JP2020045646A - Construction method of friction cutting in ground, and construction device for friction cutting in ground - Google Patents

Abstract

To provide a construction method of friction cutting in the ground capable of efficiently pulling a steel member out of the ground and burying it into the ground.SOLUTION: A construction method of friction cutting in the ground comprises: a voltage application step of applying direct voltage between an object member which is an object to be pulled out of the ground or to be buried in the ground and an anode member of which at least a part is buried in the ground at a position spaced apart from an installation position of the object member so as to make the object member a cathode and the anode member an anode; and an installation step of starting either of installations of pulling the object member out of the ground or burying it into the ground, during the direct voltage is applied within five minutes after applying the direct current voltage at the voltage application step.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a method of pulling out a steel member or the like buried underground (the ground; the same applies hereinafter) or a method of burying a steel member or the like underground.

  In order to pull out a steel member buried in the ground (for example, a steel sheet pile of a steel sheet pile wall, a steel pipe sheet pile, an H steel of a parent pile horizontal sheet pile wall) in the longitudinal direction of the steel member, friction from the ground is required. Since a force that exceeds resistance is required, it is not easy as the bonding force with the ground is large. For this reason, conventionally, by applying a DC voltage so that the steel member to be extracted is a cathode and the other member not to be extracted is an anode, the frictional force from the ground received when the steel member is extracted is reduced. Then, a method of pulling out is proposed. According to this method, the steel member can be pulled out with a smaller force than when no DC voltage is applied. It is also assumed that the roughness of the surrounding ground due to pulling out of the steel member is reduced (for example, see Patent Documents 1 and 2).

  With respect to the principle of this method, Patent Document 1 discloses that the steel member and the ground are separated from each other due to the volume expansion of hydrogen gas generated from the surface of the steel member to be extracted by applying the DC voltage, and the steel material and the ground are separated. It is described that pulling out is facilitated by weakening the bonding force of the steel or by softening the ground by collecting moisture in the ground in the steel member to be drawn out by the electroosmosis phenomenon. In addition, Patent Document 2 also describes that pulling out is facilitated by moisture in the ground gathered by the electroosmosis phenomenon.

Japanese Patent No. 3198598 JP-A-48-11807

  As described above, Patent Literatures 1 and 2 expect a gas generation by electrolysis and a friction reduction effect by water movement caused by electroosmosis. For this reason, it is necessary to wait for the generation of gas due to the electroosmosis phenomenon or electrolysis, as described in, for example, Patent Document 2 that waits for about 30 minutes at a DC voltage of about 100 V. In this regard, the present inventors have conducted intensive studies and found that the steel member to be drawn out is more likely to be caused by the Coulomb repulsion between the steel member to be drawn out and the soil particles constituting the ground, which is generated when the DC voltage is applied. We found that it was possible to pull out with a small force. According to this method, it is possible to immediately perform the application (drawing, driving, etc.) to the target steel member after the application of the DC voltage without waiting for the generation of gas due to the electroosmosis phenomenon or the electrolysis. Become.

  In view of the above circumstances, at least one embodiment of the present invention provides an underground friction cut construction method capable of more efficiently pulling out and burying a steel member from underground. With the goal.

(1) The underground friction cut construction method according to at least one embodiment of the present invention includes:
A target member to be pulled out from the ground or a target to be buried in the ground, and an anode member at least partially buried in the ground at a position separated from the installation position of the target member, A voltage applying step of applying a DC voltage so that the target member is a cathode and the anode member is an anode,
When the DC voltage is applied within 5 minutes after the application of the DC voltage by the voltage applying step, the target member is pulled out of the ground, or the target member is drawn into the ground. And a construction step of starting any of the following constructions.

  The surface of the soil particles constituting the underground (ground) has an electric charge (negatively charged), and the inventors of the present invention have determined that there is a gap between the target member and the soil particles of the earth and sand constituting the underground caused by the application of a DC voltage. It has been found that due to the Coulomb repulsion generated in the above, when a target member such as a steel member is pulled out from the ground or when the target member is driven into the ground, frictional resistance received from earth and sand constituting the ground is reduced. This Coulomb repulsion is generated in a very short time, such as immediately after the application of the DC voltage, because it is generated by the movement of charges (free electrons) between the anode and the cathode (see FIG. 5 described later).

  According to the configuration of the above (1), the target member such as a steel sheet pile, a steel pipe pile, a steel member such as H steel, and the anode member are separated from each other in the ground so that the earth and sand (soil) face each other. Applying a DC voltage so that the target member is a cathode and the anode member is an anode, and immediately after the application of the DC voltage at which the Coulomb repulsion occurs, within 5 minutes, pulling out the target member from the ground or Then, construction such as driving (burying) the target member into the ground is started. Due to the Coulomb repulsion generated between the target member and the soil particles forming the ground in a very short time immediately after the application of the DC voltage, the frictional resistance of the target member from the surrounding soil is reduced. Therefore, the application of the target member can be started immediately after the application of the DC voltage. In addition, construction can be performed with a smaller pulling load or indentation load, and construction can be completed in a short period of time as much as the start of construction for the target member is accelerated. Can be performed more efficiently.

