Method for evaluating the constructability of ground improvement materials, method for constructing sand piles, and method for manufacturing ground improvement materials.

Abstract

This invention provides a method for evaluating the workability of ground improvement materials, a method for constructing sand piles, and a method for manufacturing ground improvement materials, which allow for the evaluation of the workability of ground improvement materials for each moisture content condition from the initial moisture content to the saturated moisture content, before the actual construction of sand piles. [Solution] A method for evaluating the workability of a ground improvement material, comprising: a mixing step (step S2); a discharge status observation step (step S3); a discharge status determination step (step S4); a water addition step (step S6); and a workability determination step (step S7) in which workability is determined based on the determination results of the discharge status under multiple water content conditions obtained by repeating the mixing step (step S2), the discharge status observation step (step S3), the discharge status determination step (step S4), and the water addition step (step S6).

Description

[Technical Field]

[0001] This invention relates to a method for evaluating the constructability of ground improvement materials, a method for constructing sand piles, and a method for manufacturing ground improvement materials. [Background technology]

[0002] The sand compaction pile method is a well-known method for constructing sand piles to improve the strength of soft ground. In the sand compaction pile method, a casing pipe is driven into the soft ground, and ground improvement materials such as sand, gravel, or slag are placed inside the casing pipe. The casing pipe is then vibrated, and the process of pulling out and driving the casing pipe back in is repeated, thereby introducing the ground improvement material into the soft ground from the casing pipe and forcibly constructing piles of ground improvement material into the soft ground. By constructing multiple such piles in the soft ground, the relative density of the entire soft ground is increased, compacting it and improving its strength.

[0003] In the sand compaction pile method, ground improvement material is introduced into the soft ground via a casing pipe. Therefore, depending on the physical properties of the ground improvement material, the casing pipe may become clogged with the material, potentially worsening the constructability of the sand piles. The physical properties mentioned above include particle size distribution. If the ground improvement material contains many small particles, clogging of the casing pipe is likely to occur. Constructability refers to how easy it is to install the sand piles. Worsened constructability means that the casing pipe becomes clogged with the ground improvement material, making it difficult to install the sand piles. The physical properties of the sand and gravel used in the sand compaction pile method vary depending on the location from which the sand and gravel are extracted. In addition, the physical properties of the slag vary depending on the manufacturing method of the slag.

[0004] Methods to suppress clogging of ground improvement materials in casing pipes have been studied conventionally. For example, Patent Document 1 describes a method in which a sliding material is attached to the inner wall of a casing pipe used in the sand compaction pile method. It is stated that this improves the sliding of sand and gravel inside the casing pipe, thereby suppressing clogging of ground improvement materials in the casing pipe.

[0005] Patent Document 2 describes a material for slag compaction pile construction, which is a mixture of blast furnace granulated slag and steelmaking slag. It states that this method can suppress clogging of the ground improvement material in the casing pipe, and can improve the seismic resistance of the ground after construction while maintaining the constructability of the sand piles. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-1845 [Patent Document 2] Japanese Patent Publication No. 2019-167784 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As mentioned above, the physical properties of the sand and gravel used in the sand compaction pile method vary depending on the location where the sand and gravel are extracted. Depending on the physical properties of the sand and gravel, even if the casing pipe described in Patent Document 1 is used, there is a possibility that the ground improvement material may clog the casing pipe. Therefore, it is preferable to determine the workability of the ground improvement material before actually constructing the sand piles. However, there is currently no established method for evaluating the workability of ground improvement materials. This situation is also true when using the slag compaction pile method materials described in Patent Document 2.

