JP6905479B2 - Sensor for CP method, casing pipe for SCP method, sand pile strength evaluation method and construction management method for SCP method - Google Patents

Description

The present invention relates to a sensor for the SCP construction method, a casing pipe for the SCP construction method having this sensor, a sand pile strength evaluation method using this sensor, and a construction management method for the SCP construction method.

The sand compaction pile method (hereinafter, also referred to as the "SCP method") is a large compaction method in which sand or a similar material is press-fitted into soft ground with a casing pipe (hollow pipe made of steel) using vibration. This is a ground improvement method that creates sand piles (sand compaction piles) with a diameter in soft ground. The quality and form control standards in the SCP construction method are specified in the common specifications for port construction, for example, and are as follows.
-Quality control standard: sand (material: appearance, type, quality and particle size, content of fine particles below silt)
・ Finished shape management standard: Sand compaction pile (position, top height / tip depth, sand input amount, swelling amount)

Japanese Unexamined Patent Publication No. 10-268061

For the purpose of ground improvement in soft clay by the SCP method, a composite ground consisting of compacted sand piles and soft clay is formed to increase the bearing capacity against the loading load, and the rigidity of the entire ground including the drain effect is increased. Examples include increasing slip resistance and reducing settlement. However, the current situation is that there is no quality and finished form control standard for sand pile strength, and there are the following problems.

(1) In the conventional management method, the management during construction is to confirm the volume change rate of the input sand using a sand level gauge and a depth gauge, and it is not possible to directly measure and confirm the sand pile strength.
(2) A survey boring is conducted after the sand piles are constructed to confirm the strength of the sand piles, but this is not a 100% survey.
(3) Survey Boring may affect the sand pile density because the boring rod penetrates into the created sand pile.
(4) It is very difficult to repair after sand pile construction even if a part that does not meet the design strength is confirmed during the ex-post survey.

Patent Document 1 is configured by arranging a large number of electrode members with respect to the sensor member, and is used for measuring the specific resistance of the ground between two of the electrode members, and also supports arbitrary electrical measurement and the like. Although we disclose a ground resistance measurement sensor that can be used, it is not possible to measure and evaluate the strength of sand piles by the SCP method.

In view of the above-mentioned problems of the prior art, the present invention provides an SCP construction sensor capable of confirming and evaluating the sand pile strength in real time during construction by the SCP construction method, an SCP construction casing pipe having this sensor, and this sensor. It is an object of the present invention to provide a method for evaluating the strength of sand piles used and a method for managing construction of the SCP method.

The sensor for the sand compaction pile method for achieving the above object includes a plurality of electrodes arranged in the radial direction below the casing pipe for the sand compaction pile method, and the plurality of electrodes are formed on the ground by the casing pipe. The sand pile is provided so as to be in contact with the upper end surface of the sand pile, and the specific resistance value inside the sand pile at a predetermined depth from the upper end surface of the sand pile is measured, and the sand pile is based on the measured specific resistance value. It is for evaluating the strength of.

According to this SCP construction sensor, the upper end surface of a sand pile (or part of a sand pile under construction) in which multiple radially aligned electrodes at the bottom of the casing pipe are created in the ground by the casing pipe in the SCP construction method. By contacting with, the specific resistance value inside the sand pile at a predetermined depth from the upper end surface of the sand pile can be measured during or immediately after the construction of the sand pile. Since the sand pile strength is evaluated based on the measured resistivity value, the sand pile strength can be confirmed and evaluated in real time and non-destructively during the construction by the SCP method. Therefore, the sand pile strength can be evaluated for the total number of sand piles, and sand can be refilled or compacted according to the evaluation result of the sand pile strength. The electrodes are preferably arranged in a Wenner arrangement.

In the sensor for the SCP method, the electrodes are combined from the plurality of electrodes to perform the measurement, and the measurement depth from the upper end surface of the sand pile is changed by changing the combination of the electrodes. Can be configured in. By combining the electrodes, the electrode spacing can be changed, and the resistivity value inside the sand pile can be measured at various depths.

Further, the plurality of electrodes are arranged in series with the first radial direction at the lower end of the casing pipe in a first electrode arrangement, and further connected in series with a second radial direction different from the first radial direction. It can be configured to be arranged in a second electrode arrangement. In this case, the measurement depth from the upper end surface of the sand pile can be changed by making the electrode spacing in the first electrode arrangement different from the electrode spacing in the second electrode arrangement.

