JP2021004473A - Method of confirming ground improvement effect and measuring device used for it - Google Patents

Abstract

To provide a method and a measuring device for confirming the effect of ground improvement that reduces variation, enables direct confirmation of the quality of improved ground, eliminates the risk that a measurement probe cannot be recovered in the electrical logging, and ensures that electrodes are in contact with the hole wall.SOLUTION: After the ground improvement, a depth distribution map of the Nd value was obtained by a small dynamic cone penetration test, and the primary effect was confirmed to confirm the ground improvement effect. When the ground improvement effect is not recognized by the above primary effect confirmation, a measurement probe 2 equipped with an electrode is inserted into a penetration hole 1 of the small dynamic cone penetration test, and a depth distribution map of the specific resistance is obtained by an electrical logging for measuring the specific resistance. A secondary effect is confirmed to confirm the ground improvement effect from the amount of resistivity reduction before and after the ground improvement. In the electrical logging, when a hollow outer sleeve is detachably inserted into the measurement probe 2 and it becomes difficult to pull it out from the penetration hole 1, the measurement probe 2 can be removed from the outer sleeve and recovered.SELECTED DRAWING: Figure 1

Description

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

Conventionally, in order to strengthen the ground of soft ground such as landfills, ground improvement work has been carried out by a chemical injection method in which a chemical solution consisting of water glass (sodium silicate) or the like is injected into the ground. In the ground improvement work by the chemical injection method, after the construction, a construction confirmation survey is conducted to confirm whether the chemical is evenly distributed over the target ground.

The most common method for confirming the construction of the chemical injection method is to evaluate the improved soil by the uniaxial compressive strength qu. However, the uniaxial compressive strength of the improved soil produced by the chemical injection method is as small as qu = 50 to 100 kPa, and the strength may vary depending on the target ground, resulting in improper evaluation. That is, in the evaluation based on the uniaxial compressive strength qu, when the qu is as small as about 50 to 100 kPa, turbulence leading to a decrease in strength is likely to occur at the time of sampling in the ex-post survey or at the time of preparing the specimen. In addition, depending on the target ground, shells, wood chips, silt, organic soil, etc. may be mixed in the test body, resulting in variations in strength, which may not be evaluated properly.

As a method for directly evaluating the quality of the improved ground by a method other than such a uniaxial compression test, the piezo drive cone (PDC) was held at the study committee on the ground improvement work by the chemical injection method at the landfill site of the Ministry of Land, Infrastructure, Transport and Tourism. ), Etc., a dynamic cone penetration test that can measure pore water pressure has been proposed. The piezo drive cone penetrates the ground by hitting a hammer with a cone having a built-in pressure sensor, and measures the penetration amount for each hit 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 is estimated from the pore water pressure in the ground generated by the impact penetration, and the cumulative excess pore water pressure ratio obtained using this pore water pressure serves as an index for evaluating the penetration of the chemical solution into the ground. What to obtain is proposed by the above-mentioned review committee.

In addition, as another method for confirming the construction of the chemical injection method, there is an electrical logging method. In the electrical logging method, in the chemical logging method, the interstitial water in the ground is replaced with the chemical solution, the compressibility of the ground changes, and the strength of the ground increases as the chemical solution solidifies, so the improved ground has electrical conductivity. It utilizes the change in the characteristics of. In this electrical logging, the improvement effect can be qualitatively judged by reducing the resistivity value before and after construction. In the measurement procedure of the electrical logging, after inserting a measurement probe provided with a plurality of electrodes at predetermined intervals in the vertical direction into the boring hole, the current electrode is energized and the resistivity is obtained from the potential difference between the electrodes. ..

As a method for confirming the quality of the ground improvement work by such an electric inspection, 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 formed around the electrode mounting body. A method of energizing an improved body and obtaining a specific resistance by using the current between current electrodes and the potential difference between potential electrodes measured in such a state is disclosed. Further, Non-Patent Document 1 below discloses a method of obtaining a chemical solution filling rate from a change in electrical resistivity before and after injection of a chemical solution.