[0008] The present invention was made to solve the above problems, and aims to provide a method for evaluating the workability of a ground improvement material, a method for constructing a sand pile, and a method for manufacturing a ground improvement material, which can evaluate the workability of a sand pile by evaluating the fluidity of the ground improvement material for each moisture content condition from the initial moisture content to the saturated moisture content before actually constructing the sand pile. [Means for solving the problem]

[0009] The means to solve the above problems are as follows: [1] A method for evaluating the workability of a ground improvement material, comprising: a mixing step of mixing the ground improvement material; a discharge status observation step of observing the discharge status when the mixed ground improvement material is put into a hopper and compacted, and then discharged from the hopper; a discharge status determination step of determining whether the discharge status is good or bad based on the observed discharge status; a water addition step of adding water to the ground improvement material discharged from the hopper and returning it to the mixing step; and a workability determination step of determining the workability of the ground improvement material, wherein the workability determination step determines the workability based on the determination results of the discharge status at a plurality of water content conditions obtained by repeating the mixing step, the discharge status observation step, the discharge status determination step, and the water addition step. [2] The method for evaluating the workability of a ground improvement material according to [1], wherein the plurality of moisture content conditions include a moisture content condition in which the moisture content of the ground improvement material is the initial moisture content and a moisture content condition in which the moisture content of the ground improvement material is the saturation moisture content, and in the workability determination step, it is determined that the workability is good if the discharge condition is satisfactory in all of the plurality of moisture content conditions. [3] The method for evaluating the workability of a ground improvement material according to [1] or [2], wherein the discharge status observation step involves observing the discharge rate when the ground improvement material is discharged from the hopper as the discharge status, and the discharge status determination step determines that the discharge status is acceptable when the discharge rate when the ground improvement material is discharged from the hopper is equal to or greater than a threshold. [4] The method for evaluating the workability of a ground improvement material as described in [3], wherein the threshold for the discharge speed is 0.4 m / sec or more and 0.5 m / sec or less. [5] A method for evaluating the workability of a ground improvement material according to any one of [1] to [4], wherein if the discharge condition is determined to be unacceptable in the discharge condition determination step, the water addition step, the mixing step, and the discharge condition observation step are repeated. [6] A method for evaluating the workability of a ground improvement material according to any one of [1] to [5], further comprising a moisture content confirmation step of determining whether the moisture content of the ground improvement material is the saturation moisture content, wherein the water addition step is discontinued if it is determined in the moisture content confirmation step that the moisture content of the ground improvement material is the saturation moisture content. A method for constructing sand piles, wherein, in the workability determination step of the method for evaluating the workability of a ground improvement material described in any of [7], [1] to [6], the sand piles are constructed using a ground improvement material that has been determined to have good workability. A method for manufacturing ground improvement materials, comprising the step of obtaining ground improvement materials whose workability has been determined to be satisfactory in the workability determination step of the method for evaluating the workability of ground improvement materials described in any of [8] [1] to [6]. [Effects of the Invention]

[0010] According to the present invention, the ease of construction can be evaluated before the sand piles are actually installed. [Brief explanation of the drawing]

[0011] [Figure 1] This figure illustrates a ground improvement material constructability evaluation device to which the constructability evaluation method for ground improvement materials according to this embodiment can be applied. [Figure 2] This is a flowchart illustrating the method for evaluating the constructability of the ground improvement material according to this embodiment. [Figure 3] This is another flowchart illustrating the method for evaluating the constructability of the ground improvement material according to this embodiment. [Figure 4] This figure shows the evaluation results of the material according to the workability evaluation method for ground improvement materials according to this embodiment.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described. The present embodiments show a preferred example of the present invention and are not limited by the present embodiments in any way.

[0013] The method for evaluating the workability of a ground improvement material according to the present embodiment is a method for evaluating the quality of the workability of a ground improvement material used for improving soft ground at a point before actual construction. Examples of the method for improving soft ground using a ground improvement material include, for example, a method of constructing a plurality of piles made of firmly compacted ground improvement materials in soft ground to increase the strength of the soft ground. That is, examples of the method for improving soft ground include the sand compaction pile method that mainly uses mountain sand, gravel, or steel slag as the ground improvement material. Examples of steel slag include blast furnace granulated slag, blast furnace slowly cooled slag, steelmaking slag, or electric furnace slag.

