Excavation equipment and ground investigation method

Abstract

To eliminate the need to repeatedly recover and install a rod attached with a cone probe or a rod attached with a drilling bit even if the rod hits hard ground.SOLUTION: A drilling device 60 comprises: a main body 61 that is attached to a tip of a drilling rod 55 and has a tubular shape through which a CPT rod 50 having a cone probe 51 attached to the tip can be inserted; an annular crown bit 68 that is supported by the main body 61 and faces in an excavation direction; and a core bit 63 that is movable between a stored position in which the core bit is supported by the main body 61 within an opening 6B of the crown bit 68 and the cone probe 51 and CPT rod 50 are stored along an inner surface of the main body 61 so that they can be inserted through the opening 6B, and a digging position that occupies a substantial range within the opening 6B and faces in the digging direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an excavation device used for a cone penetration test (CPT) and a ground investigation method for investigating the ground by CPT.

Background Art

[0002] Conventionally, a cone penetration test (CPT) has been carried out in which a rod with a cone probe attached to its tip is pushed into the ground at a constant speed to measure the penetration resistance (for CPT, see Non-Patent Document 1). CPT is also used for investigating the seabed ground, and a technique has been provided for pushing a rod with a cone probe attached to its tip into the seabed ground from a working floor supported by a pier or a self-elevating platform (SEP) (for the pier and SEP, see, for example, Patent Documents 1 and 2).

[0003] When pushing a rod with a cone probe into the ground, the cone probe may hit a hard ground where it cannot penetrate. In such a case, once the rod with the cone probe is recovered to the ground, the tip of the rod is replaced from the cone probe with an excavation bit, and a rod with the excavation bit attached is inserted into the hole formed by the cone probe to excavate and remove the hard ground. After that, the rod with the excavation bit is recovered to the ground, the tip of the rod is replaced from the excavation bit with the cone probe, and a rod with the cone probe attached is inserted into the excavation hole formed by the excavation bit to install the cone probe at the excavated depth, and the CPT investigation is resumed.

[0004] During the excavation work with the rod with the excavation bit, the cone probe is recovered to the ground, but a method is also provided in which after the completion of the excavation work, the rod with the excavation bit is left in the hole, the cone probe is installed at the excavated depth, and the CPT investigation is resumed. Also in this method, the cone probe is recovered to the ground every time the excavation work is carried out.

Prior Art Documents

[0005] [Patent Document 1] Japanese Utility Model Publication No. 50-78002 [Patent Document 2] Japanese Utility Model Publication No. Showa 60-195324 [Non-patent literature]

[0006] [Non-Patent Document 1] JIS A 1220:2013 Mechanical cone penetration test method [Overview of the project] [Problems that the invention aims to solve]

[0007] When the cone probe encountered hard ground and penetration was blocked, the hard ground was removed to a depth of 1-2 meters, and the hardness of the ground was measured each time. In this case, a CPT survey had to be conducted every time 1-2 meters of excavation were performed, and the cone probe, rods, etc., had to be set up and retrieved repeatedly each time a CPT survey was conducted.

[0008] Even when investigating the seabed, if the cone probe hit hard ground and penetration was hindered, the hard ground was removed to a depth of 1-2 meters, and the hardness of the ground was measured each time. In this case, a CPT survey had to be conducted every 1-2 meters of drilling, and each time a CPT survey was conducted, it was necessary to repeatedly set up and retrieve the cone probe for the same depth as the water depth and the drilling depth of the ground. Furthermore, when conducting a CPT survey, the method of retrieving the drilling bit and the rod to which the drilling bit is attached required repeatedly extending and retrieving the rod, which is made by connecting standard-length steel pipes.

[0009] This invention is proposed in view of the above-mentioned circumstances, and aims to provide an excavation device and a ground investigation method that eliminates the need to repeatedly retrieve and install the rod with the cone probe attached or the rod with the drilling bit attached, even when encountering hard ground that the cone probe cannot penetrate during a CPT investigation of the ground. [Means for solving the problem]

[0010] To solve the above-mentioned problems, the drilling apparatus according to this invention includes a main body attached to the tip of a drilling rod and having a tubular shape through which a CPT rod with a cone probe attached to its tip can be inserted; an annular crown bit supported by the main body and facing the drilling direction; and a core bit supported by the main body within the opening of the crown bit, the core bit being movable between a storage position in which the cone probe and CPT rod are stored along the inner surface of the main body so as to be able to pass through the opening, and a drilling position that occupies a substantial area within the opening and faces the drilling direction.

[0011] The device further includes a sleeve coaxial with the main body and supported by the main body so as to be movable in the axial direction, the crown bit being mounted on the tip of the sleeve, the core bit consisting of a plurality of core bits extending from the tip of the main body in the drilling direction and arranged to surround the axis and open and close radially of the main body, the sleeve surrounding the main body and the plurality of core bits and may close the plurality of core bits as it moves distal to the main body proximal to the main body, guiding them from a stowed position to a drilling position.

[0012] Multiple core bits may have the same shape and be positioned symmetrically in the rotational direction with respect to the axis of the main body at the tip of the main body. Multiple core bits may include two or more core bits.

[0013] The sleeve may be formed such that its inner diameter gradually decreases as it moves in the drilling direction, and may include a core bit guide that slides around the outer circumference of multiple core bits to close them as the sleeve moves from distal to proximal.

[0014] The system may further include a range-of-movement limiting means that restricts the range of movement so that the sleeve can move only within a range between the distal and proximal parts of the main body. It may further include a biasing means that biases the sleeve from distal to proximal relative to the main body.

[0015] Multiple core bits may be attached to the tip of the body by hinges so as to be openable and closable. Retaining means may further be included to restrain the sleeve to the body in case of rotation around the axis of the body. The crown bit may have multiple drilling tips facing the drilling direction, and each of the multiple core bits may have a drilling tip at its tip.

[0016] The crown bit is attached to the tip of the main body, and the core bit may be attached to the main body so as to be rotatable between a storage position extending in the drilling direction and a drilling position extending toward the axis, within a plane including the axis of the main body, and may consist of multiple core bits that are biased to rotate from the drilling position toward the storage position.

[0017] Multiple core bits may have the same shape and be positioned symmetrically in the rotational direction with respect to the axis of the main body at the tip of the main body. Multiple core bits may include two or more core bits.

[0018] Multiple core bits may remain within the opening in their storage position. Multiple core bits may protrude from the opening in the drilling direction in their storage position.

[0019] Multiple core bits may rotate from the stowed position to the drilling position following the cone probe retracted into the opening. Multiple core bits may rotate from the drilling position to the stowed position following the cone probe protruding from the opening.

[0020] The plurality of core bits may be attached to the main body by hinges so as to be rotatable. It may further include biasing means for biasing the plurality of core bits to rotate from the excavation position toward the storage position. The crown bit includes a plurality of excavation tips facing the excavation direction, and the plurality of core bits may include excavation tips so as to face the excavation direction at the excavation position.