The casing pipe for the sand compaction pile method for achieving the above object is a casing pipe used for the sand compaction pile method for forming sand piles on the ground, and includes the above-mentioned sensor for the sand compaction pile method. According to this casing pipe, a sand pile can be constructed by the SCP method, and the strength of the sand pile can be evaluated at the time of constructing the sand pile.

It is preferable that the casing pipe for the SCP method has a steel plate extending in the radial direction at the lower end of the casing pipe, and the steel plate is provided with the plurality of electrodes. In order to reduce the measurement error, it is preferable to cover the casing pipe with an electrically insulating material from the lower end to a predetermined height range. Further, the electrode may be protected by providing a recess in the electrically insulating coating film and arranging the electrode in the recess.

The sand pile strength evaluation method for achieving the above object is a method of evaluating the strength of the sand pile formed on the ground by the casing pipe using the sand compaction pile method sensor described above, and is a method of evaluating the strength of the sand pile. A specimen made of sand used for preparation was prepared by changing the gap ratio, the specific resistance value of the sand was measured by the specimen, and the relational expression between the specific resistance value of the sand and the gap ratio was obtained. The relative density is determined based on the strength required for the sand pile, the gap ratio is obtained from the relative density, the specific resistance value is obtained from the obtained gap ratio and the relational expression, and the ratio of the sand pile is obtained by the sensor. The strength of the sand pile is evaluated by measuring the resistance value and comparing the obtained specific resistance value with the measured specific resistance value.

According to this sand pile strength evaluation method, the sand pile strength is evaluated based on the comparison result between the specific resistance value of the sand pile measured by the above-mentioned sensor and the specific resistance value obtained as described above. The sand pile strength can be evaluated in real time and non-destructively during construction by the SCP method.

The construction management method of the sand compaction pile method for achieving the above object is to evaluate the strength of the sand pile at the time of sand pile construction by the casing pipe by using the above-mentioned sensor or the above-mentioned sand pile strength evaluation method. Manage the construction of the sand compaction pile method.

According to this construction management method, by incorporating a process of evaluating the sand pile strength during the construction of the SCP method, the sand pile strength can be evaluated in real time and non-destructively during the construction of the SCP method, and the sand pile can also be evaluated. The sand pile strength can be evaluated for all of the sand piles, and sand can be refilled or compacted according to the evaluation result of the sand pile strength. Therefore, it is possible to surely perform construction management regarding the strength quality of the sand piles to be created on the ground, and it is possible to create high quality sand piles.

According to the present invention, a sensor for the SCP construction method that can confirm and evaluate the sand pile strength in real time during construction by the SCP construction method, a casing pipe for the SCP construction method having this sensor, a sand pile strength evaluation method using this sensor, and an SCP. It is possible to provide a construction management method of a construction method.

It is a vertical cross-sectional view (a) of a main part of a casing pipe for SCP construction method provided with a sensor for measuring a specific resistance value of a sand pile according to the present embodiment, and a bottom view (b) seen from the BB line direction. It is the main part vertical sectional view (a) and bottom view (b) of the casing pipe for SCP construction method provided with the sensor which made it different electrode arrangement by this embodiment. It is the schematic which shows the electrode arrangement example by the Wenner arrangement which arranged a plurality of electrodes at equal intervals. It is a schematic diagram which shows the example of another electrode arrangement in which a plurality of electrodes are arranged so that the distance between the potential electrodes becomes large. It is a flowchart for demonstrating the process (S01-S14) until the strength of a sand pile is evaluated based on the specific resistance value inside the sand pile measured by this embodiment. It is a schematic diagram of the experimental apparatus which measures the specific resistance value of the specimen made of sand. It is a graph which shows the relationship between the gap ratio n (%) and the specific resistance coefficient F. It is a table which shows the relationship between N value (intensity) and relative density. It is a block diagram which shows schematicly the measurement system of the specific resistance value by this embodiment. It is the schematic which shows the sand pile construction process (a)-(g) by this embodiment. It is a flowchart for demonstrating the construction management steps S21-S28 including the sand pile construction process and the sand pile strength evaluation process of FIG. In this embodiment, it is a main part vertical cross-sectional view (a), a bottom view (b), and a partial vertical cross-sectional view (c) of a casing pipe for SCP construction method having a coating film made of an electrically insulating material.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a vertical cross-sectional view (a) of a main part of a casing pipe for SCP construction method provided with a sensor for measuring a specific resistance value of a sand pile according to the present embodiment, and a bottom view (b) seen from the BB line direction.