[0014] (Apparatus for Evaluating Workability of Ground Improvement Material) FIG. 1 is a diagram for explaining an apparatus for evaluating the workability of a ground improvement material to which the method for evaluating the workability of a ground improvement material according to the present embodiment can be applied. The workability evaluation apparatus 1 shown in FIG. 1 has a mixer 2 and a hopper 3. The mixer 2 performs kneading so that the water content state of the ground improvement material is uniform without bias throughout the ground improvement material. In the example shown in FIG. 1, the mixer 2 is rotated by an actuator (not shown) to knead the ground improvement material and moisture.

[0015] Hopper 3 is used to measure the discharge rate of the ground improvement material mixed by mixer 2. In the sand compaction pile method, the ground improvement material is discharged from the casing pipe into the soft ground, and piles are constructed using the discharged material. The ease of discharge of the ground improvement material from the casing pipe, that is, the fluidity of the ground improvement material, is one of the important factors for reliably constructing piles in soft ground. Therefore, the discharge rate of the ground improvement material from hopper 3 is measured as an indicator of the fluidity of the ground improvement material. The method for measuring the discharge rate of the ground improvement material will be described later.

[0016] The hopper 3 may be funnel-shaped or cylindrical with an opening at the bottom that can be opened and closed vertically. The internal volume of the hopper 3 is 0.2 m³. 3 It is preferable that the above is true. Also, the opening area of ​​the opening is 0.030 m². 2 It is preferable that the above conditions are met. This is to ensure that the opening area of ​​the opening is 5% or more of the opening area of ​​the casing pipe used in the sand compaction pile method. By doing so, it is possible to suppress the discrepancy between the evaluation conditions of the workability evaluation method for the ground improvement material according to this embodiment and the actual construction conditions in the sand compaction pile method, thereby improving the accuracy of the evaluation of the workability of the ground improvement material. It is even more preferable that the opening area of ​​the opening of the hopper 3 is 10% or more of the opening area of ​​the casing pipe. Furthermore, it is preferable that the inner diameter of the hopper 3 and the cone angle of the hopper 3 be set so that the flow of the ground improvement material when it is discharged from the opening of the hopper 3 becomes a mass flow.

[0017] The physical properties of mountain sand and gravel used as ground improvement materials vary depending on the source, such as particle size distribution. Steel slag can be classified into blast furnace granulated slag, blast furnace slow-cooled slag, steelmaking slag, and electric furnace slag depending on the manufacturing method. Furthermore, the physical properties differ for each type of slag. The ground improvement materials are stored, for example, in a raw material yard (not shown) located outdoors, separated by particle size or type. These ground improvement materials may be exposed to rain. The initial moisture content of the ground improvement material collected from the raw material yard and used for the constructability evaluation in this embodiment is preferably about 5% or less. The moisture content is expressed as the ratio of the water content of the ground improvement material before drying to the mass of the ground improvement material after drying, with the mass of the ground improvement material after drying being set to 100.

[0018] (Method for evaluating the constructability of ground improvement materials) Figure 2 is a flowchart illustrating the method for evaluating the constructability of the ground improvement material according to this embodiment. The method for evaluating the constructability of the ground improvement material shown in the flowchart in Figure 2 is performed when evaluating the constructability of the ground improvement material. Alternatively, the method for evaluating the constructability of the ground improvement material described above is performed as one of several steps included in the manufacturing method of the ground improvement material.

[0019] In this constructability evaluation method, first, a predetermined amount of ground improvement material stored in the raw material yard is sampled (Step S1, sampling process). Under normal construction conditions, the moisture content may increase during the construction of sand piles, but it rarely decreases. Therefore, normally, the moisture content at the time of sampling of the ground improvement material can be used as the initial moisture content, and the evaluation using the constructability evaluation method of the ground improvement material according to this embodiment can be performed. If it is desired to evaluate constructability including moisture content conditions lower than the moisture content at the time of sampling from the raw material yard, the initial moisture content of the ground improvement material may be adjusted by dewatering or drying before evaluation.

