JPS6233923A - Construction work of cut-off wall - Google Patents

Abstract

PURPOSE:To keep the characteristic properties of bentonite for a long period of time by a method in which swelled bentonite sludge containing high concentrations of bentonite is prepared, mixed with soil carried from excavation site, and then embedded back into the excavated trench. CONSTITUTION:Bentonite mud water 4 is packed into a trench 4 for excavation work, and excavated soil M is delivered to a mixing pit 5. Also, independently from the excavation work of the trench 2, fresh water and bentonite are mixed together in a given mixing ratio to prepare a sludge-like bentonite mud 6. The mud 6 is mixed with excavated soil M in the pit 5 to form mixed soil 3, and the soil 3 is embedded back into the trench 2. Even in the case of the ground contaminated with salts, cut-off wall having excellent water-stopping performance can thus be constructed without affected by bases at all.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a construction method for a water-stop wall.

<Prior Art> There is a bentonite construction method in which an excavated trench is filled with muddy water containing bentonite, which is mainly composed of minerals, and a water-stopping wall is constructed by bentonite particles that have penetrated into the walls of the trench.

Problems to be Solved by the Present Invention (a) Normally, bentonite is used in powder form by being placed in a trench.

However, when bentonite in dry powder form is mixed into seawater, bentonite's swelling properties and viscosity decrease.

As a result, bentonite is no different from ordinary clay particles, and its water-stopping properties deteriorate.

Therefore, at present, depending on the degree of salt pollution,
Directly introducing powdered bentonite into seawater is avoided as much as possible.

(b) As mentioned above, when powdered bentonite is mixed into seawater, the properties such as swelling, suspending, viscosity, and thixotropic properties of bentonite deteriorate, which limits the scope of its use.

In particular, its use is restricted in areas where fresh water is difficult to obtain and only seawater can be used, as well as on reclaimed land on beaches.

OBJECT OF THE INVENTION The present invention was made to solve the above-mentioned problems, and it is possible to maintain bentonite's properties of swelling and viscosity even when construction is carried out in seawater or on ground contaminated with salt. The purpose of the present invention is to provide a construction method for a water-stop wall that can maintain good water-stop properties for a long period of time without reducing water-stop properties.

Means for Solving the Problems〉 [A] Improvement Principle The present invention uses pre-dried bentonite in a powder state,
A muddy clay (bentonite mud) is produced by swelling it in fresh water with a weight ratio of 2 to 5 times that of bentonite, and this bentonite mud is stirred and mixed with excavated soil excavated from a trench to form excavated soil on top of the bentonite mud. After stirring and mixing, the mixture is returned to the trench to construct a water stop wall.

Construction method The construction method will be explained below using an example of constructing a water-stop wall on the ground such as a reclaimed land on a beach.

(1) Excavation of trench A trench 2 of a predetermined depth is excavated using a backhoe 1 or the like.

At this time, the trench 2 is filled with bentonite mud 4 and the excavation work is performed.

The excavated soil M is transported to the kneading bit 5.

(2) Independently from the excavation work of the bentonite trench 2, fresh water and bentonite are mixed at a predetermined mixing ratio to produce bentonite mud 6 of muddy clay.

[Component ratio of muddy clay 1 The amount of bentonite added to fresh water is as follows.

Bentonite is added at a high concentration of 20% to 50% to 1 part by weight of water.

The selection of the amount of bentonite to be added will be discussed later.

(3) Ground mixing of excavated soil and bentonite mud The bentonite mud 6 manufactured at the above-mentioned mixing ratio and the excavated soil M excavated from the trench 2 are put into the mixing bit 5, and the well-known stabilizer S is used. Stir.

The excavated soil M contaminated with salt and the bentonite mud 6 that has almost completed swelling are homogeneously kneaded to produce a kneaded soil 3.

(4) Backfilling Mixed soil 3 produced by stirring and mixing bentonite mud 6 and excavated soil M in mixed bit 5 is backfilled in trench 2 again.

In other words, the bentonite between the soil grains in the cross-conductor 3 has been well swollen in clean water before being backfilled, so even if bentonite is brought into the trench 2, the swelling property of the bentonite is the same as that of the base in the trench 2. Not affected at all.

Therefore, the backfilled cross line top 3 can exhibit the original performance of bentonite and construct a water-stopping wall with a high water-stopping effect.

While repeating each process above, in the predetermined section = 4
= Build a water stop wall across the water.

(5) Examination of component ratio of bentonite mud As mentioned above, when manufacturing bentonite mud 6, the amount of bentonite added is preferably 20% to 50% with respect to 1 part by weight of fresh water.

The reason is as follows.

