JP2018104906A - Method to select soil improvement method and soil improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to select a soil improvement method capable of preventing a delay of a construction period for a soil improvement.SOLUTION: A method to select a soil improvement method is provided with: a process to sample soil; a process to produce a test piece using sampled soil and solidification material; a measurement process to measure hardness of the test piece at a period shorter than a period predetermined as a solidification period; a process to determine whether to adopt a columnar improvement method based on whether the hardness of the test piece is more than or equal to a predetermined threshold value; a provision process to provide the predetermined threshold value. In the provision process, the threshold value is set based on a hardness measured at the arrival of measurement time, of the test piece determined to meet a hardness standard value at the arrival of a solidification time.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for selecting a ground improvement method and a ground improvement method using the ground improvement method selected by the selection method.

  Conventionally, a columnar improvement method is known as one of ground improvement methods in residential land and the like. This construction method is a method in which a slurry obtained by mixing a cement-based solidifying material and water is mixed and stirred with soil in the ground to solidify the soil, and an improved pillar supporting the building is created in the ground.

  However, there are cases where local soil, such as humus soil (organic soil), does not solidify sufficiently even when mixed with a solidifying material, and is prone to solidification failure. Since such solidification failure may cause uneven settlement of the building, whether or not the columnar improvement method can be adopted by confirming the hardness of the ground, the degree of tightening and the structure of the soil layer before construction of the columnar improvement method. It is necessary to judge whether. The following Patent Document 1 describes an apparatus for performing a standard penetration test (boring investigation) for determining in advance whether or not the soil is suitable for the columnar improvement method.

JP 2001-288732 A

  If it is judged that there is no problem with the soil quality in the columnar improvement method based on the results of the boring survey, heavy machinery for carrying out the actual construction of the columnar improvement method will be brought to the site. And before this construction is started, the soil quality is confirmed again by conducting a test excavation at the site.

  Here, even if it is determined that there is no problem with the soil quality in the boring survey, soil (such as humus soil) that may be difficult to solidify may be confirmed in the test excavation survey. This is because the borehole survey has a hole with a diameter of about 10 cm in the ground and the soil is surveyed only at one location, while the test excavation survey has a hole with a diameter of about 20 cm in the ground. This is a problem caused by the narrowness of the survey area because soil surveys are conducted.

  In this case, the heavy machinery is once lifted from the site, and the soil sample collected in the prospecting survey is transported to a test laboratory in another location. And a test body is produced by mixing this soil sample and a solidification material, and the solidification condition of soil is confirmed by performing a uniaxial compression test using the said test body (indoor compounding test). This test usually takes about a week. When it is confirmed that the soil is solidified, the heavy machinery is carried in again. On the other hand, when the soil is not sufficiently solidified, a change to another construction method is considered.

  In this way, conventionally, when humus soil, etc., that may be difficult to solidify during the re-confirmation of the soil quality by the test excavation before the main construction, heavy equipment is lifted or an indoor compounding test at a place away from the site is conducted. There was a problem that the construction period was greatly delayed because it was necessary to do this.

  The present invention has been made in view of the above problems, and its purpose is to provide a method for selecting a ground improvement method capable of preventing a delay in the work period in ground improvement and a ground improvement method selected by the selection method. It is to provide a ground improvement method used.

  A method for selecting a ground improvement method according to one aspect of the present invention includes a sampling step of sampling a soil sample, the soil sample obtained in the sampling step, and a preset amount of a solidifying material. A measurement process for measuring the hardness of the specimen in a measurement time shorter than a preset solidification time for the specimen, and the hardness obtained in the measurement process is a preset hardness. A determination step of determining whether or not the columnar improvement method can be adopted based on whether or not it is equal to or greater than a threshold value, and a preparation step of preparing the threshold value are provided. In the preparation step, the hardness of the specimen that is determined to satisfy the strength standard at the time of the solidification time is measured at the time of the measurement time, and the threshold value is set based on the measured hardness. .