[0020] As described above, the method for evaluating the workability of ground improvement materials according to this embodiment allows for the evaluation of the workability of sand piles even if the absolute value of the moisture content is unknown. Therefore, it is not always necessary to measure the initial moisture content of the ground improvement material. On the other hand, if it is desired to obtain the moisture content value at the time of the workability evaluation, the ground improvement material can be dried in a dryer before the start of the evaluation, and the initial moisture content value can be calculated from the mass before and after drying. Once the initial moisture content is calculated, the moisture content value at each moisture content condition can be calculated from the amount of water added in the water addition process (step S6) described later.

[0021] Next, the collected ground improvement material is put into mixer 2 and mixed (step S2, mixing process). The rotation speed of mixer 2 and the mixing time when mixing the ground improvement material may be 24 rpm and 30 seconds.

[0022] The ground improvement material mixed in mixer 2 is fed into hopper 3, and the discharge status of the ground improvement material when it is discharged from hopper 3 is observed (step S3, discharge status observation process). Specifically in step S3, the ground improvement material mixed in mixer 2 is fed into hopper 3 in multiple batches while being compacted. This is to match the actual construction conditions. In the sand compaction pile method, the ground improvement material is fed into the inside of a casing pipe driven into soft ground. This is because the ground improvement material located below the casing pipe in the vertical direction is pressed and compacted by a load corresponding to the mass of the ground improvement material located above it.

[0023] For example, every time 100 kg of ground improvement material is added to hopper 3, a weight with a diameter of 85 mm and a weight of 5 kg is dropped onto the surface of the ground improvement material in hopper 3 from a height of 300 mm to compact it. This is done over the entire surface of the ground improvement material in hopper 3. Then, another 100 kg of ground improvement material is added on top of the compacted ground improvement material and compacted in the same way. This process of adding ground improvement material to hopper 3 and compacting it is repeated. In this embodiment, this is done until the total amount of ground improvement material in hopper 3 reaches 300 kg.

[0024] After compacting the ground improvement material, the bulk volume (m 3 ) of the ground improvement material in the hopper 3 is calculated. The internal volume (m 3 ) of the hopper 3 is determined by design. Therefore, for example, by subtracting the headspace (m 3 ) of the hopper 3 after charging the ground improvement material into the hopper 3 from the internal volume (m 3 ) of the hopper 3, the bulk volume (m 3 ) of the ground improvement material in the hopper 3 can be obtained.

[0025] After that, an opening (not shown) of the hopper 3 is opened to discharge the ground improvement material from the hopper 3, and the discharge situation is observed. It is observed whether the entire amount of the ground improvement material is discharged smoothly from the hopper 3. The observation starts simultaneously with the opening of the opening (not shown) of the hopper 3. Also, the above-mentioned observation is carried out by an operator.

[0026] Specifically, simultaneously with the opening of the opening (not shown) of the hopper 3, the time measurement by a timer (not shown) is started, and when the discharge of the entire amount of the ground improvement material is completed, the time measurement by the timer is terminated. Thus, the time (sec) from the start of the discharge of the ground improvement material to the completion of the discharge of the entire amount of the ground improvement material is measured by the timer. The start and end of the time measurement by the timer may be performed by an operator. Alternatively, the timer may be configured to operate in conjunction with the opening and closing of the opening of the hopper 3, and the time measurement may be automatically performed according to the opening and closing of the opening of the hopper 3. After the completion of the discharge of the ground improvement material from the hopper 3, the discharge rate (m / sec) is calculated by dividing the time (sec) measured by the timer and the bulk volume (m 2 ) of the ground improvement material in the hopper 3 by the opening area (m 3 ) of the opening of the hopper 3. Note that the above-mentioned discharge rate corresponds to the discharge situation of the present embodiment. In the case where clogging occurs during the discharge and the ground improvement material remains in the hopper, the discharge rate shall be 0 m / sec.

[0027] Next, the discharge rate calculated in step S3 is compared with a threshold to determine the quality of the discharge, that is, the quality of the fluidity of the ground improvement material (step S4, discharge condition determination step). Here, good fluidity of the ground improvement material means that when sand piles are actually constructed under those moisture content conditions, the entire amount of ground improvement material can be discharged smoothly from the casing pipe without clogging. The threshold mentioned above is the lower limit of the discharge rate at which the ground improvement material can be discharged from the casing pipe and sand piles can be constructed without clogging the casing pipe. Preferably, this threshold is 0.4 m / sec or more and 0.5 m / sec or less. If the discharge rate is less than 0.4 m / sec, there is a possibility that clogging will occur in the casing pipe during actual construction.

