JP7750768B2 - Ground investigation method - Google Patents

Description

The present invention relates to a ground investigation method for investigating the hardness and softness of the ground, such as whether differential settlement will occur.

When building a house or other building on the ground, it is necessary to investigate whether the ground has enough bearing capacity (bearing capacity) to support the weight of the building, as well as whether the ground is susceptible to damage due to differential settlement. It is also advisable to investigate whether the ground is susceptible to damage due to earthquakes.

For example, Patent Document 1 discloses a ground investigation device and method for investigating target ground, which uses a vibrator to penetrate a casing to determine whether the ground is susceptible to liquefaction and evaluate its bearing capacity.

Furthermore, in contrast to Patent Document 1, Patent Document 2 discloses a method that uses a Swedish sounding test machine or similar to measure the amount of penetration, and equips the penetrating rod with a strain gauge. With these methods, it is possible to obtain an index related to the rigidity of the ground, for example, from the relationship between load and amount of penetration.

Japanese Patent Application Laid-Open No. 2018-17112 JP 2019-178490 A

However, using multiple measuring devices or requiring highly accurate instruments, such as the soil survey device mentioned above, increases costs and the risk of failure, and also incurs costs for processing the data to obtain the final index.

The present invention aims to provide a ground investigation method that enables the immediate determination of the hardness of the ground through efficient ground investigation using a minimum amount of measuring equipment.

To achieve the above-mentioned objective, the ground investigation method of the present invention is a ground investigation method for investigating the hardness of the ground, and is characterized by comprising the steps of: preparing a judgment database in which the relationship between the penetration speed or an index equivalent thereto obtained when a rod is penetrated into the ground and ground constants is set; operating a vibrator or exciter that is operated when the rod penetrates the ground under investigation and measuring the elapsed time until the rod reaches a predetermined penetration depth; and judging the hardness of the ground under investigation based on the penetration depth, the elapsed time, and the judgment database.

Here, the penetration amount can be detected based on division points for each unit length that are pre-established on the rod. The penetration amount can also be detected using a displacement meter. Furthermore, the penetration amount can also be recorded using a dynamic recording device with a short sampling period.

The ground investigation method of the present invention, configured in this way, involves preparing in advance a judgment database that is set up based on the relationship between previous penetration speed-related indicators and ground constants. Ground investigations are then carried out on the ground to be investigated.

Then, using the elapsed time required for each penetration amount obtained from the ground survey and the judgment database, the hardness of the ground in the penetration area, such as each layer of the ground, is determined.

As a result, the hardness of the ground can be immediately determined by conducting a ground survey without installing any special measuring equipment, or using only the minimum necessary measuring equipment. In other words, unlike conventional methods, no special analysis processing is required for the index obtained from the survey, and it is efficient because it allows for immediate determination on site.

Furthermore, if the rod is divided into sections at each unit length, it becomes easy to check the elapsed time for each section by detecting these sections. Furthermore, by using a displacement meter, it becomes possible to determine the hardness or softness of the ground in even finer increments.

Furthermore, if the penetration amount is recorded using a dynamic recording device with a short sampling period, it will be possible to immediately determine the hardness of the ground on site, even if the ground being investigated is soft.

1 is a flowchart illustrating a processing flow of a ground investigation method according to the present embodiment. FIG. 10 is an explanatory diagram illustrating a visualized example of a determination database. 1 is an explanatory diagram illustrating the configuration of a ground investigation device and a ground investigation situation performed using the same; 1 is an explanatory diagram showing the configuration of a ground investigation device according to a first embodiment; FIG. 2 is an explanatory diagram illustrating the results of the ground investigation in Example 1. FIG. 10 is an explanatory diagram showing the configuration of a ground investigation device according to a second embodiment. FIG. 10 is an explanatory diagram illustrating the results of the ground investigation in Example 2.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The ground investigation method of this embodiment is applied to the ground to be investigated for constructing a building such as a house. The ground to be investigated is usually subjected to a ground investigation such as a penetration test directly at one or more points.

