JPH08211045A - Method for estimating strength of soil cement - Google Patents

Abstract

PURPOSE: To estimate the solidification strength at predetermined days after placement, by measuring the specific gravity, cement content, etc., of a soil cement sample and then calculating and estimating the solidification strength according to a specified formula. CONSTITUTION: A soil cement body is sampled at arbitrary points thereof prior to solidification and the specific gravity thereof is measured. On the other hand, weight of a part of the sample is measured and after evaporating the moisture therefrom, the dry weight thereof is measured thus determining the weight of moisture. The dried sample is crushed and admixed with water and an acid to cause reaction thus determining the quantity of cement based on the quantity of acid being consumed. The residual sample is screened and the weight is measured for fine aggregate and sand. Subsequently, the ratio is calculated and subtracted from 100 thus determining the ratio of clay component. Finally, the strength is estimated using the calculation results according to a formula for estimating the solidification strength while classifying into groups where the value of C/(Cl+Sd) is 0.15 or below and 0.2 or above (Y is estimated strength of soil cement, W is water, C is cement component, Cl is clay plus silt, Sd is sand component, R is fine aggregate component, and a0 -a5 are coefficients determined through multiple regression analysis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting strength of soil cement, and more particularly to a method for predicting strength of soil cement for accurately determining the solidification strength of a soil cement body that has not yet solidified.

[0002]

2. Description of the Related Art In recent years, a soil cement underground wall called a soil column wall construction method has rapidly become widespread as a water barrier wall. Since this soil cement uses aggregate in situ, it is difficult to accurately set the strength in advance like concrete, so it is necessary to measure the strength on site. For this, conventionally, the solidification strength after 28 days of age is generally measured according to JIS A 1216 "Soil uniaxial compressive strength test method".

[0003]

However, in the above method, it takes 28 days until the solidification strength can be determined,
It is unknown whether the desired solidification strength was obtained despite the completion of construction. In addition, the above-mentioned method has problems such as cost for cutting the strength, cutting out of the specimen, and labor for manufacturing. Furthermore, in the case of a construction error in which the desired solidification strength was not obtained, troublesome repair work was required.

[0004]

Means for Solving the Problems As a result of intensive studies conducted by the present inventor to overcome the drawbacks of the conventional methods, the specific gravity of soil cement immediately after construction, the water content in the soil cement, the gravel content, the sand content, Clay + silt (hereinafter simply referred to as clay)
Further, it was found that a total of 6 factors of cement content and the solidification strength after 28 days have a certain correlation, and the present invention was completed based on this finding. That is, the present invention
A method for predicting strength of soil cement that determines the solidification strength of soil cement that has not solidified immediately after construction in a short period of time, in which a sample is collected from a predetermined location of the soil cement body, and the specific gravity, water content, and fine gravel content of the sample. , Sand content, clay + silt content, and cement content were measured, and as a multiple regression prediction formula showing the correlation between moisture, gravel content, sand content, clay + silt content, and cement content, and the strength of soil cement, If C / (Cl + Sd) ≦ 0.15, the following formula (1) is set to 0.1
When 5 <C / (Cl + Sd) ≦ 0.20, C / (Cl
+ Sd)> 0.20, and provides a method for predicting strength of soil cement by calculating and predicting solidification strength from each prediction formula. Equation (1) Y = in _{a 0 + (a 1 × W} ) + (a 2 × C) + (a 3 × Cl) + (a 4 × Sd) + (a 5 × R) ( wherein, Y is soil Predicted solidification strength of cement (kgf /
cm ² ), W is water content (kg / m ³ ), C is cement content (kg / m ³ ), Cl is clay content (kg / m ³ ), Sd is sand content (kg / m ³ ), and R is fine. The gravel content (kg / m ³ ) is shown. a _{0 to} a ₅ represent coefficients obtained by multiple regression analysis. ) Three types of prediction formulas according to the above C / (Cl + Sd) value of the present invention can be expressed as follows. Formula (2) Y = α ₀ + (α ₁ × W) + (α ₂ × C) + (α ₃ × Cl) + (α ₄ × Sd) + (α ₅ × R) Formula (3) Y = β ₀ + (β ₁ × W) + (β ₂ × C) + (β ₃ × Cl) + (β ₄ × Sd) + (β ₅ × R) Formula (4) Y = γ ₀ + (γ ₁ × W ) + (Γ ₂ × C) + (γ ₃ × Cl) + (γ ₄ × Sd) + (γ ₅ × R) (wherein W, C, Cl, Sd and R have the same meanings as described above). α _{0 to} α ₅ , β _{0 to} β ₅ , and γ _{0 to} γ ₅ are (i) C.
/(Cl+Sd)≦0.15, (ii) 0.15 <C /
(Cl + Sd) ≦ 0.20, (iii) C / (Cl + Sd)
> 0.20, in each case, shows a coefficient obtained by multiple regression analysis corresponding to the a ₀ ~a _5. )