As shown in FIGS. 1A and 1B, the casing pipe 10 for the SCP construction method is composed of a hollow steel pipe, and a sand pile SC is created on the ground by the SCP construction method. A steel plate 12a is formed at the lower end 11 thereof. , 12b are arranged in the radial direction so as to be orthogonal to each other, a plurality of electrodes 21, 22, 23, 24 are arranged in series on the steel plate 12a, and a plurality of electrodes 25, 26, 27, 28 are arranged in series on the steel plate 12b. Has been done. From the plurality of electrodes 21 to 24 and the plurality of electrodes 25 to 28, a sensor 20 for the SCP construction method for measuring the specific resistance value of the sand pile SC created on the ground by the SCP construction method is configured. Of the plurality of electrodes 21 to 24, the electrodes 21 and 24 are current electrodes, the electrodes 22 and 23 are potential electrodes, and among the plurality of electrodes 25 to 28, the electrodes 25 and 28 are current electrodes and the electrodes 26 and 27. Is the potential electrode.

As shown in FIG. 1A, a closed plate 13 is installed at the lower part of the casing pipe 10 in order to prevent cohesive soil of the original ground from flowing into the casing pipe 10 during penetration into the ground. Reinforcing members 14 and 12 for preventing the closed plate 13 from falling off are arranged above and below the closed plate 13. The reinforcing member 12 is composed of steel plates 12a and 12b arranged in a cross shape, and the reinforcing member 14 is also composed of two steel plates arranged in a cross shape in the same manner. As described above, since the electrodes 21 to 24 and the electrodes 25 to 28 are arranged on the lower surfaces of the steel plates 12a and 12b of the reinforcing member 12 on the lower side of the closing plate 13, they are formed in the lower part of the lower end 11 by the casing pipe 10. The specific resistance value of the sand pile SC can be measured by contacting the upper end surface SS of the sand pile SC. By measuring this resistivity value, it is possible to evaluate the strength non-destructively without disturbing the created sand pile SC.

As shown in FIGS. 1A and 1B, the distance between the electrodes 21 and 22, the distance between the electrodes 22 and 23, and the distance between the electrodes 23 and 24 are constant, and the distance a is, for example, 300 mm. Further, the distance between the electrodes 25 and 26, the distance between the electrodes 26 and 27, and the distance between the electrodes 27 and 28 are constant, and the distance b is smaller than the distance a, for example, 200 mm.

By arranging each electrode as described above, the specific resistance value inside the sand pile SC at the depth a from the upper end surface SS of the sand pile SC can be measured by the plurality of electrodes 21 to 24, and the plurality of electrodes 25 From ~ 28, the resistivity value inside the sand pile SC at the depth b from the upper end surface SS of the sand pile SC can be measured. In this way, the specific resistance value inside the sand pile at an arbitrary depth can be measured by appropriately changing the distance between the electrodes. If the measurement depth of the sand pile may be constant, one of the electrodes 21 to 24 and the electrodes 25 to 28 may be omitted. Further, the intervals a and b may be set at equal intervals, which can improve the reliability of the resistivity measurement.

Next, another example of the electrode arrangement will be described with reference to FIG. FIG. 2 is a vertical cross-sectional view (a) and a bottom view (b) of a main part of a casing pipe for SCP construction method including a sensor having a different electrode arrangement according to the present embodiment.

In the electrode arrangement example of FIGS. 2A and 2B, a plurality of electrodes 31 to 40 are arranged in series on the steel plate 12a. The measurement depth of the sand pile can be variously changed by variously combining the electrodes 31 and 40 at both ends of the plurality of electrodes 31 to 40 as current electrodes and the electrodes 32 to 39 in between as potential electrodes. For example, the combination of electrodes 31, 35, 36, 40 measures at the depth position a1 in FIG. 2 (a), and the combination of electrodes 31, 34, 37, 40 at the depth position a2 in FIG. 2 (a). Measurement, measurement at the depth position a3 in FIG. 2 (a) by the combination of electrodes 31, 33, 38, 40, and depth in FIG. 2 (a) by the combination of electrodes 31, 32, 39, 40. Measurement at position a4 is possible. Here, the depth positions a1, a2, a3, and a4 become deeper in this order.

