while various aspects, features and concepts may be expressly identified herein as being inventive or forming part of an invention, such identification is not intended to be exclusive, but rather there may be inventive aspects, concepts and features that are fully described herein without being expressly identified as such or as part of a specific invention. Descriptions of exemplary methods or processes are not limited to inclusion of all steps as being required in all cases, nor is the order that the steps are presented to be construed as required or necessary unless expressly so stated.

Claims

1. A method for increasing load capacity of a foundation pile installed in a ground material, the method comprising:

embedding at least one electrode in the ground material at a predetermined distance from the installed pile;

providing a direct current power source including at least one cathode connection and at least one anode connection;

securing one of the at least one cathode connections to the foundation pile;

securing one of the at least one anode connections to each of the at least one electrodes; and

activating the direct current power source to generate an electric gradient between the foundation pile and the at least one electrode, the electric gradient being selected to direct charged soil particles in the ground material toward the foundation pile.

2. The method of claim 1, wherein embedding at least one electrode in the ground material comprises embedding a plurality of electrodes in the ground material at substantially equal predetermined distances around the foundation pile.

3. The method of claim 1, wherein activating the direct current power source to generate the electric gradient comprises supplying an electrical potential from approximately 1 volt DC to approximately 100 volts DC.

4. The method of claim 1, wherein activating the direct current power source to generate the electric gradient comprises generating an electric gradient of approximately 30 volts DC/ft.

5. The method of claim 1, wherein the charged soil particles comprise clay particles.

6. The method of claim 1, further comprising maintaining the electric gradient between the foundation pile and the at least one electrode for a period of at least approximately 48 hours.

7. The method of claim 1, further comprising measuring a moisture content of the ground material and adjusting one of an electrical potential supplied by the direct current power source and a duration during which the electric gradient is maintained based on the measured moisture content.

8. The method of claim 1, further comprising measuring a clay content of a soil sample obtained from the ground material and adjusting one of an electrical potential supplied by the direct current power source and a duration during which the electric gradient is maintained based on the measured clay content.

9. The method of claim 1, wherein embedding the at least one electrode in the ground material at a predetermined distance from the installed pile comprises embedding the at least one electrode at a distance of at least approximately 3 feet from the installed pile.

10. The method of claim 1, wherein embedding the at least one electrode in the ground material comprises embedding the at least one electrode to a depth of at least approximately one half of the pile length.

11. A system for electrokinetic conditioning of an installed steel foundation pile, the system comprising:

a foundation pile embedded in a cohesive ground material containing negatively charged particles;

at least one electrode embedded in the ground material at a predetermined distance from the foundation pile;

a direct current power source having a positive terminal connected to the foundation pile, and at least one negative terminal connected to each of the at least one electrodes.

12. The system of claim 11, wherein the at least one electrode comprises a plurality of electrodes embedded in the ground material at substantially equal predetermined distances around the foundation pile.

13. The system of claim 12, wherein the plurality of electrodes are embedded in the ground material at a distance of at least approximately 3 feet from the surface of the foundation pile.

14. The system of claim 11, wherein the at least one electrode in the ground material is embedded to a depth of at least approximately one half of the pile length.

15. The system of claim 11, wherein the direct current power source comprises an adjustable direct current power source having a maximum voltage of at least approximately 100 V DC.

16. The system of claim 14, wherein the negatively charged particles comprise clay particles.

17. The system of claim 11, wherein the foundation pile comprises steel.

18. A method of loosening a conductive structure embedded in a ground material, the method comprising:

embedding at least one electrode in the ground material at a predetermined distance from the embedded structure;

securing one of the at least one anode connections to the foundation pile;

securing one of the at least one cathode connections to each of the at least one electrodes; and

activating the direct current power source to generate an electric gradient between the foundation pile and the at least one electrode, the electric gradient being selected to direct charged soil particles in the ground material away from the foundation pile.

19. The method of claim 18, wherein activating the direct current power source to generate the electric gradient comprises supplying an electrical potential from approximately 1 volt DC to approximately 100 volts DC.

20. The method of claim 18, wherein the conductive structure comprises a steel foundation pile.