Ground investigation method

Abstract

To provide a ground investigation method that enables immediate determination of hardness and softness of a ground through an efficient ground investigation using a minimum number of measuring devices.SOLUTION: A ground investigation method for investigating hardness and softness of a ground comprises: a step (step S1) of preparing in advance a determination database in which a relationship between a penetration speed obtained when a rod penetrates a ground or an index equivalent to it and a ground constant is set; steps (steps S3, S4) of operating a vibration exciter operated when the rod penetrates into a ground to be investigated and measuring an elapsed time until the rod reaches a predetermined amount of penetration; and a step (step S6) of determining hardness and softness of the ground to be investigated using the amount of penetration, the elapsed time, and the determination database.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ground investigation method for investigating the hardness or softness of the ground, such as whether or not differential settlement occurs. [Background technology]

[0002] When building a house or other building on the ground, it is necessary to investigate whether the ground has enough 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.

[0003] For example, Patent Document 1 discloses a ground investigation device and a ground investigation method for investigating a target ground, which can determine the liquefaction of the ground and evaluate its support performance by penetrating a casing using a vibrator.

[0004] Furthermore, in contrast to Patent Document 1, Patent Document 2 discloses a method of using a Swedish sounding test machine or the like to measure the amount of penetration, and of equipping the penetrating rod with a strain gauge. With these methods, it is possible to obtain an index relating to the rigidity of the ground from the relationship between the load and the amount of penetration, for example. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-17112 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-178490 Summary of the Invention [Problem to be solved by the invention]

[0006] 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 increases costs for processing the data to obtain the final index.

[0007] Therefore, an object of the present invention is to provide a ground investigation method that enables the hardness of the ground to be determined instantly through an efficient ground investigation using a minimum amount of measuring equipment. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, 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 in advance 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 a ground constant is set; operating a vibrator or exciter that is operated when the rod penetrates the ground to be investigated, and measuring the elapsed time until the rod reaches a predetermined penetration amount; and judging the hardness of the ground to be investigated based on the penetration amount, the elapsed time, and the judgment database.

[0009] The penetration amount can be detected based on the division points for each unit length provided in advance on the rod. The penetration amount can also be detected by a displacement meter. Furthermore, the penetration amount can be recorded by a dynamic recording device with a short sampling period. [Effects of the Invention]

[0010] In the ground investigation method of the present invention configured as described above, a judgment database is prepared in advance based on the relationship between the existing penetration speed index and the ground constants, and then a ground investigation is carried out on the target ground.

[0011] Then, based on the elapsed time required for each penetration amount obtained by the ground survey and the judgment database, the hardness of the ground in the penetration range, such as each layer of the ground, is judged.

[0012] Therefore, the hardness of the ground can be immediately determined by conducting a ground survey using only the minimum necessary measuring equipment, or without installing any special 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 can be determined immediately on site.

[0013] 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 the section. Furthermore, by using a displacement meter, it becomes possible to judge the hardness or softness of the ground in even finer units.

[0014] 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. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart illustrating a processing flow of a ground investigation method according to the present embodiment. [Figure 2] FIG. 10 is an explanatory diagram illustrating a visualized example of a determination database. [Figure 3] 1 is an explanatory diagram illustrating the configuration of a ground investigation device and a ground investigation situation performed using the same; [Figure 4] 1 is an explanatory diagram showing the configuration of a ground investigation device according to a first embodiment. [Figure 5] FIG. 2 is an explanatory diagram illustrating the results of the ground investigation in Example 1. [Figure 6] FIG. 10 is an explanatory diagram showing the configuration of a ground investigation device according to a second embodiment. [Figure 7] FIG. 10 is an explanatory diagram illustrating the results of the ground investigation in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] Penetration tests include, for example, dynamic penetration tests, which involve drilling a hole to the target layer, dropping a weight on the layer, and evaluating the hardness of the layer based on the number of times (N value) it takes to achieve a certain penetration amount, similar to standard penetration tests.

[0018] There are also static penetration tests, such as the Swedish sounding test, which indirectly evaluate the support performance of the layer by determining whether or not there is settlement when a weight is loaded on a rod and the degree of resistance when it is rotated and penetrated.