(2) In some embodiments, in the configuration of the above (1),
In the voltage applying step, a current value of a current flowing by applying the DC voltage between the target member and the anode member was divided by a surface area of a portion of the target member embedded in the ground. The DC voltage is applied so that the current density, which is a value, is greater than 0 and equal to or less than 15 within a set value.

  The inventors of the present invention have conducted intensive studies and found that the ratio of the tensile load or indentation load when the DC voltage is applied to the tensile load or indentation load when no DC voltage is applied (for example, the load when applying a voltage / the voltage when applying no voltage / (Hereinafter referred to as a friction cut rate) has a correlation with a value (that is, current density) obtained by dividing a current flowing by applying a DC voltage by a surface area of a portion of the target member buried underground. I found that. More specifically, the friction cut rate decreases to near the lower limit as the current density increases, but after the lower limit, the friction cut rate changes so as to hardly change even when the current density is increased (see FIG. 7 described later). ).

  According to the above configuration (2), the voltage applied to the target member and the anode member is set to a set value in which the current density when the DC voltage is applied is larger than 0 and 15 or less. More specifically, the above set value is set to 3 or more and 10 or less (for example, 5). Thereby, a relatively large friction reduction effect by Coulomb repulsion can be obtained while suppressing power consumption for applying a DC voltage.

(3) In some embodiments, in the configuration of the above (2),
The method may further include a voltage adjusting step of adjusting the DC voltage so that the current density becomes the set value during the execution of the construction step.

  The surface area of the target member buried in the ground becomes smaller as the withdrawal amount of the target member increases, the driving of the target member progresses, and the construction increases as the buried portion increases, and the construction proceeds. Changes as

  According to the configuration (3), the applied voltage is adjusted by the voltage adjusting step so that the current density becomes the set value during the execution of the construction step. Accordingly, it is possible to prevent a situation where the applied voltage of the DC voltage is unnecessarily high or a situation where the applied voltage is small and the effect of reducing the frictional resistance is not sufficiently obtained, and an appropriate DC voltage can be applied.

(4) In some embodiments, in the above configurations (1) to (3),
The voltage applying step turns on and off the DC voltage applied during execution of the construction step according to a predetermined timing.

  According to the configuration (4), for example, by turning on / off a DC voltage applied in accordance with any predetermined timing, the frictional resistance of the target member from the surrounding soil is reduced by the Coulomb repulsion. Can be done.

(5) In some embodiments, in the above configurations (1) to (4),
The earth and sand forming the underground includes soil having a fine particle content of less than 0.075 mm by 40% or more.

The present inventors have conducted intensive studies and found that sand (having a fine particle content of less than 15%) is not negatively charged even with saturated sand.
According to the configuration of the above (5), the underground friction cut construction method of the present invention is applied to a case in which the soil particles of the earth and sand constituting the ground have a fine particle fraction of less than 0.075 mm by 40% or more. Is done. This is mainly classified into silt, cohesive soil, etc. (fine grain content of 50% or more) and sandy soil (fine grain content of 5% or more) in the engineering classification method of soil in the Japan Unified Soil Classification Method. (Less than 50%), and the Coulomb repulsion generated by applying the above-described DC voltage to the target member and the anode member can reduce the frictional resistance that the target member receives from the surrounding earth and sand.

(6) In some embodiments, in the above configurations (1) to (5),
In the execution step, the extraction of the target member at least partially buried below the groundwater level is started, or the driving is started so that at least a part is buried below the groundwater level.

  According to the above configuration (6), in order for Coulomb repulsion to occur, the soil must be saturated, that is, the groundwater level must be lower than the groundwater level. In the ground below the groundwater level, the space between the soil particles is filled with water. (Saturated soil) Therefore, due to the Coulomb repulsion generated by applying the above-described DC voltage to the target member and the anode member, the frictional resistance of the target member from the surrounding earth and sand can be reduced.

(7) The underground friction cut construction device according to at least one embodiment of the present invention includes:
An anode member that is at least partially buried in the ground at a position separated from the installation position of the target member to be pulled out from the ground or to be buried in the ground,
Between the target member and the anode member, the target member is a cathode, a voltage application device that applies a DC voltage so that the anode member becomes an anode,
An applied voltage determination device that calculates an instruction value of the DC voltage applied by the voltage application device,
The applied voltage determination device divides a current value of a current flowing by applying the DC voltage between the target member and the anode member by a surface area of a portion of the target member buried in the ground. The DC voltage is applied so that the calculated value is larger than 0 and equal to or smaller than 15.