Japanese Unexamined Patent Publication No. 2000-46510

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

Regarding the above-mentioned dynamic cone penetration test, the JGS standard (JGS 1437-2014) of the Japanese Geotechnical Society is based on the energy per unit area and unit penetration of a large testing machine (SRS), and is corrected by peripheral friction and energy. By doing so, it is stipulated that the results of each of the large (SRS) and medium (MRS) test equipment can be compared with each other. That is, it is recommended to use either a large or medium size testing machine. However, the large testing machine (SRS) has a hammer mass of 63.5 kg and a drop height of 500 mm, and the medium-sized tester (MRS) has a hammer mass of 30 kg and a drop height of 350 mm. All of the testing machines have high impact energy and data variation occurs. It is considered easy. In addition, according to the report of the above-mentioned review committee, in the above-mentioned dynamic cone penetration test, the uniaxial compressive strength qu is highly correlated with the increment of Nd value (ΔNd value) for each type of soil. However, the increment of Nd value (ΔNd value) at qu = 100 kPa is very small, 5 or less, and in the dynamic cone penetration test using medium and large-sized testing machines with large variations, the increment of 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 the ground improvement by the electric inspection 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 at the time of measurement. , The diameter of the penetration hole and the measurement probe must be about the same size, which increases the resistance when the measurement probe is pulled out, which causes problems such as the measurement probe becoming unrecoverable and the electrode being damaged. Was likely to occur. In addition, it is difficult for the electrode to come into contact with the wall surface of the penetration hole, and the measurement accuracy is likely to deteriorate due to poor contact. In Non-Patent Document 1, only laboratory experiments are performed, and the above-mentioned problems in field tests are not solved.

Therefore, the first object of the present invention is to provide a method for confirming the ground improvement effect, which has less variation and can directly confirm the quality of the improved ground. A second issue is to eliminate the risk of unrecoverable measurement probes in electrical logging and to ensure that the electrodes are in contact with the pore wall.

In order to solve the first problem, the present invention according to claim 1 is a method for confirming the ground improvement effect by a chemical injection method.
After the ground improvement, obtain a depth distribution map of the Nd value showing the relationship between the depth and the Nd value by a small dynamic cone penetration test, and confirm the ground improvement effect from the increment of the Nd value before and after the ground improvement. Check the next effect and
When the ground improvement effect is not recognized by the primary effect confirmation, a measuring probe equipped with an electrode is inserted into the penetration hole of the small dynamic cone penetration test to perform electrical logging to measure the specific resistance, and the depth is obtained. The ground improvement is characterized in that a depth distribution map of the resistivity showing the relationship between the resistivity and the resistivity is obtained, and the secondary effect of confirming the ground improvement effect is confirmed from the reduction amount of the resistivity before and after the ground improvement. A method of confirming the effect is provided.

In the invention according to claim 1, after the 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 increment amount of the Nd value before and after the ground improvement. Confirm the primary effect. Then, when the ground improvement effect is not recognized by this primary effect confirmation, an electrical logging is performed using the penetration hole of the small dynamic cone penetration test to obtain a depth distribution map of the specific resistance, and the ground improvement is obtained. A secondary effect confirmation is performed to confirm the ground improvement effect from the reduction amount of the specific resistance before and after.

In this way, since the depth distribution map of the Nd value is obtained by the so-called PENNY small dynamic cone penetration test, the impact is compared with the standard penetration test and the piezo drive cone using the above-mentioned medium and large-sized testing machines. It will be possible to properly evaluate the ground strength even in uneven landfill ground where there is little energy variation and variation is likely to occur.