As shown in FIG. 2, the electrodes at both ends are current electrodes 31 and 40, and the specific resistance value of the sand pile at various depths is measured by changing the combination of the two potential electrodes from the potential electrodes 32 to 39. It is possible. In FIG. 2, the electrodes are arranged only on the steel plate 12a, but the electrodes may also be arranged on the steel plate 12b. For example, by arranging the electrodes in the same manner as the steel plate 12a, the measurement accuracy can be improved and the measurement accuracy can be improved. By changing the number of electrodes arranged and the arrangement interval, the measurement depth can be further changed.

Next, the principle of measuring the specific resistance inside the sand pile by the electrode arrangement as shown in FIGS. 1 and 2 will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic view showing an example of electrode arrangement by the Wenner arrangement in which a plurality of electrodes are arranged at equal intervals. FIG. 4 is a schematic view showing another electrode arrangement example in which a plurality of electrodes are arranged so that the distance between the potential electrodes is large.

The electrode arrangements for arranging electrodes on the ground and measuring the specific resistance of the ground are pole-pole method (bipolar method), pole-dipole method (tripolar method), dipole-dipole method (quadrupole method), and Wenner. The method, the Sharamberger method, and the like are known, but in the present embodiment, the Wenner method is adopted as the arrangement of the electrodes. The reason is as follows.
(1) Since the electrode placement coefficient is small, the potential difference is large and it is easy to measure.
(2) The sensitivity distribution is large, and a region with large forward sensitivity is shown in the central part of the electrode system.
That is, according to the Wenner method, the measurement is easy and the sensitivity at the target measurement position is good.

In the example of FIG. 3, the electrodes C1, P1, P2, and C2 are arranged at equal intervals a, and the current electrodes C1 and C2 at both ends and the potential electrodes P1 and P2 on the inner side form a Wenner arrangement. In the Wenner arrangement, the apparent exploration depth coincides with the spacing of the potential electrodes. That is, as shown in FIG. 3, the distance a between the potential electrodes P1 and P2 coincides with the depth a (apparent measurement depth a) from the surface SS of the sand pile SC to the internal position D1. It can be used to measure the specific resistance at a predetermined depth inside a sand pile.

In FIG. 3, when a current I is passed through the current electrodes C1 and C2 and the potential difference V is measured by the potential electrodes P1 and P2, the resistivity value ρ _R is obtained from the following equation (1).
ρ _R = G (V / I) (1)
Here, G is an electrode arrangement coefficient (G = 2πa in the Wenner arrangement) and changes depending on the electrode arrangement.

Further, when the electrodes cannot be arranged at equal intervals as shown in FIG. 3 due to various conditions, the specific resistance can be measured by obtaining the electrode arrangement coefficient G by the following equation (2).
G = 2π {(1 / C ₁ P ₁ ) − (1 / C ₁ P ₂ ) − (1 / C ₂ P ₁ ) + (1 / C ₂ P ₂ )} ^-1 (2)
Here, C ₁ P ₁ : Distance between the electrode C1 and the electrode P1
C ₁ P ₂ : Distance between electrode C1 and electrode P2
C ₂ P ₁ : Distance between electrode C2 and electrode P1
C ₂ P ₂ : Distance between electrode C2 and electrode P2

As shown in FIG. 4, the current electrodes C1 and C2 and the potential electrodes P1 and P2 are arranged, and the distance 3a (= 3 × a) between the potential electrodes P1 and P2 is the apparent measurement depth (internal position D2 from the surface SS). The electrode arrangement coefficient G can be obtained from the equation (2) to the following equation (3), and the specific resistance value ρ _R can be obtained from the equation (1) to the following equation (4). Can be obtained by
G = 2π {(1 / a)-(1 / 4a)-(1 / 4a) + (1 / a)} ^-1 = (4/3) πa (3)
ρ _R = G (V / I) = (4/3) πa (V / I) (4)

The electrode arrangement in FIG. 1 is an evenly spaced arrangement as shown in FIG. 3, and the electrode arrangement in FIG. 2 increases the distance between the potential electrodes P1 and P2 from small to large, as can be seen from FIGS. 3 and 4. , The apparent measurement depth is changed from shallow to deep.

