Estimation method of foundation strength by compaction method

Abstract

To provide an estimation method of foundation strength by a compaction method which can easily estimate foundation strength after compaction, when the foundation is compacted by the compaction method.SOLUTION: An estimation method of foundation strength by a compaction method which estimates foundation strength after compaction by the compaction method for compacting the foundation includes: a first step of imaging an image of the foundation underground before and after compaction; a second step of acquiring a void ratio before and after compaction respectively which is a ratio between an area of a gap other than soil particles and an area of soil particles in the image of the foundation before and after compaction from the imaged images of the foundation before and after compaction; and a third step of estimating the foundation strength after compaction by the void ratio after compaction acquired in the second step by using a relational expression of the existing void ratio and the foundation strength or a relation between the void ratio and the foundation strength actually measured when construction is performed at a site in the past where foundation data is similar to that at a site where construction is performed.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a ground consolidation method for estimating the ground strength after consolidation when consolidating the ground, and more particularly to a method for estimating the ground strength in a ground consolidation method for estimating the ground strength after consolidation.

Background Art

[0002] Conventionally, as a method for consolidating the ground, there are known a consolidation method in which a consolidation improvement body is formed in the ground using a ground improvement device to consolidate the ground, or a consolidation method in which the ground is compressed from the ground surface using a consolidation machine to consolidate the ground.

[0003] In the consolidation method of forming a consolidation improvement body in the ground using a ground improvement device to consolidate the ground, granular materials such as sand, crushed stone, or a granular material obtained by adding cement, a fluidizing agent, etc. to this sand or crushed stone are injected into the ground or discharged into the ground and then rammed back, thereby forming a consolidation improvement body in the ground, and by forming this consolidation improvement body, the surrounding ground is consolidated. This consolidation method includes, for example, a sand compaction pile method in which granular materials such as sand and crushed stone are discharged into the ground and the discharged granular materials are rammed back to form a consolidation improvement body with an enlarged diameter in the ground, and the ground around the formed consolidation improvement body is improved to be strong, or a compaction grouting method in which mortar with extremely low fluidity is injected into the ground to consolidate the surrounding ground (Patent Document 1).

[0004] For example, a ground improvement device used in the sand compaction pile method includes a construction casing pipe with a mast erected at the front. The construction machine penetrates the casing pipe into the ground or pulls it out from the ground. The casing pipe is cylindrical and tubular, with its interior serving as a supply path for granular materials such as sand and crushed stone, and a discharge port is provided at the lower part to discharge the granular materials into the ground from the discharge port.

[0005] The sand compaction pile method involves driving a casing pipe to a predetermined depth in the ground, pulling out the driven casing pipe by a predetermined length while discharging granular material, and driving back the discharged granular material by driving the casing pipe by a predetermined length. The discharge of this granular material and the driving back of the granular material by the casing pipe are sequentially repeated upward. As a result, by creating a diameter-expanded compaction improvement body in the ground, the surrounding ground can be compacted and improved into a strong ground.

[0006] By the way, in the compaction method including this sand compaction pile method, when a compaction improvement body is created in the ground to compact the ground, the post-compaction ground strength is estimated to determine whether the post-compaction ground is compacted as planned. The estimation of the post-compaction ground strength is generally performed by ground investigations such as the standard penetration test and the cone penetration test, which are well known.

[0007] For example, when performing by the standard penetration test, the standard penetration test is carried out before and after the compaction of the ground, that is, before and after the creation of the compaction improvement body, to obtain the N value of the ground, which is the penetration resistance value of the ground. In this standard penetration test, the N value is obtained approximately every 1 m in the depth direction. Also, when estimating the ground strength around the compaction improvement body by the standard penetration test, the post-compaction ground strength is estimated based on whether the target N value of the ground has been reached, and it is determined whether the post-compaction ground is compacted as planned.

