JP7826112B2 - Method for determining the location of cavities or soft areas in the ground - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Announced at the 76th Annual Academic Lecture Meeting of the National Conference in 2021 (Japan Society of Civil Engineers)

This invention belongs to the technical field of methods for determining the location of cavities or soft areas in the ground, and thus their depth range (area, scale), in advance in order to take appropriate countermeasures, particularly in the construction of impermeable walls for underground dams.

When constructing a subsurface dam impermeable wall, appropriate measures must be taken depending on the location and depth range (area, scale) of any areas that may contain cavities or soft parts (N value < 10) in order to ensure watertightness.
The specifications state that for areas that are likely to be hollow or soft based on the boring results, the load current value and hanging load during preliminary drilling will be obtained, the trends in the drilling data (preliminary drilling data) will be understood, and the location of the hollow or soft area will be determined.
In addition to the drilling data, analysis of the construction data showed that by using the integrated current value (the product of the load current value and the time required to excavate 0.5 m) and the drilling speed among the drilling data, it was possible to grasp the tendency of the cavity or soft part. However, although the tendency of the layer that is thought to be the cavity or soft part was grasped, it was not possible to obtain the same tendency for all the cavity or soft parts of the test piles (near the boring), so it is currently difficult to apply this as a means of accurately determining the location of the cavity or soft part.

For example, one method is to determine whether a cavity exists based on the load current value and hanging load, but since the drilling speed affects the load current value, it is thought that accurate determination is difficult with this method. Geological changes due to injection pressure have also been checked, but since there is no clear difference in the permeability coefficient between the Ryukyu limestone and the cavity or soft part, it is thought that determination is difficult.

Incidentally, Patent Document 1 discloses a method for determining the position of a water-impermeable layer developed by the present applicant. This method for determining the position of a water-impermeable layer is a very useful technique because it allows the position of the water-impermeable layer to be determined with high accuracy.
However, in the technical field of methods for determining the location of cavities or soft parts in the ground, the reality is that there is no method yet available that is as accurate and reliable as the method for determining the location of a water-impermeable layer described in Patent Document 1.

Patent No. 5475175

Therefore, an object of the present invention is to provide a method for determining the location of cavities or soft parts in the ground that is highly reliable and can accurately determine the location of cavities or soft parts in the ground, and ultimately the depth range.
Another object of the present invention is to provide a highly reliable method for determining the location of cavities or soft areas in the ground, which can accurately determine the location of cavities or soft areas in the ground in real time while a drilling machine is drilling a hole.

As a means for solving the problems of the background art, a method for determining the location of a cavity or soft part in the ground according to claim 1 is a method for determining the location of a cavity or soft part in the ground prior to construction of a water impermeable wall, comprising:
a step of measuring the three parameters of the load current value of the reducer at the penetration depth of the drilling machine that pre-drills the ground, the pressing load obtained by subtracting the hanging load from the weight of the drilling shaft of the drilling machine, and the drilling speed of the drilling machine at set time intervals;
a step of plotting the three parameters against the penetration depth of the drilling machine after performing moving average processing on the measurement values at each set time lapse;
The method is characterized by comprising a step of determining the position of a cavity or soft part in the ground by comparing the value (load current value/pressing load/drilling speed) calculated by dividing the pressing load by the load current value and then dividing the value by the drilling speed for the three plotted parameters corresponding to the penetration depth of the drilling machine with a predetermined threshold value.

The invention described in claim 2 is characterized in that, in the method for determining the location of cavities or soft areas in the ground described in claim 1, a trimming process is performed on the measurement values obtained every set time period before performing the moving average process, removing measurement values associated with temporary lifting of the drilling shaft and extracting measurement values only when the drilling shaft is drilling.

The invention described in claim 3 is a method for determining the location of cavities or soft parts in the ground described in claim 1 or 2, characterized in that the threshold value for the cavities is set in the range of 0 to 2.0, and the threshold value for the soft parts is set in the range of greater than 2.0 and equal to or less than 4.1.

