JP2017172132A - Ground strength measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground strength measurement method for measuring ground strength at an actual excavated hole part mainly at a time of pile installation and objectively confirming that the excavated hole has reached the ground.SOLUTION: A ground strength measurement method is for measuring strength of a ground A reached by an excavated hole B when the excavated hole is formed by excavating a ground by excavation means. A measurement rod insertion hole 18 is formed on the excavation means for having a rotary support shaft 12 thereof pierce through the rod insertion hole, and when the excavated hole B has reached a desired depth, a bottom end 23 of a measurement rod 20 inserted into the measurement rod insertion hole 18 is made to reach the ground A to be measured, and ground strength of the ground A to be measured is measured by ground strength measurement means 21 that uses the measurement rod 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ground strength measurement method capable of measuring the ground strength reached at an excavation hole mainly in pile construction.

  Conventionally, when a pile is constructed, a ground survey by a “standard penetration test” is generally conducted in advance, and the survey results are used for designing a pile and making a construction plan.

  In the standard penetration test, after drilling to the measurement target ground by boring, a rod with a sampler attached to the lower end is inserted into the drilling hole, and the rod is struck downward by a hammer dropped from the desired height. The number of impacts (N value) required for the sampler to penetrate the target ground to a predetermined depth (30 cm) can be measured, and the softness of the ground can be expressed by the N value.

  However, this standard penetration test is carried out at several locations different from the pile installation position in the pile construction site, and the support layer level of the entire construction site is assumed from the measurement results (N value) at the several locations. In actual pile construction locations, the N value was not actually measured, and the ultimate ground strength of the pile insertion excavation hole could not be measured directly.

  Therefore, conventionally, the excavation resistance is measured by the load current value or torque value of the motor that drives the excavating means such as the auger during excavation, and the ground strength reached by the excavation hole is measured from the excavation resistance, and based on the excavation resistance. A method of determining whether the excavation hole has reached the support layer is taken from the correlation between the ground strength and the N value of each layer based on the preliminary ground survey (see, for example, Patent Document 1).

JP 2002-348868 A

  However, in the conventional technology as described above, since the excavation resistance varies depending on various conditions, the correlation between the excavation resistance and the N value is not necessarily clear, and the support layer level based on the N value and the support determined from the excavation resistance are not necessarily clear. There is a possibility that a difference may occur with the layer level, and even when it is determined that the support layer has been reached from the excavation resistance, there may be a case where the support layer is not actually reached.

  In addition, in the strength measurement method using excavation resistance, since the geology is not confirmed by sampling, the arrival of the support layer cannot be objectively determined by the geology of the collected samples.

  Therefore, in view of such a conventional problem, the present invention can mainly measure the ground strength in the actual excavation hole portion during pile construction, and can objectively confirm the arrival of the excavation hole in the ground. It was made for the purpose of providing a ground strength measurement method.

  The feature of the invention according to claim 1 for solving the conventional problems as described above is that the ground for measuring the strength of the ground reached by the excavation hole when the excavation means excavates the ground to form the excavation hole. In the strength measurement method, the excavating means is provided with a measuring rod insertion hole penetrating the rotation support shaft, and when the excavation hole reaches a desired depth, the excavating means is inserted into the measuring rod insertion hole. The lower end portion of the measured rod reaches the measurement target ground, and the ground strength of the target ground is measured by the ground strength measuring means using the measurement rod.

  The feature of the invention of claim 2 is that, in addition to the configuration of claim 1, the excavation work using the excavation means and the ground strength measurement using the ground strength measurement means are repeated for each desired depth. It is in.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the ground strength measuring means includes a penetration portion at a lower end portion of the measuring rod, and strikes the measuring rod, It is to measure the number of hits required for the penetration portion to penetrate to the predetermined depth of the reaching ground.

  According to a fourth aspect of the present invention, in addition to the configuration of the third aspect, the penetration portion includes a hollow portion capable of accommodating earth and sand, and a sampling hole that communicates with the hollow portion and opens at a lower end. The earth and sand of the measurement target ground is accommodated in the hollow portion through the sampling hole as it penetrates.

  According to a fifth aspect of the present invention, in addition to the structure of any one of the first to fourth aspects, the excavating fluid is supplied to the discharge port opened at the lower end of the excavating means into the measurement rod insertion hole. It is to use the supply pipe part.

  The ground strength measurement method according to the present invention, as described above, is a ground strength measurement method for measuring the strength of the ground reached by the excavation hole when excavating the ground by excavating means to form the excavation hole, A lower end portion of the measuring rod inserted into the measuring rod insertion hole when the excavating means is provided with a measuring rod insertion hole penetrating the rotation support shaft and the excavation hole reaches a desired depth. Measure the strength of the ground where the excavation hole arrived at the actual construction position such as piles by measuring the ground strength of the target ground with the ground strength measuring means using the measuring rod. can do. Moreover, it is not necessary to provide a hole for guiding the measuring rod, and the ground strength can be measured efficiently.

