Method for evaluating the hardening state of a hollow measuring tube, measuring jig, and ground improvement body.

Abstract

This invention provides a hollow measuring tube that allows for continuous monitoring at different ages immediately after the construction of the ground improvement body, enabling confirmation of the hardening progress and providing opportunities for rework or modification without having to wait until the design age. [Solution] This is a hollow measuring tube 1 that penetrates the ground improvement body when checking the hardening state of the ground improvement body using the measurement results of an elastic wave measuring instrument. The device comprises a cylindrical main tube section 11 with multiple measurement windows 13 drilled at intervals in the longitudinal direction, a conical tip cone 12 attached to the end of the main tube section, a rubber membrane 14 covering the measurement windows, and a guide section that guides the oscillator 31 and receiver 32 of the elastic wave measuring instrument to a position facing the measurement windows.

Description

Technical Field

[0001] The present invention relates to a measurement hollow tube that penetrates into a ground improvement body, a measurement jig, and a method for evaluating the hardened state of a ground improvement body when the hardened state of the ground improvement body is confirmed based on the measurement results of an elastic wave measuring instrument.

Background Art

[0002] As generally described in Non-Patent Document 1, general quality control of ground improvement is mainly performed by confirming the strength, continuity, and shape of the ground improvement body. For example, regarding the strength of the ground improvement body, it is confirmed that the uniaxial compression strength of the material with an age of 28 days collected by core boring satisfies the reference value determined at the time of design.

[0003] It is common to collect specimens for the uniaxial compression test once each from the upper, middle, and lower parts according to the depth of core boring. On the other hand, regarding continuity, it is evaluated by visual observation of core boring and the core recovery rate. Also, the shape of the improvement body is confirmed based on surveying and construction management records, such as the reference height, pile diameter, and position.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even with the same mixture design, if the target ground contains organic substances or has a different water content state, a uniform improvement quality cannot be obtained. As described above, for strength control, the uniaxial compression test is only performed at about three locations representative of a single boring core, and the rest is the continuity evaluation by visual inspection of the core boring. Therefore, the strength evaluation of the entire depth direction of the ground improvement body cannot be carried out.

[0006] In addition, for quality control, in order to confirm the continuity by core boring and the strength by uniaxial compression test with respect to the reference strength at the designed material age, quality confirmation cannot be performed until 28 days have passed after construction. If it is found that the reference strength has not been reached when 28 days have passed after construction, re-construction or correction will involve a major setback.

[0007] Therefore, an object of the present invention is to provide a hollow tube for measurement, a jig for measurement, and a method for evaluating the hardened state of a ground improvement body, which can confirm the progress of curing by continuously observing according to the material age immediately after the construction of the ground improvement body, and can obtain an opportunity for re-construction or correction without waiting until the designed material age.

Means for Solving the Problems

[0008] In order to achieve the above object, the hollow tube for measurement of the present invention is a hollow tube for measurement that penetrates into the ground improvement body when confirming the hardened state of the ground improvement body based on the measurement result of an elastic wave measuring instrument, and includes a cylindrical main tube portion in which a plurality of measurement windows are perforated at intervals in the longitudinal direction, a conical tip cone attached to the tip of the main tube portion, a rubber film covering the measurement window, and a guide portion that guides the oscillator and the vibration receiver of the elastic wave measuring instrument to a position facing the measurement window.

[0009] Here, the guide portion can be configured to have a rail portion extending on the inner peripheral surface of the main tube portion in the longitudinal direction and a stopper portion that stops the oscillator and the vibration receiver at a position facing the measurement window.

[0010] Furthermore, the invention of the measuring jig is a measuring jig to be inserted into the measuring hollow tube described above, and is characterized by comprising: a main body portion that allows the oscillator and the receiver to be mounted in accordance with the spacing of the measuring windows; a shaft portion that extends above the main body portion in the longitudinal direction; and a pressing means for bringing the oscillator and the receiver into close contact with the rubber membrane of the measuring windows.

[0011] Here, the pressing means is preferably a means for moving the main body laterally by a combination of a rack and pinion gear, a means for moving the main body laterally by the expansion of a packer, a means for moving the main body laterally by the repulsive force of an electromagnet, a means for moving the main body laterally by the rotation of an elliptical cam, or a means for moving the oscillator and the receiver laterally, respectively, by the expansion of individual packers.

[0012] Furthermore, the invention of a method for evaluating the hardening state of a ground improvement body is a method for evaluating the hardening state of a ground improvement body from the measurement results of surface waves measured by an elastic wave measuring instrument, characterized in that it comprises the steps of: setting a target value by measuring the surface waves for each age of the ground improvement body specimen during a mix design test; measuring the surface waves in relation to the depth by arranging the oscillator and receiver of the elastic wave measuring instrument on the prepared ground improvement body for each target age during on-site measurement; and determining the hardening state of the ground improvement body by comparing the target value set from the results of the mix design test with the value based on the measurement value during the on-site measurement.

