Quality evaluation method for improved ground

Abstract

To provide a quality evaluation method for improved grounds allowing high quality construction through appropriate comprehension of strength at an overlap part between improved grounds in ground improvement work by evaluating the improved grounds through sampling a plurality of measured data at the site.SOLUTION: A quality evaluation method for improved grounds is provided with: a boring process of boring a measurement bore hole 2 in a constructed improved ground 1a; a penetration test process of carrying out a penetration test on a bore wall of the measurement bore hole; a strength estimation process of determining estimated strength of the constructed improved ground 1a on the basis of the penetration test data; and a strength comparison process of comparing the estimated strength with a preset allowable strength of an overlap construction. The penetration test process carries out at least one of a first penetration test using a penetration needle, and a second penetration test using a penetration stick having section resistance larger than that of the penetration needle.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for evaluating the quality of improved ground.

Background Art

[0002] When conducting a quality evaluation test to confirm that a desired quality is ensured for improved ground formed by mixing a solidifying material or the like into soft ground, a quality evaluation test may be performed. As methods for the quality evaluation test of improved ground, there are a method of curing a sample collected during construction indoors and then performing a strength test at a predetermined age, a method of collecting a sample from the in-situ position after construction and performing a strength test, and the like. In addition, as a method for measuring the uniaxial compressive strength of a specimen or the like, Non-Patent Document 1 discloses a needle penetration test that can easily confirm the strength of ground or the like. In the needle penetration test, a penetration needle is penetrated into the ground or the like, the penetration length L and the load P during needle penetration are measured, the penetration gradient Np (= P / L), which is the ratio of the load P to the penetration length L, is obtained, and the uniaxial compressive strength is estimated from this penetration resistance (penetration gradient) Np. Further, the strength test needs to be carried out at a predetermined depth for each age until the specified strength evaluation age (for example, 3 days, 7 days, 14 days).

[0003] Regarding the method of performing a strength test on a sample cured indoors, it is necessary to consider that a difference in quality occurs between the in-situ improved body and the sample due to the difference in curing conditions. Further, when collecting a specimen in-situ, since it is necessary to collect a specimen from a predetermined depth position for each predetermined age, it takes time to collect the specimen, and it also takes time to transport and handle the specimen.

[0004] Therefore, the applicant of the present application discloses, in Patent Document 1, a method for performing a strength test on improved ground in-situ, in which a test device is inserted into a measurement hole formed in the improved ground, and the strength of the improved ground is measured based on the penetration resistance and the penetration amount when a rod is penetrated from the test device toward the hole wall. The test device of Patent Document 1 can move up and down in the measurement hole and rotate around the vertical axis (an axis extending in the depth direction of the measurement hole), enabling multiple measurements at a plurality of locations in the circumferential direction and multiple-stage measurements in the depth direction with respect to the measurement hole.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In ground improvement work, for various construction purposes, a plurality of ground improvement piles (ground improvement bodies) may be continuously installed in a state where they overlap each other. When the strength of the previously constructed ground improvement pile is high, the stirring blades may not be able to rotate completely at the overlapping part (overlap portion), which may lead to a decrease in the constructability or inability to construct the subsequently constructed ground improvement pile. Therefore, it is important to grasp the strength development tendency at the young age of the improvement body after its formation. On the other hand, it is difficult to collect cores within a few days of the young age, and it is difficult to evaluate the strength by the uniaxial compression test commonly used for general strength confirmation.

[0008] An object of the present invention is to propose an improved ground quality evaluation method that can appropriately grasp the strength at the overlap portion between ground improvement bodies in ground improvement work and enable high-quality construction by collecting a plurality of measurement data in-situ and evaluating the improved ground.

Means for Solving the Problems

[0009] The present invention for solving the above problems is a method for evaluating the quality of improved ground in a ground improvement method in which a ground improvement body to be constructed later is overlapped with a part of an already constructed ground improvement body, the method including: a drilling step of forming a measurement hole in the already constructed ground improvement body; a penetration test step of performing a penetration test on the hole wall of the measurement hole; a strength estimation step of determining the estimated strength of the already constructed ground improvement body based on the data of the penetration test; and a strength comparison step of comparing the estimated strength with a preset allowable strength for overlapping construction.