[0028] If the discharge rate is below the threshold (No in step S4), it is determined at this point that the final evaluation of workability in the subsequent workability evaluation process (step S7) will fail, so it is not necessary to observe any further moisture content conditions. In this case, the repetition of the mixing process in step S2, the discharge status observation process in step S3, and the water addition process in step S6 is terminated. In this case, the fluidity of the ground improvement material is determined to be poor at least one of the moisture content conditions from the initial moisture content to the saturated moisture content in the discharge status observation process (step S3). Therefore, the workability of the ground improvement material is determined to be unsatisfactory (step S7, workability evaluation process), and the workability evaluation of the ground improvement material is terminated.

[0029] In contrast, if the discharge rate is above a threshold (Yes in step S4), it is determined whether the water content of the ground improvement material is at or above the saturation water content (step S5, water content confirmation step). The saturation water content refers to the upper limit of the water content that the ground improvement material can hold. If the water content of the ground improvement material is below the saturation water content, all the water contained in the ground improvement material is retained within the material. On the other hand, if the water content of the ground improvement material is above the saturation water content, the water exceeding the saturation water content (sometimes referred to as excess water) drips from the ground improvement material. Therefore, whether or not the water content of the ground improvement material has reached the saturation water content can be confirmed by visually observing the dripping state of excess water from the ground improvement material. In this evaluation method, the evaluation is repeated while gradually adding water, but the conditions under which water first drips in the water content confirmation step (step S5) are defined as the saturation water content conditions. Note that the method for confirming whether or not the saturation water content has been reached is not limited to observing the dripping of excess water. For example, one could determine the void ratio and initial moisture content of the ground improvement material in advance, and then confirm that the saturation moisture content has been reached when the amount of water added during the water addition process fills the voids in the ground improvement material.

[0030] The moisture content confirmation step (step S5) can be performed by checking the water dripping from the hopper opening when the ground improvement material is loaded into the hopper 3 during the discharge status observation step (step S3). The timing of the moisture content confirmation step (step S5) is not limited to when the hopper is filled during the discharge status observation step (step S3), but may also be performed after the mixing step (step S2).

[0031] In the moisture content confirmation step, if the moisture content of the ground improvement material is below the saturation moisture content (No in step S5), water is added to the ground improvement material and the process is returned to the mixing step in step S2 (step S6, water addition step). The amount of water added to the ground improvement material in step S6 may be, for example, about 1.0 to 3.0 mass% of the mass of the ground improvement material at the initial moisture content. After that, the process is returned to step S2 and the added water and ground improvement material are mixed. Then, the process from steps S2 to S6 is repeated until it is determined to be repeated in step S4 or S5 as described above. This is because the fluidity of the ground improvement material changes as the moisture content in the ground improvement material increases from the initial moisture content. Therefore, by observing the fluidity of the ground improvement material for all moisture content conditions from the initial moisture content to the saturation moisture content, it is possible to accurately evaluate the workability of sand piles even in construction environments where the moisture content increases during construction.

[0032] In the moisture content confirmation step (step S5), if the moisture content of the ground improvement material reaches the saturation moisture content (Yes in step S5), further water addition will not reduce its fluidity. Therefore, the water addition step in step S6 is stopped and the repetition is terminated. In this case, the fluidity of the ground improvement material is judged to be good under all moisture content conditions from the initial moisture content to the saturation moisture content in the discharge status observation step (step S3). Therefore, the workability of the ground improvement material is judged to be acceptable (step S7, workability judgment step), and the workability evaluation of the ground improvement material is terminated.

