DEVICE AND METHOD FOR ELECTROCHEMICALLY REINFORCING SOFT CLAY

Abstract

The present disclosure discloses a device and a method for electrochemically reinforcing soft clay. The device includes a power supply, an anode, a cathode, and a central tube, where a cation exchange membrane is provided in a region, close to the cathode, of a soil mass to be reinforced, and the cation exchange membrane only allows cations to migrate from an interior of the soil mass toward the cathode and physically blocks anions generated by an electrolytic reaction at the cathode from reversely diffusing toward the soil mass; and the cation exchange membrane is wrapped around an outer surface of the cathode or is arranged as an independent isolation layer in a soil mass around the cathode to form an ion filtering interface that completely surrounds the cathode.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serial no. 202610073203.6, filed on Jan. 20, 2026. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The present disclosure relates to a device and a method for reinforcing soil used in engineering foundations, and in particular, to a device and a method for electrochemically reinforcing soft clay.

Description of Related Art

With the rapid development of coastal economic zones and the advancement of urbanization, land resources have become increasingly scarce. Land reclamation from the sea and land formation by dredged sediment filling have become important means for alleviating the contradiction between land supply and demand. However, such dredged fill soft soils and widely distributed marine and lacustrine deposited soft clays typically exhibit extremely unfavorable engineering properties, including high natural water content (often greater than the liquid limit), large void ratio, extremely low permeability (k<1×10-7 cm/s), low shear strength, strong rheological properties, and the like. If such soils are directly used as engineering foundations without treatment, excessive settlement, uneven deformation, or even foundation instability is likely to occur, which imposes serious threats to engineering safety.

Currently, treatment methods for soft soil foundations mainly include physical reinforcement methods and chemical reinforcement methods. The chemical reinforcement methods include electrochemical reinforcement methods; however, the existing electrochemical reinforcement methods still have the following unresolved problems:

(1) Cathodic “softening” phenomenon: Under existing anode grouting modes, modifying ions such as calcium and potassium are difficult to migrate to regions far away from the anode, particularly to regions near the cathode. Meanwhile, OH— ions generated at the cathode accumulate in the cathode region. As a result, the soil mass in this region not only fails to be chemically reinforced, but instead undergoes structural dispersion due to a strongly alkaline environment, thereby exhibiting extremely low strength and becoming a weak part of the foundation.

(2) Non-uniform reinforcement: Due to the limited migration rate of ions, and as energization time increases, the electrical resistance distribution in the soil mass becomes non-uniform, such that the chemical grouting slurry tends to remain near the anode and uniform reinforcement throughout the entire field cannot be achieved.

(3) Reduced drainage efficiency: Native metal cations in the soil mass and those migrated from the anode (such as Ca²⁺, Mg²⁺, and Al³⁺) encounter OH⁻ generated by the electrolytic reaction at the cathode and undergo precipitation reactions, forming non-conductive solid particles. These particles may block pore channels, resulting in a reduction in drainage efficiency.

SUMMARY

Objective of the present disclosure: The present disclosure aims to provide a device for electrochemically reinforcing soft clay, and the device is capable of effectively isolating OH⁻ generated by the electrolytic reaction at the cathode from reversely diffusing toward the soil mass, and achieving uniform distribution of chemical grouting slurry within the soil mass, thereby improving the overall effect and uniformity of electrochemical reinforcement.

Another objective of the present disclosure is to provide a method for electrochemically reinforcing soft clay using the above device.

Technical solution: The device for electrochemically reinforcing soft clay of the present disclosure includes a power supply, an anode connected to a positive electrode of the power supply, a cathode connected to a negative electrode of the power supply, and a central tube disposed between the anode and the cathode, where a cation exchange membrane is provided in a region, close to the cathode, of a soil mass to be reinforced, and the cation exchange membrane only allows cations to migrate from an interior of the soil mass toward the cathode and physically blocks anions generated by an electrolytic reaction at the cathode from reversely diffusing toward the soil mass; and the cation exchange membrane is wrapped around an outer surface of the cathode or is arranged as an independent isolation layer in a soil mass around the cathode to form an ion filtering interface that completely surrounds the cathode.

