JPH0453915B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for dealing with soft rock that exists as a rock underground, but which absorbs moisture and collapses when exposed to the atmosphere, and for preventing the collapse.

[Conventional technology]

"Soft rocks" such as mudstone, weathered serpentinite, and metamorphosed andesite
A group of rocks, called a rock, takes the form of a rock while it is in its endemic state, i.e., underground, but when it is dug out, released from stress, and its fresh surface is exposed to the atmosphere,
It has the property of absorbing moisture and disintegrating. When this progresses rapidly and turns into clay, it is called "swelling".
A case in which the particles progress relatively slowly and become fragmented is called "slaking." The latter also occurs quickly when it comes into direct contact with water. These developments are a troublesome problem for civil engineering works. In order to achieve high-speed traffic, the roads and railways constructed in recent years choose straight routes to avoid twists and turns, so they are forced to pass through excavations regardless of the nature of the rock or soil. When soft rock is encountered, there are problems in tunnel excavation where the cross section of the excavation cannot be supported by shoring, and in cutting through, the slope is unstable. Cement mortar is often sprayed onto unstable slopes, but if the target is soft rock, the mortar will peel off along with some of the rock mass and fall. In addition, rock fragments called "zuri" generated during construction are generally reused as roadbed material.
This is preferable, but it cannot be used because it turns soft rock into fine powder or clay. Attempts have been made to stabilize Okinawan mudstone by mixing slaked lime, but this has not been effective, and the current situation is that soil is being replaced unavoidably.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for preventing the collapse of soft rock by taking the current state of the art one step further. This makes tunneling easier, stabilizes the slope, and allows the waste to be used as roadbed material.

[Means to solve the problem]

The method of preventing the destruction of soft rocks of the present invention is to apply an aqueous alkaline silicate solution to the free surface of the rock mass, then apply an aqueous solution of magnesium or aluminum salt to the free surface of the rock mass, and then air-dry the soft rock. Afterwards, it is coated with a water-impermeable substance, and as a coating material,
It is characterized by the use of materials selected from coal-based or petroleum-based tar, boiled oil, drying or semi-drying oil, synthetic resin emulsion (water-based paint), alkyd resin paint, silicone water repellent, and chlorinated rubber-based paint. . Although it is possible to determine whether the main component of the soft rock in question belongs to the kaolinite or smectite system by placing a sample in water and observing its behavior for a while, the well-known montmorillonite This becomes immediately clear using characteristic tests. That is, if a saturated aqueous solution of para-phenylenediamine is dropped onto the surface of a sample and a deep blue to green color develops, the mineral is montmorillonite. The materials used for the covering will vary depending on the conditions of use, such as the required mechanical strength, resistance to sunlight, wind, rain, and ice and snow, difficulty in construction, and ease of acquisition, so it is important to consider these factors and economic efficiency. This will be decided by considering both. Among the above, water-based paints do not use organic solvents, can be applied to slightly damp surfaces, can be colored to any color by adding pigments if desired, and are easy to check the completion of the coating. It is the most useful from the point that it is said that there is. Oils and fats are suitable when buried in the soil, but since there is a risk of decomposition by microorganisms in the soil over time, it is advisable to mix and use an appropriate anti-mold agent. Semi-drying oils that are polymerized by heating, such as cooking oil waste, can be applied thickly and are effective in one treatment. Since the cost is supposed to be low, it is an advantageous covering material as long as it can be collected. Silicone-based and alkyd resin-based paints have high weather resistance and are effective, but their disadvantage is that they are expensive. Traditionally, cement mortar has been used to cover slopes in civil engineering work, but mortar is both air permeable and water permeable and cannot prevent moisture in the air from entering and exiting soft rock surfaces. It is not useful as a coating material for use in the invention. however,
There is no problem in using it in combination with the above-mentioned materials. The aqueous alkali silicate solution is preferably an aqueous solution of 10 to 90% (by volume) of commercially available water glass (sodium silicate), and may be applied by spraying, brushing, or the like. If there is a risk that groundwater may leak around the construction area and wet the construction surface, it is best to inject a silicic acid-based chemical solution in advance to stop the water. The method is known in the art. The aqueous solution of magnesium, aluminum, or ferric salt is preferably a concentrated aqueous solution of salts that are highly soluble in water, such as chlorides or sulfates.
It is preferably applied within 2 hours, also by spraying or brushing. The thus treated material no longer disintegrates immediately when it comes in contact with water, so it is then lightly washed with water and allowed to air dry before proceeding to the above-mentioned coating step. When the object to be treated is a piece of rock, it is preferable to apply the alkali silicate aqueous solution and salt aqueous solution and wash it by immersion, since this is most effective.

