Survey boring method

Abstract

This invention provides an exploratory boring method that allows for the collection of precisely oriented boring cores regardless of the ground conditions. [Solution] A first hole 11 with a first diameter D1 is drilled into the ground 1 to be investigated. A first orientation member 7, marked with orientations 73N and 73S, is inserted so that the marked orientations are aligned with the orientation of the ground 1 and it extends along the first hole 11. An injection material 2 that expands and hardens in a controlled time is injected into the first hole 11 under no pressure and hardened under no pressure. A second diameter D2, larger than the first diameter D1, is drilled around the first hole 11 concentrically with the first hole 11, and the core drilled by the core boring is taken as the first sample S1.

Description

Technical Field

[0001] The present invention relates to an investigation boring method, and particularly to a method for collecting a borehole core in a specific orientation.

Background Art

[0002] In the investigation of deep underground by investigation boring, in order to grasp the accurate strike and dip of fractures, faults, and fracture zones in the strata, directional boring investigations are carried out. As conventional directional boring methods, (1) improving boring equipment and using a drilling tool (inner pipe with a fixed orientation) whose orientation can be known, and after sampling, determining the orientation from the relationship between the drilling tool and the captured core; (2) marking or embedding the orientation on the upper surface of the ground where the boring core is to be collected before drilling, and sampling the core together; (3) after boring, inserting a camera whose orientation is known and taking pictures, and inferring the orientation of the core from the image development diagram of the shaft wall, etc. are known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, method (1) above has the problem that it cannot be applied to ground where such high-quality cores cannot be collected, as it assumes that the sampled core is a continuous, undisturbed, high-quality core. Also, method (2) above has the problem that the orientation of the top surface of the core can only be determined, so in the case of ground where there are voids in the middle of the sampled core or the ground is disturbed with soil-like material, the orientation of the core other than the top surface cannot be determined. Furthermore, method (3) above has the problem that while it is possible to insert a camera and take pictures if the borehole wall is self-supporting, if the borehole wall is not self-supporting, a casing pipe is inserted to support the borehole wall, making it impossible to take pictures.

[0005] The problem that this invention aims to solve is to provide an investigation boring method that can collect boring cores at a fixed orientation regardless of the ground conditions. [Means for solving the problem]

[0006] This invention involves boring a first hole of a first diameter into the ground to be investigated. A first orientation member, which has an orientation marked on it, is inserted so that the marked orientation is aligned with the orientation of the ground and extends along the first hole. The injection material, which foams and hardens at a controlled time, is injected into the previous 1st hole without pressure and hardened without pressure. A core boring hole is drilled around the first hole, concentric with the first hole and having a second diameter larger than the first diameter. The above problem is solved by taking the core drilled by the core boring as the first sample. [Effects of the Invention]