  As a result of intensive studies, the inventor has focused on the fact that the strength of the specimen and the hardness of the specimen have a substantially proportional relationship when the time for solidification of the specimen is relatively short. And about the test piece which satisfy | fills the standard of intensity | strength at the progress of normal solidification time, when the hardness in the time (measurement time) before it was measured, the hardness in measurement time is so high that the intensity | strength in normal solidification time is high. I found it high and came up with the present invention.

  In the method for selecting the ground improvement method, a specimen is prepared using the collected soil sample and the solidified material, and the hardness of the specimen is measured for a predetermined measurement time. Then, based on whether or not the measured hardness of the specimen is equal to or higher than a preset hardness threshold, it is determined whether or not the columnar improvement method can be adopted. This measurement time is shorter than the solidification time set in advance for the specimen. For this reason, compared with the case where the intensity | strength of a test piece is measured at the time of the solidification time arrival, the number of days required to judge whether the adoption of the columnar improvement method can be reduced. In addition, since this hardness measurement can be performed locally using a portable hardness meter, the work of transporting the soil sample to the laboratory and the lifting work of heavy machinery are not required. Therefore, according to the method for selecting the ground improvement method, it is possible to prevent a delay in the construction period in the ground improvement.

  In the method for selecting the ground improvement method, in the preparation step, the hardness of the specimen that is determined not to satisfy the strength standard at the time of the solidification time may be measured. And, in the preparation step, the hardness value at the time of the measurement time of the specimen satisfying the strength standard at the time of the solidification time, and the specimen of the specimen not satisfying the strength standard at the time of the solidification time. You may set the said threshold value between the hardness value at the time of measurement time arrival.

  Thereby, the threshold value can be set more easily than the case where the threshold value is set only based on the hardness value at the time when the measurement time of the specimen that satisfies the strength criterion when the solidification time arrives.

  The selection method of the ground improvement construction method may further include a determination step of determining whether or not the soil sample obtained in the sampling step is easily soiled. And only when it determines with the said soil sample being hard to solidify at the said determination process, the said preparation process, the said measurement process, and the said determination process may be performed.

  Thereby, since the hardness measurement of the specimen is performed only when it is determined that the soil sample is difficult to solidify, it is not necessary to perform an unnecessary test, and a delay in the construction period can be prevented. In addition, when the soil sample is easily solidified, the time during which the hardness of the specimen can be measured is limited to a short time. It can be expanded.

  In the method for selecting the ground improvement method, in the measurement step, the hardness of the specimen is measured at the measurement time when the amount of tension or compression of the spring body is 30 mm or less using a Yamanaka soil hardness meter. Good. In the time range in which the amount of tension or compression of the spring body is 30 mm or less, a strong correlation is observed between the hardness and strength of the specimen, so that a more reliable measurement value can be obtained.

  In the method for selecting the ground improvement method, the production step includes a mixing step of obtaining a mixed sample by mixing the soil sample, the solidifying material, and water, and a filling step of filling the cylinder with the mixed sample. , May be included. In the measurement step, the hardness of the specimen that is housed in the cylinder may be measured. Thereby, since it can prevent that the shape of a test piece collapses during a measurement, hardness measurement can be performed correctly.

  A ground improvement method according to another aspect of the present invention is a method for improving the ground by a method selected using the method for selecting a ground improvement method. For this reason, less time is required in the method selection stage, and the delay in the construction period can be prevented.

  As is apparent from the above description, according to the present invention, the ground improvement method using the ground improvement method selected by the selection method and the ground improvement method selected by the selection method can be prevented according to the present invention. A method can be provided.

It is a flowchart which shows the flow of the selection method of the ground improvement method and ground improvement construction method which concern on Embodiment 1 of this invention. It is a schematic diagram which shows a mode that the mixed sample was filled in the cylinder. It is a schematic diagram which shows the structure of a Yamanaka type soil hardness meter. It is a schematic diagram which shows a mode before making the cone part of a Yamanaka type soil hardness meter penetrate a test body. It is a schematic diagram which shows a mode when the cone part of the Yamanaka type | system | group soil hardness meter is penetrated in the test body. It is a graph which shows the relationship between the age of a test body and intensity | strength. It is a schematic diagram for demonstrating a columnar improvement construction method. It is a schematic diagram for demonstrating a steel pipe pile construction method. It is a graph which shows the relationship (the amount of compression is 35 mm or less) between the hardness value measured using the Yamanaka type soil hardness meter, and compressive strength. It is a graph which shows the relationship (the range of compression amount of 30 mm or less) between the hardness value measured using the Yamanaka type soil hardness meter, and compressive strength.