[0019] Here, if a vibrator is attached to a penetration testing machine used in boring or Swedish sounding tests, and the machine is designed to dynamically strike the stratum being investigated, the excavation will destroy the ground as it progresses, making it possible to obtain an index that is related to strength.

[0020] In the ground investigation method of this embodiment, as visualized and exemplified in Figure 2, a judgment database is prepared in advance in which the relationship between the N value of the standard penetration test, which is one of the ground constants related to strength, 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 is set.

[0021] In detail, Figure 2(a) shows a judgment database in which the relationship between the "N value" on the horizontal axis and the "time (seconds) required to penetrate 1 m" on the vertical axis is set. The "time (seconds) required to penetrate 1 m" can also be converted to the penetration speed, so it is an index equivalent to the penetration speed.

[0022] 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 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 penetration" on the vertical axis is set.

[0023] The configuration of the ground investigation device 1 used in the ground investigation method of this embodiment will be described below with reference to Fig. 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 reconnaissance at the building construction site, document investigation related to the construction site, and tests (described later) are carried out at one or more points on the target ground G.

[0024] The penetration test 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 test machine that has a proven track record in soil investigations of small buildings.

[0025] The rod 22 is made up of unit rods 221 of 1 m or 50 cm connected together. In other words, the ground investigation is carried out by adding the unit rods 221. Then, by attaching a vibrator 3 to the penetration test machine 2 and applying impacts, it becomes possible to evaluate the hardness or softness of the ground more efficiently than with the Swedish sounding test.

[0026] 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 operation of the vibrator 3, such as starting and stopping, can be controlled by operating a switch 31.

[0027] When switch 31 is turned on to start the vibrator 3, the rod 22 starts to penetrate, and when it reaches a predetermined 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 to the end of penetration 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.

[0028] 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.

[0029] The data that forms the basis for creating the judgment database can be the results of existing ground investigations 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 of various soil types, and create the judgment database in advance from the results of those investigations. In other words, the data that forms the basis of this judgment database is not the results of the ground investigation of the ground to be investigated.

[0030] 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 above-mentioned ground investigation device 1. That is, as shown in Fig. 3, the vibration exciter 3 continues to apply impacts to the target ground G, which is the ground to be investigated, while measuring the elapsed time (step S3).

[0031] When the upper end of the uppermost unit rod 221 is struck by the vibrator 3, the load is transmitted through the rod 22, and the screw point 23 at the tip advances while receiving resistance from the target ground G.

[0032] Therefore, the time is measured from the time when the vibrator 3 is started and penetration begins (see the left diagram in FIG. 3) to the time when the entire length of the unit rod 221 is penetrated (see the right diagram in FIG. 3). In short, the length of 1 m of the unit rod 221 is set as the predetermined penetration amount, and when the penetration of the entire length of the unit rod 221 is completed, the switch 31 is operated to stop the vibrator 3 (step S4).

[0033] In step S5, the relationship with the ground constants is confirmed based on the results (penetration amount and elapsed time) of the ground investigation by the ground investigation device 1. In other words, a comparison is made with the determination database shown in Fig. 2(a).

[0034] 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 FIG. 2(a).

[0035] Next, the operation of the ground investigation method of this embodiment will be described. In the ground investigation method of this embodiment configured as 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.

[0036] Then, based on the elapsed time required for each penetration amount and the judgment database obtained in a ground survey in which a rod 22 is penetrated into the target ground G by striking it with a vibrator 3, the hardness of the ground in the penetrated area, such as each layer of the ground, is determined.

[0037] For this reason, 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 speed 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. [Example]

[0038] Hereinafter, another embodiment of the ground investigation method different from the embodiment described above will be described with reference to Figures 4 and 5. Note that the same or equivalent parts as those described in the embodiment will be described using the same terms or symbols.

[0039] 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 a plurality of division portions 41.

[0040] Specifically, the processed rod 4 is provided with grooves that go around the cylindrical shaft at intervals of 20 cm in the axial direction as division sections 41. In other words, a 1 m unit rod is divided into divisions at unit lengths of 20 cm.