Next, the steps (S01 to S14) until the strength of the sand pile is evaluated based on the specific resistance value inside the sand pile measured according to the present embodiment will be described with reference to FIGS. 5 to 8. FIG. 5 is a flowchart for explaining the steps (S01 to S14) until the strength of the sand pile is evaluated based on the specific resistance value inside the sand pile measured according to the present embodiment. FIG. 6 is a schematic view of an experimental device for measuring the specific resistance value of a specimen made of sand. FIG. 7 is a graph showing the relationship between the pore space in soil n (%) and the resistivity coefficient F. FIG. 8 is a table showing the relationship between the N value and the relative density.

Explaining with reference to FIG. 5, first, by a laboratory experiment, the sand used for the sand pile to be measured is put into the container of the experimental apparatus shown in FIG. 6 in a saturated state (S01). At this time, the pore space in soil is controlled to be constant.

Next, as shown in FIG. 6, a constant current is passed through the specimen from the electrodes on both sides, and the potential difference at that time is measured by a pair of internal electrodes (S02).

Next, the specific resistance value of the sand used by the following formula (5) is obtained (S03).
_{ρ R = (S A / ΔL} ) · (ΔV / I) (5)
Here, [rho _R: specific resistance of the soil, S _A: sectional area of specimen, [Delta] L: potentiometric measurement interval length, [Delta] V: measuring the potential difference, I: current value is.

Next, the gap ratio of sand in the specimen is changed, and the above steps S01 to S03 are repeated (S04).

Next, the relationship between the specific resistance value of sand and the pore space is clarified using Archie's equation (the following equation (6)) (S05).
ρ _R = an ^-m・ S ^-l・ ρ _w (6)
Here, ρ _w : specific resistance of water (measured value), n: porosity (porosity), S: saturation, a, m, l: constants depending on the properties of soil, a: detour coefficient, m : Cementation coefficient, l: Saturation coefficient.

When the saturation is 100%, the resistivity coefficient F (formation factor) is defined by the following equation (7).
F = ρ _R / ρ _w = an ^-m (7)
From the equation (7), a graph showing the relationship between the pore space in soil n (%) and the resistivity coefficient F can be created as shown in FIG. 7, and the constants a and m become clear.

On the other hand, the strength (N value) required for the sand pile is set from the table shown in FIG. 8 (S06), and the relative density corresponding to this strength (N value) is determined (S07).

In addition, the soil particle density of the sand sample used for the sand pile is measured by the soil particle density test (JIS A 1202) (S08).

Next, the minimum density ρdmin and the maximum density ρdmax of the sand sample used for the sand pile are measured by the minimum density / maximum density test of sand (JIS A 1224), and the maximum gap ratio emax and the maximum gap ratio of sand are measured from the following equation (8). The minimum gap ratio emin is obtained (S09).
emax (min) = {(ρS / ρdmin (max))-1} (8)

Further, using the maximum porosity e _max obtained in step S09, the minimum porosity e _min , and the relative density D _r determined in step S07, the porosity e is obtained from the following equation (9) (S10), and then (10) is used to convert to a porosity n (S11).
D _r = (e _max −e) / (e _max −e _min ) (9)
n = 100 × e / (1 + e) (10)

Next, the pore space in soil n obtained in step S11 is substituted into the formula (7) obtained in step S05 to determine the specific resistance value required for the sand pile to be created (S12). This specific resistance value is determined in a predetermined range corresponding to the range of the relative density Dr in FIG.

On the other hand, as shown in FIGS. 1 and 2, a sensor 20 in which a plurality of electrodes are arranged on the casing pipe 10 is used to measure the specific resistance value inside the sand pile SC actually formed on the ground by the casing pipe 10. (S13).

Next, the specific resistance value of the sand pile SC measured in the step S13 is compared with the range of the specific resistance value determined based on the laboratory test results as in the steps S01 to S12, and the range of the specific resistance value is satisfied. By confirming this, it is evaluated whether the strength (N value) of the sand pile SC under construction satisfies the design strength (S14).

According to previous research (Nao Kunimatsu, Motoharu Jingu "Method of measuring relative density at in-situ of sand ground" 55th Annual Scientific Lecture Meeting of the Society of Civil Engineers (September 2000)), resistivity in sand ground It has been confirmed that there is a certain correlation between the value and the relative density, but since the resistivity value may differ depending on the sand sample used, the ratio is as shown in the present embodiment of FIG. It is necessary to obtain the relationship between the resistance value ρ _{R and the resistivity n in advance.}

As described above, according to the sand pile strength evaluation method according to the present embodiment, in the case of saturated ground, attention is paid to the high correlation between the resistivity value and the relative density, and Archie's equation and the like are based on the experimental results. The relative density is calculated in advance by, and at the time of sand pile construction, the specific resistance value of the sand pile is measured by a plurality of electrodes provided on the casing pipe, and the sand pile strength during construction is measured based on the measured specific resistance value. Can be evaluated in real time.

