JPH11280055A - Support ground position detection method in ground improving machine and support ground position detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a support ground position supporting an improved column body precisely without causing a difference among individual persons. SOLUTION: Digging energy E per 0.1 m in 1 m in the vicinity of support ground is obtained based on a current value of a rotating and driving motor 5 driving stirring shaft 4, the number of rotation of the stirring shaft 4, and passing-in speed of the stirring shaft 4, and changes of digging energy per 0.1 m are sequentially displayed on a screen of a monitor 16. When it is judged that a tip of the stirring shaft 4 reaches a support ground position when digging energy E per 0.1 m becomes digging reference energy E, of the support ground obtained by boring and surveying in advance, the support ground position can be detected with high precision because display span is 1 m. Moreover, the support ground position can be detected without causing differences among individual persons merely by monitoring the screen of the monitor 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement which is capable of reliably and easily detecting the position of a supporting ground when forming an improved pillar on a supporting ground in a soft ground. The present invention belongs to the technical field of a support ground position detection method and a support ground position detection device in a machine.

[0002]

2. Description of the Related Art As is well known, a ground improvement machine is configured such that a stirring shaft having a stirring blade attached to the tip is made vertical along a reader, the stirring shaft is rotated by a rotary drive motor, and a driving device such as a winch is driven. The stirrer shaft is lowered by the stirrer, and after the stirrer penetrates to a predetermined depth in the ground, the stirrer shaft is pulled up by the driving device while the improver such as cement is sprayed from the tip of the stirrer shaft together with the stirrer blades. An improved pillar is formed therein. In the ground improvement by the ground improvement machine, in order to effectively transmit the overload acting on the improved pillar to the supporting ground, the tip of the stirring shaft that injects the improving material must be surely extended to the supporting ground below the soft layer. It is necessary to penetrate to form an improved pillar that reliably reaches the supporting ground position. Incidentally, a supporting ground position detecting method and a supporting ground position detecting device for detecting that the tip of the stirring shaft of the ground improvement machine has reached the supporting ground position are disclosed in, for example, Japanese Patent Application Laid-Open No. 62-280411 (conventional example 1). Kaisho 62
-280412 (conventional example 2).

First, FIG. 6 is a schematic explanatory view showing the state of construction of a conventional example 1 disclosed in Japanese Unexamined Patent Publication No. 62-280411, which shows a construction state by a ground improvement machine, and FIG. A description will be given based on FIG. As shown in FIG. 6, the ground improvement machine is equipped with a base machine 1 equipped with a reader 2 and a stirring shaft 4 having a stirring blade 3 at a tip end thereof.
A rotary drive motor 5 for rotating and driving the stirring shaft 4, a drive device 6 for driving the lifting shaft up and down, and the like are provided. A hose 7 from an improved material plant (not shown) is connected to an upper end of the stirring shaft 4 via a swivel joint 8. Configuration.
In addition, the code | symbol S 'which shows the surface of the ground is a topsoil layer, The code | symbol S which shows the lower part of this topsoil layer S' is soft ground,
The symbol H indicating the lower part of the soft ground S is a hard supporting ground. The symbol P, which penetrates the topsoil layer S 'and the soft ground S and whose lower end is supported on the upper surface of the hard support ground H, is an improved pillar.

[0004] As shown in FIG. 7, there is provided a supporting ground position detecting device A which detects the position of the supporting ground based on the current value of the rotary drive motor 5 and controls the drive device 6 to stop driving. Hereinafter, a method of detecting the supporting ground position by the supporting ground position detecting device A will be described. The current value of the rotary drive motor 5 for rotating the stirring shaft is detected by the current value detector 10, and this detected value and the current value The current value comparison circuit 11 compares the allowable current value of the rotary drive motor 5 set by the setting device 9 with a current value comparison circuit 11, and sends a signal when the current value detected by the current value detector 10 is larger than the allowable current value, The transmitted signal is integrated by a time counter 12, and the signal integration time obtained by the integration is compared with a set time value previously set by a time value setting unit 13 by a time value comparison circuit 14, and the signal integration time is set. When the time value is larger than the time value, the drive device 6 for raising and lowering the stirring shaft is stopped assuming that the tip of the stirring shaft has reached the supporting ground position having a certain strength. In short, the current value has exceeded the set current value. With a when the integrated value between exceeds the set value, is taken as the tip of the stirring shaft reaches the support ground position.