[0041] When conducting a ground survey using such a processed rod 4, the vibrator 3 is started and penetration begins, and then the operation of the vibrator 3 is stopped at intervals 41 every 20 cm to check the time taken for each interval.

[0042] The ground investigation device 1A can also be provided with a detection device 5 for detecting the delimitation point 41. For example, the detection device 5, which can detect the delimitation point 41 using a physical mechanism or minimal optical measuring equipment, can be attached to the base 24 of the penetration tester 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.

[0043] 5 is an explanatory diagram illustrating the results of a ground investigation performed by the ground investigation method of Example 1 using the ground investigation device 1A equipped with the processing rod 4. In this example, the vibrator 3 is not stopped at each division point 41, but the division detection signal generated by the detection device 5 is recorded in addition to the elapsed time.

[0044] 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.

[0045] 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 degree of hardness of the ground (stratum) in that section.

[0046] In short, the penetration amount can be associated with a stratum that can be identified by the depth of the target ground G, and a stratum with a short elapsed time in the section can be determined to be soft ground with a small N value, while a stratum with a long elapsed time in the section can be determined to be hard ground with a large N value.

[0047] With the ground investigation method of Example 1, it is possible to check the average ground strength (N value) of the target ground G over a 20 cm area without using high-precision instruments. That is, by using a rod with divisions 41 provided every 20 cm, such as the processed rod 4, it becomes easy to check 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 a ground investigation efficiently.

[0048] The other configurations and effects are substantially the same as those of the above-described embodiment or other examples, and therefore the description thereof will be omitted. [Example]

[0049] Hereinafter, an embodiment different from the ground investigation method of the above-described embodiment and Example 1 will be described with reference to Figures 6 and 7. Note that the same or equivalent parts as those described in the above-described embodiment or Example 1 will be described using the same terms or symbols.

[0050] 6 is an explanatory diagram showing the configuration of a ground investigation device 1B of Example 2. A minimum, simple potentiometer-type displacement meter 6 is attached to the penetration testing machine 2 of the ground investigation device 1B of Example 2.

[0051] 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 a wire 61 drawn out from the displacement meter 6 is connected to the stage of the base machine 21, which descends as the rod 22 penetrates.

[0052] 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, which is averaged over 1 cm and is almost continuous in the depth direction.

[0053] 7 is an explanatory diagram illustrating, in the form of a table, the results of a ground investigation performed by the ground investigation method of Example 2 using the ground investigation device 1B equipped with the 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.

[0054] 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.

[0055] According to the ground investigation method of Example 2, it becomes possible to instantly determine the hardness of the ground on site in units smaller than the length of a unit rod of 1 m (for example, 1 cm).

[0056] In this case, even if we assume soft ground with almost no penetration resistance and the rod 22 being penetrated at a speed close to that of a drop, 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.

[0057] The other configurations and effects are substantially the same as those of the above-described embodiment or other examples, and therefore the description thereof will be omitted.

[0058] The embodiments of the present invention have been described above in detail with reference to the drawings, but the specific configuration is not limited to these embodiments or examples, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0059] For example, in the above-mentioned embodiment and examples, a ground investigation of the ground to be investigated is described as being carried out by attaching a vibrator 3 to a penetration testing machine 2 for a Swedish sounding test, but this is not limited to this.

[0060] For example, a ground survey of the target ground can be carried out using a vibration exciter that penetrates the rod 22 by vibration and a laser displacement meter that measures the distance between the vibration exciter and the ground surface. In short, the ground survey of the target ground can be carried out by any method that directly strikes the ground with a rod and checks the strength (hardness) of the ground from the time required for the rod to penetrate to a predetermined depth. [Explanation of symbols]

[0061] G: Target ground (survey target ground) 1: Ground investigation equipment 22: Rod 3: Vibrator 1A: Ground investigation equipment 4: Processing rod (rod) 41: Break point 5:Detection device 1B: Ground investigation equipment 6: Displacement meter

Claims

[Claim 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 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.

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