Ground investigation device and ground investigation method

Abstract

To provide a ground investigation device and a ground investigation method that can obtain a high-quality N-value of a standard penetration test with work efficiency equivalent to that of a dynamic cone penetration test by reducing the lifting and lowering work after the standard penetration test.SOLUTION: A ground investigation device is composed of a steel pipe for excavating ground, which has a ground excavation tool at its lower end and a connecting part at its upper end, a boring rod that can move in a substantially vertical direction inside the steel pipe, an SPT sampler that has a connecting part for the steel pipe for excavating ground and a detachable part to be connected at its lower end, and a drain hole and a shoe for penetrating the ground at its lower end, and a boring machine. When the connecting part and the part to be connected are in a connected state, the drain hole is blocked or semi-blocked by the steel pipe for excavating ground, and water is sent to the SPT sampler, and the soil sample remaining inside is pushed out by water pressure. When the connecting part and the part to be connected are not connected, the drain hole is in an open state, and the boring rod, the part to be connected, and the SPT sampler can move inside the steel pipe for excavating ground.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a ground investigation device and a ground investigation method for streamlining work and improving quality in a standard penetration test for obtaining the N value, which is one of the design parameters for civil structures and building foundations.

Background Art

[0002] The "standard penetration test" refers to a test method for obtaining the N value, which is one of the parameters used in the design of civil structures and building foundations. The original investigation method was developed in the United States in 1902 and was organized as a standard penetration test method in 1948. It was introduced to Japan in 1951 and then standardized as JIS A 1219 in 1961. The N value obtained from the standard penetration test is currently widely used in the design of civil structures in Japan and is the most important parameter not only for judging the looseness and compactness of the ground in geological surveys but also for estimating various physical property values.

[0003] As an overview of the standard penetration test, an anvil is attached to the boring rod connected to the ground from the SPT sampler lowered to the bottom of the boring hole, and a guide rod is further connected above the anvil. With a 63.5 kg hollow hammer penetrating the guide rod, it is freely dropped from a height of 76 cm above the upper surface of the anvil to strike the anvil, and the SPT sampler connected to the tip of the boring rod is penetrated into the ground by the impact energy. The penetration from the bottom of the hole to a depth of 15 cm is regarded as "pre-drilling", and the 30 cm impact penetration performed after pre-drilling is organized as "main drilling". In the main drilling, the number of blows required to penetrate the SPT sampler by 30 cm is recorded as the N value.

[0004] Since the standard penetration test has a problem of disturbing the ground deeper than the tip of the sampler due to the negative pressure generated when pulling out the SPT sampler from the ground, usually the test is not carried out on the ground immediately below where the standard penetration test is performed. After the test, the SPT sampler is pulled up to the ground and recovered, then a steel pipe for ground excavation is connected to the tip of the boring rod and lowered to the bottom of the boring hole. After digging down 1 m from the bottom of the hole, the steel pipe for ground excavation is pulled up to the ground and recovered. After reconnecting it to the tip of the SPT sampler boring rod again, it is lowered to the bottom of the hole to conduct the standard penetration test. Therefore, in principle, the standard penetration test is carried out once every 1 m.

[0005] When the standard penetration test was introduced in Japan, it was difficult to collect samples by coring for unconsolidated ground materials. Therefore, in geological surveys, the method of making the ground materials into a slurry state by boring and water injection with a steel pipe for ground excavation and discharging them to the ground was common. However, nowadays, even for unconsolidated ground, it is possible to collect ground samples by coring. It is also commonly practiced to conduct coring and sampling in a hole separate from the standard penetration test hole, or to alternately perform the standard penetration test and coring in a single hole. However, when alternately performing the standard penetration test and coring in a single hole, the problem of disturbing the ground deeper than the bottom of the hole due to the negative pressure generated when pulling up the steel pipe for ground excavation by coring has been left unaddressed without in-depth discussion.

[0006] The SPT sampler used in the standard penetration test has a function of collecting ground samples in addition to the purpose of obtaining the N value, so it is called a "sampler". In order not to let the ground samples taken into the SPT sampler fall due to the 15 cm + 30 cm impact penetration in the standard penetration test, a check valve is built into the connector head part of the SPT sampler. When the SPT sampler is pulled up, a negative pressure acts inside the SPT sampler, making the structure such that the taken-in ground samples are not likely to fall. Among foreign SPT samplers, products with a bucket-type catcher for preventing sample dropout built in addition to the check valve are also popular. In addition, modern coring technology has developed to the extent that it can collect unconsolidated ground samples with a quality equal to or better than that obtained by collecting ground materials with an SPT sampler.