[0013] Here, the determination can be configured to be based on the surface wave velocity obtained from the surface wave measurement results. Alternatively, the determination can use two indicators: the surface wave velocity and frequency, both obtained from the surface wave measurement results. [Effects of the Invention]

[0014] The present invention, configured as described above, involves using a measuring hollow tube, measuring jig, and method for evaluating the hardening state of a ground improvement body. Inside the hollow tube, which is inserted immediately after the construction of the ground improvement body, the oscillator and receiver of an elastic wave measuring instrument are raised and lowered using the measuring jig, and elastic wave exploration of the ground improvement body is performed through a measuring window via a rubber membrane.

[0015] Therefore, it becomes possible to continue monitoring the ground improvement structure at different ages immediately after its construction, allowing for confirmation of the hardening progress. Furthermore, since the hardening state of the ground improvement structure can be evaluated without waiting until the design age, opportunities for early rework or correction can be obtained, reducing the burden of rework. [Brief explanation of the drawing]

[0016] [Figure 1] This diagram illustrates the configuration of the hollow measuring tube of this embodiment, where (a) is an external view and (b) is an explanatory diagram showing the internal state during use. [Figure 2] This is an explanatory diagram showing an overview of measurements using an elastic wave measuring instrument. [Figure 3] This is an explanatory diagram of the measurement results obtained using an elastic wave measuring instrument. [Figure 4] This is an explanatory diagram showing the detailed structure of a hollow tube. [Figure 5] This diagram illustrates the internal structure of a hollow tube, where (a) is an overall view and (b) is a cross-sectional view of each section shown in the direction of the arrows in (a). [Figure 6] This diagram illustrates the configuration of the measuring jig of this embodiment, where (a) is an explanatory diagram illustrating the operation of the pressing means, (b) is an explanatory diagram illustrating the function of the stopper part, and (c) is an explanatory diagram illustrating the pressing operation by the rack and pinion gear. [Figure 7] This is a flowchart illustrating each step of the method for evaluating the hardening state of the ground improvement body in this embodiment. [Figure 8] This is an explanatory diagram illustrating a Vr estimation curve. [Figure 9] This is a schematic diagram illustrating the process of ground improvement work. [Figure 10]This is a schematic diagram illustrating the process of measuring surface waves. [Figure 11] This is an explanatory diagram illustrating the measurement results of surface waves. [Figure 12] This is an explanatory diagram illustrating the results of determining the hardening state of a ground improvement structure. [Figure 13] This is a flowchart illustrating each step of the method for evaluating the hardening state of the ground improvement body in Example 1. [Figure 14] This figure illustrates the results of FFT analysis of the measured waveform; (a) is a graph illustrating the relationship between the peak of the spectral intensity and the frequency f, and (b) is a graph illustrating the increasing trend of the frequency f. [Figure 15] This is an explanatory diagram illustrating the validity of evaluating the hardening state of the ground improvement body using surface wave velocity, as confirmed by the experiment in Example 2. [Figure 16] This is an explanatory diagram illustrating the validity of the evaluation of the hardening state of the ground improvement body by frequency, as confirmed by the experiment in Example 2. [Figure 17] This diagram illustrates the pressing means of Example 3, where (a) is an explanatory diagram of the means using rubber packers, and (b) is an explanatory diagram of the means using individual rubber packers. [Figure 18] This diagram illustrates the pressing means of Example 3, where (a) is an explanatory diagram of the means using an electromagnet, and (b) is an explanatory diagram of the means using a cam. [Modes for carrying out the invention]

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a diagram illustrating the configuration of the hollow tube used for measurement in this embodiment. Figure 2 is an explanatory diagram showing an overview of measurement using an elastic wave measuring instrument.

[0018] This embodiment describes a hollow tube 1 and a measuring jig 2 used to check the hardening state of a ground improvement body based on the measurement results of an elastic wave measuring instrument 3, and a method for evaluating the hardening state of the ground improvement body based on the measurement results.

[0019] Ground improvement bodies are created by performing intermediate-layer mixing or deep-layer mixing treatments on the target ground. For example, as shown in Figure 9, cylindrical ground improvement bodies G can be created by injecting and agitating the ground with a ground improvement machine G1. Typically, cylindrical ground improvement bodies G are created continuously on adjacent ground while overlapping them.

[0020] Furthermore, cylindrical or wall-shaped ground improvement bodies G can also be created by mechanically agitating the ground using auger mixers or trencher mixers. In either agitation method, the ground is mixed with a cement-based solidifying agent during the agitation process.

