JP6508525B2 - Ground improvement method - Google Patents

Description

  The present invention relates to a method for improving ground strength by mixing a cement-based solidifying material with ground such as sandy soil having a small amount of fine particles, and to a method for reducing the amount of the solidifying material to improve ground strength.

  A ground improvement method for solidifying the ground by mixing cement-based solidifying material obtained by adding gypsum to cement or cement to soil such as soft ground has been known conventionally, and the composition of cement-based solidifying material is also considered according to the type of soil It is done. For example, a dedicated cement-based solidifying material has been developed for the ground improvement of volcanic clay-like clay such as organic soil or Kanto loam, and the amount of solidifying material used has been reduced (Non-Patent Document 1).

  On the other hand, sandy soil with little fine grain content is often compacted to improve the ground, and there are few cases using cement or cement-based solidifying material, but ground improvement using cement or cement-based solidifying material is also known The ground improvement using ordinary Portland cement and blast furnace cement is carried out. In particular, as is clear from the damage caused by liquefaction in Urayasu City after the Great East Japan Earthquake, sandy soils with small fine particles are easy to liquefy, so soil improvement will be necessary as a countermeasure for liquefaction in the future, From the viewpoint of shortening construction period and cost, it is expected that the ground improvement method using cement or cement-based solidifying material is applied more than the reduction of the groundwater level or the sand compaction method.

  The powder addition method and the slurry addition method are known as a typical mechanical stirring method of the ground improvement method using cement and cement-based solidifying material, but when the powder addition method has large frictional resistance of the surrounding ground In many cases, the mixing of soil and solidifying material is insufficient. Also, in the case of cement slurry method, if the cement slurry has a small amount of solidifying material, the solidifying material is not sufficiently mixed with the soil and the ground improvement is insufficient. Therefore, in many cases, a large amount of solidifying material is used. There is a problem that

  In order to suppress the amount of solidifying material used, a method is known in which the adding time of the solidifying material is divided into two stages of pre-addition and main addition, and the pre-addition amount and main addition amount are made 1/14 to 2/1. (Patent Document 1). However, this ground improvement method is intended for peat soils with a moisture content of 500 wt% or more and an organic matter content of 60 wt% or more, and the soil to be treated is limited to special soils such as sandy soils. Application of is not considered.

  In addition, as a ground improvement method that divides the addition time of the cement-based solidifying material into two stages, the solidifying material addition is performed a second time after the soil reaches the preparation stage by the first solidifying material addition, and at least any solidifying A treatment method is known in which a hexavalent chromium elution reducing agent is added at the time of material addition (Patent Document 2). However, this ground improvement method is a method of enhancing the ground strength and the elution suppression effect of hexavalent chromium, and is intended for soils with a large amount of hexavalent chromium.

Unexamined-Japanese-Patent No. 5-230821 gazette Patent No. 4600812 (Unexamined-Japanese-Patent No. 2006-193971)

Ground improvement manual with cement-based solidifying material (4th edition), issued October 10, 2012, 4th edition 1st edition, published by Japan Society of Cement Association

  The ground improvement method according to the present invention is different from the conventional ground improvement methods in which peat soils, hexavalent chromium-containing soils, etc. are treated, and grounds for sandy soils with a small amount of fine particles are different. It is an improvement method. The ground improvement method of the present invention is different from the conventional ground improvement method in which the addition time of the solidifying material is simply two steps, and the addition time of the solidifying material slurry is divided into the first addition and the second addition, It is a ground improvement method that reduces the amount of solidifying material used and effectively increases the ground strength by using a slurry in which the concentration of solidifying material is changed in 1 addition and 2nd addition, which is sufficient with conventional ground improvement methods Provide a method to exert an excellent ground improvement effect for soils that have not been effective.

The present invention is a ground improvement method having the following configuration.
[1] In the ground improvement method of enhancing the ground strength by adding and mixing a slurry of cement-based solidifying material (referred to as cement slurry) to the soil, the fine particles having a particle size of less than 0.075 mm are less than 50% and the water content ratio For sandy soils with a content of 30% or less , the addition and mixing of the cement slurry is divided into a first addition and a second addition, and a cement slurry having a water solidifying material ratio of 100% or more in the first addition is used after the first addition. Mixing cement slurry with soil using a cement slurry having a water solidifying agent ratio of less than 100% in the second addition, and the first addition amount of the cement slurry being 1/5 times to the equivalent of the second addition amount; Ground improvement method characterized by
[2] The ground improvement method described in the above [1], wherein the water solidifying material ratio of the first addition of cement slurry is 100% to 300%, and the water solidifying material ratio of the second addition is 50% to 95%.
[3] The ground improvement method as described in said [1] or said [2] whose total addition amount of cement slurry is 10 to 40% with respect to soil weight.