Next, a second conventional example disclosed in Japanese Patent Application Laid-Open No. 62-280412 will be described with reference to FIG. 8 which is a block diagram of a main part of a supporting ground position detecting device. In addition,
Since the basic configuration of the ground improvement machine is the same as that of the first embodiment, only the support ground position detecting device A of the ground improvement machine will be described. That is, the current value of the rotary drive motor 5 for rotating the stirring shaft is detected by the current value detector 10, and the detected value is compared with the allowable current value of the rotary drive motor 5 set in advance by the current value setter 9. The current value detector 10
A signal is transmitted when the current value detected in step S1 is larger than the allowable current value, and the excess current value is obtained by the current value calculator 13, and the excess time and excess current value obtained by integrating the signal transmission time are calculated. Calculate excess electric quantity from
7, when it is determined that the accumulated excess electricity amount obtained by integrating the excess electricity amount is larger than the preset electricity amount set by the electricity amount setting unit 16, it is assumed that the tip of the stirring shaft has reached the supporting ground position having a certain strength. The drive device 6 that raises and lowers the stirring shaft is stopped, and the tip of the stirring shaft reaches the support ground position when the accumulated excess electricity exceeds a set value.

[0006]

By the way, when the ground is improved by the ground improvement machine, when it is detected that the tip of the stirring shaft of the ground improvement machine has reached the supporting ground position, the following items must be satisfied. Is required. Able to detect in real time that the tip of the stirring shaft has reached the support ground position. Able to objectively judge that the tip of the stirring shaft has reached the support ground position. Excavation data can be recorded.

[0007] From the above point of view, looking at the ground improvement method according to Conventional Example 1 or Conventional Example 2, all of them satisfy the above items and are considered to be useful as such. Can be However, since the entire excavation range is calculated and displayed on the monitor in any case, the display span is too large to be able to grasp the change in excavation energy near the support ground. There is a problem to be solved that cannot be detected.

[0008] Further, after the tip of the stirring shaft reaches the support ground position so as not to leave an unimproved portion at the tip of the stirring shaft, one end of the stirring shaft is pulled out by the difference between the upper and lower stages of the stirring blade. When the operation of re-penetrating the stirring shaft to the supporting ground while injecting the material is performed, as described above, the conventional example 1
It is assumed that the tip of the stirring shaft reaches the support ground position when the integrated value of the time exceeding the set current value exceeds the set value, and in the conventional example 2, the integrated excess electric amount exceeds the set value. Since the tip of the stirring shaft reaches the supporting ground position at the time of the arrival, it is impossible to accurately grasp the re-penetration depth of the stirring shaft. There is a problem to be solved that not only may not reach the support ground position, but also waste may occur due to excessive penetration.

Accordingly, it is an object of the present invention to accurately detect that the tip of the stirring shaft has reached the support ground position, and to reliably know the re-penetration depth of the stirring shaft. An object of the present invention is to provide a supporting ground position detecting method and a supporting ground position detecting device in a ground improvement machine to be used.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and accordingly, the features of the means adopted by the method for detecting a supported ground position in a ground improvement machine according to claim 1 of the present invention. When the ground is improved by a ground improvement machine having a stirring shaft driven by a rotary drive motor and driven up and down by a driving device, the ground for detecting that the tip of the stirring shaft has reached the support ground position. In the support ground position detection method in the improved machine, the current value or the rotation torque of the rotary drive motor that rotates the stirring shaft, the rotation speed of the stirring shaft, and the penetration speed of the stirring shaft, and the penetration depth of the unit near the support ground per unit penetration depth The excavation energy per unit depth of penetration was calculated, and the calculated excavation energy was equal to the excavation reference energy of the supporting ground obtained from the drilling survey in advance. Can the tip of the stirring shaft is in place and has reached the supporting ground located.

According to a second aspect of the present invention, there is provided a method of detecting a supported ground position in a ground improvement machine according to the first aspect of the present invention. Calculation of energy,
This is to be performed when the stirring shaft reaches a depth obtained by subtracting a predetermined excavation depth from the depth of the ground to be improved obtained by a drilling survey in advance.

According to a third aspect of the present invention, there is provided a method for detecting a supporting ground position in a ground improvement machine according to claim 1, wherein The excavation energy per unit penetration depth is displayed on a monitor for each unit penetration depth.

According to a fourth aspect of the present invention, there is provided a method for detecting a supported ground position in a ground improvement machine according to a fourth aspect of the present invention. The drilling energy per penetration depth is scrolled so that the latest constant section is always displayed on the monitor.