[0033] According to this embodiment, the water addition process (step S6), mixing process (step S2), discharge status observation process (step S3), discharge status determination process (step S4), and water content confirmation process (step S5) are repeatedly performed until the water content of the ground improvement material changes from the initial water content to the saturation water content. For all of the multiple water content conditions obtained in this way, the ground improvement material whose discharge rate is above a threshold is evaluated as having good workability. Therefore, ground improvement material evaluated as satisfactory by the workability evaluation method of ground improvement material according to this embodiment has good workability regardless of the water content of the ground improvement material and is less likely to clog the casing pipe. Therefore, even in construction environments where it is difficult to adjust the water content of the ground improvement material, sand piles can be constructed in soft ground without clogging the casing pipe. An example of a construction environment where it is difficult to adjust the water content of the ground improvement material is the construction environment of the offshore sand compaction pile method, which constructs sand piles in soft ground on the seabed from the sea.

[0034] It should be noted that the present invention is not limited to the embodiments described above. In the embodiments described above, the discharge rate is compared with a threshold, and if the discharge rate is less than the threshold (No in step S4), the repetition of the water addition process, mixing process, discharge status observation process, etc. is terminated, and it is determined that the workability of the ground improvement material is unacceptable. However, instead, the discharge rate may be measured for all of the multiple moisture content conditions from the initial moisture content to the saturated moisture content of the ground improvement material, and the discharge rate at all moisture content conditions may be compared with a threshold to determine whether the discharge status of the ground improvement material is good or bad. After that, the workability of the ground improvement material may be determined based on the determination results of the discharge rate at all moisture content conditions.

[0035] The flowchart in Figure 3 illustrates an example. In the flowchart shown in Figure 3, the discharge rate is measured (step S3), and then the discharge rate is compared with a threshold to determine the quality of the discharge, that is, the quality of the fluidity of the ground improvement material (step S8, discharge condition determination step). Then, the water addition step (step S6), mixing step (step S2), discharge rate measurement step (step S3), discharge condition determination (step S8), and moisture content confirmation step (step S5) are repeated until excess moisture is confirmed from the ground improvement material. In this way, the discharge rate is measured for all of the multiple moisture content conditions from the initial moisture content to the saturated moisture content of the ground improvement material. Then, in the workability determination step (step S7), the workability of the ground improvement material is determined based on the results of the discharge rate determination for each moisture content condition. Thus, even in the example shown in the flowchart in Figure 3, the workability of the ground improvement material can be evaluated in the same way as in the embodiment described above. In the example shown in the flowchart in Figure 3, steps S3 and S8 described above correspond to the emission status monitoring process for monitoring the emission status in this embodiment.

[0036] In this embodiment, the discharge speed is used as an indicator of the discharge status, but the indicator of the discharge status is not limited to the discharge speed. For example, the indicator of the discharge status may be whether or not hopper clogging occurs, and in the discharge status determination process (steps S4, S8), if hopper clogging does not occur and the entire amount can be discharged, it may be determined that the fluidity is good, and if the entire amount cannot be discharged and some remains in the hopper, it may be determined that the fluidity is poor.

[0037] The construction process for sand piles incorporates an evaluation step for ground improvement materials using the method for evaluating the constructability of ground improvement materials according to this embodiment. By using ground improvement materials that have been judged to have satisfactory constructability, problems such as clogging of casing pipes during construction can be suppressed.

[0038] Furthermore, the manufacturing process for producing ground improvement materials will incorporate an evaluation process for ground improvement materials based on the workability evaluation method for ground improvement materials according to this embodiment. By acquiring only ground improvement materials that have been judged to have acceptable workability and using them as products, it will be possible to manufacture ground improvement materials that do not cause casing pipe clogging. [Examples]

[0039] This section describes examples of actions taken to confirm the function and effects of the present invention. In these examples, the workability of four types of ground improvement materials with different steelmaking slag compositions was evaluated using a ground improvement material workability evaluation device configured similarly to the ground improvement material workability evaluation device 1 shown in Figure 1.

