JP7248241B2 - Confirmation method of ground improvement effect and measuring device used therefor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for confirming the effect of ground improvement by a chemical injection method mainly aimed at countermeasures against liquefaction, and a measuring device used therefor.

2. Description of the Related Art Conventionally, in order to reinforce soft ground such as landfill sites, ground improvement work has been carried out using a chemical injection method in which a chemical solution such as water glass (sodium silicate) is injected into the ground. In ground improvement work using the chemical injection method, a construction confirmation survey is conducted after construction to confirm whether the chemical solution has spread evenly over the target ground.

The most common method for confirming the construction of the chemical grouting method is to evaluate the improved soil by the unconfined compressive strength qu. However, the unconfined compressive strength of soil improved by the chemical injection method is as small as qu=50 to 100kPa. That is, in the evaluation based on the unconfined compressive strength qu, in the case of the ground with a small qu of about 50 to 100 kPa, turbulence that leads to a decrease in strength is likely to occur during sample collection in the post-survey and during preparation of the test specimen. In addition, depending on the target ground, the mixture of shells, wood chips, silt, organic soil, etc. in the test body may cause variations in strength and may not be evaluated properly.

As a method for directly evaluating the quality of improved ground by methods other than the uniaxial compression test, the Piezo Drive Cone (PDC ), a dynamic cone penetration test that can measure pore water pressure has been proposed. The piezo drive cone penetrates into the ground by hammering a cone with a built-in pressure sensor, and measures the amount of penetration for each hammering and the response value of the pore water pressure at the time of penetration. From the penetration amount, the dynamic penetration resistance value (Nd value) of the ground corresponding to the N value of the standard penetration test is calculated for each impact. In addition, the fine particle content Fc can be estimated from the pore water pressure in the ground generated by impact intrusion, and the cumulative excess pore water pressure ratio obtained using this pore water pressure can be used as an index to evaluate the penetration of the chemical solution into the ground. It is proposed by the above-mentioned review committee, etc.

In addition, electrical logging is another method for confirming the construction of the chemical injection method. In the chemical injection method, the pore water in the ground is replaced with a chemical solution, which changes the compressibility of the ground and the solidification of the chemical solution increases the strength of the ground. It utilizes the fact that the characteristics of With this electrical logging, it is possible to qualitatively judge the improvement effect by the decrease in the resistivity value before and after construction. In the measurement procedure of the electrical logging, after inserting a measuring probe equipped with a plurality of electrodes at predetermined intervals in the vertical direction into the borehole, current is applied to the electrodes, and the specific resistance is obtained from the potential difference between the electrodes. .

As a method for confirming the quality of ground improvement work by such electric logging, in the following Patent Document 1, an electrode mounting body having an annular electrode attached to the outer surface is inserted into the improved body, and an electrode mounting body is created around the electrode mounting body. A method is disclosed in which a current is applied to the modified body and the resistivity is obtained using the current between the current electrodes and the potential difference between the potential electrodes measured in such a state. In addition, Non-Patent Document 1 below discloses a method of obtaining a chemical solution filling rate from changes in electrical resistivity before and after chemical solution injection.

JP-A-2000-46510

Hideo Komine, ``Evaluation method of filling rate of chemical solution injection improvement part by electrical resistivity'', JSCE Journal, No.463/III-22, p.153-162, March 1993

Regarding the above-mentioned dynamic cone penetration test, according to the JGS standard (JGS 1437-2014) of the Japan Geotechnical Society, the energy per unit area and unit penetration amount of a large testing machine (SRS) is used as the standard, and it is corrected by peripheral friction and energy. It is stipulated that the results of large (SRS) and medium (MRS) test rigs can be compared with each other. That is, it is recommended to use either a large or medium sized testing machine. However, the large testing machine (SRS) has a hammer mass of 63.5 kg and a drop height of 500 mm, while the medium-sized testing machine (MRS) has a hammer mass of 30 kg and a drop height of 350 mm. considered to be easy. In addition, according to the report of the above-mentioned review committee, in the above-mentioned dynamic cone penetration test, the unconfined compressive strength qu is said to have a high correlation with the increment of the Nd value (ΔNd value) for each type of soil. However, the increment of the Nd value (ΔNd value) at qu = 100 kPa is very small at 5 or less, and in the dynamic cone penetration test using medium- and large-sized testing machines with large variations, the increment of the Nd value is due to ground improvement. It is difficult to judge whether it is the result or the error range of the testing machine, and a judgment method that can be clearly evaluated has been desired.