[When the amount of bentonite added is 20% or less] If the amount of bentonite added is 20% or less, the water content ratio of the mixed soil 3 with the excavated soil M becomes too high when obtaining the desired bentonite addition rate, When the trench 2 is backfilled, it becomes fluidized and the slope of the backfilled soil cannot be maintained.

In addition, there is a problem in that the compaction phenomenon on backfilling becomes significant, and the water cutoff wall that is constructed is likely to shrink or sink in the horizontal direction.

[When the amount of bentonite added exceeds 50%] When the amount of bentonite added exceeds 50%, the concentration of bentonite increases, and the mud becomes gelatinous lumps, which reduces the workability of mixing with excavated soil M. Problems such as a decrease in

Furthermore, in order to find a suitable mixing ratio of bentonite and fresh water, a test was conducted on bentonite water permeability.

Test Example 1〉 (Sample soil) 20% of salt-containing sediment with a particle size of 4 μm or less Soil hydraulic conductivity: 4 x 10-'cm/se
C. Sample earthwork・1 Sample soil in which powdered bentonite is directly mixed with the soil ■: Sample in which the above soil is mixed with bentonite mud, which is made by swelling bentonite in fresh water (added amount of bentonite) Soft soil Three types of bentonite were added at 4%, 6%, and 8% by weight.

The following is a margin (Water permeability test result 1) (Unit of permeability coefficient: cm/sec) It was confirmed that the permeability coefficient of the sample earthwork was about 2 to 3 times lower than that of sample soil ■.

In other words, a low water permeability coefficient means good water-stopping properties.

Test Example 2 (Sample Soil) 20% of the grain size of sand and soil that is not contaminated by salt is 4μm or less.Sample Soil ■: Sample soil in which bentonite in a tax state is directly mixed and stirred with the above earth and sand■; Sample mixed with bentonite mud in which bentonite is swollen (amount of bentonite added) Three types of bentonite, 2%, 4%, and 6%, were added to the weight of soft soil.

(Water permeability test result 2) (Unit of permeability coefficient: cm/sec) Even for soil that is not contaminated with salt, sample soil ■ mixed with bentonite mud swollen with fresh water is better than sample soil ■
It was confirmed that the water-stopping properties were better than that of .

Test Example 3 (Figure 3) In this test, changes in the permeability coefficient of a water-stop wall made of two types of soil samples manufactured according to the following conditions were examined over time.

(Sample soil) 20% of the soil particles have a particle size of 4 μm or less Sample soil V: A sample in which bentonite in a direct tax state is mixed with the above soil Sample soil ■: The above soil is swollen with 0.5% bentonite to 1 part fresh water. Sample mixed with bentonite mud (test method) As shown in Fig. 3, the above sample soils V and Vl were each stored in a container 7 having small openings at the top and bottom ends, and seawater 8 was injected from the top side of the container 7. do.

Then, a pressure of 3 kg/cm2 was applied from the top side of the container 7 to test the water permeability from the bottom side.

(Amount of bentonite added) Three types of bentonite were added at 4%, 6%, and 8% based on the weight of soft soil.

The following margin (water permeability test result 3) (Unit of water permeability coefficient: cm/5ee) In the case of sample soil V, the water permeability coefficient changes greatly over time, but in the case of sample soil ■, it lasts for a long time. The hydraulic conductivity does not change much over time.

In other words, it has been proven that bentonite produced by swelling bentonite in advance can maintain good water-stopping properties over time, rather than using powdered bentonite mixed with salt-contaminated soil.

Effects> Since the present invention is as explained above, the following effects can be obtained.

(a) Bentonite is swollen in clear water, which has a large swelling effect, and then mixed with excavated soil and backfilled into the trench.

Therefore, even if the ground is contaminated with salt, a water-stopping wall with excellent water-stopping properties can be constructed without being affected by the base at all.

(Explanation) Bentonite mud, which is a mixture of bentonite and water prepared in advance, mixes well with excavated soil, making it possible to construct a homogeneous water-stop wall.

(c) Even in the case of salt-contaminated soil and uncontaminated soil, if hentonite is mixed in the muddy state,
Compared to when bentonite is mixed in powder form, it is 1/1
Equivalent water-stopping performance can be obtained with a smaller amount of bentonite, about 2 to 2/3.

Therefore, it is economically advantageous.

[Brief explanation of drawings]

Figure 1: Explanatory diagram of how to construct a water-stop wall Figure 2: Explanatory diagram of crosstalk between excavated soil and bentonite mud

Claims (1)

[Claims] 20% bentonite is added to 1 part by weight of fresh water in advance.
Bentonite mud is produced by adding swollen bentonite to a high concentration of ~50%, and after adding and kneading the soil excavated and carried out from the ground scheduled for ground improvement, this mixed soil is used for ground improvement. A method of constructing water-stop walls, which is characterized by backfilling in trenches cut in the ground.