[0021] The ground investigation method according to this application uses the above-mentioned excavation device to conduct a CPT investigation on the ground, penetrates a cone probe attached to the tip of the CPT rod into the ground at a predetermined speed for the CPT investigation, and the cone probe is inserted into the excavation device attached to the tip of the excavation rod. When the process of conducting the CPT investigation is interrupted due to the penetration of the cone probe being blocked by hard ground existing in the ground, the cone probe is pulled into the excavation device, and the hard ground is removed using the core bits of the excavation device. After removing the hard ground, it includes the step of resuming the CPT investigation.

[0022] The step of excavating the hard ground may include rotating the core bits together with the crown bit around the axis of the main body to excavate the hard ground. The step of removing the hard ground may further include the step of advancing the excavation device in the excavation direction until it contacts the hard ground, and the step of retracting the CPT rod over a predetermined length so that the cone probe is pulled into the excavation device and the core bits are in the excavation position.

[0023] The step of advancing the excavation device may include rotating the crown bit around the axis of the main body to excavate the ground. The step of resuming the CPT investigation may include, when the hard ground is removed by the step of removing the hard ground, protruding the cone probe attached to the tip of the CPT rod from the excavation device to resume the CPT investigation.

Effect of the Invention

[0024] According to this invention, even when the CPT investigation is interrupted because a hard ground makes it impossible to penetrate the cone probe during the CPT investigation of the ground, the investigation can be continued without repeatedly recovering and installing the rod with the cone probe or the rod with the excavation bit.

Brief Description of the Drawings

[0025] [Figure 1] It is a diagram showing a schematic configuration of a seabed ground investigation device. [Figure 2] It is a cross-sectional view of a rod used in a seabed ground investigation device. [Figure 3] It is a diagram showing the structure of an excavation device according to the first embodiment. [Figure 4] It is a diagram showing the structure of an excavation device according to the first embodiment. [Figure 5] It is a diagram schematically explaining a seabed ground investigation method according to the first embodiment. [Figure 6] It is a diagram explaining a seabed ground investigation method according to the first embodiment. [Figure 7] It is a diagram explaining a seabed ground investigation method according to the first embodiment. [Figure 8] It is a diagram showing the structure of an excavation device according to the second embodiment. [Figure 9] It is a diagram showing the structure of an excavation device according to the second embodiment. [Figure 10] It is a diagram schematically explaining a seabed ground investigation method according to the second embodiment. [Figure 11] It is a diagram showing the structure of an excavation device according to a modification of the second embodiment. [Figure 12] It is a diagram showing the structure of an excavation device according to a modification of the second embodiment. [Figure 13] It is a diagram explaining a seabed ground investigation method of a comparative example. <​​​​​​Hereinafter, embodiments of the drilling apparatus and ground investigation method of this embodiment will be described in detail with reference to the drawings. In this embodiment, it is assumed that the seabed ground is investigated by a cone penetration test (CPT) in which a rod with a cone probe attached to its tip is driven into the ground at a constant speed from a working platform above the seawater surface supported by a rig installed on the seabed, and the penetration resistance force is measured at different depths.

[0027] Figure 1 shows a schematic configuration of a seabed ground investigation device 10 for implementing the ground investigation method of this embodiment. The seabed ground investigation device 10 has a frame 11 installed on the seabed 201, a tower 12 supported by the frame 11 and extending to the sea surface, and a work platform 20 supported on the sea surface by the tower 12. The frame 11 is made of steel or concrete structural members, with its bottom seated on the seabed and supporting the tower 12 attached to its upper part. The tower 12 is made of steel structural members and extends vertically from the top of the frame 11 to the sea surface. The work platform 20 is supported by the top of the tower 12 and is provided at a predetermined height above the sea surface so as not to be affected by waves from the sea surface.

[0028] A guide pipe 16 made of steel is attached to the derrick 12, extending vertically from directly below the work platform 20 to the seabed 201. The guide pipe 16 guides the drilling device 60 from the work platform 20 to the seabed 201 by passing a drilling rod 55 made of steel, to which the drilling device 60 is attached, through. The drilling device 60 has a cone probe 51 that penetrates the ground 200 of the seabed 201, through which a CPT rod 50 made of steel is attached. The tip of the drilling device 60 is provided with an annular crown bit through which the cone probe 51 and the CPT rod 50 can be inserted. When the cone probe 51 hits hard ground that cannot be sufficiently drilled by the crown bit, the cone probe 51 is pulled into the drilling device 60, and a core bit built into the drilling device 60 moves in the opening of the crown bit so as to face the drilling direction, and the drilling bit made up of the crown bit and core bit drills through the hard ground.

[0029] Figure 2 is a cross-sectional view of the CPT rod 50 and other components used in the seabed geotechnical investigation device 10. Figure 2(a) is a cross-section taken along the cutting line IIA-IIA at the depth of the frame 11, and Figure 2(b) is a cross-section taken along the cutting line IIB-IIB at a depth not reached from the drilling device 60 attached to the tip of the drilling rod 55 in the ground 200 of the seabed 201. As shown in Figure 2(a), the drilling rod 55 is inserted through the guide pipe 16, and the CPT rod 50 is further inserted through the drilling rod 55. In the ground 200 of the seabed 201 shown in Figure 2(b), the CPT rod 50 is inserted through the drilling rod 55.

[0030] Referring again to Figure 1, the working platform 20 has a two-layer structure. On the first layer 21 located at the top of the hoist 12, directly above the guide pipe 16, there is a drilling drive machine 25 for gripping and rotating to propel a drilling rod 55 that is inserted into the guide pipe 16 and reaches the ground 200 of the seabed 201. The drilling rod 55 protrudes from the upper end of the guide pipe 16, which opens directly below the working platform 20, and its upper end reaches a height exceeding that of the drilling drive machine 25. The drilling rod 55 is constructed by connecting standard-length steel pipes and can be connected and extended on the working platform 20, or detached and recovered.

[0031] In the second layer 22, which is above the first layer 21, a CPT pusher 27 is provided directly above the guide pipe 16 and the drilling rod 55. This CPT pusher 27 grips the CPT rod 50, which is inserted through the guide pipe 16 and the drilling rod 55 and reaches the seabed ground 200, and pushes the CPT rod 50 so that a cone probe 51 attached to the tip of the CPT rod 50 penetrates the seabed ground 200. The CPT rod 50 protrudes from the upper end of the drilling rod 55 that opens in the first layer 21, and its upper end reaches a height exceeding the CPT pusher 27. The CPT rod 50 is also constructed by connecting standard-length steel pipes and can be connected and extended or detached and retrieved on the work platform 20. The work platform 20 may be equipped with a crane capable of suspending standard-length steel pipes for the purpose of extending or retrieving the CPT rod 50 and the drilling rod 55.

