Ground strength investigation method and ground strength investigation device

Abstract

To investigate ground strength by an RS method more easily than a conventional method.SOLUTION: When drilling a hole by penetrating an object ground G while rotating a boring rod 10 having a bit 11 at a tip end around an axial center and obtaining a ground strength of the object ground G based on an excavation speed, a drilling coefficient, a bit rotation speed, a bit load, and a drilling diameter, the object ground G is drilled by repeating a drilling state in which the boring rod 10 is penetrated at a constant excavation speed while rotating the boring rod 10 at a constant bit rotation speed and a temporary stop state in which the boring rod 10 is rotated at a constant bit rotation speed while stopping penetration of the boring rod 10. A bit load in each temporary stop state is used as a reference value, and an increment from the reference value of the bit load detected in a drilling state immediately after each temporary stop state is used as a measured value for determining the ground strength of the object ground G.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground strength investigation method and a ground strength investigation device. [Background technology]

[0002] In the construction of residential land development, road embankments, river levees, etc., methods for assessing the bearing capacity (strength) of the developed ground include SWS (Screw Weight Sounding; formerly Sweden Sounding) and standard penetration tests (N-values), as well as a method for estimating ground strength based on drilling parameters (see Patent Document 1).

[0003] This method is known as the rotary sounding method (hereinafter referred to as the RS method), and determines ground strength based on the following general formula (1). R=K f(N) f(W) f(d) f(S) …(1) Here, R is the excavation speed (drilling speed), K is the drilling coefficient (drillability), N is the bit rotation speed, W is the bit load (bit thrust), d is the drilling diameter (bit diameter), and S is the ground strength (drilling strength).

[0004] The above general formula (1) is expressed as follows in the Somerton WH formula: R=K·N·d·(W / d 2 S) 2 …(2)

[0005] Furthermore, the above general formula (1) is expressed as follows in the Maurer formula in Patent Document 2, for example: R=K·{(N·W 2 ) / (d 2 ·S 2 )} …(3)

[0006] On the other hand, the present inventors have found from a large amount of test data that it is desirable to apply the following relational expression (4): R=K·{(N 3.1 ·W 1.5 ) / (d 1.2 ·S1.5 )} …(4)

[0007] Here, the drilling coefficient K is determined by a preliminary test, and the drilling diameter d is determined as a value specific to the equipment. Therefore, the ground strength S can be calculated by measuring the drilling speed R, bit rotation speed N, and bit load W.

[0008] Although the drilling speed R and bit rotation speed N can be measured on the ground, the bit load is affected by the increase in rotational friction resistance between the hole wall and the boring rod as the drilling depth increases. Therefore, in the past, sensors to measure the bit load and rotational torque were installed directly above the bit.

[0009] However, when installing a sensor directly above the bit, the sensor must be built into the boring rod and the detected data must be recorded and retrieved, which creates the problem of complicated measurement equipment. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 63-142114 [Patent Document 2] Japanese Patent Application Publication No. 2-308006 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, the main object of the present invention is to enable ground strength survey using the RS method more easily than the above-mentioned conventional methods. [Means for solving the problem]

[0012] The present invention, which has solved the above problems, is as follows. <First aspect> A method for drilling a hole by penetrating a boring rod having a bit at the tip into a target ground while rotating it around an axis, and determining the ground strength of the target ground based on the excavation speed, drilling coefficient, bit rotation speed, bit load or rotation torque, and drilling diameter during the drilling, At least one of the bit load and the rotational torque is detected by a sensor provided on the above-ground portion of the boring rod; The drilling is performed by repeating a drilling state in which the boring rod is rotated at a constant bit rotation speed and penetrated into the target ground at a constant excavation speed, and a temporary stop state in which the boring rod is rotated at the constant bit rotation speed while stopping the penetration of the boring rod, The detection value detected by the sensor in each of the temporary stop states is set as a reference value, and the increment of the detection value detected by the sensor in the boring state immediately after each of the temporary stop states from the reference value is set as a measurement value for determining the ground strength of the target ground. A ground strength investigation method characterized by:

