Site improvement construction methods

Abstract

To provide a ground improvement method capable of carrying out suitable ground improvement for a soft ground or the like.SOLUTION: The ground improvement method is a method for establishing a ground improvement body by stirring and mixing a soil and an improvement material. The improvement material contains cement milk and a high-performance AE water-reducing agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground improvement method for improving the ground by stirring and mixing soil and an improvement material. [Background technology]

[0002] Soil improvement has been performed for ground that does not have the desired strength. A known method for such soil improvement involves mixing cement milk as an improvement material into the crushed and cut soil at the original location, and then rotating a mixing blade to mix and disperse the mixture, thereby creating a soil improvement body (soil improvement pile) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-64759 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-105522 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of ground improvement method, the water-cement ratio of cement milk is generally set to between 80% and 120%. However, for soft ground such as clayey soil or peat, the amount of cement must be increased (resulting in a water-cement ratio lower than the above range) or a special cement must be used to achieve the desired strength.

[0005] However, if the amount of cement is increased, it may exceed the soil's capacity, causing problems such as leakage to the ground surface and ground heave. Furthermore, since an increased amount of cement makes it more difficult to mix with the soil, in order to sufficiently mix and disperse it, the force with which the mixing blades rotate must be increased or the outer diameter of the mixing blades must be reduced. In other words, in order to rotate the mixing blades with greater force, larger equipment must be introduced, and since a smaller outer diameter of the mixing blades results in a smaller ground improvement body, the number of constructions must be increased accordingly.

[0006] Patent Document 2 also describes a method for improving soft ground from a different perspective, in which cement milk is mixed into the ground while excavating it to form primary improvement columns, and then cement milk is mixed into the solidified primary improvement columns while crushing them to form secondary improvement columns. However, this method requires a great deal of man-hours because it is necessary to form columns that are twice as large as usual.

[0007] In view of the above-mentioned conventional problems, the present invention proposes a ground improvement method that can suitably improve the ground of soft ground and the like. [Means for solving the problem]

[0008] The present invention is a ground improvement method for creating a ground improvement body by stirring and mixing soil and an improvement material, and the improvement material contains cement milk and a high-performance AE water reducing agent. The high-performance AE water-reducing agent is a high-performance AE water-reducing agent containing a PAE compound as a main component, and the improvement material is such that the water-cement ratio of the cement milk is 60% or more and 100% or less, and the content of the high-performance AE water-reducing agent relative to the total mass of the cement milk is 0.2% by mass or more and 0.3% by mass or less. It is characterized by: [Effects of the Invention]

[0011] After extensive research, the inventors of the present invention have found that when a high-range air-entraining water-reducing agent, which has conventionally been used as an admixture for concrete, is added to cement milk as an improvement material, mixing and diffusion with the soil is more effective than in the past, even in soft ground such as clayey soil or peat. In other words, the ground improvement method of the present invention does not require the introduction of large-scale equipment as in the past, and does not lead to an increase in the number of steps during construction, making it possible to carry out ground improvement in an efficient manner. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the relationship between the amount of high-performance AE water-reducing agent added and the fluidity of the improvement material. [Figure 2] FIG. 1 is a graph showing the fluidity and bleeding rate of an improving material over time. [Figure 3] FIG. 1 is a diagram showing conditions for mixing soil and improvement material. [Figure 4] FIG. 4 is a diagram showing the fluidity of the mixture under the conditions shown in FIG. 3. [Figure 5] FIG. 4 is a graph showing the compressive strength of test specimens under the conditions shown in FIG. [Figure 6] This is a diagram showing the compressive strength when applying ground improvement methods to a peat layer. [Figure 7] This is a diagram showing the compressive strength when applying ground improvement methods to a clayey soil layer. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, one embodiment of the ground improvement method according to the present invention will be described with reference to the drawings. The ground improvement method according to the present invention may be any method that creates an improved ground body by stirring and mixing soil and improvement materials, and there are no particular limitations on the equipment (mixing blades, etc.) used when carrying out this method.

[0014] The improving material according to the present invention contains cement milk and a high-range air-entraining water-reducing agent. In this specification, "cement milk" refers to a mixture of cement or a cement-based solidification material with water. The cement-based solidification material is a material whose main component (usually 50% by mass or more) is cement, and which contains various active ingredients (such as ground granulated blast furnace slag) as secondary components. The "high-range air-entraining water-reducing agent" refers to a chemical admixture that has air-entraining properties, higher water-reducing properties than air-entraining water-reducing agents, and better slump retention properties, and is defined as a "chemical admixture for concrete specified in JIS A 6204."

[0015] As mentioned above, the inventors of the present invention have found that adding a high-range water-reducing agent, which has been conventionally used as an admixture for concrete, to cement milk makes it easier to mix with soil, even in soft ground such as clayey soil or peat. In order to understand this point in detail, the following investigations were carried out.