On the other hand, in the quality confirmation of ground improvement by electrical logging described in Patent Document 1, it is necessary to bring the annular electrode provided on the peripheral surface of the measurement probe into contact with the wall surface of the penetration hole during measurement. , the diameter of the penetration hole and the measurement probe must be about the same size, which increases the resistance of the measurement probe when it is pulled out, making it impossible to retrieve the measurement probe or damaging the electrode. was likely to occur. In addition, the electrodes are less likely to come into contact with the walls of the through-holes, and poor contact tends to cause deterioration in measurement accuracy. The non-patent document 1 only conducts laboratory experiments and does not solve the above problems in field tests.

Therefore, the first object of the present invention is to provide a method for confirming the effect of ground improvement that has little variation and can directly confirm the quality of the improved ground. The second problem is to eliminate the risk of the measurement probe being unrecoverable in electrical logging and to ensure that the electrode can contact the hole wall.

In order to solve the first problem, the present invention according to claim 1 is a method for confirming the effect of ground improvement by a chemical injection method,
After ground improvement, a small dynamic cone penetration test is performed to obtain a depth distribution map of the Nd value that shows the relationship between depth and Nd value, and the effect of ground improvement is confirmed from the amount of increase in the Nd value before and after the ground improvement. Confirm the following effects,
If the ground improvement effect is not recognized by the confirmation of the primary effect, an electrical logging is performed to measure the resistivity by inserting a measurement probe equipped with an electrode into the penetration hole of the small dynamic cone penetration test, and the depth A ground improvement characterized by obtaining a depth distribution map of specific resistance showing the relationship between and specific resistance, and confirming the secondary effect of confirming the ground improvement effect from the decrement amount of the specific resistance before and after the ground improvement. A method for checking effectiveness is provided.

In the invention according to claim 1, after ground improvement, first, a depth distribution map of the Nd value is obtained by a small dynamic cone penetration test, and the ground improvement effect is confirmed from the amount of increase in the Nd value before and after the ground improvement. Confirm the primary effect. Then, if the ground improvement effect is not recognized by this primary effect confirmation, electrical logging is performed using the penetration hole of the small dynamic cone penetration test to obtain a depth distribution map of resistivity and ground improvement. Secondary effect confirmation is performed to confirm the soil improvement effect from the amount of decrement in the resistivity before and after.

In this way, a small dynamic cone penetration test called PENNY is used to obtain a depth distribution map of the Nd value. With little variation in energy, it becomes possible to properly evaluate the ground strength even in uneven reclaimed ground where variation is likely to occur.

In addition, in confirming the ground improvement effect, first of all, the primary effect is confirmed by the depth distribution map of the Nd value obtained in the small dynamic cone penetration test. Since the effect is confirmed in two stages, such as confirming the secondary effect from the depth distribution map of resistivity by electrical logging, even if the ground improvement effect cannot be judged only by the amount of increase in the Nd value , the ground improvement effect can be clearly grasped from the decrement amount of the resistivity, and the quality of the improved ground can be directly confirmed.

As the present invention according to claim 2, there is provided the method for confirming the ground improvement effect according to claim 1, wherein the electrical logging is performed by the electrode arrangement of the bipolar method.

In the second aspect of the invention, electrical logging is performed by the electrode arrangement of the two-pole method to obtain the specific resistance. In the electrode arrangement of the two-pole method, current is returned to the current far electrode installed near the ground surface, and the potential is measured with the potential electrode while a constant current is flowing from the current electrode with the potential far electrode installed near the ground surface as the reference. This makes it possible to more clearly grasp the ground improvement effect compared to other electrode arrangements.