[0032] (First Embodiment) Figures 3 and 4 illustrate the structure of the drilling apparatus 60 according to the first embodiment. Figure 3 shows the cone probe 51 protruding from the drilling apparatus 60 for CPT investigation, and Figure 4 shows the cone probe 51 retracted into the drilling apparatus 60 for drilling hard ground, so that the core bit 63 faces the crown bit 68 in the drilling direction. In Figures 3 and 4, (a) is a front view, (b) is a bottom view, and (c) is a cross-sectional view, respectively. The cross-sectional view in Figure 3(c) follows the cutting line IIIC-IIIC in Figures 3(a) and 3(b), and the cross-sectional view in Figure 4(c) follows the cutting line IVC-IVC in Figures 4(a) and 4(b).

[0033] Referring to Figure 3, the drilling device 60 has a tubular body 61 that surrounds and supports the cone probe 51 and the CPT rod 50 so that they can be inserted through it. Three claw-shaped core bits 63 are attached to the tip of the body 61 so as to extend in the drilling direction and to surround the axis of the body 61 (hereinafter sometimes simply referred to as the axis or axial direction) in positions that are rotationally symmetrical around the axis. The bases of these core bits 63 are attached to the tip of the body 61 by hinges 64 so that they can be moved radially in the body 61 and opened and closed. A drilling tip 65 is attached to the tip of the core bits 63, which is movable in the opening and closing direction together with the core bits 63. The core bits 63 and drilling tip 65 may be made of cemented carbide or the like.

[0034] Furthermore, the drilling device 60 is coaxial with the main body 61 and has a sleeve 67 that surrounds the main body 61 and the core bit 63. The sleeve 67 has a tubular shape with a predetermined length in the axial direction, and a crown bit 68 with an annular shape is attached to its tip. The cone probe 51 and the CPT rod 50 can be inserted through the opening 6B of the crown bit 68. Three drilling tips 69 are arranged on the surface of the crown bit 68 facing the drilling direction in rotationally symmetrical positions around the axis. The crown bit 68 and the drilling tips 69 may be made of cemented carbide or the like.

[0035] A sleeve support portion 62 is formed on the outer surface of the main body 61, which supports the sleeve 67 so that it can move axially over a predetermined range in the axial direction. The sleeve support portion 62 is formed with a sleeve guide portion 62b having a first outer diameter that guides the sleeve 67 so that it can move axially, a first sleeve stopper 62a having a second outer diameter larger than the first outer diameter that limits the range of movement of the sleeve 67 in the retrieval direction, and a second sleeve stopper 62c having a third outer diameter larger than the first outer diameter that limits the range of movement of the sleeve 67 in the excavation direction. Here, the retrieval direction is the direction in which the cone probe 51 and the like are retrieved into the work bed 20, opposite to the excavation direction. A projection 66 is also formed on the sleeve guide portion 62b.

[0036] The first sleeve stopper 62a and the second sleeve stopper 62c constitute a movement range limiting means that restricts the range of movement of the sleeve 67 relative to the main body 61. As will be described later, the range of movement of the sleeve 67 in the recovery direction is further restricted by a coil spring 6A interposed between the sleeve 67 and the first sleeve stopper 62a. Three projections 66 may be arranged in positions that are rotationally symmetrical around the axis. The projections 66 restrain the sleeve 67 in the circumferential direction of the main body 61 so that the sleeve 67 rotates together with the main body 61 about the axis.

[0037] At the base of the sleeve 67, a fitting portion 67a is formed, which has a second inner diameter smaller than the first inner diameter that is fitted and supported by the sleeve guide portion 62b in the sleeve support portion 62 of the main body 61, so that the sleeve 67 can move in the axial direction. The sleeve 67 is supported by the fitting portion 67a so that it can slide and move on the sleeve guide portion 62b.

[0038] The fitting portion 67a has guide holes 67d that extend longitudinally in the axial direction at positions corresponding to the projections 66. Three guide holes 67d may be arranged in rotationally symmetrical positions around the axis to correspond to the positions of the projections 66. The projections 66 engage with the guide holes 67d and are guided axially along the guide holes 67d. The guide holes 67d and the projections 66 constitute a restraining means that allows the sleeve 67 to move axially relative to the body 61, but restricts its circumferential movement, i.e., rotation around the axis, to the body 61. This restraining means ensures that when the body 61 rotates around the axis, the sleeve 67 also rotates with it.

[0039] In the sleeve 67, a core bit storage portion 67b is formed in a predetermined range on the inner surface in the axial direction between the sleeve support portion 62 and the tip to which the crown bit 68 is attached, having a first inner diameter that can accommodate a predetermined range of the core bit 63 from its base to its tip. The core bit storage portion 67b can store the core bit 63 in a fully open storage position where the core bit 63 extends in the drilling direction and contacts the inner surface of the sleeve 67. In addition, in the sleeve 67, a core bit guide portion 67c is formed in a tapered shape on the inner surface in the axial direction from the core bit storage portion 67b towards the tip, with the inner diameter gradually decreasing from the inner diameter of the core bit storage portion 67b to a third inner diameter at the tip of the sleeve 67. The core bit guide portion 67c slides along the tapered inner surface of the outer circumference of the openable and closable core bit 63, guiding the core bit 63 so that it gradually closes as it advances in the drilling direction relative to the sleeve 67.

[0040] A coil spring 6A is wound around the sleeve guide portion 62b of the sleeve support portion 62 of the main body 61. The coil spring 6A has a diameter that is larger than the first outer diameter of the sleeve guide portion 62b, but smaller than the second outer diameter of the first sleeve stopper 62a and the outer diameter of the sleeve 67, and biases the fitting portion 67a of the first sleeve stopper 62a and the sleeve 67 to separate. The sleeve 67 is advanced in the excavation direction away from the main body 61 by the biasing force of the coil spring 6A, and is biased until the fitting portion 67a of the sleeve 67 contacts the second sleeve stopper 62c of the main body 61. The coil spring 6A constitutes a biasing means that biases the sleeve 67 in the excavation direction relative to the main body 61.

[0041] Here, the position where the fitting portion 67a of the sleeve 67 contacts the second sleeve stopper 62c is where the sleeve 67 is furthest from the main body 61, and therefore the sleeve 67 is referred to as being distal to the main body 61. Conversely, the position where the fitting portion 67a is closest to the first sleeve stopper 62a with the coil spring 6A interposed is where the sleeve 67 is closest to the main body 61, and therefore the sleeve 67 is referred to as being proximal to the main body 61. The distance between the sleeve 67 and the main body 61 may be determined, for example, by the distance between the respective centers of gravity of the sleeve 67 and the main body 61.