[0008] However, in the standard penetration test, when determining the N value of the ground, immediately after constructing the compaction improvement body, the excess pore water pressure in the ground rises, and due to the influence of this increase in excess pore water pressure, it may not be possible to obtain the correct N value. The increase in excess pore water pressure in this ground varies depending on the properties of the ground, but it rises for several days to several weeks after constructing the compaction improvement body. For example, in a ground with a high content of fine particles, sufficient strength development was not observed in the immediately conducted investigation (standard penetration test), but there is an example where sufficient strength development was observed in the re-investigation conducted 20 days later. As described above, when compacting the ground, there is a problem that it is difficult to accurately estimate the ground strength after compaction and to determine whether the ground after compaction has been compacted as planned.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of such problems, and its object is to provide a method for estimating the ground strength in a compaction method that can easily estimate the ground strength after compaction when the ground is compacted by a compaction method.

Means for Solving the Problems

[0011] The present invention relates to a compaction method for compacting the ground, and a method for estimating the ground strength in the compaction method for estimating the ground strength after compaction. The method includes a first step of taking images of the ground in the ground before and after compaction, a second step of obtaining, from the taken images of the ground before and after compaction, the void ratios before and after compaction, which are the ratios of the area of voids other than soil particles to the area of soil particles in the images of the ground before and after compaction, respectively, and a third step of estimating the ground strength after compaction from the void ratio after compaction obtained in the second step using the relational expression between the existing void ratio and the ground strength or the relationship between the void ratio and the ground strength measured when construction was carried out at a past site where the site data to be constructed is similar to the ground data.

Effect of the Invention

[0012] According to the present invention, when the ground is compacted by the compaction method, the ground strength after compaction can be easily estimated, and thereby, it is possible to accurately and easily determine whether the ground after compaction has been compacted as planned.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiment for Carrying Out the Invention

[0014] An embodiment of a method for determining the ground improvement effect in the compaction method of the present invention will be described with reference to the drawings. The method for estimating the ground strength in the compaction method according to this embodiment is used to estimate the ground strength after compaction in a compaction method that creates a compaction improvement body in the ground to compact the ground, or a compaction method that compresses the ground from the ground surface to compact the ground. By estimating the ground strength after compaction, it is determined whether the ground after compaction has been compacted as planned. Here, the ground strength is the N value (penetration resistance value) of the ground. However, it is not limited to this.

[0015] In this embodiment, for example, when the ground is compacted by creating a compaction improvement body (also referred to as "compacted sand piles" in the sand compaction pile method) in the ground by the sand compaction pile method or the like, the strength of the ground (the ground after compaction) around the compaction improvement body is estimated, and it is determined whether the ground after compaction has been compacted as planned. The surrounding ground here refers to the ground between adjacent compaction improvement bodies when a plurality of compaction improvement bodies are created or the ground at a point a predetermined distance away from the created compaction improvement body.

[0016] Further, the method for estimating the ground strength in the compaction method here is not limited to the sand compaction pile method, and can also be used in other compaction methods that create a compaction improvement body in the ground by pressing granular materials such as sand and crushed stone into the ground or discharging them into the ground and then ramming them back, and compact the surrounding ground by creating this compaction improvement body. The granular materials such as sand and crushed stone include not only sand and crushed stone, but also those obtained by adding cement, fluidizing agents, etc. to this sand and crushed stone.

[0017] The device used in the method for estimating the ground strength in the compaction method will be described. The device includes ground photographing equipment for photographing an image of the ground and a processing device for performing various processing operations based on the information obtained from the ground photographing equipment. FIG. 1 is a front view of the ground imaging device of the apparatus used in the method for estimating ground strength in the compaction method. FIG. 2 is a view of the tip cone of the ground imaging device, where FIG. 2A is a front view of the tip cone and FIG. 2B is a longitudinal sectional view of the tip cone.

[0018] As shown in FIG. 1, the ground imaging device 10 uses a cone penetration test device 13. The cone penetration test device 13 includes a rod 11 that penetrates into the ground and a tip cone 12 that is attached to the tip (lower end) of the rod 11 and mounts a video camera 14. With the cone penetration test device 13, the rod 11 and the tip cone 12 are penetrated into or withdrawn from the ground.