  Hereinafter, based on the drawings, a method for selecting a ground improvement method and a ground improvement method according to an embodiment of the present invention will be described in detail. FIG. 1 is a flowchart showing the overall flow of the ground improvement method. In the ground improvement method according to the present embodiment, first, it is determined whether or not the columnar improvement method can be adopted using the selection method of the ground improvement method in steps S10 to S80, and the ground improvement book is based on the determination. Construction (S90) is performed.

  First, the carrying-in process S10 is performed. In this step S10, humus soil is not confirmed in the standard penetration test (boring survey) performed in the previous step, and it is determined that there is no problem with the local soil quality in the columnar improvement method (the soil is sufficiently solidified by the solidifying material). After that, the heavy machinery used for the actual construction of the columnar improvement method is brought into the site.

  Next, sampling process S20 is performed. In this step S20, before starting the actual construction of the columnar improvement method, the soil quality is confirmed again by collecting a soil sample from the site where the actual construction is scheduled (experimental survey). Specifically, two to three holes with a diameter of about 200 mm are made in the local ground by the heavy equipment that has been carried in, and a soil sample is collected from each hole to a predetermined depth (for example, 1 m).

  Next, determination process S30 is performed. In this step S30, by visually observing the soil sample obtained in the collecting step S20, it is determined whether or not the soil sample is easily soiled. Specifically, it is confirmed by visual inspection whether the collected soil sample contains soil that is hard to solidify, such as humus soil, and whether there is any problem in soil quality in the columnar improvement method based on the presence or absence. Determine. When it is determined that humus soil or the like is not confirmed and there is no problem in soil quality (soil sample is easily solidified) (S30: YES), the adoption of the columnar improvement method is determined as it is (S70).

  Humus soil has the property that it is difficult to solidify even when mixed with cement-based solidifying material in the columnar improvement method. For this reason, when the humus soil is contained even in a small amount in the local ground, there is a possibility that the ground cannot be sufficiently strengthened due to poor solidification, and there is a possibility that the building will be unevenly subsidized.

  Even if humus soil is not confirmed in the previous drilling survey, the humus soil may be confirmed in the prospecting survey. This is because, in the boring survey, a soil sample is collected by drilling only one hole with a diameter of about 10 cm in the ground, whereas in the test excavation survey, a hole sample with a diameter of about 20 cm is drilled in two or three locations as described above. This is due to the difference in the scope of the soil survey.

  When humus soil or the like is confirmed in the determination step S30, it is determined that the soil sample is difficult to solidify (S30: NO). In this case, it is necessary to further perform a test for confirming the degree of solidification of the soil by mixing the soil sample and the solidified material and measuring the strength and the like without directly determining the adoption of the columnar improvement method. This is because it is difficult to determine whether or not the soil is sufficiently solidified by the solidifying material only by visual confirmation or the like.

  Usually, when such a solidification test is performed, a heavy machine is once lifted from the site, and the collected soil sample is transported to a laboratory in another place. Next, a specimen is prepared by mixing the soil sample and the solidifying material, and after curing the preset solidification time (for example, 28 days) for the specimen, a uniaxial compression test is performed using the specimen. Do. Then, it is determined whether or not the soil solidifies normally based on the measured compressive strength.

  On the other hand, in this embodiment, a specimen is produced using a soil sample collected from the field and a solidifying material, and the hardness of the specimen is measured on the spot for a measurement time shorter than the solidification time. Then, based on whether or not the measured hardness of the specimen is equal to or higher than a preset hardness threshold, it is determined whether or not the columnar improvement method can be adopted.

