JP2671028B2 - In-situ test method to determine horizontal pressure of the ground by in-situ freezing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a test method for determining a horizontal pressure of a ground, which is carried out as a part of a soil investigation for examining mechanical properties of a non-viscous ground, In-situ frozen by the in-situ freezing method The in-situ characterized by obtaining the horizontal restraining pressure of the ground by utilizing the deformation phenomenon of the ground that occurs toward the drilled hole as the frozen ground melts It relates to the test method.

2. Description of the Related Art It is widely known that the mechanical properties of the ground affect the constraint pressure that the ground receives. That is, the ground receives a vertical restraint pressure in the vertical direction based on the amount of load on the formation, and also receives a horizontal restraint pressure in the two horizontal axes, thereby maintaining a static balance. Of these, the vertical restraint pressure is uniquely determined if the unit volume weight of the ground and the position of the groundwater level are known.

On the other hand, the constraint pressure in the horizontal direction is a so-called indeterminate quantity that any value may be used as long as it is balanced in the directions of the two axes, and is generally unknown. Therefore, the mechanical characteristics of the ground will become clear only after clarifying this horizontal restraint pressure.

However, conventionally, there is almost no in-situ test method for obtaining the horizontal restraining pressure of the ground.

For example, as shown in FIG. 3, a boring hole b is dug in the in-situ ground a, a loading test device c using a rubber bag is inserted into the boring hole b, and water is put in the rubber bag. The hole wall is pressurized to cause deformation of the hole wall and the surrounding ground, and the change of the pressure-deformation curve is taken as shown in the graph of FIG. In-situ test methods for estimating the magnitude of pressure are in place. Usually, in the graph of FIG. 4, the pressure at the point P ₀ where the curve changes linearly is estimated as the horizontal restraining pressure (static earth pressure).

However, this in-situ test method is originally a test for obtaining a horizontal deformation coefficient of the ground, and is only applied to a test for obtaining a static earth pressure coefficient of the ground as a kind of expanded interpretation.

Problems to be Solved by the Invention In the case of the above-mentioned conventional in-situ test method, firstly, stress release is always caused by excavation of the boring hole b, and the hole wall is deformed, loosened, or collapsed, so that the original state is changed. Has been disturbed. Therefore, it has been criticized that it is almost impossible to measure the true horizontal restraining pressure of the ground.

Secondly, in the ground with coarse particles such as gravel ground, the excavated hole wall is in a bumpy state, so if you put water in a rubber bag and apply pressure, the pressure will be uneven. Since they act as forces perpendicular to each other, the pressure of the water contained in the rubber bag does not necessarily push the hole walls equally outward in the radial direction. Such an error in the function of pressure causes the measurement accuracy to be disturbed.

Thirdly, even if the hole wall is formed smoothly,
The theoretical background for estimating the point P ₀ on the pressure-deformation curve as shown in Fig. 4 as the horizontal constraining pressure of the in-situ ground is weak. Also, depending on the properties of the ground and the conditions of excavation, P ₀
In some cases, the points do not appear clearly, and in the end, the true horizontal constraining pressure of the in-situ ground cannot be accurately obtained, and there is a problem that it cannot be estimated.

Means for Solving the Problems As means for solving the problems of the prior art,
The in-situ test method for determining the horizontal pressure of the ground by the in-situ ground freezing method according to the present invention is as follows: a) Freezing the in-situ ground 1 as shown in the preferred embodiment in FIGS. Cutting the in-situ frozen ground 3 with a core tube 4 to form a hole 6; b) inserting a test device 7 using a rubber bag into the hole 6 of the in-situ frozen ground 3; (3) Inflate with a predetermined fluid pressure to prepare for the test, and c) Wait for the in-situ frozen ground 3 to melt, and to prevent the ground from deforming in the radial direction of the hole 6 as the ground melts. Adjust the fluid pressure to always prevent deformation to zero,
The fluid pressure of the test apparatus when the in-situ frozen ground 3 is completely melted is determined as the horizontal restraining pressure of the in-situ ground 1, and the constitution is constituted.

The frozen in-situ frozen ground 3 completely retains the stress state generated in the in-situ ground 1 immediately before freezing, and completely fixes the stress state.

Therefore, this in-situ frozen ground 3 is replaced by the core tube 4
The stress state does not change even if cut out with, and stress release does not occur in particular. Further, the wall surface of the hole is formed extremely smooth by the core tube 4.

When the rubber bag test device 7 is inserted into the hole 6 and waiting for the in-situ frozen ground 3 to melt, the ground is deformed in the radial direction of the hole 6. Therefore, test equipment (rubber bag) 7
When the in-situ frozen ground 3 is completely thawed, the fluid pressure in the test apparatus is adjusted to the horizontal level of the in-situ ground 1 by adjusting the fluid pressure in the ground so that the deformation of the ground is always zero. It can be obtained as the restraining pressure in the direction.

Examples Next, examples shown in the drawings will be described.

First, FIG. 1 shows that in order to determine the horizontal restraining pressure of the ground at a depth H in the original ground 1, a freezing pipe 2 is installed in the ground 1 to a required depth. By supplying a refrigerant to freeze the ground sufficiently to a region including the depth H point, the hole 6 reaching the target point (depth H) of the in-situ frozen ground (part) 3 is cut out by the core tube 4. The step of drilling is shown.