[0019] The rod 11 has a cylindrical tubular shape and extends vertically. It is penetrated into or withdrawn from the ground by the cone penetration test device 13. Also, as shown in FIGS. 2A and 2B, the tip cone 12 is attached to the tip (lower end) of the rod 11 and penetrates into the ground. Its shape is a cylindrical tube and it faces vertically. The tip cone 12 mounts a video camera 14 for taking images of the ground. The video camera 14 has a photographing opening 15 on the side surface of the tip cone 12 and is arranged inside this opening 15. By directing the video camera 14 in a direction perpendicular to the axial direction of the tip cone 12, an image of the ground can be taken during penetration or withdrawal. Note that the opening 15 and the video camera 14 provided on the tip cone 12 are one here, but they may be plural.

[0020] The processing device is a computer that stores various programs and performs various processing operations using the stored programs. In the processing device, from the images of the ground in the ground before and after compaction (before and after the formation of the compacted improvement body) taken by the ground imaging device 10, the void ratios before and after compaction, which are the ratios of the area of the gaps other than the soil particles to the area of the soil particles in the images of the ground before and after compaction, are respectively obtained. Subsequently, a processing operation is performed to estimate the ground strength after compaction from this void ratio after compaction. As shown in FIG. 1, this processing device 30 is mounted on the ground imaging device 10. However, it is not limited to this, and it may be installed in the office at the work site or within the construction company at another location, etc.

[0021] Next, a method for estimating the ground strength in the compaction method will be described using the flowchart of FIG. 3. The method for estimating the ground strength in the compaction method includes a first step (S1) of taking images of the ground in the ground before and after compaction (before and after the formation of the compacted improvement body), a second step (S2) of respectively obtaining the void ratios before and after compaction from the taken images of the ground before and after compaction, and a third step (S3) of estimating the ground strength (N value of the ground) after compaction from the void ratio after compaction obtained in the second step (S2).

[0022] 〔First step〕 The first step (S1) is a step of taking images of the ground in the ground before and after compaction. Using the ground imaging device 10, images of the ground in the ground before and after the formation of the compacted improvement body, that is, before and after the compaction of the ground, are taken. That is, before and after forming the compacted improvement body in the ground, the rod 11 and the tip cone 12 of the ground imaging device 10 are penetrated into the ground with the cone penetration test device 13, and an image of the ground during penetration is taken with the video camera 14 mounted on the tip cone 12. The images of the ground in the ground before and after the formation of the compacted improvement body taken by this video camera 14 are color image videos. Also, the images of the ground are taken while the rod 11 and the tip cone 12 are being penetrated into the ground, but after the rod 11 and the tip cone 12 have been penetrated into the ground and when the rod 11 and the tip cone 12 are being pulled out, that is, when pulling out, an image of the ground may be taken.

[0023] In addition, the points where the ground images are taken after constructing the compaction improvement bodies in the ground are between adjacent compaction improvement bodies when a plurality of compaction improvement bodies are constructed or at points a predetermined distance away from the constructed compaction improvement bodies. Also, before and after constructing the compaction improvement bodies in the ground, the video camera 14 may take pictures of the entire length of the compaction improvement body in the depth direction, or only at necessary locations. For example, in a stratum where a sand layer and a clay layer are mixed, if the sand layer part is, for example, at a depth of 5 m to 10 m, the range from this depth of 5 m to 10 m may be photographed.

[0024] As described above, in the first step (S1), an image of the ground in the ground before compaction (before constructing the compaction improvement body) is taken, and an image of the ground in the ground after compaction (after constructing the compaction improvement body) is taken.

[0025] 〔Second step〕 The second step (S2) is a step of respectively obtaining the void ratios before and after compaction, which are the ratios of the area of the voids other than the soil particles to the area of the soil particles in the ground images before and after compaction, from the ground images before and after compaction taken in the first step (S1).