  For this reason, in this embodiment, compared with the case where the strength of the specimen is measured when the solidification time arrives as in the normal uniaxial compression test, the number of days required to determine whether or not the columnar improvement method can be adopted is smaller. can do. In addition, since this hardness measurement can be performed locally using a portable hardness meter, the work of transporting the soil sample to the laboratory and the lifting work of heavy machinery are not required. Accordingly, it is possible to prevent the construction period from being delayed in the ground improvement. Hereinafter, the hardness measurement of the specimen will be described in detail.

  First, the production step S40 is performed. In this step S40, the mixing step S41 and the filling step S42 are performed in order, whereby a specimen is produced using the soil sample obtained in the sampling step S20 and a preset amount of solidified material.

  First, in the mixing step S41, the soil sample obtained in the sampling step S20, a preset amount of solidified material, and water are mixed on site. Specifically, the soil sample obtained in the collecting step S20 is put into a predetermined mixing container (not shown), and a preset amount of solidifying material and water are put into the mixing container. As the solidifying material, a cement-based solidifying material is used as in the columnar improvement method. Then, by mixing and stirring the soil sample, the solidifying material, and water in the mixing container, a mixed sample in which the soil sample, the solidifying material, and water are uniformly mixed is obtained.

  Next, in the filling step S42, first, the cylindrical tubular body 10 shown in FIG. 2 is prepared. The cylindrical body 10 is provided with an opening 11 on one side (upper side) in the axial direction and the other side (lower side) in the axial direction closed with a bottom part 12, and has a hollow part 10 </ b> A that can be filled with the mixed sample 13. . The inner diameter D1 of the cylindrical body 10 is, for example, 50 mm, and the height H1 is, for example, 100 mm. Thereafter, as shown in FIG. 2, the mixed sample 13 is uniformly filled in the entire hollow portion 10 </ b> A of the cylindrical body 10. Thereby, the specimen 14 for hardness measurement which has a cylindrical shape is produced.

  Next, a measurement step S50 for measuring the hardness of the specimen 14 is performed. First, the configuration and mechanism of the hardness meter 1 used in this step S50 will be described with reference to FIGS.

  The hardness meter 1 is a Yamanaka-type soil hardness meter, and as shown in FIG. 3, includes a conical portion 2, a support portion 6, a spring body 3, a butting rod 5, and an idle indicator portion 4. . The conical part 2 is a part for penetrating into the specimen 14 by being pressed against a cylindrical upper surface 14A (FIGS. 4 and 5) serving as a measurement surface in the specimen 14. The support portion 6 has a cylindrical shape, and supports the cone portion 2 so that the cone portion 2 can move in the axial direction of the support portion 6.

  The spring body 3 has the support portion 6, the cone portion 2, and the spring portion 3 so that the spring portion 3 can be compressed and deformed in accordance with the axial movement of the cone portion 2 with respect to the support portion 6 by the force applied to the cone portion 2 from the specimen 14. It is provided between. Specifically, as shown in FIGS. 4 and 5, when the cone 2 is pressed against the specimen 14, the cone 2 is pushed into the support 6 by the force received from the specimen 14. The spring body 3 is compressible. As shown in FIG. 3, the spring body 3 is accommodated in the support portion 6, and one end is connected to the bottom portion side of the conical portion 2 and the other end is connected to the bottom portion side of the support portion 6. .

  The butting rod 5 is a portion for bringing the cone portion 2 into contact with the cylindrical upper surface 14A of the specimen 14 as shown in FIG. The butting rod 5 has a disk shape having a diameter larger than that of the support portion 6. In the hardness meter 1, the depth at which the cone portion 2 penetrates into the specimen 14 before the butting rod 5 contacts the cylindrical upper surface 14A is set in advance as "the penetration depth of the cone portion 2 with respect to the specimen 14". Has been.

  The idle indicator portion 4 is provided in a slit portion 6A in which a part of the outer peripheral surface of the support portion 6 is cut out along the axial direction. As shown in FIGS. 4 and 5, the floating index portion 4 moves in the axial direction along the slit portion 6 </ b> A according to the compression amount of the spring body 3 when the conical portion 2 is pressed against the specimen 14. A scale is provided around the slit portion 6A, whereby the compression amount of the spring body 3 can be read.

