JPH0452804B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention investigates the physical properties and mechanical properties of sandy and gravel ground, especially those containing gravel, which are required in the design of various structures in the fields of civil engineering and architecture. This paper relates to an effective method of frozen sampling of soil samples.

(Prior art and its problems, etc.) Conventionally, as a sampling method for sandy ground applying the freezing method, multiple freezing pipes are installed in the ground to greatly freeze the surrounding ground, and the surrounding ground is surrounded by a group of frozen pipes. A method for collecting frozen samples from a frozen area is to install a single freezing pipe in the ground, freeze the ground around the pipe to an appropriate thickness, and then freeze the soil along with the pipe around the frozen pipe. There are two methods: Core topping and soil samples taken from areas that are considered undisturbed as part of demolition.

However, the above method had the following drawbacks.

(a) In areas surrounded by multiple frozen pipes, as freezing progresses, groundwater becomes trapped and eventually freezes in a state where drainage is impossible or very difficult to drain. Therefore, there is an extremely high possibility that the sample will be disturbed by the volume expansion during freezing.

(b) The volume of frozen ground is several times larger than the volume of the soil sample to be collected, making it inefficient and uneconomical.

Furthermore, the above method had the following drawbacks.

(c) Freeze in a large-diameter single-core tube with a diameter approximately 6 to 8 times the outer diameter of the cryo-outer tube, centering on the cryo-outer tube, including the area disturbed by the installation of the cryo-outer tube. In order to core sample the soil, not only the core tube but also the cutting machine becomes large and expensive. In addition, it takes a long time to extract the core, and there is a concern that the frozen sample may thaw.

(d) There is waste in collecting frozen soil from the disturbed area, which is not necessary as a sample, at the same time.

(e) The work of dismantling the frozen soil that has been brought up to the ground and extracting samples of the required size is troublesome.

(Objective of the Invention) Therefore, the object of the present invention is to provide a method that is effective for collecting soil samples particularly in sandy ground containing gravel;
Moreover, it is possible to directly collect as much as necessary from an undisturbed area.
Therefore, the core tube and cutting machine can be downsized, the time required for core sampling can be shortened, and frozen samples can be easily dismantled.
The object of the present invention is to provide a frozen sampling method for soil samples containing gravel, which has been improved to have a highly economical configuration.

(Structure of the Invention) In order to achieve the above object, the frozen sampling method for soil samples containing gravel according to the present invention includes: (a) First, a hole for installing a frozen outer pipe is formed with a large diameter according to the diameter of the collected sample. The hole is dug until it reaches the upper limit of the sampling depth, and a steel pipe is installed to prevent the wall from collapsing, and a through hole is provided at the bottom of the hole at the location where the frozen outer tube will be installed and where the core tube will be inserted. a step of installing a positioning bottom plate; (b) a hole having a diameter substantially equal to the outer diameter of the freezing outer tube and having a depth substantially equal to the sample collection depth through the through hole of the positioning bottom plate at substantially the center of the lower bottom of the hole; (c) Installing an outer cryotube into the second hole through the first hole, and inserting and installing an inner cryotube into the outer cryotube, with a sample sampling depth formed on its outer periphery. (d) Supplying a refrigerant, such as liquid nitrogen or a mixture of ethanol and dry ice, through the inner freezing tube to the required level of the outer ground of the outer freezing tube. (e) inserting a double core tube through a hole at a desired position in the positioning bottom plate to raise the frozen soil to the ground;

(Example) Further, details will be explained based on the illustrated example.

Figure 1 shows how hole 1 for installing a frozen outer pipe is located at the sampling depth D for target ground A where soil samples are to be collected.
This shows the stage where the excavation is done almost vertically to the upper limit of 1D ₁ (Figure 4). The diameter of this hole 1 is determined according to the diameter of the collected sample, taking into account the diameter of the gravel, that is, the diameter of the hole 1 is usually
It is said to be ranked 500 to 1000. This hole 1 is excavated by the usual muddy method.

FIG. 2 shows a stage in which the steel pipe 12 has been inserted and installed along the hole 1.

In addition, FIG. 3A shows a through hole 15a at the bottom of the hole 1, and a through hole 15a for installing a frozen outer tube in the center as shown in FIG.
A positioning bottom plate 1 having a through hole 15b for inserting and installing a core tube in its periphery.
5 is installed. This positioning bottom plate 15 is usually made of concrete.

FIG. 4 shows a second hole 1' having a diameter slightly larger than the outside diameter of the freezing outer tube (usually about 50 to 70 degrees), which is inserted through the central through hole 15a of the positioning bottom plate 15 and into the substantially central part of the bottom of the hole 1. , the sampling depth (typically 3m to 7m
It shows the stage where only 1000 yen) have been excavated. This hole 1' is also excavated by the usual muddy method.