[0007] According to the present invention, even if there are cavities or voids in the ground, the injection material is filled and hardens together with the first orientation member which is marked with an orientation, so that a boring core with a fixed orientation can be collected regardless of the condition of the ground. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view (part 1) showing one embodiment of the investigation boring method according to the present invention. [Figure 2] This is a cross-sectional view (part 2) showing one embodiment of the investigation boring method according to the present invention. [Figure 3] This is a cross-sectional view (part 3) showing one embodiment of the investigation boring method according to the present invention. [Figure 4] This is a cross-sectional view (part 4) showing one embodiment of the investigation boring method according to the present invention. [Figure 5] This is a cross-sectional view (part 5) showing one embodiment of the investigation boring method according to the present invention. [Figure 6] This is a cross-sectional view (part 6) showing one embodiment of the investigation boring method according to the present invention. [Figure 7] This is a cross-sectional view (part 7) showing one embodiment of the investigation boring method according to the present invention. [Figure 8] This is a cross-sectional view (part 8) showing one embodiment of the investigation boring method according to the present invention. [Figure 9] This is a cross-sectional view along the IX-IX line in Figure 1. [Figure 10] This is a cross-sectional view along line XX in Figure 5. [Figure 11] This is a cross-sectional view along the line XI-XI in Figure 4. [Figure 12] This is a cross-sectional view along the line XII-XII in Figure 6. [Figure 13] This is a cross-sectional view along the line XIII-XIII in Figure 6. [Figure 14] This is a cross-sectional view along the line XIV-XIV in Figure 8. [Figure 15] This is a cross-sectional view (part 1) showing another embodiment of the investigation boring method according to the present invention. [Figure 16] This is a cross-sectional view (part 2) showing another embodiment of the investigation boring method according to the present invention. [Figure 17] This is a cross-sectional view (part 3) showing another embodiment of the investigation boring method according to the present invention. [Figure 18]Cross-sectional view (Part 4) showing another embodiment of the investigation boring method according to the present invention. [Figure 19] Cross-sectional view (Part 5) showing another embodiment of the investigation boring method according to the present invention. [Figure 20] Cross-sectional view (Part 6) showing another embodiment of the investigation boring method according to the present invention. [Figure 21] Cross-sectional view (Part 7) showing another embodiment of the investigation boring method according to the present invention. [Figure 22] Cross-sectional view (Part 8) showing another embodiment of the investigation boring method according to the present invention. [Figure 23] Cross-sectional view (Part 9) showing another embodiment of the investigation boring method according to the present invention. [Figure 24] Cross-sectional view (Part 10) showing another embodiment of the investigation boring method according to the present invention. [Figure 25] Cross-sectional view (Part 11) showing another embodiment of the investigation boring method according to the present invention. [Figure 26] Cross-sectional view (Part 12) showing another embodiment of the investigation boring method according to the present invention. [Figure 27] Front view showing the first orientation member used in the investigation boring method according to the present invention. [Figure 28] Cross-sectional view taken along line XXVIII-XXVIII of FIG. 27. [Figure 29] Longitudinal sectional view showing the first orientation member, mixer, and feeder used in the investigation boring method according to the present invention. [Figure 30] Cross-sectional view taken along line XXX-XXX of FIG. 29.

Embodiments for Carrying Out the Invention

[0009] 《First Embodiment》 Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the drawings. Figures 1 to 8 are cross-sectional views showing one embodiment of the investigation boring method according to the present invention, Figure 9 is a cross-sectional view along the line IX-IX in Figure 1, Figure 10 is a cross-sectional view along the line XX in Figure 5, Figure 11 is a cross-sectional view along the line XI-XI in Figure 4, Figure 12 is a cross-sectional view along the line XII-XII in Figure 6, Figure 13 is a cross-sectional view along the line XIII-XIII in Figure 6, and Figure 14 is a cross-sectional view along the line XIV-XIV in Figure 8.

[0010] In this embodiment of the investigation boring method, as shown in Figures 1 and 2, a first hole 11 with a first diameter D1 is drilled into the ground 1 to be investigated (hereinafter also referred to as the first step), and then, as shown in Figures 3 and 4, a first orientation member 7 with an orientation marked is inserted so that the marked orientation matches the orientation of the ground and extends along the first hole 11, and an injection material 2 that expands and hardens in a controlled time is injected into the first hole 11 and allowed to expand and harden. (Hereinafter referred to as the second step.) Next, with the first orientation member 7 remaining in the first hole 11 where the injected material 2 has foamed and hardened, core boring is performed around the first hole 11 with a second diameter D2 that is concentric with the first hole 11 and larger than the first diameter D1, as shown in Figures 5 and 6 (hereinafter referred to as the third step). Finally, as shown in Figures 7 and 8, core boring is performed and the core containing the first orientation member 7 is collected as the first sample S1 (hereinafter referred to as the fourth step). Then, by observing the first sample S1, which is collected in this manner and contains the first orientation member 7, based on the orientation marked on the first orientation member 7, the precise strike and dip of the cracks, faults, and fracture zones in the ground that are the subject of the investigation can be determined. The following describes each step in detail.

[0011] In the first step shown in Figures 1 and 2, a first borehole 11 with a first diameter D1 is drilled into the ground 1 that is the subject of the investigation. Although not particularly limited, a first double core tube 3 with an outer diameter φ of 46 mm is attached to a boring machine (not shown), and using this boring machine, a first borehole 11 is drilled, for example, with a drilling diameter (=first diameter D1) of 46 mm and a first drilling depth DP1 of 1 m, as shown in Figures 1 and 2. Figure 3 shows the state after the first borehole 11 has been drilled into the ground 1. In Figures 1 to 7, the symbol L indicates a layer in which a cavity or void exists and the injection material described later escapes (hereinafter also referred to as the cavity layer L). The drilling depth is not particularly limited, and drilling may be done to the desired depth, however, if the groundwater level of the ground is high and the borehole wall is not self-supporting, it is preferable to shorten the drilling depth.