The method for determining the location of a cavity or soft part in the ground according to the present invention has the following advantages.
(1) By comparing the newly devised numerical values (load current value/pressing load/drilling speed) with the threshold values derived by the applicant based on tests and actual construction work, the location of cavities or soft areas in the ground, and in turn the depth range (area, scale), can be accurately determined (detected, identified). Furthermore, if necessary, accurate determination can be made in real time while the drilling machine is drilling.
Therefore, when constructing the subsequent impermeable wall, conventionally, measures such as mixing tough materials have been applied depending on the scale of the impermeable wall to be constructed by triaxial excavation for all depth ranges (areas, scales) where cavities or soft parts are expected in the design stage, but by applying the present invention, the location of cavities or soft parts, and therefore the depth range, can be determined, making it possible to implement appropriate measures and contributing to reducing material costs and environmental load. Therefore, a method for determining the location of cavities or soft parts in the ground can be realized that is excellent in workability, economy, and global environment friendliness.
(2) This method can be implemented in conjunction with the method for determining the position of a water-impermeable layer according to Patent No. 5475175, the patent of which is held by the present applicant, thereby enabling rational and highly accurate construction management.

1 is an elevational view showing an outline of an embodiment of the present invention; 1 is an elevational view showing an outline of an embodiment of the present invention; 1 is a table showing experimental conditions of a model experiment (model test) conducted by the applicant. As an example of the experiment shown in Figure 3, for the measurement results (drilling data) of Test No. 1 (Condition 1-1) under Experimental Condition 1, the load current value (current) of the reducer at the penetration depth of the drilling machine, the pressing load obtained by subtracting the hanging load from the weight of the drilling shaft of the drilling machine, and the drilling speed (speed) of the drilling machine are plotted as a graph. 3, the graph plots the three parameters for the measurement results of Test No. 1 (Condition 2-1) under Experimental Condition 2, as an example, following FIG. 4. The graph on the left plots the numerical values (load current value/pressing load/drilling speed) that are characteristic of the present invention at the penetration depth of the drilling machine, based on the plotted data of Test No. 1 (Condition 2-1) of Experimental Condition 2 in Figure 5, and the graphs in the center and on the right are graphs of Condition 2-2 and Condition 2-3, respectively, following Condition 2-1. Following the example of condition 2-1, the figures are graphs of the values (load current value/pressing load/drilling speed) for test Nos. 1 and 3 (conditions 3-1 and 3-3) under experimental condition 3 in the experiment shown in Figure 3. Note that condition 3-2 was excluded because the values were negative. Following the above-mentioned condition 2-1, the above-mentioned numerical values (load current value/pressing load/drilling speed) are graphed for Test Nos. 1, 2, and 3 (conditions 4-1, 4-2, and 4-3) under experimental condition 4 in the experiment shown in FIG. Following the above-mentioned condition 2-1, the above-mentioned numerical values (load current value/pressing load/drilling speed) are graphed for Test Nos. 1, 2, and 3 (condition 1-1, condition 1-2, and condition 1-3) under experimental condition 1 in the experiment shown in FIG. Following the example of condition 2-1, the figures are graphs of the values (load current value/pressing load/drilling speed) for test Nos. 1 and 2 (conditions 5-1 and 5-2) under experimental condition 5 in the experiment shown in Figure 3. Note that condition 5-3 was excluded because the values were negative. 4 is a table showing threshold values derived by the present applicant from a large amount of data based on the results of model experiments for the experimental conditions 1 to 5 shown in FIG. 3. This is a graph that randomly shows the drilling data (pile data) of one of the drilling data (pile data) obtained during the actual construction (part 1) (called pile number 13 during the actual construction). Of the graphs randomly shown in Figure 12, this is an enlarged view of the second graph from the right at the bottom, i.e., a graph plotting the numerical values (load current value/pressing load/drilling speed) that are characteristic of the present invention at the penetration depth of the drilling machine. 4 is a table showing specifications of the model experiment conducted by the present applicant according to FIG. 3 . 4 is a table showing material data used in the model experiment conducted by the present applicant according to FIG. 3.