[0042] In Figure 3, the sleeve 67 is distal to the main body 61. When the sleeve 67 is distal to the main body 61, a predetermined range of the core bit 63 extends from the base to the tip in the drilling direction and opens to contact the inner surface of the sleeve 67, allowing the core bit 63 to be in a stored position where it is housed in the core bit storage section 67b of the sleeve 67. Since the sleeve 67 is biased in the drilling direction away from the main body 61 by the coil spring 6A, the sleeve 67 is distal to the main body 61 when no external force is applied to the main body 61 or the sleeve 67. By advancing the cone probe 51 and the CPT rod 50 between the core bits 63 in the drilling direction, the core bits 63 gradually open and move to a stored position where they contact the inner surface of the sleeve 67 and extend in the drilling direction. The gap formed in the core bit 63 in the stored position supports the cone probe 51 and the CPT rod 50, through which the core bit 63 is inserted, so that they can move axially.

[0043] In Figure 4, the sleeve 67 is located proximal to the main body 61. As mentioned above, the sleeve 67 is biased in the drilling direction away from the main body 61 by the coil spring 6A. Therefore, the sleeve 67 becomes proximal to the main body 61 when the drilling device 60 hits hard ground, and the resistance force from the hard ground overcomes the biasing force of the coil spring 6A, causing the coil spring 6A to compress to its maximum extent.

[0044] When the sleeve 67 is proximal to the main body 61, the cone probe 51 and the CPT rod 50 are positioned such that the tip of the cone probe 51 is at least positioned in the retrieval direction relative to the core bit 63. At this time, the core bit 63 is guided and closed by the core bit guide portion 67c, which has a tapered inner surface, without interfering with the cone probe 51, and its tips are in contact with each other. At this time, the tips of the core bit 63 converge within the opening 6B of the crown bit 68 at the tip of the sleeve 67, occupying a substantial area within the opening 6B, and facing the digging direction together with the crown bit 68. Thus, the core bit 63 together with the crown bit 68 is able to constitute a digging bit for digging soil.

[0045] Such a drilling device 60 is attached to the tip of the drilling rod 55 so as to be coaxial with the drilling rod 55 that extends in the drilling direction. The body 61 of the drilling device 60 may be composed of a rod having the same diameter as the drilling rod 55. The drilling device 60 may have different axial lengths depending on whether the sleeve 67 is proximal or distal to the body 61, but may have approximately the same length as the standard-length steel pipe that makes up the drilling rod 55. The drilling device 60 may be made of a metal such as steel.

[0046] In the first embodiment, when the sleeve 67 is distal to the main body 61, as shown in Figure 3, the drilling device 60 allows for CPT investigation by inserting a CPT rod 50 with a cone probe 51 attached to its tip. Furthermore, since the sleeve 67 is equipped with an annular crown bit 68 at its tip, it enables excavation of the soil around the cone probe 51 or the CPT rod 50. As shown in Figure 4, when the sleeve 67 is proximal to the main body 61, the cone probe 51 is pulled into the drilling device 60, and the tips of the core bits 63 are gathered into the opening 6B of the crown bit 68. By forming a drilling bit with the crown bit 68 and core bit 63 facing each other in the drilling direction, excellent drilling performance can be achieved.

[0047] Therefore, in the first embodiment, the drilling device 60 is normally configured such that the sleeve 67 is distal to the main body 61, and the cone probe 51 is driven in the depth direction by the CPT rod 50 passed through the drilling device 60 to perform a CPT survey. However, when the penetration of the cone probe 51 is blocked by hard ground 210, the cone probe 51 is pulled back into the drilling device 60, and then the sleeve 67 is positioned proximal to the main body 61 to form a drilling bit with a crown bit 68 and a core bit 63 facing the drilling direction, and the hard ground 210 can be removed with this drilling bit. After the hard ground 210 has been removed, the CPT rod 50 and cone probe 51 can be pushed out of the drilling device 60 and the CPT survey can be resumed. In the drilling device 60, three core bits 63 were provided, but two or four or more core bits 63 may be provided. Also, three sets of projections 66 and guide holes 67d were formed, but two or fewer sets or four or more sets may be provided.

[0048] Figure 5 is a schematic diagram illustrating the seabed ground investigation method of the first embodiment. In Figure 5, the treadle 12 and working platform 20 of the seabed ground investigation device 10 shown in Figure 1 are omitted.

[0049] As shown in Figure 5(a), the CPT rod 50, with a cone probe 51 attached to its tip, is inserted through the guide pipe 16, the drilling rod 55, and the drilling device 60 attached to the tip of the drilling rod 55, and guided to the ground 200 of the seabed 201. Then, the cone probe 51 is pushed in the depth direction by a CPT pusher 27 on a work platform 20 (not shown) so that it penetrates the ground 200 at a predetermined speed. In the drilling device 60, as shown in Figure 3, the sleeve 67 is biased in the drilling direction away from the main body 61 by a coil spring 6A. Therefore, the sleeve 67 is distal to the main body 61, and the core bit 63 (not shown) stored in the sleeve 67 is open, supporting the cone probe 51 and the CPT rod 50 so that they can be inserted through the gap. A hard ground 210 exists at a predetermined depth from the seabed 201. This hard ground 210 is so hard that the cone probe 51 cannot penetrate it, and the crown bit 68 at the tip of the sleeve 67 of the drilling device 60 cannot excavate it sufficiently.

[0050] When the cone probe 51 reaches hard ground 210 and the CPT investigation is blocked, the CPT investigation is interrupted. A drilling drive 25 on a work platform 20 (not shown) rotates a drilling device 60, which has a crown bit 68 attached to the tip of a sleeve 67, and advances the drilling device 60 until it reaches hard ground 210. When the drilling device 60 reaches hard ground 210, the crown bit 68 of the drilling device 60 is insufficient to drill through the hard ground 210, and the advance of the drilling device 60 is blocked. When the advance of the drilling device 60 is blocked, the rotational drive of the drilling device 60 is stopped, and the CPT pusher 27 on the work platform 20 retrieves the CPT rod 50 that has reached hard ground 210 over a predetermined length, and pulls the cone probe 51 back into the drilling device 60 so that the cone probe 51 is positioned in the retrieval direction relative to the core bit 63.

[0051] As shown in Figure 5(b), the CPT rod 50 is gripped by the CPT pusher 27, and the cone probe 51 is left in place at a predetermined height from the hard ground 210. The drilling drive 25 then applies a pressing force to the drilling rod 55, to which the drilling device 60 is attached at its tip, and moves it further. At this time, in the drilling device 60, the resistance force exerted by the hard ground 210 overcomes the biasing force of the coil spring 6A, which biases the main body 61 and the sleeve 67 apart. The coil spring 6A compresses, and the sleeve 67 moves closer to the main body 61. As shown in Figure 4, the core bit 63 is guided to close by the core bit guide portion 67c of the sleeve 67, and the tip of the core bit 63 is brought into contact with it. The tip of the core bit 63 converges within the opening 6B of the crown bit 68 at the tip of the sleeve 67 and, together with the crown bit 68, faces the drilling direction, forming a drilling bit for excavating soil. In such a drilling bit, the crown bit 68 and core bit 63 work together to provide excellent drilling capability, and the rotational drive by the drilling drive machine 25 makes it possible to drill even hard ground 210.