  Further, in the present invention, by repeating the excavation work using the excavation means and the ground strength measurement using the ground strength measurement means for each desired depth, the actual local level in parallel with the excavation work is obtained. The ground strength at can be measured.

  Furthermore, in the present invention, the ground strength measuring means includes a penetration portion at a lower end portion of the measurement rod, hits the measurement rod, and the penetration portion penetrates to a predetermined depth of the reaching ground. By measuring the number of hits required for the ground, highly reliable ground strength data can be measured.

  Further, in the present invention, the penetration part includes a hollow part capable of accommodating earth and sand, and a sampling hole that communicates with the hollow part and opens at a lower end. By storing the earth and sand of the measurement target ground, objective judgment can be made not only by ground strength data but also by geological samples.

  Furthermore, in the present invention, the measurement rod insertion hole needs to be separately provided by using a supply pipe portion that supplies a drilling fluid to the discharge port opened at the lower end of the excavation means. Therefore, the cost can be reduced.

It is sectional drawing which shows the outline of the embodiment of the ground strength measuring method which concerns on this invention. It is a side view which shows an example of the pile driving device provided with the excavation means. It is an enlarged view which shows the excavation head part in FIG. 2, Comprising: It is a figure which shows the state at the time of excavation. FIG. 2 is an exploded perspective view showing an example of a penetration part in FIG. FIG. 2 is a cross-sectional view showing a state of a bottom of a drilling hole at the time of ground strength measurement in FIG.

  Next, an embodiment of the ground strength measuring method according to the present invention will be described based on the examples shown in FIGS.

  In this embodiment, the case where the ultimate ground strength of the excavation hole B in the medium digging method is measured will be described as an example. In the figure, reference numeral 1 denotes a pile such as a PC pile, and reference numeral 2 denotes a pile driving device.

  As shown in FIG. 2, the pile driving device 2 includes a device main body 3 that can be moved by a traveling unit that is a crawler, and a support column 4 that is erected on the device main body 3. The pile insertion means 6 is supported so as to be movable in the vertical direction.

  The pile insertion means 6 includes a pile support portion 6 a that holds the upper end of the pile 1, and a slide drive means 6 b that moves the pile 1 downward in a suspended state. Is moved in the settling direction.

  The excavation means 5 includes a rotation drive unit 10 that is movably supported by the support column 4 and a excavation means body 11 such as a spiral auger that is detachably connected to the rotation drive unit 10. The main body 11 rotates about the vertical axis and can move up and down along the support column 4.

  The excavation means main body 11 such as a spiral auger has a structure in which a ribbon-shaped screw blade 13 is wound around the outer periphery of a cylindrical rotation support shaft 12 in a spiral manner with its edge fixed. The excavation head 14 is supported in a continuous arrangement at the lower end.

  The excavation head 14 includes a cylindrical head rotation support shaft 15, a screw blade 16 supported on the outer periphery of the head rotation support shaft 15, and excavation bits 17, 17. It has.

  The head rotation support shaft 15 is connected to the lower end of the rotation support shaft 12 in a continuous arrangement, and both rotation support shafts 12 and 15 are provided with measuring rod insertion holes 18 penetrating in the axial direction.

  The measurement rod insertion hole 18 also serves as a supply pipe portion that supplies a drilling fluid to the discharge port 19 opened at the lower end of the excavation head 14, and during excavation work, a supply hose is connected to the upper end of the supply pipe portion. Fluid supply means (not shown) such as a compressor is connected so that drilling fluid such as drilling water, compressed air and cement milk can be supplied to the discharge port 19 through the supply pipe.

  On the other hand, both ends of the measurement rod insertion hole 18 have openings in the axial direction of the rotation support shafts 12 and 15, and the measurement rod 20 is inserted and penetrated therethrough so that the lower end portion of the measurement rod 20 is formed. By reaching the measurement target ground A, the ground strength of the target ground A can be measured by the ground strength measuring means 21 using the measuring rod 20.

  The ground strength measuring means 21 uses, for example, the penetration test apparatus shown in FIG. 1, and a long rod-shaped measuring rod 20 inserted into the measuring rod insertion hole 18 and a batting that strikes the measuring rod 20 downward. And the striking device 22 measures the number of striking (N values) required for the penetration portion 23 at the lower end of the measuring rod 20 to penetrate to a predetermined depth of the target ground A.

  The measuring rod 20 includes a plurality of rod members connected in the axial direction and a penetration portion 23 fixed to the lower end, and the length can be adjusted by adding the rod members.