[0013] (Action and effect) In the above formula (1), the drilling diameter d (= bit diameter) can be determined in advance. In addition, in this method, drilling is performed with a constant bit rotation speed. Of the remaining factors, in this method, the boring rod penetration is controlled so that the excavation speed (= drilling speed) R is constant. It is easier to control the excavation speed R at a constant value than to control the bit load W (= bit thrust). Therefore, in this method, only the bit load W needs to be measured. In other words, in this method, the drilling coefficient K is calculated collectively assuming that all parameters other than the bit load W, including R, N, and d, are constant. renew Therefore, the above formula (1) can be expressed as the following formula (5). S=K renew ·W …(5) Furthermore, since the rotational torque T of the boring rod is correlated with the bit load W, the rotational torque T can be measured instead of or in addition to the bit load W. Since the shape of the bit changes depending on the target ground, test drilling is performed using sample ground (or a box) with known ground strength, and the drilling coefficient K renew It is necessary to determine in advance. In this method, at least one of the bit load and rotational torque is detected by a sensor installed above ground on the boring rod, allowing for easy measurement without the need for a sensor directly above the bit. Furthermore, the method involves alternating between a drilling state in which the boring rod is rotated at a constant bit rotation speed and penetrated at a constant excavation speed, and a paused state in which the boring rod is stopped from penetrating and rotated at a constant bit rotation speed. The sensor readings detected during each pause are used as a reference value, and the increment of the sensor readings from the reference value in the drilling state immediately after each pause is used as the measured value for determining the ground strength of the target ground. This eliminates or reduces the influence of rotational friction between the hole wall and the boring rod on the detected values. Therefore, the RS method enables ground strength surveys more easily than the conventional methods described above.

[0014] <Second aspect> a boring rod having a bit at its tip; a support part that supports the boring rod so that the boring rod can rotate freely around the axis and move up and down in the axial direction, The boring rod is rotated around its axis while penetrating into the target ground to drill a hole, and the ground strength of the target ground is determined based on the drilling speed, drilling coefficient, bit rotation speed, bit load or rotation torque, and drilling diameter. The support unit includes a rotation drive device that rotates the boring rod around its axis, a lifting device that moves the boring rod at a constant speed and stops the boring, and a sensor that detects at least one of the bit load and rotation torque of the boring rod, Equipped with a drilling speed measuring device, the sensor is provided on the above-ground portion of the boring rod, The drilling control device drills the target ground by repeating a drilling state in which the boring rod is rotated at a constant bit rotation speed by the rotary drive device and penetrated into the target ground at a constant excavation speed by the lifting device, and a temporary stop state in which the penetration of the boring rod is stopped by the lifting device and the boring rod is rotated at the constant bit rotation speed by the rotary drive device, A measurement device is provided, which uses the detection value detected by the sensor in each of the temporary stop states as a reference value, and acquires the increment from the reference value of the detection value detected by the sensor in the drilling state immediately after each of the temporary stop states as a measurement value by the sensor. A ground strength investigation device characterized by:

[0015] (Action and effect) This provides the same effects as the first embodiment.

[0016] <Third aspect> The support portion comprises: a support body having a guide rail along the ascending and descending direction of the boring rod; A return guide provided on the upper part of the support body; a sprocket provided at the lower part of the support body; an elevation drive device that rotates the sprocket at a constant speed and stops the rotation; a platform supported between the return guide and the sprocket and capable of freely moving up and down along the guide rail; a power transmission body having one end connected to the frame and another end connected to the frame below the one end, the power transmission body being wound around the return guide and the sprocket in this order from the one end to the other end; The rotation drive device is installed on the stand; and The boring rod has at least one of a rotary torque sensor provided on an upper portion thereof and a load cell interposed between the one end of the transmission body and the return guide, The boring rod and the rotary drive device are integrally mounted on the base and can be freely raised and lowered. In the drilling state, the lifting drive device is controlled so that the excavation speed is constant, and in the temporary stop state, the lifting drive device is controlled so that the excavation speed is zero. A ground strength investigation device according to a second aspect.