  The hardness meter 1 is not limited to the Yamanaka soil hardness meter, and the structure thereof is not particularly limited as long as it has a similar function (if the hardness of the specimen 14 can be measured).

  Here, a preparation process for preparing a threshold value of the hardness of the specimen 14 for determining whether or not the hardness of the specimen 14 obtained in the measurement step S50 is acceptable will be described. This preparation process is performed in advance before the carrying-in process S10.

  In the preparation step, the hardness threshold S2 of the specimen 14 is set as follows (FIG. 6). First, a plurality of types of soil samples (1) to (3) are prepared, and specimens are respectively prepared using these soil samples and a solidifying material. Then, the relationship between the age of the specimen (elapsed time from the preparation time of the specimen) and the strength of the specimen is investigated, and a graph as shown in FIG. 6 is obtained. In the graph of FIG. 6, the horizontal axis indicates the age of the specimen, and the vertical axis indicates the strength of the specimen. Further, “T1” in the horizontal axis represents “measurement time” for measuring the hardness of the specimen 14 in the measurement step S50, and “T2” represents “solidification time” in which a normal uniaxial compression test is performed. As shown in FIG. 6, the specimens (1) and (2) satisfy the strength standard S1 when the solidification time T2 arrives, and the specimen (3) has the strength standard S1 when the solidification time T2 arrives. Does not meet. FIG. 10 shows the relationship between the hardness (horizontal axis) of the specimen 14 and the compressive strength (vertical axis) of the specimen 14 at the measurement time T1. As shown in the graph of FIG. 10, at the measurement time T1, the hardness of the specimen 14 and the compressive strength of the specimen 14 have a substantially proportional relationship.

  The hardness at the measurement time T1 of the specimens of (1) and (2) in FIG. 6 is measured by the hardness meter 1, and the hardness at the measurement time T1 of the specimen at (3) is measured by the hardness meter 1. Then, a hardness threshold value S2 is set between the hardness values of (1) and (2) and the hardness value of (3). When the measurement time T1 exceeds the threshold value S2 (specimens (1) and (2)), the solidification time T2 also satisfies the standard S1, and when the measurement time T1 does not exceed the threshold value S2 (specimen (3) ) Does not satisfy the standard S1 even in the solidification time T2. Therefore, based on the threshold value S2 set as described above, it can be evaluated with high reliability whether or not the soil sample is normally solidified at the measurement time T1 shorter than the normal solidification time T2.

  In the measurement step S50, measurement is performed based on the amount of compression of the spring body 3 when the cone portion 2 is pressed against the specimen 14 at a measurement time T1 (FIG. 6) shorter than the solidification time T2 set in advance for the specimen 14. The hardness of the specimen 14 at time T1 is measured. Specifically, the measurer holds the hardness meter 1 in his hand and projects the tip of the cone portion 2 vertically to the center of the measurement surface (cylindrical upper surface 14A) of the specimen 14 as shown in FIG. Next, by pressing the tip of the cone portion 2 against the measurement surface of the specimen 14, the cone portion 2 is penetrated into the specimen 14. And as shown in FIG. 5, the whole cone part 2 is penetrated in the test body 14 until the butting rod 5 contacts the measurement surface (cylindrical upper surface 14A). The amount of compression of the spring body 3 at this time is read from the scale, and the hardness of the specimen 14 is measured based on this.

  The measurement time T1 is set in advance so that the cone portion 2 can be penetrated into the specimen 14 to a preset penetration depth (that is, the butting rod 5 can contact the cylindrical upper surface 14A). For example, it can be 18 hours. Thereby, for example, after preparing the specimen 14 at about 4 pm on the previous day, the hardness measurement can be started at about 10 am on the next day, so the test can proceed smoothly.

  In the present embodiment, in the hardness measurement of the specimen 14, since a strong correlation is observed between the hardness and strength of the specimen 14 in a range where the compression amount of the spring body 3 is 30 mm or less, the reliability is higher. Measurements can be obtained.

  Moreover, in this embodiment, as shown in FIG.4 and FIG.5, the cone part 2 is pressed with respect to the test body 14 of the state accommodated in the cylinder 10. As shown in FIG. Thereby, since it can prevent by the cylinder 10 that the shape of the test body 14 collapse | crumbles when the cone part 2 is pressed, hardness measurement can be performed correctly.

