JPH0621446B2 - Ground survey method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ground investigation method for investigating properties of the ground by performing a penetration test in which a test piece penetrates into the ground.

[Conventional technology]

As a penetration test of the above-mentioned ground survey method, a test piece called a sampler is driven into the ground by a free fall of a hammer, and the number of hits required for penetrating this sampler by 30 cm is the relative hardness and softness of soil. The value N
The standard penetration test for value is widely known.

From the N value obtained by this standard penetration test, it is possible to estimate the properties of various types of soil as described above, and on the basis of this, the design of pile foundations in buildings and the like is performed.

By the way, in addition to a vertical load such as the self-weight of a building, a pulling load acts on the pile foundation during an earthquake or the like. Therefore, it is necessary to consider the pull-out load when designing the pile. In order to do so, it is necessary to know the peripheral frictional force of the pile, which is the pull-out strength together with the weight of the pile.

Conventionally, the following means have been adopted to obtain the above-mentioned peripheral frictional force.

One of them is a means for performing a standard penetration test as a penetration test, and calculating and obtaining the circumferential surface frictional force using the N value obtained by the standard penetration test and the design formula.

The other is a method to be carried out as a part of the static penetration test, as shown in Japanese Examined Patent Publication No. 46-1498, as a test piece for penetration into the ground, as a detection part for detecting penetration resistance and at the time of penetration. It is a means for obtaining the test piece by statically penetrating the test piece and measuring the peripheral frictional force at the time of the static penetration, using a measuring cone provided with a detecting section for detecting the peripheral frictional force.

[Problems to be solved by the invention]

However, among the conventional techniques described above, when the means for obtaining the peripheral frictional force using the N value obtained by the former standard penetration test and the design formula is used, the N value also includes the element of the tip supporting force. Due to the fact that the peripheral friction force calculated from this design formula is set to be on the safe side, the peripheral friction force obtained will be a small value that allows for an unnecessarily large safety factor. .

Therefore, when designing using the peripheral frictional force obtained by this former means, the pulling load at the time of an earthquake will be exclusively resisted by the own weight of the pile, and the pile will be large and sometimes unusable. There was a fear that a large scale one would be used as needed. In other words, the ratio of the peripheral frictional force to the reference of the design of the pile foundation, such as the one with a large peripheral frictional force or the one with a small peripheral frictional force, is obtained, and the rational pile foundation design with little excess performance is obtained. It has been difficult to obtain a practically accurate peripheral frictional force that is sufficiently useful for

On the other hand, when the latter means is used, the peripheral friction force is obtained by measurement, so it is easy to obtain the peripheral friction force of practical accuracy, but the peripheral friction force during static penetration of the measuring cone is measured. There was such a drawback.

Since the penetration resistance applied to the measuring cone changes due to the change in the hardness of the ground, even if a highly precise penetrating device for penetrating the measuring cone is used, the measuring cone is affected by the change in the penetrating resistance. It was difficult to measure the frictional force on the peripheral surface with high accuracy. That is, it is difficult to obtain a highly accurate frictional force on the peripheral surface and the reliability is low. Moreover, it is considered that static penetration of the measurement cone is not possible on the ground where the N value is 20 in sandy soil and the N value is larger than approximately 10 in cohesive soil. The peripheral frictional force could be measured only on the ground with a small N value, and it was not possible to investigate all of the ground with an N value within the range where a general standard penetration test could be carried out. .

An object of the present invention is to provide a ground survey method which can easily obtain a highly accurate peripheral frictional force of a pile and can be carried out if the ground can carry out a standard penetration test.

[Means for solving problems]

The feature of the ground investigation method according to the present invention is that, as the penetration test, N is obtained by driving a test piece into the ground until a predetermined amount of penetration is achieved.
The point is to perform a standard penetration test to measure the value and measure the pull-out resistance when the test piece after driving in the standard penetration test is pulled out from the ground.