FIG. 5 shows that the second hole 1' is inserted through the first hole 1 and the through hole 15a of the positioning bottom plate 15 at its lower bottom.
This shows the stage in which the cryotube 2 has been inserted and installed until it reaches the bottom of the tube.

This freezing outer tube 2 has a thick-walled vinyl chloride tube 2a with good insulation in the shallow part above the second hole 1', that is, the part shallower than the upper limit position _D1 of the sampling depth D, and the deeper part. The pipe 2b is made of a metal (for example, iron) with good thermal conductivity, and both the pipes 2a and 2c are
are connected in series by threaded joints.

A vinyl chloride round rod 8 with good heat insulation is fixed to the lower end of this outer freezing tube 2 as a lid (stopper). Three (but not limited to) thermocouples 10 are installed on the vinyl chloride round bar 8 at a pitch of, for example, 2 cm in the vertical direction for checking the frozen thickness of the ground.

That is, as the ground freezes, each thermocouple 10
... detects zero degrees in order of depth, so the frozen thickness can be confirmed.

Next, FIG. 6 shows that an inner freezing tube 3 made of stainless steel or vinyl chloride with an outer diameter of about 16 to 20 is inserted and installed in the central axial direction of the outer freezing tube 2. The outer periphery of the inner frozen tube 3 and the outer frozen tube 2
The figure shows the stage where a thick-walled vinyl chloride heat-insulating pipe 4 with an outer diameter of 40 to 50 mm and an inner diameter of 35 to 45 mm is inserted and installed between the two.

The inner cryotube 3 has a desired length by connecting a series of short tubes with a module length of approximately 2 m using threaded joints, and its lower end opening is connected to the lid 8 of the outer cryotube 2. On the other hand, they are installed so that they are close to each other, approximately 20cm to 30cm apart.

The heat insulating pipe 4 is installed with a length that approximately reaches the upper limit position _D1 of the sampling depth D.

Further, at this stage, the upper end of the frozen outer tube 2 is sealed, and a refrigerant outlet nozzle 6 is attached to the above-ground portion of the frozen outer tube 2.

FIG. 7 shows that a refrigerant such as liquid nitrogen is supplied through the inner frozen tube 3, and the refrigerant that has risen inside the outer frozen tube 2 is led out from the outlet nozzle 6 to the outer peripheral ground of the outer frozen tube 2.
In particular, it shows the stage in which the outer ground at sampling depth portion D has been frozen to a required thickness.

That is, the frozen outer tube 2 is ejected from the lower end of the frozen inner tube 3.
The refrigerant flowing to the side passes through the tube wall of the metal tube 2b with good thermal conductivity that constitutes the freezing outer tube 2.
Heat is efficiently removed from the outer ground at point b, thereby rapidly freezing the outer ground at the sampling depth D. Since it is also one-dimensional freezing in the horizontal direction,
Drainage conditions are good, and adverse effects associated with freezing (disturbance due to volumetric expansion) can be prevented. In addition, freezing costs can be reduced.

The frozen thickness of the ground is usually 500 to 1000,
As described above, the thickness can be almost accurately confirmed (detected) on the ground using the thermocouple 10.

On the other hand, the portion shallower than the sampling depth D is
First, the inner freezing pipe 3 is surrounded by a heat insulating pipe 4, and the second
In addition, since the freezing outer pipe 2 is also formed of a vinyl chloride pipe 2a with good insulation properties, the loss caused by freezing the surrounding ground is slight.

In this way, as a result of freezing the surrounding ground only at the sampling depth D, not only can freezing costs be greatly reduced, but later core sampling of frozen samples is significantly easier than when freezing the whole depth. It's easy and simple.

FIG. 8 shows that the double core tube 11 is inserted from the ground surface through one of the through holes 15b in the positioning bottom plate 15 installed at the bottom of the hole 1 toward the frozen soil a formed as described above. a
This figure shows the core sampling stage in which the core was cut until it penetrated the unfrozen part of the lower end.

Therefore, the double core tube 11 will reliably core out an undisturbed area, regardless of the depth of the sampling depth D. This is because the insertion position of the double core tube 11 (the position of the through hole 15b) is determined at an outer circumferential position that is more than twice the outer diameter of the outer cryotube 2 from the outer surface of the outer cryotube 2.