According to a fifth aspect of the present invention, there is provided a method for detecting a supported ground position in a ground improvement machine according to the first aspect of the present invention. The latest depth reached by the tip of the shaft is displayed on the monitor.

According to a sixth aspect of the present invention, there is provided a method for detecting a supported ground position in a ground improvement machine according to the sixth aspect of the present invention. The tip of the shaft is where the drilling energy is calculated when the drilling is first performed in the depth direction and is displayed on the monitor.

According to a seventh aspect of the present invention, there is provided a ground improvement machine, wherein a supporting ground position detecting device employs a stirring shaft which is driven to rotate by a rotary driving motor and is driven to move up and down by a driving device. In a support ground position detection device in a ground improvement machine that detects that the tip of the stirring shaft of the ground improvement machine has reached a support ground position, a current detector that detects a current value of a rotary drive motor that rotationally drives the stirring shaft. And, a depth / speed detector that detects the penetration speed of the stirring shaft, a rotation speed detector that detects the rotation speed of the stirring shaft, and the current value, the rotation speed, and the penetration speed detected by these detectors. An arithmetic unit that calculates the excavation energy per unit penetration depth for each predetermined unit penetration depth from
And a monitor for displaying the calculation result calculated by this calculation device on a screen.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a ground improvement machine provided with a support ground position detection device according to an embodiment for realizing a method for detecting a support ground position in a ground improvement machine according to the present invention. FIG. 1 (a), FIG. 1 (b) of the block diagram thereof, and FIG. 2 showing the relationship between the N value and the excavation depth.
(A), FIG. 2 (b) showing the relationship between the excavation energy and the excavation depth, FIG. 3 showing the monitor screen, FIG. 4 (a) showing the relationship between the excavation depth and the current, and FIG. FIG. 4B, which is an explanatory diagram of the relationship between the depth and the penetration speed, FIG. 4C, which is an explanatory diagram of the relationship between the excavation depth and the excavation energy E, and FIG. This will be described sequentially. However, since the basic configuration of the ground improvement machine is the same as that of the conventional example 1 described in the paragraph [0003], only the differences will be described.

Reference numeral 1 shown in FIG. 1A indicates a ground improvement machine.
The ground improvement machine 1 is provided with a support ground position detecting device 10. That is, a stirring shaft 4 supported by the ground improvement machine 1 by the leader 2 and provided with a stirring blade 3 at the lower end.
A current detector 11 for detecting a current value of a rotary drive motor 5 for rotating the shaft, a depth / speed detector 12 for detecting an excavation depth and a penetration speed of the stirring shaft 4, and a rotation speed of the stirring shaft 4. A rotation speed detector 13 to be detected is attached. Then, as shown in FIG.
, The excavation depth and penetration speed of the stirring shaft 4 detected by the depth / speed detector 12, and the rotation speed of the stirring shaft 4 detected by the rotation speed detector 13. Is input to an A / D converter 14 that converts an analog value to a digital value, and the current value digitally converted by the A / D converter 14, the excavation depth and the penetration speed, and the rotation speed are calculated. The information is input to the device 15.

The arithmetic unit 15 obtains a digitally converted and inputted excavation depth based on a drilling survey in advance based on the digitally converted and inputted current value, the penetration speed and the rotation speed. From the excavation depth based on the N value of the ground to be improved, a predetermined excavation depth, for example, 1
m, the digging energy E (kW · h / kW) per 0.1 m depth is incremented by 1 m, which is a predetermined digging depth set in advance, at every 0.1 m depth.
m) and the excavation reference energy E from the N value and the rotation speed.
_S (kWh / m), and the excavation energy E and the excavation reference energy E _S are obtained from the following equations. The distance for calculating the excavation energy E was set to 1 m because it was found that the support ground position is usually within the range of 1 m.

Here, the rotational torque of the stirring shaft 4 is T
(N · m), the penetration speed of the stirring shaft 4 is v (m / min),
Assuming that N is the N value of the ground to be improved and a, b, c and d are coefficients determined by the quality of the ground to be improved, the general formula of the rotational torque T of the stirring shaft 4 can be expressed by the following formula. . T = a (v + b) (N + c) + d ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ This equation is transformed to (T−d) / (v + b) = a (N + c), and The rotation speed n of the stirring shaft 4 for each of the right side
Multiply by gives drilling energy. (T−d) n / (v + b) = a (N + c) n ‥‥‥‥‥‥‥‥‥‥‥

That is, on the left side of the above equation, the molecule is
, And the denominator is the penetration speed (m / mi).
Since it is n), it is excavation energy. Then, the excavation energy E and the excavation reference energy E _S are obtained from the left side and the right side.
And can be asked. E = (T-d) n / (v + b) ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ E S = a (N + c) n ‥‥‥‥‥‥‥‥‥‥‥‥‥ ‥‥‥‥‥‥‥‥

In order to verify the validity of the use of the above equation, the degree of correlation between the N value of the ground to be improved and the excavation energy E is shown in FIG.
As is well understood from (b), the excavation energy E near the excavation depth of 20 m obtained by the preliminary drilling survey
It is understood that the N value and the excavation energy E are almost correlated. This suggests that the support ground position can be detected by using the above equation.