[0007] In geological surveys that combine the standard penetration test, every time the standard penetration test and boring are repeated, the tools such as the SPT sampler and the steel pipe for ground excavation are raised and lowered twice. In order to omit the labor of such work, steel pipes for ground excavation with built-in SPT samplers have been developed as in Patent Documents 1 to 3, etc. In recent years, couplings for incorporating the SPT sampler into the steel pipe for ground excavation have been sold by several companies. By using such a steel pipe for ground excavation with a built-in SPT sampler, it has become possible to reduce the raising and lowering of the tools, which used to be two round trips for every 1 m of excavation, to one round trip.

[0008] The steel pipe for ground excavation with a built-in SPT sampler not only improves work efficiency, but also enables the standard penetration test to be carried out without pulling up the steel pipe for ground excavation. Therefore, it is also effective as a means to avoid the problem of generating negative pressure at the bottom of the hole when pulling up the steel pipe for ground excavation and disturbing the ground deeper than the bottom of the hole. Also, usually the standard penetration test may be carried out with cuttings and sediment fallen from the hole wall deposited at the bottom of the hole. By continuously carrying out the standard penetration test without pulling up the steel pipe for ground excavation after boring, the problem of taking in cuttings can be solved, and the quality of the standard penetration test can be improved, such as the steel pipe for ground excavation also serving as a centralizer to assist the verticality of the boring rod in the boring hole.

[0009] On the other hand, although the steel pipe for ground excavation with a built-in SPT sampler has advantages in terms of work efficiency and quality, it has also been pointed out that improper use methods may cause low quality problems such as incorrect tests being carried out with the sample clogged and inaccurate N values being obtained, and it is not yet widely popular.

[0010] Since the Great East Japan Earthquake in 2011, seismic performance surveys of various civil structures have been conducted. For survey targets with long extensions such as river levees, in order to interpolate boring survey points combined with the standard penetration test, the JIS A 1230 dynamic cone penetration test, which is simpler and has higher working efficiency than the standard penetration test, may be used. The dynamic cone penetration test is a survey method with excellent efficiency compared to the standard penetration test because it does not require sampling of soil samples and boring of boreholes. However, the Nd value obtained by the dynamic cone penetration test is not completely interchangeable with the N value obtained by the standard penetration test, such as the impact energy being different from that of the standard penetration test and the need to correct the influence of the friction generated between the rod and the ground, so it is often treated as a reference value.

[0011] In recent years, offshore ground surveys using spud barges and steel masts for the construction of offshore wind power facilities have increased. However, in Japan, since the standard penetration test is an important parameter in design, the standard penetration test is also carried out in offshore surveys. Different from onshore surveys, in offshore surveys, the height of the scaffolding from the stage where the boring machine is installed to the seabed is added to the boring advance length. Therefore, the operation of raising and lowering the tools in offshore surveys is a greater burden than onshore surveys, and a ground survey method with fewer raising and lowering operations of the tools is required.

[0012] Specific issues for improving work efficiency are to reduce the number of raising and lowering operations of the tools related to the standard penetration test and boring excavation. According to the standard penetration test methods shown in Patent Document 1 to Patent Document 3, etc., the lifting operation after boring hole excavation is reduced, but there is a problem that raising and lowering operations occur after the standard penetration test.

[0013] In addition, the dynamic cone penetration test, which is mainly implemented as an alternative method to the standard penetration test due to cost issues, is superior in the survey quantity per cost compared to the standard penetration test. However, there is a problem that the Nd value obtained by the dynamic cone penetration test is different from the N value obtained by the standard penetration test.

[0014] Specific issues regarding quality improvement can be broadly classified into those related to the quality of standard penetration tests in general in Japan and those specific to the steel pipes for ground excavation equipped with SPT samplers.

[0015] Specific issues regarding the quality of standard penetration tests in general are as follows: eliminating the loosening of the ground under test caused by raising and lowering tools such as steel pipes for ground excavation and SPT samplers (hereinafter referred to as "tools"), ensuring the verticality of the boring rod during the standard penetration test to prevent buckling, and avoiding conducting the standard penetration test when cuttings and sediment accumulate at the bottom of the hole.

[0016] Regarding eliminating the loosening of the ground under test caused by raising and lowering tools, when pulling up the excavation tool from the bottom of the boring hole after boring, a phenomenon called "boiling" is known, where strong negative pressure is generated at the bottom of the hole, causing groundwater to rise and disturbing the ground. Since no good data can be obtained by conducting the standard penetration test on disturbed ground, disturbing the ground under test after boring is a major problem.