[0012] The first double core tube 3 used for drilling the first hole 11, as shown in the cross-sectional view of Figure 9, has a cylindrical inner core tube 31 and a cylindrical outer core tube 32. Drilling fluid (water, etc., in this embodiment) circulates between the inner core tube 31 and the outer core tube 32, and a drilling bit is provided at its tip, making it a boring tool.

[0013] In the second step shown in Figures 3 and 4, a first orientation member 7, which has an orientation marking, is inserted into the first hole 11 drilled in the first step described above, with the marked orientation aligned with the orientation of the ground 1 and extending along the first hole 11. An injection material 2 that expands and hardens over a set period of time is then injected into the first hole 11. Figure 27 is a front view showing the first orientation member 7 used in the investigation boring method according to the present invention, and Figure 28 is a cross-sectional view along the line XXVIII-XXVIII in Figure 27.

[0014] As shown in Figure 27, the first orientation member 7 of this embodiment is a long, rigid, hollow member made of plastic, metal, or ceramic, extending from the upper end 71 to the lower end 72. The first orientation member 7 is not limited to a hollow member; it may also be a solid member. For geological layers with cavities or voids (void layer L) as indicated by the symbol L in Figures 3 and 4, a hollow member may be used, while for geological layers without void layer L, a solid member may be used. Furthermore, for geological layers with large void layer L, the hollow orientation member 7 may be equipped with a long bag comprising a permeable and water-retentive inner layer and a permeable outer layer to prevent the injection material 2 from leaking into the void layer L. The first orientation member 7 of this embodiment is formed with an outer diameter smaller than the inner diameter of the first hole 11 and with a length approximately equal to the depth of the first hole 11.

[0015] As shown in Figures 27 and 28, the first orientation member 7 of this embodiment is provided with markings 73N and 73S indicating orientation (a representation of the direction in the horizontal plane at a given point in relation to a certain reference direction). The markings 73N and 73S in the illustrated embodiment consist of two holes formed at two locations in the diametrical direction DM on the side surface of the first orientation member 7, with one marking 73N indicating the direction of "north" and the other marking 73S indicating the direction of "south".

[0016] The markings of the present invention provided on the first orientation member 7 are not limited to the holes shown in the figure, but may be convex parts, protrusions, grooves, colors, different materials, or any other shape, color, structure, or material that can be visually distinguished from the surroundings. Furthermore, while it is sufficient to provide at least one marking of the present invention on the first orientation member 7, it is preferable to provide at least two markings or markings along the upper and lower lines of the orientation member 7 in order to facilitate the identification of the direction. As shown in Figure 28, by providing two markings, 73N indicating the north direction and 73S indicating the south direction, it is easy to identify that the straight line connecting these two markings 73N and 73S (diameter direction DM in the figure) coincides with the north-south direction.

[0017] As shown in Figures 29 and 30, the first orientation member 7 of this embodiment is a pipe having a length corresponding to or shorter than the depth of the first hole 11, and is not particularly limited, but for example, a heat-resistant polyvinyl chloride pipe can be used. The lower end of the mixer 9 is attached to the upper end 71 of the first orientation member 7 of this embodiment via a detachable socket joint (not shown), and the upper end of the mixer 9 is connected to a first liquid supply device 21A and a second liquid supply device 21B of the injection material. After completing the second step shown in Figures 3 and 4, the first orientation member 7 of this embodiment is detached from the mixer 9 at the socket joint, and as shown in Figures 5 and 6, the first orientation member 7 remains in the first hole 11.

[0018] The first orientation member 7 may be left in the first borehole 11 over the entire first drilling depth DP1 of the first borehole 11, or it may be left only in a part of the first drilling depth DP1 of the first borehole 11. If the first orientation member 7 is included over the entire axial direction of the first sample S1 shown in Figure 8, various laboratory tests such as X-ray CT tomography and shear tests cannot be performed. Therefore, for example, if the length to be tested in the laboratory is 20 cm from the bottom of a total length of 1 m of the first sample S1, the first orientation member 7 may be left only in the upper 80 cm range of the core, and the lower 20 cm range of the core may be an area where the first orientation member 7 does not exist. Regardless of whether the first orientation member 7 is present or not, if a length of 1 m of the first sample S1 can be taken, the strata can be considered continuous, and various laboratory tests such as X-ray CT tomography and shear tests can be performed on the core whose orientation is known, for example, by considering the slip direction of the fault.