[0017] (Action and effect) This ground strength investigation device is characterized by its ability to easily perform drilling at a constant drilling speed. That is, in this ground strength investigation device, the boring rod and the rotary drive unit are freely raised and lowered together with the base, and by controlling the lowering of the base with the lifting drive unit, it is possible to alternate between a drilling state in which the weight of the base and the equipment supported by it (including the boring rod and rotary drive unit) is the maximum bit load, at a constant drilling speed, and a paused state.

[0018] <Fourth aspect> The support portion comprises: a slide screw having an axis aligned with the ascending and descending direction of the boring rod; a support body that supports the slide screw so that it can rotate freely around its axis; an elevation drive device that rotates the slide screw at a constant speed and stops the rotation; a stand having a nut portion through which the slide screw threadably penetrates; The rotation drive device is installed on the stand; and a rotational torque sensor provided on an upper portion of the boring rod, The boring rod and the rotary drive device are integrally mounted on the base and can be freely raised and lowered. In the drilling state, the lifting drive device is controlled so that the excavation speed is constant, and in the temporary stop state, the lifting drive device is controlled so that the excavation speed is zero. A ground strength investigation device according to a second aspect.

[0019] (Action and effect) The basic principle of this ground strength investigation device is almost the same as that of the third embodiment, but it differs in that the platform is raised and lowered using a slide screw and that it does not have a load cell for detecting bit load, which has the advantage of making the device configuration simpler. [Effects of the Invention]

[0020] According to the present invention, it is possible to carry out a ground strength survey using the RS method more easily than with the conventional method described above. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of a ground strength investigation device having a base machine. [Figure 2] FIG. 2 is a cross-sectional view taken along line ii-ii of FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line iii-iii of FIG. [Figure 4] This is a schematic diagram of the case where it is used by being suspended by a crane. [Figure 5] FIG. 10 is a schematic diagram of another ground strength investigation device. [Figure 6] 6 is a cross-sectional view taken along line iv-iv of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Figures 1 to 3 show an example of a ground strength investigation device 1, which includes a boring rod 10 having a bit 11 at its tip, and a base machine 20 that supports the boring rod 10 so that it can rotate freely around its axis and move up and down in the axial direction.

[0023] The base machine 20 shown in Figure 1 comprises a support body 30 having a guide rail 31 along the lifting direction UD of the boring rod 10, a pulley 40 as a return guide provided on the upper part of the support body 30, a sprocket 41 provided on the lower part of the support body 30, an elevation drive device 42 that rotates the sprocket 41 at a constant speed and stops its rotation, a base 50 supported so as to be able to move up and down freely along the guide rail 31 between the pulley 40 and the sprocket 41, and a transmission body 60 having one end 61 connected to the base 50 and the other end 62 connected lower than the one end of the base 50, and wound around the pulley 40 and the sprocket 41 in this order from the one end to the other end.

[0024] The support column 30 of the example shown in FIGS. 1 to 3 has a pair of parallel side panels 32, a back panel 35, and an upper pedestal 33 and a lower pedestal 34 provided at the top and bottom of the support column 33. Guide rails 31 are provided on the opposing surfaces of the pair of side panels 32, respectively, along the ascending and descending direction UD of the boring rod 10. A channel steel or the like can be used for the support column 30. A platform 50 is disposed between the upper pedestal 33 and the lower pedestal 34, and has guide rollers 51 that are guided along the guide rails 31 on both sides of the portion disposed between the side panels 32. The guide rollers 51 are rotatably supported, so that the platform 50 is supported by the support column 30 and can ascend and descend freely along the guide rails 31.

[0025] By rotating the sprocket 41 forward or backward, the platform 50 can be lifted or lowered via the portion of the power transmission body that runs from the sprocket 41 to the platform 50 via the pulley 40. In the illustrated example, the power transmission body 60 is made of a chain 63 only in the portion that needs to mesh with the sprocket 41 when the platform 50 is raised or lowered, and the portion that is wound around the pulley 40 when the platform 50 is raised or lowered is made of a wire 64, but the entire body may also be made of a chain 63.

