JPS61251744A - Freezing and sampling method for soil quality sample including pebble - Google Patents

Abstract

PURPOSE:To make possible the direct drawing of a soil quality sample of the pebble ground by as much as needed from the region where the sample is not disturbed by inserting an inside freezing pipe applied with the heat insulation arriving at the upper limit of the sample drawing depth on the outside periphery into an outside freezing pipe and supplying a refriger ant through the inside freezing pipe so that the outside peripheral ground of the outside freezing pipe is frozen down to the desired thickness. CONSTITUTION:A hole 1 of the large diameter corresponding to the diameter of the sample to be drawn is first bored down to the upper limit position D1 of the sample drawing depth D. A steel pipe 12 for preventing collapsion and a bottom plate 15 having through-holes 15a, 15b are installed. A hole 1' of the diameter approximately equal to the outside diameter of the outside freezing pipe 2 and the depth approximately equal to the depth D is bored through the hole 15a at the center in the bottom of the hole 1. The outside pipe 2 is further installed through the holes 1, 1' and the inside freezing pipe 3 applied with the heat insulation 4 to the neighborhood of the upper limit D1 of the depth D on the outside periphery is inserted into the pipe 2. The refrigerant is supplied through the pipe 3 to freeze the outside periphery ground of the outside pipe 2 down to the desired thickness. A double-cored tube 11 is then inserted through the hole 15b of the plate 15 to sample the frozen soil (a). The tube is there after drawn up onto the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is required in the fields of civil engineering and architecture when designing various structures. In particular, it relates to a freezing sampling method for soil samples that can be effectively implemented to investigate the physical and mechanical properties of gravel-containing ground.

(Conventional techniques and their problems, etc.) Conventionally, the freezing method is used as a sampling method for sandy ground.

■A method in which multiple freezing tubes are installed in the ground to significantly freeze the surrounding ground, and frozen samples are collected from the area surrounded by the group of freezing tubes.

■ A single frozen pipe is installed in the ground, the ground around the pipe is frozen to an appropriate thickness, and then the frozen soil is core sampled around the frozen pipe, and then it is dismantled. There are two methods: collecting soil samples from areas that are thought to be undisturbed.

However, in the case of method (2) above, there were the following drawbacks.

(a) In an area surrounded by a plurality of frozen pipes, groundwater is trapped as the freezing progresses, and eventually becomes frozen 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) Since the volume of frozen ground is several times larger than the volume of the soil sample to be collected, it is inefficient and uneconomical.

Furthermore, the method (2) above had the following drawbacks.

(c) Freezing with a large-diameter single-core tube with a diameter approximately 6 to 8 times the outer diameter of the freezing tube, centering on the freezing tube and including the area disturbed by the installation of the freezing tube. Core sampling of soil requires not only core tubes but also cutting machines, which increases costs.

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 that the frozen soil in the disturbed area, which is not necessary as a sample, is also collected at the same time.

(e) It is troublesome to dismantle the frozen soil that has been brought up to the ground and take out a sample of the required size.

(Objective of the Invention) Therefore, the object of the present invention is to provide a method that is effective for collecting soil samples, especially in sandy and gravelly ground containing gravel, and that is capable of directly collecting samples of the necessary size from an undisturbed area. Therefore, the core tube and cutting machine can be downsized, the time required for core sampling can be shortened, frozen samples can be easily dismantled, and the structure has been improved to be highly economical. The object of the present invention is to provide a freezing sampling method for soil samples containing gravel.

(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 tube is formed with a large diameter according to the diameter of the collected sample. Then, a steel pipe is installed to prevent the hole wall from collapsing, and a through hole is made at the bottom of this hole at the location where the frozen outer tube will be installed and where the core tube will be inserted. (b) At approximately the center of the lower bottom of the hole, a hole having a diameter approximately equal to the outer diameter of the freezing outer tube and having a depth approximately equal to the sampling depth is formed through the through hole of the positioning bottom plate. and (c) installing an outer cryotube into the second hole through the first hole, inserting an inner cryotube into the outer cryotube, and setting a sampling depth on the outer periphery of the outer cryotube. A process of inserting and installing an insulated pipe that reaches the upper limit of the height.

(d) supplying a refrigerant, such as liquid nitrogen or a mixture of dipolynol and dry ice, through the freezing inner tube;
(e) inserting a double core tube through a hole at a desired position in the positioning bottom plate and raising the frozen soil to the ground;

It is said to be composed of

(Example) Furthermore, details will be explained based on the illustrated embodiment.

Figure 1 shows the hole 1 for installing the frozen outer tube at the upper limit position D of the sampling depth D for the target area gIA where soil samples are to be collected.
+ (Fig. 4) shows the stage of almost vertical digging. The diameter of this hole 1 is determined according to the diameter of the collected sample in consideration of the diameter of the gravel, that is, usually about φ500 to φ1000. Excavation of this hole 1 is carried out by the usual muddy method.

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

In addition, as shown in FIG. 3A, the lower bottom of the hole 1 has a through hole 15a for installing a cryotube in the center as shown in FIG. through hole 15b
. . , the positioning bottom plate 15 having been installed is shown. This positioning bottom plate 15 is usually made of concrete.

FIG. 4 shows that the outer diameter of the freezing outer tube (usually φ5
0 to φ70) with a slightly larger diameter (1'
) is shown at the stage where the sample collection depth is usually about 3 m to 7 m). This hole 1' is also excavated by the usual muddy method.

FIG. 5 shows a stage in which the outer cryotube 2 is inserted and installed through the first hole 1 and the through hole 15a of the positioning bottom plate 15 at its bottom until it reaches the bottom of the second hole 1'. There is.