The present invention relates to a method for determining the location and depth range (area, scale) of cavities or soft parts in the ground 1 using a drilling machine 10 such as an earth auger, as shown in Figures 1 and 2, prior to the construction of a water barrier wall using a ground improvement treatment machine such as a triaxial (multiaxial) ground improvement machine.
In short, the present invention is suitable for use in construction of impermeable walls, particularly for construction of underground dam impermeable walls, where measures such as mixing toughened materials are carried out only as needed rather than over the entire area, and where work efficiency (construction ease and economy) is required.
Specifically, the present invention analyzes drilling data from a drilling machine 10 such as an earth auger to determine (in real time as necessary) the location of cavities or soft areas in the ground 1, and thus the depth range (area, scale). The drilling data to be analyzed includes three parameters: the load current value (C) of the reducer at the penetration depth of the drilling machine 10, the pressing load (L) obtained by subtracting the suspended load from the weight of the drilling shaft of the drilling machine 10, and the drilling speed (S) of the drilling machine. In particular, no determination (detection) technology focusing on the pressing load (L) obtained by subtracting the suspended load from the weight of the drilling shaft of the drilling machine 10 has been found in the past, and is therefore very distinctive and innovative.
The drilling data is displayed on a computer screen in the measurement room via various measuring instruments mounted on the drilling machine 10. The penetration depth may refer to GL (ground level) or EL (altitude).

The drilling process using the drilling machine 10 is generally conventional. For example, as shown in FIG. 1, the drilling machine 10, which includes a casing 12 surrounding the auger 11, first drills a hole to a predetermined depth using the auger 11 and the casing 12, and drilling data is acquired. Next, as shown in FIG. 2, the casing 12 is disconnected, and the auger shaft is extended while the casing 12 is left in place. Further drilling is performed using only the auger 11, and drilling data is acquired. The two drilling data sets are then analyzed to determine (in real time, if necessary) the location of any cavities or soft areas in the ground, and thus the depth range (area, scale). The casing 12 left in place is then removed as appropriate.
The predetermined depth (length dimension of the casing 12) and the extension dimension of the auger 11 are set based on geological survey (drilling data) and the like provided in advance by the client.

Below, we will explain an example of a method for determining the location of cavities or soft areas in the ground according to the present invention.

The ground 1 to be drilled by the drilling machine 10 to which the present invention is applied is assumed to have a structure in which cavities or soft sections (soft alternating layers) are scattered (internal) in certain areas of an unconsolidated limestone layer (omitted for convenience of illustration).
The method of determining the position of a cavity or soft part in the ground 1 according to the present invention first follows the procedure described in paragraph [0013] above, and measures the three parameters of the load current value (C) of the reducer at the penetration depth of the drilling machine 10 that is pre-drilling the ground 1, the pressing load (L) obtained by subtracting the hanging load from the weight of the drilling shaft of the drilling machine 10, and the drilling speed (S) of the drilling machine 10 every set time (1 second in this embodiment).
Next, the three parameters (C), (L), and (S) are plotted against the penetration depth of the drilling machine after the measurement values at each set time interval have been subjected to moving average processing.
Next, for the three plotted parameters (C), (L), and (S) corresponding to the penetration depth of the drilling machine 10, the load current value (C) is divided by the pressing load (L), and then divided by the drilling speed (S) to calculate a numerical value (load current value/pressing load/drilling speed = C/L/S), which is then compared with a predetermined threshold value to determine the location of the cavity or soft part in the ground 1.
In addition, for the measurement values obtained every set time, a trimming process is performed to remove measurement values associated with temporary lifting of the drilling shaft and extract measurement values only when the drilling shaft is drilling.