Next, the specific resistance value measurement system according to the present embodiment will be described with reference to FIG. FIG. 9 is a block diagram schematically showing a specific resistance value measurement system according to the present embodiment.

As shown in FIG. 9, the measurement system 50 includes a connecting portion 51 and a connecting portion 51 which are electrically connected to a plurality of electrodes 21 to 24, 25 to 28 arranged at the lower end 11 of the casing pipe 10 of FIG. 1 through a wiring L. The specific resistance is based on the potential difference measured by the measurement side connection portion 52 that makes an electrical connection by wire, the electrode switching device 53 that switches between the electrodes 22, 23 and the electrodes 26, 27, and the potential electrode 22, 23 or 26, 27. The specific resistance measuring device 54 for measuring the above and the power supply device 55 for supplying a constant current to the current electrodes 21, 24 or 25, 28 are provided. A plurality of electrodes 21 to 24, 25 to 28 and a connecting portion 51 are installed on the casing pipe 10, and the measuring side connecting portion 52, the electrode switching device 53, the resistivity measuring device 54, and the power supply device 55 work, for example. By installing it in the operation room of the ship, the measuring system 50 can measure the specific resistance value inside the sand pile being constructed at the bottom of the water.

The wiring L for electrically connecting the plurality of electrodes 21 to 24, 25 to 28 and the connecting portion 51 can be passed through, for example, the air pressure feeding pipe provided on the side surface of the casing pipe 10. Further, in the case of the electrode arrangement as shown in FIG. 2, the electrode switching device 53 switches so as to change the combination of the two potential electrodes from the potential electrodes 32 to 39. Further, the connection portion 51 and the measurement side connection portion 52 in FIG. 9 may be omitted, the wiring L may be extended to the operation room of the work ship, and the electrode switching device 53 and the power supply device 55 may be directly connected. Further, the connection unit 51 of FIG. 9 and the measurement side connection unit 52 may be connected by wireless communication.

Next, the construction management method of the SCP method based on the strength evaluation of the sand pile at the time of creating the sand pile according to the present embodiment will be described with reference to FIGS. 10 and 11. FIG. 10 is a schematic view showing sand pile construction steps (a) to (g) according to the present embodiment. FIG. 11 is a flowchart for explaining the construction management steps S21 to S28 including the sand pile construction step and the sand pile strength evaluation step of FIG. 10.

As shown in FIG. 10, in the present embodiment, a sand pile SC is constructed by a casing pipe 10 by an SCP method in a submerged ground GG having a surface soft clay layer G1 and a support layer G2 below the surface layer. be. The work boat SP is equipped with an SCP construction machine 15 for penetrating and creating sand piles, and the SCP construction machine 15 drives the casing pipe 10 and its accessories, and the vibro hammer 16 vibrates the casing pipe 10 while vibrating the surface layer. The sand is penetrated into the ground from G1 and the sand supplied from the sand supply port 10a is press-fitted into the ground, and a compacted sand pile is formed in the ground in a substantially vertical direction. The construction management method of the SCP construction method of the present embodiment incorporates a step of evaluating the sand pile strength during and immediately after the construction of the SCP construction method.

First, as shown in FIG. 10A, the casing pipe 10 is set at the sand pile construction position by the SCP construction machine 15 using the work boat SP (S21).

Next, as shown in FIG. 10B, the casing pipe 10 is driven into the soft cohesive soil layer G1 on the surface layer by the SCP construction machine 15 (S22).

Next, as shown in FIG. 10C, when the tip of the casing pipe 10 reaches the support layer G2, sand SD is charged from the sand supply port 10a and supplied into the casing pipe (S23).

Next, as shown in FIG. 10D, the casing pipe 10 is pulled out by the SCP construction machine 15 (S24).