Further, the current value A, the penetration speed v, and the excavation energy E, which change with the excavation depth, are monitored by the monitor 16.
And a recorder 17 for recording changes in the current value A, the penetration speed v, and the excavation energy E with respect to the excavation depth for data accumulation.

The monitor 16 has a depth-drive condition display screen 16a for displaying the excavation depth of the stirring shaft 4 and the driving conditions (speed, rotation speed and current value) of the stirring shaft 4 shown on the upper left side in FIG. The vertical axis shown on the lower left side is the digging depth, the horizontal axis is the digging depth-digging energy relationship display screen 16b, and the ordinate shown on the right side is the digging depth.
The horizontal axis is formed from an excavation depth-excavation elapsed time relationship display screen 16c which is an excavation elapsed time. Then, on the excavation depth-excavation energy relationship display screen 16b, the excavation depth from 29.6m to the deepest excavation depth is 30.5m,
Drilling energy E per 0.1 m, ie 29.6
The excavation energy E of m, 29.7 m,... 30.4, 30.5 m is displayed as ten horizontal bar graphs, and the excavation depth-excavation elapsed time relationship display screen 16 c includes:
It is configured to display the excavation elapsed time with respect to the excavation depth.

In this case, the excavation energy E from the depth of 29.6 m to 30.5 m is displayed every 0.1 m on the excavation depth-excavation energy relation display screen 16 b of the monitor 16. When the deepest excavation depth reaches 30.6 m, it goes from 29.7 m to 30.m.
The drilling energy E per 0.1 m during 6 m is displayed as ten bar graphs, and the drilling depth is scrolled every 0.1 m. Note that the excavation depth 29.5 m at which the calculation of the excavation energy E starts and the deepest excavation depth 30.5 m are for a certain construction site, and these depths naturally change when the construction site changes.

FIG. 4 (a) and FIG.
As shown in (b) and (c), the relationship between the excavation depth and the current value, the relationship between the excavation depth and the penetration speed, the excavation depth and the excavation from the excavation depth of 29.5 m to the maximum excavation depth of 30.5 m. The relation to the energy is recorded for each data collection.

Since the depth of the supporting ground is known by drilling in advance, if the excavation reference energy E _S at the time when the tip of the stirring shaft 4 reaches the supporting ground position is determined in advance, the monitor 16 can be used during the excavation. By monitoring the excavation energy E displayed on the excavation depth-drive condition display screen 16b, it is possible to know that the tip of the stirring shaft 4 has reached the support ground position of 30.5 m in real time and without individual differences. it can.

By the way, according to the supporting ground position detecting apparatus 10 according to the present embodiment, as described above, the excavation depth is set in advance from the excavation depth based on the N value of the ground to be improved obtained by the drilling survey. After reaching a depth reduced by 1 m, the excavation energy E (kWh
/ M) is calculated and displayed on the monitor 16, but after the tip of the stirring shaft 4 reaches the supporting ground position so that the unimproved portion does not remain on the tip side of the stirring shaft 4. In the case of performing the tip treatment of pulling out the stirring shaft 4 once by the difference between the upper and lower stages of the stirring blade 3 and re-penetrating the pulled-out stirring shaft 4 again while spraying the improving material to the depth of the supporting ground, the stirring shaft 4 is used. The excavation energy E is displayed on the monitor 16 on the screen from the depth at which the tip first reaches the unexcavated ground.

Hereinafter, a method of detecting the support ground position by the support ground position detection device 10 according to the present embodiment will be described with reference to FIG. The excavation depth of the stirring shaft 4 which is detected by the depth / speed detector 12 and is converted into a digital signal by the A / D converter 14 and inputted is based on the N value of the ground to be improved which is obtained through a drilling survey in advance. A depth obtained by subtracting a predetermined 1 m predetermined excavation depth from the depth, specifically 2
When the depth reaches 9.5 m, the support ground position detection flow is automatically started, and the process proceeds to step 1 where the stirring shaft 4
The penetration speed, the current value, and the rotation speed are detected, and the routine proceeds to step 2.