[0021] The ground improvement body G created in this manner develops strength over time due to the solidification agent. As mentioned above, quality control is typically performed by conducting a uniaxial compression test when the ground has reached its design age of 28 days to confirm whether or not it has reached the required strength.

[0022] In this embodiment, before reaching the design age, it is evaluated whether the constructed ground improvement body G can reach the standard strength set at the time of design, based on the data obtained from the measurement results of the elastic wave measuring instrument 3.

[0023] Figure 1 illustrates the structure of a hollow pipe 1 that penetrates a ground improvement body G immediately after construction. Figure 1(a) shows the external view, and Figure 1(b) shows the internal state during use. The hollow pipe 1 in this embodiment comprises a cylindrical main pipe section 11 and a conical tip cone 12 attached to the end of the main pipe section 11.

[0024] The main pipe section 11 is formed from a hollow, rigid pipe material such as stainless steel, aluminum, or iron, and multiple measuring windows 13 are drilled on its circumferential surface at intervals along its longitudinal direction. Figure 1 illustrates an example in which the measuring windows 13 are spaced 150 mm apart along the longitudinal direction. The detailed configuration will be described later.

[0025] This measurement window 13 is covered with an insulating rubber membrane 14. The rubber membrane 14 can be made of natural rubber, urethane rubber, silicone rubber, etc. It is also preferable to attach a protective sheet to the outer surface of the rubber membrane 14 for protection.

[0026] By sealing the measurement window 13 with the rubber membrane 14 and the protection sheet, the interface with the improved body is protected, preventing soil and groundwater from entering the hollow tube 1. Furthermore, the attenuation of propagating waves caused by the air layer between the oscillator 31 or receiver 32 and the improved body can be suppressed by ensuring close contact between the oscillator 31 (receiver 32) and the improved body via the rubber membrane 14.

[0027] Then, during measurement using the elastic wave measuring instrument 3, as shown in Figure 1(b), the oscillator 31 and receiver 32 of the elastic wave measuring instrument 3 are guided to a position facing the measurement window 13. The oscillator 31 and receiver 32 are attached to the measurement jig 2 and guided to a predetermined position by the guide section of the hollow tube 1. Details of this guide section will be described later.

[0028] In other words, the measuring jig 2 is a jig to be inserted into the hollow tube 1, and comprises a main body 21 to which the oscillator 31 and the receiver 32 are attached, a shaft 22 extending longitudinally above the main body 21, and a pressing means for bringing the oscillator 31 and the receiver 32 into close contact with the rubber membrane 14 of the measuring window 13.

[0029] The main body 21 is a long body formed to have an outer diameter smaller than the inner diameter of the main pipe 11, and the oscillator 31 and the receiver 32 are mounted to match the vertical spacing of the measurement window 13. An upper plate 23 is provided at the upper end of the main body 21, and a base plate 24 is provided at the lower end, but details will be described later.

[0030] Next, the measurement method using the elastic wave measuring instrument 3 will be explained with reference to Figure 2. The elastic wave measuring instrument 3 is a measuring device that generates high-frequency elastic waves from an oscillator 31 and receives them with a receiver 32. The elastic wave measuring instrument 3, the oscillator 31, and the receiver 32 are electrically connected by cables 33.

[0031] The oscillator 31 and receiver 32 of the elastic wave measuring instrument 3 are placed in close contact with the surface of the improved body at a known distance (L). The oscillation wave applied to the improved body by the oscillator 31 propagates inside the improved body as a body wave and a surface wave. However, when the oscillator 31 and receiver 32 are arranged in parallel, one above the other, the receiver 32 is better able to observe the surface wave (Rayleigh wave).

[0032] The advantages of focusing on surface waves include the fact that surface waves have a larger amplitude than body waves and are easier to capture, and that single-hole measurements become possible because the oscillator 31 and receiver 32 can be arranged in parallel.

[0033] Furthermore, the change in the hardening state of the improved material is measured using the surface wave velocity V r Another advantage is that it can be confirmed using just two values: the frequency f. Furthermore, it has the advantage that the propagation speed of the S-wave, which is a body wave, can be estimated from the propagation speed of the Rayleigh wave, and it becomes possible to convert and evaluate it to uniaxial intensity.

[0034] Therefore, in this embodiment, waveform data obtained by generating and receiving surface waves is recorded. In other words, physical property exploration is performed using surface waves. Figure 3 is an explanatory diagram of the received waveform data, which is the measurement result by the elastic wave measuring instrument 3.