[0026] The lifting drive device 42 is not particularly limited as long as it can rotate the sprocket 41 at a constant speed and stop rotation by braking control. However, a geared stepping motor, as shown in FIG. 3, is suitable. Using a stepping motor as the rotary drive source allows for easy and accurate control of the constant speed rotation and stop of the sprocket 41 supporting the platform 50. In this case, the descent speed of the platform 50, i.e., the excavation speed, can be determined by detecting the rotational speed of the stepping motor. When a stepping motor is not used, constant speed rotation control can be performed using a brake based on friction or electromagnetic force. Furthermore, when a stepping motor is not used, rotation stop control can be performed using a brake based on friction or electromagnetic force or a locking claw. Furthermore, an intermittent gear or clutch can be combined to cut off the drive transmission from the rotary drive source when rotation is stopped. These methods can also be applied when a stepping motor is used.

[0027] The base 50 is equipped with a rotation drive 52 for the boring rod 10, such as a geared motor, and the boring rod 10 and the rotation drive 52 can be freely raised and lowered together with the base 50. Therefore, ignoring the lifting resistance (frictional resistance of the guide rail 31, rotational resistance of the sprocket 41, etc.), the total weight of the lifting equipment (the base 50, the boring rod 10, the rotation drive 52, and other equipment supported only by the base 50) can be used as the substantial maximum drilling load. When the drilling load is insufficient due to the hard target ground G, a weight may be attached to the base 50 or the boring rod 10, the rotation drive 52, and the base 50 may be lowered. From this perspective, a heavier boring rod 10 is preferable, and therefore, it is desirable to minimize the number of water supply holes (not shown) at the tip of the boring rod 10 for drilling water.

[0028] The drive shaft of the rotary drive device 52 is concentrically connected to the boring rod 10 via a torque sensor attachment 12 incorporating a rotational torque sensor S1 and a tachometer attachment 13 that detects the rotational speed of the boring rod 10. A load cell S2 is interposed in the transmission body at a portion located between one end of the base 50 and the pulley 40, and this load cell S2 measures the bit load. Furthermore, the drilling depth can be calculated from, for example, the length of the drill bit 11, the length of the number of boring rods 10, and the distance between the upper end of the rod in the lifting direction UD and the reference position of the base 50 (for example, the position of the guide roller 51).

[0029] Furthermore, it is preferable that the ground strength investigation device 1 has a drilling control device (not shown) that records the detection results of the rotation torque, bit load, rotation speed, excavation speed, etc., and controls the lifting drive device 42 and the rotation drive device 52. Such a drilling control device can be configured with known devices such as a computer, a sensor I / F, a programmable controller, and a motor driver.

[0030] When investigating the ground strength, the drilling diameter d (= diameter of the bit 11) of the boring rod 10 to be used is measured in advance. In addition, constant drilling parameters such as the bit rotation speed and excavation speed are determined in advance. Furthermore, under the same conditions, test drilling is performed using a sample ground (or box) with known ground strength, and the drilling coefficient K renew Please ask in advance.

[0031] The target ground G is drilled by repeating a drilling state in which the rotary drive device 52 rotates the boring rod 10 at a constant bit rotation speed while the lifting device penetrates the target ground G at a constant excavation speed, and a pause state in which the lifting device stops the penetration of the boring rod 10 while the rotary drive device 52 rotates the boring rod 10 at a constant bit rotation speed. The duration of the drilling state can be determined appropriately depending on the target ground G and the purpose of the investigation, as long as the drilling depth increases to a certain extent. For example, based on test drilling in a sample ground, a standard duration is determined in which the increase in the effect of rotational friction resistance between the hole wall and the boring rod 10 with increasing drilling depth is negligible (substantially unchanged). The duration can be extended for ground in which the increase in rotational friction resistance with increasing drilling depth is small, and shortened for the opposite purpose. The duration of the pause state can also be determined appropriately. For example, the duration of the pause state is preferably 3 seconds or more to stably measure the effect of rotational friction resistance. On the other hand, from the perspective of work efficiency, the upper limit of the duration of the paused state is preferably short, for example, 10 seconds or less, more preferably 5 seconds or less. As long as the paused state duration is not longer than necessary, the duration of the drilling state will be longer than the paused state duration. The detected value detected by the load cell S2 or the rotational torque sensor S1 during each paused state is used as a reference value, and the increment of the detected value detected by the load cell S2 or the rotational torque sensor S1 during the drilling state immediately after each paused state from the reference value is calculated and recorded as the sensor measurement value. Therefore, without installing a sensor directly above the bit 11, the influence of rotational friction resistance between the hole wall and the boring rod 10 can be eliminated or reduced from the detected value, making ground strength investigation using the RS method easier than conventional methods. The measurement value can be calculated in real time during drilling of the target ground G, or it can be calculated after drilling based on the detected values ​​recorded during drilling.