In order to solve the second problem, the present invention according to claim 3 is a measuring device used in the method for confirming the ground improvement effect according to any one of claims 1 and 2,
The measuring device includes a hollow outer sleeve into which the measuring probe is detachably inserted,
The outer sleeve has a hollow portion into which the measurement probe is inserted over a range including a mounting position of the electrode from a distal end side of insertion into the penetration hole, and a position corresponding to the electrode of the measurement probe. an outer electrode penetrating from the hollow portion to the outer surface and having an inner tip in contact with the electrode when the measurement probe is inserted into the hollow portion;
Confirmation of ground improvement effect characterized in that when it becomes difficult to pull out the measurement probe from the penetration hole, the measurement probe is pulled out of the exterior sleeve and the measurement probe can be recovered. A measuring device for use in the method is provided.

The invention according to claim 3 defines a hollow outer sleeve that is detachably fitted to the measurement probe during electrical logging, and the outer sleeve allows the measurement probe to pass through the penetration hole. A hollow portion inserted from the insertion tip side over a range including the mounting position of the electrode, and a position corresponding to the electrode of the measurement probe are penetrated from the hollow portion to the outer surface, and the measurement probe is inserted into the An outer electrode is provided in which the tip of the inner side is in contact with the electrode while being inserted into the hollow portion. Further, when it becomes difficult to pull out the measurement probe from the penetration hole, the measurement probe can be pulled out of the exterior sleeve by pull-out resistance and can be recovered. In this way, due to the pull-out resistance when the measurement probe is pulled out, the outer sleeve is pulled out and left in the ground, and the measurement probe can be reliably recovered, eliminating the risk of not being able to recover the expensive measurement probe in electrical logging. . Further, since the outer sleeve having a diameter larger than that of the measurement probe is fitted around the measurement probe, the outer electrode provided on the outer sleeve can reliably come into contact with the hole wall of the penetration hole.

According to a fourth aspect of the present invention, the outer sleeve has a contact promoting projection projecting outward on the opposite side of the outer electrode so as to bring the outer electrode into contact with the hole wall when the outer sleeve is inserted into the through hole. A measuring device for use in the method for confirming a ground improvement effect according to claim 3 is provided.

In the invention according to claim 4, when the outer sleeve in which the measurement probe is inserted is inserted into the through hole, the outer electrode provided in the outer sleeve is brought into contact with the hole wall. A contact promoting protrusion projecting outward is provided. This ensures that the outer electrode provided on the outer sleeve is in better contact with the hole wall of the through hole.

According to a fifth aspect of the present invention, the outer sleeve and the measurement probe are connected to each other by fitting a circumferential fixing convex portion provided on the peripheral surface of the measurement probe into a fitting portion provided on the outer sleeve. There is provided a measuring device used for the confirmation method of ground improvement effect according to any one of claims 3 and 4, wherein rotation in the circumferential direction with the probe is fixed.

In the invention according to claim 5, when the outer sleeve is attached to the measuring probe, the electrode of the measuring probe and the outer electrode of the outer sleeve are aligned, and the measuring probe to which the outer sleeve is fitted is inserted into the through hole. In order to prevent relative circumferential rotation between the outer sleeve and the measurement probe when the outer sleeve is inserted into the It is designed to mate with

As described in detail above, according to the present invention, it is possible to directly check the quality of the improved ground with little variation. It also eliminates the risk of irrecoverable measurement probes in electrical logging and ensures that the electrodes can contact the borehole walls.