[0010] In the penetration test step, it is preferable to perform at least one of a first penetration test of performing a penetration test with a penetration needle defined by "Standard of the Japanese Geotechnical Society, Standard No.: JGS3431-2012, Standard / Standard Name: Penetration Test Method with a Penetration Needle" and a second penetration test of performing a penetration test with a penetration rod having a larger cross-sectional resistance than the penetration needle.

[0011] The penetration test step, the strength estimation step, and the strength comparison step are repeatedly performed until the construction date of the overlap portion. Note that the construction date of the overlap portion is set according to the result of the strength comparison step.

[0012] According to such a method for evaluating the quality of improved ground, in a ground improvement work including an overlap portion, by determining the estimated strength of the already constructed ground improvement body and judging the situation of the already constructed ground improvement body based on the estimated strength, reliable construction can be achieved. Therefore, construction defects and damage to construction machinery in the overlap portion can be avoided. In addition, by repeatedly measuring for each material age, the strength development tendency can be grasped. Furthermore, since a second penetration test using a penetration rod having a larger cross-sectional resistance than the penetration needle is performed, measurement is possible even for a low-strength improvement body that is difficult to measure with a penetration needle.

[0013] When the first penetration test and the second penetration test are measured repeatedly, by using the larger estimated strength among the estimated strength calculated from the data of the first penetration test and the estimated strength calculated from the data of the second penetration test in the strength comparison step, a safe-side prediction becomes possible.

Effects of the Invention

[0014] According to the improved ground quality evaluation method of the present invention, by collecting a plurality of measurement data in-situ and evaluating the improved ground, the strength of the overlap part between the ground improvement bodies in the ground improvement work can be appropriately grasped, enabling high-quality construction.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

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Embodiments for Carrying Out the Invention

[0016] In the present embodiment, as shown in FIG. 1, an improved ground quality evaluation method in a ground improvement work in which a plurality of ground improvement bodies 1, 1,... are continuously provided in a state of overlapping each other will be described. FIG. 1 is a plan view showing an example of a ground improvement work. FIG. 2 shows an overview of the test situation of the improved ground quality evaluation method of the present embodiment. As shown in FIG. 2, in the present embodiment, in the part where the ground improvement body 1b to be constructed later overlaps with a part of the already constructed ground improvement body 1a, the age change and strength characteristics are verified in-situ. FIG. 3 shows the improved ground quality evaluation method of the present embodiment. The improved ground quality evaluation method of the present embodiment includes a boring process S1, a penetration test process S2, a strength estimation process S3, and a strength comparison process S4, as shown in FIG. 3.

[0017] The boring process S1 is a process of forming a measurement hole 2 in the already constructed ground improvement body 1a. As shown in Fig. 2, the measurement hole 2 is preferably formed in a portion of the already constructed ground improvement body 1a that overlaps with the ground improvement body 1b to be constructed later. In this embodiment, a pipe insertion operation S11 of inserting a pipe 3 into the already constructed ground improvement body 1a and a pipe pulling operation S12 of forming the measurement hole 2 by pulling out the pipe 3 are performed. Fig. 4 is a conceptual diagram of the boring process S1. When performing a penetration test on the already constructed ground improvement body 1a after the overlap construction date, the measurement hole 2 may be formed in a portion of the already constructed ground improvement body 1a that does not overlap with the ground improvement body 1b to be constructed later.

[0018] In the pipe insertion operation S11, as shown in Fig. 4(a), a thin-walled pipe (pipe 3) is inserted (pushed in) into the ground improvement body immediately after ground improvement (age 0 days). At this time, the unconsolidated cement-improved soil 11 enters the pipe 3.

[0019] In the pipe pulling operation S12, as shown in Fig. 4(b), the pipe 3 is pulled out from the already constructed ground improvement body 1a at age 1 day. At this time, the cement-improved soil 11 in the pipe 3 is pulled up together with the pipe 3. By pulling out the pipe 3, a measurement hole 2 having a diameter equal to the outer diameter of the pipe 3 is formed in the already constructed ground improvement body 1a.