[0052] As shown in Figure 5(c), the crown bit 68 and core bit 63 work together to excavate the hard ground 210. Once the drilling device 60 penetrates the hard ground 210, the resistance force exerted on the drilling device 60 by the hard ground 210 is eliminated. The biasing force of the coil spring 6A, which biases the body 61 of the drilling device 60 and the sleeve 67 to separate them, causes the coil spring 6A to stretch, and the sleeve 67 moves distal to the body 61. As shown in Figure 3, the core bit 63 is stored in the core bit storage section 67b of the sleeve 67, and the core bit 63 can be opened to form a gap that supports the insertion of the cone probe 51 and the CPT rod 50. In Figure 5(b), the cone probe 51, which was positioned at a predetermined height from the hard ground 210, is advanced by the CPT pusher 27 and, together with the CPT rod 50, passes through the drilling rod 55 and the drilling device 60, penetrating the hard ground 210 and being guided to the ground 200. Then, the cone probe 51 is pushed in the depth direction so that it penetrates the ground at a predetermined speed, and the CPT investigation is resumed.

[0053] Figures 6 and 7 illustrate the steps of the seabed ground investigation method according to the first embodiment. These figures provide a more detailed explanation of the outline of the seabed ground investigation method according to the first embodiment, which was described with reference to Figure 5. In Figures 6 and 7, the frame 11, treadle 12, and guide pipe 16 of the seabed ground investigation device 10 shown in Figure 1 are omitted, and the configuration of the working platform 20 shows only the drilling drive machine 25 and the CPT pusher 27.

[0054] Figures 6(a) and 6(b) correspond to Figure 5(a). As shown in Figure 6(a), a CPT survey is conducted in which a CPT rod 50 with a cone probe 51 attached to its tip is pushed into the ground 200 of the seabed 201 at a predetermined speed by a CPT pusher 27 installed on a work platform 20 (not shown). The CPT rod 50 is guided into the ground 200 of the seabed through a drilling rod 55 and a drilling device 60 attached to the tip of the drilling rod 55, and is pushed in the depth direction so that the cone probe 51 penetrates the ground 200 at a predetermined speed. The CPT rod 50 and the drilling rod 55 can each be extended by connecting standard-length steel pipes on the work platform 20.

[0055] In the drilling device 60, the sleeve 67 is biased in the drilling direction away from the main body 61 by a coil spring 6A, and the sleeve 67 is distal to the main body 61. For this reason, a predetermined range from the base to the tip of the core bit 63 is stored in the core bit storage section 67b of the sleeve 67, and the core bit 63 is in an open state so that the cone probe 51 and the CPT rod 50 can be inserted through it.

[0056] A hard layer of ground 210 exists at a predetermined depth from the seabed 201. When the cone probe 51 hits this hard layer of ground 210, penetration is prevented. The hard layer of ground 210 is so hard that the cone probe 51 cannot penetrate it, and the crown bit 68 at the tip of the sleeve 67 of the drilling device 60 cannot drill sufficiently.

[0057] As shown in Figure 6(b), when the cone probe 51 hits hard ground 210 and penetration is prevented, the CPT investigation is interrupted, and the CPT pusher 27 stops pushing the CPT rod 50. The grip of the CPT rod 50 by the CPT pusher 27 may also be released. Then, the drilling rod 55 and the drilling device 60 are rotated and propelled by a drilling drive 25 provided on a work platform 20 (not shown). In the drilling device 60, as shown in Figure 3, the sleeve 67 is distal to the main body, and the core bit 63 is stored in the sleeve 67. Therefore, the drilling device 60 excavates the ground 200 using only the crown bit 68 provided at the tip of the sleeve 67. Since the crown bit 68 alone is insufficient for excavating hard ground 210, the propulsion of the drilling device 60 is stopped when it reaches hard ground 210.

[0058] Figures 6(c) and 7(d) correspond to Figure 5(b). As shown in Figure 6(c), when the crown bit 68 of the drilling device 60 is obstructed by the hard ground 210, the rotational drive of the drilling rod 55 and the drilling device 60 by the drilling drive 25 is interrupted. The CPT rod 50 is retrieved over a predetermined length by the CPT pusher 27, and the cone probe 51 is drawn into the drilling device 60. The CPT rod 50 is gripped by the CPT pusher 27, and the cone probe 51 is positioned at a predetermined height from the hard ground 210 so that it is located in the drilling device 60 in the retrieval direction relative to the core bit 63.

[0059] Subsequently, when the drilling rod 55 is pressed by the drilling drive 25 to advance the drilling device 60, the drilling device 60 hits the hard ground 210. As a result, the force from the hard ground 210 overcomes the biasing force of the coil spring 6A that biases the main body 61 and the sleeve 67 apart, the main body 61 is pushed against the sleeve 67, and the sleeve 67 becomes positioned closer to the main body 61. At this time, the core bit 63 is guided to close by the core bit guide portion 67c of the sleeve 67, and the tip of the core bit 63 converges into the opening 6B of the annular crown bit 68, forming a drilling bit together with the crown bit 68. In such a drilling bit, the crown bit 68 and the core bit 63 work together to exhibit excellent drilling ability and are rotationally driven by the drilling drive 25, enabling drilling even in the hard ground 210.

[0060] As shown in Figure 7(d), the crown bit 68 and core bit 63 of the drilling device 60 excavate the hard ground 210, and when the drilling device 60 penetrates the hard ground 210 and reaches the ground 200, the resistance from the hard ground 210 is eliminated, and the sleeve 67 becomes distal to the main body 61 due to the biasing force of the coil spring 6A, which biases the sleeve 67 in the drilling direction so that it moves away from the main body 61. A predetermined range from the base to the tip of the core bit 63 is stored in the core bit storage section 67b of the sleeve 67 and can be opened.

[0061] Figures 7(e) and 7(f) correspond to Figure 5(c). As shown in Figure 7(e), the cone probe 51, which was placed at a predetermined height from the hard ground 210, is advanced in the excavation direction together with the CPT rod 50 by the CPT pusher 27 and guided into the ground 200 through the excavation rod 55 and the excavation device 60. As shown in Figure 7(f), the cone probe 51 penetrates the ground 200 in the depth direction, and the interrupted CPT investigation is resumed.

[0062] (Second Embodiment) Figures 8 and 9 illustrate the structure of the drilling device 70 according to the second embodiment. Figure 8 shows the cone probe 51 protruding from the drilling device 70 for CPT investigation, and Figure 9 shows the cone probe 51 retracted into the drilling device 70 for drilling hard ground 210 so that the core bit 74 is positioned in the opening 7A. In Figures 8 and 9, (a) is a front view, (b) is a bottom view, and (c) is a cross-sectional view, respectively. The cross-sectional view in Figure 8(c) follows the cutting line VIIIC-VIIIC in Figures 8(a) and 8(b), and the cross-sectional view in Figure 9(c) follows the cutting line IXC-IXC in Figures 9(a) and 9(b).