The present invention will be described in more detail below. In the present invention soil cement refers to what is kneaded while injecting a predetermined amount of cement milk into in-situ soil,
It has a composition in which in-situ soil, cement, and an appropriate amount of supplementary materials are uniformly mixed. Soil cement is usually
It is formed as a columnar body. More specifically, when drilling the ground with a drilling kneader equipped with a drilling kneading mechanism, while injecting a hardening liquid suitable for the purpose from the tip, mixing with in-situ soil in the soil and drilling kneading And the soil cement columnar body is formed in situ. This soil cement columnar body is continuously formed to form a soil columnar wall. The type and conditions of the ground to which the method of the present invention can be applied are not particularly limited, and can be applied to all sites where the soil column wall construction method is implemented.

In the present invention, in order to predict the solidification strength, a sample is taken from an arbitrary position of the soil cement body immediately after the completion of drilling (before the hardening of the soil cement), and its specific gravity, water content, gravel content, sand content, clay Six factors are measured: min and cement. The solidification strength is predicted from the prediction formula showing the correlation between this result and the solidification strength of soil cement. In order to measure the above six factors, first, a sample is taken from a predetermined place where the strength of the soil cement body is to be judged. Examples of the method of collecting the sample include collecting the material that overflows from the excavation hole, attaching a sampling box to the core material, and collecting from the deep portion. First, the specific gravity of the sample is measured. On the other hand, after measuring the weight of a part of the collected sample, the moisture of the sample is evaporated and the dry weight is measured to calculate the weight of the moisture. The method of evaporating the water is not particularly limited, but a method of heating the sample using a microwave oven, a frying pan or the like can be easily carried out. To measure the weight of the sample, various weight measuring devices such as an electronic balance can be used. Alternatively, the moisture may be obtained by directly evaporating the moisture while measuring the weight using an infrared moisture meter. Then, the dried sample after water content measurement is crushed, a certain amount of water and acid are added and stirred, reacted, the amount of acid consumed is measured using an alkali, the type of cement,
Calculate the amount of cement using the amount of acid consumption that is known in advance by the brand. At this time, hydrochloric acid, sulfuric acid or the like can be used as the acid, and sodium hydroxide or the like can be used as the alkali. Alternatively, a method of calculating the cement weight by adding an acid to the dried sample to dissolve and remove the cement content, washing and drying, and measuring the weight of the residue can also be used. Also in this case, hydrochloric acid, sulfuric acid or the like can be used as the acid.

The remaining sample, whose weight was previously measured, was sieved by laying two kinds of sieves having different mesh sizes on top of each other and thoroughly washed with water. Dry by method and weigh fines and sand. The sieves are preferably 0.05 to 2 mm and 2 to 20 mm, and the residue of the sieve of 4.75 to 2 mm is fine pebbles, 2 to
The residue of the 0.074 mm sieve is sand. From the above results, the ratio of water, cement, fine gravel, and sand (% by weight) was calculated, and 1
The value obtained by subtracting the sum of these values from 00 is the proportion (wt%) of the clay content.

According to the present invention, it is possible to accurately predict the solidification strength of soil cement, but this is also a reference when adjusting the cement amount, injection amount, etc. to avoid construction errors in the next excavation work at the same site. You get the value you can.

[0009]

EXAMPLES Next, the present invention will be described in more detail based on examples. In the examples, the prediction formula was selected from the following formulas (5), (6) and (7) and used.