One type of penetration test, like the standard penetration test, involves drilling a hole to the target layer, dropping a weight onto the layer, and evaluating the hardness of the layer based on the number of times (N value) it takes to achieve a certain penetration depth.

There are also static penetration tests, such as the Swedish sounding test, which indirectly evaluate the bearing capacity of a layer by determining whether or not there is settlement when a weight is loaded onto a rod, and the degree of resistance when it is rotated and penetrated.

If a vibrator is attached to a boring or Swedish sounding test penetration testing machine, and the machine is used to dynamically impact the geological layer being investigated, the excavation will destroy the ground as it progresses, making it possible to obtain an index that is related to strength.

In the ground investigation method of this embodiment, as visualized and exemplified in Figure 2, a judgment database is prepared in advance that sets the relationship between the N value of the standard penetration test, which is one of the strength-related ground constants, the converted N value obtained from the relationship between the N value of the standard penetration test and the penetration resistance value of the Swedish sounding test, and the penetration speed or an index equivalent thereto.

In detail, Figure 2(a) shows a judgment database that sets the relationship between the "N value" on the horizontal axis and the "time (seconds) required to penetrate 1 m" on the vertical axis. The "time (seconds) required to penetrate 1 m" can also be converted to penetration speed, and is therefore an index equivalent to penetration speed.

Similarly, Figure 2(b) is a judgment database in which the relationship between the "N value" on the horizontal axis and the "time (seconds) required for 20 cm of penetration" on the vertical axis is set. And Figure 2(c) is a judgment database in which the relationship between the "N value" on the horizontal axis and the "time (seconds) required for 1 cm of penetration" on the vertical axis is set.

The configuration of the ground investigation device 1 used in the ground investigation method of this embodiment will be described below with reference to Figure 3. This ground investigation device 1 is directly applied to the ground to be investigated (target ground G) on which a building such as a house will be constructed. In other words, on-site surveys of the building construction site, document investigations related to the construction site, and tests (described below) are conducted at one or more points on the target ground G.

The penetration testing machine 2 for the Swedish sounding test (SWS test) shown in Figure 3 is mainly composed of a base machine 21, a rod 22, and a screw point 23 attached to the tip of the rod 22. The base machine 21 is a Swedish sounding testing machine with a proven track record in soil surveys for small-scale buildings.

The rods 22 are made up of unit rods 221 of 1 m or 50 cm length connected together. In other words, the ground investigation is carried out by adding more unit rods 221. Then, by attaching a vibrator 3 to the penetration tester 2 and applying impacts, it becomes possible to evaluate the hardness or softness of the ground more efficiently than with a Swedish sounding test.

In the ground investigation method of this embodiment, a rod 22 with a screw point 23 attached to its tip is inserted in 1 meter increments. The vibration exciter 3 can be controlled by operating a switch 31 to start and stop the operation.

When switch 31 is turned on to start the vibrator 3, the rod 22 begins to penetrate, and when it reaches the specified penetration amount (1 m length of the unit rod 221), switch 31 is turned off to stop the vibrator 3. At this time, the elapsed time from the start of penetration to its completion is confirmed, and by applying this to the judgment database shown in Figure 2(a), the average strength of the ground over 1 m (N value) can be confirmed.

Next, the ground investigation method of this embodiment will be described.
As shown in the flowchart of FIG. 1, which explains the processing flow of the ground investigation method, in step S1, a determination database is created.

The data that forms the basis for creating the judgment database can be the results of existing ground surveys that have been accumulated up to that point, or ground data obtained from literature, etc. It is also possible to use the ground investigation device 1 to conduct preliminary tests on ground with various soil types, and create a judgment database in advance from the results of those surveys. In other words, the data that forms the basis of this judgment database is not the results of ground surveys of the ground being surveyed.

Next, in step S2, a ground investigation is carried out on the ground to be investigated where the house will actually be constructed. The ground investigation is carried out, for example, using the ground investigation device 1 described above. That is, as shown in Figure 3, the vibrator 3 continues to apply impacts to the target ground G, which is the ground to be investigated, while measuring the elapsed time (step S3).