[0019] As shown in Figure 3, before inserting the first orientation member 7, marked with markings 73N and 73S, along the first hole 11, the orientation of the ground 1 in the first hole 11 is measured, and the orientations marked with 73N and 73S are aligned with this measured orientation. Then, while maintaining the aligned orientation, the first orientation member 7 is inserted along the first hole 11.

[0020] The mixer 9 in this embodiment is a stationary mixer equipped with spiral blades inside. When the first liquid from the first liquid supply unit 21A and the second liquid from the second liquid supply unit 21B flow into the upper part of the mixer 9, these first and second liquids flow downward along the spiral blades. This allows the first and second liquids of the two-component curing type injection material 2 to be thoroughly mixed, enabling good foaming and curing. Alternatively, a heat-resistant rubber water packer (a water balloon-shaped member) may be provided on the outer surface of the mixer 9 in this embodiment to suppress the rise of the foamed injection material 2 around the first orientation member 7.

[0021] The injection material 2 used in this embodiment can be exemplified by a two-component curing foamed urethane resin, but is not particularly limited and may be any material that foams and hardens in a controlled time. Alternatively, any material that hardens in a controlled time may be used. Since the injection material 2 is injected into the ground 1 that is the subject of the investigation, it is preferable that the injection material 2 does not contain harmful substances. Furthermore, since there is a third step after the injection of the injection material 2, it is preferable that the material has a curing time that can be flexibly adjusted. In addition, since the sample taken in the investigation is from a very limited area (for example, about φ86 mm of the second diameter described later), it is preferable that the injection material 2 has a viscosity that does not penetrate too deeply into the ground 1.

[0022] As shown in Figure 3, the injection material 2, such as the two-component curing foamed urethane resin, is supplied to the mixer 9 using a supply machine 21A that supplies the first liquid of the injection material 2 and a supply machine 21B that supplies the second liquid of the injection material 2. When the first and second liquids of the injection material 2 are supplied to the mixer 9 at a predetermined pumping pressure, both liquids are agitated as they pass through the mixer 92, and the curing reaction begins.

[0023] Then, the injection material 2, which has been stirred by the mixer 9, is allowed to fall naturally, and a portion of it is injected into the interior and exterior of the first directional member 7 without pressure. By injecting with zero or near-zero injection pressure, the material can be injected without disturbing the ground 1. If the first directional member 7 is made of a solid rod, all of the injection material 2 stirred by the mixer 9 is injected into the exterior of the first directional member 7 without pressure.

[0024] As a result of the second step described above, as shown in Figure 4, the injection material 2 that has spread throughout the inside and outside of the first orientation member 7 in the first hole 11 foams and hardens. After injecting the injection material 2, wait until it hardens and develops sufficient strength. Once the injection material 2 has hardened, separate the first orientation member 7 and the mixer 9 at the socket joint, and as shown in Figures 5 and 6, leave the first orientation member 7, in which the injection material 2 has foamed and hardened, in the first hole 11, and pull out the mixer 9 from the first hole 11. Figure 11 is a cross-sectional view along the line XI-XI in Figure 4. As shown in the figure, the orientation of the markings 73N and 73S on the first orientation member 7 (diameter direction DM in the figure) coincides with the orientation NS of the ground 1.

[0025] In the third step shown in Figures 5 and 6, the first orientation member 7, which has been foamed and hardened by the injected material 2, remains in the first hole 11, and a core boring is performed around the first hole 11 with a second diameter D2 that is concentric with the first hole 11 and is larger than the first diameter D1. Although not particularly limited, a second double core tube 4 with an outer diameter φ of 86 mm is mounted on a boring machine (not shown), and using this boring machine, a second hole 12 is drilled, for example, with a drilling diameter (= second diameter D2) of 86 mm and a first drilling depth DP1 of 1 m, as shown in Figures 5 and 6. Figure 7 shows the second hole 12 after the core, which will be used as the first sample S1, has been taken.

[0026] The second double core tube 4 used for drilling the second hole 12, as shown in the cross-sectional view of Figure 10, has a cylindrical inner core tube 41 and a cylindrical outer core tube 42. Drilling fluid (water, etc., in this embodiment) circulates between the inner core tube 41 and the outer core tube 42, and a drilling bit is provided at the tip of the boring tool. The core that will become the first sample S1 is held in the inner core tube 41.