[Specific description]
Hereinafter, the present invention will be specifically described. In addition,% is wt% according to each general definition and unless otherwise indicated.

The present invention relates to a method for improving ground strength by adding and mixing a slurry of a cement-based solidifying material (referred to as a cement slurry) to soil, wherein fine particles having a particle size of less than 0.075 mm are less than 50% and contain water. For sandy soils with a ratio of 30% or less , the addition and mixing of cement slurry is divided into the first addition and the second addition, and a cement slurry with a water solidifying material ratio of 100% or more in the first addition is used after the first addition The cement slurry is mixed with the soil such that the first addition amount of the cement slurry is 1⁄5 times to the equivalent of the second addition amount using cement slurry having a water solidifying material ratio of less than 100% in the second addition of It is a ground improvement method characterized by

  The target soil of the ground improvement method of the present invention is a soil having a fine particle fraction of less than 0.075 mm in particle size less than 50% and a water content ratio of 30% or less. Preferably, it is a sandy soil having a fine particle fraction of less than 0.075 mm in particle size less than 50% and a water content ratio of 30% or less.

  Soil constituent materials are classified into fine particles having a particle diameter of less than 0.075 mm, coarse particles having a particle diameter of 0.075 mm or more and less than 75 mm, and stones having a particle diameter of 75 mm or more according to their particle sizes. The fine particles are divided into clay having a particle size of less than 0.05 mm and silt having a particle size slightly larger than that of clay. The coarse grain fraction is divided into sand having a particle size of at least 0.075 mm and less than 2 mm, and a weir having a larger particle size than sand. The soil is roughly divided into fine-grained soil and coarse-grained soil according to the content of these fine-grained and coarse-grained components.

  The target soil of the ground improvement method of the present invention is a coarse soil having a fine fraction of less than 50% and thus containing 50% or more of coarse fractions. Coarse-grained soil is divided into sandy soil with high sand content and sandy soil with high content, but the target soil of the ground improvement method of the present invention is preferably sandy soil with high sand content.

  Sandy soil is known to be easily liquefied. In sandy soils containing a large amount of sand and sand ground, the ground is kept stable by friction due to shear stress of sand particles, but when continuous vibrations such as earthquakes and construction work are added at locations where the groundwater level is high, repeated shearing is performed. The volume decreases and the pore water pressure increases, and the shear stress decreases accordingly, causing liquefaction, and the ground rapidly loses its strength. The ground improvement method of the present invention can suppress the liquefaction by increasing the ground strength of such sandy soil with a lot of sand.

In addition, soils with a low water content ratio are generally in a clumped state, for example, sandy soils with a water content ratio of 30% or less have a low water content, so they have high penetration resistance to cement slurry, etc. It is difficult for cement slurry to be sufficiently mixed in the ground. The ground improvement method of the present invention can efficiently mix cement slurry with such coarse soil having a water content ratio of 30% or less, particularly sandy soil.
On the other hand, soil with a moisture content over 30% is in a state where soil is loosely deposited because there is much pore water between soil particles, and cement slurry easily penetrates, so the effect of dividing cement slurry in stages and mixing is small .

  The cement slurry used in the ground improvement method of the present invention is a slurry of a solidifying material mainly composed of cement, which uses cement as a solidifying material, and is a solidifying material in which gypsum, blast furnace slag, fly ash, slaked lime, etc. is blended with cement. A slurry can be used. The water-solidifier ratio of the cement slurry is adjusted by the step of mixing in the soil.

  The ground improvement method of the present invention divides the addition of cement slurry into the first addition and the second addition, and mixes the cement slurry with a water solidifying agent ratio of 100% or more (solidifying agent concentration 50% or less) in the first addition to the soil In the second addition after the first addition, a cement slurry having a water solidifying agent ratio of less than 100% (solidifying agent concentration of more than 50%) is mixed with the soil.

