JPH04254690A - Method of processing muddy water used to excavate ground - Google Patents

Abstract

PURPOSE:To remove very fine grains from sediment contained in muddy water. CONSTITUTION:After being used for excavation, muddy water 18 is delivered from the inside of a channel 16 to a primary processing apparatus 20, where coarse grains are removed from sediment contained in the muddy water 18. After being made free from coarse grains through the primary processing apparatus 20, primary processed water 22 is delivered to a screw decanter 23, where fine grains are removed from sediment. After being made free from fine grains, intermediately processed water 25 is delivered to a secondary processing vessel 26, where very fine grains are removed from sediment. The secondary processing vessel 26 has a pair of opposedly installed electrode plates 28, 28. These electrode plates 28 have a DC positive electrode and a DC negative electrode connected thereto so that very fine grains are moved to the positive electrode side and adhere to the electrode plate 28 in conformity with the principle of electrophoresis. The very fine grains adhering to the electrode plate 28 are discharged out of the system, by pulling the electrode plate 28 upward.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating muddy water for ground excavation.

0002

2. Description of the Related Art As a ground excavation method, the muddy water method is known, in which the hole is filled with muddy water in order to maintain the stability of the wall of the hole. In this type of construction method, muddy water is recycled, and as the number of circulations increases, excavated soil gets mixed into the muddy water, and when the amount increases, the pump load increases, excavation efficiency decreases, and slime increases. Such inconveniences may occur. Therefore, it has been conventional practice to classify and remove the earth and sand mixed in muddy water and recycle it.

[0003] Screens, cyclones, and the like have been used for classification and removal in such cases, but fine particles of silt, clay, etc. mixed in the muddy water cannot be sufficiently removed. For this reason, construction is carried out by discarding a portion of the muddy water and replenishing the treated muddy water with high-quality muddy water, but this method has the problem of inefficiency. As a method to solve such problems, a method has been proposed in which mixed soil is classified and removed using a high-precision centrifugal separator, but this method has the following technical problems.

0004

[Problem to be solved by the invention] In other words, the method of classifying and removing mixed soil using a high-precision centrifuge can remove finer soil and sand particles than the method of classifying and removing mixed soil using a screen or cyclone, but Since it is not possible to remove the ultrafine particles that are present in the slurry, as the number of times the muddy water is circulated increases, the ultrafine particles accumulate in the muddy water, causing problems such as an increase in the pump load. The present invention has been made in view of these conventional problems, and its purpose is to provide a method for treating muddy water for ground excavation that can remove ultrafine particles mixed in the muddy water. It is in.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for treating muddy water to which clay components such as bentonite have been added and which is used for ground excavation. After the treatment, it is characterized in that it is housed in a tank to which a DC voltage is applied and undergoes secondary treatment by energization classification. A thickening agent may be added to the muddy water when performing the secondary treatment.

[0006]

[Operation] According to the method for treating muddy water for ground excavation having the above configuration, the muddy water after primary treatment is stored in a tank to which a DC voltage is applied, and secondary treatment is performed by electric classification. Therefore, ultrafine particles mixed in the muddy water are attracted to the anode side by the principle of electrophoresis and removed from the muddy water.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of the method for treating muddy water for ground excavation according to the present invention. The treatment method shown in the figure shows the case where the present invention is applied to the treatment of muddy water used for constructing continuous underground walls.
New mud water 12 made by the mud making device 10 fills the groove hole 16 excavated by the excavator 14.

[0008] The muddy water 18 used for excavation is sent from the trench 16 to a primary treatment device 20, where coarse particles of earth and sand mixed in the muddy water 18 are removed. In this embodiment, the primary treatment device 20 includes a sediment removal device 20a equipped with a sieve-type screen and a cyclone that removes sediment using centrifugal force, and a sedimentation tank 20b that stores muddy water 18 for a predetermined period of time and removes the sediment. It consists of

The primary treated water 22 from which the coarse particles have been removed in the primary treatment device 20 is then sent to a screw decanter 23, where the fine particles of earth and sand are removed. In the screw decanter 23, a flocculant is supplied from a flocculant tank 24 as needed, and the removed fine particles are discharged outside the system. The intermediate treated water 25 from which fine particles have been removed is then sent to a secondary treatment tank 26, where ultrafine particles of earth and sand are removed.

The secondary treatment tank 26 is equipped with a pair of electrode plates 28, 28 placed opposite each other.
The anode and negative electrode of the DC power supply are connected. When the intermediately treated water 25 is supplied into the secondary treatment tank 26, the ultrafine particles move toward the anode and adhere to the electrode plate 28 according to the principle of electrophoresis. The amount of ultrafine particles adhering to the electrode plate 28 at this time is approximately proportional to the voltage and the current application time, and the ultrafine particles adhering to the electrode plate 28 are discharged from the system by pulling the electrode plate 28 up.