[0017] If the boring rod is tilted during the standard penetration test, the impact energy from the ground causes the boring rod to buckle and absorb the impact energy, making it impossible to obtain the correct N value. Overseas, ISO requires measures using centralizers and stabilizers, but in Japan's JIS standards, regulations regarding similar measures have been postponed.

[0018] When conducting the standard penetration test with cuttings deposited at the bottom of the hole, it is possible that the cuttings may mix into the collected samples and affect the N value. However, cuttings may also accumulate while pulling up the excavation tool and inserting the SPT sampler, and repeated raising and lowering of the tools may cause the hole wall to collapse and sediment to accumulate at the bottom of the hole. Trying to recover the sediment with a core barrel will also exert negative pressure on the bottom of the hole and disturb the ground under test. Therefore, it is an issue to conduct the standard penetration test promptly before cuttings and sediment accumulate as much as possible.

[0019] Regarding the specific problems of the existing steel pipes for ground excavation with built-in SPT samplers shown in Patent Document 1 to Patent Document 3, etc., there is an incorrect test in which the standard penetration test is carried out with the ground sample taken into the SPT sampler. Since this problem can be carried out maliciously in order to reduce labor and increase the daily output, it has also become a cause for hindering the popularization of the steel pipes for ground excavation with built-in SPT samplers.

Prior Art Documents

Patent Documents

[0020]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0021] In view of the above-mentioned conventional drawbacks, the present invention aims to provide a ground investigation device and a ground investigation method that can reduce the lifting and lowering operations after the standard penetration test, have an operation efficiency comparable to that of the dynamic cone penetration test, and obtain the N value of a high-quality standard penetration test.

Means for Solving the Problems

[0022] In order to achieve the above object, the reset step 18 described in claim 4 that eliminates the need for the operation of recovering the SPT sampler to the ground after the standard penetration test has been invented. To implement the present invention, the ground investigation device 1 described in claim 1 includes a steel pipe 5 for ground excavation having a ground excavation tool 3 at its lower end and a connection part at its upper end, a boring rod 6 that can move in a substantially vertical direction inside the steel pipe for ground excavation, a cylindrical connected part 7 provided at the lower end of the boring rod and detachable from the connection part 4 at the upper end of the steel pipe for ground excavation, an SPT sampler 10 provided at the lower end of the connected part and having a drain hole 8, and a shoe 9 for ground penetration at its lower end, and a boring machine connected to the boring rod. When the connection part 4 at the upper end and the cylindrical connected part 7 are in a connected state, the drain hole 8 is in a closed or semi-closed state by the inner peripheral wall of the steel pipe 5 for ground excavation, and by sending water to the SPT sampler 10 through the boring rod 6, the ground sample remaining in the SPT sampler can be extruded by water pressure. On the other hand, when the connection part 4 at the upper end and the cylindrical connected part 7 are in a non-connected state, the drain hole 8 is in an open state, and the boring rod 6, the cylindrical connected part 7, and the SPT sampler 10 can move in a substantially vertical direction inside the steel pipe 5 for ground excavation.

[0023] The inner peripheral wall surface of the steel pipe for ground excavation of the ground investigation device according to claim 2 further includes an annular attachment removing means, and by sliding the SPT sampler up and down inside the steel pipe for ground excavation, the attachments adhering to the outer peripheral surface of the SPT sampler can be removed.

[0024] When the steel pipe for ground excavation of the ground investigation device according to claim 3 conducts a standard penetration test in a state where the attachment removing means is provided, the water pressure in the steel pipe for ground excavation including the SPT sampler is increased by the boring water discharged from the SPT sampler into the steel pipe for ground excavation, and a pressure for pushing up the SPT sampler is generated. In order to solve this problem, when the connecting portion of the steel pipe for ground excavation and the cylindrical connected portion of the SPT sampler are connected, the boring water in the steel pipe for ground excavation is not discharged, and when the connection between the connecting portion and the connected portion is released, a drainage hole is provided so that the boring water in the steel pipe for ground excavation can be discharged to the outside of the pipe. When performing a standard penetration test with the SPT sampler in the steel pipe for ground excavation, the same amount of boring water as the excavation water discharged from the water drainage hole of the SPT sampler is drained from the drainage hole to the outside of the steel pipe for ground excavation, so that the SPT sampler can perform the standard penetration test without being affected by water pressure.

