JP2564436B2 - Treatment method of excavated soil in earth pressure system shield method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for treating excavated earth and sand in an earth pressure system shield construction method, and more particularly, to a system from a face by adding various chemicals to soft excavated earth and sand discharged by the earth pressure system shield construction method. The present invention relates to a method of efficiently carrying out to the outside and modifying the excavated soil after carrying out to a state where it can be easily treated.

[0002]

2. Description of the Related Art The earth pressure shield method is a type of tunnel excavation method applied to soft ground. A chamber for taking in excavated earth and sand is provided behind the cutter, and the earth pressure in this chamber is balanced with the earth pressure of the face. The shield machine is dug forward while making it proceed. As a concrete means of the balance, the excavated earth and sand taken into the chamber is discharged by a screw conveyor penetrating and installed in the chamber, and the transfer speed of this screw conveyor is synchronized with the excavation speed of the shield machine so that the chamber A method of keeping the earth pressure inside the container at a predetermined value is adopted. However, when this earth pressure system shield method is applied to sandy ground, since the sand component, which is the main component of the ground, is easily separated from groundwater, the diluted mud water in the excavated soil taken into the chamber There is a risk that only the air will squirt through the screw conveyor, which will lower the earth pressure in the chamber and upset the overall balance, causing the face and surrounding rocks to collapse. In addition, sand excavated earth and sand have low water retention and large internal friction, so plastic flowability is low and excavated earth and sand cannot be discharged efficiently.

Therefore, when the earth pressure type shield construction method is used for sandy ground, the excavated earth and sand conventionally taken in the chamber is made of fine particles such as clay, bentonite and carboxymethyl cellulose (hereinafter abbreviated as CMC). A method has been adopted in which an appropriate viscosity is imparted and the water retention and plastic flowability of excavated earth and sand are enhanced by adding the additive. Of these, clay is inexpensive, but its water retention is low, so that water is separated in a short time and sufficient water stopping performance cannot be obtained. For this reason, bentonite and CM are usually used.
Used in combination with C. Further, as a material exhibiting a high viscosity at a low concentration, a mixture of xanthan gum and CMC added to bentonite is proposed in JP-A-1-121396, which shows high viscosity at a low shear rate and smooth excavation. It is supposed to be.

On the other hand, the excavated earth and sand discharged from the soft ground by the earth pressure system shield method is soft or mud-like due to the influence of various additives consisting of the above-mentioned fine particles, so that it can be directly used in a predetermined treatment plant or the like. Since it is difficult to handle for transportation and there is a facility limitation for drying and solidifying on site, the treatment has been a big problem. To solve this problem, when a cellulosic polymer such as CMC is used as an additive, it is decomposed by using cellulase, which is a degrading enzyme, to reduce the viscosity (Japanese Patent Laid-Open No. 1-174795).
Or a soft excavated sediment by adding a water-soluble polysaccharide or a modified polysaccharide, a substance composed of a cation having two or more valences, a water-soluble polymer, or the like (JP-A-64-51198). issue,
JP-A 1-139198, JP-A-176499, and JP-A-207384) have been proposed, but none of them has sufficient advantages and disadvantages to achieve sufficient results.

[0005]

Therefore, an object of the present invention is to smoothly and efficiently carry out the soft excavated earth and sand discharged by the earth pressure system shield method from the cutting face to the outside of the system, and to carry out the excavation after the discharge. It is intended to provide a method for treating excavated sediment, which is capable of modifying the sediment so that it can be easily treated.

[0006]

A method for treating excavated earth and sand according to the present invention is a shield construction method using a closed type shield machine having a chamber behind a cutter head, wherein xanthan gum is contained in the excavated earth and sand or the face of the chamber,
Carboxymethyl cellulose with an average degree of substitution of 0.8 or more,
It is characterized in that clay and water are injected, and a cation salt having a valence of 2 or more and a high-molecular-weight flocculant are sequentially added by an earth discharging device for discharging the excavated earth and sand out of the system.

Next, details of the method for treating excavated soil according to the present invention will be described with reference to FIG. 1, which illustrates one embodiment of a shield construction method. In the figure, 1 is a sealed shield machine,
A cutter head 2 is provided in the front part thereof, and a partition wall 3 is provided in the rear part thereof, and a chamber 4 is formed between the cutter head 2 and the partition wall 3. Denoted at 5 is an earth discharging device such as a screw conveyor provided rearward from the bottom of the chamber 4, and in the figure, three earth discharging devices (5
-1 to 5-3) are shown. The cutter head 2 is in contact with the face 6, and the earth and sand excavated along with the rotation thereof are taken into the chamber 4 and filled. In the chamber 4, the stirring blade provided coaxially on the back surface of the cutter head 2 and the rotating movement of the stirring blade separately driven from the cutter head 2 (neither of which is shown), the discharging movement by the soil discharging device 5 The excavated earth and sand are discharged from the system through the earth-discharging device 5 while rolling by the movement of the excavated earth and sand sent from the cutter head 2.