[0032] Based on the bit load W measured in this way, the ground strength S can be calculated using the above-mentioned formula (5). Since the rotational torque T of the boring rod 10 is correlated with the bit load W, the ground strength S may be calculated using the rotational torque T instead of or in addition to the bit load W. Furthermore, the calculation of the ground strength S may be performed in real time during drilling or after drilling.

[0033] 5 and 6 show another example of a ground strength investigation device 5. The basic principle of this ground strength investigation device 5 is similar to that of raising and lowering a platform 50 using a sprocket 41 and a chain 63, but it differs in that it raises and lowers the platform 50 using a slide screw and does not have a load cell S2 for detecting the bit load W, which has the advantage of making the device configuration simpler. Note that the same names and symbols are used for components with the same functions as the above-mentioned ground strength investigation device 1.

[0034] That is, this ground strength investigation device 5 has a slide screw 70 having an axis along the lifting and lowering direction UD of the boring rod 10, a support body 80 that supports the slide screw so that it can rotate freely around its axis, an elevation drive device 42 that rotates the slide screw 70 at a constant speed and stops its rotation, and a stand 50 having a nut portion 53 through which the slide screw 70 threads and passes.

[0035] The illustrated support column 80 has a pair of guide rods 81 arranged in parallel, and an upper pedestal 83 and a lower pedestal 84 that integrate the upper and lower parts of the guide rods 81, with the platform 50 disposed between the upper and lower pedestals 83 and 84. The lower pedestal 84 has legs 84L that protrude downward, allowing it to be supported on the target ground G without the need for a base machine 20 or a crane, but it can also be supported on the ground using a base machine 20 or a crane, as in the above-mentioned ground strength investigation device 1. The platform 50 also has a pair of guide rod insertion holes 54 that are aligned with the lifting and lowering direction UD of the boring rod 10, and the pair of guide rods 81 are slidably inserted into these guide rod insertion holes 54, allowing the platform 50 to be freely raised and lowered relative to the support column 80.

[0036] The base 50 is configured to be pushed up or down via the nut portion 53 by rotating the slide screw 70 forward or backward.

[0037] The lifting drive device 42 is not particularly limited as long as it can rotate the slide screw 70 at a constant speed and stop rotation, but a geared stepping motor is preferred. By using a stepping motor as the rotation drive source, it is possible to easily and accurately control the constant speed rotation and stop of the slide screw 70 that supports the platform 50. In this case, the descent speed of the platform 50, i.e., the excavation speed, can be determined by detecting the rotation speed of the stepping motor.

[0038] Other than that, it is the same as the device described above, except that it has a rotational torque sensor S1 but does not have a load cell S2. Also, when investigating ground strength, this device does not use the bit load W, but is limited to measuring the rotational torque T to calculate the ground strength, but is the same as when using the device described above.

[0039] (others) The above-mentioned ground strength investigation devices 1 and 5 can be supported by a base machine 20 as in the example shown in Figure 1, or by being suspended by a crane as in the example shown in Figure 4, or can be supported against the target ground G by legs 84L or the like as in the example shown in Figure 6.

[0040] Furthermore, the techniques described in Patent Documents 1 and 2 can be appropriately adopted as long as they do not contradict the above-mentioned principles of ground strength investigation. [Industrial Applicability]

[0041] The present invention can be applied to ground strength surveys using the rotary sounding method (RS method). [Explanation of symbols]

[0042] 1,5...ground strength investigation device, 10...boring rod, 11...bit, 12...torque sensor attachment, 13...tachometer attachment, 20...base machine, 30,80...support body, 31...guide rail, 32...side panel, 33...upper base, 34...lower base, 35...rear panel, 40...pulley, 41...sprocket, 42...lifting drive device, 50...frame, 51...guide roller, 52...rotation drive device, 53...nut part, 60...transmission body, 63...chain, 64...wire, 70...slide screw, 81...guide rod, G...target ground, S1...rotation torque sensor, S2...load cell, UD...lifting direction.