Formula (5) Y = −78.59 + (− 0.015 × W) + (− 0.037 × C) + (0.165 × Cl) + (0.135 × Sd) + (− 0.008 x R)

Formula (6) Y = −30.51 + (− 0.032 × W) + (0.041 × C) + (0.092 × Cl) + (0.068 × Sd) + (0. (001 x R)

Formula (7) Y = 24.45 + (− 0.070 × W) + (− 0.051 × C) + (0.080 × Cl) + (0.023 × Sd) + (0. 078 x R)

(Where Y is the predicted solidification strength (kgf / cm ² ) of soil cement, W is the water content (kg / m ³ ), C is the cement content (kg / m ³ ), and Cl is the clay content (kg / kg ³ ). m
³ ), Sd is sand content (kg / m ³ ), R is fine gravel content (kg / m ³ ).
m ³ ) is shown. When C / (Cl + Sd) ≦ 0.15, the above formula (5), 0.15 <C / (Cl + Sd) ≦ 0.2
When 0, the above formula (6), C / (Cl + Sd)> 0.2
When it is 0, the formula (7) is adopted. )

Example 1 At the site 1 where the soil column wall construction method was constructed using cement milk obtained by adding bentonite and ordinary Portland to water,
A sample of soil cement was analyzed by the following procedure, and a predicted solidification strength and an actually measured solidification strength were obtained. [Sample collection] Immediately after the completion of drilling (before hardening of soil cement) in the drilling work following the drilling, a sampling box was attached to the core material (H steel) and a sample was taken from a depth of 10 m. [Measurement of Specific Gravity] A dry measuring graduated cylinder having a stopper of 500 ml was placed on an electronic balance, and the indicated value of the balance was set to 0.00 (tare removal). Then turned about 100~200ml a soil cement in graduated cylinder (and S _a (g)). An appropriate amount of water was injected into the graduated cylinder, the stopper was closed, and the mixture was shaken to remove air in the cement milk. Further, the deposit on the inner wall of the graduated cylinder was washed with water, and the volume after washing with water (assumed to be V _a (ml)) and the weight (assumed to be W _a (g)) were read. The specific gravity was calculated by the following formula.

[0015]

[Equation 1]

[Measurement of Water Content] The collected sample is 4.75 mm.
After passing through a sieve of No. 2, the weight was measured with an electronic balance. This sample was dried to a constant weight in a microwave oven and weighed.
Drying was repeated several times in a short period of time to prevent scattering of the sample with a cloth or paper. The water content W _p (% by weight) was calculated from these weights.

[0017]

[Equation 2]

(In the formula, W _p represents water content (wt%), S _b represents sample weight (g), and S _b ′ represents sample dry weight (g).)

[Measurement of Cement Content] 10 to 20 g of a dried sample after water content measurement was crushed in a mortar, and this was placed in a beaker of about 3 g, and about 5 ml of water was added to form a slurry. To this, 5 ml of 5N hydrochloric acid was added, and the mixture was lightly shaken, allowed to stand for 5 to 10 minutes, and then diluted with distilled water to 75 to 100 ml.
The pH of this liquid was measured with a pH meter while stirring using a stirrer and a stirrer, and a 1N sodium hydroxide solution was dropped using a buret until the pH reached 4.0, and the dropping amount was measured. From this drop amount and the cement acid consumption for each type and brand of cement shown in Table 1, the cement content C _p
(Wt%) was calculated.

[0020]

[Table 1]

[0021]

(Equation 3)

(Where C _p is the cement content (% by weight), W
_p represents water content (% by weight), and A represents the amount of sodium hydroxide added dropwise (ml). (Because ordinary Portland type cement was used at this site, 25.59 is substituted for the cement acid consumption amount for calculation.)

[Measurement of fine gravel, sand, and clay content] 2 mm and 0.074 mm sieves are stacked on top of each other, and a mixture of a sample and water whose weight is measured in advance is further poured completely onto the sieve using water. after sufficient sieved with water, the residue of each of the sieve was collected and the dry weight was measured similarly to the measurement of water content by using a microwave oven, Hosotsubute component R _p (wt%) and sand fraction Sd _p (% by weight) was calculated.