[0027] Figure 12 shows a cross-section along the line XII-XII in Figure 6, and Figure 13 shows a cross-section along the line XIII-XIII in Figure 6. At the borehole depth where the cavity layer L shown in Figure 12 does not exist, the same geological layer as the ground 1 exists between the central injection material 2 and the outer second double core tube 4. In contrast, at the borehole depth where the cavity layer L exists, as shown in Figure 13, a geological layer 2a into which the injection material 2 has penetrated exists between the central injection material 2 and the outer second double core tube 4.

[0028] In the fourth step, shown in Figures 7 and 8, the second double core tube 4 is lifted, and the core held by the inner core tube 41 is collected as the first sample S1. Figure 8 shows a cross-section of the collected first sample S1, and Figure 7 shows the second hole 12 after the first sample S1 has been collected. The collected first sample S1 is a cylindrical mass with a diameter equal to the inner diameter of the inner core tube 41 and a length equal to the first drilling depth DP1. It is used to investigate whether or not there are cavities or voids in the ground, which is one of the purposes of the investigation, and is observed visually.

[0029] Figure 14 is a cross-sectional view along the line XIV-XIV, which is part of the first sample S1. At the drilling depth where the cavity layer L shown in the figure exists, the outer layer of the first sample S1 contains a geological layer 2a into which the injection material 2 has penetrated. Therefore, by simply visually observing the collected first sample S1, it is easy to confirm which first drilling depth DP1 contains the cavity layer L.

[0030] In addition, the orientation of the ground 1 can be determined from the markings 73N and 73S on the first orientation member 7 included in the first sample S1. By observing based on the orientation of the ground 1, the precise strike and dip of the cracks, faults, and fracture zones in the ground that are the subject of the investigation can be determined.

[0031] 《Second Embodiment》 The first embodiment described above is an example in which a first sample S1 is taken at a first drilling depth DP1. Subsequently, a second sample S2 from a deeper layer than the first drilling depth DP1 can be taken using a second borehole 12. Figures 15 to 26 are cross-sectional views showing other embodiments of the investigation boring method according to the present invention.

[0032] In the investigation boring method of this embodiment, a second sample S2 from a first drilling depth DP1 to a second drilling depth DP2 is collected by performing the same first to fourth steps as in the first embodiment described above. At this time, if a means for supporting the boring tool is provided in the second hole 12 as shown in Figure 7, drilling can be performed with even greater accuracy. Therefore, in this embodiment, as shown in Figures 15 and 16, a cylindrical casing 5 with a diameter corresponding to the diameter of the second hole 12 is inserted and installed in the second hole 12 from which the first sample S1 was taken (fifth step). Then, as shown in Figures 17 and 18, a center riser 6 for guiding the boring rod is inserted and installed in the cylindrical casing 5 (sixth step). Then, as shown in Figures 19 and 20, a third hole 13 with a first diameter D1 is drilled in the bottom surface of the second hole 12 using a boring rod guided by the center riser 6 (seventh step).

[0033] Next, as shown in Figures 21 and 22, the second orientation member 8, which has an orientation marking, is inserted so that the marked orientation matches the orientation of the ground and extends along the third hole 13. Then, an injection material 2 that foams and hardens in a controlled time is injected into the third hole 13 and allowed to foam and harden (step 8). Next, with the second orientation member 8 remaining in the third hole 13 where the injection material 2 has foamed and hardened, a core boring is performed around the third hole 13 with a second diameter D2 that is larger than the first diameter D1 and concentric with the third hole 13, as shown in Figures 23 and 24 (step 9). Finally, as shown in Figures 25 and 26, a core boring is performed and the core containing the second orientation member 8 is taken as the second sample S2 (step 10). Each step will be described in detail below.

[0034] First, in the fifth step shown in Figures 15 and 16, in order to reinforce the second hole 12 drilled in the third step shown in Figures 5 and 6, a cylindrical casing 5 with a diameter corresponding to the second diameter D2 of the second hole 12 is inserted into the second hole 12. Although not particularly limited, if the second diameter D2 is φ86 mm, a steel cylindrical casing 5 with an inner diameter of φ90.2 mm, an outer diameter of φ101.6 mm, and a plate thickness t of 5.7 mm can be used. As shown in Figure 16, by inserting a cylindrical casing 5 with a diameter slightly larger than the second diameter D2 of the second hole 12, the hole wall of the second hole 12 is firmly reinforced.

