JPH0625414B2 - Composition for strengthening organic soft ground and ground strengthening method using this composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for strengthening organic soft ground and a ground strengthening method using this composition.

[0002]

2. Description of the Related Art As the range of effective use of land is gradually narrowed in the course of social development, civil engineering works and land that have been constructed by selecting locations with relatively good ground conditions have been used. The development gradually came to be restricted in its choice.

For this reason, various construction methods have been studied for locations with poor ground conditions, and improvement and strengthening of defective ground is an indispensable condition. If the soft ground that constitutes the defective ground is limited to cohesive soil, it has the widest distribution in Japan and is extremely soft in terms of compressibility and strength. Most problems are organic soft ground such as peat, humus, humic cohesive soil, and clay mixed with organic matter, and the actual situation is that it is difficult to grasp the actual situation even with the current technology of Nisshin Rapidly. Is.

As one of the methods for safely and quickly constructing a structure on such soft ground, a pouring method for pouring a solidifying material into the ground to stop water or improve the ground is used.

Regarding the ground injection method, there are the following three injection methods as well-known techniques that have been generally performed so far. 1. Gap injection for injecting a chemical solution into the space between soil particles and local split injection 2. Pile-like shape in which a soft layer is stirred on a cylinder, a solidifying material is added to it, and it is solidified into a column and supported on the supporting ground. Stirring injection 3. Consolidation injection Ground injection is performed by controlling the density and liquid pressure of the injection liquid and injection pressure using a specific injection device, and a plurality of plate-shaped bodies in the oblique vertical direction are created on the target ground to perform consolidation at the original position.・ A ground injection method that creates stable composite ground by immediately obtaining the four effects of dehydration, drainage, replacement, and solidification.

The outline of each of the above-mentioned known techniques will be described. The gap injection of 1 is usually a method called a chemical solution injection method, which is mainly applied to a loose sand ground or a gravel ground, and an injection material (chemical solution). ) Is the principle of the construction method that fills the gaps between the soil particles to increase the water-blocking effect and the strength of the ground. Regarding the extremely soft cohesive ground, the gap between the soil particles that make up the cohesive soil is very small, unlike the sand ground, so only local injection is possible, so the injection range is extremely limited, and at best It spreads to a very small scale. Therefore, in the case of wide-area injection, it is very difficult to control the injection, and because the injection often interferes with the dehydration and drainage of pore water and causes abnormal pore water pressure, which often disturbs the injection ground, the viscosity of natural sedimentation ground It is rarely applied to soil.

The pile-shaped agitation injection of No. 2 is not a ground injection method of improving and strengthening without disturbing the natural sedimentation ground itself, but is characterized by a heterogeneous structure consisting of a pile-like improved body and an unimproved portion around the pile. Cement-based solidifying material is mainly used for stirring.

The consolidation injection of 3 differs from the gap injection of 1 in that
The injection material is a cement milk-based liquid rather than a quick-setting liquid medicine, and is solidified within 24 hours after ground injection. If the injection material is a quick-setting material, it is difficult to improve it in a wide area because the improvement range is limited to a local area. Generally, the solidification time of the injection material is closely related to the time of dewatering and draining the pore water of the target ground, and the injection time and the injection pressure are also greatly related to the degree to which the injection ground is disturbed. That is, in the case of consolidation injection, the setting time of the injection liquid is within 24 hours, which means that the target ground will not be disturbed and the pore water in the ground will be dehydrated and drained within the setting time, so that it will cover a wide area. Means that it can be improved.

However, the above-mentioned drawbacks of the consolidation injection of the prior art are that the cement milk-based liquid is used as the injection material, so that the cement particles are small and the fluidity is good, so that the boundary surface between the injection liquid and the ground is small. As shown in FIG. 2, the injection liquid diffuses out of the range H to be improved because the frictional force is small and the density of the injection liquid is too large compared to the density of the target ground. Therefore, the desired improvement effect cannot be expected at all. In other words, it is not possible to achieve the intended improvement objectives by performing accurate injection management within the range that requires improvement.

Next, the specific problems of the prior art will be described in detail. 1. The most economical injection material, and the most commonly used injection material is mainly cement such as Portland cement or fly ash cement, and since it is an inorganic material, the material itself is different from chemical injection. It is pollution-free. However, it has been pointed out that the use of cement-based injection materials has the following drawbacks with respect to organic soil. That is, 60% of the components of cement are occupied by calcium, which has the function of solidifying by the reaction of calcium ions.
If the ground to be injected contains an organic component, the organic component adsorbs the calcium ion of the cement, so that the curing property is lost and the necessary strength after consolidation is lowered. For this reason, it has been considered taboo to carry out cement treatment on soft soil with a lot of organic matter. Therefore, it is a known fact that lime treatment is performed instead of cement. However, even when lime is used, humus such as peat and humus is 0.05%.
It is also recognized that it does not solidify when included above.