[0063] Referring to Figure 8, the drilling device 70 has a tubular body 71 that surrounds and supports the cone probe 51 and the CPT rod 50 so that they can be inserted through it. An annular crown bit 78 is attached to the tip of the body 71. The cone probe 51 and the CPT rod 50 can be inserted through the opening 7A of the crown bit 78. On the face of the crown bit 78 facing the drilling direction, four drilling tips 79 are arranged in positions that are substantially rotationally symmetrical around the axis. The crown bit 78 and the drilling tips 79 may be made of cemented carbide or the like.

[0064] Furthermore, a pair of wing-shaped core bits 74 are attached to the main body 71 at positions opposite each other across the axis near the tip. These core bits 74 are supported by hinges 75 at their bases within a frame of a core bit support section 73, which is provided in a predetermined range from the tip of the main body 71 in the retrieval direction, so that they can rotate in a plane including the axis. The core bit support section 73 limits the range in which the core bits 74 can rotate between a storage position where the core bits 74 are stored in the core bit support section 73 with the core bits 74 extended toward the drilling direction, and a drilling position where the core bits 74 are closed toward the axis and face the drilling direction within the opening 7A (see Figure 9(c)). A coil spring 76 is wound around the axis of the hinge 75 of the core bit support section 73 as a biasing means, biasing the core bits 74 to rotate from the storage position toward the drilling position. A drilling tip (not shown) is attached to the core bit 74 on the surface facing the drilling direction at the drilling position. The core bits 74 and the drilling tip may be made of cemented carbide or the like.

[0065] In Figure 8, the core bit 74 is in a stored position, housed in the core bit support section 73. As the cone probe 51 and CPT rod 50 advance towards the tip inside the main body 71, the biased core bit 74, which is in the drilling position, is pushed open by the cone probe 51 and maintained in its stored position, housed in the core bit support section 73, supported by the side of the cone probe 51 or the CPT rod 50.

[0066] When the core bit 74 is in its retracted position, it is stored in the core bit support 73, so only the crown bit 78 faces the drilling direction. The crown bit 78 is positioned around the cone probe 51 or CPT rod 50 so as to surround it. Therefore, drilling around the cone probe 51 or CPT rod 50 can be carried out while conducting a CPT survey. For example, if the ground resistance becomes too high and it becomes difficult to continue the CPT survey, the ground around the cone probe 51 or CPT rod 50 can be excavated to reduce the ground resistance.

[0067] In Figure 9, the cone probe 51 and CPT rod 50 are retracted into the main body 71. When the cone probe 51 and CPT rod 50, which were protruding from the main body 71, are retracted into the main body 71, the core bit 74, which is biased to rotate toward the drilling position, closes in accordance with the retracted cone probe 51. When the cone probe 51 and CPT rod are retracted into the main body 71, the core bit 74 is biased to be in a drilling position opposite to the drilling direction within the opening 7A.

[0068] When the core bit 74 is in the drilling position, it closes and occupies a substantial area within the opening 7A, facing the drilling direction together with the crown bit 78. Thus, the core bit 74, together with the crown bit 78, is able to constitute a drilling bit for drilling soil.

[0069] Such a drilling device 70 is attached to the tip of the drilling rod 55 so as to be coaxial with the drilling rod 55 that extends in the drilling direction. The main body 71 is screw-connected to the tip of the drilling rod 55 by a threaded portion 72 provided at its base. The drilling device 70 may be made of a metal such as steel.

[0070] The drilling device 70 of the second embodiment enables CPT investigation by inserting a CPT rod 50 with a cone probe 51 attached to its tip, as shown in Figure 8. Furthermore, since the main body 71 is equipped with an annular crown bit 78 at its tip, it enables excavation of the soil around the cone probe 51 or the CPT rod 50. As shown in Figure 9, when the cone probe 51 is retracted into the main body 71, the core bit 74 is biased to be in an excavation position facing the excavation direction within the opening 7A of the crown bit 78. By forming an excavation bit with the crown bit 78 and core bit 74 facing the excavation direction, excellent excavation capacity can be achieved.

[0071] Therefore, the crown bit 78 works in cooperation with the core bit 74 at the drilling position to advance drilling even into hard ground 210. Also, since the core bit 74 is closed according to the cone probe 51 which is pulled in by biasing force, the core bit 74 is stored in the opening 7A while covering the cone probe 51. As the core bit 74 is pulled in by the cone probe 51, it can reach the drilling position without hindering soil intrusion, thus ensuring stable operation of the opening and closing of the core bit 74. In this case the drilling device 70 was equipped with two core bits 74, but it may be equipped with three or more core bits 74.

[0072] Figure 10 is a schematic diagram illustrating the seabed ground investigation method of the second embodiment. In Figure 10, the treadle 12 and working platform 20 of the seabed ground investigation device 10 shown in Figure 1 are omitted.

[0073] As shown in Figure 10(a), the cone probe 51, with a cone probe 51 attached to its tip, is inserted into the guide pipe 16, the drilling rod 55, and the drilling device 70 attached to the tip of the drilling rod 55, and guided to the ground 200 of the seabed 201. Then, the cone probe 51 is pushed in the depth direction by the CPT pusher 27 of the work platform 20 (not shown) so that it penetrates the ground 200 at a predetermined speed. A hard ground 210 exists at a predetermined depth from the seabed 201. This hard ground 210 is so hard that the cone probe 51 cannot penetrate it, and the crown bit 78 attached to the tip of the main body 71 of the drilling device 70 cannot drill sufficiently.

[0074] When the cone probe 51 reaches hard ground 210 and the CPT investigation is blocked, the CPT investigation is interrupted. The drilling drive 25 of the work platform 20 (not shown) rotates the drilling device 70 to excavate the soil with the crown bit 78 and advances the drilling device 70 until it reaches hard ground 210. When the drilling device 70 reaches hard ground 210, the crown bit 78 is insufficient to excavate the hard ground 210, and the advance of the drilling device 70 is blocked. When the advance of the drilling device 70 is blocked, the rotational drive of the drilling device 70 is stopped, and the CPT pusher 27 of the work platform 20 retrieves the CPT rod 50 that has reached hard ground 210 over a predetermined length, and pulls the cone probe 51 back into the drilling device 70. At this time, the core bit 74 in the storage position in the drilling device 70 is closed by biasing force according to the cone probe 51 and is placed in an excavation position facing the excavation direction within the opening 7A in the main body 71 of the drilling device 70.