[0035] In the sixth step shown in Figures 17 and 18, a center riser 6, which guides a boring rod such as the first double core tube 3, is inserted and installed into the cylindrical casing 5. The center riser 6 in this embodiment is used to center the first double core tube 3 when drilling the third hole 13 with the first double core tube 3. For this reason, the center riser has an inner diameter corresponding to the outer diameter of the first double core tube 3, and as shown in Figure 17, protrusions 61 that discretely contact the inner surface of the cylindrical casing 5 are provided at equal intervals in the circumferential direction. As shown in Figure 18, when the center riser 6 is inserted into the cylindrical casing 5, its protrusions 61 contact the inner surface of the cylindrical casing 5, so that the center riser 6 is positioned concentrically with the cylindrical casing 5.

[0036] In the seventh step shown in Figures 19 and 20, a first hole 11 with a first diameter D1 is drilled into the bottom surface of the second hole 12, similar to the first step described above. Although not particularly limited, a first double core tube 3 with an outer diameter φ of 46 mm is mounted on a boring machine (not shown), and guided by a center riser 6, a third hole 13 is drilled using the boring machine, for example, with a drilling diameter (=first diameter D1) of 46 mm and a second drilling depth DP2 of 1 m. Figure 20 shows the state in which the third hole 13 has been drilled below the second hole 12 in the ground 1.

[0037] In the subsequent eighth step shown in Figures 21 and 22, the second orientation member 8, which has an orientation marking, is inserted into the third hole 13 drilled in the seventh step described above, with the marked orientation aligned with the orientation of the ground 1 and extending along the third hole 13. An injection material 2 that foams and hardens over a set period of time is then injected into the third hole 13. The second orientation member 8 of this embodiment has the same configuration as the first orientation member 7 of the first embodiment shown in Figures 27 and 28, so the description of the first orientation member 7 is used herein by reference. Therefore, the second orientation member 8, although not shown, has an upper end portion 81 and a lower end portion 82, similar to the first orientation member 7 shown in Figures 27 and 28, and is provided with markings 83N and 83S indicating orientation (a representation of the direction in the horizontal plane at a given point in relation to a certain reference direction). In the illustrated embodiment, the markings 83N and 83S consist of two holes formed at two locations in the diametrical direction DM on the side surface of the second orientation member 8. One marking 83N indicates the "north" direction, and the other marking 83S indicates the "south" direction. The second orientation member 8 is also connected to the mixer 10 via a socket joint, similar to the first orientation member 7 shown in Figure 29, although it is not shown in the illustration.

[0038] Furthermore, the injection material 2 used here is the same as the injection material 2 used in the first embodiment described above. Figure 22 shows the state in which the injection material 2 has been filled into the third hole 13 via the mixer 10. As shown in Figure 22, once the injection material 2 has been filled into the third hole 13, the system is left to wait until the injection material 2 hardens and develops sufficient strength. Once the injection material 2 has hardened, the second orientation member 8 and the mixer 10 are separated at the socket joint, and as shown in Figures 23 and 24, the second orientation member 8 is left in the third hole 13 where the injection material 2 has foamed and hardened, and the mixer 10 is withdrawn from the second hole 12.

[0039] The second orientation member 8 may be left in the third borehole 13 over the entire second drilling depth DP2 of the third borehole 13, or it may be left only in a part of the second drilling depth DP2 of the third borehole 13. In the second sample S2 shown in Figure 26, if the second orientation member 8 is included over the entire axial direction, various laboratory tests such as X-ray CT tomography and shear tests cannot be performed. Therefore, for example, if the length to be tested in the laboratory is 20 cm from the bottom of a total length of 1 m of the second sample S2, the second orientation member 8 may be left only in the upper 80 cm range of the core, and the lower 20 cm range of the core may be left without the second orientation member 8. Regardless of whether the second orientation member 8 is present or not, if a length of 1 m of the second sample S2 can be taken, the strata can be considered continuous, and various laboratory tests such as X-ray CT tomography and shear tests can be performed on the core whose orientation is known, for example, by considering the slip direction of the fault.