[0025] The ground investigation method according to claim 4 includes a boring hole drilling step of drilling a boring hole to the position of the ground to be investigated, a standard penetration test step of penetrating an SPT sampler into the ground to be investigated and calculating an N value after the boring hole drilling step, and a reset step of discharging the ground sample remaining in the SPT sampler to the outside of the SPT sampler by water pressure and returning the SPT sampler to the state before the standard penetration test step after the standard penetration test step.

[0026] In the reset step of the ground investigation method according to claim 5, the deposits adhering to the outer peripheral surface of the SPT sampler are also removed by an annular deposit removing means. With the ground investigation device and the ground investigation method shown above, the SPT sampler can be reset in the hole without being pulled up to the ground, and the boring hole drilling step and the standard penetration test step can be repeatedly performed cyclically.

Advantages of the Invention

[0027] As is clear from the above description, the following advantages can be obtained in the present invention. (1) In each of the inventions described in claim 1 and claim 4, since the drain hole 8 can be closed, the inner peripheral wall can be cleaned without pulling up an SPT sampler or the like, and it can be returned to the state before the standard penetration test process. Therefore, operations such as raising and lowering an SPT sampler or the like, replacing it, and cleaning work on the ground can be omitted, and an increase in productivity of 2 to 3 times or more can be expected compared to a general standard penetration test. Also, a productivity of about 1.5 times can be expected compared to a standard penetration test using an existing steel pipe for ground excavation with an SPT sampler built-in. (2) Further, by minimizing the process of raising and lowering an SPT sampler or the like, the labor of workers can be significantly reduced. (3) In addition, problems such as ground loosening, buckling of the boring rod, and deposition of drilling cuttings and earth and sand at the bottom of the hole, which are concerns in conventional investigation methods, can be solved, and a high-quality N value can be obtained. (4) In each of the inventions described in claim 2 and claim 5, the same operational effects as those in (1) to (3) can be obtained, and deposits such as earth and sand adhering to the outer peripheral portion of the SPT sampler 10 can also be removed. (5) In the invention described in claim 3, the same operational effects as those in (1) to (4) can be obtained. When a connecting portion and a connected portion are connected to the steel pipe for ground excavation, the drilling water in the steel pipe for ground excavation is not discharged. When the connection between the connecting portion and the connected portion is disconnected, a drain hole is formed so that the drilling water in the steel pipe for ground excavation can be discharged to the outside of the pipe. By draining the same amount of drilling water as the drilling water discharged from the drain hole of the SPT sampler from the drain hole to the outside of the steel pipe for ground excavation when performing the standard penetration test, the SPT sampler can perform the standard penetration test without being affected by water pressure.

Brief Description of the Drawings

[0028] Figs. 1 to 6 are explanatory views showing a first embodiment of the present invention.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0029] Hereinafter, the present invention will be described in detail according to the mode for carrying out the present invention shown in the drawings.

[0030] In the first mode for carrying out the present invention shown in FIGS. 1 to 6, reference numeral 1 denotes a ground investigation device that can mainly investigate the ground 2. As shown in FIG. 1, this ground investigation device 1 includes a pipe-shaped steel pipe 5 for ground excavation having a ground excavation tool 3 at its lower end and a Menzi type connection part 4 at its upper end, a boring rod 6 that can move substantially vertically inside the steel pipe for ground excavation in a state of being inserted into the steel pipe for ground excavation, a cylindrical connected part 7 provided at the lower end of the boring rod and detachable from the Menzi type connection part 4 at the upper end of the steel pipe for ground excavation, a pipe-shaped SPT sampler 10 provided at the lower end of the cylindrical connected part and having a plurality of drainage holes 8 in the radial direction and no check valve but provided with a ground penetration shoe 9 at the lower end, and a boring machine (not shown) connected to the boring rod. When the Menzi type connection part 4 at the upper end and the cylindrical connected part 7 are in a connected state, the drainage holes 8 are in a closed or semi-closed state by the inner peripheral wall of the steel pipe 5 for ground excavation, and by sending water to the SPT sampler 10 through the boring rod 6, the ground sample remaining in the SPT sampler can be extruded by water pressure. On the other hand, when the Menzi type connection part 4 at the upper end and the cylindrical connected part 7 are in a non-connected state, the drainage holes 8 are in an open state, and the boring rod 6, the cylindrical connected part 7, and the SPT sampler 10 can move substantially vertically inside the steel pipe 5 for ground excavation.

[0031] The inner diameter dimension, shape, and length of the pipe-shaped steel pipe 5 for ground excavation are appropriately designed within the range of achieving the object of the invention. Also, although not particularly shown, a known boring machine can be used as the boring machine.