2. Since the organic ground is extremely soft,
Since the ground is not constrained, the following defects will appear if an attempt is made to improve the structure of the pile type like the pile-type stirring injection described above. B. Since the frictional resistance of organic soil can hardly be expected, once weak points are created in some of the piles due to vibrations, etc., there is a possibility that the whole ground will be destroyed one after another. (2) Since the organic soil and pile structure are not integrated, stable composite ground cannot be obtained, and after improvement, when stress such as loading load or dynamic load is applied, stress is applied only to the pile, causing the pile to break. Not only that, but the whole ground becomes extremely unstable. Since it does not have the effect of frictional resistance for the reason of high, it must be supported on the supporting ground, so it is an extremely uneconomical method when the soft layer is thick.

3. On the other hand, as a method for improving and strengthening the organic ground without ground injection, in the conventional method, (a) installation of vertical drains and dehydration and consolidation methods using loading load such as embankment and (b) There are replacement methods for replacing a part of the soft layer and (c) dewatering consolidation method by slow-step embankment, but the following problems are pointed out as common problems with these methods. That is, in the usual case, the method of (a) and (c) requires a load, but including the sand mat,
Sand is often used as the material. In addition, (b)
The same applies to the replacement material in the case of replacement.

Since the organic soft ground constitutes an alluvium with high groundwater, the amount of subsidence due to the applied load is naturally extremely large. If sand is continuously used as a load, the saturated loose sand layer will be formed under the shallow water table. If the thickness of such a sand layer exceeds 2 m and its upper part is covered with an impermeable structure composed of, for example, a pavement surface of a road, a land for construction, or an embankment of cohesive soil on a road, it is bound to this. It is well known in the example of the Niigata earthquake that abnormal pore water pressure is generated in this loose sand layer under the water table at the time of an earthquake, causing a so-called fluidization phenomenon and catastrophically destroying the entire structure.

[0014]

As described above, the method of the present invention solves the problems of the ground pouring technique for the organic soft ground, and 2. The injection material is resource saving, that is, industrial waste. It also serves to recycle and reuse waste or agricultural waste. Furthermore, it is possible to prevent ground disturbance and weakening due to vibration or fluidization phenomenon at the time of earthquake, which is an excellent earthquake resistance for ground disaster prevention. In addition, it aims to obtain an epoch-making construction method that has excellent workability, can be constructed in a short construction period, and can economically reduce costs by 30% or more compared to conventional construction methods. To do.

[0015]

[Means for Solving the Problems]

The present invention has been made in view of the above points of view, and a cement: sand: bentonite: water weight ratio of 1.0:
Strengthening of organic soft ground such as peat, humus soil, humus cohesive soil, and organic mixed clay obtained by blending in a ratio of 2.0 to 8.0: 0.2 to 1.5: 0.5 to 3.0 Composition and cement: sand: bentonite: water in a weight ratio of 1.0:
The composition obtained by blending in a ratio of 2.0 to 8.0: 0.2 to 1.5: 0.5 to 3.0 is a soft layer when the organic soft ground is a thin layer. All-layer ground improvement method by ground injection to improve and strengthen all layers, and cement:
Sand: bentonite: water weight ratio 1.0: 2.0-80:
When the organic soft ground forms a thick layer, the composition obtained by blending in the ratio of 0.2 to 1.5: 0.5 to 3.0 mainly improves and strengthens the shallow layer to the middle layer. It is intended to provide a soil improvement method by injecting the soil to do so.

[0016]

Next, the contents of the present invention will be described in detail. Broadly speaking, the improvement principles of conventional ground improvement and strengthening are as follows:
Although there are four principles of 1. consolidation, 2. dehydration, 3. consolidation, and 4. substitution, in the present invention, the first is that these four principles can be easily applied in the same process in the range intended for improvement. FIG. 1 is a basic diagram of the present invention, which provides a characteristic technique. That is, when the replacement material is successively injected from a white arrow to a predetermined portion of the organic soft ground having a thickness of H ′ using a specific injection device, the injection liquid flows in the direction of the arrow, and each time it is consolidated → dehydration → This is an injection method in which drainage is repeatedly controlled so that the required soil strength can be obtained in the target area H for ground improvement, and the area replaced by the final injection material is semi-solid in the area indicated by the dotted line. It becomes a solidified substitute.

Further, by applying the principle that the ground once reinforced by consolidation is irreversible and does not easily return to the original soft state before improvement unless extreme external conditions are applied. The invention is an invention of a technique for improving / strengthening an organic soft ground that achieves the ground strength necessary for stabilizing the target ground and an injection material used as the means.

The second feature is that in the prior art, it was extremely difficult to limit the construction range in advance and to improve and strengthen the range by the cement type injection material except for the injection method by chemical injection. The method of the present invention overcomes this drawback and is improved. There are only two alternatives to this chemical injection. That is, one of them is to increase the frictional resistance at the boundary surface between the target ground and the fluid of the injecting liquid to limit the displacement region by the fluid to the intended local range, and the other one is The density of the injection liquid is reduced to localize the replacement region by the injection liquid, and in the example of FIG. 1, it is a method of concentrating in the shallow layer portion. Comparing these two methods, the former method is advantageous in the case where the layer of the organic soft ground is relatively thin, especially when the concept of total layer replacement of the soft layer is adopted. Further, the latter method is suitable for the purpose of improving and strengthening the shallow layer portion of the soil condition in which the organic soft soil is developing in a thick layer.