[0016] First, we investigated the relationship between the amount of high-performance AE water-reducing agent added (Cx%) and the fluidity of the improvement material while changing the type of cement hardener, the water-cement ratio of cement milk, and the combination of high-performance AE water-reducing agent. The results are shown in Figure 1. The fluidity of the improvement material was confirmed by a table flow test in which the improvement material was filled into a φ50 mm cylindrical container and the spread was observed when it was inverted on a table. The amount of high-performance AE water-reducing agent added in Figure 1 is shown as a mass percentage of the total mass of the cement milk.

[0017] Figure 1(a) shows the results of the investigation using a cement-based solidification agent for general soil, Figure 1(b) shows the results of the investigation using a cement-based solidification agent for general soft soil, Figure 1(c) shows the results of the investigation using a cement-based solidification agent for special soil, and Figure 1(d) shows the results of the investigation using a cement-based solidification agent for peat. In Figures 1(a)-(d), the solid line and circles indicate the results without the addition of a high-performance air-entraining water-reducing agent. The dashed line and triangles indicate the results with the addition of a high-performance air-entraining water-reducing agent (PCE) based on a polycarboxylic acid ether compound. The solid line and squares indicate the results with the addition of a high-performance air-entraining water-reducing agent (PAE) based on a PAE compound. The water-cement ratio (W / C) of the cement milk is shown directly in Figures 1(a)-(d).

[0018] As can be seen from the results for the 80% water-cement ratio shown in Figure 1(a), even a small amount of high-performance water-reducing agent (e.g., 0.1% by mass relative to the total mass of cement milk) improved the fluidity of the improvement material. This trend was observed regardless of the type of cementitious solidification agent. Furthermore, the addition of PAE tended to improve the fluidity of the improvement material more than PCE. As shown in Figure 1(d), the improvement in fluidity of the improvement material tended to be more gradual as the amount of high-performance water-reducing agent added increased, particularly when using a peat cementitious solidification agent. For example, in Figure 1(d), when a water-cement ratio of 70% was used and PAE was added (solid line and squares), the slope of the curve for amounts of high-performance water-reducing agent added exceeding 0.7% by mass relative to the total mass of cement milk was less steep than the slope for amounts of 0.3% by mass added. Note that increasing the amount of high-performance water-reducing agent also increases costs. Therefore, from the viewpoint of improving the fluidity of the improvement material while suppressing costs, the amount of high-performance AE water-reducing agent added to the total mass of cement milk is preferably 0.1% by mass to 0.7% by mass, and more preferably 0.1% by mass to 0.6% by mass. Furthermore, when the water-cement ratios in Figures 1(a) to 1(d) were checked at 70% and 60%, improvements in the fluidity of the improvement material were observed in both cases, so it is preferable that the water-cement ratio be 60% or more.

[0019] Next, the same cement-based solidification materials were used (all cement-based solidification materials for peat), but the water-cement ratio of the cement milk and the combination of high-performance AE water-reducing agents were changed to check the fluidity and bleeding rate of the improvement material over time. The results are shown in Figure 2.

[0020] Figures 2(a) and (d) show the results for a water-cement ratio (W / C) of 100%, Figures 2(b) and (e) show the results for a water-cement ratio (W / C) of 80%, and Figures 2(c) and (f) show the results for a water-cement ratio (W / C) of 70%. The solid line and circles in Figure 2 represent the results without the addition of a high-performance water-reducing agent, the dashed line and triangles represent the results with the addition of PCE, and the solid line and squares represent the results with the addition of PAE. In Figures 2(e) and 2(f), the results with the addition of PCE and PAE are nearly identical, resulting in the lines overlapping on the graph. The Cx value in Figure 2 indicates the amount of high-performance water-reducing agent added relative to the total mass of cement milk. For example, Cx 0.3% indicates that the amount of high-performance water-reducing agent added relative to the total mass of cement milk is 0.3% by mass.

[0021] As shown in Figure 2(a), even a small amount of high-performance water-reducing agent (even about 0.1% by mass relative to the total mass of cement milk) was found to improve the fluidity of the improved material. Furthermore, although the fluidity of the improved material decreased over time after mixing, the rate of decrease when a high-performance water-reducing agent was added was roughly equivalent to the rate of decrease when no high-performance water-reducing agent was added. Furthermore, as shown in Figures 2(a)-(c), the fluidity of the improved material tended to improve more when PAE was added than when PCE was added. Furthermore, the rate of decrease in the fluidity of PCE and PAE after a certain time had passed after mixing was roughly equivalent regardless of the water-cement ratio or the amount of water-reducing agent added.