  Next, determination process S60 is performed. In this step S60, it is determined whether or not the columnar improvement method can be adopted based on whether or not the hardness obtained in the measuring step S50 is equal to or greater than a preset hardness threshold S2 (FIG. 6). When the hardness obtained in the measurement step S50 is equal to or greater than the threshold value S2 (S60: YES), it is determined that the local soil is normally solidified by the solidifying material, and the adoption of the columnar improvement method is determined ( S70). On the other hand, when the hardness obtained in the measurement step S50 is less than the threshold value S2 (S60: NO), it is determined that the soil causes poor solidification. In this case, a construction method other than the columnar improvement construction method is determined as the ground improvement construction method (S80). Specifically, a steel pipe pile method or a method using a ready-made concrete pile is determined as an alternative to the columnar improvement method. The ground improvement method can be determined by the above steps S10 to S80, and the selection method of the ground improvement method according to the present embodiment is completed.

  Next, construction process S90 is performed. In this step S90, the main construction using the ground improvement method determined in the judgment step S60 is started. When the columnar improvement method is determined (S70), as shown in FIG. 7 (left), cement milk is injected from the tip of the screw 21 while the screw 21 is inserted to excavate the ground. And after digging down to design depth (FIG. 7 (center)), the screw 21 is rotated and the screw 21 is pulled up, stirring soil and cement milk. As a result, as shown in FIG. 7 (right), an improved pillar 22 made of cement having a predetermined design length and supporting force is created in the ground, thereby strengthening the ground.

  On the other hand, when a construction method other than the columnar improvement construction method (for example, steel pipe pile construction method) is determined (S80), as shown in FIG. 8, the steel pipe pile 31 is rotated using a heavy machine and penetrates into the ground. The ground is strengthened by driving to the predetermined design depth while adding the steel pipe pile 31. As described above, the ground is strengthened in the construction of the house, and the ground improvement method according to the present embodiment is completed.

  The above-described embodiment is an exemplification of the present invention, and for example, the following modifications can be employed in the present invention.

  Like the said embodiment, after measuring the hardness of the test body 14 by measurement process S50, you may estimate the compressive strength in the measurement time T1 based on this hardness value. Further, the compression strength at the normal solidification time T2 may be calculated by correcting the compression strength at the measurement time T1 by a predetermined coefficient.

  In the above embodiment, the case where the hardness measurement is performed in a state where the specimen 14 is housed in the cylinder 10 has been described. However, the hardness measurement may be performed after the specimen 14 is taken out from the cylinder 10.

  In the above-described embodiment, the case where the hardness meter 1 in which the spring body 3 can compressively deform in accordance with the movement of the cone portion 2 has been described, but the hardness meter in which the spring body 3 can be tensile deformed in accordance with the movement of the cone portion 2. May be used. In this case, the hardness of the specimen 14 at the measurement time T1 can be measured based on the tensile amount of the spring body 3 when the conical portion 2 is pressed against the specimen 14.

  Moreover, although the said embodiment demonstrated the case where a Yamanaka type soil hardness meter was used in measurement process S50, as above-mentioned, it is not limited to this. In the measurement step S50, the hardness meter is different from the Yamanaka type soil hardness meter, and includes a cone portion, a support portion that supports the cone portion so that the cone portion is movable, and a force applied to the cone portion from the specimen. A spring body provided between the support portion and the conical portion so as to be able to be deformed by tension or compression in accordance with the movement of the conical portion with respect to the support portion, and a conical portion for hardness measurement You may use the hardness meter by which the penetration depth with respect to the specimen of this was preset. Then, the cone portion is pressed against the specimen at a preset measurement time so that the cone portion can be penetrated into the specimen to the penetration depth, and based on the amount of tension or compression of the spring body, The hardness of the specimen may be measured. Moreover, in this invention, you may measure the hardness of a test body using things other than the hardness meter provided with a cone part, a support part, and a spring body.