  The reason for using a cement slurry with a water solidifying agent ratio of 100% or more in the first addition is because, for example, in sandy soil with a water content ratio of 30% or less, the frictional resistance of the soil particles is large when the slurry enters the voids between the soil particles When the concentration of the solidifying material in the slurry is high, the solidifying material particles receive resistance of the soil particles, and the slurry is less likely to enter between the soil particles. On the other hand, in the case of a cement slurry having a large amount of water and a low solidifying agent concentration, the moisture of the slurry easily gets into the soil particles, so the resistance to the solidifying agent particles becomes small and the cement slurry easily enters the soil. Therefore, in the ground improvement method of the present invention, in the first addition, a cement slurry having a water content ratio of 100% or more (solidification material concentration of 50% or less) equal to or larger than the solidification material amount is used.

  The specific range of the water solidifying material ratio of 100% or more of the cement slurry used for the first addition may be determined according to the state of the soil (water content ratio, soil quality, etc.). In general, it is preferable to use a cement slurry having a water solidifying agent ratio of 100% to 300% in the first addition.

  The ground improvement method of the present invention uses a cement slurry having a water solidifying agent ratio of less than 100% in the second addition after the first addition of the cement slurry. The cement slurry enters the soil by the first addition, but the cement slurry of the first addition has a water solidifying agent ratio of 100% or more and the solidifying agent concentration is low. Add cement slurry with high solidifying agent concentration of less than 50% (solidifying agent concentration> 50%) to improve ground strength.

  In the second addition of cement slurry, since the cement slurry is in the state of being intruded into the soil by the first addition, the cement slurry of the second addition is easy to infiltrate into the soil, and the solidified material particles of the cement slurry are well dispersed in the soil Therefore, the amount of solidified material can be reduced to obtain high ground strength.

  The specific range of the water solidifying agent ratio of less than 100% of the cement slurry used for the second addition may be determined according to the state of the soil after the first addition. In general, it is better to use a cement slurry having a water solidifying agent ratio of 50% to 95% in the second addition.

  The total amount of cement slurry added is determined according to the condition of the soil. Generally, the total amount of cement slurry added is generally 10 to 40% based on the weight of the soil. The amount of the first addition slurry is preferably 1⁄5 to 1⁄2 times the total addition, and the amount of the second addition slurry is preferably 4⁄5 to 1⁄2 times the total addition. Therefore, it is preferable that the first addition amount of the cement slurry is approximately 1/5 times to the equivalent amount of the second addition amount.

  After addition of the cement slurry, the soil may be agitated to thoroughly mix the slurry into the soil. After the first addition, the second addition may be performed continuously, or after the first addition, the second addition may be performed with an interval of several minutes to several hours.

According to the ground improvement method of the present invention, in a sandy soil or the like having a low water content ratio, cement slurry is well dispersed in the soil, so that a large ground strength can be obtained, and the amount of solidifying material can be reduced. Therefore, the amount of soil discharged can be reduced at the site, which contributes to the reduction of construction cost and environmental load. Specifically, for example, if it is possible to reduce the amount of solidifying material added by 50 kg / m ³ in general, it is said that construction sludge that is industrial waste can be reduced by about 9%. The reduction effect is significant.

Hereinafter, examples of the present invention will be shown together with comparative examples. In each example and each comparative example, after adding and mixing cement slurry to soil (1 m ³ ), a part of the soil is formed into a sample (diameter 50 mm, height 100 mm) and uniaxial compression test of 7 days age The ground strength was measured by The uniaxial compressive strength was measured in accordance with the standard (JIS A 1216 "uniaxial compressive test method of soil").

Example 1
A cement slurry prepared by adding water to ordinary portland cement to this soil using sandy soil from Urayasu City, Chiba Prefecture (wet density 1.980 g / cm ³ , water content ratio 16.8%, fine particle 20.5%) The ground strength was measured by additive mixing. The cement slurry is divided into two steps of the first addition and the second addition, and the water solidifying material ratio (W / C ratio) is, as shown in Table 1, the water solidifying material ratio of the first addition 100% or more, the second The water solidifying agent ratio of the addition was adjusted to less than 100%. The second addition was performed at intervals of 1 minute after the first addition (Examples A1 to A4). The results are shown in Table 1.
A comparative example B1 was obtained without dividing the addition of the cement slurry twice, and a comparative example B2 having a water solidifying agent ratio of 100% for each of the first addition and the second addition of the cement slurry was taken as a comparative example B2. Is shown in Table 1.
As shown in Table 1, each of A1 to A4 in this example has a ground strength of 3000 kN / m ² or more in a total amount of 500 kg of the first addition and the second addition of the slurry. On the other hand, the comparative samples B1 and B2 have ground strength of 2810 to 2820 kN / m ² at a total addition amount of 500 kg of the slurry, which is significantly lower than A1 to A4 of this example.