[Work]

That is, in performing a penetration test such as a standard penetration test, there is always a process of pulling out the test piece from the ground.
In addition, when the test piece is pulled out, the moving speed of the test piece can be easily maintained at a constant speed, as compared with the case where the test piece is penetrated, because there is no penetration resistance that changes due to changes in the hardness of the ground.

Focusing on the above points, in the pulling out process of the test piece after the penetration test, since the pulling resistance force that correlates with the peripheral friction force is measured, regardless of the hardness change of the ground,
The pull-out speed of the test piece can be easily maintained at a constant speed, and the pull-out resistance force can be accurately detected.As a result, the pull-out resistance force can be obtained from the pull-out resistance force based on the correlation between the pull-out resistance force and the peripheral friction force. The peripheral frictional force generated can be made highly accurate.

Moreover, as a penetration test as a preparatory work for measuring the pull-out resistance, a standard penetration test, which is one of the dynamic penetration tests that can target the ground with a larger N value than the static penetration test, is performed. Therefore, it is possible to measure the pull-out resistance force if the ground has an N value that can perform a standard penetration test, and the peripheral surface friction of the ground with a larger N value than before, which was obtained in the static penetration test, was obtained. Not only can you gain power,
If the ground is capable of performing a standard penetration test, the peripheral frictional force of the pile can be obtained on that ground.

Furthermore, in addition to the peripheral frictional force obtained from the pull-out resistance, the peripheral frictional force obtained by using the N value by the standard penetration test and the design formula can also be obtained. Therefore, both types of peripheral frictional force are compared. This makes it possible to determine whether or not the peripheral frictional force obtained from the pull-out resistance is appropriate, and the reliability of the peripheral frictional force obtained can be improved.

Furthermore, since the pull-out resistance is measured at the time of pulling out the test piece in the standard penetration test, simply modifying the standard penetration tester for performing the standard penetration test by simply attaching a load detection sensor such as a load cell Therefore, the standard penetration tester can be used to perform a series of standard penetration tests and pullout resistance measurements in series, and there is no need for a dedicated machine for measuring pullout resistance, and only the standard penetration test is possible. It is possible to perform the standard penetration test and the measurement of the pull-out resistance with good workability in the same amount of labor as in the case of

〔The invention's effect〕

Therefore, according to the present invention, it is possible to design a pile without unnecessarily considering a large safety factor, reduce the material cost and construction cost of the pile, and reduce the construction cost as a whole. It is possible to obtain the peripheral frictional force of a pile that is objective, highly accurate, and highly reliable, and that can be subjected to a standard penetration test on all grounds to be investigated. In addition, it has become possible to provide a ground survey method that can be performed with good workability and low cost.

〔Example〕

An embodiment of the ground survey method according to the present invention will be described below with reference to the drawings.

First, the outline of an apparatus for performing ground survey will be described. This device is a well-known device for performing a standard penetration test. As shown in FIG. 2, a yagura (1), a hammer (2), and a yagura (1) assembled on the ground (G). ), A wire (4) for hoisting the hammer (2) wrapped around a pulley (3), and a rod (5) that is fitted inside the hammer (2) and stands upright. Has been done.

At the tip of the rod (5), a drilling tool for drilling a boring hole in the ground (G) and a sampler as a test piece for investigating the properties of the ground (G) should be mounted separately. It is configured to be able to. Also, this rod (5)
The rotation driving device (6) is configured to be switched between a state in which it is linked and a state in which it is not linked.

Then, by attaching a punching tool to the tip of the rod (5) and interlocking the rod (5) with the rotary drive device (6),
To be able to drill a boring hole (H) in (G),
On the other hand, by attaching a sampler to the tip of the rod (5) and disconnecting the interlocking between the rod (5) and the rotary drive (6), a hammer is placed on the knocking head (7) attached to the rod (5).
(2) is allowed to fall freely and the sampler can be driven into the ground (G).