[0026] That is, image processing operations are performed on the ground images in the ground before and after compaction (before and after constructing the compaction improvement body) taken by the video camera 14 using a predetermined image processing program. This image processing operation is an operation of converting the color image of the ground image taken by the video camera 14 into a binary image.

[0027] A binary image is an image represented by two colors, white and black. The conversion from the color image to the binary image here is to first convert the captured color image into a grayscale image using a predetermined program. This grayscale image is an image representing black and white shades. For example, one pixel is 8 bits, and in this 8-bit image, the shades are represented in 256 gradations. Pixel value 0 is black, and the color gradually becomes lighter from there, with pixel value 255 being white. Subsequently, at the pixel values of the converted grayscale image, if the pixel value is greater than or equal to the set threshold, it is converted to white W, and if it is less than the threshold, it is converted to black B. In this way, it can be converted into a binary image represented by two colors, white W or black B, for each pixel. The threshold value is set to a value that can represent the soil particle part in the ground as white W and the gap part other than the soil particles (such as air and water) in the ground as black B. Note that soil particles refer to particles such as soil and sand in the ground.

[0028] This binary image is shown in, for example, FIGS. 4A and 4B. FIG. 4A is a diagram showing a binary image of an image of the ground in the ground before constructing the compaction improvement body, and FIG. 4B is a diagram showing a binary image of an image of the ground in the ground after constructing the compaction improvement body.

[0029] Next, in the images of the ground before and after compaction (before and after constructing the compaction improvement body), the void ratio e before and after compaction, which is the ratio of the area of the gaps other than soil particles to the area of soil particles, is obtained respectively.

[0030] That is, from the binary image of the image of the ground in the ground after constructing the compaction improvement body, the area of the gaps other than soil particles (the area of black B) in the binary image is calculated. At the same time, from the binary image of the image of the ground in the ground after constructing the compaction improvement body, the area of the soil particles in the ground (the area of white W) in the binary image is calculated. Subsequently, the void ratio e after compaction, which is the ratio of the calculated area Vv of the gaps other than soil particles to the area Vs of soil particles, is obtained. Also, from the binary image of the image of the ground in the ground before constructing the compaction improvement body, in the same manner as described above, the void ratio e before compaction, which is the ratio of the area Vv of the gaps other than soil particles to the area Vs of soil particles, is obtained.

[0031] The void ratio e of this ground is obtained by the following formula.

[0032]

Number

[0033] In the above formula, Vv is the area of the gaps other than the soil particles in the ground, and Vs is the area of the soil particles.

[0034] As described above, in the second step (S2), the void ratio e after consolidation, which is the ratio of the area Vv of the gaps other than the soil particles to the area Vs of the soil particles in the image of the ground after consolidation, is obtained, and the void ratio e before consolidation, which is the ratio of the area Vv of the gaps other than the soil particles to the area Vs of the soil particles in the image of the ground before consolidation, is obtained.

[0035] 〔Third step〕 The third step (S3) is a step of estimating the ground strength (N value of the ground) after consolidation from the void ratio after consolidation obtained in the second step (S2), using the relational expression between the existing void ratio and the ground strength, or the relationship between the void ratio and the ground strength measured when construction was carried out at a past site where the ground data is similar to the site where construction is to be carried out. Here, it is the case of estimating the ground strength (N value of the ground) after consolidation using the relational expression between the existing void ratio and the ground strength.

[0036] The method (way of obtaining) of estimating the N value (ground strength) of the ground after consolidation using the relational expression between the existing void ratio and the ground strength is as follows. First, from the void ratio e after consolidation obtained from the image of the ground taken in the second step (S2), the relative density Dr (%) of the ground is obtained. The relative density Dr of the ground is obtained by the following relational expression between the void ratio e and the relative density Dr of the ground.

[0037]

Number

[0038] In the above formula, e maxis the maximum void ratio of the ground, e min is the minimum void ratio of the ground.