In step 2, it is determined whether or not the depth has increased by a predetermined depth, specifically, 0.1 m. If it is determined that the depth has not increased by 0.1 m, N
In the case of "o", the process returns to Step 1, and in the case of "Yes" in which the depth is determined to have increased by 0.1 m, the process proceeds to Step 3.

[0031] In Step 3, the above equation and expressions, i.e. E = (T-d) n / (v + b), E S = a (N +
c) The excavation energy E per 0.1 m and the excavation reference energy E _S are calculated by the equation of n, and step 4 is performed.
Proceed to.

In step 4, the excavation energy E corresponding to the excavation depth is displayed on the excavation depth-excavation energy relationship display screen 16b of the monitor 16, and the process proceeds to step 5.

In step 5, it is determined whether the excavation energy E has exceeded the excavation reference energy E _S ,
When it is determined that the excavation energy E has not reached the reference excavation energy E _S , the process returns to step 1 and
In the case of Yes in which drilling energy E per 0.1m is determined to have reached the drilling reference energy E _S proceeds to step 6. Magnitude comparison determination and drilling energy E and the reference drilling energy E _S per 0.1m until drilling energy E reaches the drilling reference energy E _S, 0.1
It is repeated every m.

In Step 6, since the excavation energy E reaches the excavation reference energy E _S and the tip of the stirring shaft 4 reaches the support ground position of 30.5 m, the excavation work of the improved ground by the stirring shaft 4 is stopped. At the same time, the improvement column is formed by pulling out the stirring shaft 4 while spraying the improvement material such as cement, and the process proceeds to step 7.

In step 7, when the stirring shaft 4 is completely pulled out of the improved ground and the formation of the improved pillar is completed, the process proceeds to step 8.

In step 8, in order to accumulate data that can be used as improvement data for later ground improvement work, changes in the penetration speed, current value, and excavation energy with respect to the excavation depth are recorded by the recorder 17, and one improvement is performed. Construction of the pillars is completed. Then, the ground improvement machine 1 is moved to the next improvement column forming position.

As described above, according to the supporting ground position detecting apparatus 10 according to the embodiment of the present invention, the entire excavation area is not calculated and displayed on the monitor as in the conventional example 1 or 2. 1m shallower than the depth reached for the first time
Is calculated on the monitor 16 by calculating the excavation energy E per 0.1 m every 0.1 m, and is displayed by scrolling by 0.1 m each time the improved ground is excavated by 0.1 m. is there. Therefore, the span is about 1/30 of the span when the entire excavation depth of 30.5 m is displayed on the monitor, so that the visibility is good and the supporting ground position can be detected with high accuracy.

Further, according to the supporting ground position detecting apparatus 10 according to the present embodiment, as described above, the excavation energy E is displayed on the monitor 16 from the depth at which the tip of the stirring shaft 4 first reaches the unexcavated ground. With this configuration, the reaching depth of the tip of the stirring shaft 4 can be reliably detected and displayed.
In the case of performing the above-described tip processing, there is a fear that the improved column does not reach the supporting ground position due to insufficient re-penetration depth of the stirring shaft as in Conventional Examples 1 and 2, There is no danger of waste.

In the supporting ground position detecting apparatus 10 according to the present embodiment, as described above, the rotation driving motor 5 for rotating the stirring shaft 4 is used to obtain the excavation energy.
However, the excavation energy can be obtained using the rotational torque of the rotary drive motor 5.

[0040]

As described above, according to the method for detecting the position of the supporting ground in the ground improvement machine according to the first to sixth aspects of the present invention, the per-unit-penetrating depth per unit penetrating depth near the supporting ground is improved. Since the display span is smaller than that of the conventional example 1 or 2, which calculates the excavation energy, the supporting ground position is detected with higher accuracy than that of the conventional example 1 or 2. There is an excellent effect that can be.

Further, according to the method for detecting the position of a supported ground in a ground improvement machine according to a third aspect of the present invention, only by monitoring the excavation energy per unit penetration depth displayed on the display screen of the monitor, real-time monitoring is performed. Moreover, there is an excellent effect that it is possible to know that the tip of the stirring shaft has reached the supporting ground position without any individual difference.