[0075] As shown in Figure 10(b), the CPT rod 50 is gripped by the CPT pusher 27, and the cone probe 51 is left in place at a predetermined height above the hard ground 210. The drilling drive 25 then applies a pressing force to the drilling rod 55, to which the drilling device 70 is attached at its tip, to advance it further. At this time, in the drilling device 70, the core bit 74 at the drilling position faces the drilling direction together with the crown bit 78, forming a drilling bit for excavating soil. In such a drilling bit, the crown bit 78 and the core bit 74 work together to exhibit excellent drilling ability, and the rotational drive by the drilling drive 25 makes it possible to excavate even the hard ground 210.

[0076] As shown in Figure 10(c), the crown bit 78 and core bit 74 work together to excavate the hard ground 210. Once the excavation device 70 penetrates the hard ground 210, the cone probe 51, which was positioned at a predetermined height above the hard ground 210 in Figure 10(b), is advanced by the CPT pusher 27 and, together with the CPT rod 50, passes through the excavation rod 55 and the excavation device 70, penetrating the hard ground 210 and being guided to the ground 200. At this time, the core bit 74, which was in the excavation position in the excavation device 70, is pushed open by the cone probe 51 protruding from the opening 7A and returned to its stored position in the core bit support section 73. Then, the cone probe 51 is pushed in the depth direction so that it penetrates the ground at a predetermined speed, and the CPT investigation is resumed.

[0077] (modified version) Figures 11 and 12 illustrate the structure of a modified drilling device 70 of the second embodiment. In the drilling device 70 of the second embodiment, the core bit 74 in the storage position is stored in the core bit support part 73 and does not contribute to soil excavation, whereas in the modified drilling device 70, the core bit 74 in the storage position has its tip protruding from the tip of the main body 71 and contributes to soil excavation together with the crown bit 78. The other configurations of the modified version are the same as those of the second embodiment, so the corresponding components will be given common reference numbers.

[0078] Figure 11 shows the modified drilling device 70 with the cone probe 51 extended for CPT investigation, and Figure 12 shows the modified drilling device 70 with the cone probe 51 retracted so that the core bit 74 is positioned in the opening 7A for drilling hard ground 210. In Figures 11 and 12, (a) is a front view, (b) is a bottom view, and (c) is a cross-sectional view, respectively. The cross-sectional view in Figure 11(c) is based on the cutting line XIC-XIC in Figures 11(a) and 11(b), and the cross-sectional view in Figure 12(c) is based on the cutting line XIIC-XIIC in Figures 12(a) and 12(b).

[0079] Referring to Figure 11, the modified drilling device 70 has a tubular body 71 that surrounds and supports the cone probe 51 and the CPT rod 50 so that they can be inserted through it. An annular crown bit 78 is attached to the tip of the body 71. The cone probe 51 and the CPT rod 50 can be inserted through the opening 7A of the crown bit 78. On the face of the crown bit 78 facing the drilling direction, four drilling tips 79 are arranged in positions that are substantially rotationally symmetrical around the axis. The crown bit 78 and the drilling tips 79 may be made of cemented carbide or the like.

[0080] Furthermore, a pair of wing-shaped core bits 74 are attached to the main body 71 at positions opposite each other across the axis near the tip. These core bits 74 are supported by hinges 75 at their bases within the frame of a core bit support section 73, which is provided in a predetermined range from the tip of the main body 71 in the retrieval direction, so that they can rotate in a plane including the axis. The core bit support section 73 limits the range in which the core bits 74 can rotate between a storage position in which the core bits 74 are opened and stored in the core bit support section 73 so that they extend in the drilling direction, and a drilling position (see Figure 9(c)) in which the core bits 74 are closed so that they face the axis and are opposed to the drilling direction within the opening 7A. In the modified example, even in the storage position, the entire core bit 74 is not stored in the core bit support section 73, and the tip of the core bit 74 extends outside the core bit support section 73 in the drilling direction and protrudes in the drilling direction from the opening 7A of the crown bit 78 attached to the tip of the main body 71. A coil spring 76 is wound around the axis of the hinge 75 of the core bit support 73 as a biasing means, biasing the core bit 74 to rotate from the storage position toward the drilling position. In the modified core bit 74, a drilling tip (not shown) is attached to the surface facing the drilling direction in the drilling position, as well as to the tip protruding from the opening 7A of the crown bit 78 in the storage position. The core bit 74 and the drilling tip may be made of cemented carbide or the like.

[0081] In Figure 11, the core bit 74 is in a stored position, housed in the core bit support section 73. As the cone probe 51 and CPT rod 50 advance towards the tip inside the main body 71, the biased core bit 74, which is in the drilling position, is pushed open by the cone probe 51 and maintained in its stored position, housed in the core bit support section 73, supported by the side of the cone probe 51 or the CPT rod 50.

[0082] When the core bit 74 is in its retracted position, the core bit 74 of the modified example has its tip protruding from the opening 7A of the crown bit 78, so the core bit 74 faces the crown bit 78 in the drilling direction. The crown bit 78 and core bit 74 are positioned around the cone probe 51 or CPT rod 50 so as to surround the cone probe 51 or CPT rod 50. Therefore, drilling around the cone probe 51 or CPT rod 50 can be advanced while conducting a CPT survey. For example, when the ground resistance becomes too high and it becomes difficult to continue the CPT survey, the ground around the cone probe 51 or CPT rod 50 can be drilled to reduce the ground resistance.

[0083] In Figure 12, the cone probe 51 and CPT rod 50 are retracted into the main body 71. When the cone probe 51 and CPT rod 50, which were protruding from the main body 71, are retracted into the main body 71, the core bit 74, which is biased to rotate toward the drilling position, closes in accordance with the retracted cone probe 51. When the cone probe 51 and CPT rod are retracted into the main body 71, the core bit 74 is biased to be in a drilling position opposite to the drilling direction within the opening 7A.

[0084] When the core bit 74 is in the drilling position, it closes and occupies a substantial area within the opening 7A, facing the drilling direction together with the crown bit 78. Thus, the core bit 74, together with the crown bit 78, is able to constitute a drilling bit for drilling soil.

[0085] In this modified form, the drilling device 70 is attached to the tip of the drilling rod 55 so as to be coaxial with the drilling rod 55 that extends in the drilling direction. The main body 71 is screw-connected to the tip of the drilling rod 55 by a threaded portion 72 provided at its base. The drilling device 70 may be made of a metal such as steel.

[0086] The modified drilling device 70, as shown in Figure 11, enables CPT investigation by inserting a CPT rod 50 with a cone probe 51 attached to its tip. Furthermore, the modified drilling device 70 enables excavation of the soil around the cone probe 51 or CPT rod 50 by a crown bit 78 arranged to surround the cone probe 51 or CPT rod and a core bit 74 in a retracted position. As shown in Figure 12, when the cone probe 51 is retracted into the main body 71, the core bit 74 is biased to be in an excavation position facing the excavation direction within the opening 7A of the crown bit 78. By forming an excavation bit with the crown bit 78 and core bit 74 facing the excavation direction, excellent excavation capacity can be achieved.