As a method of installing the freezing pipe 2, according to the size and depth of the in-situ frozen portion 3 of the target ground, a hole having a diameter of about φ87 is drilled by, for example, the seal boring method,
The freezing tube 2 having an outer diameter of φ83 is inserted into the hole.

As a refrigerant for freezing the ground, use brine (approximately -28 ° C) if there is enough time for construction, and use liquid nitrogen (approximately -196 ° C) or a mixture of ethanol and dry ice (approximately- (70 ° C.) is used, and these are supplied to the freezing tube 2 and circulated to perform the freezing treatment.

The excavation of the hole 6 is performed by a method of cutting the frozen soil from the original position by pushing the core tube 4 having the required diameter from the ground as shown in FIG. 1 after the ground 1 is frozen.

Next, FIG. 2 shows that the casing 5 is first installed on the ground portion of the hole 6 excavated as described above, and the length l is 1.0 to
A test device 7 consisting of a circular rubber bag of about 2.0 m was inserted into the hole 6 to a predetermined depth point, and the air pipe 8 of the test device 7 came into contact with the compressed air source 10 via the air meter 9 on the ground. The test apparatus 7 shows a stage (or a test) in which the test apparatus 7 is inflated with a predetermined air pressure to prepare for the test and wait for the in-situ frozen ground 3 to melt. In the figure, 11 is a pressure gauge.

Therefore, as the in-situ frozen ground 3 is melted, the ground is deformed in the radial direction toward the hole 6.
Such deformation of the ground appears as a change in the air pressure in the test device (rubber bag) 7 and can be read, so the air pressure is adjusted to adjust the restraining pressure so that the deformation of the hole wall is always returned to zero. The hole wall is controlled so as not to be deformed in the radial direction.

Thus, the reading value of the air meter 9 at the time when the in-situ frozen ground 3 is completely melted and the deformation of the ground is completely terminated can be recognized and grasped as the true horizontal restraining pressure in the in-situ ground. Of.

Different Embodiment In the test facility for in-situ ground freezing of FIG. 2, the air pipe 8 is a liquid injection pipe, the air meter 9 is a liquid meter,
Replacing the air pressure source 10 with a hydraulic pressure generator, and supplying an antifreeze liquid to the test device 7 so that it does not freeze at about the freezing temperature of the frozen ground 3, and expanding the test device 7 with an antifreeze liquid of a predetermined pressure to prepare for the test. The pressure in the horizontal direction of the in-situ ground can be tested and determined in exactly the same manner as in the above embodiment.

That is, since the air used in the above-mentioned examples has a high compressibility, while the liquid is so-called incompressible, the use of an antifreeze liquid as in the present embodiment does not cause an error due to compression, and thus the measurement accuracy. Is greatly increased. Ethylene glycol aqueous solution as antifreeze (freezing point -50 ℃
To about −60 ° C., which may vary depending on the concentration).

In short, the in-situ test method of the present invention can improve the accuracy as much as possible by using, of the so-called fluids, a gas or liquid having a small compressibility and antifreezing as a test medium.

The in-situ test method for determining the horizontal pressure of the ground by the in-situ ground freezing method according to the present invention includes the in-situ ground 1 Since this is an in-situ test method in which the test device 7 is inserted into the hole 6 where the stress state of the ground at that time is completely fixed and the ground deformation phenomenon accompanying melting is used, excavation of the ground ( This is a very reasonable test method that leaves no room for stress release and other disturbances associated with drilling).

In particular, since the hole wall formed by the core tube 4 is formed extremely smooth, there is no room for an error in the pressure of the rubber bag. Coefficient) can be obtained. Therefore, this in-situ testing method contributes by grasping and analyzing the mechanical characteristics of the ground with high accuracy.

The in-situ test method has a feature that it is suitable for non-viscous ground, for example, sandy ground and gravel ground with coarse grain size.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a stage of freezing the ground and drilling by a core tube to be tested by the method of the present invention, and FIG. 2 is a cross-sectional view showing a state where a test device is installed in a hole of the frozen ground in situ. , FIG. 3 is an explanatory view of a conventional in-situ test method, and FIG. 4 is a pressure-deformation diagram obtained by the previous conventional method. 1 ... In-situ ground, 2 ... Freezing pipe, 3 ... In-situ freezing ground, 4 ... Core tube, 6 ... Hole, 7 ... Testing device,
9 ... Air meter, 10 ... Air pressure source

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Atsura Ohara 2-11-16 Higashigaoka, Meguro-ku, Tokyo Within Tokyo Soil Research Co., Ltd. No. Stock Company Tokyo Soil Research Co., Ltd. (56) Reference JP-A-169013 (JP, A) JP-A-54-3579 (JP, A) JP-A-61-116828 (JP, U)

Claims (1)

(57) [Claims] 1. A) freezing the in-situ ground and cutting out the in-situ frozen ground with a core tube to form a hole; and b) a test device using a rubber bag in the hole of the in-situ frozen ground. Inserting, inflating the rubber bag with a predetermined fluid pressure to prepare for the test, and c) waiting for the in-situ frozen ground to melt and for the ground to try to deform in the radial direction of the hole as it melts. Adjusting and blocking the fluid pressure of the test equipment, and determining the fluid pressure of the test equipment when the frozen in-situ ground is completely melted as the horizontal restraint pressure of the in-situ ground. , In-situ test method for obtaining horizontal pressure of the ground by in-situ freezing method.