It is a longitudinal section showing an outline of a measuring device used for electrical logging. 1 is a front view of a measuring probe 2 with an outer sleeve 8 attached; FIG. 2 is a front view of the measurement probe 2; FIG. Fig. 3 shows an exterior sleeve body 12, (A) is a front view, (B) is a cross-sectional view along B-B of (A), (C) is a rear view, and (D) is a cross-sectional view along D-D of (A). (A) is a front view and (B) is a top view showing the tip 13 of the outer sleeve. It is a top view which shows the range of ground improvement and a measurement position. It is the sectional view (VII-VII line arrow line view of FIG. 6). It is a soil histogram. (A) is a depth distribution map of Nd value, (B) is a depth distribution map of resistivity, and (C) is a depth distribution map of uniaxial compressive strength in improvement A. FIG. (A) is a depth distribution map of Nd value, (B) is a depth distribution map of resistivity, and (C) is a depth distribution map of uniaxial compressive strength in improvement B. FIG. In the improved DP, (A) is a depth distribution map of Nd value, (B) is a depth distribution map of resistivity, and (C) is a depth distribution map of uniaxial compressive strength.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The present invention is a method for confirming the effect of ground improvement by a chemical injection method in which a chemical solution made of water glass (sodium silicate) is injected into the ground for strengthening the ground of soft ground such as a landfill. Depends on procedure.

After ground improvement, a small dynamic cone penetration test is performed to obtain a depth distribution map of the Nd value that shows the relationship between depth and Nd value, and the effect of ground improvement is confirmed from the amount of increase in the Nd value before and after the ground improvement. Confirm the following effects,
When the ground improvement effect is not recognized by the confirmation of the primary effect, as shown in FIGS. Electrical logging is performed to measure the specific resistance R by inserting it, obtaining a depth distribution map of the specific resistance R that shows the relationship between the depth and the specific resistance R, and using the decrement amount of the specific resistance R before and after the ground improvement Perform secondary effect confirmation to confirm the improvement effect.

That is, in the present invention, after confirming the primary effect by the depth distribution map of the Nd value obtained by the small dynamic cone penetration test, the secondary effect by the depth distribution of the resistivity obtained by electrical logging I am checking. This procedure will be described in detail below.

(Primary effect confirmation)
The small dynamic cone penetration test is a penetration test performed using a small dynamic cone penetration tester called PENNY manufactured by Tecnotest of Italy. The test method is to let a hammer with a mass of 294 N (30 kgf) fall automatically from a height of 20 cm using a hydraulic motor, and to penetrate a tip cone with a cross-sectional area of 10 cm ² and a tip angle of 60° for 10 cm. Continuously measure the number of impacts (Nd value). By measuring the rotational torque of the rod every 1m and correcting the influence of the frictional force acting on the rod, it can be converted to the Nd value equivalent to the N value of the standard penetration test. Advantages of the compact dynamic cone penetration test compared to the standard penetration test include:

(1) In the standard penetration test, the measurement points are arranged at a pitch of 1m, so if the layer thickness of the chemical solution is about 1 to 2m, the measurement points cannot be secured. .
(2) The unconfined compressive strength qu of the improved soil is about 50 to 100 kPa, so the standard penetration test requires too much impact energy for accuracy, whereas the small dynamic cone penetration test requires too much impact energy. It is small (just right for the target intensity range) and ensures measurement accuracy. In the case of the standard penetration test, the free fall energy with a hammer mass of 63.5 kg and a drop height of 76 cm was 473 J. Approximately 12% impact energy.
(3) Since the drop operation is fully automatic, there is little variation in impact energy.
(4) The tester is light and easy to handle.

In this way, by measuring the Nd value using the small dynamic cone penetration test, compared to the standard penetration test, the installation space is narrow and excellent in portability. Therefore, it is possible to reliably confirm the effect of ground improvement even on uneven landfill ground, etc., which tends to cause variations.

A depth distribution diagram of the Nd value showing the relationship between the depth and the Nd value is obtained by the small dynamic cone penetration test (see FIGS. 9 to 11 (A)).

Using the Nd value depth distribution map obtained by the small dynamic cone penetration test, the primary effect confirmation of the ground improvement effect is performed. The confirmation method of the ground improvement effect in this primary effect confirmation is performed by the amount of increase in the Nd value before and after the ground improvement, as shown in FIGS. 9(A), 10(A) and 11(A). The increment of the Nd value is not so large in the ground where the Nd value before ground improvement is close to the target improvement strength, and the ground improvement effect by this Nd value may not be recognized. In that case, a secondary effect confirmation is carried out by electrical logging as described below.