The cation exchange membrane has an ion exchange capacity of not less than 1.5 meq/g, and has resistance to acid and alkali corrosion.

Grouting holes are uniformly provided on surfaces of the anode and the central tube, with an opening ratio ranging from 15% to 25%; a drainage hole is formed at a corresponding position at a bottom of the cathode; and the drainage hole is connected to a drainage pipe.

For ease of testing, the drainage hole is connected to an external drainage collection system, and the drainage collection system includes a graduated cylinder and an electronic balance for measuring and recording changes in drainage volume in real time. The graduated cylinder has an accuracy of not less than 0.1 mL.

The central tube is made of a conductive metal or an insulating polymer material, and when the conductive metal material is used, the central tube is connected into a circuit as an auxiliary anode to enhance current intensity in middle and later stages.

The method for electrochemically reinforcing soft clay using the above device includes the following steps:

• • arranging, in a soft clay region to be reinforced, the anode, the cathode, and the central tube according to a preset geometric array; arranging the cation exchange membrane between the cathode and a soil mass to be reinforced;
  • injecting a first electrolyte solution into the interior of the soil mass through the anode to initiate a first-stage grouting; connecting a direct current power supply, and applying a constant or pulsed direct current electric field between the anode and the cathode to initiate a first-stage electroosmotic drainage, such that cations at the anode and the first electrolyte solution are driven by an electric field force to migrate toward the cathode, and meanwhile, hydroxide ions generated by the electrolytic reaction at the cathode are blocked from entering the soil mass by the cation exchange membrane;
  • monitoring current intensity and drainage volume in real time during the electroosmotic process; initiating a second-stage grouting when it is monitored that the current intensity starts to decay from a peak value or when a energization time reaches 40%-60% of a total design duration; injecting a second electrolyte solution into a middle portion of the soil mass through the central tube, and activating a conductive channel in a deep portion of the soil mass by using a fresh ion source injected into the middle portion to form a secondary electroosmotic peak value;
  • maintaining an action of the direct current electric field until the electrolyte solution injected in the middle portion covers a region near the cathode under driving of the electric field and a drainage rate is reduced to a preset threshold; and stopping power supply, recovering reusable electrodes and grouting equipment, and performing curing of the soil mass.

The first electrolyte solution is selected from a potassium chloride solution and/or a calcium chloride solution; and a concentration of the first electrolyte solution is 2.0 mol/L-5.0 mol/L.

A chemical composition of the second electrolyte solution is the same as that of the first electrolyte solution, and a volume ratio of an injection volume of the second electrolyte solution to an injection volume of the first electrolyte solution is 0.8:1-1.2:1.

The second-stage grouting is initiated between 12 hours and 13 hours after energization, or when the current intensity decreases to 70% of an initial peak value.

An applied direct current voltage gradient is 0.8 V/cm-1.2 V/cm.

Between the first-stage grouting and the second-stage grouting, a power-off interval of 2 hours-12 hours is set based on a dissipation condition of pore water pressure.

Before performing curing of the soil mass, reusable electrodes and grouting equipment are recovered.

Beneficial effects: Compared with the prior art, the present disclosure achieves the following significant effects:

(1) By introducing a cation exchange membrane around the cathode, OH-generated by the electrolytic reaction at the cathode is effectively isolated from the soil mass. Tests show that, under the same energization conditions, the electroosmotic drainage rate according to the method of the present disclosure does not exhibit the sharp attenuation over time as in conventional methods, but instead maintains a sustained and efficient state. Compared with a comparative example without the cation exchange membrane, the present disclosure effectively avoids blockage of drainage channels and an increase in electrical resistance of the soil mass caused by precipitates due to reactions between cations and OH⁻ in the soil mass, thereby successfully overcoming key problems that have long restricted the development of electroosmosis technologies, including “cathodic clogging” and “reverse electroosmosis”. (2) The “stepwise grouting” method provided by the present disclosure, in which anode grouting is performed first and then grouting via the central tube is performed, effectively solves the problem of “hard anode and soft cathode” caused by the limited effective range in conventional electroosmotic grouting techniques. By secondarily delivering a highly active modifying grouting slurry directly to a middle portion of the soil mass through the central tube, and driving the grouting slurry by an electric field in a later stage such that the grouting slurry fully covers the cathode region, and in combination with suppression of softening effect of the cathode by the cation exchange membrane, the present disclosure successfully achieves uniform reinforcement of the soil mass from the anode to the cathode, thereby significantly improving overall strength and stability. (3) The present disclosure employs an intermittent stepwise grouting technique, where the ion concentration of the solution is replenished promptly during the electroosmotic process, effectively restoring and enhancing the electroosmotic driving force. The experimental drainage rate curve exhibits a typical “double-peak” characteristic, indicating that the electroosmotic flow is reactivated after grouting in the intermediate stage, and the drainage efficiency is significantly improved. Within the same energization duration, the present disclosure can achieve the discharge of more pore water, thereby greatly shortening the time required for the foundation to reach a target degree of consolidation and significantly improving electrochemical reinforcement efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of the device according to the present disclosure;

FIG. 2 is a schematic diagram of the electrode arrangement and different test positions of the device according to the present disclosure;

FIG. 3 shows curves of the variation of cumulative drainage volume with energization time during the electroosmotic process according to Example S5 and Comparative Examples S1, S2, and S3 of the present disclosure;

FIG. 4 shows curves of the variation of instantaneous drainage rate with energization time according to Example S5 and Comparative Examples S1, S2, and S3 of the present disclosure;

FIG. 5A~FIG. 5E show curves of the variation of measured settlement at different positions of a soil mass after reinforcement with energization time according to Example S5 and Comparative Examples S1, S2, and S3 of the present disclosure, where FIG. 5A corresponds to measuring point 1 #, FIG. 5B corresponds to measuring point 2 #, FIG. 5C corresponds to measuring point 3 #, FIG. 5D corresponds to measuring point 4 #, and FIG. 5E corresponds to measuring point 5 #;

FIG. 6 shows curves of the variation of cumulative drainage volume with energization time during the electroosmotic process according to Example S5 and Comparative Examples S3 and S4 of the present disclosure;

FIG. 7A to FIG. 7E show curves of the variation of measured settlement at different positions of a soil mass after reinforcement with energization time according to Example S5 and Comparative Examples S3 and S4 of the present disclosure, where FIG. 7A corresponds to measuring point 1 #, FIG. 7B corresponds to measuring point 2 #, FIG. 7C corresponds to measuring point 3 #, FIG. 7D corresponds to measuring point 4 #, and FIG. 7E corresponds to measuring point 5 #;

FIG. 8 shows curves of the variation of cumulative drainage volume with energization time during the electroosmotic process according to Example S5 and Comparative Examples S6 and S7 of the present disclosure; and

FIG. 9A to FIG. 9E show curves of the variation of measured settlement at different positions of a soil mass after reinforcement with energization time according to Example S5 and Comparative Examples S6 and S7 of the present disclosure, where FIG. 9A corresponds to measuring point 1 #, FIG. 9B corresponds to measuring point 2 #, FIG. 9C corresponds to measuring point 3 #, FIG. 9D corresponds to measuring point 4 #, and FIG. 9E corresponds to measuring point 5 #.

Reference numerals: 1: electrokinetic cell; 2: power supply; 3: anode; 4: cathode; 5: central tube; 6: cation exchange membrane; 7: data acquisition system; 8: drainage hole; 9:

drainage pipe; 10: dial gauge; 11: voltage probe.

DESCRIPTION OF THE EMBODIMENTS

The present disclosure is further described in detail below.