In addition, in confirming the ground improvement effect, first, the primary effect is confirmed by the depth distribution map of the Nd value obtained in the small dynamic cone penetration test, and when the ground improvement effect is still not recognized. Since the effect is confirmed in two steps, such as confirming the secondary effect from the depth distribution map of the resistivity by electrical logging, even if the ground improvement effect cannot be judged only by the increment of the Nd value. , The ground improvement effect can be clearly grasped from the reduction amount of the specific resistance, and the quality of the improved ground can be directly confirmed.

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

In the invention according to claim 2, the specific resistance is obtained by performing electrical logging by the electrode arrangement of the bipolar method. In the two-pole electrode arrangement, the current is returned to the current far electrode installed near the ground surface, and the potential is measured by the potential electrode while a constant current is flowing from the current electrode with reference to the potential far electrode also installed near the ground surface. This makes it possible to more clearly grasp the effect of improving the ground compared to other electrode arrangements.

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

The invention according to claim 3 defines a hollow outer sleeve that is detachably fitted to a measuring probe during electrical inspection, and the outer sleeve allows the measuring probe to enter the penetration hole. A hollow portion to be 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 measurement probe. It is provided with an outer electrode provided with the inner tip in contact with the electrode while being inserted into the hollow portion. Then, when it becomes difficult to pull out the measuring probe from the penetration hole, the measuring probe can be pulled out from the outer sleeve due to the pulling resistance and can be recovered. In this way, the pull-out resistance when pulling out the measurement probe causes the outer sleeve to come off and remain in the ground, and the measurement probe can be reliably recovered, thus eliminating the risk of unrecoverability of the expensive measurement probe in the electrical logging. .. Further, since the outer sleeve having a diameter larger than that of the measurement probe is fitted onto the measurement probe, the outer electrode provided on the outer sleeve can be reliably contacted with the hole wall of the penetration hole.

According to the fourth aspect of the present invention, when the exterior sleeve is inserted into the penetration hole, the outer electrode is brought into contact with the hole wall, so that the outer electrode protrudes outward on the opposite side of the outer electrode for promoting contact. Provided is a measuring device used for the method for confirming the ground improvement effect according to claim 3, wherein the unit is provided.

In the invention according to claim 4, when the outer sleeve into which the measurement probe is inserted is inserted into the penetration hole, the outer electrode provided in the outer sleeve is brought into contact with the hole wall, so that the outer electrode is on the opposite side of the outer electrode. A convex portion for promoting contact is provided so as to project outward. As a result, the outer electrodes provided on the outer sleeve can be reliably contacted by the hole wall of the penetration hole.

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

In the invention according to claim 5, the measurement probe in which the outer sleeve is fitted is penetrated for alignment of the electrode of the measurement probe and the outer electrode of the outer sleeve when the outer sleeve is attached to the measurement probe. In order to prevent the relative rotation of the outer sleeve and the measuring probe in the circumferential direction when the measuring probe is inserted into the measuring probe, a convex portion for fixing in the circumferential direction provided on the peripheral surface of the measuring probe is provided in the fitting portion provided on the outer sleeve. It is designed to fit into.

As described in detail above, according to the present invention, there is little variation and the quality of the improved ground can be directly confirmed. In addition, the risk of uncollectible measurement probe in the electrical logging is eliminated, and the electrode can be reliably contacted with the hole wall.

It is a vertical cross-sectional view which shows the outline of the measuring apparatus used for electrical logging. It is a front view of the measuring probe 2 to which the outer sleeve 8 is attached. It is a front view of the measurement probe 2. The exterior sleeve main body 12 is shown, (A) is a front view, (B) is a B-B sectional view of (A), (C) is a back view, and (D) is a D-D sectional view of (A). The outer sleeve tip 13 is shown, (A) is a front view, and (B) is a top view. It is a top view which shows the range of the ground improvement and the measurement position. It is the cross-sectional view (the VII-VII line arrow view of FIG. 6). It is a soil log. In the improved A, (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 the improved B, (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 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.