A pull-out wire (8) for pulling out the sampler driven into the ground (G) is fixed to the upper end of the rod (5). A load cell (9) for measuring the pulling resistance force when pulling out the sampler is provided in the middle of the pulling wire (8). From the pull-out resistance force measured by the load cell (9), the peripheral frictional force of the pile can be obtained.

Next, a ground survey using this device will be described in the order of steps.

First, as shown in FIG. 1 (a), a drilling tool (5A) having a bit (5a) attached to the tip of a rod (5) is mounted, and a boring hole (H) is drilled in the ground (G). When the boring hole (H) reaches a predetermined depth (for example, 1 m from the ground surface), the boring is stopped. After that, the rod (5) is pulled up, and as shown in Fig. 1 (b), the puncher (5A) is replaced with a sampler (5B), and the sampler (5) is attached as shown in Fig. 1 (c). Set 5B) at the bottom of the boring hole (H).

Then, disconnect the interlocking between the rod (5) and the rotation drive device (6),
As shown in FIG. 1 (d), the hammer (2) is pulled up, dropped freely on the knocking head (7) and struck, and the sampler (5B) is penetrated into the ground (G).
The N value is a value obtained by counting the number of hits required for the sampler (5B) to penetrate into the ground (G) by 30 cm, which is an index showing the hardness and softness of soil and the tightness.

After the N value has been counted, the penetrating portion of the sampler (5B) is pulled out using the pulling wire (8) as shown in FIG. 1 (e). At this time, the pullout resistance is measured by the load cell (9). From this pull-out resistance, the peripheral frictional force of the pile can be obtained. The pulling out of the sampler (5B) using the pulling wire (8) may be performed manually, or may be performed by a mechanical force such as winding the pulling wire (8) around a winch.

After pulling out the sampler (5B), sampler (5B) again
In place of the rod (5), attach the perforator (5A) with bit (5a).
The boring hole (H)
To drill. Since a hole of 30 cm has already been formed by driving the sampler (5B), a further 70 cm is excavated using the bit (5A).

After that, the punching tool (5A) is replaced with a sampler (5B), the N value and the pull-out resistance are measured, and thereafter, the boring hole (H) is gradually dug while repeating the above operation. As a result, the N value and the pull-out resistance can be obtained every 1 m from the ground surface. The number of 1 m can be changed as appropriate, and if a precise survey is to be carried out, it may be done, for example, every 50 cm or 75 cm from the ground surface. Further, the number of times of repeating the measurement is not limited, and the measurement may be performed only once at a predetermined depth.

The configuration for pulling out the sampler (5B) penetrating into the ground (G) can be changed as appropriate. For example, as shown in FIG. 3, the rod (5) may be held by an oil jack (10) and lifted with the surface of the ground (G) as a reaction point. In this case, finer control such as drawing speed can be easily performed, and thereby more accurate drawing resistance force can be measured.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the method embodied by the structure of the accompanying drawings by the entry.

[Brief description of drawings]

The drawings show an embodiment of the ground survey method according to the present invention.
Figures (a) to (e) are schematic cross-sectional views of each step, FIG. 2 is a schematic cross-sectional view of an inspection apparatus, and FIG. 3 is equivalent to FIG. 2 showing another embodiment of the inspection apparatus. It is a schematic sectional drawing. (5B) …… Survey strip, (G) …… Ground.

Front Page Continuation (72) Inventor Asao Otsuki 2-11-16 Higashigaoka, Meguro-ku, Tokyo Within Tokyo Soil Research Co., Ltd. (56) References (JP, B1)

Claims (1)

[Claims] 1. A ground investigation method for investigating the properties of the ground (G) by performing a penetration test by penetrating the test piece (5B) into the ground (G), wherein the test piece is used as the penetration test. Ground (5B)
Perform a standard penetration test to measure the N value by driving into the (G) until a predetermined amount is penetrated, and in the standard penetration test, when pulling out the test piece (5B) after driving from the ground (G), the pull-out resistance force Ground survey method to measure.