[0032] A note on the steel pipe 5 for ground excavation. In the present embodiment, the steel pipe has an outer diameter of 150 mm or less, a connection part 4 is provided at the upper end part, and a ground excavation tool 3 is provided at the lower end part. By providing such a ground excavation tool 3, a boring hole can be excavated by this steel pipe 5 for ground excavation up to the position of the ground to be investigated. The outer diameter of 150 mm of the steel pipe 5 for ground excavation shown here is the maximum recommended hole diameter for applying the standard penetration test shown in JIS A1219.

[0033] Also, the inside near the upper end part of the steel pipe 5 for ground excavation is substantially in contact with the drain hole 8 of the SPT sampler 10, and a closing part 11 having a smaller inner diameter than other parts is provided so that the drain hole 8 can be in a closed state or a semi-closed state. That is, when the drain hole 8 substantially contacts the closing part 11 on the inner peripheral wall of the steel pipe for ground excavation, it becomes a closed or semi-closed state. On the other hand, when the connection state between the connection part 4 and the connected part 7 is released, the drain hole 8 becomes an open state, and for example, with the position where the connection part 4 and the connected part 7 are connected (for example, the state in FIG. 1) as the upper limit, the boring rod 6, the connected part 7, and the SPT sampler 10 are configured to be movable substantially vertically inside the steel pipe 5 for ground excavation. Here, "substantially in contact" includes not only a state where the drain hole 8 and the closing part 11 are in perfect contact but also a state where they face each other with a slight gap.

[0034] Specifically, in this embodiment, the steel pipe 5 for ground excavation is formed such that the inner diameter of other parts of the steel pipe 5 for ground excavation is 53.6 mm or more, and the closing part 11 is 51 mm. The specified inner diameter of 53.6 mm is the minimum diameter required for the clearance cross-sectional area between the SPT sampler 10 and the steel pipe 5 for ground excavation to be larger than the cross-sectional area of the water passage hole 14 in the sampler, so that the drainage from the drain hole 8 can be carried out without any problem. Since the drain hole 8 can be in a closed state or a semi-closed state in this way, after the SPT sampler 10 is penetrated into the ground to be investigated and the N value is measured, by sending water through the boring rod 6 to the SPT sampler 10 without a check valve, the soil sample remaining on the inner peripheral wall of the SPT sampler 10 can be extruded by water pressure, and the inner peripheral wall of the SPT sampler 10 can also be cleaned.

[0035] That is, it can be reset to the state before the penetration test, and the SPT sampler 10 and the like can be repeatedly penetrated into the ground without pulling them up to the ground, and the "N value" can be obtained.

[0036] In addition, the steel pipe 5 for ground excavation is provided with a drain hole 12 through which water can be drained to the outside when water enters the steel pipe 5 for ground excavation from the drain hole 8 of the SPT sampler 10. In this embodiment, the drain hole 12 is formed in the closing part 11, but it may be formed in other parts. When the SPT sampler 10 penetrates into the bottom 2b ground by the standard penetration test, in order to take in the soil sample in the SPT sampler 10, the boring water in the SPT sampler 10 is drained into the steel pipe 5 for ground excavation through the drain hole 8. When the SPT sampler 10 is penetrated, the male and female screwing state of the connecting part 4 and the connected part 7 is released, and the drain hole 8 is in an open state. Therefore, the pressure of the boring water discharged from the drain hole 8 is transmitted to the steel pipe 5 for ground excavation, and the boring water in the steel pipe 5 for ground excavation is drained from the drain hole 12 to the boring hole 2a. By forming such a drain hole 12, the boring water can be efficiently drained to the outside.

[0037] Furthermore, in the present embodiment, the inner peripheral wall surface of the steel pipe 5 for ground excavation is provided with an annular attachment removing means 13 formed of a resin having elasticity such as rubber or the like. By sliding the SPT sampler vertically within the steel pipe for ground excavation, attachments such as soil adhering to the outer peripheral surface of the SPT sampler can be removed.

[0038] In the present embodiment, a hole drilling component called a metal crown or a diamond bit is used as the ground excavation tool 3. In the present embodiment, the ground excavation tool 3 is composed of an openable and closable metal crown 3a and wings 3b. Specifically, during excavation, the wings 3b close so as to cross the opening of the metal crown 3a at the lower end of the steel pipe 5 for ground excavation. During the standard penetration test, when the steel pipe 5 for ground excavation and the SPT sampler 10 are lifted by several centimeters, the wings 3b droop with the fixed point of the metal crown 3a as a fulcrum, and it has an openable and closable structure that opens the opening of the metal crown 3a.