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 ground improvement effect by a chemical solution injection method of injecting a chemical solution composed of water glass (sodium silicate) or the like into the ground in order to strengthen the ground of soft ground such as a landfill. According to the procedure.

After the ground improvement, obtain a depth distribution map of the Nd value showing the relationship between the depth and the Nd value by a small dynamic cone penetration test, and confirm the ground improvement effect from the increment of the Nd value before and after the ground improvement. Check the next effect and
When the ground improvement effect is not recognized by the primary effect confirmation, as shown in FIGS. 1 and 2, a measuring probe provided with electrodes 3 and 4 in the penetration hole 1 of the small dynamic cone penetration test is used. An electrical logging is performed by inserting and measuring the resistivity R, a depth distribution map of the resistivity R showing the relationship between the depth and the resistivity R is obtained, and the ground is obtained from the reduction amount of the resistivity R before and after the ground improvement. Confirm the improvement effect Perform the secondary effect confirmation.

That is, in the present invention, after confirming the primary effect by the depth distribution map of the Nd value obtained in the small dynamic cone penetration test, the secondary effect is obtained by the depth distribution of the resistivity obtained by the electrical logging. We are checking. Hereinafter, a specific description will be given according to this procedure.

(Confirmation of primary effect)
The small dynamic cone penetration test is a penetration test performed using a small dynamic cone penetration tester manufactured by Tecnotest of Italy, which is so-called PENNY. The test method is necessary to automatically drop a hammer with a mass of 294N (30kgf) from a height of 20cm using a hydraulic motor to penetrate a tip cone with a cross-sectional area of 10cm ² and a tip angle of 60 ° by 10cm. The number of hits (Nd value) is continuously measured. By measuring the rotational torque of the rod every 1 m and correcting the influence of the frictional force acting on the rod, it is possible to convert it to the Nd value equivalent to the N value of the standard penetration test. The advantages of the small dynamic cone penetration test compared to the standard penetration test are as follows.

(1) Since the measurement points are 1 m pitch in the standard penetration test, the measurement points cannot be secured if the layer thickness of the chemical injection is about 1 to 2 m, whereas the small dynamic cone penetration test can measure every 10 cm. ..
(2) Since the uniaxial compressive strength qu of the improved soil is about 50 to 100 kPa, the impact energy is too large for the standard penetration test and the accuracy cannot be obtained, whereas the impact energy for the small dynamic cone penetration test is high. It is small (just right for the target intensity range) and measurement accuracy can be ensured. In the standard penetration test, the free fall energy with a hammer mass of 63.5 kg and a drop height of 76 cm is 473 J, while in the small dynamic cone penetration test, the free fall energy with a hammer mass of 30 kg and a drop height of 20 cm is 58.8 J. It has a striking energy of about 12%.
(3) Since the falling work is fully automatic, there is little variation in striking energy.
(4) The testing machine 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, it has excellent portability in a narrow installation space, and because it is fully automatic, there is little variation in impact energy. Therefore, the ground improvement effect can be surely confirmed even in uneven landfill ground where variations are likely to occur.

The small dynamic cone penetration test obtains a depth distribution map of the Nd value showing the relationship between the depth and the Nd value (see (A) of FIGS. 9 to 11).

Using the depth distribution map of the Nd value obtained by the small dynamic cone penetration test, the primary effect of confirming the ground improvement effect is confirmed. The method of confirming the ground improvement effect in this primary effect confirmation is performed by increasing the Nd value before and after the ground improvement, as shown in FIGS. 9 (A), 10 (A) and 11 (A). The amount of increase in the Nd value is not so large in the ground where the Nd value before the 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, the secondary effect confirmation by the electrical logging described below is performed.

