Method for estimating the likelihood of occurrence of mixing defects due to co-rotation phenomenon in ground improvement

Abstract

To provide a method capable of estimating factors in occurence of mixing defect in ground improvement.SOLUTION: An agitation blade mechanism 1 is made to penetrate soil to be agitated as a sample with rotating, and then the agitation blade mechanism 1 is pulled out of the sample with rotating. A mass of the sample sticking to the agitation blade mechanism 1 pulled out of the sample (an object sticking soil) is measured. Then, factors of corotation phenomenon is estimated by using the measurement result of the mass of the sample.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for estimating the co-rotation phenomenon in the mechanical agitation method for ground improvement. Possibility of occurrence of mixing failure

Background Art

[0002] When performing ground improvement, one of the commonly used construction methods is the mechanical agitation method. This is a construction method in which a solidifying material and soil are agitated and mixed by rotating agitation blades in the ground, and a consolidated body is formed in the ground. One of the problems in this construction method is the co-rotation phenomenon. The co-rotation phenomenon is a phenomenon in which soil adheres to the agitation blades and the agitation blades and the soil rotate as a single body. As a result, poor mixing of the solidifying material and the soil may occur, and poor mixing may occur during ground improvement. Therefore, a method has been proposed for predicting in advance the possibility of occurrence of the co-rotation phenomenon at the blending test stage and suppressing the occurrence of the phenomenon (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, at present, although it is known that co-rotation is likely to occur in highly plastic mixing target soil and there is a high possibility of poor mixing, other occurrence conditions have not been clarified.

[0005] Therefore, an object of the present invention is to provide a method capable of estimating the co-rotation phenomenon. Possibility of occurrence of mixing failure

Means for Solving the Problems

[0006] The method for estimating the likelihood of occurrence of poor mixing due to the co-rotation phenomenon of the present invention is​​ A method for estimating the likelihood of occurrence of poor mixing in a mechanical agitation method for ground improvement, comprising: After penetrating the target soil as a sample while rotating the agitation blade mechanism, a step of pulling out the agitation blade mechanism from the sample while rotating it; Measuring the amount of adherent target soil on the agitation blade mechanism pulled out from the sample; Determine the correlation between the amount of adherent soil to the stirring vane mechanism withdrawn from the sample and the water content ratio or liquidity index of the target soil, and based on the correlation, from the range of the water content ratio or liquidity index at which the amount of adherent soil to the stirring vane mechanism withdrawn from the sample is equal to or greater than the threshold value And a step of estimating the likelihood.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4

Modes for Carrying Out the Invention

[0008] For the target soil with the water content ratio changed, penetration and extraction are performed while rotating the agitation blade mechanism, and by measuring the mass of the target soil (amount of adherent target soil) adhering to the agitation blade after extraction, Due to the co-rotation phenomenon Judge the likelihood of occurrence of poor mixing.

[0009] For example, as shown in FIG. 1, the stirring blade mechanism 1 includes a substantially prismatic column 10 and a pair of stirring blades 12 that are attached to opposite side surfaces of the column 10 at an inclination to the horizontal plane. The column 10 is configured to be rotatable about its axis by an actuator such as an electric motor. As shown in FIG. 1, three pairs of stirring blades 12 are arranged at intervals in the axial direction (vertical direction) of the column 10, and the pairs of stirring blades 12 are attached to the column 10 with their phases shifted by 90° from each other in a top view in the order along the axial direction.

[0010] Kaolin, in-situ target soil, and a mixed target soil in which dry kaolin and in-situ target soil with natural water content ratio were mixed at a mass ratio of 1:1 were used as samples. Table 1 shows the soil properties of each sample.

[0011]

Table 1

[0012] The penetration experiment was carried out by penetrating the stirring blade mechanism 1 into the target soil placed in a bucket while rotating it about its axis.

[0013] After 1 minute, while rotating the stirring blade mechanism 1 about its axis, it was pulled out in the axial direction, and the target soil attached to the stirring blade 12 (and the column 10) was removed, and the mass of the target soil was measured. Experiments were carried out when the rotational speed of the stirring blade mechanism 1 was adjusted to 20 rpm and 40 rpm respectively. The penetration speed and the pulling-out speed of the stirring blade mechanism 1 were controlled to 10 cm / min.

[0014] For the liquid drop test, for the sample after agitation, an experiment was conducted in the same procedure as the liquid limit test (JIS A 1205), and the number of drops was measured when the groove of the target soil closed by about 1.5 cm. Note that this liquid limit test may also be in accordance with "Method for Liquid Limit Test of Soil Using a Fall Cone (Soil Mechanics Society Standard JGS 0142-2009)".

[0015] The vane test (Soil Mechanics Society Standard JGS1411-2012) was carried out with the vane penetrating into the bucket after agitation of the sample.