In the method for treating excavated earth and sand according to the present invention, xanthan gum, carboxymethylcellulose having an average degree of substitution of 0.8 or more, clay and the like are first injected into the excavated earth and sand in the chamber 4 or the earth and sand being excavated in the cutting face 6. .
These chemicals are mixed plant 11 installed on the ground.
After being adjusted to the specified concentration in the stock tank 12
Stored in the pump, and pumped by the liquid feed pump 13 through the pipe 14 to the underground sealed shield machine 1 and added and mixed into the respective earth and sand through the inlets 15 and 16 provided in the cutter head 2 and the partition wall 3. It At that time, when the soil is sandy, gravelly, or viscous sand with a small amount of binder, the addition of the above-mentioned chemicals increases the water stopping property, and the internal friction angle causes a small plastic flow. Since it is converted into good soil, excavation can be stabilized and soil can be discharged smoothly.

The xanthan gum used here is a water-soluble polysaccharide produced by the metabolic action of a bacterium of the genus Xanthomonas, and its chemical structure is pyruvate in the main chain structure in which D-glucose, D-mannose and glucuronic acid are bound. It is presumed to be bound with or acetate. When this xanthan gum is dissolved in water, it has a large viscosity at a low shear rate and exhibits a high viscosity at a low concentration. When xanthan gum having such properties is used together with CMC and clay which have been conventionally used, it effectively acts to prevent the spouting of groundwater.

The CMC having an average degree of substitution of 0.8 or more, which is used in combination with xanthan gum, is produced from alkali cellulose and monochloroacetic acid by an alkali multistage addition method, a multistage reaction method or the like. Generally, those having an average degree of substitution of less than 0.8 are prone to putrefaction, which significantly reduces the viscosity. On the other hand, as the average degree of substitution approaches 3.0, industrial manufacturing becomes difficult and the cost becomes higher.
2.0 is preferable. For CMC, a water-soluble salt such as an alkali metal salt such as a lithium salt, a potassium salt and a sodium salt, or an ammonium salt is used, but a sodium salt which is widely produced industrially is most commonly used. The viscosity is 10 at the value of 2% aqueous solution at 25 ℃.
It is preferably about 10,000 cP.

The above-mentioned xanthan gum can improve the dehydration property of xanthan gum when used in combination with this CMC, and the effect of soil removal can be improved by increasing the proportion of xanthan gum. The mixing ratio of xanthan gum and CMC is xanthan gum 95
5 to 95% by weight of CMC, preferably 5 to 70% by weight of CMC to 95 to 30% by weight of xanthan gum, and more preferably 20 to 70% by weight of CMC to 80 to 30% by weight of xanthan gum. Also, xanthan gum,
Although the mixing ratio of CMC and clay to water varies depending on the nature of the ground, etc., the total amount of xanthan gum and CMC is 0.05 to 5 parts by weight and the clay is 0 to 100 parts by weight of water.
It is 200 parts by weight. Clay may not be necessary if the excavated soil contains clay. These components are injected into the excavated sediment in the chamber 4 or the excavated soil in the cutting face 6 described above individually or by mixing two or more components by an appropriate means as shown.

In this shield construction method, the excavated earth and sand in the chamber 4 is discharged rearward by the earth discharging device 5 while keeping the fluidity by the addition of these chemicals, but these earth discharged are generally weak. It is difficult to handle because of its nature, and may cause a jet in the case of high water pressure. Therefore, in the method for treating excavated soil according to the present invention, the salt in the soil discharging device 5 is further sequentially added with a salt composed of a cation having a valence of 2 or more and a polymer-based coagulant. The former salt consisting of divalent or higher cations is adjusted to a predetermined concentration in the tank 21, and then sent to the first earth removing device 5-1 through the pipe 23 by the liquid feed pump 22 to be discharged. Xanthan gum and CMC, which are ionic water-soluble polymers in the soil mixed with
Agglomerates to significantly reduce the viscosity of soil discharge. The latter polymer-based coagulant is adjusted to a predetermined concentration in the tank 26, then sent to the second earth discharging device 5-2 through the pipe 28 by the liquid feed pump 27 and mixed with the earth discharging, The softness of soil removal is improved to obtain earth and sand having an appropriate hardness, and it serves as a plug for preventing jetting at the outlet of the soil discharging device 5. Both drugs are 2
The pressure resistance of the plug for preventing jetting can be adjusted by appropriately changing the timing from the addition of the salt composed of a cation having a valency or more to the addition of the polymeric flocculant. In addition, although the case where both chemicals are added in two different soil discharging devices is shown in the figure, it is also possible to change the places such as front and rear portions of a single soil discharging device. The amount of both chemicals added to the soil depends on the water content and properties of the soil, but is 0.01 to 10k for salts consisting of divalent or higher cations.
g / m ^3, preferably 0.001~1kg / m ³ in the polymeric flocculant. As described above, according to the method of the present invention, it is possible to easily handle the soil by treating the soil in the soil discharging device 5.