Claims

1. A method for drilling a hole by penetrating a boring rod having a bit at the tip into a target ground while rotating it around an axis, and determining the ground strength of the target ground based on the excavation speed, drilling coefficient, bit rotation speed, bit load or rotation torque, and drilling diameter during the drilling, At least one of the bit load and the rotational torque is detected by a sensor provided on the above-ground portion of the boring rod; The drilling is performed by repeating a drilling state in which the boring rod is rotated at a constant bit rotation speed and penetrated into the target ground at a constant excavation speed, and a temporary stop state in which the boring rod is rotated at the constant bit rotation speed while stopping the penetration of the boring rod, The detection value detected by the sensor in each of the temporary stop states is set as a reference value, and the increment of the detection value detected by the sensor in the boring state immediately after each of the temporary stop states from the reference value is set as a measurement value for determining the ground strength of the target ground. A ground strength investigation method characterized by:

2. a boring rod having a bit at its tip; a support part that supports the boring rod so that the boring rod can rotate freely around the axis and move up and down in the axial direction, The boring rod is rotated around its axis while penetrating into the target ground to drill a hole, and the ground strength of the target ground is determined based on the drilling speed, drilling coefficient, bit rotation speed, bit load or rotation torque, and drilling diameter. The support unit includes a rotation drive device that rotates the boring rod around its axis, a lifting device that moves the boring rod at a constant speed and stops the boring, and a sensor that detects at least one of the bit load and rotation torque of the boring rod, Equipped with a drilling speed measuring device, the sensor is provided on the above-ground portion of the boring rod, The drilling control device drills the target ground by repeating a drilling state in which the boring rod is rotated at a constant bit rotation speed by the rotary drive device and penetrated into the target ground at a constant excavation speed by the lifting device, and a temporary stop state in which the penetration of the boring rod is stopped by the lifting device and the boring rod is rotated at the constant bit rotation speed by the rotary drive device, A measurement device is provided, which uses the detection value detected by the sensor in each of the temporary stop states as a reference value, and acquires the increment from the reference value of the detection value detected by the sensor in the drilling state immediately after each of the temporary stop states as a measurement value by the sensor. A ground strength investigation device characterized by:

3. The support portion comprises: a support body having a guide rail along the ascending and descending direction of the boring rod; A return guide provided on the upper part of the support body; a sprocket provided at the lower part of the support body; an elevator drive device that rotates the sprocket at a constant speed and stops the rotation; a platform supported between the return guide and the sprocket and capable of freely moving up and down along the guide rail; a power transmission body having one end connected to the frame and another end connected to the frame below the one end, the power transmission body being wound around the return guide and the sprocket in this order from the one end to the other end; The rotation drive device is installed on the stand; and The boring rod has at least one of a rotary torque sensor provided on an upper portion thereof and a load cell interposed between the one end of the transmission body and the return guide, The boring rod and the rotary drive device are integrally mounted on the base and can be freely raised and lowered. In the drilling state, the lifting drive device is controlled so that the excavation speed is constant, and in the temporary stop state, the lifting drive device is controlled so that the excavation speed is zero. The ground strength investigation device according to claim 2.

4. The support portion comprises: a slide screw having an axis aligned with the ascending and descending direction of the boring rod; a support body that supports the slide screw so that it can rotate freely around its axis; an elevation drive device that rotates the slide screw at a constant speed and stops the rotation; a stand having a nut portion through which the slide screw threadably penetrates; The rotation drive device is installed on the stand; and a rotational torque sensor provided on an upper portion of the boring rod, The boring rod and the rotary drive device are integrally mounted on the base and can be freely raised and lowered. In the drilling state, the lifting drive device is controlled so that the excavation speed is constant, and in the temporary stop state, the lifting drive device is controlled so that the excavation speed is zero. The ground strength investigation device according to claim 2.

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