[Effect]

Soft rocks can be roughly divided into two groups based on their behavior with water: those that undergo slaking and become fragments, and those that undergo loss swelling and turn into clay. When the minerals constituting this were investigated, it was found that (a) is halloysite, hydrated halloysite, etc. belonging to the kaolinite clay mineral, and (b) is mainly montmorillonite, which is a clay mineral of the smectite series. Among the kaolinite halloysite types,
The interlayer region of the single crystal lattice is of a size (less than 3 Å) that allows free water to enter and exit. On the other hand, the montmorillonite (B) has a large ion exchange capacity (approximately 6 Å) that allows cations and anions to exist together with free water in the interlayer region. Moreover, since the crystal particles have a strong tendency to absorb a large amount of water and disperse,
When released from the endowment state, it is thought that the rock tries to return to the original clay state, that is, the equilibrium state. In other words, in kaolinite-based soft rocks, as the humidity in the atmosphere increases or decreases, the number of water molecules in the interlayer regions of grain boundaries increases or decreases, which causes microcracks to develop and fragmentation to progress. Naturally, cracks grow from surfaces exposed to the outside air, and even if microcracks occur, their progress will be minimal unless air-dry conditions continue and humidity increases. If a fresh rock face is immediately surrounded by water, the fragmentation process will be slower than when it is placed in air, but if it is taken out of the water and air-dried, it will fragment rapidly, and if it is left in the water for several days, it will fragment rapidly. Even if it appears that it retains its original shape, it will collapse into fine powder with the slightest external force. Taking these facts together, it was found that kaolinite-based soft rocks fragment into small pieces due to slight changes in the moisture content in the surrounding environment. Therefore, to prevent slaking of soft rock, the ingress and egress of water through the free surface of the soft rock mass should be suppressed, and by covering all the free surfaces of the rock mass with water-impermeable material, That will come true. However, it has been confirmed that the above-mentioned collapse prevention measures for kaolinite soft rock cannot be used to deal with smectite soft rock. Even if the coating is thick or coated multiple times, the effect will not be sufficient. The reason for this is that, due to the above-mentioned structural differences, smectite minerals have a strong tendency to absorb water intensely and turn themselves into clay. Therefore, the inventor chemically treated montmorillonite, a smectite mineral that is sensitive to water, and created a mineral similar to vermiculite or chlorite, which is a mineral in the same series but is relatively insensitive to water. We thought that if it could be converted to silicate alkali-magnesium (or aluminum) salt aqueous solution, we thought that it would be easier to deal with it by losing the extreme swelling property, and as a result of various experiments to find a solution, we found that They found that this treatment was effective. The mechanism of the above treatment is that silicic acid anions first penetrate between the grain boundaries of montmorillonite, causing it to lose its sensitivity to water, which is a characteristic of montmorillonite. This conversion can be immediately confirmed by the absence of discoloration of a saturated aqueous solution of para-phenylenediamine, which is the characteristic test for montmorillonite described above. The penetration of silicate ions is rapid, and although it varies depending on the density of the soft rock, it takes several minutes to several millimeters from the surface.
A few 10 minutes is sufficient. Subsequently, by applying an aqueous solution of magnesium, aluminum or ferric salts, cations of Mg ² , Al ³ and Fe ³ are removed from the silicate anions SiO which have already penetrated into the interlayer regions of the montmorillonite crystal grains. ₃ Combines with ² to form a water-insoluble salt, which prevents further entry of water molecules. In this way, the tendency of smectite-based soft rocks such as montmorillonite to collapse due to water absorption can be made weaker than that of kaolinite-based soft rocks. However, there is still a risk of collapse, so by coating the free surface with a water-impermeable material, collapse is completely prevented. It goes without saying that the method of the present invention can be applied to cases where the soft rock has a complex composition, including a mixture of kaolinite and smectite, or is composed of metamorphosed andesite or serpentinite. .