(Secondary effect confirmation)
In the secondary effect confirmation, first, after the small dynamic cone penetration test, electrical logging is performed using the penetration hole 1 . The electrical logging was performed by an indentation device shown in FIG. 1 into the penetration hole 1 of the miniature dynamic cone penetration test, one current electrode 3 and two potential electrodes 4, as shown in FIGS. , 4 is inserted, and while these electrodes 3 and 4 are in contact with the hole wall, the potential when a current is applied to the current electrode 3 is detected by the potential electrode 4, and the ground near the hole wall is detected. It is a geophysical exploration method that continuously measures the specific resistance R of the depth direction.

As shown in FIG. 1, the press-fitting device has pistons 20, 20 which are vertically extendable on both sides of the through-hole 1 on the ground surface directly above the through-hole 1. These pistons A chuck 22 for clamping the penetration rod 5 having the measurement probe 2 connected to the lower end thereof is provided in the center of the frame 21 straddling the upper ends of the pistons 20 and 20, and controls the operation of the pistons 20 and 20. A control unit 23 is provided. A hydraulic unit 24 including an engine and a hydraulic pump is connected to the control unit 23 .

In the press-fitting device, the pistons 20, 20 on both sides expand and contract in synchronism, and the pedestal 21 moves vertically, thereby moving the penetration rod 5 clamped by the chuck 22 vertically. is pushed into and pulled out of the penetration hole 1.

As shown in FIG. 2, the measuring device used for electrical logging includes a measuring probe 2 provided with the electrodes 3, 4, . It includes an electric cable 7 connected to the electrodes 3, 4, . . . The electric cable 7 extends to the ground through the hollow portion of the penetrating rod 5 formed in a hollow cylindrical shape, and the tip thereof is connected to the measuring device on the ground.

The measurement probe 2 has a rod-like appearance with a substantially circular cross section, and has an upper end formed with a male threaded portion 6 for connecting the penetration rod 5, and a female threaded portion provided at the lower end of the penetration rod 5. It can be screwed together. Further, a body portion 10 having a plurality of electrodes arranged at predetermined intervals in the axial direction (vertical direction) is provided continuously from the lower end of the male screw portion 6 via an intermediate portion 9 . A distal end portion 11 having a diameter smaller than that of the main body portion 10 is provided continuously from the lower end of the portion 10 .

The electrode arrangement for the electrical logging may be a 4-pole method or a 3-pole method, but is preferably a 2-pole method. As shown in FIGS. 2 and 3, in the electrode arrangement of the two-pole method, one current electrode 3 and two potential electrodes 4, 4 are arranged at predetermined intervals in the vertical direction and installed near the ground surface. A current is returned to a current far electrode (not shown), and with a potential far electrode (not shown) installed near the ground surface as a reference, a constant current is passed from the current electrode 3 while the potential is applied to the potential electrodes 4 and 4. It is what you measure. Compared to the electrode arrangement of the 4-pole method and the 3-pole method, the ground improvement effect can be grasped more clearly.

As shown in FIG. 2, of the three electrodes provided on the main body 10 of the measurement probe 2, the uppermost electrode is the current electrode 3, and the two electrodes below it are the current electrodes 3. Each is a potential electrode 4 . It is preferable that the electrode spacing a between the current electrode 3 and the upper potential electrode 4 is 2.5 cm, and the electrode spacing b between the current electrode 3 and the lower potential electrode 4 is 5 cm. By arranging the two potential electrodes 4, 4 with different electrode spacings from the current electrode 3 in this way, two potential differences with different electrode spacings can be measured at the same time. Time can be shortened.

The electrodes 3, 4, .

Next, the exterior sleeve 8 attached to the distal end side of the measurement probe 2 when the measurement probe 2 is inserted into the penetration hole 1 will be described. In order to facilitate manufacturing, the outer sleeve 8 is fitted to an outer sleeve main body 12 fitted to the main body portion 10 of the measurement probe 2 and to the distal end portion 11 of the measurement probe 2, as shown in FIG. It is preferable to divide into an outer sleeve tip 13 that

As shown in FIG. 4, the outer sleeve body 12 is formed in a substantially cylindrical shape open at both ends in the axial direction, and as shown in FIG. It is formed so as to be larger than the outer diameter of the measurement probe 2 . By making the outer diameter of the outer sleeve 8 larger than the outer diameter of the measurement probe 2 , when the outer sleeve 8 penetrates into the penetration hole 1 , the outer sleeve 8 easily comes into contact with the hole wall. Damage can be suppressed. The outer diameter of the outer sleeve 8 is preferably approximately the same as the outer diameter of the tip cone used in the small dynamic cone penetration test.