  As shown in FIG. 4, the penetration part 23 includes a hollow part 24 composed of a pair of half-cylinders 24a and 24a each having a half-cylinder shape, and the half-cylinders 24a and 24a are combined. The coupling 25 having its upper end fixed to the lower end of the rod is screwed, and the lower end is fixed to the lower end of the measuring rod 20 by screwing the shoe part 26 having the sampling hole 26a.

  The penetration portion 23 is formed so that the outer diameter is slightly smaller than the inner diameter of the measurement rod insertion hole 18 and can be moved in a guided state in the measurement rod insertion hole 18.

  The striking device 22 has a rod 30 installed on the ground surface, a striking block 31 fixed at a predetermined position of the measuring rod 20, and a cylindrical shape that is movably guided to the measuring rod 20 above the striking block 31. A hammer 32 (weight 63.5 ± 0.5 kg), lifting the hammer 32 to a predetermined height, and free-falling the hammer 32 from that position, thereby allowing the measuring rod 20 to pass through the striking block 31. It is designed to blow downward.

  Next, a specific method for measuring the strength of the target ground A to which the excavation hole B has reached when such a pile driving device 2 is used will be described.

  First, as a pre-preparation for pile construction, a ground survey at the pile driving construction site, specifically, a standard penetration test is performed at a desired multiple locations within the site, and the entire construction site is measured from the measurement results (N value) at several places. Assume a support layer level.

  Next, the pile driving device 2 is carried into the construction site, and the column 4 is made upright at a predetermined pile embedding position, and the excavating means 5 made of a spiral auger or the like is inserted into the pile 1 suspended by the pile inserting means 6, After that, the excavation means main body 11 composed of the pile 1 and the spiral auger is lifted by a winch, and the upper ends are fixed to the pile insertion means 6 and the rotation drive unit 10 respectively and are suspended.

  In this state, the excavation head 14 is pushed into the ground while the excavation head 14 is rotated by the rotation drive unit 10, the ground is excavated ahead of the lower end of the pile 1, and the pile 1 is pushed in while being discharged by the spiral auger. To insert it into the ground.

  Then, when the excavation hole B reaches the desired depth, specifically, the upper end of the design support layer based on the preliminary investigation, excavation is interrupted and the rotary support shaft 12 such as a spiral auger is removed from the rotation driving means. The supply hose connecting the supply pipe part and the fluid supply means is removed.

  Next, as shown in FIG. 1, the pile driving device 2 is moved to secure a space at the periphery of the upper end opening of the excavation hole B, and the ground strength measuring means 21 is installed there.

  That is, the impact device 22 is installed, and the measurement rod 20 is inserted into the rotation support shaft 12 of the excavating means main body 11 through the measurement rod insertion hole 18, and the lower end of the measurement rod 20, ie, the rod member is added. The penetration portion 23 is made to reach the bottom of the excavation hole B.

  At that time, the measuring rod 20 protrudes the upper end portion by a certain length from the upper end of the rotating support shaft 12, fixes the striking block 31 at a predetermined position of the protruding measuring rod 20, and measures the hammer 32. A lifting wire 34 is connected to the hammer 32 via a pulley 33 that is guided by the rod 20 and supported by the rod 30.

  Then, as shown in FIGS. 1 and 5, the strength of the target ground to which the excavation hole B has reached is measured by the ground strength measuring means 21 using the measuring rod 20 in this state.

  First, the lifting wire 34 is pulled and pulled up to a predetermined height h (a height of 76 ± 1 cm from the striking block 31), the hammer 32 is freely dropped from the position h, and the measuring rod 20 is struck downward. Is repeated until the penetration part 23 penetrates to a depth of 15 cm from the bottom surface of the pile 1 hole (preliminary driving operation).

  Next, from the state where the preliminary driving is completed, the lifting wire 34 is pulled up to a predetermined height h (a height of 76 ± 1 cm from the hitting block 31), and the hammer 32 is freely dropped from that position for measurement. The operation of hitting the rod 20 downward is repeated, and the number N of hits required for the penetration portion 23 to penetrate from the depth of the preliminary hit to a predetermined depth (30 cm) is measured (main hitting operation).

  In addition, in the main driving work, as a general rule, the number of hits is measured every time 10 cm is penetrated. In addition, an upper limit value (50 to 60 times) is set for the number of hits, and when the upper limit value of the number of hits is reached before the penetration portion 23 penetrates the ground to a predetermined depth (30 cm). Measure the amount of penetration at that time.

  In addition, the penetrating part 23 takes in the earth and sand constituting the measurement target ground A into the hollow part 24 through the sampling hole 26a opened at the lower end by the preliminary driving work and the main driving work, and accommodates the geological sample.

  After the measurement of the ground strength is completed, the measuring rod 20 is pulled out through the measuring rod insertion hole 18, the penetration portion 23 is disassembled, and the ground sample is taken out from the hollow portion 24.