(Confirmation of secondary effect)
In the secondary effect confirmation, first, after the small dynamic cone penetration test, an electrical logging is performed using the penetration hole 1. The electrical inspection layer is formed by the press-fitting device shown in FIG. 1 in the penetration hole 1 of the small dynamic cone penetration test, as shown in FIGS. 2 and 3, one current electrode 3 and two potential electrodes 4. The measurement probe 2 provided with 4 is inserted, and the potential when a current is passed through the current electrode 3 is detected by the potential electrode 4 while bringing these electrodes 3 and 4 into contact with the hole wall, and the ground near the hole wall is detected. This is a physical exploration method for continuously measuring the specific resistance R of the current in the depth direction.

As shown in FIG. 1, in the press-fitting device, pistons 20 and 20 which are stretchable in the vertical direction are arranged on both sides of the penetration hole 1 on the ground surface directly above the penetration hole 1, respectively. A chuck 22 for sandwiching the penetration rod 5 to which the measuring probe 2 is connected to the lower end is provided at the central portion of the gantry 21 straddling the upper ends of the 20 and 20, and controls the operation of the pistons 20 and 20. A control unit 23 is provided. Further, 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 and 20 on both sides are synchronized and expanded and contracted, and the gantry 21 moves in the vertical direction, whereby the penetration rod 5 sandwiched by the chuck 22 moves in the vertical direction, and the measurement probe 2 Is pushed into and pulled out into the penetration hole 1.

As shown in FIG. 2, the measuring device used for the electrical inspection is a measuring probe 2 provided with the electrodes 3, 4, ..., Extending from the upper end of the measuring probe 2, and having a tip inside the measuring probe 2. It includes an electric cable 7 connected to the electrodes 3, 4, ... And a hollow outer sleeve 8 into which the measurement probe 2 is detachably inserted. The electric cable 7 extends to the ground through a hollow portion of a penetration rod 5 formed in a hollow cylindrical shape, and the tip thereof is connected to a measuring device on the ground.

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

The electrode arrangement of the electrical logging may be a 4-pole method or a 3-pole method, but a 2-pole method is preferable. As shown in FIGS. 2 and 3, one current electrode 3 and two potential electrodes 4 and 4 are arranged at predetermined intervals in the vertical direction, and the electrodes are arranged near the ground surface. The current is returned to the current far electrode (not shown), and the potential is measured by the potential electrodes 4 and 4 while passing a constant current from the current electrode 3 with reference to the potential far electrode (not shown) also installed near the ground surface. It is to measure. Compared with the electrode arrangement of the 4-pole method and the 3-pole method, the improvement effect of the ground 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 electrode arranged at the uppermost portion is the current electrode 3, and the two electrodes arranged on the lower side thereof are Each is a potential electrode 4. It is preferable that the electrode distance a between the current electrode 3 and the upper potential electrode 4 is 2.5 cm, and the electrode distance b between the current electrode 3 and the lower potential electrode 4 is 5 cm. By arranging the two potential electrodes 4 and 4 having different electrode spacings from the current electrode 3 in this way, the two potential differences having different electrode spacings can be measured at the same time, so that the measurement accuracy is improved and the measurement is performed. Time can be shortened.

The electrodes 3, 4, ... Are made of a conductive metal material and are provided so as to penetrate from the inside to the outer surface of the measurement probe 2, and the tips of the electric cables 7 are connected to the insides of the measurement probe 2, respectively.

Next, the exterior sleeve 8 attached to the tip end side of the measurement probe 2 when the measurement probe 2 is penetrated into the penetration hole 1 will be described. As shown in FIG. 2, the exterior sleeve 8 is externally fitted to the outer sleeve main body 12 that is externally fitted to the main body 10 of the measurement probe 2 and the tip 11 of the measurement probe 2 in order to facilitate production. It is preferable that the outer sleeve tip 13 is divided into two parts.

As shown in FIG. 4, the outer sleeve main body 12 is formed in a substantially cylindrical shape open at both ends in the axial direction, and as shown in FIG. 2, the outer diameter is large when the outer sleeve body 12 is inserted into the measurement probe 2. 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 measuring probe 2, the outer sleeve 8 can easily come into contact with the hole wall when penetrating into the penetration hole 1, improving the measurement accuracy and the measuring probe 2. Damage can be suppressed. The outer diameter of the outer sleeve 8 is preferably substantially the same as the outer diameter of the tip cone used in the small dynamic cone penetration test.