As shown in FIG. 5, the front end 13 of the outer sleeve is formed into a bottomed cylindrical shape with an upper part open upward and a conical (cone-shaped) outer shape of the lower part that points downward. It is The outer diameter of the upper bottomed cylindrical portion is formed substantially equal to the outer diameter of the outer sleeve main body 12 . The tip angle of the cone is preferably about 45° to 90°, more preferably 60°.

As shown in FIGS. 4 and 5, the outer sleeve 8 is a hollow body into which the measuring probe 2 is inserted over a range from the distal end of the insertion hole 1 to the attachment positions of the electrodes 3, 4, . and the electrodes 3, 4, . . . Outer electrodes 15, 16, 16 are provided whose inner tips are in contact with the electrodes 3, 4, . . . , respectively. The electrodes 3, 4, . . . provided on the measuring probe 2 correspond to the outer electrodes 15, 16, . The two lower outer electrodes 16, 16 are potential electrodes.

When it becomes difficult to pull out the measurement probe 2 from the penetration hole 1 after the measurement probe 2 with the outer sleeve 8 attached is inserted into the penetration hole 1 by the press-fitting device to perform electrical logging, Due to the resistance, the measuring probe 2 is pulled out of the outer sleeve 8 so that the measuring probe 2 can be recovered. In this way, due to the pull-out resistance when the measuring probe 2 is pulled out, the outer sleeve 8 is pulled out and remains in the ground, and the measuring probe 2 pulled out of the outer sleeve 8 can be reliably recovered. The risk of unrecoverable measurement probe 2 is eliminated. As described above, the measurement probe 2 is formed to have an outer diameter smaller than that of the outer sleeve 8, so that it can be pulled out relatively smoothly from the insertion hole 1 into which the outer sleeve 8 is attached. Become.

In order to bring the outer electrodes 15, 16 into contact with the hole wall when the outer sleeve 8 is inserted into the through-hole 1, the outer surface of the outer surface opposite to the outer electrodes 15, 16, . Preferably, a portion 17 is provided. The contact promoting projection 17 is a vertically elongated projection formed in a range including the entire length of the arrangement section of the outer electrodes 15 , 16 . . . The height is preferably 1-8 mm, more preferably 3-5 mm. By providing the contact promoting projections 17, the outer electrodes 15, 16, .

As shown in FIG. 3 , a circumferential fixing protrusion 18 is provided on the peripheral surface of the measurement probe 2 , and this circumferential fixing protrusion 18 is fitted into a fitting portion 19 provided on the outer sleeve 8 . Thereby, the circumferential rotation of the outer sleeve 8 and the measuring probe 2 is preferably fixed. The circumferential fixing convex portion 18 is formed at the upper end portion of the main body portion 10 of the measurement probe 2 , and the fitting portion 19 is formed at the upper end portion of the outer sleeve main body 12 of the outer sleeve 8 . By fitting the circumferential fixing projection 18 into the fitting portion 19, the measurement probe 2 and the outer sleeve main body 12 of the outer sleeve 8 are prevented from rotating in the circumferential direction. 1 of the measuring probe 2 and the outer electrodes 15, 16 of the outer sleeve 8 are not misaligned.

In the electrical logging procedure, after performing the small dynamic cone penetration test, the press-fitting device shown in FIG. The measurement probe 2 is inserted into the penetration hole 1, and the specific resistance R is continuously measured in the depth direction while the measurement probe 2 is gradually press-fitted. The measurement interval of the specific resistance R is arbitrary, but it is preferably 10 cm or less, preferably 5 cm or less, more preferably 1 cm. After the measurement is completed up to a predetermined depth, the measurement probe 2 is pulled out from the penetration hole 1 and recovered.