  According to the configuration of the above (7), the same effect as the above (2) can be obtained.

  According to at least one embodiment of the present invention, there is provided an underground friction cut construction method capable of more efficiently extracting a steel member from the ground or burying the steel member in the ground.

It is a figure showing the underground friction cut construction method concerning one embodiment of the present invention. It is a figure showing roughly an underground friction cut construction device concerning one embodiment of the present invention. It is a figure which shows the image of the adhesion force of the soil particle to the target member by the friction reduction effect obtained by Coulomb repulsion which concerns on one Embodiment of this invention. It is a figure showing the relation between pull-out resistance and pull-out quantity concerning one embodiment of the present invention. It is a figure which shows the time transition of the load measured by the settlement experiment of the steel member which concerns on one Embodiment of this invention. It is a figure which shows the mode of the attached sediment when the steel member which concerns on one Embodiment of this invention is pulled out from a simulated ground, (a) When a DC voltage is applied, (b) When no DC voltage is applied. Show. FIG. 3 is a diagram illustrating a relationship between a friction cut rate and a current density according to an embodiment of the present invention. It is a figure showing the result of the settlement experiment of the steel member according to the kind of earth and sand concerning one embodiment of the present invention. It is a figure which shows the relationship between the friction cut rate and applied voltage according to the composition ratio of clay and sand which concern on one Embodiment of this invention, and a friction cut rate is a ratio at the time of 50 mm insertion of a target member.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Absent.
For example, expressions representing relative or absolute arrangement such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly described. Not only does such an arrangement be shown, but also a state of being relatively displaced by an angle or distance that allows the same function to be obtained.
For example, expressions such as "identical", "equal", and "homogeneous", which indicate that things are in the same state, not only represent exactly the same state, but also have a tolerance or a difference to the extent that the same function is obtained. An existing state shall also be represented.
For example, the expression representing a shape such as a square shape or a cylindrical shape not only represents a shape such as a square shape or a cylindrical shape in a strictly geometrical sense, but also an uneven portion or a chamfer as long as the same effect can be obtained. A shape including a part and the like is also represented.
On the other hand, the expression “comprising”, “comprising”, “including”, “including”, or “having” one component is not an exclusive expression excluding the existence of another component.

  FIG. 1 is a diagram showing an underground friction cut construction method according to an embodiment of the present invention. FIG. 2 is a diagram schematically illustrating an underground friction cut construction device 1 according to an embodiment of the present invention. FIG. 3 is a diagram illustrating an image of a decrease in the adhesion of the soil particles g to the target member 2 due to the friction reduction effect obtained by the Coulomb repulsion according to one embodiment of the present invention. FIG. 4 is a diagram illustrating the relationship between the pull-out resistance and the pull-out amount according to an embodiment of the present invention. FIG. 5 is a diagram showing a time transition of a load measured by a settlement test of a steel member according to an embodiment of the present invention. FIGS. 6A and 6B are diagrams showing the state of the attached sediment when the steel member according to one embodiment of the present invention is pulled out from the simulated ground Gm, and FIG. This shows a case where no voltage is applied.

  The underground friction cut construction method of the present invention (see FIG. 1) is used when, for example, a target member 2 such as a steel sheet pile, a steel pipe pile, or a steel member such as H steel is pulled out from an underground G (ground; the same applies hereinafter). This is a method used when buried underground G. Specifically, the steel member to be the target member 2 is, for example, a steel sheet pile of a steel sheet pile wall, a steel pipe sheet pile, an H steel of a parent pile horizontal sheet pile wall, or the like. The sheet pile is a plate-shaped member for preventing soil (earth and sand; the same applies hereinafter) or water from entering the opposite side of the sheet pile in the foundation work or the civil engineering work of the building. Then, usually, a plurality of steel members or the like that can be the target member 2 such as a plurality of sheet piles are driven into the underground G side by side around a foundation of a building or a structure, and buried in the underground G. In addition, the target member 2 buried in the underground G is usually pulled out of the underground G when it becomes unnecessary.

  Normally, the sediment existing around the steel member when it is buried in the underground G adheres to the drawn steel member (object member 2). If the steel member is pulled out while being adhered, a gap is formed between the underground G and the steel member (adhered soil and sand rise together). If there is a possibility of a trouble such as settlement of a nearby buried structure or ground surface due to the co-rise, the steel member may be forced to remain in the underground G. In particular, in the case of soft viscous ground, a large amount of soil may come off together with the sheet pile with the viscous soil adhered to the sheet pile or the like, and considerable voids may be generated in the ground. Further, the drawn steel member is washed for reuse or the like, so that the attached earth and sand is removed.