[0040] (Example of Invention 1) In Invention Example 1, the first type of ground improvement material was used. In the mixing process, the material was mixed in a mixer at 24 rpm for 30 seconds. The internal volume was 0.2 m³. 3 The opening area of ​​the opening is 0.045 m². 2 A hopper was prepared, and a total of 300 kg of the ground improvement material of Invention Example 1 was poured into it. For every 100 kg of ground improvement material poured into the hopper, a weight with a diameter of 85 mm and a weight of 5 kg was dropped onto the ground improvement material from a height of 300 mm to compact it. After that, the opening of the hopper was opened, and the discharge rate of the ground improvement material as it was discharged from the opening was measured using a timer. The measurement of the discharge rate and the addition of water to the ground improvement material were repeated until the water content of the ground improvement material reached the saturation water content. In other words, the workability of the ground improvement material of Invention Example 1 was evaluated in accordance with the workability evaluation method shown in the flowchart in Figure 2. When water was added to the ground improvement material, water was added to the extent that the water content increased by 2.5%. In the water content confirmation step, it was visually confirmed whether or not water was dripping from the opening at the bottom of the hopper. In addition, in this invention example, the initial water content was also measured, and the water content value was obtained.

[0041] (Example of Invention 2) Invention Example 2 is an example in which the constructability of a second type of ground improvement material was evaluated in the same manner as in Invention Example 1.

[0042] (Example of Invention 3) Invention Example 3 is an example in which the constructability of a third type of ground improvement material was evaluated in the same manner as in Invention Example 1.

[0043] (Example of Invention 4) Invention Example 4 is an example in which the constructability of a fourth type of ground improvement material was evaluated in the same manner as in Invention Example 2.

[0044] (evaluation) Figure 3 summarizes the measurement results of the discharge speed of each ground improvement material for Invention Examples 1 to 4. In cases where the hopper became clogged during measurement and the entire amount of ground improvement material was not discharged, the discharge speed was set to 0 m / sec. The threshold for discharge speed was set to 0.4 m / sec. For Invention Examples 1 and 2, as shown in Figure 3, the discharge speed never fell below the threshold regardless of the water content. For Invention Examples 1 and 2, the fluidity was judged to be good at all water content levels, and the workability evaluation was satisfactory. In contrast, for Invention Examples 3 and 4, the discharge speed fell below the threshold during the process of increasing the water content, that is, before the water content of the ground improvement material reached the saturation water content. For Invention Examples 3 and 4, the fluidity was judged to be poor at some water content levels, and the workability evaluation was unsuccessful. [Examples]

[0045] Example 2 describes an example in which a ground improvement material was manufactured. A ground improvement material was manufactured by crushing and magnetically separating slag raw materials, mainly steelmaking slag generated at a steel mill. When the ground improvement material was evaluated using the workability evaluation method for ground improvement materials according to this embodiment, the result was the same as in Invention Example 3, and it failed to meet the workability requirements. Therefore, the steelmaking slag mixture was changed and the ground improvement material was manufactured again and evaluated using the workability evaluation method for ground improvement materials according to this embodiment. As a result, the result was the same as in Invention Example 1, and it passed the workability requirements. The ground improvement material that passed the workability requirements was shipped as a product. [Examples]

[0046] In Example 3, the ground improvement materials from Invention Examples 1 to 4 were used as raw materials for sand piles, and a demonstration experiment was conducted to construct sand piles in soft ground on the seabed using the offshore sand compaction pile method. The opening area was 0.470 m². 2 Aside from the use of casing pipes, sand piles were constructed in the soft ground of the seabed in accordance with conventionally known offshore sand compaction pile construction methods. The presence or absence of clogging of the casing pipes was confirmed by the change in the level of the ground improvement material when the casing pipes were lifted with the ground improvement material packed inside them.