[0039] Subsequently, the N-value of the ground is obtained from the determined relative density Dr of the ground. The N-value of the ground is obtained using the following relational expression (Meyerhof's formula) between the N-value of the ground and the relative density Dr of the ground.

[0040]

Equation

[0041] In the above formula, σv is the effective overburden pressure (kgf / cm 2 ).

[0042] As described above, in the third step (S3), the N-value of the compacted ground is obtained using the relational expression between the existing void ratio and the ground strength (N-value of the ground). Thereby, the N-value (ground strength) of the compacted ground can be estimated.

[0043] Also, in this third step (S3), the N-value of the compacted ground is obtained using the relational expression between the existing void ratio and the ground strength. At this time, the obtained N-value of the ground may be corrected. For example, the N-value of the ground before compaction is estimated from the void ratio before compaction obtained in the second step (S2). Next, the N-value of the ground before compaction is estimated using the relational expression between the existing void ratio and the ground strength (N-value of the ground). At the same time, the N-value of the ground before compaction is measured. This measurement of the N-value of the ground is performed by a standard penetration test or the like. Subsequently, the N-value of the ground before compaction estimated using the relational expression between the existing void ratio and the ground strength is compared with the measured N-value of the ground before compaction, and a correction value is obtained based on the comparison result (S4). The N-value of the compacted ground obtained in the third step (S3) is corrected based on the obtained correction value (S5).

[0044] That is, the correction of the N value of the ground is obtained by investigating multiple times the N value of the ground before compaction estimated using the relational expression and the actually measured N value of the ground before compaction in the ground before compaction. Subsequently, the N value of the ground before compaction estimated using the relational expression is compared with the actually measured N value of the ground before compaction, and the deviation between the two is obtained from the result. The deviation obtained in this way is used as the correction value. That is, as shown in FIG. 5, the N value of the ground before compaction estimated using the relational expression is shown on the horizontal axis, the actually measured N value of the ground before compaction is shown on the vertical axis, the values obtained from multiple investigations are arranged, and the arranged values are connected by line A. From the connected line A, the gradient is obtained. If the gradient is, for example, 1.2, this value of 1.2 becomes the correction value, which is the deviation between the N value of the ground before compaction estimated using the relational expression and the actually measured N value of the ground before compaction. Next, this correction value of 1.2 can be multiplied (×1.2) by the N value of the ground after compaction obtained using the relational expression between the existing void ratio and the ground strength in the third step (S3) to correct the N value of the ground. Note that the value of 1.2 for this correction value is an example and is not limited thereto.

[0045] In this way, based on the correction value obtained from the N value of the ground before compaction estimated using the relational expression and the actually measured N value of the ground before compaction, by correcting the N value of the ground after compaction obtained in the third step (S3), it is possible to correct in a form corresponding to each site, and thereby, the N value of the ground after compaction to be obtained can be made an accurate value suitable for each site where the ground compaction is carried out.

[0046] Also, the estimation of the N value (ground strength) of the ground after compaction in the aforementioned third step (S3) is carried out using the relational expression between the existing void ratio and the ground strength, but it is not limited thereto. For example, the N value of the ground after compaction may be estimated (obtained) using the relationship between the void ratio and the ground strength actually measured when construction was carried out at a past site where the site to be constructed and the ground data are similar.

[0047] That is, at the site where construction was carried out in the past, the void ratio and the ground strength (the N-value of the ground) at the time of construction are respectively measured, and the values are converted into data as the relationship between the void ratio and the ground strength in the ground according to the ground data. This ground data includes soil classification such as sand and coarse sand, or the fine particle content of sand or soil containing fine particles.

[0048] Using this converted data, the N-value of the ground after compaction (estimating the ground strength) is obtained from the void ratio after compaction obtained in the second step (S2). Also by this, the N-value (ground strength) of the ground after compaction can be estimated.