  The underground friction cut execution method is performed in a state where the target member 2 is connected to the underground friction cut execution apparatus 1 as shown in FIG. As shown in FIG. 2, at least a part of the underground friction cut construction device 1 (hereinafter simply referred to as the construction device 1) is buried in the underground G at a position separated from the installation position of the target member 2 by a predetermined distance L. Voltage member that applies a DC voltage so that the anode member 3 is installed in a state where the object member 2 is to be pulled out from the underground G or the object member 2 to be buried in the underground G is a cathode, and the anode member 3 is an anode. Device 4. Then, by constructing a state in which the positive side (positive side) of the voltage applying device 4 is connected to the anode member 3 and the negative side (negative side) is connected to the target member 2 functioning as a cathode member, the construction apparatus 1 The above-described DC voltage can be applied.

  More specifically, the installation position of the target member 2 is a position where the target member 2 is buried when the content of the work performed on the target member 2 is the drawing from the underground G. On the other hand, in the case where the construction content for the target member 2 is to be driven into the underground G, the target member 2 is to be driven to be driven. Moreover, since a part of the anode member 3 is buried in the underground G, a part of the side surface of the anode member 3 comes into contact with the surrounding earth and sand. For the anode member 3, a dedicated member such as a steel member or the like that can be used as an electrode is separately prepared, and before being applied to the target member 2, the ground member is placed at a position separated from the installation position of the target member 2 by a predetermined distance L. It may be embedded in the middle G. Alternatively, a steel member or the like already buried in the underground G, which may be a candidate for the target member 2, and a member different from the target member 2 may be used as the anode member 3. For example, in the case of a sheet pile, one of the plurality of buried sheet piles may be the target member 2 and another sheet pile at a position separated from the target member 2 by a predetermined distance L may be the anode member 3. The two sheet piles are prevented from coming into contact with each other through another sheet pile.

And as shown in FIG. 1, the underground friction cut construction method includes a voltage application step (S1) and a construction step (S2).
Hereinafter, the above-mentioned steps included in the underground friction cut construction method will be described respectively.

  The voltage application step (S1) is a step of applying a DC voltage between the target member 2 and the anode member 3 so that the target member 2 functions as a cathode and the anode member 3 functions as an anode. Specifically, as described above, the DC voltage is applied by operating the voltage applying devices 4 connected to the target member 2 (cathode member) and the anode member 3, respectively.

  The construction step (S2) is to pull out the target member 2 from the underground G or to execute the target member within 5 minutes after the application of the DC voltage in the voltage application step (S1) and when the DC voltage is applied. 2 is a step of starting the construction of any one of driving into the underground G. Specifically, a heavy machine 9 such as a crane truck or a steel pipe driving machine capable of pulling the target member 2 along its longitudinal direction is operated to start construction. More specifically, when the construction of the target member 2 is a drawing from the underground G, a tensile load is applied to the target member 2 by operating the heavy equipment 9 or the like. On the other hand, when the construction of the target member 2 is driving into the underground G, a pushing load other than its own weight is applied to the target member 2 by operating the heavy equipment 9 or the like.

  Thus, immediately after the execution of the voltage application step (S1), the execution step (S2) can be executed immediately because the soil particles g that are immediately generated by applying the DC voltage in the above-described voltage application step (S1). This is because the Coulomb repulsion generated between the target member 2 serving as the cathode and the target member 2 reduces the frictional resistance that the target member 2 receives from the earth and sand. The soil particles g constituting the underground G are in a state of being negatively (negatively) charged by moisture in the ground, but as shown in FIG. 3A, when no DC voltage is applied to the target member 2. (When not energized), it is in a state of being strongly attached to the target member 2. However, as shown in FIG. 3 (b), when electrons are supplied from the anode member 3 to the target member 2 (cathode) via a power supply by applying a DC voltage (during energization), instantaneously, A Coulomb repulsion (repulsion) is generated between the negatively charged soil particles g and the target member 2. In the state where the DC voltage is applied, Coulomb repulsion is maintained.

  Then, the adhesive force of the soil particles g to the target member 2 is reduced by the Coulomb repulsion. Specifically, as shown in FIG. 4, the pull-out resistance when the DC voltage is applied (solid line) is smaller by the same amount than when the DC voltage is not applied (dashed line). It can be seen that the friction resistance is reduced by the Coulomb repulsion. The vertical axis in FIG. 4 indicates the pullout resistance [N: Newton], and the horizontal axis indicates the pullout amount (mm).