[0035] surface wave velocity V r It can be calculated from the vibration generation / reception distance L and the propagation time Δt using the following formula. V r =L / Δt

[0036] Here, we assume that the age n is n=0 immediately after improvement, n=1 at age 1, and n=2 at age 2, and the surface wave velocity V at each stage. n =L / Δt n By finding this, we can derive the following relationship. Δt0 > Δt1 > Δt2 → V0 < V1 < V2

[0037] On the other hand, the frequency f of the received waveform is expressed as the reciprocal of the period T (1 / T), and is related to the age n of the material. n = 1 / T nWhen written this way, the following relationships can be derived. T0>T1>T2→ f0< f1< f2

[0038] In short, the surface wave velocity V r It can be seen that the frequency f increases as the hardening state of the ground improvement body G progresses and its strength increases. Therefore, as will be described later, the hardening state of the ground improvement body G is evaluated by surface wave exploration from an early age.

[0039] Since this surface wave exploration can be performed at each location where a measurement window 13 is provided, it becomes possible to continuously evaluate the ground improvement body G at any depth without hindering the increase in the strength of the ground improvement body G. In other words, it becomes possible to continuously evaluate the strength of the ground improvement body G.

[0040] Furthermore, while the strength and rigidity of the ground improvement body G change significantly in the early stages of age, the surface wave velocity also changes similarly, making it possible to determine the improvement quality of the ground improvement body G at an early stage.

[0041] The following describes the detailed configuration of the hollow tube 1 and the measuring jig 2, which enable accurate surface wave exploration. Figure 4 is an explanatory diagram showing the detailed configuration of the hollow tube 1.

[0042] The hollow tube 1 is a stainless steel pipe with a diameter of approximately 60 mm to 80 mm. Figure 4 shows a main tube section 11 and a tip cone 12 with a unit length of 700 mm. Threaded grooves are provided at both ends of the main tube section 11, allowing for the creation of hollow tubes 1 of desired length by connecting the main tube sections 11.

[0043] Inside the hollow tube 1, a guide section is provided to guide the main body 21 of the measuring jig 2 to a predetermined position. The guide section mainly consists of a rail section 151 that extends along the longitudinal direction of the hollow tube 1 to the inner circumferential surface of the main tube section 11, and a stopper section 152.

[0044] Figure 5 is a diagram illustrating the internal structure of the hollow tube 1, where Figure 5(a) is an overall view from the side, and Figure 5(b) is a cross-sectional view of each section shown in the direction of arrows AA and BB in Figure 5(a). The rail section 151 is a strip-shaped guide rail member, and is provided on the inner circumferential surface of the main tube section 11 facing the measurement window 13, so as to be continuous in the longitudinal direction of the hollow tube 1.

[0045] On the other hand, the stopper section 152 is a guide stopper component for stopping the oscillator 31 and receiver 32, which are attached to the main body 21 of the measuring jig 2, at a position facing the measuring window 13. For example, it is constructed by attaching right-angled triangular plate material that tapers toward the tip cone 12 side to both sides of the rail section 151.

[0046] The amount of the rail section 151 protruding toward the center of the main pipe section 11 (15 mm in Figure 5(b)) is longer than the amount of the stopper section 152 protruding (7 mm in Figure 5(b)). The rail section 151 guides the main body section 21 to move, and the upper plate 23 hooks onto the stopper section 152 to stop the main body section 21.

[0047] Figure 6 illustrates the relationship between the guide section and the measuring jig 2. It also illustrates the pressing operation of the rack 25 and pinion gear 26, which serve as the pressing means in this embodiment.

[0048] The main body 21 of the measuring jig 2 is attached to the tip of the shaft 22. Notches are provided in the upper plate 23 and bottom plate 24 of the main body 21, and by aligning these notches with the rail 151, the oscillator 31 and the receiver 32 can be raised and lowered while keeping their orientation toward the measuring window 13.

[0049] Furthermore, when the oscillator 31 and receiver 32 approach the measurement window 13 of the depth to be measured, moving the main body 21 towards the stopper 152 will cause the upper plate 23 of the main body 21 to hit the upper surface of the stopper 152 as shown in Figure 6(b), thereby stopping the descent of the main body 21.

[0050] The stopper section 152 is positioned such that when the upper plate 23 makes contact, the oscillator 31 and the receiver 32 are each positioned directly in front of the measurement window 13, thus enabling accurate alignment of the oscillator 31 and the receiver 32 in the depth direction.

[0051] In the state shown in Figure 6(b), where the main body 21 is stopped by the stopper 152, the oscillator 31 and receiver 32 are separated from the measurement window 13 and are not in close contact with the rubber membrane 14. Therefore, during measurement, the oscillator 31 and receiver 32 are brought into close contact with the rubber membrane 14 by the pressing means.

[0052] The pressing means in this embodiment is composed of a combination of a rack 25, which is horizontally fixed to the main body portion 21 and has teeth on its side surface, and a pinion gear 26, which is provided on the shaft portion 22 and has teeth on its circumferential surface.