Example 1

As shown in FIG. 1, the present disclosure provides a device for electrochemically reinforcing soft clay. The device includes a power supply 2, an anode 3 serving as a positive electrode, a cathode 4 serving as a negative electrode, and a central tube 5 disposed between the anode 3 and the cathode 4. A chemical solution is introduced into the anode 3 and the central tube 5 in an external injection manner, such that stepwise grouting for different regions is achieved during the electroosmotic process. A cation exchange membrane 6 is provided between the cathode 4 and the soil mass to be reinforced. The cation exchange membrane 6 only allows cations to migrate from the interior of the soil mass toward the cathode 4 and physically blocks anions generated by an electrolytic reaction at the cathode 4 from reversely diffusing toward the soil mass. The cation exchange membrane 6 is wrapped around the outer surface of the tubular cathode 4 or is arranged as an independent isolation layer in a soil mass around the cathode 4 to form an ion filtering interface that completely surrounds the cathode 4.

This example further includes an electrokinetic cell 1, and the cathode 4, the anode 3, and the central tube 5 are all disposed within the electrokinetic cell 1. The electrokinetic cell 1 is made of a high-transparency acrylic plate, having internal dimensions of 400 mm in length, 300 mm in width, and 140 mm in height, and a wall thickness of 10 mm, which is sufficient to withstand the lateral pressure of the soil mass.

In this example, the anode 3 is a 304 stainless steel pipe having an outer diameter of 10 mm and a wall thickness of 1 mm. Grouting holes having a diameter of 2 mm are uniformly drilled on the pipe wall with a spacing of 20 mm. The holes are arranged in a quincunx pattern and have an opening ratio in a range of 15%-25%. A layer of geotextile of 200 g/m² is wrapped around the outer surface of the pipe to prevent soil particles from clogging the grouting holes.

In this example, the cathode 4 is made of the same material as the anode 3. A drainage hole 8 is formed at a corresponding position at the bottom of the cathode 4, and the drainage hole 8 is connected to a drainage pipe 9. A layer of cation exchange membrane (CEM) 6 is wrapped on the outer side of the geotextile. In this example, a sulfonated polystyrene-divinylbenzene copolymer cation exchange membrane 6 is utilized, which has excellent chemical stability and permselectivity, allowing only cations to pass therethrough while strictly blocking anions, i.e., OH⁻. For ease of testing, in this example, the drainage hole 8 at the bottom of the cathode 4 is connected to an external drainage collection system. The drainage collection system includes a graduated cylinder (not shown in the figure) and an electronic balance (not shown in the figure) for measuring and recording changes in drainage volume in real time. The graduated cylinder has an accuracy of not less than 0.1 mL.

The central tube 5 is made of a conductive metal or an insulating polymer material, and when the conductive metal material is used, the central tube 5 is connected into a circuit as an auxiliary anode to enhance current intensity in middle and later stages. In this example, the central tube 5 has the same structural material as the anode 3 and is arranged at the geometric midpoint between the anode 3 and the cathode 4. Grouting holes are uniformly provided on the surface of the central tube 5, with an opening ratio in a range of 15%-25%.

In this example, the test soil was dredged slurry obtained from the site of a land reclamation project. The basic physical properties of the test soil, as determined by an indoor geotechnical test, are shown in Table 1 below:

TABLE 1
	Numerical
Property	value	Remark
Specific gravity (Gs)	2.73	—
Liquid limit (ωL)	43%	—
Plastic limit (ωP)	23%	—
Plasticity index (IP)	20	Classified as low liquid
		limit clay (CL)
Initial water	42%	Near liquid limit, in a
content (ω0)		plastic flow shape
Initial dry	1.21	g/cm3	—
density (ρd)
Permeability	3.0 × 10 − 7	cm/s	Extremely low, difficult
coefficient (k)			to drain conventionally
pH value	6.5	Weakly acidic
Note:
Chemical solution: Pure potassium chloride (KCl) was selected to prepare an electrolyte solution with a concentration of 4.0 mol/L.

Example 2

The device of Example 1 was used to reinforce a soil sample according to the following steps:

Step 1: Soil Sample Loading and Electrode Arrangement

The soil sample collected from the site was oven-dried, crushed, and passed through a 2 mm sieve. Distilled water was added and the mixture was stirred to reach a water content of 42%. The mixture was left to stand for 24 h to ensure uniform moisture distribution. The treated soil sample was then filled into a model box in layers, and vibration and tamping were applied to eliminate air bubbles, with the filling dry density controlled at 1.21 g/cm³.