[0047] (evaluation) In Invention Examples 1 and 2, which passed the workability evaluation in Example 1, no clogging of the ground improvement material occurred in the casing pipe. In contrast, in Invention Examples 3 and 4, which failed the workability evaluation in Example 1, clogging of the ground improvement material occurred in the casing pipe. From these results, it was confirmed that clogging of the ground improvement material in the casing pipe can be suppressed during actual construction by using ground improvement material that has been judged to pass the workability evaluation method of the ground improvement material according to this embodiment. In other words, the usefulness of the workability evaluation method of the ground improvement material according to this embodiment was confirmed. [Explanation of symbols]

[0048] 1. Workability evaluation device 2 Mixer 3 Hopper S1 Collection process S2 Kneading process S3 Emission Status Observation Process S4, S8 Emission status determination process S5 Moisture content confirmation process S6 Water addition process S7 Workability judgment process

Claims

1. A method for evaluating the constructability of ground improvement materials, The mixing process involves mixing the ground improvement material, A discharge status observation step involves placing the mixed ground improvement material into a hopper and compacting it, and then observing the discharge status when the ground improvement material is discharged from the hopper. A discharge status determination step that determines whether the discharge status is good or bad based on the observed discharge status, A watering step is to add water to the ground improvement material discharged from the hopper and return it to the mixing step, The process includes a workability determination step for determining the workability of the ground improvement material, The workability evaluation method for a ground improvement material is a method in which the workability evaluation step determines the workability based on the results of the discharge status evaluation at multiple water content conditions obtained by repeating the mixing step, the discharge status observation step, the discharge status evaluation step, and the water addition step.

2. The aforementioned plurality of moisture content conditions include a moisture content condition in which the moisture content of the ground improvement material is the initial moisture content, and a moisture content condition in which the moisture content of the ground improvement material is the saturation moisture content. The method for evaluating the workability of a ground improvement material according to claim 1, wherein in the workability determination step, it is determined that the workability is good if the discharge condition is satisfactory under all of the plurality of water content conditions.

3. The discharge status observation step involves observing the discharge rate when the ground improvement material is discharged from the hopper as the discharge status, The method for evaluating the workability of a ground improvement material according to claim 1 or 2, wherein the discharge status determination step determines that the discharge status is acceptable when the discharge rate when the ground improvement material is discharged from the hopper is equal to or greater than a threshold.

4. The method for evaluating the workability of a ground improvement material according to claim 3, wherein the threshold for the discharge rate is 0.4 m / sec or more and 0.5 m / sec or less.

5. A method for evaluating the workability of a ground improvement material according to claim 1 or 2, wherein if the discharge condition is determined to be unacceptable in the discharge condition determination step, the repetition of the water addition step, the mixing step, and the discharge condition observation step is terminated.

6. The method for evaluating the workability of a ground improvement material according to claim 3, wherein if the discharge condition is determined to be unacceptable in the discharge condition determination step, the repetition of the water addition step, the mixing step, and the discharge condition observation step is terminated.

7. The system further includes a moisture content confirmation step for determining whether the moisture content of the ground improvement material is the saturation moisture content, The method for evaluating the workability of a ground improvement material according to claim 1 or 2, wherein, in the water content confirmation step, the water addition step is stopped if it is determined that the water content of the ground improvement material is the saturation water content.

8. The system further includes a moisture content confirmation step for determining whether the moisture content of the ground improvement material is the saturation moisture content, The method for evaluating the workability of a ground improvement material according to claim 3, wherein, in the water content confirmation step, the water addition step is stopped if it is determined that the water content of the ground improvement material is the saturation water content.

9. A method for constructing sand piles, comprising the workability determination step of the method for evaluating the workability of a ground improvement material according to claim 1 or 2, wherein the sand piles are constructed using a ground improvement material that has been determined to have good workability.

10. A method for constructing sand piles, comprising the workability determination step of the method for evaluating the workability of a ground improvement material according to claim 3, wherein the sand piles are constructed using a ground improvement material that has been determined to have good workability.

11. A method for manufacturing a ground improvement material, comprising the step of obtaining a ground improvement material whose workability has been determined to be satisfactory in the workability determination step of the method for evaluating the workability of a ground improvement material according to claim 1 or 2.

12. A method for manufacturing a ground improvement material, comprising the step of obtaining a ground improvement material whose workability has been determined to be satisfactory in the workability determination step of the method for evaluating the workability of a ground improvement material according to claim 3.

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