By the electrical logging, a depth distribution map of the resistivity R showing the relationship between the depth and the resistivity R can be obtained (see FIGS. 9 to 11 (B)).

Using the depth distribution map of resistivity R obtained by the above electric logging, the ground improvement effect is confirmed. The confirmation method of the ground improvement effect is performed by comparing the decrement amount of the specific resistance R before and after the ground improvement. As shown in FIGS. 10 (A), (B) and FIGS. 11 (A), (B), even if the improvement effect is not clearly recognized only by the depth distribution map of the Nd value for confirming the primary effect , The ground improvement effect can be clearly confirmed from the depth distribution map of resistivity, which is a secondary effect confirmation. From the viewpoint of work efficiency and cost reduction, it is desirable to confirm the effect by electrical logging (secondary effect confirmation) only when no effect is recognized by the above-mentioned primary effect confirmation. Even if the ground improvement effect is clearly recognized by the confirmation of the effect, a secondary effect confirmation may be performed to further improve reliability.

Hereinafter, the method for confirming the ground improvement effect in detail will be described using specific examples carried out on site. As shown in FIGS. 6 and 7, ground improvement with different specifications was constructed at three locations, improvement A, improvement B, and improvement DP, for the target ground, and the effect was confirmed. A standard penetration test was performed on the target ground (preliminary Bor) near the improvement area, and the soil log shown in Fig. 8 was obtained. As a result, silt-mixed fine sand contains organic soil at GL-2m to -4m, and silt layered at depths below GL-5m. The construction specifications for each ground improvement are shown in Table 1. The improvement body age at the time of measurement is about 11 months.

In Fig. 6, the ▲ marks are the small dynamic cone penetration test and electrical logging sites, the ■ marks are the block sampling sites for measuring the unconfined compressive strength qu, and the ● mark indicates the measured unconfined compressive strength qu. This is the site where the rotary type triple tube sampling is carried out. The small dynamic cone penetration test and electrical logging indicated by the ▲ mark were conducted at two locations (A1 and A2) 10 cm and 40 cm away from the improvement center for Improvement A, and at 40 cm, 70 cm and 100 cm away from the improvement center for Improvement B. In the case of improved DP, this was performed at one point (DP1) 30 cm away from the center of improvement.

9 is a depth distribution map of improvement A, FIG. 10 is a depth distribution map of improvement B, and FIG. 11 is a depth distribution map of improvement DP. The depth distribution map of the specific resistance R in (B) is the specific resistance R at an electrode interval of 2.5 cm. (C) The depth distribution map of the unconfined compressive strength qu is the test result of 28 days old.

The ground before improvement has Nd value = 0 to 20 (average Nd value = 9), R = 40 to 120Ω・m ( Average R = 65 Ω・m), and specific resistance R is 30 to 40 Ω・m at GL-2 m to GL-4 m, which includes organic soil, and GL-5 m, which includes layers of silt. It is assumed that there are places with many fine grains in the range.

In Improvement A, as shown in Fig. 9(A), the increment of the average Nd value due to improvement is about 4 at the improvement center + 10 cm position (●) and about 12 at the improvement center + 40 cm position (▲). An increase in the Nd value due to the improvement is recognized, and the improvement effect can be confirmed. As shown in FIG. 9(B), the average value of the specific resistance R is 4 Ω・m at the improvement center +10 cm position (●) and 2 Ω・m at the improvement center +40 cm position (▲). In comparison, it has decreased to about 1/10 to 1/100. In addition, almost uniform values are shown over the entire improvement range. On the other hand, as shown in FIG. 9(C), the unconfined compressive strength qu of the specimens mixed with organic soil and silt is small and varies greatly.

In improvement B, as shown in FIG. 10(A), no increase in the average Nd value due to the improvement was observed at any of the measurement points of improvement center +40 cm, +70 cm, and +100 cm. As shown in Fig. 10(B), the average value of the specific resistance R is 5 to 7Ω·m at GL-2.0m to -3.5m, but 35 to 80Ω·m at GL-3.5m to -4.0m. It shows a value close to m and unimproved ground. At GL-2.0 m to -2.5 m, where the specific resistance R is low, as shown in FIG. 10(C), the unconfined compressive strength qu also exhibits the target improved strength qu=50 kPa (average value).