The anode 3, the cathode 4, and the central tube 5 were vertically inserted into the soil mass, with an electrode insertion depth of 100 mm, and the spacing between the anode 3 and the cathode 4 was maintained at 350 mm. Meanwhile, settlement observation points 1 #-5 #, voltage probes 11, and dial gauges 10 were arranged at different positions, as shown in FIG. 2.

Specifically, measuring point 1 # was located at the anode 3, measuring point 3 # was located at the central tube 5, and measuring point 5 # was located at the cathode 4, measuring point 2 # was located at the midpoint between measuring points 1 # and 3 #, and measuring point 4 # was located at the midpoint between measuring points 3 # and 5 #. In addition, the spacing between adjacent measuring points was equal. The voltage probes 11 and the dial gauges 10 were separately arranged at measuring points 1 #-5 #, and the voltage probe marker at measuring point 3 # in FIG. 2 was obscured by a black dot. Each voltage probe 11 was connected to the data acquisition system 7 for automatic reading of voltage data. The dial gauge 10 was a general-purpose dial-type length measuring instrument for measuring the settlement of soil mass, and the data were manually read.

Step 2: First-Stage Electroosmosis with Anode 3 Grouting

Grouting: 70 mL of a KCl solution with a concentration of 4.0 mol/L was injected into the soil mass through the anode 3 pipe. The solution infiltrated into the soil mass around the anode 3 under the action of gravity and electric current.

Energization: A direct current regulated power supply 2 (model RXN-605D) was connected, and the output voltage was set to 30 V, corresponding to a potential gradient of 0.86 V/cm.

Process: Energization was maintained for 12.5 hours. During this period, current variation was recorded via the voltage probes 11 and the data acquisition system 7 to monitor current intensity in real time. The drainage hole 8 was connected to an external drainage collection graduated cylinder and an electronic balance to monitor changes in drainage volume in real time. At this time, high-concentration K⁺ ions in the anode 3 region migrated toward the cathode 4 under driving of the electric field, replacing Na⁺ on the surface of soil particles and compressing the electric double layer. Pore water migrated along with K⁺. At the cathode 4, the CEM membrane intercepted OH generated by electrolysis, and the discharged water was mainly pore water.

Step 3: Second-Stage Grouting Via Central Tube

Grouting: When energization reached 12.5 hours, the power supply was paused, and 70 mL of a KCl solution with a concentration of 4.0 mol/L was injected into the central tube 5; alternatively, the KCl solution could also be injected into the central tube 5 in an energized state.

Continued energization: The voltage was maintained at 30 V, and energization was continued for another 12.5 hours, for a total duration of 25 hours.

At this time, the ions injected in the first stage had partially migrated or diffused, and the current exhibited a decreasing trend. The freshly injected electrolyte solution in the middle portion rapidly reduced the electrical resistance of the middle portion of the soil mass, thereby accelerating electroosmotic flow again and forming a second peak value of the drainage rate, as shown in FIG. 3.

Step 4: Termination and Testing

After completion of energization, the power supply 2 was disconnected, and the soil mass was allowed to stand for 24 hours to dissipate pore water pressure. Subsequently, soil samples were collected to determine the final water content.

Related Test and Result Analysis:

To verify the superiority of Test No. S5 of the present disclosure, six groups of comparative tests were set, and the conditions are shown in Table 2 below:

TABLE 2
	Solution		CEM membrane
Test No.	type	Grouting method	and arrangement	Remark
Comparative	KCl (4.0	Anode 3 + middle	No CEM membrane	Conventional
Example S1	mol/L)	portion; simultaneous		electroosmosis
		grouting		method
Comparative	KCl (4.0	Anode 3 + middle	No CEM membrane	Electroosmosis
Example S2	mol/L)	portion; Stepwise		method with
		grouting, time		stepwise
		interval of 12.5 h		grouting
Comparative	KCl (4.0	Anode 3 + middle	With CEM membrane	To compare the
Example S3	mol/L)	portion; simultaneous	wrapped around	influence of
		grouting	cathode 4	grouting
Comparative	KCl (4.0	Anode 3 + middle	With CEM membrane	methods
Example S4	mol/L)	portion; stepwise	wrapped around
		grouting, time	cathode 4
		interval of 6 hours
S5 of the	KCl (4.0	Anode 3 + middle	With CEM membrane	To compare the
present	mol/L)	portion; stepwise	wrapped around	influence of
disclosure		grouting, time	cathode 4	CEM membrane
		interval of 12.5 hours		arrangement
Comparative	KCl (4.0	Anode 3 + middle	With CEM membrane	positions
Example S6	mol/L)	portion; stepwise	wrapped around
		grouting, time	anode 3
		interval of 12.5 hours
Comparative	KCl (4.0	Anode 3 + middle	With CEM membrane
Example S7	mol/L)	portion; stepwise	wrapped around the
		grouting, time	central tube 5
		interval of 12.5 hours

(1) Analysis of Drainage Volume and Drainage Rate

FIG. 3 shows curves of the variation of cumulative drainage volume with energization time for four groups of tests S1, S2, S3, and S5.

0-12.5 h stage: During the first energization, in the S1 and S3 tests, the KCl solution was simultaneously injected into the anode 3 and the central tube 5, resulting in a relatively high ion concentration in the soil mass. Therefore, the drainage volumes of S1 and S3 tests were significantly higher than those of S2 and S5 tests. In addition, the drainage volume of S3 test was slightly greater than that of S1 test, and the drainage volume of S5 test was slightly greater than that of S2 test, indicating that the CEM membrane wrapped around the cathode 4 had already begun to inhibit the diffusion of OH-into the interior of the soil mass, although the effect was not yet significant.

12.5-25 h stage: At 12.5 h, in the S2 and S5 tests, the KCl solution was injected again through the central tube 5, thereby reactivating the electrochemical reactions within the interior of the soil mass. The drainage volume of S2 test exceeded that of S1 test after 15 h, and the drainage volume of S5 test exceeded that of S3 test after 15 h, indicating that the stepwise grouting method can effectively increase the total drainage volume of the soil sample. Furthermore, the drainage volume of S5 test was significantly greater than that of S2 test after 15 h, indicating that with the increase of energization time, the CEM membrane wrapped around the cathode 4 significantly inhibited the diffusion of OH into the interior of the soil mass, thereby markedly improving the total drainage volume during the electroosmotic process.

Completion of energization: After the completion of energization, the cumulative drainage volume of S5 of the present disclosure was the largest as compared with those of Comparative Examples S1, S2, and S3.

FIG. 4 shows curves of the variation of instantaneous drainage rate with energization time for four groups of tests S1, S2, S3, and S5.

All four groups of tests exhibited a peak value in instantaneous drainage rate at 2-3 h after energization and grouting. In S2 and S5 tests, a second peak value of instantaneous drainage rate appeared after the second stepwise grouting. After the stepwise grouting in the middle portion in the second stage, the instantaneous drainage rate of S5 of the present disclosure exhibited the lowest decay rate and was maintained at a relatively high level compared with Comparative Examples S1, S2, and S3. The drainage rate of Comparative Example S2 decreased significantly in the second stage, indicating that OH-generated by electrolysis at the cathode 4 substantially reduced electroosmotic efficiency. In contrast, in S5 of the present disclosure, the CEM membrane was used to prevent the OH-generated by electrolysis from diffusing into the interior of the soil mass, thereby ensuring that the effect of stepwise grouting was maximized.