[0016] Fig. 2A shows the relationship between the water content ratio of each sample and the amount of target soil adhering when the rotational speed of the agitation blade mechanism 1 is controlled at 20 rpm. Fig. 2B shows the relationship between the water content ratio of each sample and the amount of target soil adhering when the rotational speed of the agitation blade mechanism 1 is controlled at 40 rpm. From Fig. 2A and Fig. 2B, it can be seen that at a certain water content ratio, the amount of target soil adhering shows a maximum value, and thus, there is a water content ratio for each sample at which the target soil is most likely to adhere, that is, the co-rotation phenomenon is likely to occur.

[0017] For example, based on the correlation between the mass of the target soil adhering to the agitation blade mechanism 1 pulled out from the sample, as shown in Fig. 2A and Fig. 2B, and the water content ratio of the target soil, the range of the water content ratio at which the mass becomes equal to or greater than the threshold value is estimated as a factor of the co-rotation phenomenon. As the threshold value, a value of 0.85 times the maximum value of the mass of the target soil adhering to the agitation blade mechanism 1 pulled out from the sample may be used.

[0018] Furthermore, it can be seen that the water content ratio showing the maximum amount of target soil adhering is close to the liquid limit shown in Table 1. Therefore, in order to consider the correlation between the water content ratio of the target soil and the liquid limit, the natural water content w, the plastic limit w p and the liquid limit w L are used to adopt the liquidity index I L represented by the relational expression (1).

[0019] I L =(w - w p ) / (w L - w P )...(1).

[0020] Figure 3A shows the liquidity index I of each sample when the rotational speed of the stirring vane mechanism 1 is controlled to 20 rpm L and the relationship with the amount of soil to be adhered. Figure 3B shows the liquidity index I of each sample when the rotational speed of the stirring vane mechanism 1 is controlled to 40 rpm L and the relationship with the amount of soil to be adhered. From Figures 3A and 3B, it can be seen that for each sample, the amount of soil to be adhered shows the maximum value when the liquidity index I L is around 1.0.

[0021] For example, based on the correlation between the mass of the target soil adhering to the stirring vane mechanism 1 pulled out from the sample, as shown in Figures 3A and 3B, and the liquidity index I L of the target soil, the range of water content ratio at which the mass becomes equal to or greater than the threshold value is estimated as a factor of the co-rotation phenomenon. As the threshold value, a value 0.85 times the maximum value of the mass of the target soil adhering to the stirring vane mechanism 1 pulled out from the sample may be used.

[0022] Also, based on the empirical finding that the co-rotation phenomenon is likely to occur in highly plastic target soil, Figure 4 shows the correlation between the plasticity index of the sample and the maximum value of the amount of target soil to be adhered to the sample. From Figure 4, it can be seen that the larger the plasticity index, the proportionally greater the maximum amount of target soil to be adhered.

[0023] The fact that the plasticity index of the target soil is large means that the amount of adhesion of the target soil to the stirring vane mechanism 1 is large. Therefore, there is a high possibility that the target soil adheres to the stirring vane mechanism 1 and causes co-rotation, which in turn causes poor mixing. Thus, by measuring the plasticity index of the target soil, the mass of the target soil adhering to the stirring vane mechanism 1 can be estimated, and thereby the possibility of the co-rotation phenomenon occurring, and in turn the possibility of poor mixing occurring, can be estimated.

[0024] (Other Embodiments of the Present Invention) In the above embodiment, the mixed target soil mixed with the cement-based solidifying material is used as a sample, and the mass of the mixed target soil adhering to the stirring vane mechanism 1 pulled out from the sample is used for the co-rotation phenomenonPossibility may be estimated. Similar to the above embodiment, based on the correlation between the mass of the soil to be mixed adhering to the stirring blade mechanism 1 and the water content ratio of the soil to be mixed, the Possibility may be estimated (see FIGS. 2A and 2B). Similar to the above embodiment, based on the correlation between the mass of the soil to be mixed adhering to the stirring blade mechanism 1 and the liquidity index of the soil to be mixed, the Possibility may be estimated (see FIGS. 3A and 3B).

[0025] In addition to the mass of the soil to be mixed adhering to the stirring blade mechanism 1 extracted from the sample, based on the elapsed time since the cementitious solidifying material was mixed into the soil Possibility of co-rotation phenomenon may be estimated.

Explanation of Signs

[0026] 1... Stirring blade mechanism, 10... Support column, 12... Stirring blade.

Claims

1. A method for estimating the likelihood of occurrence of poor mixing due to co-rotation phenomenon in a mechanical agitation method for ground improvement, comprising: a step of inserting a stirring blade mechanism into a target soil as a sample while rotating the stirring blade mechanism, and then pulling out the stirring blade mechanism from the sample while rotating the stirring blade mechanism; measuring the amount of target soil adhering to the stirring blade mechanism pulled out from the sample, determining the correlation between the amount of target soil adhering to the stirring blade mechanism pulled out from the sample and the water content ratio or liquidity index of the target soil, and estimating the likelihood of occurrence of poor mixing based on the correlation from the range of the water content ratio or liquidity index at which the amount of target soil adhering to the stirring blade mechanism pulled out from the sample is equal to or greater than a threshold value.

2. The method according to claim 1, wherein a method for estimating the likelihood of occurrence of poor mixing using soil containing a cement-based solidifying material as the target soil.

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