[0053] In other words, by controlling the rotation of the shaft section 22 from the ground, the oscillator 31 and receiver 32 can be pressed against the measurement window 13 or moved away from the measurement window 13, as shown in Figure 6(c). Note that the number of shaft sections 22, pinion gears 26 and racks 25 shown in Figure 6 is just one example and can be set to any number.

[0054] Next, each step of the method for evaluating the hardening state of the ground improvement body according to this embodiment will be explained with reference to Figures 7-12. Figure 7 is a flowchart illustrating each step of the method for evaluating the hardening state of the ground improvement body according to this embodiment.

[0055] First, before carrying out the actual ground improvement work, a mix design test is conducted in the laboratory (Step S1). In the mix design test, the target age and target strength are set to evaluate the hardening state of the ground improvement body.

[0056] In the mixing test, a rectangular prism specimen is fabricated based on the mixing design, and an oscillator 31 and a receiver 32 are placed in close contact with the side of the specimen with a vibration emission distance L in the vertical direction, as shown in Figure 2, and surface wave waveform data is measured using an elastic wave measuring instrument 3.

[0057] When performing the measurement, the judgment material age d t and the surrounding material age d n are set. For example, set d1 = 6 hours, d2 = 1 day, d3 = 2 days, d4 = 3 days, d5 = 7 days, d6 = 28 days, etc. as the material ages for measurement. Then, from the measured waveform, the surface wave velocity V r of each material age is calculated (see Figure 3).

[0058] Subsequently, in step S2, an estimation curve of the surface wave velocity V r is created. Figure 8 is an explanatory diagram illustrating the V r estimation curve. The V r estimation curve is a curve created by plotting the material age measured in step S1 and the surface wave velocity V r calculated at that time on a graph with the time t on the horizontal axis and the surface wave velocity V r on the vertical axis, and then performing regression analysis or the like based on this.

[0059] Specifically, after confirming that the uniaxial compressive strength of the designed material age (material age of 28 days) of the specimen meets the design standard strength, set the judgment material age d t as the target material age before that, and read the surface wave velocity V r of the judgment material age d t from the V r estimation curve, and based on this, set the target value V r (target value).

[0060] In this way, after setting the judgment material age d t and V r (target value) through the mixing test, the actual construction of the ground improvement work is carried out (step S3). Note that the judgment material age d t and the associated V r (target value) can also be set in multiple steps.

[0061] Figure 9 is a schematic diagram illustrating the process of ground improvement work. First, as shown on the left, the rod of the ground improvement machine G1 is driven into the ground, and a cylindrical ground improvement body G is created by rotating the rod while spraying cement-based solidifying material.

[0062] After the construction of one section of the ground improvement structure G is completed, as shown in the center of Figure 9, a hollow pipe 1 is attached to the boring machine G2 and driven into the deepest part of the constructed ground improvement structure G.

[0063] The positions and number of hollow pipes 1 inserted into the ground improvement body G can be arbitrarily set. For example, hollow pipes 1 can be inserted around the central part of the ground improvement body G, which is almost circular in plan view, in overlapping sections where adjacent ground improvement bodies G overlap, or near the periphery to confirm the design improvement diameter of the ground improvement body G.

[0064] If the hollow pipe 1 has been inserted, as shown on the right side of Figure 9, the measuring jig 2 connected to the elastic wave measuring instrument 3 can be inserted into the hollow pipe 1 at any time, and surface waves can be measured at various depths from the deep to the shallow part of the ground improvement body G.

[0065] Figure 10 is a schematic diagram illustrating the process of measuring surface waves. In short, in step S4, a hollow pipe 1 is inserted into the ground improvement body G to measure the surface wave velocity V at different depths. r The measurement is performed. If the depth D is where the measurement window 13 of the main pipe section 11 is provided, the surface wave velocity V r Measurements can be taken.

[0066] In step S5, the surface wave velocity V at each depth D is r Each age d n and target age d t Several measurements were taken up to the depth direction, and the surface wave velocity V r Create a distribution map. Figure 11 shows the distribution of each age d measured at a certain depth D. n and surface wave velocity V r This is a graph plotting the relationship between values.

[0067] V created in the formulation test r Plots below the estimated curve (dashed line in Figure 11) are estimated to be poorly formed. Therefore, in step S6, the target age d for evaluation is set. t V is a measured value of the surface wave velocity measured at [location]. r Determine the (measured value).

[0068] Figure 12 is an explanatory diagram illustrating the results of determining the hardening state of the ground improvement body G. At each depth D, the age d of the material to be determined is... t The target value of V r (Target value) r If the (measured value) has been determined, proceed to step S7, where hollow pipe 1 is withdrawn from the ground improvement body G, and the remaining cavity is backfilled by injecting a filler material such as cement bentonite.