[0020] The penetration test process S2 is a process of performing a penetration test on the hole wall of the measurement hole 2. In the penetration test process S2, a first penetration test performed with a penetration needle and a second penetration test performed with a penetration rod are performed. Fig. 5 shows the construction status of the penetration test process S2. In this embodiment, the penetration test measuring device 4 inserted into the measurement hole 2 is rotated around the vertical axis (i.e., the central axis of the measurement hole 2) and moved up and down in the measurement hole 2, so that a plurality of measurements are performed at a plurality of locations in the circumferential direction of the measurement hole 2 in a plurality of stages in the depth direction. In this embodiment, it is assumed that the penetration test is performed every day from age 2 days to the day before the overlap construction date (for example, age 4 days) of the overlap construction date (for example, age 5 days). For example, the penetration test is performed at 5 points in the horizontal direction and 5 stages in the depth direction (25 points for each measurement hole 2).

[0021] In this embodiment, the same penetration test measuring device 4 shall be used in the first penetration test and the second penetration test. That is, in the first penetration test and the second penetration test, after either one of the penetration tests is carried out, the penetration test measuring device 4 shall be lifted up once, and the penetration needle and the penetration rod provided on the penetration test measuring device 4 shall be replaced, and then the other penetration test shall be carried out. Here, as the penetration needle, a needle (cotton needle No. 2, large chisel needle (φ0.84 mm or 0.89 mm, length 54.5 ± 1.4 mm)) defined by "Soil Mechanics Society Standard, Standard No.: JGS3431-2012, Standard and Standard Name: Needle Penetration Test Method" shall be used. Also, as the penetration rod, a rod thicker than the penetration needle and having a larger cross-sectional resistance shall be used. For example, a round rod with a diameter of φ3 mm shall be used.

[0022] As shown in FIG. 5, the penetration test measuring device 4 of this embodiment includes a housing 41, a penetrator (penetration needle or penetration rod) 42 provided on the housing 41 so as to be able to advance and retreat toward the hole wall 21 of the measurement hole 2, a rotary wheel 43 supported by the housing 41 so as to be rotatable in the circumferential direction of the measurement hole 2, a reaction force arm 44 that can advance and retreat or rotate with respect to the housing 41, a suspension means 45 for suspending the housing 41, an azimuth sensor 46 provided on the housing 41, a power source 47, a video server 48, and a camera 49.

[0023] The housing 41 is composed of a hollow cylindrical member with its upper and lower ends shielded. The housing 41 houses the penetrator 42, the reaction force arm 44, the azimuth sensor 46, the power source 47, the video server 48, and the camera 49. In the central part of the housing 41, a rod-shaped or wall-shaped fixing part 41b for fixing each device is formed. Also, on the housing 41, two openings 41a penetrating inside and outside are formed at positions corresponding to the penetrator 42 and the reaction force arm 44.

[0024] The penetrator 42 is provided at the lower part of the housing 41 facing the opening 41a. The penetrator 42 is capable of advancing and retreating with respect to the base 42a fixed to the fixing portion 41b. The penetrator 42 projects from the opening 41a toward the hole wall 21 by advancing in a direction orthogonal to the central axis of the housing 41 (that is, the radial direction of the measurement hole 2) by a penetration motor (not shown). In the present embodiment, a camera (CCD camera) 49 is provided near the penetrator 42, and is configured to be able to photograph the advancing and retreating direction of the penetrator 42. The image photographed by the camera 49 is transmitted to a terminal (personal computer, tablet terminal, smartphone, etc.) provided outside the measurement hole 2 via the video server 48. The penetration motor and the camera 49 are operated by the electric power supplied from the power source 47.

[0025] A plurality of rotating wheels 43 are provided at the upper part of the housing 41. The rotating wheel 43 projects outside the outer surface of the housing 41, or is provided so as to be able to advance and retreat laterally with respect to the housing 41, and can contact the hole wall 21. The rotating wheel 43 rotates horizontally about the vertical axis by the rotational force of a wheel motor (not shown). The wheel motor rotates by the power (electric power) supplied from the power source 47. The housing 41 rotates about the vertical axis as the rotating wheel 43 travels on the surface of the hole wall 21 of the measurement hole 2.