[0039] In the present embodiment, the connection part 4 is a female coupling-shaped part formed on the inner peripheral wall surface on the upper end side of the steel pipe 5 for ground excavation.

[0040] The boring rod 6 is a rod-shaped member formed with an outer diameter that can slide on the inner peripheral wall of the steel pipe 5 for ground excavation. A boring machine (not shown) is connected to the upper end thereof. The rotational force and driving force of this boring machine are transmitted to the connection part 4 screwed to the connected part via the boring rod 6, enabling hole drilling with the steel pipe 4 for ground excavation. In the present embodiment, it is also formed so that water can be injected into the SPT sampler 10 via this boring rod 6.

[0041] The connected part 7 is provided so as to be interposed between the boring rod 6 and the SPT sampler 10. This connected part 7 is formed in a male coupling shape that is screwed to the female coupling-shaped connection part 4.

[0042] The SPT sampler 10 is a pipe-shaped member with its upper end connected to the connected part 7 and a shoe 9 at its lower end. On the upper end side, a connector head part 10a without a check valve, which is provided with a drain hole 8 for discharging the water on the inner peripheral wall of the SPT sampler 10 to the outside and a water passage hole 14 inside the sampler, is connected. The connected part 7 is connected through this connector head part 10a.

[0043] When the SPT sampler 10 penetrates into the bottom 2b of the hole ground, in order to prevent the water pressure in the steel pipe 5 for ground excavation from rising and interfering with the penetration of the SPT sampler 10, it is a condition that the total opening area of the steel pipe 5 for ground excavation is larger than the opening area of the water passage hole 14 inside the sampler. The drain hole 12 can be installed other than the steel pipe 5 for ground excavation. In that case, however, it is necessary to install a on-off valve that closes at least when drilling the boring hole 2a or when water is supplied to the SPT sampler 10 for cleaning, and opens when conducting the standard penetration test.

[0044] The ground investigation method 15 of the present invention performed using such a ground investigation device 1 includes a boring hole drilling step 16 of drilling a boring hole 2a to the position (depth) of the ground to be investigated, a standard penetration test step 17 of releasing the connection state between the connection part 4 and the connected part 7 after the boring hole drilling step 16, penetrating the SPT sampler 10 into the ground to be investigated, and measuring the N value, and a reset step 18 of cleaning the outer periphery of the SPT sampler by the deposit removing means 13 when storing the SPT sampler in the steel pipe 5 for ground excavation after this standard penetration test step 17, discharging the ground sample remaining in the SPT sampler 10 to the outside of the SPT sampler 10 by water pressure, and returning the SPT sampler 10 to the state before the standard penetration test step 17.

[0045] In the boring hole drilling step 16, the boring hole 2a is drilled to the position where the standard penetration test is to be conducted by the ground excavation tool 3 of the steel pipe 5 for ground excavation. At this time, since the connection part 4 and the connected part 7 of the steel pipe 5 for ground excavation, the SPT sampler 10, and the boring rod 6 are screwed together, they drill the boring hole 2a integrally.

[0046] Specifically, the SPT sampler 10 and the boring rod 6 are integrated by fitting (threading) the connecting portion 4 and the connected portion 7 in a state of penetrating the steel pipe 5 for ground excavation. The outer periphery of the upper end portion of the SPT sampler 10 and the upper end of the inner peripheral wall of the closing portion 11 are in close contact. The closing portion 11 closes or semi-closes the drain hole 8 to limit the drainage volume, and also has a structure to prevent the drilling water discharged from the shoe 9 from leaking through the drain hole 12.

[0047] In addition, by providing the drain hole 12 in the steel pipe 5 for ground excavation, when the connecting portion 4 of the steel pipe 5 for ground excavation and the cylindrical connected portion 7 of the SPT sampler 10 are connected, the water passage path from the drain hole 8 and the shoe 9 to the drain hole 12 is blocked, and the drilling water in the steel pipe 5 for ground excavation cannot be discharged from the drain hole 12. When the connection between the connecting portion 4 and the connected portion 7 is released, the blockage of the water passage path from the drain hole 8 and the shoe 9 to the drain hole 12 is released, and the drilling water in the steel pipe 5 for ground excavation can be discharged from the drain hole 12 to the outside of the pipe. Thereby, when performing a standard penetration test with the SPT sampler 10 in the steel pipe 5 for ground excavation, the same amount of drilling water as the drilling water discharged from the drain hole 8 of the SPT sampler 10 is drained from the drain hole 12 to the outside of the steel pipe 5 for ground excavation, so that the SPT sampler 10 can perform a standard penetration test without being affected by water pressure.