As shown in FIG. 5, the outer sleeve tip 13 is formed in a bottomed cylindrical shape in which the upper portion is open upward, and the outer shape of the lower portion is formed in a conical shape (cone shape) pointed downward. Has been done. The outer diameter of the upper bottomed cylindrical portion is formed to be substantially the same as the outer diameter of the exterior sleeve main body 12. The cone tip angle is preferably about 45 ° to 90 °, more preferably 60 °.

As shown in FIGS. 4 and 5, the exterior sleeve 8 is hollow in which the measurement probe 2 is inserted from the insertion tip side into the penetration hole 1 over a range including the mounting positions of the electrodes 3, 4, ... A state in which the measurement probe 2 is inserted into the hollow portion 14 while continuously penetrating from the inside to the outer surface of the hollow portion 14 at positions corresponding to the electrodes 3, 4, ... Of the portion 14 and the measurement probe 2. Outer electrodes 15, 16 and 16 whose inner tips come into contact with the electrodes 3, 4 ... Are provided, respectively. The electrodes 3, 4 ... Provided on the measurement probe 2 and the outer electrodes 15, 16 ... Provided on the outer sleeve 8 correspond to each other, and the outer electrode 15 arranged on the uppermost side is the current electrode. The two outer electrodes 16 and 16 arranged on the lower side are potential electrodes.

After the measuring probe 2 to which the outer sleeve 8 is attached is penetrated into the penetration hole 1 by the press-fitting device to perform electrical logging, and then it becomes difficult to pull out the measuring probe 2 from the penetration hole 1, it is pulled out. The resistance allows the measuring probe 2 to come 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 left in the ground, and the measuring probe 2 pulled out from the outer sleeve 8 can be reliably recovered, which is expensive in the electrical logging. There is no risk of uncollectible measurement probe 2. As described above, since the measurement probe 2 is formed to have an outer diameter smaller than that of the outer sleeve 8, it can be pulled out relatively smoothly from the penetration hole 1 press-fitted with the outer sleeve 8 attached. Become.

When the exterior sleeve 8 is inserted into the penetration hole 1, the outer electrodes 15, 16 ... Are brought into contact with the hole wall, so that the outer surface on the opposite side of the outer electrodes 15, 16 ... It is preferable that the portion 17 is provided. The contact promoting convex portion 17 is a vertically long convex portion formed in a range including the entire length of the arrangement section of the outer electrodes 15, 16 ... With respect to the axial direction of the exterior sleeve 8. The height is preferably 1 to 8 mm, more preferably 3 to 5 mm. By providing the contact promoting convex portion 17, the outer electrodes 15, 16 ... Provided on the outer sleeve 8 can be reliably contacted by the hole wall of the penetration hole 1, and the measurement accuracy of the electrical logging can be further improved.

As shown in FIG. 3, a circumferential fixing convex portion 18 is provided on the peripheral surface of the measurement probe 2, and the circumferential fixing convex portion 18 is fitted to the fitting portion 19 provided on the outer sleeve 8. Thereby, it is preferable that the rotation of the outer sleeve 8 and the measuring probe 2 in the circumferential direction is fixed. The circumferential fixing convex portion 18 is formed on the upper end portion of the main body portion 10 of the measurement probe 2, and the fitting portion 19 is formed on the upper end portion of the outer sleeve main body 12 of the outer sleeve 8. By fitting the circumferentially fixing convex portion 18 to the fitting portion 19, rotation of the measurement probe 2 and the outer sleeve main body 12 of the outer sleeve 8 in the circumferential direction is prevented, and the measurement probe 2 is inserted into the penetration hole. When penetrating into 1, the displacement between the electrodes 3, 4 ... Of the measuring probe 2 and the outer electrodes 15, 16 ... Of the outer sleeve 8 does not occur.