[0026] The reaction force arm 44 is provided above the penetrator 42. The reaction force arm 44 is rotatably attached to the arm base 44a fixed to the fixing portion 41b. The reaction force arm 44 projects outside the housing 41 from the opening 41a and contacts the hole wall 21 by rotating by the power of an arm motor (not shown). The housing 41 is fixed to the measurement hole 2 by pressing the reaction force arm 44 against the hole wall 21. The arm motor is driven by the power (electric power) supplied from the power source 47.

[0027] The hanging means 45 is provided at the orifice of the measurement hole 2 and suspends the housing 41. The hanging means 45 is constituted by, for example, a wire 45a attached to the housing 41, a reel 45b around which the wire 45a is wound, a motor 45c that applies a rotational force to the reel 45b, and a pedestal 4d that supports the reel 45b and the motor 45c. By rotating the reel 45b by the power of the motor 45c, the wire 45a wound around the reel 45b is wound and fed out, and accordingly, the housing 41 moves up and down within the measurement hole 2.

[0028] The azimuth sensor 46 measures the orientation of the housing 41 (the penetration body 42). In the present embodiment, based on the measurement result of the azimuth sensor 46, the rotation wheel 43 is controlled to rotate the housing 41 about the vertical axis within the measurement hole 2.

[0029] In the penetration test process S2, the housing 41 is inserted into the measurement hole 2 and lowered to a predetermined depth within the measurement hole 2 using the suspension means 45. When the housing 41 reaches the predetermined depth, the orientation of the housing 41 is adjusted using the rotary wheel 43 so that the position of the penetrator 42 becomes 0 degrees in azimuth. After the orientation adjustment of the housing 41 is completed, the reaction arm 44 is pressed against the hole wall 21 to fix the housing 41 within the measurement hole 2. When the reaction arm 44 is pressed against the hole wall 21, the side surface of the housing 41 contacts the hole wall 21 on the side opposite to the reaction arm 44. After fixing the housing 41, the penetrator 42 is projected toward the hole wall 21 to conduct a penetration test (measurement of penetration force, penetration amount, etc.). After the measurement, the fixation by the reaction arm 44 is released, and the rotary wheel 43 is operated at the same depth to rotate the housing 41 by a predetermined amount (72° in this embodiment). After rotating the housing 41, the housing is fixed using the reaction arm 44, and a penetration test is carried out. Similarly, the rotation and penetration test of the housing 41 are carried out multiple times. After conducting the penetration test a predetermined number of times (5 times in this embodiment) at the same depth, the suspension means 45 is operated to lower the housing 41 by a predetermined depth (20 mm in this embodiment). After lowering the housing 41, the penetration test and the rotation of the housing 41 are carried out multiple times. The same operation is repeated until the required depth is reached. The measurement data is transmitted to a terminal (personal computer, tablet terminal, smartphone, etc.) provided outside the measurement hole 2.

[0030] The penetration test process S2 is carried out for the same measurement hole 2 at each age (for example, 2-day age, 3-day age, 4-day age). The following shows an example of the penetration test process. Fig. 6 is an example of the developed view inside the measurement hole 2. In the present embodiment, in the measurement hole 2 with a diameter of about 115 mm, the penetration resistance Np at 25 points is measured for each age, but the number of penetration tests is not limited. As shown in Fig. 6, in the present embodiment, at each age, the penetration test is carried out at the same depth for different orientations. That is, when the penetration test starts at azimuth 0° at 2-day age, the penetration test starts from azimuth 24° at 3-day age, and the penetration test starts from azimuth 48° at 4-day age, so that the penetration positions for each age do not overlap. In the measurement hole (with a diameter of about 115 mm) of the present embodiment, the horizontal interval in the developed view is 24 mm and the depth interval is 20 mm, but the position and number of penetration positions are not limited. It is desirable to confirm that the position of the penetration test does not overlap with the previous (previous age) measurement position by photographing the measurement position of the penetrator 42 with the camera 49. It is desirable to have lighting means that irradiates light in the photographing direction of the camera 49 together with the camera 49.