Here, the circumstances by which the applicant came up with the above numerical values (load current value/pressing load/drilling speed = C/L/S) will be explained.
Based on experience and insight, the applicant has estimated that there is some correlation between the load current value (C) and cavities or soft areas in the ground when the impact load (L) and the drilling speed (S) are constant. The basis for this is that, when examining the characteristics of soft areas from the results of model experiments (model tests), it was confirmed that both the impact load (L) and the load current value (C) tend to decrease when the drilling speed (S) is constant. However, in actual construction, it is difficult to maintain a constant drilling speed (S), which affects the impact load (L) and the load current value (C), making it difficult to grasp the decreasing trend as in model experiments. Therefore, we devised the load current value (C) when the pressing load (L) and the drilling speed (S) are kept constant as an index that can be determined from the two parameters of the pressing load (L) and the load current value (C), excluding the influence of the drilling speed (S), i.e., the above-mentioned numerical value (load current value/pressing load/drilling speed = C/L/S), and we estimated that this numerical value (hereinafter abbreviated as the "CLS value"), which did not exist until now, has some correlation with cavities or soft parts in the ground.
Below, we will explain the model experiments (model tests) and actual construction work conducted by the applicant to determine whether there is a correlation between the CLS value and cavities or soft parts in the ground.

<Model experiment>
The applicant carried out a model experiment for verification purposes. The experimental conditions are shown in Figure 3.
(How to make a wooden earthenware tank)
A wooden earthen tank measuring 200 x 250 x H600 mm was used as the test specimen. A mudstone layer (H200) simulating Shimajiri Group mudstone was created at the bottom, and a layer (H400) simulating Ryukyu limestone was created before solidification. The Shimajiri Group mudstone layer was created by mixing gairome clay with cement and water, and the Ryukyu limestone layer was created by mixing granular Ryukyu limestone (maximum particle size: 5 mm) with cement and water. The cavity was created using a simulated void pipe (φ100 x H200 mm). The void pipe was removed after construction was complete.
Based on the cores collected on-site, the mix was determined to have a target uniaxial compressive strength of ^{approximately} 2,000 kN/m2 and a permeability coefficient of approximately ^10-5 for the Ryukyu limestone layer, and a target uniaxial compressive strength of approximately 500 kN/ ^m2 and a permeability coefficient of approximately ^10-5 for the mudstone layer (see also Figure 15).
(Setting values, etc.)
Drilling speed 40mm/min (21.2Hz)
Auger φ80mm
Auger rotation speed 20 rpm (9.5 Hz)
Drilling fluid injection amount 0.1L/min (24.8Hz)
The drilling fluid is discharged from one point in the center of the auger tip. Other information is shown in Figure 14.
(Measurement method)
For measurements in the experiment, a load cell was installed between the auger rotation gear motor and the swivel to measure the pressing load (reaction force from the ground) pressing the auger against the ground. The load current value of the auger rotation gear motor was output from an inverter, and the injection pressure of the drilling fluid was measured by installing a pressure gauge in a branched pipe connected to the swivel. The excavation depth was measured by measuring the lift length of the auger fixing stand using a wire displacement meter.
(Model experiment results)
Next, some of the results of the model experiment are shown in Figures 4 and 5 (for details, see the above [Brief Description of the Drawings]).
Focusing on the load current value (C), pressing load (L), and drilling speed (S), it was confirmed that under the condition that the drilling speed (S) was kept constant, both the pressing load (L) and the load current value (C) tended to decrease.

Next, graphs of the CLS values, which are a feature of the present invention and which have been recently devised by the present applicant, are shown in FIGS. 6 to 10 (for details, see the above-mentioned [Brief Description of the Drawings]).
FIG. 11 shows the threshold values derived based on the graphs showing the CLS values in FIGS.
From the above, it was found that a hollow portion or a soft portion can be determined based on the CLS value, using a predetermined threshold value as a guide.
Specifically, when the CLS value is compared with the threshold value, it is determined to be a hollow portion when it is in the range of 0 to 2.0, and it is determined to be a soft portion when it is in the range of more than 2.0 and not more than 4.1.
Furthermore, it was found that the threshold value differs depending on the type of fill soil, so it was possible to determine not only whether the area is soft, but also the type of fill soil in more detail. Knowing the type of fill soil makes it possible to consider countermeasure work in advance.