In the procedure of the electrical logging, after the small dynamic cone penetration test was performed, the press-fitting device shown in FIG. 1 was installed on the ground surface directly above the penetration hole 1, and the exterior sleeve 8 was attached. The measuring probe 2 is inserted into the penetration hole 1, and the resistivity R is continuously measured in the depth direction while gradually press-fitting the measuring probe 2. The measurement interval of the resistivity R is arbitrary, but it is preferably 10 cm or less, preferably 5 cm or less, and more preferably 1 cm. When the measurement is completed to a predetermined depth, the measurement probe 2 is pulled out from the penetration hole 1 and collected.

The electrical logging provides a depth distribution map of the resistivity R showing the relationship between the depth and the resistivity R (see (B) in FIGS. 9 to 11).

The effect of ground improvement is confirmed by using the depth distribution map of the resistivity R obtained by the above electrical logging. The method of confirming the ground improvement effect is performed by comparing the reduction amount of the resistivity R before and after the ground improvement. As shown in FIGS. 10 (A) and 10 (B) and 11 (A) and 11 (B), even if the improvement effect cannot be clearly recognized only by the depth distribution map of the Nd value of the above primary effect confirmation. Second, the ground improvement effect can be clearly confirmed by the depth distribution map of the resistivity of the secondary effect confirmation. It is desirable to confirm the effect by electrical logging (secondary effect confirmation) only when the effect is not recognized by the above primary effect confirmation, from the viewpoint of work efficiency and cost reduction, but the primary effect is confirmed. Even if the improvement effect of the ground is clearly recognized by the confirmation of the effect, the secondary effect may be confirmed in order to further improve the reliability.

Hereinafter, a detailed method for confirming the ground improvement effect will be described with reference to specific examples performed at the site. As shown in FIGS. 6 and 7, ground improvements having different specifications were applied to the target grounds at three locations, improvement A, improvement B, and improvement DP, and their effects were confirmed. A standard penetration test was conducted on the target ground (preliminary Bor) near the improved site, and the soil log shown in FIG. 8 was obtained. As a result, the silt-mixed fine sand contains organic soil in GL-2m to -4m and silt in layers below GL-5m. In addition, the construction specifications for the improvement of each board are as shown in Table 1. The improved body material ordinance at the time of measurement is about 11 months.

In FIG. 6, ▲ indicates the location where the small dynamic cone penetration test and electrical logging are performed, ■ indicates the location where block sampling is performed to measure the uniaxial compressive strength qu, and ● indicates the location where the uniaxial compressive strength qu is measured. This is the place where rotary triple tube sampling is performed. The small dynamic cone penetration test and electrical logging indicated by ▲ are performed at two locations (A1 and A2) 10 cm and 40 cm away from the improvement center in improvement A, and 40 cm, 70 cm and 100 cm away from the improvement center in improvement B. It was performed at three locations (B1 to B3), and in the improved DP, it was performed at one location (DP1) 30 cm away from the improvement center.

9 is a depth distribution map of improved A, FIG. 10 is a depth distribution map of improved B, and FIG. 11 is a depth distribution map of improved DP. The depth distribution diagram of the specific resistance R in (B) is the specific resistance R with an electrode spacing of 2.5 cm. The depth distribution map of the uniaxial compressive strength qu in (C) is the test result on the 28th of the material age.

The ground before improvement has Nd value = 0 to 20 (average Nd value = 9) and R = 40 to 120Ω ・ m (as shown by ○ in (A) and (B) of FIGS. 9 to 11). Average R = 65Ω ・ m), and resistivity R was improved by confirming a depth of 30 to 40Ω ・ m at a depth of GL-2m to GL-4m containing organic soil and GL-5m containing silt in layers. It is assumed that there are many fine particles in the area.