[0087] Therefore, the crown bit 78 works in cooperation with the core bit 74 at the drilling position to advance drilling even into hard ground 210. Also, since the core bit 74 is closed according to the cone probe 51 which is pulled in by biasing force, the core bit 74 is stored in the opening 7A while covering the cone probe 51. As the core bit 74 is pulled in by the cone probe 51, it can reach the drilling position without hindering soil intrusion, thus ensuring stable operation of the opening and closing of the core bit 74. In this case the drilling device 70 was equipped with two core bits 74, but it may be equipped with three or more core bits 74.

[0088] As described above, with the drilling apparatus and seabed ground investigation method of this embodiment, even if the cone probe 51 encounters hard ground 210 that prevents penetration when investigating the ground 200 of the seabed 201 using CPT, the crown bit at the tip of the drilling apparatus and the core bit located inside the opening work together to remove the hard ground 210. Therefore, the investigation can be continued without the need to repeatedly retrieve and install the CPT rod 50 with the cone probe 51 attached or the drilling rod 55 with the drilling bit attached.

[0089] Therefore, according to this embodiment, the survey period can be shortened, resulting in cost reductions by shortening the number of days the support vessel is used, as well as reductions in survey labor costs and survey equipment leasing costs. In addition, because the survey period is shortened, it becomes easier to respond to sudden changes in sea conditions, improving the safety of the survey. Furthermore, when encountering hard ground 210, the work can be quickly changed from CPT survey to excavation and removal of the ground, and the excavation pitch can be shortened as needed, and the strength of the excavated ground can be quickly confirmed by CPT survey each time. As a result, ground surveys can be conducted almost continuously even in hard ground.

[0090] Although this embodiment describes a seabed ground investigation method using a work platform 20 supported by a raft 12 on the sea surface, it is not limited to this. For example, the work platform 20 may be installed on a self-elevating work platform (SEP). Furthermore, although this embodiment describes a seabed ground investigation method, it is not limited to this. This embodiment can be applied not only to seabed ground investigation methods but also to land-based ground investigation methods. In this case, the work platform 20 would be installed on land, and the guide pipe 16 connecting the work platform 20 and the seabed 201 would become unnecessary.

[0091] (Comparative example) Figure 13 is a diagram illustrating a comparative example of a drilling apparatus and seabed ground investigation method. In Figure 13, as with Figures 6 and 7, the frame 11 and treadmill 12 of the seabed ground investigation apparatus 10 shown in Figure 1 are omitted, and the configuration of the working platform 20 shows only the drilling drive machine 25 and the CPT pusher 27.

[0092] As shown in Figure 13(a), the cone probe 51 attached to the tip of the CPT rod 50 is guided from the work platform above the seawater surface through the guide pipe 16 to the seabed ground 200, and is pushed in at a predetermined speed by the CPT pusher 27. The PCT survey has been interrupted because the cone probe 51 has been blocked by the hard ground 210.

[0093] As shown in Figure 13(b), the CPT rod 50 with a cone probe 51 attached to its tip is completely retrieved onto the work platform. Then, the drilling rod 55, with a non-core type bit 80 (a drilling bit made of cemented carbide or the like) attached to its tip, is rotated and propelled by the drilling drive 25 to remove the hard ground 210.

[0094] After removing the hard ground 210 with the non-core bit 80, the drilling rod 55 with the non-core bit 80 attached to its tip is completely retrieved into the work platform. Then, the CPT rod 50 with the cone probe 51 attached to its tip is guided through the drilled hole of the non-core bit 80 to the ground 200 below the hard ground 210, and the CPT investigation resumes. [Industrial applicability]

[0095] This invention can be used for ground investigation using CPT. [Explanation of Symbols]

[0096] 10. Seabed geological survey equipment 11. Stand 12 Towers 16 Guide tubes 20 Work platform 25 Excavation drive machine 27 CPT pushing machine 50 CPT Rod 51 Cone probe 55 Drilling Rod 60 Drilling equipment 61 Main unit 63 core bits 67 sleeves 68 Crown Bit 69 drilling chips 70 Drilling equipment 71 Main unit 74 core bits 78 Crown Bit 200 Ground 201 Undersea 210 Hard ground

Claims

1. A drilling device attached to the tip of a drilling rod, A main body having a tubular shape through which a CPT rod with a cone probe attached to its tip can be inserted, An annular crown bit supported by the main body and facing the drilling direction, A core bit supported within the opening of the crown bit by the main body, the core bit being movable between a storage position in which the cone probe and the CPT rod are stored along the inner surface of the main body so as to be able to pass through the opening, and a drilling position that occupies a substantial area within the opening and faces the drilling direction. Drilling equipment including.

2. The drilling apparatus according to claim 1, further comprising a sleeve coaxial with the main body and supported by the main body so as to be movable in the axial direction, wherein the crown bit is attached to the tip of the sleeve, the core bit is composed of a plurality of core bits extending from the tip of the main body in the drilling direction, arranged to surround the axis and open and close in the radial direction of the main body, and the sleeve surrounds the main body and the plurality of core bits, and as it moves distal to the main body to proximal, it closes the plurality of core bits to guide them from the storage position to the drilling position.

3. The drilling apparatus according to claim 2, wherein the plurality of core bits have the same shape and are positioned symmetrically in the rotational direction with respect to the axis of the main body at the tip of the main body.

4. The drilling apparatus according to claim 2 or 3, wherein the plurality of core bits include two or more core bits.

5. The drilling apparatus according to claim 2, wherein the sleeve is formed such that the inner diameter gradually decreases as it moves in the drilling direction, and includes a core bit guide that slides around the outer circumference of the plurality of core bits to close them as the sleeve moves from distal to proximal.

6. The drilling apparatus according to claim 2, further comprising a movement range limiting means that restricts the movement range so that the sleeve can move only within the range between the distal and proximal parts of the main body.

7. The drilling apparatus according to claim 2, further comprising a biasing means for biasing the sleeve relative to the main body from the proximal to the distal end.

8. The drilling apparatus according to claim 2, wherein the plurality of core bits are attached to the tip of the main body by hinges so that they can be opened and closed.

9. The drilling apparatus according to claim 2, further comprising a restraining means for restraining the sleeve to the main body with respect to its rotation around the axis of the main body.

10. The drilling apparatus according to claim 2, wherein the crown bit is provided with a plurality of drilling tips facing the drilling direction, and each of the plurality of core bits is provided with a drilling tip.

11. The drilling apparatus according to claim 1, wherein the crown bit is attached to the tip of the main body, and the core bit is attached to the main body so as to be rotatable between a storage position extending toward the drilling direction and a drilling position extending toward the axis in a plane including the axis of the main body, and comprises a plurality of core bits that are biased to rotate from the storage position toward the drilling position.

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