[0040] In the ninth step shown in Figures 23 and 24, with the second orientation member 8 remaining in the third hole 13 where the injected material 2 has foamed and hardened, a core boring hole is drilled around the third hole 13 concentrically with the third hole 13 and with a second diameter D2 that is larger than the first diameter D1. Although not particularly limited, after removing the center riser 6, a second double core tube 4 with an outer diameter φ of 86 mm is mounted on a boring machine (not shown), and using this boring machine, a fourth hole 14 is drilled, for example, with a drilling diameter (= second diameter D2) of 86 mm and a second drilling depth DP2 of 1 m, as shown in Figures 23 and 24. Figure 25 shows the fourth hole 14 after the core for the second sample S2 has been taken.

[0041] In the tenth step, shown in the final Figures 25 and 26, the second double core tube 4 is lifted, and the core held by the inner core tube 41 is collected as the second sample S2. Figure 26 shows a cross-section of the collected second sample S2, and Figure 25 shows the fourth hole 14 after the second sample S2 has been collected. The collected second sample S2 is a cylindrical mass with a diameter equal to the inner diameter of the inner core tube 41 and a length equal to the second drilling depth DP2. It is used to investigate whether or not cavities or voids exist in the ground under investigation, and is observed visually. In addition, the orientation of the ground 1 can be determined from the markings 83N and 83S of the second orientation member 8 included in the second sample S2. By observing based on the orientation of the ground 1, the precise strike and dip of cracks, faults, and fracture zones in the ground under investigation can be determined.

[0042] Furthermore, if a sample is to be taken from a portion deeper than the bottom surface of the fourth hole 14 shown in Figure 25, the above steps 5 through 10 should be repeated. [Explanation of Symbols]

[0043] 1...Ground 11...1st hole 12…Second hole 13…3rd hole 14...4th hole 2…Injection material 21A,21B…Feeding machine 2a...Stratum into which the injection material has penetrated 3…First double core tube 31…Inner core tube 32…Outer core tube 4…Second double core tube 41…Inner core tube 42…Outer core tube 5. Cylindrical casing 6... Center riser 61…Convex part 7…First orientation member 71...Top end 72...Lower end 73N, 73S… Markings indicating direction 8…Second orientation member 81...Top end 82…Lower end 83N, 83S… markings 9,10… Mixer S1…First sample S2…2nd sample D1…1st caliber D2…Second caliber DP1…1st drilling depth DP2…Second drilling depth L... Cavity layer (a layer where injection material escapes, such as cavities or voids) DM…Diameter direction

Claims

1. A first borehole of the first diameter is drilled into the ground targeted for investigation. A first orientation member, which has an orientation marked on it, is inserted so that the marked orientation is aligned with the orientation of the ground and extends along the first hole. An injection material that foams and hardens in a controlled time is injected into the previous first hole without pressure and hardened without pressure. A core boring hole is drilled around the first hole, concentric with the first hole and with a second diameter larger than the first diameter. A survey boring method in which the core drilled by the aforementioned core boring is taken as a first sample.

2. A cylindrical casing with a diameter corresponding to the diameter of the second hole is inserted into the second hole from which the core was removed and installed. A center riser for guiding the boring rod is inserted into the aforementioned cylindrical casing and installed. Using the boring rod guided by the center riser, a third hole of the first diameter is drilled into the bottom surface of the second hole. A second orientation member, which has an orientation marked on it, is inserted so that the marked orientation is aligned with the orientation of the ground and extends along the third hole. The aforementioned injection material is injected into the third hole without pressure and allowed to harden without pressure. A core boring hole is drilled around the third hole, concentric with the third hole and with a second diameter larger than the first diameter. The investigation boring method according to claim 1, wherein the core drilled by the core boring method is taken as a second sample.

3. The investigation boring method according to claim 1, wherein the first sample includes the first orientation member in part of its axial length.

4. The investigation boring method according to claim 2, wherein the second sample includes the second orientation member in part of its axial length.

5. The investigation boring method according to claim 1 or 2, wherein the injection material that foams and hardens in the adjusted time is a foamed urethane-based material that foams with moisture.

6. The investigation boring method according to claim 1, wherein an injection material that hardens in a controlled time is injected into the first hole in place of or in addition to the injection material that foams and hardens in a controlled time.

7. The investigation boring method according to claim 2, wherein an injection material that hardens in a controlled time is injected into the third hole in place of or in addition to the injection material that foams and hardens in a controlled time.

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