When the vibrator 3 strikes the upper end of the top unit rod 221, the load is transmitted through the rod 22, and the screw point 23 at the tip is propelled forward while receiving resistance from the target ground G.

The time is measured from the time when the vibrator 3 is started and penetration begins (see the left diagram in Figure 3) to the time when the entire length of the unit rod 221 is penetrated (see the right diagram in Figure 3). In other words, the length of the unit rod 221, 1 m, is set as the predetermined penetration amount, and once the entire length of the unit rod 221 has penetrated, the switch 31 is operated to stop the vibrator 3 (step S4).

In step S5, based on the results of the ground investigation performed by the ground investigation device 1 (penetration amount and elapsed time), the relationship with the ground constants is confirmed. In other words, a comparison is made with the determination database shown in Figure 2(a).

Then, in step S6, the hardness of each layer of the target ground G is determined based on the N value obtained by applying the elapsed time to the determination database in Figure 2(a).

Next, the operation of the ground investigation method of this embodiment will be described.
In the ground investigation method of this embodiment configured as described above, a judgment database is prepared in advance based on the relationship between the previous penetration speed index and the ground constants, and then a ground investigation is carried out on the ground to be investigated.

Then, based on the elapsed time required for each penetration amount obtained in the ground survey in which the rod 22 is penetrated into the target ground G by striking it with the vibrator 3 and the judgment database, the hardness of the ground in the penetrated area, such as each layer of the ground, is determined.

As a result, the hardness of the ground can be immediately determined by conducting a ground survey using only the minimum necessary measuring equipment, or without installing special measuring devices such as high-precision instruments. In other words, unlike conventional methods, no special analytical processing is required for the penetration rate index obtained from the survey (such as the elapsed time required for a certain amount of penetration), and it is efficient because it can be determined immediately on site.

An embodiment of the ground investigation method different from the embodiment described above will be described below with reference to Figures 4 and 5. Note that parts that are the same or equivalent to those described in the embodiment above will be described using the same terms or symbols.

Figure 4 is an explanatory diagram showing the configuration of the ground investigation device 1A of Example 1. The rod attached to the penetration testing machine 2 of the ground investigation device 1A of Example 1 is a processed rod 4 provided with multiple divisions 41.

In detail, the processed rod 4 has grooves that run around the cylindrical shaft every 20 cm in the axial direction, forming divisions 41. In other words, for a 1 m unit rod, divisions are provided every 20 cm of unit length.

When conducting a ground survey using such a processed rod 4, the vibrator 3 is started and penetration begins, then the operation of the vibrator 3 is stopped at intervals 41 every 20 cm, and the time taken for each interval is checked.

The ground investigation device 1A can also be equipped with a detection device 5 for detecting the delimitation point 41. For example, a detection device 5 capable of detecting the delimitation point 41 using a physical mechanism or minimal optical measuring equipment can be attached to the base 24 of the penetration testing machine 2, which is less susceptible to the impact force when the processing rod 4 is struck. For example, the vibrator 3 can be set to automatically stop in response to a detection signal from the detection device 5.

Figure 5 is an explanatory diagram illustrating the results of a ground investigation using the ground investigation method of Example 1, performed using the ground investigation device 1A equipped with a processing rod 4. In this example, rather than stopping the vibrator 3 at each division point 41, the division detection signal generated by the detection device 5 was recorded along with the elapsed time.

The points where a convex boundary detection signal appears in Figure 5 indicate the time when boundary point 41 was passed, and the elapsed time for each section until the penetration amount reached 20 cm, 40 cm, 60 cm, 80 cm, and 100 cm can be calculated.

The calculated elapsed time for each section is compared with the judgment database shown in Figure 2(b), and the N value obtained by applying the elapsed time becomes the judgment result indicating the hardness or softness of the ground (stratum) in that section.

In other words, the penetration amount can be associated with a stratum that can be identified by the depth of the target ground G, and it can be determined that a stratum with a short elapsed time in the section is soft ground with a small N value, while a stratum with a long elapsed time in the section is hard ground with a large N value.