(2) Analysis of Settlement Deformation

FIG. 5A to FIG. 5E show curves of the variation of the measured settlement amount of the soil mass at five different measuring points in FIG. 2 with energization time in four groups of tests S1, S2, S3, and S5, where FIG. 5A corresponds to measuring point 1 #, FIG. 5B corresponds to measuring point 2 #, FIG. 5C corresponds to measuring point 3 #, FIG. 5D corresponds to measuring point 4 #, and FIG. 5E corresponds to measuring point 5 #. As can be seen from FIG. 5A to FIG. 5E, with the increase of energization time, after the completion of energization, the final settlements at all 5 measuring points in Example S5 of the present disclosure were the maximum. Specifically, for measuring points 14, 2 #, and 3 #, since these points were relatively far from the cathode 4 and were less affected by the CEM membrane, the differences in final settlement between Example S5 of the present disclosure and Comparative Examples S1, S2, and S3 were not significant. For measuring points 4 # and 5 #, due to the influence of the CEM membrane, the final settlements of Example S5 of the present disclosure were significantly greater than those of Comparative Examples S1, S2, and S3, indicating that Example S5 of the present disclosure can solve the problem of “hard anode and soft cathode” that is difficult to address by conventional electrochemical reinforcement techniques, and can significantly improve the uniformity of soil mass reinforcement.

(3) Analysis of the Influence of Grouting Method, i.e., Grouting Time Interval on Electroosmosis Effect

FIG. 6 shows curves of the variation of cumulative drainage volume with energization time for three groups of tests S3, S4, and S5, and FIG. 7A to FIG. 7E show curves of the variation of the measured settlement amount of the soil mass at five different measuring points in FIG. 2 with energization time in three groups of tests S3, S4, and S5, where FIG. 7A corresponds to measuring point 1 #, FIG. 7B corresponds to measuring point 2 #, FIG. 7C corresponds to measuring point 3 #, FIG. 7D corresponds to measuring point 4 #, and FIG. 7E corresponds to measuring point 5 #. By comparing the three groups of tests S3, S4, and S5, it can be seen that after the completion of energization, the final settlements at all five measuring points in S5 of the present disclosure were the maximum. For measuring points 1 #, 2 #, and 3 #, the stepwise grouting time interval had little effect on the final settlement amount of the soil mass at different measuring points. For measuring points 4 # and 5 #, the stepwise grouting time interval had a significant influence on the final settlement amount of the soil mass at different measuring points.

(4) Analysis of the Influence of the Arrangement Position of the Cation Exchange Membrane 6 on Electroosmosis Effect

FIG. 8 shows curves of the variation of cumulative drainage volume with energization time for three groups of tests S5, S6, and S7, and FIG. 9A to FIG. 9E show curves of the variation of the measured settlement amount of the soil mass at five different measuring points in FIG. 2 with energization time in three groups of tests S5, S6, and S7, where FIG. 9A corresponds to measuring point 1 #, FIG. 9B corresponds to measuring point 2 #, FIG. 9C corresponds to measuring point 3 #, FIG. 9D corresponds to measuring point 4 #, and FIG. 9E corresponds to measuring point 5 #. By comparing the three groups of tests S5, S6, and S7, it can be seen that after the completion of energization, the final settlements at all five measuring points in S5 of the present disclosure were the maximum.

In addition, wrapping the CEM membrane around the anode 3 significantly reduced the electroosmosis effect; wrapping the CEM membrane around the central tube 5 did not significantly improve the electroosmosis effect; whereas wrapping the CEM membrane around the cathode 4 could significantly improve the electroosmosis effect.

Example 3

Application scenarios: land reclamation foundation treatment in coastal new areas, soft ground reinforcement for highways, and sludge reinforcement for deep foundation pits of subway stations.

Recommended Parameters:

Electrode spacing: 0.8 m-1.2 m.

Voltage: 30 V-60 V DC, depending on safety specifications.

Grouting material: For general soft soils, a saturated KCl solution is recommended, which has high solubility (about 4.5 mol/L at room temperature) and high electrical conductivity, and does not produce precipitates that clog the grouting pipes. For local areas requiring extremely high strength, CaCl₂) may be used, but it is required to be used in strict combination with the CEM membrane.

Grouting timing: A current control method is used. That is, when the monitored current decreases to 70% of the peak value, grouting through the intermediate pipe is automatically triggered, thereby achieving intelligent construction.