[Reference example]

Shimajiri mudstone (kaolinite type) produced in Naha City, Okinawa Prefecture is crushed into pieces of 3 to 10 cm in size, and the following coating material is applied to the entire surface of the rock pieces, followed by solar drying once or twice. Ta. The coated rock pieces were immersed in water for 12 hours, then removed and left in the atmosphere for 12 hours, a cycle repeated. Recording the cycle through which rock fragments disintegrate, or the cracks and embrittlement that lead to it, are observed;
The following results were obtained. After one application of Ital Pitch, small cracks formed in the film, which expanded and became brittle after three cycles. With two applications, it was able to withstand more than 10 cycles. B. Semi-drying oil (waste cooking oil) It can withstand more than 10 cycles after one application, but it has an odor so it is not suitable for exposed surfaces and is suitable for buried underground. C Drying oil Same as above. However, to ensure the desired effect, it is preferable to apply it twice. D. Synthetic resin emulsion A commercially available water-based paint for DIY use manufactured by Nippon Paint Co., Ltd. was used. This paint is
The product is a water-based emulsion of acrylic resin with pigment added, and the coating film after one brush application is maintained at a temperature of 20°C.
It dries in about 2 hours in an environment of ℃ and 73% RH. Cracks occurred after one application, but no change was observed after 10 cycles or more when two applications were applied, and collapse was completely prevented. Alkyd resin paint A commercially available oil-based paint manufactured by Asahipen Co., Ltd. was used. This paint is a product made by dissolving alkyd resin in an organic solvent and adding pigment to it, and although it can be thinned with Lutzker thinner, it was used as is. The results are almost the same. There are safety, odor and cost issues associated with the use of organic solvents. Silicone water repellent One application left pinholes in the coating and caused slaking. After two applications, the prevention of disintegration was completely achieved.

【Example】

The Shiiya layer mudstone at Nabetateyama on the Hokuriku-Hokusen Line is a soft rock that is identified as montmorillonite by the p-phenylenediamine color test.When placed in water, it begins to swell within one minute, turns into clay, and loses its original shape. leading to. This piece of rock was immersed in a 30% (volume) water glass aqueous solution for 20 minutes, then pulled out and drained, then immersed in a 50% aluminum chloride aqueous solution and left for 20 minutes, then pulled out and lightly washed with water. After 5-8 hours of air-drying, some samples were observed to crack and a small amount of clay oozed out from within, breaking into several pieces even with the slightest external force. However, almost no phenomenon that could be called swelling occurred. The sample that was put in water did not disintegrate in the water, and when it was taken out, air-dried, and immersed in water again, cracks appeared and clay was observed, but it was silt-like as a whole, and the original shape was formed by swelling. It didn't collapse to the point where I lost it. Both samples showed weak color development in the para-phenylenediamine test. The same synthetic resin emulsion as used in the reference example was applied once to the material that had been almost air-dried after the above treatment and was dried. This sample did not exhibit any swelling even when immersed in water. There were some rock fragments with cracks, but no further swelling occurred, the naturally formed fragments did not change any further, and no formation of clay or silt was observed. There was no reaction at all in the para-phenylenediamine color test. For comparison, a sample that was directly coated with a synthetic resin emulsion and dried without being treated with the aqueous salt solution was immersed in water. After a few hours, cracks appeared in several places on the coating, and clay-like particles appeared from inside. started to leak.
After a long period of time, the original rock fragments disintegrated, leaving only the coating behind.

【Effect of the invention】

By treating soft rock made of smectite minerals according to the method of the present invention, collapse of soft rock can be appropriately prevented. Therefore, when excavating a tunnel, the expansion of the rock layer can be suppressed and the tunnel can be dug efficiently, and when cutting through, the slope can be stabilized and there is no need to worry about falling off.
By treating the sludge caused by construction to prevent collapse according to the present invention, it can be used as roadbed material. As described above, the present invention provides a safe and economical construction method for civil engineering work, and greatly contributes to construction technology.

Claims (1)

[Claims] 1. For soft rocks made of smectite minerals, an aqueous alkali silicate solution is applied to the free surface of the rock mass, followed by an aqueous solution of magnesium, aluminum or ferric salts, and the mixture is air-dried. Afterwards, it is coated with a water-impermeable material, and coating materials include coal-based or petroleum-based tar, boiled oil, drying oil or semi-drying oil, synthetic resin emulsion, alkyd resin paint, silicone water repellent. A method for preventing collapse of soft rock, characterized by using a material selected from chlorinated rubber-based paints. 2. The method for preventing collapse of soft rock according to claim 1, which employs a method of dropping a saturated aqueous solution of para-phenylenediamine onto the surface of the soft rock and determining that it is a smectite mineral when the color changes to deep blue or green.