Next, as shown in FIG. 10 (e), the casing pipe 10 is hit back by the SCP construction machine 15 and the sand SD is compacted while being vibrated up and down by the vibro hammer 16 to compact the large diameter downward. Part of the sand pile SC1 is made (S25). If necessary, the sand feeding step S23, the casing pipe 10 pulling step S24, and the backing (compacting) step S25 are repeated.

Next, the compaction due to the backlash in step S25 is interrupted, and the inside of a part of the sand pile SC1 is used by the sensor 20 composed of the plurality of electrodes 21 to 24, 25 to 28 in FIG. The specific resistance value of (S26) is measured, the sand pile strength is evaluated as shown in FIG. 5, and as a result of the evaluation, if the sand pile strength does not satisfy the target value (S27), it is backed up (compacted). ) Returning to step S25, steps S25 to S27 are repeated until the sand pile strength satisfies the target value.

Next, when the sand pile is constructed to the next depth (S28), the process returns to step S23, and through the same step, a part SC2 of a large-diameter sand pile as shown in FIG. 10 (f) (FIG. 10 (e). ) Is partly higher than SC1), and it is confirmed that the sand pile strength satisfies the target value through the specific resistance value measurement step (S26).

Through the above steps, a sand pile SC is formed in the soft cohesive soil layer G1 of the surface layer as shown in FIG. 10 (g), and the sand pile strength is increased through the step of measuring the specific resistance value of the sand pile SC (S26). Confirm that the target value is satisfied. In the present embodiment, the strength of the sand pile is measured by measuring the specific resistance value at the stage where a part (SC1, SC2) of the sand pile (SC1, SC2) shown in FIGS. Since the evaluation is executed and it is confirmed that the target value is satisfied, the construction management regarding the strength quality of the sand pile to be constructed on the ground can be surely performed, and the high quality sand pile can be constructed. In addition, various construction conditions for sand pile construction (for example, sand input amount and sand pile construction growth) can be reviewed and appropriately changed during construction based on the evaluation result of sand pile strength, so that appropriate construction management becomes possible.

As described above, according to the construction management method of the SCP method according to the present embodiment, the following effects are obtained.
(1) In the past, it was not possible to evaluate the sand pile strength during sand pile construction, but it is possible to evaluate and confirm the sand pile strength (N value) in real time during sand pile construction.
(2) Since the strength is evaluated at the time of sand pile construction, 100% survey is possible, and as an extraction method when boring in the ex-post survey, the sand pile strength (N value) based on the measured specific resistance value By extracting sand piles with relatively weak strength in the evaluation, the number of post-survey boring can be reduced and labor can be saved.
(3) Since the specific resistance value can be measured simply by pressing the lower end of the pipe casing against the upper end surface of the created sand pile, the strength can be evaluated without disturbing the created part of the sand pile, and the strength of the sand pile can be evaluated. Non-destructive inspection becomes possible.
(4) Since the strength can be evaluated and confirmed every time a sand pile is constructed, for example, about 1 m, it is possible to find a part that does not meet the design value at an early stage, and refill or compact the sand. It can be repaired immediately and high quality sand piles can be created. Rework after sand pile construction, which was difficult in the past, is no longer necessary.

Next, a configuration for electrically insulating the electrodes provided on the casing pipe for the SCP method according to the present embodiment will be described with reference to FIG. FIG. 12 is a vertical cross-sectional view (a), a bottom view (b), and a partial vertical cross-sectional view (c) of a casing pipe for SCP construction method having a coating film made of an electrically insulating material.

The electrodes for measuring the specific resistance value of sand piles have no directivity, and there is a concern that they may be affected by metal members such as casing pipes. Therefore, the casing pipe 10A of FIGS. 12A and 12B has a coating film 60 (shown by hatching) coated with an electrically insulating material in order to reduce measurement errors. The coating range of the coating film 60 is preferably a range that affects the measurement, and is, for example, about the same as the distance between the current electrodes 21 and 24.

Further, since the electrodes 21 to 24, 25 to 28 are considered to receive a large force when penetrating the casing pipe or compacting the sand pile, a recess 61 is provided in the coating film 60 as shown in FIG. 12 (c). The electrode 21 is arranged so that a part of the electrode 21 is embedded in the coating film 60. The other electrodes 22 to 24 and 25 to 28 have the same structure.