  In the preparation step, as shown in FIG. 6, the hardness at the time of arrival of the measurement time T1 is measured for a plurality of (for example, two) specimens satisfying the standard S1 when the solidification time T2 arrives, and the lower value is set as the threshold value S2. May be set as Alternatively, the hardness at the time of arrival of the measurement time T1 may be measured for only one specimen that satisfies the standard S1 when the solidification time T2 arrives, and the threshold value S2 may be set in consideration of the tolerance of the hardness value.

  In order to confirm the correlation between the hardness value measured using the Yamanaka type soil hardness tester and the compressive strength by the uniaxial compression test, the following experiment was conducted.

First, a sandy soil was prepared, and a specimen 14 was prepared by mixing a cement-based solidifying material and water. And the compression amount (mm) and hardness (kN / m < ² >) of the spring body 3 when the cone part 2 was penetrated in the test body 14 using the hardness meter 1 (Yamanaka type soil hardness meter) were measured. This measurement was performed for each of the material ages of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 9 hours, 18 hours and 24 hours. Moreover, the uniaxial compression test was done using the same specimen 14, and the compressive strength (kN / m < ² >) of the specimen was measured.

  Moreover, cohesive soil and soft cohesive soil were prepared, and the hardness measurement by the Yamanaka soil hardness tester and the compression strength measurement by the uniaxial compression test were performed in the same manner as in the case of sandy soil.

  Table 1 below shows the experimental results when sandy soil is used, Table 2 below shows the experimental results when viscous soil is used, and Table 3 below shows the experimental results when soft viscous soil is used. ing. The graph of FIG. 9 plots the data of Tables 1 to 3, and the graph of FIG. 10 plots the data of Tables 1 to 3 excluding the data whose compression amount exceeds 30 mm.

(Discussion)
As is apparent from the graphs of FIGS. 9 and 10, there is a constant proportional relationship between the hardness value (horizontal axis) and the compressive strength (vertical axis) measured by the Yamanaka soil hardness tester regardless of the soil quality. I understood. However, as shown in the graph of FIG. 9, when the hardness value (hardness meter support strength) increases, the data variation increases and the correlation with the compression strength deteriorates (the square value of the correlation coefficient R is 0.7468). On the other hand, as shown in the graph of FIG. 10, when the amount of compression of the spring body 3 is within a range of 30 mm or less, a strong correlation was observed between the hardness value and the compression strength (the square value of the correlation coefficient R is 0.9937).

  Considering the upper limit of the time that can be measured for each type of soil, in the case of sandy soil and viscous soil that are relatively easily solidified, if the age is within 9 hours, the compression amount of the spring body 3 is 30 mm or less, and the soft viscosity is low. In soil, the amount of compression of the spring body 3 was 30 mm or less even when the material age was 24 hours. Considering the lower limit of the measurement time, the correlation between the hardness and the compressive strength can be confirmed in any kind of soil from the age of 6 hours or more. Therefore, it is considered that a strong correlation between hardness and compressive strength can be obtained in any kind of soil as long as it is in the range of 6 hours to 9 hours. Considering the result of soft and viscous soil, it is considered that a correlation between hardness and compressive strength can be obtained even when 24 hours have passed in the case of soil that is hard to solidify, such as humus soil. Therefore, it is considered that the measurement time T1 can be set to a preferable 18 hours in the test schedule.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Hardness meter 2 Conical part 3 Spring body 6 Support part 10 Tube 13 Mixed sample 14 Specimen S20 Collection process S30 Judgment process S40 Preparation process S41 Mixing process S42 Filling process S50 Measurement process S60 Judgment process T1 Measurement time T2 Solidification time

Selection of ground improvement method according to an aspect of the present invention, using a collecting step of collecting soil samples, and a solidifying material amount set in advance and the soil sample obtained in the collection step, soil improvement a producing step of producing a specimen in the local, and the measurement step of measuring the hardness of the specimen in the field in a short measurement time than a preset set time for said specimen, obtained in said measuring step The method includes a determination step of determining whether or not the columnar improvement method can be adopted based on whether the hardness is equal to or higher than a preset hardness threshold value, and a preparation step of preparing the threshold value. In the preparation step, the hardness of the specimen that is determined to satisfy the strength standard at the time of the solidification time is measured at the time of the measurement time, and the threshold value is set based on the measured hardness. . In the measurement step, the hardness of the specimen in a state of being accommodated in a cylinder is measured using a Yamanaka type soil hardness meter.