  Further, the graph shown in FIG. 5 shows that a steel member is installed on earth and sand (soil (simulated ground Gm) in which tochiclay and silica sand 7 are mixed), and the steel member and the anode member 3 previously embedded in the earth and sand are shown. The measurement result (vertical axis) obtained by measuring the sinking load (tensile load) [N] applied along the direction of gravity when a DC voltage is applied during the sinking by its own weight is applied to the time transition (horizontal axis). It is a graph plotted against this. The vertical axis also shows the voltage value of the applied DC voltage (hereinafter, applied voltage V) and the current value flowing at the time of application. The sinking load can be obtained by pressing a steel member into the simulated ground Gm and measuring the press-in resistance (upward of the steel member). A downward load (squatting load) is generated on the meter. Referring to FIG. 5, it can be seen that the sinking load increases immediately after the application of the DC voltage (self-destroying), and the Coulomb repulsion immediately reduces the frictional resistance.

  In other words, the surface of the soil particles g constituting the underground G (ground) has an electric charge (negatively charged), and the present inventors have found that the target member 2 and the earth and sand constituting the underground G are generated by applying a DC voltage. When the target member 2 such as a steel member is pulled out from the underground G or when the target member 2 is driven into the underground G, it is received from the earth and sand constituting the underground G by the Coulomb repulsion generated between the underground G and the soil particles g. It has been found that frictional resistance is reduced. This Coulomb repulsion is generated in a very short time, such as immediately after the application of the DC voltage, because it is generated by the movement of charges (free electrons) between the anode and the cathode (see FIG. 5). Therefore, unlike the related art, after the application of the DC voltage, the application to the target member 2 may be performed after a shorter time after the application of the DC voltage without waiting for the generation of gas due to the electroosmosis phenomenon or the electrolysis. Thus, the target member 2 can be pulled out or driven with a smaller force.

  The embodiment shown in FIG. 1 will be described. In FIG. 1, in step S0, setting for construction (pulling / implantation) of the target member 2 is executed. Specifically, the installation (setting) of the construction apparatus 1 described above is performed on the target member 2. In this step S0, the connection of the heavy equipment 9 to the target member 2 may be performed. Then, in FIG. 1, after performing the above-mentioned voltage application step in step S1, the above-mentioned construction step is performed in step S2.

  In the embodiment shown in FIG. 1, the voltage applying step (S1) applies a constant DC voltage during the execution of the construction step (S2). However, in some other embodiments, the voltage applying step (S1) is applied. In (S1), the DC voltage applied during the execution of the construction step (S1) may be turned on and off according to any predetermined timing that is periodic as shown in FIG. From the results of the subsidence experiment shown in FIG. 5, it can be seen that the load along the direction of gravity increases when the DC voltage is turned on, and the load becomes constant or decreases when the DC voltage is turned off.

  The embodiment shown in FIG. 1 is an embodiment in which step S0 is included in the underground friction cut execution method, but the configuration corresponding to step S0 is not included in the underground friction cut execution method. May be. In other words, in this case, an embodiment in which the underground friction cut construction method is applied since the operation corresponding to step S0 has already been completed. Further, the connection of the heavy equipment 9 to the target member 2 executed in step S0 may be performed between step S1 and step S2.

  According to the above configuration, the DC voltage is applied so that the target member 2 becomes the cathode and the anode member 3 becomes the anode, and the target member 2 is applied within 5 minutes immediately after the application of the DC voltage at which the Coulomb repulsion occurs. Construction such as pulling out the member from the ground and driving (burial) the target member into the ground is started. Due to the Coulomb repulsion between the target member 2 and the soil particles g constituting the underground G, which is generated in a very short time immediately after the application of the DC voltage, the frictional resistance of the target member 2 from the surrounding soil is generated. Reduced. Therefore, the application of the target member 2 can be started immediately after the application of the DC voltage. In addition, the construction can be performed with a smaller pulling load or indentation load, and the construction can be completed in a short period of time by the time required to start the construction of the target member 2 earlier. Construction can be performed more efficiently.

  Further, by performing the drawing operation in a state where the frictional resistance to the target member 2 is reduced as described above, it is possible to reduce the amount of earth and sand attached to the target member 2 when the target member 2 is pulled out. For example, in the example illustrated in FIG. 6, when a DC voltage is applied such that the steel member to be drawn is a cathode and the anode member 3 is an anode (see FIG. 6A), the soil attached to the target member 2 is approximately 1.2 g. When no DC voltage was applied (see FIG. 6 (b)), the amount of sediment adhering to the target member 2 was about 81.3 g. It has been reduced to about 1/70. Therefore, a large amount of soil is pulled out together with the pulled-out target member 2 (coexistence), so that a gap generated in the underground G can be reduced, and a trouble such as ground surface settlement due to the gap may occur. Can be reduced. In addition, it is possible to reduce the burden and cost required for cleaning work performed for reuse of the target member 2 and the like.