[0069] On the other hand, as illustrated in Figure 12, if ground improvement defects are found at any depth, the process proceeds to step S8. In step S8, the hollow pipe 1 is withdrawn from the ground improvement body G as needed, and the ground improvement work is redone or the area around the depth where the ground improvement body G was found to have ground improvement defects is corrected.

[0070] Next, the operation of the measuring hollow tube, measuring jig, and method for evaluating the hardening state of the ground improvement body according to this embodiment will be described. The method for evaluating the hardening state of the hollow tube 1, measuring jig 2, and ground improvement body G configured in this way involves inserting the hollow tube 1 immediately after the construction of the ground improvement body G, raising and lowering the oscillator 31 and receiver 32 of the elastic wave measuring instrument 3 inside the hollow tube 1, and performing elastic wave exploration through the measurement window 13 via the rubber membrane 14.

[0071] Therefore, it becomes possible to continue monitoring the ground improvement structure G at different ages immediately after its construction, allowing for confirmation of the hardening progress. Furthermore, since the hardening state can be evaluated without waiting until the long design age of 28 days, opportunities for rework or correction can be obtained earlier, reducing the burden of rework.

[0072] Furthermore, by continuing observations at different ages, it becomes possible to continuously check the progress of hardening in the depth direction at the same location in the original ground, which is usually non-uniform. This eliminates the time lost by taking a boring core at 28 days old, taking it to a testing laboratory, and waiting for the strength measurement results, allowing for a smoother transition to the next construction step. In other words, it contributes to labor savings in ground improvement work. [Examples]

[0073] Hereinafter, a method for evaluating the hardening state of a ground improvement body, different from the method for evaluating the hardening state of the ground improvement body described in the above-mentioned embodiment, will be explained with reference to Figures 13 and 14. Note that the same or equivalent parts described in the above-mentioned embodiment will be denoted by the same terms or reference numerals.

[0074] In the above embodiment, the surface wave velocity V is calculated from the received waveform data measured by the elastic wave measuring instrument 3. r While only the frequency of the vibration waveform f was used to evaluate the hardening state of the ground improvement body G, Example 1 describes a method for evaluating the hardening state of the ground improvement body that also uses the frequency of the vibration waveform f.

[0075] Figure 13 is a flowchart illustrating each step of the method for evaluating the hardening state of the ground improvement body in Example 1. Steps S11 and S13 are the same as steps S1 and S2 described above, so their explanation is omitted.

[0076] In step S12, Fast Fourier Transform (FFT) analysis is performed on each measurement waveform obtained from the measurement of the prismatic specimen by the elastic wave measuring instrument 3 in step S11, and the frequency f at which the spectral intensity peaks is calculated.

[0077] Figure 14 illustrates the results of FFT analysis of the measured waveform, with Figure 14(a) showing a graph of the relationship between the peak of the spectral intensity and the frequency f. Since the frequency f is calculated for each age of the wood, it can be re-plotted on the graph in Figure 14(b), with time t on the horizontal axis and frequency f on the vertical axis.

[0078] In other words, Figure 14(b) is a graph showing the tendency for frequency f to increase over time. By understanding this increasing trend of frequency f, in step S13 V r After creating the estimated curve, in step S14, ground improvement work is carried out in the same manner as in step S3 described above.

[0079] Then, in step S15, a hollow pipe 1 is inserted into the ground improvement body G, and the surface wave velocity V at different depths is measured. r The measurement is performed. Meanwhile, in step S16, each age d n In this process, FFT analysis is performed on the measured waveforms at each depth D, and the respective frequencies f are calculated.

[0080] On the other hand, in step S17, similar to step S5 described above, the surface wave velocity V at each depth D is r Each age d n and target age d t Several measurements were taken up to the depth direction, and the surface wave velocity V r Create a distribution map.

[0081] First, in step S18, the target age for evaluation d t Surface wave velocity V measured at r (Measured value) V r A judgment is made by comparing it with (the target value). Based on the result of the judgment, V r (Target value) V r If the (measured value) is higher, proceed to step S19, where hollow pipe 1 is removed from the ground improvement body G and the remaining cavity is backfilled.

[0082] In response to this, in step S18, V r (Measured value) rIf the value falls below the target value, proceed to step S20 to consider extending the judgment age. That is, check whether there is an increasing trend by looking at the frequency f of the measured waveform at the judgment age and the previous age.

[0083] In step S21, the target age for evaluation d t A comparison is made between the frequency f (judgment age) and the frequency f (judgment age - 1) of the previous age. That is, judgment age d t This determines whether the frequency f (age of the material being judged) is on an increasing trend.