The coating thickness of the coating film 60 shall be as thin as possible within the range in which the electrodes can be embedded, as shown in FIG. 12 (c). For example, the lower steel plates 12a and 12b in which the electrodes 21 to 24, 25 to 28 are located are covered with a coating thickness of 10 mm so as to cover the entire casing pipe 10A within a range of about 1 m from the lower end 11 of the casing pipe 10A. Covers with a thickness of 25 mm for the convenience of implanting electrodes.

Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in FIGS. 10 (e) to 10 (g) and 11, it is determined that the sand pile strength is evaluated by measuring the specific resistance value of some of the sand piles SC1 and SC2 and the sand pile SC to satisfy the target value. To confirm, it may be performed at a predetermined height (for example, 1 m) at many depths in multiple stages. Further, in FIG. 11, it goes without saying that the specific resistance value may be measured by the electrode arrangement of FIG.

Further, FIG. 10 shows an example of creating a sand pile on the bottom of the water, but the present invention is not limited to this, and of course, it can be applied to the case of creating a sand pile on saturated ground on land.

Further, the sensor composed of the electrodes provided on the steel plates 12a and 12b of FIGS. 1 and 2 may be removed together with the steel plate and diverted to another casing pipe for repeated use.

According to the present invention, the strength of the sand pile can be confirmed and evaluated in real time in a non-destructive manner during and immediately after the sand pile is constructed on the ground by the SCP method, so that high quality sand pile can be constructed.

10,10A SCP construction casing pipe, casing pipe 10a Sand supply port 12 Reinforcing member 12a, 12b Steel plate 20 SCP construction sensor, sensor 21-24 Electrodes 21,24 Current electrodes 22,23 Potential electrodes 25-28 Electrodes 25,28 Current electrodes 26,27 Current electrodes 31-40 Electrodes 31,40 Current electrodes 50 Measuring system 60 Coating film 61 Recesses a, b Electrode spacing C1, C2 Current electrodes P1, P2 Current electrodes GG Underwater ground G1 Soft viscous soil layer, Surface layer G2 Support layer L Wiring SC Sand pile SC1, SC2 Part of sand pile SS Top surface, surface

Claims (8)

It has multiple electrodes arranged in the radial direction at the bottom of the casing pipe for the sand compaction pile method.
The plurality of electrodes are provided so as to be in contact with the upper end surface of the sand pile created in the ground by the casing pipe, and the specific resistance value inside the sand pile at a predetermined depth from the upper end surface of the sand pile is measured.
A sensor for the sand compaction pile method for evaluating the strength of the sand pile based on the measured resistivity value. The sand compaction according to claim 1, wherein the electrodes are combined from the plurality of electrodes to perform the measurement, and the measurement depth from the upper end surface of the sand pile is changed by changing the combination of the electrodes. Sensor for pile method. The plurality of electrodes are arranged at the lower end of the casing pipe in series with the first radial direction in a first electrode arrangement, and further connected in series with a second radial direction different from the first radial direction. The sensor for the sand compaction pile method according to claim 1 or 2, which is arranged in the electrode arrangement of the above. The sand compaction pile method according to claim 3, wherein the measurement depth from the upper end surface of the sand pile is changed by making the electrode spacing in the first electrode arrangement different from the electrode spacing in the second electrode arrangement. Sensor for. A casing pipe used in a sand compaction pile method for forming sand piles on the ground, which comprises the sensor for the sand compaction pile method according to any one of claims 1 to 4. It has a steel plate extending in the radial direction at the lower end of the casing pipe.
The casing pipe for the sand compaction pile method according to claim 5, wherein the steel plate is provided with the plurality of electrodes. A method for evaluating the strength of a sand pile formed on the ground by the casing pipe using the sensor for the sand compaction pile method according to any one of claims 1 to 4.
Specimens made of sand used for the construction of the sand piles were prepared by changing the pore space.
The specific resistance value of the sand was measured with the specimen, and the relational expression between the specific resistance value of the sand and the pore space was obtained.
The relative density is determined based on the strength required for the sand pile.
Obtain the porosity from the relative density
The specific resistance value was obtained from the obtained clearance ratio and the relational expression.
The resistivity value of the sand pile is measured by the sensor.
A sand pile strength evaluation method for evaluating the strength of a sand pile by comparing the obtained specific resistance value with the measured specific resistance value. Using the sand compaction pile method sensor according to any one of claims 1 to 4 or the sand pile strength evaluation method according to claim 7, the strength of the sand pile is evaluated when the sand pile is constructed by the casing pipe. A construction management method that manages the construction of the sand compaction pile method.

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