  Therefore, conventionally, as a countermeasure against settlement due to the pulling out of such steel members, a method of pulling out while suppressing the generation of cavities by extremely slowing down the pulling speed, or injecting sand or soil cement etc. from the surface immediately after pulling out Although the method of filling the cavity has been adopted, the necessity can be reduced. For this reason, it is possible to avoid an increase in the time required for the construction and inefficiency due to the settlement measures, and an increase in cost such as preparing a material for injection.

Next, some embodiments relating to the above-described voltage application step (S1) will be described.
FIG. 7 is a diagram illustrating a relationship between a friction cut rate and a current density according to an embodiment of the present invention.

  In some embodiments, as shown in FIG. 7, the voltage application step (S1) is to reduce the current value of the current flowing by applying a DC voltage between the target member 2 and the anode member 3 to the target member 2. The above-mentioned DC voltage is applied so that the current density, which is a value obtained by dividing the surface area of the portion buried in the underground G, is larger than 0 and equal to or less than 15 within a range. That is, the voltage value (applied voltage V) of the applied DC voltage is determined so that the current density becomes the set value α, and the applied voltage V is actually applied by using the above-described voltage application device 4 or the like. .

  The inventors of the present invention have conducted intensive studies to determine the ratio of the tensile load or indentation load when the DC voltage is applied to the tensile load or indentation load when no DC voltage is applied (for example, load when voltage is applied 電 圧 voltage when no voltage is applied). The load at the time (hereinafter, referred to as a friction cut rate) is correlated with a value (that is, current density) obtained by dividing a current flowing by applying a DC voltage by a surface area of a portion of the target member 2 buried underground. Was found. Specifically, as shown in FIG. 7, the friction cut rate decreases to near the lower limit (a value between 0.3 and 0.4 in FIG. 7) as the current density increases. After the vicinity of the value, even if the current density is increased, there is little change.

  Specifically, the present inventors have proposed a steel member having various shapes (such as a flat shape and an H shape) and a size, and a state in which the longitudinal direction is buried in earth and sand along the direction of gravity, By changing the magnitude of the applied voltage V of the DC voltage applied so that the steel member becomes a cathode and the anode member 3 becomes an anode with respect to the steel member in a state of being buried in earth and sand so that the short side direction is along the direction of gravity. And the friction cut rate was measured. Then, the present inventors, through trial and error, are not the relationship between the applied DC voltage or current value and the friction cut rate, but the measurement data of the friction cut rate and the portion of the steel member embedded in the soil. The correlation between the friction cut rate and the current density as shown in FIG. 7 was found by paying attention to the data of the surface area and the measurement data of the current value when the DC voltage was applied.

The graph in FIG. 7 is a graph in which the vertical axis represents the friction cut rate and the horizontal axis represents the current density [A / m ² ]. As shown in FIG. 7, the friction cut rate decreases as a quadratic function (exponential function) as the current density increases until the current density reaches a predetermined value (near 10 in the example of FIG. 7). As shown in FIG. 7, the tensile load on the steel member is reduced as compared with the case where no DC voltage is applied. Further, even if the current density is larger than the predetermined value, the friction cut ratio hardly changes, and it can be seen that the friction cut ratio changes to approach a constant value.

  Then, as shown in FIG. 7, if the set value α of the current density at the time of applying the DC voltage is 3 or more and 10 or less, the friction cut ratio is between 0.3 and 0.4 which is close to the lower limit. In the vicinity of 5, the reduction ratio of the friction cut ratio to the reduction ratio of the current density is relatively large. Therefore, by setting the set value α of the current density at the time of application of the DC voltage to 3 or more and 10 or less, or near 5, the power supply for the DC voltage is reduced as much as possible and the effect of reducing the frictional resistance is maximized. It is possible to

  According to the above configuration, the voltage V applied to the target member 2 and the anode member 3 is set to a set value α in a range where the current density when the DC voltage is applied is larger than 0 and 15 or less. More specifically, the setting value α is set to 3 or more and 10 or less (for example, 5). Thereby, a relatively large friction reduction effect by Coulomb repulsion can be obtained while suppressing power consumption for applying a DC voltage.

  In some embodiments, as shown in FIG. 1, the underground friction cut construction method uses a DC voltage such that the above-mentioned current density becomes the above-mentioned set value α during the execution of the construction step (S2). May be further provided with a voltage adjusting step (S3) of adjusting the voltage. The surface area of the target member 2 buried in the underground G decreases as the withdrawal amount of the target member 2 increases, and increases as the driving of the target member 2 progresses and the buried portion increases. Changes as the construction proceeds. Therefore, during the construction of the target member 2, the current density is adjusted so as to reach the set value α.