In the method for selecting the ground improvement method, a specimen is prepared using the collected soil sample and the solidified material, and the hardness of the specimen is measured for a predetermined measurement time. Then, based on whether or not the measured hardness of the specimen is equal to or higher than a preset hardness threshold, it is determined whether or not the columnar improvement method can be adopted. This measurement time is shorter than the solidification time set in advance for the specimen. For this reason, compared with the case where the intensity | strength of a test piece is measured at the time of the solidification time arrival, the number of days required to judge whether the adoption of the columnar improvement method can be reduced. In addition, since this hardness measurement can be performed locally using a portable hardness meter, the work of transporting the soil sample to the laboratory and the lifting work of heavy machinery are not required. Therefore, according to the method for selecting the ground improvement method, it is possible to prevent a delay in the construction period in the ground improvement. Further, by measuring the hardness of the specimen that is accommodated in the cylinder, it is possible to prevent the specimen from being deformed during the measurement, so that the hardness measurement can be accurately performed.

In selecting the method of the ground improvement method, the measurement step, the amount of tension or compression of the spring member of the Yamanaka type soil hardness meter may measure the hardness of the specimen at the measurement time to be 30mm or less. In the time range in which the amount of tension or compression of the spring body is 30 mm or less, a strong correlation is observed between the hardness and strength of the specimen, so that a more reliable measurement value can be obtained.

In selecting the method of the ground improvement method, the preparation step, by mixing with water the solidifying material and the soil sample, a mixing step of obtaining a mixed sample, the filling step of filling the mixed sample into the cylindrical body And may be included .

A ground improvement method according to another aspect of the present invention is a method of selecting a ground improvement method using the above-described method for selecting a ground improvement method and improving the ground by the selected method. For this reason, less time is required in the method selection stage, and the delay in the construction period can be prevented.

Claims (6)

A sampling process for collecting soil samples;
Using the soil sample obtained in the collecting step and a preset amount of solidification material, a production step for producing a specimen,
A measurement step of measuring the hardness of the specimen in a measurement time shorter than a preset solidification time for the specimen;
Based on whether the hardness obtained in the measurement step is equal to or greater than a preset hardness threshold, a determination step of determining whether or not the columnar improvement method can be adopted,
A preparation step of preparing the threshold value,
In the preparation step, the hardness of the specimen that is determined to satisfy the strength standard at the time of the solidification time is measured at the time of the measurement time, and the threshold value is set based on the measured hardness. This is a method for selecting a ground improvement method. In the preparation step,
Measure the hardness at the time of the measurement time of the specimen that is determined not to meet the strength criteria at the time of the solidification time,
The hardness value at the time of the measurement time of the specimen that satisfies the strength standard at the time of the solidification time and the hardness at the time of the measurement time of the specimen that does not meet the strength standard at the time of the solidification time The method for selecting a ground improvement method according to claim 1, wherein the threshold value is set between values. A determination step of determining whether or not the soil sample obtained in the collecting step is easily solidified;
The selection of the ground improvement method according to claim 1 or 2, wherein the preparation step, the measurement step, and the determination step are performed only when it is determined that the soil sample is difficult to solidify in the determination step. Method.   In the said measurement process, the hardness of the said test body is measured in the said measurement time when the amount of tension | tensile_strength or compression of a spring body is 30 mm or less using a Yamanaka type soil hardness meter, The 1-3 characterized by the above-mentioned. The selection method of the ground improvement construction method of any one of these. The manufacturing process includes
A mixing step of obtaining a mixed sample by mixing the soil sample, the solidifying material, and water;
Filling the cylinder with the mixed sample, and
The method for selecting a ground improvement method according to any one of claims 1 to 4, wherein, in the measuring step, the hardness of the specimen that is housed in the cylinder is measured.   The ground improvement method characterized by improving a ground by the construction method selected using the selection method of the ground improvement construction method of any one of Claims 1-5.

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