[0031] The second penetration test using the penetration rod is carried out on the constructed ground improvement body 1a where the strength required for measuring the resistance value by the penetration needle is considered to have not yet appeared. Therefore, at the initial stage (for example, 2-day age), both the first penetration test and the second penetration test are carried out. On the other hand, after sufficient strength for measurement by the penetration needle has appeared in the constructed ground improvement body 1a (for example, 4-day age), it is not necessary to carry out the second penetration test.

[0032] The strength estimation process S3 is a process of determining the estimated strength of the constructed ground improvement body 1a based on the data of the penetration test.

[0033] In the penetration test, the penetration length of the penetration needle or the penetration rod and the load P when the penetration needle or the penetration rod penetrates are measured, the penetration gradient P / L which is the ratio of the load P to the penetration length is obtained, and the uniaxial compressive strength is estimated from this penetration gradient.

[0034] Then, based on the converted uniaxial compression strength qu for each material age, as shown in Fig. 7, a strength estimation curve is created to estimate the strength of the improved ground before reaching the specified strength evaluation material age date. When both the first penetration test and the second penetration test are carried out at the same material age, the larger estimated strength among the estimated strength calculated from the data of the first penetration test and the estimated strength calculated from the data of the second penetration test is used.

[0035] The strength comparison step S4 is a step of comparing the estimated strength with the allowable strength of the overlapping construction set in advance. As a result of the comparison, it is confirmed that the allowable strength of the overlapping construction is not exceeded. In this embodiment, the penetration test step S2, the strength estimation step S3, and the strength comparison step S4 are repeatedly performed for each material age, and the overlapping construction date is set based on the strength estimation curve created using the estimated strength for each material age. The allowable strength of the overlapping construction uses the strength estimated from past construction results.

[0036] According to the improved ground quality evaluation method of this embodiment, in the ground improvement work including the overlapping part, the estimated strength of the constructed ground improvement body 1a is determined, and the situation of the constructed ground improvement body 1a is judged based on the estimated strength, so that reliable construction can be realized. Therefore, construction defects in the overlapping part and damage to construction machinery can be avoided. Also, by repeatedly measuring for each material age, the strength development tendency can be grasped.

[0037] In addition, since the second penetration test using a penetration rod with a larger cross-sectional resistance than the penetration needle is carried out, it is possible to measure even for a low-strength improvement body that is difficult to measure with the penetration needle. When the first penetration test and the second penetration test are measured repeatedly, by using the larger estimated strength among the estimated strength calculated from the data of the first penetration test and the estimated strength calculated from the data of the second penetration test in the strength comparison step, a safe-side prediction is made possible.

[0038] By rotating the penetration test measuring device 4 within the measurement hole 2, it is possible to conduct penetration tests at multiple points at the same depth. Also, while confirming with the azimuth sensor 46, by rotating the penetration test measuring device 4, the penetration position of the penetrator can be adjusted at predetermined angles and intervals. Therefore, penetration tests at different ages can be carried out using the same measurement hole 2, which is superior in workability compared to the conventional measurement method that required using a large number of specimens. Also, by using the same measurement hole 2, the change in age and the variation in strength can be verified more accurately. Also, since it is not necessary to form the measurement hole 2 for each predetermined age, it is excellent in workability. Also, by rotating the penetration test measuring device 4, measurements can be taken at positions different in the circumferential direction of the measurement hole 2 from the positions measured at other ages. Also, even at the stage when the specified strength age is reached, the strength can be grasped by in-situ tests, and quality evaluation can be performed in combination with the test data before reaching the specified strength age.

[0039] Also, since the penetration test measuring device 4 can move up and down within the measurement hole 2, it is also possible to conduct penetration tests at different depths. Therefore, it is possible to conduct a large number of penetration tests using the same measurement hole 2. Also, since measurements are taken in-situ, the strength of the constructed ground improvement body 1a can be directly grasped.