  Specifically, as shown in FIG. 2, the construction apparatus 1 further includes an ammeter 5 for measuring a current flowing between the target member 2 and the anode member 3. Then, the current density is calculated during the construction based on the measurement value I of the ammeter 5 and the measurement value of the construction amount h, which is the amount of pulling out or driving of the target member 2, and the calculated value is the set value α. Thus, the applied voltage V of the DC voltage is adjusted by operating the voltage applying device 4 or the like. In addition, how the surface area of the portion buried in the underground G changes according to the construction amount h is prepared in advance as a table or a calculation formula, and is easily obtained from the measured value of the construction amount h. Good to have been.

  More specifically, as shown in FIG. 2, the application apparatus 1 includes an applied voltage determination apparatus 6 that calculates an instruction value of a DC voltage to be applied by the voltage application apparatus 4, thereby providing contents corresponding to step S <b> 3. May be executed. In the embodiment shown in FIG. 2, the measured value I of the ammeter 5 and the measured value of the construction amount h are input to the applied voltage determining device 6, and the applied voltage determining device 6 And a calculation function such as the above-mentioned table or calculation formula capable of calculating the surface area of the portion buried in the underground G from the construction amount h held in an internal storage device (not shown), The current density is calculated based on. Then, the applied voltage determination device 6 automatically adjusts the voltage of the voltage application device 4 so that the calculated current density becomes the set value α.

  However, the present invention is not limited to this embodiment. In some other embodiments, the applied voltage determination device 6 performs the calculation of the current density on the display, and the adjustment of the applied voltage V applied by the voltage application device 4 is displayed on the display. The calculation may be performed manually so that the calculation result of the current density becomes the set value α.

  According to the above configuration, the applied voltage V is adjusted by the voltage adjusting step (S3) so that the current density becomes the set value α during the execution step (S2). This prevents a situation where the applied voltage V of the DC voltage is unnecessarily high or a situation where the applied voltage is small and the effect of reducing the frictional resistance cannot be sufficiently obtained, and an appropriate DC voltage can be applied.

  However, the present invention is not limited to this embodiment. In some other embodiments, the applied voltage V is determined so that the current density becomes the set value α before the application, and during the application, the applied voltage V in the voltage adjustment step (S3) as described above is determined. The adjustment need not be performed. If the length of the portion of the target member 2 buried in the underground G is unknown, an assumed value of the surface area of the portion or the entire surface area may be used.

Next, a description will be given of earth and sand suitable for performing the above-described underground friction cut construction method (construction apparatus 1).
FIG. 8 is a diagram showing the results of a settlement test of a steel member according to the type of earth and sand according to one embodiment of the present invention. The friction cut ratio is a ratio when the target member is inserted at 50 mm. FIG. 9 is a diagram showing a relationship between a friction cut rate and an applied voltage V according to a composition ratio of clayey soil and sand according to an embodiment of the present invention.

  In some embodiments, the earth and sand constituting the underground G described above includes soil having a grain size of less than 0.075 mm and a grain size of 40% or more. More specifically, the earth and sand constituting the underground G may include soil having a fine particle size of 0.065 mm or less and 40% or more (see FIG. 9). This is because the inventors of the present invention have conducted intensive studies and found that sand (having a fine particle content of less than 15%) is not negatively charged even with saturated sand.

  More specifically, the graph shown in FIG. 8 shows that when a steel member is installed on various types of earth and sand, and a DC voltage is applied between the steel member and the anode member 3 previously embedded in the earth and sand. 4 is a graph in which measurement results (vertical axis) obtained by measuring a sinking load [N] applied along the direction of gravity when sinking by its own weight are plotted against a time axis (horizontal axis). FIG. 8 shows sand (soil having a fine grain fraction of less than 15%), dry cohesive soil (Kibushi cohesive soil), and saturated kibushi cohesive soil ( Experimental results for the plastic limit Wp = 40% of knotty clay) are shown. As shown in FIG. 8, when a DC voltage is applied, even if the sand is saturated sand, it does not self-settle, and the settlement load does not increase. That is, it is understood that the sand is not negatively charged and no Coulomb repulsion is generated.

  Further, in the graph of FIG. 9, a plurality of types of soil having different composition ratios of clay (soil having a particle size of 0.065 mm or less) and sand (soil having a fine particle content of less than 15%) are shown. A change in the friction cut ratio when the magnitude of the applied voltage V of the DC voltage applied so that the steel member is the cathode and the anode member 3 is the anode by installing the steel member and the anode member 3, respectively. It is shown. When the sand content is 60% or less, the effect of reducing friction by Coulomb repulsion when the same applied voltage V is applied generally decreases as the proportion of sand (sand content) increases. Conversely, when the amount of clay is 40% or more, as the proportion of clay increases, the friction reducing effect due to Coulomb repulsion when the same applied voltage V is applied generally increases. In other words, it can be said that the greater the clay content in the earth and sand, the greater the reduction in insertion resistance at the start of driving.