Regarding the structure of the secondary treatment tank 26, for example, if the tank 26 is made of metal, the tank itself can be used as, for example, an electrode plate on the anode side.

[0012] In the removal of ultrafine particles by this secondary treatment tank 26, for example, if a thickening agent such as CMC (carboxymethyl cellulose) is not added to the new mud water 12, the thickening agent is added at 0.2% by weight. If a certain amount is added, more ultrafine particles can be removed, but in underground wall construction, about 0.2 to 1% by weight of this may be added to the new mud water 12 in advance, and such mud water has a high viscosity. There is no need to add thickeners.

The secondary treated water 30 from which ultrafine particles have been removed is
After being stored in the tank 32, it is returned to the groove hole 16 and used again for excavation. In addition, in FIG. 1, the trench hole 16 is excavated to a predetermined depth, and a reinforcing bar cage is built in the trench hole 16.
The muddy water 34 collected when pouring the concrete C is temporarily stored in the tank 36, and then sent to the sand settling tank 20b.
Thereafter, the muddy water is sent to a screw decanter 23 and a secondary treatment tank 26 for treatment, and the process of using the recovered muddy water 34 for excavating other trenches is also shown. Also, in the same figure, reference numeral 3
8 is a final treatment tank when disposing of muddy water. In this final treatment tank 38, a neutralizing agent is supplied from a neutralizing agent tank 40, and separated water is disposed of after being neutralized. Ru.

FIGS. 2 to 5 are graphs showing the results of experiments conducted to confirm the effects of the present invention. In this experiment, alluvial clay was deflocculated and the viscosity was adjusted using a water sieve to create muddy water similar to that obtained when excavating earth and sand.
Add 0 CMC to muddy water whose specific gravity has been adjusted to 1.05 to 1.15.
~0.6% added was used. And 30×3
Use electrode plates of 0 cm and 4 x 10 cm, and the distance between the electrodes is 1.
A DC voltage of 5 to 20 V was applied at 0 cm.

FIG. 2 shows the relationship between the amount of solid matter adhering to the electrode plate and the voltage at this time. FIG. 3 shows the relationship between the amount of adhered solid content and the current application time. FIG. 4 shows changes in mud specific gravity when solid content is removed from mud. As is clear from these results, it can be seen that the treatment method of the present invention reliably removes ultrafine particles from muddy water.

FIG. 5 shows the results of measuring the amount of solid matter adhering to the electrode plate when a thickening agent was added to the muddy water. When a thickening agent is added to muddy water, the thickening agent and ultrafine particles form a protective colloid, and the dissociative groups of the protective colloid move the ultrafine particles to the anode side more than the ultrafine particles alone, reducing the amount of adhesion to the electrode plate. There will be more.

In the above embodiment, the secondary treatment tank 26 is installed on the rear side of the screw decanter 23 for removing fine particles of earth and sand, but the installation location of the secondary treatment tank 26 is The location is not limited to this, and may be on the front side of the decanter 23. Furthermore, the muddy water to be treated is not limited to that used for excavating continuous underground walls, but may also be muddy water used for, for example, excavating cast-in-place piles or muddy water shield construction methods.

[0018]

[Effects of the Invention] As explained in detail in the examples above,
According to the method for treating muddy water for ground excavation according to the present invention,
Since the ultrafine particles of earth and sand mixed in the muddy water can be reliably removed, the number of times the muddy water can be circulated can be extended without increasing the pump load or reducing excavation efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the entire process of a method for treating mud for ground excavation according to the present invention.

FIG. 2 is a graph showing the relationship between the solid content attached to the electrode plate and the applied voltage.

FIG. 3 is a graph showing the relationship between the solid content attached to the electrode plate and the current application time.

FIG. 4 is a graph showing the relationship between the specific gravity of muddy water and the solid content attached to an electrode plate.

FIG. 5 is a graph showing changes in solid content attached to electrode plates when a thickening agent is added to muddy water.

[Explanation of symbols]

18 Mud water used 20 Primary processing equipment 26 Secondary treatment tank 28 Electrode plate

Claims (2)

[Claims] Claim 1: A method for treating muddy water to which clay components such as bentonite have been added and used for ground excavation, in which the muddy water is primarily treated with a screen, cyclone, etc., and then stored in a tank to which a DC voltage is applied. A method for treating mud for ground excavation, characterized by performing secondary treatment by energizing classification. 2. The method for treating muddy water for ground excavation according to claim 1, wherein a thickening agent is added to the muddy water when performing the secondary treatment.