The most suitable injection materials for these two cases are medium or fine-grained sand or sandy soil in the former case, resource-saving volcanic ash in the latter case, residual ash produced in an incinerator for industrial waste, Waste plastic powder, waste wood powder, volcanic ash,
It is a material having a low specific gravity such as coal ash that remains in thermal power generation, and its combination and blending ratio are summarized in the above-mentioned claims based on the results confirmed from the results accumulated in many experiments. In particular, the mortar mixture that could be injected into the ground by the conventional technology had a specific gravity of cement: sand of up to about 1: 3, but in the present invention, there is no precedent for improving the mixture to 1: 8. It is characterized as a poorly mixed mortar.

The role of bentonite in the above contents is as follows. (1) Make each composition homogeneous and make a stable colloidal suspension. (2) The injection liquid must have the appropriate fluidity required and the injection range must be regulated. (3) Knead water and other admixtures and add cement at the end to make the injection liquid swellable and adjust the volume change rate during consolidation. (4) In order to prevent toxic substances that may be contained in industrial waste from melting or diffusing into groundwater, other composition in the fluid until it solidifies. It should be confined so that it will be integrated with the parts, and it will give a glue role to prevent the injected material from leaking into the riverbed and contaminating the river during river rehabilitation work. Therefore, it does not cause pollution problems associated with ground injection, which is a problem with some types of chemicals.

From an economical viewpoint of this method, as described above, the four principles of consolidation and dehydration, drainage, solidification, and substitution, which are the basic principles of ground improvement, are carried out in the same process. Since the target area is consolidation / dewatering and drainage of the target ground, replacement with the injection material is an in-situ loading means for performing dehydration / consolidation rapidly and economically, and solidification creates a more stable composite ground. It is a means to add the minimum strength for. Therefore, the injection material is required to be easily available and the cheapest. Therefore, the injection material is selected mainly from the viewpoints of resource saving and recycling and reuse of industrial waste and agricultural waste. , Is the third feature of this method.

As described above, regarding the problem of the low degree of solidification of the cement material with respect to the organic soil, which is one of the biggest problems in the current injection technology, the cement used in this method is a replacement formed after injection. Since it is necessary to give a minimum strength to the body, it is not a construction method for the purpose of consolidation effect and expected for consolidation degree, so in extreme terms it is equivalent to the ground strength judged from the finally obtained compaction density. The strength of will be good. However, from the viewpoint of (a) ground disaster prevention, it is necessary to consider the purpose of preventing the fluidization phenomenon predicted during an earthquake, and (b) to solidify harmful substances that may be contained in industrial waste. Since it also includes the purpose of fixing the range of the injection target ground so that harmful substances do not flow out or diffuse outside the injection target ground, as a result of integrating these, various construction results, The composition of the present invention has been determined, and the drawbacks of the prior art have been greatly improved. At the same time, it is a safe and reliable construction method for ground disaster prevention, and is the fourth feature of this construction method.

[0023]

INDUSTRIAL APPLICABILITY As described above, the present invention uses the injection material as a resource-saving material for both recycling and reuse of industrial waste or agricultural waste, and further, when the ground is disturbed or weakened by vibration or an earthquake occurs. Since it can prevent the fluidization phenomenon, it has excellent earthquake resistance for ground disaster prevention, and because it has excellent workability, it can be constructed in a short construction period, and economically compared with the conventional construction method. It is possible to significantly reduce the cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the principle of an improved strengthening method for organic soft ground in the method of the present application.

FIG. 2 is a schematic diagram of ground improvement in the case of pulse injection or columnar injection using only a conventional cement-based injection material.

[Explanation of symbols]

 H Target area for ground improvement H'Thickness of organic soft ground

Claims (3)

[Claims] 1. Peat, humus, humic cohesive soil, characterized by being obtained by mixing cement: sand: bentonite: water in a weight ratio of 1.0: 2.0-8.0: 0.2-1.5: 0.5-3.0.
Composition for strengthening organic soft ground such as organic mixed clay. 2. A composition obtained by mixing cement: sand: bentonite: water in a weight ratio of 1.0: 2.0 to 8.0: 0.2 to 1.5: 0.5 to 3.0, when the organic soft ground has a thin layer. In addition, all-layer ground improvement method by ground injection to improve and strengthen all soft layers. 3. A weight ratio of cement: sand: bentonite: water of 1.0: 2.0 to 8.0: 0.2 to 1.5: 0.5.
A ground improvement method by ground injection mainly for improving and strengthening the shallow layer part to the middle layer part when the above organic soft ground forms a thick layer with a composition obtained by mixing in a ratio of 3.0.