  Therefore, the underground friction cut construction method of the present invention is applied when the soil particles g of the earth and sand constituting the underground have a fine particle fraction of less than 0.075 mm by 40% or more. This is mainly classified into silt, cohesive soil, etc. (fine grain content of 50% or more) and sandy soil (fine grain content of 5% or more) in the engineering classification method of soil in the Japan Unified Soil Classification Method. (Less than 50%), and the Coulomb repulsion generated by applying the above-described DC voltage to the target member 2 and the anode member 3 can reduce the frictional resistance that the target member 2 receives from the surrounding earth and sand. .

In addition, it can be seen from FIG. 8 that the Coulomb repulsion does not occur even in the case of the dried clayey soil even if the clayey soil is dry. Further, it can be seen that even in the case of a saturated clay soil, the finer the grain, the higher the plasticity, the higher the electrical activity, and the more easily the Coulomb repulsion effect can be obtained. In other words, according to previous studies on the activity of clayey soil, the degree of charging of the soil particles g is proportional to the specific surface area and the ζ potential, and the specific surface area and ζ potential are proportional to the clay content and the plasticity index (Ip). Therefore, the higher the plasticity index, the greater the clay content, the greater the friction cut effect.
Therefore, in some embodiments, in the construction step (S2), the extraction of the target member 2 at least partially buried below the groundwater level is started, or at least a part is buried below the groundwater level. To start driving.

  That is, in order for the Coulomb repulsion to occur, the soil must be saturated, and in the ground below the groundwater level, the space between the soil particles g is filled with water (saturated soil). The frictional resistance of the target member 2 from the surrounding earth and sand can be reduced by the Coulomb repulsion generated by applying the DC voltage described above. The saturated state is a state in which the soil particles g are ionized (charged), and water is present in all gaps between the soil particles g.

  In short, unless the soil is saturated, the soil particles g are not ionized and are not charged (no friction cut effect). Furthermore, since sand (mineral) is not charged even in the saturated state, it can be said that the target of this method is appropriate for the viscous ground below the groundwater level. It should be noted that even in the case of silt or clayey soil, the non-plastic silt / clay having a plasticity index of zero has a low degree of electrification, so that the friction cut effect is reduced (advantageous in the ground where Ip> 15).

  The present invention is not limited to the above-described embodiment, and includes a form in which the above-described embodiment is modified and a form in which these forms are appropriately combined.

Reference Signs List 1 underground friction cut construction device 2 target member 3 anode member 4 voltage application device 5 ammeter 6 applied voltage determination device 9 heavy equipment G underground Gm simulated ground L predetermined distance h construction amount g soil particle I current measured value V applied voltage Wp plastic limit

Claims (7)

A target member to be pulled out from the ground or a target to be buried in the ground, and an anode member at least partially buried in the ground at a position separated from the installation position of the target member, A voltage applying step of applying a DC voltage so that the target member is a cathode and the anode member is an anode,
When the DC voltage is applied within 5 minutes after the application of the DC voltage by the voltage applying step, the target member is pulled out of the ground, or the target member is drawn into the ground. An underground friction cut construction method, comprising:   In the voltage applying step, a current value of a current flowing by applying the DC voltage between the target member and the anode member was divided by a surface area of a portion of the target member embedded in the ground. The underground friction cut construction method according to claim 1, wherein the DC voltage is applied such that a current density, which is a value, is greater than 0 and equal to or less than a set value within a range of 15 or less.   The underground friction cutting method according to claim 2, further comprising a voltage adjusting step of adjusting the DC voltage so that the current density becomes the set value during the execution of the execution step.   The underground friction cut according to any one of claims 1 to 3, wherein the voltage application step turns on and off the DC voltage applied during execution of the construction step according to a predetermined timing. Construction method.   The underground friction cut according to any one of claims 1 to 4, wherein the earth and sand constituting the underground includes soil having a fine particle content of less than 0.075 mm by 40% or more. Construction method.   In the construction step, the extraction of the target member at least part of which is buried below the groundwater level is started, or the driving is started so that at least a part is buried below the groundwater level. The underground friction cut construction method according to any one of claims 1 to 5, wherein: An anode member that is at least partially buried in the ground at a position separated from the installation position of the target member to be pulled out from the ground or to be buried in the ground,
Between the target member and the anode member, the target member is a cathode, a voltage application device that applies a DC voltage so that the anode member becomes an anode,
An applied voltage determination device that calculates an instruction value of the DC voltage applied by the voltage application device,
The applied voltage determination device divides a current value of a current flowing by applying the DC voltage between the target member and the anode member by a surface area of a portion of the target member buried in the ground. The underground friction cut construction device, wherein the DC voltage is applied so that the value obtained is larger than 0 and equal to or smaller than 15.