As is already known, the double core tube 11 has a structure in which an inner tube 11a and an outer tube 11b are combined in a mutually rotatable relationship. A hollow shaft 9 driven by a cutting machine (not shown) is fixed thereto. The outer diameter of this double core tube 11 is
Depending on the outer diameter of the collected sample, it is usually about 70 to 400.

During core sampling using the double core tube 11, circulating water at an appropriate temperature (low-temperature non-freezing circulating mud) is supplied through the hollow shaft 9 to facilitate core extraction cutting.

Thus, as a result of core sampling using the double core tube 11, firstly, the frozen sample is not directly exposed to the cooling circulation muddy water that facilitates the core extraction cutting (the frozen sample is wrapped in the inner tube 11a). ), frozen samples can be collected that do not easily melt and are not disturbed.

Second, the dropout of the frozen sample is caused by the inner tube 1
This can be prevented with catcher 1a.

In this way, once the core tube 11 has penetrated the frozen soil a and reached the unfrozen portion below, the core tube 11 is lifted above the ground. Then, disassemble the core tube,
The frozen soil inside is collected as a soil sample.
That is, since the collected soil sample is from an area that has not been disturbed at all as mentioned above, it can be provided as a sample as it is.

(Function and Effect) As described above in detail in conjunction with the embodiments, according to the frozen sampling method for soil samples containing gravel according to the present invention, the excavation accuracy of punch cutting during core sampling is determined by positioning. Since it is properly secured by the through hole 15b of the bottom plate 15, it is possible to collect as many undisturbed high-quality soil samples as necessary from deep strata from several meters to several tens of meters underground, and from sandy and gravelly ground containing gravel. Can be done.

Therefore, the diameter of the core tube 11 required for core sampling of a frozen sample is approximately equal to and smaller than the sample diameter, so that the cutting machine can be small and costs can be reduced.

The pulled soil sample only needs to be cut into the size required as a specimen, that is, dismantling is extremely easy. Furthermore, it is possible to reduce the space and time required for disassembly, and to downsize the equipment, thereby reducing costs.

In addition, it is possible to reliably collect a sample with a good shape for the experiment, and it is possible to easily shape the sample.

In addition, because one-dimensional horizontal freezing is performed using a single freezing tube, the amount of refrigerant required for ground freezing is reduced compared to when multiple tubes are used, making it possible to shorten freezing time and reduce costs. be.

[Brief explanation of the drawing]

Figures 1 to 3A are process explanatory diagrams sequentially showing the important steps of carrying out the frozen sampling method of the present invention, Figure 3B is a plan view of the positioning bottom plate, and Figures 4 to 8 are similar to this. FIG. 2 is a process explanatory diagram sequentially showing important steps for carrying out the frozen sampling method of the invention.

Claims (1)

[Claims] 1 (a) A hole 1 for installing the outer cryotube 2 is dug to have a large diameter corresponding to the diameter of the sample to be collected, and until it reaches the upper limit position _D1 of the sample collection depth D, and the hole wall collapses. In addition to installing the steel pipe 12 for prevention, the installation position of the freezing outer pipe 2 and the core tube 1 are located at the bottom of this hole 1.
(b) inserting the freezing outer tube 2 through the through hole 15a of the positioning bottom plate 15 into the approximate center of the lower bottom of the hole 1; (c) digging a second hole 1' having a diameter substantially equal to the outer diameter of the sample sampling depth D; Step of installing the tube 2, inserting the inner freezing tube 3 into the outer freezing tube 2, and inserting and installing the insulated tube 4 that reaches the upper limit position _D1 of the sampling depth D around the outer circumference of the tube 2. (d) A step of supplying a refrigerant through the freezing inner tube 3 to freeze the outer peripheral ground of the freezing outer tube 2 to a required thickness; and (e) freezing the double core tube through the through hole 15b at a desired position in the positioning bottom plate 15. 11, core sampling is performed by cutting the frozen soil a to the non-frozen part, and then lifting the core tube 11 above the ground. Freezing sampling method. 2 Freezing outer tube 2 described in claim 1
is a freezing template for a soil sample containing gravel, in which the part shallower than the upper limit position D ₁ of the sampling depth D is made up of an insulating tube 2a, and the deeper part is made up of a tube 2b with good thermal conductivity. Method. 3 Freezing outer tube 2 described in claim 1
This is a freezing sampling method for a soil sample containing gravel, which comprises a heat insulating lid 8 at the lower end, and a thermocouple 10 on the lid 8 for checking the frozen thickness of the ground. 4. A freezing sampling method for soil samples containing gravel, in which the step of core sampling using the double core tube 7 described in claim 1 is performed while supplying circulating mud water at an appropriate temperature to the double core tube 7.