Further, according to the supporting ground position detecting device according to claim 7 of the present invention, the excavation energy per unit penetration depth is obtained for each unit penetration depth near the supporting ground.
Since the display span is smaller than that of the conventional example 1 or 2, which calculates the entire excavation range, the support ground position can be detected with high accuracy, and the excavation energy is displayed on a monitor. By simply monitoring the display screen of the monitor, there is an excellent effect that it is possible to know that the tip of the stirring shaft has reached the supporting ground position in real time and without individual differences.

[Brief description of the drawings]

FIG. 1A is a schematic structural explanatory view of a ground improvement machine provided with a supporting ground position detecting device according to an embodiment of the present invention, and FIG. 1B is a diagram of the supporting ground position detecting device. It is a block diagram.

FIG. 2A is a diagram illustrating the relationship between the N value and the excavation depth, and FIG. 2B is a diagram illustrating the relationship between the excavation energy and the excavation depth.

FIG. 3 is a diagram showing a monitor screen of the support ground position detecting device according to the embodiment of the present invention.

4 (a) is an explanatory diagram of a relationship between excavation depth and current, FIG. 4 (b) is an explanatory diagram of a relationship between excavation depth and penetration speed, and FIG. 4 (c) according to the embodiment of the present invention. () Is an explanatory diagram of the relationship between the excavation depth and the excavation energy E.

FIG. 5 is an explanatory diagram of a support ground position reaching flow according to the embodiment of the present invention.

FIG. 6 is a schematic explanatory view showing a state of construction by a ground improvement machine according to Conventional Example 1.

FIG. 7 is a block diagram of a main part of a supporting ground position detecting device according to Conventional Example 1.

FIG. 8 is a block diagram of a main part of a support ground position detecting device according to Conventional Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ground improvement machine, 2 ... Leader, 3 ... Stirring blade, 4 ... Stirring shaft, 5 ... Rotation shaft drive motor, 10 ... Supporting ground position detection device, 11 ... Current detector, 12 ... Depth / speed detector, 13
... Rotation speed detector, 14 ... A / D converter, 15 ... Calculator, 16 ... Monitor, 16a ... Depth-drive condition display screen, 16b ... Drilling depth-digging energy relation display screen, 16c ... Drilling depth-digging Elapsed time relation display screen,
17: Recorder.

Claims (7)

[Claims] 1. A ground for detecting that a tip of a stirring shaft has reached a supporting ground position when a ground is improved by a ground improvement machine having a stirring shaft which is rotated by a rotary drive motor and driven up and down by a driving device. In the support ground position detection method in the improved machine, the current value or the rotation torque of the rotary drive motor that rotates the stirring shaft, the rotation speed of the stirring shaft, and the penetration speed of the stirring shaft, and the penetration depth of the unit near the support ground per unit penetration depth The excavation energy per unit penetration depth was determined, and when the obtained excavation energy became equal to the excavation reference energy of the support ground obtained by pre-boring survey, the tip of the stirring shaft reached the support ground position. A method for detecting a support ground position in a ground improvement machine. 2. The method according to claim 1, wherein the calculation of the excavation energy is performed when the stirring shaft reaches a depth obtained by subtracting a predetermined excavation depth from the depth of the ground to be improved, which is obtained in advance by a boring survey. Item 2. A method for detecting a support ground position in a ground improvement machine according to item 1. 3. The method according to claim 1, wherein the excavation energy per unit penetration depth is displayed on a monitor for each unit penetration depth on a monitor. 4. The method according to claim 3, wherein the excavation energy per unit penetration depth is scrolled so that the latest constant section is always displayed on a monitor. . 5. The method according to claim 1, wherein the latest depth reached by the tip of the stirring shaft is displayed on a monitor. 6. The detection of a ground support position in a ground improvement machine according to claim 1, wherein the excavation energy is calculated when the tip of the stirring shaft is first excavated in the depth direction and is displayed on a monitor. Method. 7. A supporting ground in a ground improvement machine for detecting that the tip of the stirring shaft has reached a supporting ground position of a ground improvement machine having a stirring shaft driven to rotate by a rotary drive motor and driven up and down by a driving device. In the position detecting device, a current detector that detects a current value of a rotary drive motor that rotationally drives the stirring shaft, a depth / speed detector that detects a penetration speed of the stirring shaft, and a rotation speed of the stirring shaft is detected. A rotation speed detector, a calculation device for calculating the excavation energy per unit penetration depth for each predetermined unit penetration depth from the current value, the rotation speed, and the penetration speed detected by these detectors, and this calculation A support ground position detecting device for a ground improvement machine, comprising: a monitor for displaying a calculation result calculated by the device on a screen.