The salts consisting of the above-mentioned divalent or higher cations include the periodic tables 2a, 2b, 3a, 3b, 4b, 5
Water-soluble hydroxides, chlorides, sulfates or nitrates of elements selected from the groups b, 6b, 7b and 8 and more specifically water such as magnesium, calcium and aluminum. Oxides, magnesium, calcium,
Examples thereof include chlorides such as barium, aluminum, zirconium, chromium and manganese, sulfates or nitrates. Further, a compound which is anionized with an oxygen compound of these elements, for example, borate, aluminate, chromate, permanganate and the like can also be used for this. Of these, the sulfuric acid band [Al
₂ (SO ₄ ) ₃ · 18H ₂ O], ferric sulfate [Fe ₂ (SO ₄ ) ₃ ], polyaluminum chloride [Al ₂ · (OH) _n Cl _6-n ] _{m, and the} like are preferable.

As the polymer-based flocculant, polyacrylamide, polyethylene oxide, polyacrylic acid salt, polyvinyl sulfonate, polydialkylaminoalkyl acrylate, polyvinylpyridinium, polydiallylammonium halogen salt, polyaminomethyl acrylamide, polyvinyl imidazoline, chitosan. , Sodium alginate and copolymers thereof are used, and these may be used alone or in combination of two or more, and of these, polyacrylamide is most preferable.

[0015]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples. Examples 1 to 3 clay 20% by weight, xanthan gum 0.
16% by weight and 0.04% by weight of CMC were used as the test materials, and the water content ratio was changed as shown in Table 1 to make mud-like materials with different slump values. After adding the agent and kneading, the slump value was measured, and the results are also shown in Table 1. Before adding the improver, the slump value
Although it was a soft soil of 15 cm or more, after addition of the improving agent, the slump value became 0 cm and the soil quality became easy to handle in all cases.

[0016]

[Table 1]

Examples 4 to 6 20% by weight of clay and xanthan gum were added to the same soil as in Example 1.
16% by weight and 0.04% by weight of CMC are added to the soft sand with a water content of 20%, and a sulfuric acid band and polyacrylamide as improving agents are 0.5 kg / m ³ , respectively, and the following order is applied for each example. After adding and kneading, measure the slump value,
The results are shown in Table 2. Example 4: Sulfate band and polyacrylamide were premixed and then added.・ 〃 5: After adding polyacrylamide, add the sulfuric acid band.・ 〃 6: Add polyacrylamide after adding the sulfuric acid band. From this, it was found that the method of Example 6 was effective.

[0018]

[Table 2]

[0019] In Example 7-8 Example 6, a sulfate 0.3 kg / m ³ and polyacrylamide 0.1 kg / m ^3, when added in both powder (Example 7), aluminum sulfate concentration of 7% The same test was performed and the slump value was measured when polyacrylamide was added as an aqueous solution having a concentration of 1% (Example 8). The results are shown in Table 3.

[0020]

[Table 3]

[0021]

According to the present invention, it is possible to smoothly and efficiently carry out the soft excavated earth and sand discharged by the earth pressure system shield construction method from the face face to the outside of the system, and to easily treat the excavated earth and sand after the carry-out. It can be reformed to a ready state.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view illustrating one embodiment of a shield construction method to which the method of the present invention is applied.

[Explanation of symbols]

1 ... Sealed shield machine, 2 ... Cutter head, 4 ... Chamber, 5 ... Soil removal device, 6 ... Face cutting.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tsutomu Yamakawa Tsutomu Yamakawa 1 of 28, Nishi-Fukushima, Kubiki-mura, Nakakubiki-gun, Niigata Pref. No. 28, Nishi-Fukushima, Mura Daiji Shin-Etsu Chemical Co., Ltd. Synthetic Technology Laboratory (56) References JP-A-61-216994 (JP, A)

Claims (1)

(57) [Claims] 1. A shield construction method using a closed type shield machine having a chamber behind a cutter head, wherein xanthan gum is present in the excavated earth or face of the chamber,
Carboxymethyl cellulose with an average degree of substitution of 0.8 or more,
An earth pressure system shield construction method characterized by sequentially adding a divalent or higher cation salt and a polymeric coagulant with an earth discharging device for injecting clay and water and discharging the excavated sand out of the system. Method of excavated sediment in Japan.