[0048] The rotational force of forward rotation (right rotation) transmitted from the boring machine by the boring rod 6 is transmitted to the steel pipe 5 for ground excavation through the connected portion 7, and the hole bottom 2b is excavated by the ground excavation tool 3. When excavating the ground, the ground excavation tool 3 (metal crown 3a and wing 3b) is in a closed state by being pressed against the ground, and the entire opening surface of the ground excavation tool 3 is excavated.

[0049] When drilling the boring hole 2a, the drilling water supplied from a ground pump is discharged from the shoe 9 at the tip of the SPT sampler 10 through the boring rod 6. The drilling water cools and cleans the open metal crown 3a and wings 3b that generate heat due to friction with the ground during drilling, and is discharged from the open metal crown 3a into the boring hole 2a. Drilling is carried out up to the upper surface of the planned depth where a standard penetration test is to be performed.

[0050] In the standard penetration test process 17, the connection part 4 and the connected part 7 are disengaged, and the boring rod 6 is advanced by a boring machine, so that the standard penetration test device 19 composed of the boring rod 6, the connected part 7, and the SPT sampler 10 is penetrated into the ground to be investigated, and the N value at this time is recorded.

[0051] Specifically, after pulling up the standard penetration test device 19 integrated by fitting the connection part 4 and the connected part 7 and the steel pipe 5 for ground excavation until the wing 3b hangs down and the tip of the wing 3b touches the hole bottom 2b, the fitting between the connection part 4 and the connected part 7 is released by reversely rotating (left rotating) the boring rod 6. In this state, the SPT sampler 10 is slid and dropped into the steel pipe 5 for ground excavation and landed on the hole bottom 2b, and then a standard penetration test is carried out by the method shown in JIS A 1219.

[0052] When the SPT sampler 10 penetrates the bottom-hole 2b ground by the standard penetration test, in order to take in the ground sample into the SPT sampler 10, the drilling water in the SPT sampler 10 is drained into the steel pipe 5 for ground excavation from the drain hole 8 through the water passage hole 14 in the sampler. For example, in FIG. 1, the drain hole 8 was in a blocked / semi-blocked state by the blocking part 11, but in the state of FIG. 4, since the drain hole 8 is located at a place other than the blocking part 11 of the steel pipe 5 for ground excavation, the drain hole 8 is in an open state. The pressure of the drilling water discharged from the drain hole 8 is transmitted into the steel pipe 5 for ground excavation, and the pressure dissipates when the drilling water in the steel pipe 5 for ground excavation is drained from the drain hole 12 to the boring hole 2a. When the SPT sampler 10 penetrates the bottom-hole 2b ground, in order to prevent the water pressure in the steel pipe 5 for ground excavation from rising and hindering the penetration of the SPT sampler 10, it is a condition that the total opening area of the drain hole 12 is larger than the opening area of the water passage hole 14 in the sampler. The drain hole 12 can be installed outside the steel pipe 5 for ground excavation, but in that case, it is necessary to additionally provide an on-off valve that closes at least when the SPT sampler 10 is washed in the boring hole drilling process 16 and the reset process 18 and opens during the standard penetration test process 17.

[0053] The reset process 18 is a process of discharging the ground sample remaining in the SPT sampler 10 to the outside of the SPT sampler 10 by water pressure and returning the SPT sampler 10 to the state before the standard penetration test process 17.

[0054] Specifically, after extracting the SPT sampler 10 from the bottom of the hole 2b, the connecting portion 4 and the connected portion 7 are fitted (screwed) by pulling up the boring rod 6 while rotating it forward using a boring machine. In a state where the connecting portion 4 and the connected portion 7 are fitted, since the drain hole 8 is closed or semi-closed by the closing portion 11, the water pressure inside the SPT sampler 10 increases due to water supply by a pump on the ground, and the ground sample can be discharged. Here, the inner surface of the SPT sampler 10 into which the ground sample is taken is subjected to water repellent treatment such as fluorine coating or glass coating, or low friction treatment, etc., so that the discharge and cleaning of the ground sample become easier. When the drain hole 8 is closed with the clearance between the outer peripheral portion of the drain hole 8 and the closing portion 11 being zero, the water pressure inside the SPT sampler 10 can be efficiently increased with a small water supply amount to discharge the ground sample. Therefore, when it is predicted that the ground sample will be difficult to discharge from the SPT sampler 10 due to the expansive characteristics, the closing portion 11 that closes the drain hole 8 is selected. On the other hand, in the case of a ground that can be easily discharged by water supply but is likely to become turbid water, by using a closing portion 11 with a large inner diameter that is semi-closed, a small amount of water flow is generated from the clearance between the drain hole 8 and the closing portion 11, so that the floating particles inside the SPT sampler 10 can be discharged.