In the modified DP, as shown in FIG. 11(A), no increase in the average Nd value due to the modification was observed at the modification center +30 cm position (●). As shown in FIG. 11(B), the average value of the specific resistance R is about 5 Ω·m in the GL-3.0 m to -5.0 m range, but 20 to 40 Ω·m in the other improved ranges. .

From the above examination results, it is possible to clearly confirm the ground improvement effect in Improvement A by confirming the primary effect using the Nd value depth distribution map. On the other hand, in the improvement B and the improvement DP, the target improvement strength was lower than that of the improvement A, so it could not be judged by the primary effect confirmation, but the secondary effect confirmation using the depth distribution map of the specific resistance R clearly showed The ground improvement effect can be confirmed.

[Other form examples]
In the above embodiment, the outer sleeve 8 is composed of two members consisting of the outer sleeve main body 12 and the outer sleeve tip 13, but it may be composed of one integrated member.

DESCRIPTION OF SYMBOLS 1... Through-hole 2... Measurement probe 3... Current electrode 4... Potential electrode 5... Penetration rod 6... Male screw part 7... Electric cable 8... Exterior sleeve 9... Intermediate part 10... Body part, DESCRIPTION OF SYMBOLS 11... Tip part 12... Exterior sleeve main body 13... Exterior sleeve tip 14... Hollow part 15... Outer electrode (current electrode) 16... Outer electrode (potential electrode) 17... Contact promotion convex part 18... Circumferential fixing convex portion 19 Fitting portion 20 Piston 21 Base 22 Chuck 23 Control unit 24 Hydraulic unit

Claims (5)

A method for confirming the ground improvement effect by the chemical injection method,
After ground improvement, a small dynamic cone penetration test is performed to obtain a depth distribution map of the Nd value that shows the relationship between depth and Nd value, and the effect of ground improvement is confirmed from the amount of increase in the Nd value before and after the ground improvement. Confirm the following effects,
If the ground improvement effect is not recognized by the confirmation of the primary effect, an electrical logging is performed to measure the resistivity by inserting a measurement probe equipped with an electrode into the penetration hole of the small dynamic cone penetration test, and the depth A ground improvement characterized by obtaining a depth distribution map of specific resistance showing the relationship between and specific resistance, and confirming the secondary effect of confirming the ground improvement effect from the decrement amount of the specific resistance before and after the ground improvement. How to confirm the effect. 2. The method for confirming a ground improvement effect according to claim 1, wherein said electrical logging is performed by a bipolar electrode arrangement. A measuring device used in the method for confirming the ground improvement effect according to any one of claims 1 and 2,
The measuring device includes a hollow outer sleeve into which the measuring probe is detachably inserted,
The outer sleeve has a hollow portion into which the measurement probe is inserted over a range including a mounting position of the electrode from a distal end side of insertion into the penetration hole, and a position corresponding to the electrode of the measurement probe. an outer electrode penetrating from the hollow portion to the outer surface and having an inner tip in contact with the electrode when the measurement probe is inserted into the hollow portion;
Confirmation of ground improvement effect characterized in that when it becomes difficult to pull out the measurement probe from the penetration hole, the measurement probe is pulled out of the exterior sleeve and the measurement probe can be recovered. Measuring device used in the method. 3. The outer sleeve is provided with a contact-promoting protrusion protruding outward on the opposite side of the outer electrode so as to bring the outer electrode into contact with the hole wall when the outer sleeve is inserted into the through hole. A measuring device used for the confirmation method of the described ground improvement effect. A circumferential fixing convex portion provided on the peripheral surface of the measurement probe is fitted into a fitting portion provided on the outer sleeve, so that the outer sleeve and the measurement probe are rotated in the circumferential direction. 5. A measuring device used in the method for confirming a ground improvement effect according to claim 3 or 4, wherein the measuring device is fixed.

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