[0084] If the judgment result shows that frequency f(judgment age - 1) is greater than frequency f(judgment age), it is determined that the increasing trend of frequency f is continuing, and the process proceeds to step S22, and judgment age d t The next age d t+1 The process is extended until step S17 is reached. In short, the decision is postponed.

[0085] In contrast, if the frequency f (judgment age) is less than or equal to frequency f (judgment age - 1) and no increasing trend in frequency f is observed, the process proceeds to step S23. In step S23, the hollow pipe 1 is withdrawn from the ground improvement body G as needed, and the ground improvement work is redone or the area around the depth where the ground improvement body G was deemed to have poor construction is corrected.

[0086] With the method for evaluating the hardening state of the ground improvement body of Example 1 configured in this way, the surface wave velocity V obtained from the surface wave waveform data can be used. r By using two indicators, and frequency f, it is possible to confirm the changes in the hardening state of the ground improvement body G.

[0087] Therefore, it becomes possible to perform more accurate evaluations with fewer rework issues, and if there are construction defects, it becomes possible to carry out rework or corrections early without it being too late.

[0088] Furthermore, the other configurations and effects are substantially the same as those of the above embodiment or other examples, so their explanation will be omitted. [Examples]

[0089] The following describes the evaluation method for the hardening state of the ground improvement body in the above-described embodiment and Example 1, and explains the experiment conducted to confirm its validity, with reference to Figures 15 and 16. Note that the same or equivalent parts described in the above embodiment or Example 1 will be described using the same terms or reference numerals.

[0090] Figure 15 illustrates the validity of evaluating the hardening state of the ground improvement body using surface wave velocity, as confirmed by the experiment in Example 2. In the experiment, improved soil and wet sand were packed into a box to be used as a test specimen, and waveform data was obtained by measuring the surface wave using an oscillator and a receiver.

[0091] The graph shown at the bottom of Figure 15 has the age of the material (days) on the horizontal axis and the surface wave velocity V on the vertical axis. r The experimental results are plotted on the graph. For comparison, the results measured using prismatic specimens are also plotted here.

[0092] First, the results for "improved soil," where surface waves were propagated only within the improved soil area, were close to those of the "prismatic specimen," which represents an ideal improved body. In contrast, for "improved 1 (original ground)," where surface waves were measured only in wet sand, which is assumed to be the original ground, the surface wave velocity V r The value remained low and almost constant, and did not increase with the passage of time.

[0093] On the other hand, the results for "Improvement Failure 2 (Half Original Ground)," in which surface waves were propagated across both wet sand and improved soil, showed that the surface wave velocity V remained high even as the age increased. r The rate of increase was low, indicating that poor construction was evident from an early stage, resulting in the ground not reaching the design strength.

[0094] Figure 16 is an explanatory diagram illustrating the validity of the evaluation of the hardening state of the ground improvement body by frequency, as confirmed by the experiment in Example 2. In this experiment as well, improved soil and wet sand were packed into a box that served as the test specimen, and surface waves were measured using an oscillator and a receiver.

[0095] The graph shown at the bottom of Figure 16 plots the experimental results on a graph with the horizontal axis representing age (days) and the vertical axis representing frequency f. Here, for comparison, the results measured using prismatic specimens are also plotted.

[0096] This graph shows two results where surface waves were propagated only in the improved soil. The results for the "improved body (B1-B2)," where surface waves were propagated between improved soil B1 and B2, and the results for the "improved body (C1-C2)," where surface waves were propagated between improved soil C1 and C2, both showed the same trend as the results for the "prismatic specimen," confirming that the tendency for strength to develop can be grasped by frequency f.

[0097] Thus, the surface wave velocity V obtained from the waveform data of the surface wave r Experiments have confirmed that the changes in the hardening state of the ground improvement body G can be grasped using two indicators: and frequency f.

[0098] Furthermore, the other configurations and effects are substantially the same as those of the above embodiment or other examples, so their explanation will be omitted. [Examples]

[0099] Hereinafter, a pressing means other than the pressing means described in the above-mentioned embodiment will be described with reference to Figures 17 and 18. Note that the same or equivalent parts described in the above-mentioned embodiment or Examples 1 and 2 will be described using the same terms or reference numerals.

[0100] Figure 17(a) is an explanatory diagram of the pressing mechanism using a rubber packer. Specifically, after stopping the main body 21 in a predetermined position, the packer, which is subjected to a reaction force by the inner circumferential surface of the main pipe 11, is expanded, thereby pushing out the main body 21 and causing it to move laterally.

[0101] By moving the main body 21 laterally, the oscillator 31 and receiver 32 can be brought into close contact with the rubber membrane 14 of the measurement window 13. In the deeper parts of the ground improvement body G, the rubber membrane 14 expands inward towards the main pipe section 11 due to the lateral pressure of the improved body before hardening. By bringing the oscillator 31 and receiver 32 into close contact with the inner surface of the expanded rubber membrane 14, highly accurate surface wave measurements can be performed.