<Implementation work (part 1)>
(Setting values, etc.)
Average drilling speed: 0.5 m/min Auger: φ600 mm (same shape as the one used for the model experiment)
Auger rotation speed: 20 rpm
Drilling fluid injection rate: 45L/min. Drilling fluid is discharged from one point in the center of the auger tip.

Areas where soft parts are expected will be confirmed during construction.
Among the drilling data (pile data) acquired by the applicant, one piece of drilling data (designated pile number 13) is randomly shown in Figure 12. As a result, it was confirmed that the CLS value (load current value/pressing load/drilling speed = C/L/S) decreased in the range of N values of 10 or less, which was confirmed by nearby boring (see the N value diagram at the bottom right of Figure 12 compared with the CLS value diagram in Figure 12 (enlarged in Figure 13)).
Since the depth matched the soft part previously detected by drilling, it was assumed that it was a soft part and not a cavity.

<Implementation work (part 2)>
Drilling data was used from a drilling point 2 m away from a drilling point where an N value of 10 or less is expected between GL-16.0 m and 19.2 m. The indices examined were the CLS value, load current value x thrust load, and load current value / thrust load. From the drilling data, it was confirmed that in the range where the N value is 10 or less (GL-16.0 m to 19.2 m), the CLS value decreases at depths of GL-16.0 m to 19.2 m. Therefore, based on this fact, it is believed that by determining a threshold value for the CLS value and determining whether a cavity or soft part exists, it is possible to determine the location of the cavity or soft part, and ultimately the depth range (area, scale).

Although the embodiments of the present invention have been described above with reference to the drawings and the like, it should be emphasized that the present invention is not limited to the above-described embodiments, and includes the range of design modifications and application variations that would normally be made by a person skilled in the art, provided that they do not deviate from the technical concept of the present invention.
For example, in the above embodiment, the set time for measuring the drilling data is 1 second, but it may be 2 seconds or more, and the design can be changed as appropriate depending on the ground properties, etc.
In addition, the moving average processing time is set to 30 seconds, but this can be changed as appropriate depending on the ground conditions, etc.
Furthermore, the trimming process can be omitted if the drilling data does not overlap or if the behavior of the plot points is clearly visible.
In addition, the length of the casing 12 and the extension length of the auger 11 can be appropriately changed in design depending on the boring data obtained in advance. The average drilling speed (penetration speed) of the drilling machine 10 is not limited to about 0.5 m/min, and can be appropriately changed in design depending on the ground properties.

1 Target ground 10 Drilling machine 11 Auger 12 Casing

Claims (3)

A method for determining the location of a cavity or soft part in the ground prior to construction of a water barrier wall, comprising:
a step of measuring the three parameters of the load current value of the reducer at the penetration depth of the drilling machine that pre-drills the ground, the pressing load obtained by subtracting the hanging load from the weight of the drilling shaft of the drilling machine, and the drilling speed of the drilling machine at set time intervals;
a step of plotting the three parameters against the penetration depth of the drilling machine after performing moving average processing on the measurement values at each set time lapse;
a step of determining the location of a cavity or soft part in the ground by comparing a numerical value (load current value/pressing load/drilling speed) calculated by dividing the pressing load from the load current value and then dividing the calculated value by the drilling speed for the three plotted parameters corresponding to the penetration depth of the drilling machine with a preset threshold value;
A method for determining the location of a cavity or soft part in the ground, comprising: The method for determining the location of cavities or soft areas in the ground described in claim 1, characterized in that, before performing the moving average process on the measurement values obtained every set time, a trimming process is performed to remove measurement values associated with the temporary lifting of the drilling shaft and extract measurement values only when the drilling shaft is drilling. A method for determining the location of cavities or soft parts in the ground described in claim 1 or 2, characterized in that the threshold for the cavities is set in the range of 0 to 2.0, and the threshold for the soft parts is set in the range of greater than 2.0 and less than or equal to 4.1.