[0049] As described above, according to the present embodiment, when the ground is compacted by the compaction method, the N-value (ground strength) of the ground after compaction can be easily estimated. Thereby, it is possible to accurately and easily determine whether the ground after compaction is compacted as planned.

[0050] Further, in the above-described embodiment, in the compaction method (such as the sand compaction pile method) of forming a compaction improvement body in the ground using a ground improvement device to compact the ground, the ground strength after compaction is estimated. However, the method for estimating the ground strength in the compaction method of the present invention is not limited to the above compaction method, and the ground strength after compaction may be estimated in a compaction method of compressing the ground from the ground surface using a compaction machine to compact the ground.

[0051] That is, as a compaction method of compressing the ground from the ground surface to compact the ground, for example, there is a method of compacting embankment performed in the work of embankment. That is, as shown in FIG. 6, when performing the compaction work of the embankment M, the embankment M is compressed and compacted using a compaction machine 40 from the ground surface of the embankment M. The compaction machine 40 here is a large machine such as a tire roller 41 in which a roller 43 is provided on a vehicle body 42 and an operator rides and works while traveling. However, the compaction machine 40 is not limited to this, and may be a large machine such as a road roller or a vibrating roller, or a small machine such as a rammer or a plate compactor that compacts the embankment M by hitting the ground with an impact plate that moves up and down.

[0052] After compacting the fill soil M by compressing it from the ground surface using this compaction machine 40 to compact the fill soil M, the compacted fill soil M is subjected to the first step (S1), which is the step of taking images of the ground in the ground before and after compaction, in the same manner as in the above-described embodiment. From the images of the ground before and after compaction taken, the second step (S2), which is the step of obtaining the void ratios before and after compaction respectively, and the third step (S3), which is the step of estimating the N value (ground strength) of the ground after compaction from the void ratio after compaction, are performed to estimate the N value (ground strength) of the ground after compaction. By estimating the N value of the ground after compaction, it is possible to accurately and easily determine whether the ground (fill soil M) after compaction has been compacted as planned.

Explanation of Signs

[0053] 10... Equipment for ground imaging, 11... Rod, 12... Tip cone, 13... Cone penetration test device, 14... Video camera, 15... Opening, 30... Processing device, 40... Compaction machine, 41... Tire roller, 42... Vehicle body, 43... Roller.

Claims

1. A ground compaction method for compacting the ground and estimating the ground strength after compaction, which is a method for estimating the ground strength in a compaction method, comprising: a first step of taking images of the ground in the ground before and after compaction; a second step of obtaining, from the images of the ground before and after compaction taken, the void ratios before and after compaction, which are the ratios of the area of voids other than soil particles to the area of soil particles in the images of the ground before and after compaction, respectively; a third step of estimating the ground strength after compaction from the void ratio after compaction obtained in the second step, using an existing relational expression between the void ratio and the ground strength, or the relationship between the void ratio and the ground strength measured when construction was carried out at a past site where the ground data is similar to the site where construction is to be carried out; A method for estimating the ground strength in a compaction method, characterized by comprising the above steps.

2. In the method for estimating the ground strength in a compaction method according to Claim 1, when estimating the ground strength after compaction in the third step using an existing relational expression between the void ratio and the ground strength, the ground strength before compaction is estimated using the existing relational expression between the void ratio and the ground strength, and the ground strength before compaction is measured. The ground strength before compaction estimated using the relational expression is compared with the measured ground strength before compaction to obtain a correction value. When estimating the ground strength after compaction, the estimated ground strength after compaction is corrected by the obtained correction value. A method for estimating the ground strength in a compaction method.

3. In the method for estimating the ground strength in a compaction method according to Claim 1, when estimating the ground strength after compaction in the third step using the relationship between the void ratio and the ground strength measured when construction was carried out at a past site where the ground data is similar to the site where construction is to be carried out, the ground data is the soil classification of sand or coarse sand, or the fine particle content of sand or soil containing fine particles. A method for estimating the ground strength in a compaction method.

Images