Example 2
(I) Sandy soil from Kawaguchi City, Saitama Prefecture (wet density 1.915 g / cm ³ , moisture ratio 24.4%, fine grain 31.8%), (ii) Sandy soil from Kita Ward, Tokyo (wet density) 1.889 g / cm ³ , moisture content 28.4%, fine content 42.2%), (C) Cohesive soil from Kawasaki-ku, Kanagawa Prefecture (wet density 1.754 g / cm ³ , moisture content 31.7%, fine content 51.6%) It was used. Soil (c) is a cohesive soil for comparison.
The cement slurry prepared by adding water to ordinary portland cement was added to and mixed with the test soil (B) (B) to measure the ground strength. In the present embodiment (A5 to A8), with regard to the soil (i) (ii), the cement slurry is divided into two, the first addition and the second addition, and the water solidifying material ratio (W / C ratio) is shown in Table 2 As shown, the water solidifying agent ratio of the first addition was adjusted to 200%, 150%, and the water solidifying agent ratio of the second addition was adjusted to 75%, 50%. The second addition was performed at intervals of 1 minute after the first addition. The results are shown in Table 2.
As a comparative example (B3, B4), the addition of the cement slurry was carried out without dividing it twice for the soil (A) (B). The results are shown in Table 2. Further, as a comparative example (B5, B6), the same test as the above A6 to A7 and B3 to B4 was conducted on the soil (3) of the viscous soil. The results are shown in Table 2.
As shown in Table 2, with regard to the soil (i) (ii), the comparative samples B3 and B4 have a ground strength of less than 2300 kN / m ^{2 when the} amount of slurry is 500 kg, but the present examples A5 and A6 It shows ground strength of 2300 kN / m ² or more when the total amount is 500 kg.
Further, this embodiment A7, A8, in total amount of the slurry 350 kg (weight solidifying material 200kg), 2255kN / ^{m 2} Soil (b), a ground strength of 1995kN / ^{m 2} Soil (b) Even if the amount of solidified material is smaller than the amount of solidified material (250 kg) of Comparative Samples B3 and B4, it has ground strength equivalent to B3 and B4, and high ground strength is obtained even if the amount of solidified material is reduced. It shows that it is possible.
Sample A9 is an example in which 1% of dispersing agent (Flowric Co., Ltd. product: Geosuper K) was added to water at the time of the second addition, and the water of the second addition slurry is added by adding the dispersing agent. The solidifying material ratio can be reduced to 50% (the solidifying material concentration is high) to enhance the ground strength.
In addition, as for the soil (3) of the cohesive soil, as shown in Comparative Samples B5 and B6, even if the addition of the slurry is divided twice, the ground strength does not differ much.

Claims (3)

In the ground improvement method of enhancing the ground strength by adding and mixing a slurry of cement-based solidifying material (referred to as cement slurry) to the soil, the fine particles with a particle size of less than 0.075 mm are less than 50% and the water content ratio is 30% With regard to sandy soil which is the following , the addition and mixing of cement slurry is divided into the first addition and the second addition, and in the first addition, a cement slurry having a water solidifying material ratio of 100% or more is used, and the second addition after the first addition Mixing the cement slurry with the soil using a cement slurry having a water solidifying agent ratio of less than 100% , and making the first addition amount of the cement slurry 1/5 times to the equivalent of the second addition amount. Ground improvement method. The ground improvement method according to claim 1, wherein the first addition water solidifying agent ratio of the cement slurry is 100% to 300%, and the second addition water solidifying agent ratio is 50% to 95%. The ground improvement method according to claim 1 or 2, wherein the total addition amount of the cement slurry is 10 to 40% with respect to the weight of the soil.