  Next, the ground strength measuring means 21 is removed, the rotation driving part 10 of the pile driving device 2 and the upper end of the excavation means main body 11 such as a spiral auger are reconnected, and the supply pipe part and the fluid supply means are connected. Install hose and resume excavation and pile driving.

  And every time it excavates to predetermined depth, excavation work using excavation means 5 and ground strength measurement using ground strength measurement means 21 are repeated for every desired depth as needed.

  In the ground strength measuring method configured as described above, when forming the excavation hole B such as a pile insertion hole, the actual ground strength of the excavation site can be directly measured using the measuring rod 20, and the target ground Since the geological sample of A can be taken, it is possible to objectively grasp the state of the target ground A at the position where the excavation hole B has reached, and determine whether the excavation hole B has reached the support layer. It can be done reliably.

  Further, in this ground strength measuring method, since the measuring rod 20 is guided to the rotating support shaft 12 of the excavating means 5, it is not necessary to separately provide a guide hole for guiding the measuring rod 20, and the excavating hole B is efficiently provided. It is possible to measure the strength of the ground that has reached.

  In the above-described embodiment, the rotary support shafts 12 and 15 of the excavating means 5 are provided with the supply pipe portion, and at the time of excavation, the excavating fluid is supplied through the supply pipe portion, and then the supply pipe portion is inserted into the measuring rod. The example in which the measuring rod 20 is inserted as the hole 18 has been described, but the measuring rod 20 is not used as the supply pipe for supplying the excavating fluid, and the measuring rod 20 is inserted into the measuring rod insertion hole. 18 may be inserted in advance.

  Moreover, although the above-mentioned Example demonstrated the example which used the penetration test apparatus for the ground strength measuring means 21, the ground strength measuring means 21 used the other measuring means using the measuring rod 20, for example, A cone penetration test or a sounding test may be applied.

  Furthermore, in the above-described embodiment, the description has been given by taking the digging method as an example, but the embodiment of the present invention is not limited to this, and can be applied to, for example, a pre-boring method and a cast-in-place pile construction, In the above-described embodiment, the excavation hole B at the time of pile construction has been described as an example. However, the present invention can also be applied to other excavation work using the excavation means 5 having the rotary support shaft 12 such as a spiral auger. it can.

  Furthermore, in the above-described embodiment, the screw auger provided with the screw blade 13 on the outer periphery of the rotary support shaft 12 has been described as an example of the excavating means. However, the mode of the excavating means is not limited to this and is cylindrical. If there is the rotating support shaft 12, the presence or absence of a screw blade, the shape of the blade supported on the outer periphery of the rotating support shaft, and the like can be appropriately selected according to the excavation situation.

  Moreover, in the above-mentioned Example, the pile to be used is not limited to a PC pile, Other concrete piles, a steel pipe pile, a rotation penetration pile, etc. may be sufficient.

DESCRIPTION OF SYMBOLS 1 Pile 2 Pile driving device 3 Apparatus main body 4 Support | pillar 5 Excavation means 6 Pile insertion means 10 Rotation drive part 11 Excavation means main body 12 Rotation spindle 13 Screw blade 14 Excavation head 15 Head rotation spindle 16 Screw blade 17 Excavation bit 18 Measurement Rod insertion hole 19 Discharge port 20 Measuring rod 21 Ground strength measuring means 22 Blowing device 23 Penetration part 24 Hollow part 25 Coupling 26 Shoe part 30 櫓 31 Blow block 32 Hammer 33 Pulley 34 Lifting wire

Claims (5)

A ground strength measurement method for measuring the strength of the ground reached by the excavation hole when the excavation means excavates the ground to form the excavation hole,
A lower end portion of the measuring rod inserted into the measuring rod insertion hole when the excavating means is provided with a measuring rod insertion hole penetrating the rotation support shaft and the excavation hole reaches a desired depth. Reaching the measurement target ground, and measuring the ground strength of the target ground by the ground strength measurement means using the measurement rod.   The ground strength measurement method according to claim 1, wherein excavation work using the excavation means and ground strength measurement using the ground strength measurement means are repeated for each desired depth.   The ground strength measuring means includes a penetration portion at a lower end portion of the measuring rod, hits the measuring rod, and measures the number of hits required for the penetration portion to penetrate to a predetermined depth of the reaching ground. The ground strength measuring method according to claim 1 or 2.   The penetration portion includes a hollow portion capable of containing earth and sand, and a sampling hole communicating with the hollow portion and opened at a lower end, and the soil of the measurement target ground is inserted into the hollow portion through the sampling hole along with the penetration. The ground strength measuring method according to claim 3, which is accommodated.   The ground strength measuring method according to any one of claims 1 to 4, wherein a supply pipe portion that supplies a drilling fluid to a discharge port opened at a lower end of the excavation means is used for the measurement rod insertion hole.

Images