[0055] After discharging the ground sample, the cleaning is completed by pumping water until the turbidity of the water in the boring hole 2a is removed, and the reset of the steel pipe 5 for ground excavation and the SPT sampler 10 is completed.

[0056] In addition, in the present embodiment, an attachment removing means 13 is provided on the inner peripheral wall surface of the steel pipe 5 for ground excavation. In this reset step 18, the SPT sampler 10 is slid up and down inside the steel pipe 5 for ground excavation, so as to remove attachments such as soil adhering to the outer peripheral surface of the SPT sampler 10, and more reliably return the SPT sampler 10 to the state before the standard penetration test.

Industrial Applicability

[0057] The present invention is used in industries that perform standard penetration tests and measure N values.

Description of Symbols

[0058] 1: Ground investigation device, 2: Ground 2a: Boring hole, 2b: Bottom of boring hole 3: Ground excavation tool, 3a: Metal crown 3b: Wing, 4: Connection part 5: Steel pipe for ground excavation, 6: Boring rod 7: Connected part, 8: Drain hole 9: Shoe, 10: SPT sampler 10a: Connector head part, 11: Closing part 12: Drainage hole, 13: Attachment removing means 14: Water passing hole in sampler, 15: Ground investigation method 16: Boring hole drilling process, 17: Standard penetration test process 18: Reset process, 19: Standard penetration test device

Claims

1. A ground investigation device comprising: a steel pipe for ground excavation having a ground excavation tool at its lower end and a connection part at its upper end; a boring rod movable substantially vertically inside the steel pipe for ground excavation; a cylindrical connected part provided at the lower end of the boring rod and detachable from the connection part at the upper end of the steel pipe for ground excavation; an SPT sampler provided at the lower end of the connected part, having a drain hole, and having no check valve and a shoe for ground penetration at its lower end; and a boring machine connected to the boring rod. When the connection part at the upper end and the cylindrical connected part are in a connected state, the drain hole is in a blocked or semi-blocked state by the inner peripheral wall of the steel pipe for ground excavation, and by sending water through the boring rod to the SPT sampler, the ground sample remaining on the inner peripheral wall of the SPT sampler can be extruded by water pressure. On the other hand, when the connection part at the upper end and the cylindrical connected part are in a disconnected state, the drain hole is in an open state, and the boring rod, the cylindrical connected part, and the SPT sampler can move substantially vertically inside the steel pipe for ground excavation.

2. The ground investigation device according to claim 1, further comprising an annular deposit removing means on the inner peripheral wall surface of the steel pipe for ground excavation, wherein by sliding the SPT sampler up and down inside the steel pipe for ground excavation, deposits adhering to the outer peripheral surface of the SPT sampler can be removed.

3. The steel pipe for ground excavation has a drain hole such that when the connection part of the steel pipe for ground excavation and the cylindrical connected part of the SPT sampler are connected, the drilling water inside the steel pipe for ground excavation is not discharged, and when the connection between the connection part and the connected part is disconnected, the drilling water inside the steel pipe for ground excavation can be discharged to the outside of the pipe. When performing a standard penetration test with the SPT sampler inside the steel pipe for ground excavation, by draining the same amount of drilling water as the drilling water discharged from the drain hole of the SPT sampler from the drain hole to the outside of the steel pipe for ground excavation, the SPT sampler can perform a standard penetration test without being affected by water pressure. The ground investigation device according to claim 2.

4. A ground investigation method, which is carried out cyclically in a boring hole without recovering the ground investigation device to the ground, comprising: a boring hole drilling step of drilling a boring hole to the position of the ground to be investigated; a standard penetration test step of calculating an N value by penetrating an SPT sampler into the ground to be investigated after the boring hole drilling step; and a reset step of discharging the ground sample remaining in the SPT sampler to the outside of the SPT sampler by water pressure and returning the SPT sampler to the state before the standard penetration test step after the standard penetration test step.

5. The ground investigation method according to claim 4, wherein in the reset step, deposits adhering to the outer peripheral surface of the SPT sampler are also removed by an annular deposit removing means.

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