[0022] Furthermore, as shown in Figure 2(d), the bleeding rate of the improved material tended to increase whether or not a high-performance AE water-reducing agent was added (the cement becomes more susceptible to separation over time). As shown in Figures 2(d)-(f), there was no significant difference in the bleeding rate over time when PCE was added and when PAE was added, and there was no significant difference between the two when the water-cement ratio or the amount of water-reducing agent added was changed.

[0023] As shown in Figure 2(d), the bleeding rate increases with increasing amounts of superplasticizer. However, as is clear from a comparison of Figures 2(e) and 2(f), the bleeding rate can be kept at a similar level by decreasing the water-cement ratio as the amount of superplasticizer added increases. Even when the bleeding rates without the addition of superplasticizer (see the solid line and circles in Figure 2(d)) and with the addition of superplasticizer (see Figures 2(e) and (f)) are the same, the fluidity of the concrete with the addition of superplasticizer (see Figures 2(b) and (c)) is improved compared to the concrete without the addition of superplasticizer (see the solid line and circles in Figure 2(a)). This trend remains unchanged even after time has passed since mixing.

[0024] Next, the soil and improvement material were mixed under the conditions shown in Figure 3, and the fluidity and compressive strength of the mixture were confirmed. The results are shown in Figures 4 and 5. To investigate the fluidity of the mixture shown in Figure 4, the soil and improvement material were mixed in a cylindrical container with a diameter of 100 mm, and after a specified time had passed, the mixture was inverted on a table and vibrated a specified number of times, and the spread on the table was observed. The compressive strength was also measured on test specimens formed from the mixture at ages of 3, 7, and 28 days (σ3, σ7, σ28).

[0025] As is clear from the comparison of Test Examples 1 to 3 in Figure 4(a) and Figure 5, as the amount of cement-based solidification material added increases, the fluidity of the mixture improves and the compressive strength (especially the compressive strength at ages of 7 and 28 days) also increases. In other words, as the amount of cement-based solidification material added increases, the soil and improvement material tend to mix more easily, and the compressive strength tends to increase.

[0026] Furthermore, as can be seen from comparing Test Examples 2 and 4 in Figure 4(b), the fluidity of the mixture was reduced when PCE was added compared to when PAE was added within approximately 2 minutes of mixing the soil and improvement material. In other words, when PCE was used, the soil and improvement material were less likely to mix immediately after mixing compared to when PAE was used. Furthermore, as can be seen from Test Examples 2 and 4 in Figure 5, the compressive strength (especially at 7 and 28 days) tended to be higher when PAE was added compared to when PCE was added. Therefore, PAE has superior fluidity and workability even immediately after mixing with the soil compared to when PCE was used, and it can be said that it achieves higher compressive strength over time.

[0027] As is clear from the comparison of Test Examples 2 and 5 shown in Figures 4(b) and 5, increasing the amount of superplasticizer improves the fluidity of the mixture, but no significant difference in compressive strength was observed. Specifically, when PAE was used, the fluidity of the mixture improved when the amount added relative to the total mass of cement milk was 0.5% (Test Example 5) compared to 0.3% (Test Example 2), but the compressive strength was the same. Furthermore, increasing the amount of superplasticizer added also increases costs. Therefore, in terms of cost savings even if the compressive strength is the same, it can be said that an amount of superplasticizer added relative to the total mass of cement milk of 0.3% by mass is preferable to 0.5% by mass.

[0028] Furthermore, the results of Test Examples 2, 6, and 9 shown in Figures 4(c) and 5 indicate that the fluidity and compressive strength of the mixtures are roughly equivalent. In other words, even if the amount of PAE added is reduced to reduce costs (specifically, from 0.6% by mass (Test Examples 6 and 9) to 0.3% by mass (Test Example 2)), the fluidity and compressive strength of the mixtures can be maintained by increasing the water-cement ratio (specifically, by increasing the water-cement ratio from 60% to 80%).

[0029] As is clear from a comparison of Test Example 7 and Test Example 8 shown in Figure 4(c) and Figure 5, when a small amount of high-range AE water-reducing agent was added (about 0.1 mass% added relative to the total mass of the cement milk), the fluidity of the mixture did not change significantly compared to when it was not added, but the compressive strength (especially the compressive strength at 28 days) was higher. Therefore, it can be said that adding a high-range AE water-reducing agent is preferable in terms of increasing compressive strength.

[0030] Based on the above considerations, the ground improvement method according to the present invention was actually implemented using equipment such as agitating blades, and an investigation was carried out into the compressive strength. The results are shown in Figures 6 and 7.

[0031] Figures 6(a) and (b) show the compressive strength and strength elongation rate at ages of 7 and 28 days (σ7, σ28) when ground improvement was performed on a peat layer. The investigation in Figure 6(a) was carried out under the conditions that the water-cement ratio of the cement milk contained in the improvement material was 80%, a peat grade cement solidification material was used, and 0.3 mass% of PAE was added to the total mass of the cement milk. The amount of cement contained in the cement solidification material was 150, 300, and 450 kg / m 3 The investigation in Figure 6(b) was carried out under the conditions that the water-cement ratio of the cement milk contained in the improvement material was 100%, a peat-grade cement solidification material was used, and no high-performance AE water-reducing agent was added.