In improvement A, the amount of increase in 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 (▲), as shown in FIG. 9 (A). The increase in Nd value due to the improvement is observed, and the improvement effect can be confirmed. As shown in FIG. 9B, the average value of the resistivity R is 4Ω ・ m at the improvement center +10cm position (●) and 2Ω ・ m at the improvement center +40cm position (▲). In comparison, it has decreased to about 1/10 to 1/100. In addition, the values are almost uniform over the entire improvement range. On the other hand, as shown in FIG. 9C, the uniaxial compressive strength qu has a small strength and a large variation in the specimen in which organic soil and silt are mixed.

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

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

From the above examination results, in improvement A, the ground improvement effect can be clearly confirmed by the primary effect confirmation using the depth distribution map of the Nd value. On the other hand, in improved B and improved DP, the target improvement intensity was lower than that in improved A, so it could not be judged by the primary effect confirmation, but it was clarified by the secondary effect confirmation using the depth distribution map of the resistivity R. The ground improvement effect can be confirmed.

[Examples of other forms]
In the above embodiment, the exterior sleeve 8 is composed of two members including the exterior sleeve main body 12 and the exterior sleeve tip 13, but it may be composed of one member in which these are integrated.

1 ... Through hole, 2 ... Measuring probe, 3 ... Current electrode, 4 ... Potential electrode, 5 ... Penetration rod, 6 ... Male thread part, 7 ... Electric cable, 8 ... Exterior sleeve, 9 ... Intermediate part, 10 ... Main body part, 11 ... Tip part, 12 ... Exterior sleeve body, 13 ... Exterior sleeve tip, 14 ... Hollow part, 15 ... Outer electrode (current electrode), 16 ... Outer electrode (potential electrode), 17 ... Contact promotion convex part, 18 ... Convex part for fixing in the circumferential direction, 19 ... Fitting part, 20 ... Piston, 21 ... Stand, 22 ... Chuck, 23 ... Control unit, 24 ... Hydraulic unit

Claims (5)

It is a method of confirming the ground improvement effect by the chemical injection method.
After the ground improvement, obtain a depth distribution map of the Nd value showing the relationship between the depth and the Nd value by a small dynamic cone penetration test, and confirm the ground improvement effect from the increment of the Nd value before and after the ground improvement. Check the next effect and
When the ground improvement effect is not recognized by the primary effect confirmation, a measuring probe equipped with an electrode is inserted into the penetration hole of the small dynamic cone penetration test to perform electrical logging to measure the specific resistance, and the depth is obtained. The ground improvement is characterized in that a depth distribution map of the resistivity showing the relationship between the resistivity and the resistivity is obtained, and the secondary effect of confirming the ground improvement effect is confirmed from the reduction amount of the resistivity before and after the ground improvement. How to check the effect. 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. A measuring device used for 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 from the insertion tip side into the penetration hole over a range including the mounting position of the electrode, and a position corresponding to the electrode of the measurement probe. Along with penetrating from the hollow portion to the outer surface, an outer electrode provided with the inner tip in contact with the electrode with the measurement probe inserted in the hollow portion is provided.
Confirmation of the ground improvement effect, which is characterized in that when it becomes difficult to pull out the measuring probe from the penetration hole, the measuring probe is pulled out from the outer sleeve so that the measuring probe can be recovered. Measuring device used in the method. 3. Claim 3 in which the outer sleeve is provided with an outwardly projecting convex portion for promoting contact on the opposite side of the outer electrode in order to bring the outer electrode into contact with the hole wall when the outer sleeve is inserted into the penetration hole. A measuring device used for the method for confirming the ground improvement effect described. By fitting the convex portion for fixing in the circumferential direction provided on the peripheral surface of the measurement probe into the fitting portion provided on the outer sleeve, the outer sleeve and the measurement probe can be rotated in the circumferential direction. The measuring device used for the method for confirming the ground improvement effect according to any one of claims 3 and 4 which is fixed.

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