[0024]

[Equation 4]

[0025]

(Equation 5)

(In the formula, R _p is fine gravel content (% by weight), Sd _p
Is the sand content (wt%), S _c is the weight of the sample (g), S _c ″ is the dry weight (g) of the residue of a 2 mm sieve, and S _c ″ is 0.0
Represents the dry weight (g) of the residue on a 74 mm sieve. ) The clay content Cl _p (% by weight) was calculated using clay as a component other than water, cement, fine gravel and sand. Cl _p = 100− (W _p + C _p + Sd _p + R _p ) (wherein Cl _p is clay content (wt%), W _p is water content (wt%), C _p is cement content (wt%), Sd _p Represents sand content (% by weight), and R _p represents fine gravel content (% by weight).)

The water content W _p (% by weight) thus obtained,
Cement content C _p (wt%), clay content Cl _p (wt%),
The sand content Sd _p (wt%) and the fine gravel content R _p (wt%) were multiplied by the value of the specific gravity × 10 obtained above to calculate the weight (kg) per 1 m ^{3 of} each component.

From the above results, the value of the ratio of the cement content to the sand content + the clay content (C / (Sd + Cl)) is 0.12. Therefore, the expected solidification strength was calculated using the above formula (5). . On the other hand, the above sample was filled in a vinyl chloride mold and cured to obtain a 5 × 10 cm specimen for strength measurement.
Further, the specimen was aged in a constant temperature water bath at 20 ° C. for 28 days, and then a compressive strength test was conducted to measure the solidification strength. Three test pieces were prepared, and the average of these solidification strengths was taken as the measured solidification strength.

Examples 2 to 6 Samples of soil cement were collected and analyzed in the same procedure as in Example 1 from the other sites 2 to 6 where the soil column wall construction method was applied. Table 2 shows the cement type, bentonite type, excavation type and sampling position used. The predicted solidification strength was calculated by selecting one of the above formulas (5) to (7) from the value of the ratio of the cement content to the sand content + the clay content (C / (Sd + Cl)) as the analysis result. On the other hand, the measured solidification strength of each sample was measured by the same method as in Example 1. The results of Examples 1 to 6 above are shown in Table 2.

[0030]

[Table 2]

From the comparison between the predicted solidification strength and the actually measured solidification strength in Table 2, it can be seen that according to the method of the present invention, the solidification strength after 28 days could be accurately predicted within the working day.

[0032]

As described above, according to the present invention, the cement content in the soil cement body immediately after construction can be confirmed, and at the same time, the solidification strength after 28 days of construction can be predicted by analyzing the soil cement. The reliability of soil column construction can be increased. That is, by appropriately adjusting the cement amount, the injection amount, etc. in the next excavation work at the same site with reference to the predicted solidification strength, it is possible to stably achieve the predetermined solidification strength and avoid construction errors. it can. Further, according to the method of the present invention, it is possible to save the labor of cutting out the specimen for measuring the solidification strength, which is required after the solidification, and to reduce the strength measurement cost.

Claims (1)

[Claims] 1. A method for predicting the strength of soil cement that determines the solidification strength of soil cement that has not yet solidified immediately after construction, in a short time, by collecting a sample from a predetermined location of the soil cement body, and measuring the specific gravity of the sample. Moisture, fine gravel, sand, clay + silt and cement are measured,
C / (Cl + Sd) ≦ 0.15 as the multiple regression equation prediction formula showing the correlation between the fine gravel content, sand content, clay + silt content, and cement content and the strength of soil cement.
In the case of 0.15 <C / (Cl + Sd) ≦ 0.20, and in the case of C / (Cl + Sd)> 0.20, the solidification strength is calculated from each prediction formula. Prediction method. Formula (1) Y = a ₀ + (a ₁ × W) + (a ₂ × C) + (a ₃ × C
l) + (a ₄ × Sd) + (a ₅ × R) (where Y is the predicted solidification strength of soil cement (kgf /
cm ² ), W is water content (kg / m ³ ), C is cement content (kg / m ³ ), Cl is clay + silt content (kg / m ³ ).
³ ), Sd is sand content (kg / m ³ ), R is fine gravel content (kg / m ³ ).
m ³ ) is shown. a _{0 to} a ₅ represent coefficients obtained by multiple regression analysis. )