[0032] Figures 7(a) and (b) show the compressive strength and strength elongation rate at ages of 7 and 28 days (σ7, σ28) when ground improvement was performed on a clayey soil layer. The investigation in Figure 7(a) was carried out under the conditions that the water-cement ratio of the cement milk contained in the improvement material was 80%, a clayey soil type was used as the cement-based solidification material, and PAE was added at 0.3 mass% of the total mass of the cement milk. The amount of cement contained in the cement-based solidification material was 100, 200, and 300 kg / m 3The investigation in Figure 7(b) was carried out under the conditions that the water-cement ratio of the cement milk contained in the improvement material was 100%, a clayey soil type cement was used as the cement-based solidification material, and no high-performance AE water-reducing agent was added.

[0033] When the ground improvement method was applied to a peat layer under the conditions shown in Figure 6(a) above, it was confirmed that the soil and improvement material were well mixed. Furthermore, when the created ground improvement body was sampled and inspected, no particular problems were found. Furthermore, as shown in Figure 6(a), the compressive strength at both 7 and 28 days increased linearly as the amount of cement increased. Furthermore, the increase in compressive strength at 28 days relative to the compressive strength at 7 days was stable. Furthermore, as shown in Figure 7(a), the results of ground improvement of a clayey soil layer under the conditions described above were also good.

[0034] On the other hand, when the ground improvement method was carried out on the peat layer under the conditions shown in Figure 6(b) above, the ground improvement body was constructed unevenly, and there were some places where it was impossible to extract it. In particular, when the cement amount was 150 kg / m 3 In this case, the soil improvement body could not be extracted effectively, and the compressive strength could not be measured under this condition. 3 The compressive strength also varies widely. For example, the compressive strength at 7 days old is 3 to 450 kg / m 3 Furthermore, as shown in Figure 7(b), even when ground improvement was performed on a clayey soil layer under the above conditions, the improved soil was uneven and there was a large variation in compressive strength.

[0035] These results suggest that the use of an improvement material containing cement milk and a high-range water-reducing agent can ensure sufficient mixing and diffusion of the soil and improvement material, even in soft ground such as clayey soil or peat, resulting in the creation of a ground improvement body with a specified strength. Based on the above survey range and the survey results shown in Figures 1(a)-(d), the water-cement ratio of the cement milk in the improvement material is preferably 60% to 100%. Furthermore, based on the survey results shown in Figure 1, the content of the high-range water-reducing agent relative to the total mass of the cement milk is preferably 0.1% to 0.7% by mass. Furthermore, based on the survey results shown in Figures 1(a)-(d) and Figures 4 and 5 (e.g., a comparison between Test Example 2 and Test Example 6), it is more preferable that the water-cement ratio of the cement milk in the improvement material be 80% to 100% and that the content of the high-range water-reducing agent relative to the total mass of the cement milk be 0.1% to 0.6% by mass. Furthermore, based on the survey results shown in Figure 4 (for example, a comparison between Test Example 2 and Test Example 5) and the survey results shown in Figures 6 and 7, it can be said that it is particularly preferable to set the water-cement ratio of cement milk to 80% (75% to 85% taking into account variations in actual use) and the content of high-performance AE water-reducing agent relative to the total mass of cement milk to 0.3% by mass (0.2% to 0.4% by mass taking into account variations in actual use).In addition, when tests were also conducted using hard clay (N value indicating ground strength is approximately 8≦N≦10) in accordance with the above example, it was confirmed that the clay lumps were loosened and mixed and diffused sufficiently with the improvement material, resulting in the creation of a ground improvement body with the specified strength.

[0036] Although one embodiment of the present invention has been described above, the present invention is not limited to the specific embodiment, and unless otherwise limited in the above description, various modifications and changes are possible within the scope of the spirit of the present invention as set forth in the claims. Furthermore, the effects of the above embodiment are merely examples of the effects that can be obtained from the present invention, and do not mean that the effects of the present invention are limited to the above effects.

Claims

[Claim 1] A ground improvement method in which soil and improvement materials are stirred and mixed to create a ground improvement body, The improvement material includes cement milk and a high-performance air-entraining water-reducing agent, The high-range air-entraining water-reducing agent is a high-range air-entraining water-reducing agent containing a PAE compound as a main component, The improvement material is a ground improvement method in which the water-cement ratio of the cement milk is 60% or more and 100% or less, and the content of the high-performance air-entraining water-reducing agent relative to the total mass of the cement milk is 0.2% by mass or more and 0.3% by mass or less.

Images