With the ground investigation method of Example 1, it is possible to confirm the average ground strength (N value) over a 20 cm area of the target ground G without using high-precision instruments. In other words, by using a rod with divisions 41 every 20 cm, such as the processed rod 4, it becomes easy to confirm the elapsed time for each section. Furthermore, by combining it with a detection device 5 that detects the divisions 41, it becomes possible to carry out ground investigations efficiently.

Note that other configurations and effects are generally similar to those of the above-described embodiment and other examples, so explanations will be omitted.

An embodiment different from the ground investigation method of the embodiment and Example 1 described above will be described below with reference to Figures 6 and 7. Note that parts that are the same or equivalent to those described in the embodiment or Example 1 will be described using the same terms or symbols.

Figure 6 is an explanatory diagram showing the configuration of the ground investigation device 1B of Example 2. A simple potentiometer-type displacement meter 6 is attached to the penetration testing machine 2 of the ground investigation device 1B of Example 2.

In detail, a potentiometer-type displacement meter 6 is installed on the base 24 of the penetration testing machine 2, which is less susceptible to the impact force when the rod 22 is struck, and the upper end of the wire 61 drawn from the displacement meter 6 is connected to the stage of the base machine 21, which descends as the rod 22 penetrates.

By installing the displacement meter 6 in this way, it is possible to detect the amount of penetration, for example, every 1 cm, by measuring with the displacement meter 6. Then, by recording the time required for penetration every 1 cm, it is possible to confirm the strength (N value) of the ground G, averaged over 1 cm of the target ground, and in a nearly continuous manner in the depth direction.

Figure 7 is an explanatory diagram showing, in table format, the results of a ground investigation performed using the ground investigation method of Example 2, performed using the ground investigation device 1B equipped with a displacement meter 6. As can be seen from this diagram, the elapsed time for each section can be calculated from the elapsed time measured for each 1 cm of penetration.

The calculated elapsed time for each section is then compared with the judgment database shown in Figure 2(c), and the N value obtained by applying the elapsed time can be used as a judgment result indicating the hardness or softness of the ground (stratum) in that section.

The soil investigation method of Example 2 makes it possible to instantly determine the hardness of the ground on-site in units smaller than the length of a 1-meter unit rod (for example, 1 cm).

In this case, even if we assume soft ground with almost no penetration resistance, where the rod 22 penetrates at a speed close to falling, it will be possible to make a sufficient judgment by using a dynamic recording device with a sampling period of, for example, 1/1000 of a second or less.

Note that other configurations and effects are generally similar to those of the above-described embodiment and other examples, so explanations will be omitted.

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment or example, and design changes that do not deviate from the gist of the present invention are included in the present invention.

For example, in the above-described embodiment and examples, a ground survey of the target ground is described as being carried out by attaching a vibrator 3 to a Swedish sounding test penetration testing machine 2, but the present invention is not limited to this.

For example, a ground survey of the target ground can be carried out using a vibration exciter that penetrates the rod 22 with vibration, and a laser displacement meter that measures the distance between the exciter and the ground surface. In other words, any method can be used to directly strike the ground with a rod and determine the strength (hardness) of the ground from the time required for the rod to penetrate to a predetermined depth.

G: Target ground (survey target ground)
1: Ground investigation device 22: Rod 3: Vibrator 1A: Ground investigation device 4: Processing rod (rod)
41: Separation point 5: Detection device 1B: Ground investigation device 6: Displacement meter

Claims (1)

A ground investigation method for investigating the hardness and softness of the ground,
a step of preparing a determination database in which the relationship between the time required to penetrate a unit length of the ground and a ground constant is set;
A step of operating a vibration exciter or vibration generator that is operated when the rod penetrates into the ground to be investigated, and measuring the elapsed time until the penetration amount of the unit length that can be detected by the division points for each unit length that are previously provided on the rod is reached;
A ground investigation method characterized by comprising a step of determining the hardness or softness of the ground to be investigated based on the penetration amount per unit length , the elapsed time, and the determination database.