[0102] Figure 17(b) also shows a pressing mechanism composed of packers, but here individual rubber packers are placed for both the oscillator 31 and the receiver 32. As described above, the rubber membrane 14 will expand into the interior of the main pipe section 11, but the amount of expansion may differ depending on the depth, so individual packers are used to accommodate the respective amounts of expansion.

[0103] Figure 18(a) is an explanatory diagram of the pressing mechanism using an electromagnet. In this example, after stopping the main body 21 in a predetermined position, the main body 21 is moved laterally by generating a repulsive force on the electromagnet attached to the main body 21 against a permanent magnet fixed to the inner circumferential surface of the main pipe 11.

[0104] Figure 18(b) is an explanatory diagram of the pressing mechanism using a cam. In this example, after stopping the main body 21 in a predetermined position, the main body 21 is moved laterally by rotating an elliptical cam attached to the main body 21.

[0105] Thus, the pressing means for bringing the oscillator 31 and the receiver 32 into close contact with the rubber membrane 14 of the measurement window 13 can be made to function with various configurations.

[0106] Furthermore, the other configurations and effects are substantially the same as those of the above embodiment or other examples, so their explanation will be omitted.

[0107] While embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and examples, and any design modifications that do not depart from the spirit of the present invention are included in the present invention.

[0108] For example, while the above embodiments and examples describe the use of the hollow tube 1 for measuring surface waves, the invention is not limited to this. The hollow tube 1 can also be used when measuring body waves such as P-waves and S-waves, transmitted waves near the surface, and diffracted waves using the elastic wave measuring instrument 3. [Explanation of symbols]

[0109] 1: Hollow tube (hollow tube for measurement) 11: Main pipe section 12: Tip cone 13: Measurement window 14: Rubber membrane 151: Rail section (guide section) 152: Stopper part (guide part) 2: Measuring fixtures 21: Main body 22: Shaft section 25: Rack (pressing mechanism) 26: Pinion gear (pressure mechanism) 3: Elastic wave measuring instrument 31: Oscillator 32: Geophone G: Ground improvement body

Claims

1. A hollow measuring tube that penetrates the ground improvement body when confirming the hardening state of the ground improvement body by measurement results of an elastic wave measuring instrument, A cylindrical main tube section with multiple measuring windows perforated at intervals along its length, A conical tip cone attached to the end of the main pipe section, A rubber membrane covering the measurement window, A hollow measuring tube characterized by comprising a guide section for guiding the oscillator and receiver of the elastic wave measuring instrument to a position facing the measuring window.

2. The guide portion includes a rail portion that extends in the longitudinal direction toward the inner circumferential surface of the main pipe portion, The measuring hollow tube according to claim 1, further comprising a stopper portion for stopping the oscillator and the receiver at a position facing the measuring window.

3. A measuring jig for insertion into a hollow measuring tube according to claim 1 or 2, A main body that allows the oscillator and the receiver to be mounted in accordance with the spacing of the measurement windows, Above the main body portion is a shaft portion extending in the longitudinal direction, A measuring jig characterized by comprising a pressing means for bringing the oscillator and the vibration receiver into close contact with the rubber membrane of the measuring window.

4. The measuring jig according to claim 3, characterized in that the pressing means is a means for moving the main body laterally by a combination of a rack and a pinion gear, a means for moving the main body laterally by the expansion of a packer, a means for moving the main body laterally by the repulsive force of an electromagnet, a means for moving the main body laterally by the rotation of an elliptical cam, or a means for moving the oscillator and the receiver laterally, respectively, by the expansion of individual packers.

5. A method for evaluating the hardening state of a ground improvement body, which evaluates the hardening state of the ground improvement body from the measurement results of surface waves measured by an elastic wave measuring instrument, The steps include setting target values ​​by measuring the surface waves of the ground improvement specimens at different ages during the mix design test, During on-site measurements, the oscillator and receiver of the elastic wave measuring instrument are placed on the prepared ground improvement body according to the target age of the material, and the surface waves are measured in relation to the depth. A method for evaluating the hardening state of a ground improvement body, characterized by comprising the step of determining the hardening state of the ground improvement body by comparing the target value set from the results of the aforementioned mix design test with the value based on the measurement value at the aforementioned site measurement.

6. The method for evaluating the hardening state of a ground improvement body according to claim 5, characterized in that the determination is made based on the surface wave velocity obtained from the surface wave measurement results.

7. The method for evaluating the hardening state of a ground improvement body according to claim 5, characterized in that the determination uses two indicators, surface wave velocity and frequency, obtained from the measurement results of the surface wave.

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