[0040] As described above, the embodiments of the present invention have been explained. However, the present invention is not limited to the above-described embodiments, and each of the above-described components can be appropriately changed without departing from the spirit of the present invention. The number of times (age) of conducting the penetration test is not limited and may be appropriately determined according to the strength. For example, if the overlap construction date set based on the strength measured at age 2 days is age 3 days, it is not necessary to conduct the penetration test after age 3 days.

[0041] Also, in the above-described embodiment, the measurement hole 2 is formed using the pipe 3 in the drilling process. However, the method of forming the measurement hole 2 is not limited, and for example, drilling may be performed using an earth drill or the like. Also, the cement-improved soil 11 in the pipe 3 lifted together with the pipe 3 by the hole-drilling process may be used as a specimen for the strength test.

[0042] In the above embodiment, the first penetration test and the second penetration test are carried out using the same penetration test measuring device 4. However, the first penetration test and the second penetration test may be carried out by two penetration test measuring devices 4, 4 respectively.

[0043] Also, in the above embodiment, after carrying out either the first penetration test or the second penetration test, the penetration test measuring device 4 is lifted, the penetrator 42 is replaced, and the other test is carried out. However, the penetration test measuring device 4 may be configured such that the penetration needle and the penetration rod can be replaced automatically or remotely.

[0044] The configuration of the penetration test measuring device 4 is not limited. For example, the penetrator 42 may move forward and backward along the guide rail. Also, although the housing 41 is configured to rotate about the vertical axis by the rotating wheel 43, an endless belt-like member may be used instead of the rotating wheel 43. In this case, the housing 41 is rotated by rotating the belt-like member in contact with the hole wall 21. Also, the number of rotating wheels 43 is not limited, and for example, it may be one or a plurality. Also, the reaction force arm 44 does not necessarily need to be rotatable, and for example, it may be composed of a cylindrical member and may be configured to be telescopic. The configuration of the suspension means 45 is not limited and may be configured as appropriate.

[0045] The penetration test measuring device 4 may be automatically controlled, or the operator may operate while checking the data transmitted from the penetration test measuring device 4 and the photographed image by the camera 49.

Explanation of reference numerals

[0046] 1 Ground improvement body 1a Constructed ground improvement body 1b Ground improvement body to be constructed later 11 Cement-improved soil 2 Measurement hole 21 Hole wall 3 Pipe 4 Penetration test measuring device 41 Housing 42 Penetrating body 43 Rotating wheel 44 Reaction force arm 45 Suspension means 46 Azimuth sensor S1 Drilling process S11 Pipe insertion operation S12 Pipe extraction operation S2 Penetration test process S3 Strength estimation process S4 Strength comparison process

Claims

1. A method for evaluating the quality of improved ground in a ground improvement method of overlapping a ground improvement body to be constructed later with a part of an already constructed ground improvement body, comprising: a drilling step of forming a measurement hole in the already constructed ground improvement body; a penetration test step of performing a penetration test on the hole wall of the measurement hole; a strength estimation step of determining the estimated strength of the already constructed ground improvement body based on the data of the penetration test; a strength comparison step of comparing the estimated strength with a preset allowable strength for overlapping construction, In the penetration test step, at least one of a first penetration test performed by a penetration needle and a second penetration test performed by a penetration rod having a larger cross-sectional resistance than the penetration needle is performed; In the strength estimation step, the estimated strength is calculated by a conversion formula created in advance according to the penetration needle or the penetration rod; The penetration test step, the strength estimation step, and the strength comparison step are repeatedly performed until the overlapping construction date; The overlapping construction date is set according to the result of the strength comparison step. A method for evaluating the quality of improved ground.

2. In the strength comparison step, the larger estimated strength among the estimated strength calculated from the data of the first penetration test and the estimated strength calculated from the data of the second penetration test is used. The method for evaluating the quality of improved ground according to Claim 1.

3. The measurement hole is formed in a part of the already constructed ground improvement body that overlaps with the ground improvement body to be constructed later. The method for evaluating the quality of improved ground according to Claim 1.

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