Claims

1. A device for electrochemically reinforcing soft clay, comprising a power supply (2), an anode (3) connected to a positive electrode of the power supply (2), a cathode (4) connected to a negative electrode of the power supply (2), and a central tube (5) disposed between the anode (3) and the cathode (4), wherein a cation exchange membrane (6) is provided in a region, close to the cathode (4), of a soil mass to be reinforced, and the cation exchange membrane (6) only allows cations to migrate from an interior of the soil mass toward the cathode (4) and physically blocks anions generated by an electrolytic reaction at the cathode (4) from reversely diffusing toward the soil mass; the cation exchange membrane (6) is wrapped around an outer surface of the cathode (4) or is arranged as an independent isolation layer in a soil mass around the cathode (4) to form an ion filtering interface that completely surrounds the cathode (4); and the central tube (5) is made of a conductive metal or an insulating polymer material, and when the conductive metal material is used, the central tube (5) is connected into a circuit as an auxiliary anode to enhance current intensity in middle and later stages.

2. The device for electrochemically reinforcing soft clay according to claim 1, wherein the cation exchange membrane has an ion exchange capacity of not less than 1.5 meq/g, and has resistance to acid and alkali corrosion.

3. The device for electrochemically reinforcing soft clay according to claim 1, wherein grouting holes are uniformly provided on surfaces of the anode (3) and the central tube (5), with an opening ratio ranging from 15% to 25%; and a drainage hole (8) is formed at a corresponding position at a bottom of the cathode (4).

4. A method for electrochemically reinforcing soft clay using the device according to claim 1, comprising the following steps:

arranging, in a soft clay region to be reinforced, the anode (3), the cathode (4), and the central tube (5) according to a preset geometric array; arranging the cation exchange membrane (6) in a soil mass to be reinforced close to the cathode (4);

injecting a first electrolyte solution into the interior of the soil mass through the anode (3) to initiate a first-stage grouting; connecting a direct current power supply (2), and applying a constant or pulsed direct current electric field between the anode (3) and the cathode (4) to initiate a first-stage electroosmotic drainage, such that cations at the anode (3) and the first electrolyte solution are driven by an electric field force to migrate toward the cathode (4), and meanwhile, OH-generated by the electrolytic reaction at the cathode (4) is blocked from entering the soil mass by the cation exchange membrane;

monitoring current intensity and drainage volume in real time during the electroosmotic process; initiating a second-stage grouting when it is monitored that the current intensity starts to decay from a peak value or when a energization time reaches 40%-60% of a total design duration; injecting a second electrolyte solution into a middle portion of the soil mass through the central tube (5), and activating a conductive channel in a deep portion of the soil mass by using a fresh ion source injected into the middle portion to form a secondary electroosmotic peak value;

maintaining an action of the direct current electric field until the electrolyte solution injected in the middle portion covers a region near the cathode (4) under driving of the electric field and a drainage rate is reduced to a preset threshold; and stopping power supply and performing curing of the soil mass.

5. The method for electrochemically reinforcing soft clay according to claim 4, wherein the first electrolyte solution is selected from a potassium chloride solution and/or a calcium chloride solution; and a concentration of the first electrolyte solution is 2.0 mol/L-5.0 mol/L.

6. The method for electrochemically reinforcing soft clay according to claim 4, wherein a chemical composition of the second electrolyte solution is the same as that of the first electrolyte solution, and a volume ratio of an injection volume of the second electrolyte solution to an injection volume of the first electrolyte solution is 0.8:1-1.2:1.

7. The method for electrochemically reinforcing soft clay according to claim 4, wherein the second-stage grouting is initiated between 12 hours and 13 hours after energization, or when the current intensity decreases to 70% of an initial peak value.

8. The method for electrochemically reinforcing soft clay according to claim 4, wherein an applied direct current voltage gradient is 0.8 V/cm-1.2 V/cm.

9. The method for electrochemically reinforcing soft clay according to claim 4, wherein between the first-stage grouting and the second-stage grouting, a power-off interval of 2 hours-12 hours is set based on a dissipation condition of pore water pressure.