This frozen outer tube 2 has a shallow part above the second hole 1',
That is, the part placed from the upper limit position D1 of the sampling depth D is a thick-walled PVC pipe 2a with good heat insulation, and the part deeper than that is a pipe 2b made of metal (for example, iron) with good thermal conductivity. The pipes 2a and 2C are connected in series by a threaded joint.

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). On this vinyl chloride round bar 8, three (but not limited to three) thermocouples IO are installed vertically at a pitch of, for example, about 2 cm 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 thickness of the frozen ground can be confirmed.

Next, FIG. 6 shows that in the axial direction of the central part of the frozen outer tube 2,
Insert and install an inner freezing tube 3 made of stainless steel or vinyl chloride with an outer diameter of about φ16 to φ20, and place a tube between the outer periphery of the inner freezing tube 3 and the outer freezing tube 2 with an outer diameter of about φ16 to φ20. φ40
~φ50, the inner diameter is approximately φ35 to φ45, and a thick-walled vinyl chloride heat insulating pipe 4 is inserted and installed.

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

The heat insulating tube 4 is approximately at the upper limit W D of the sampling depth D.
It is installed with a length that reaches +.

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 freezing tube 3, and the refrigerant that has risen inside the outer freezing tube 2 is led out from the outlet nozzle 6 to the ground around the outer periphery of the outer freezing tube 2, especially at the sampling depth. This indicates the stage at which the surrounding ground has been frozen to the required thickness.

That is, the refrigerant that has spouted from the lower end of the frozen inner tube 3 and flowed into the frozen outer tube 2 side flows from the outer circumferential ground of the intermediate tube 2b through the pipe wall of the metal tube 2b with good thermal conductivity that constitutes the frozen outer tube 2. Heat is efficiently removed, thereby rapidly freezing the outer ground at the sampling depth D portion. Since it is also one-dimensional freezing in the horizontal direction, drainage conditions are good and the adverse effects (disturbance due to volume expansion) caused by freezing can be prevented. In addition, freezing costs can be reduced.

The frozen thickness of the ground is usually about φ500 to φ1000, and as described above, the thickness can be almost accurately confirmed (detected) on the ground using the thermocouple 10.

On the other hand, for the injection part from the sample collection depth D, firstly, the inner cryotube 3 is surrounded by a heat insulating tube 4, and secondly, the outer cryotube 2 is surrounded by a heat insulating tube 4.
Since it is also made of PVC pipe 2a with good insulation properties,
The loss caused by freezing the surrounding ground is minor.

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.

Figure 8 shows the frozen soil a formed as described above.
The double core tube 1 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 l.
This figure shows the stage of core sampling in which the frozen soil a was cut until it penetrated the unfrozen part at its lower end.

Therefore, the double core tube 11 ensures that the undisturbed region is cored and cut, regardless of the depth of the sampling depth D. Because,
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 is
It has a structure in which an inner tube lla and an outer tube llb are combined in a mutually rotatable relationship, and the closed upper end surface of the outer tube llb has a hollow hole driven by a cutting machine (not shown) on the ground. A shaft 9 is fixed. The outer diameter of this double core tube 11 is usually φ70 to φ400 depending on the outer diameter of the sample to be collected.
It is considered to be a rank.

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

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 removal cutting (the frozen sample is wrapped in the inner tube lla). , frozen samples can be collected that are not disturbed by melting.

Second, falling of the frozen sample can be prevented by the catcher of the inner tube 11a.

In this way, once the core tube 11 has penetrated the frozen soil a and reached the unfrozen portion below it, the core tube 11 is lifted above the ground. The core tube is then dismantled and the frozen soil inside is collected as a soil sample.

That is, since the collected soil sample is from an area that is completely undisturbed as described above, it can be provided as a sample as it is.

(Operation and Effect) As described above in detail in conjunction with the examples,
According to the frozen sampling method for soil samples containing gravel according to the present invention, the excavation accuracy of core extraction cutting during core sampling is properly ensured by the through hole 15b of the positioning bottom plate 15, so that It is possible to collect as many undisturbed, high-quality soil samples as necessary for deep strata, and moreover, for sandy soil containing gravel.

Therefore, the diameter of the core tube 11 required for core sampling of a frozen sample is small and approximately equal to 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. It also reduces the space and time required for demolition,
It is possible to downsize the instrument and reduce costs.

Furthermore, 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, since one-dimensional horizontal freezing is performed using a single freezing pipe, the amount of refrigerant required for ground freezing is reduced compared to when using multiple pipes, making it possible to shorten freezing time and reduce costs. It is.

[Brief explanation of the drawing]

Figures 4 to 8A are process explanatory diagrams sequentially showing important steps for carrying out the frozen sampling method of the present invention, and Figure 3B
1 is a plan view of the positioning bottom plate, and FIGS. 4 to 8 are process explanatory diagrams sequentially showing the important steps of carrying out the frozen sampling method of the present invention. Figure 1 Figure 2 Figure 3 @A Figure 4 bb 11!5IEl Figure 6 Figure 711 Intestine No. 8! I! 1

Claims (1)

[Scope of Claims] [1] (a) The hole (1) for installing the frozen outer tube (2) has a large diameter according to the diameter of the sample to be collected, and the upper limit position (D_1) of the sample collection depth (D) ), and install a steel pipe (12) to prevent wall collapse. At the bottom of this hole (1), locate the installation position of the frozen outer pipe (2) and the core tube (11).
) installing a positioning bottom plate (15) having through holes (15a, 15b) respectively at the insertion positions of the positioning bottom plate (15); Freeze outer tube (2) through the through hole (15a)
(c) digging a second hole (1') having a diameter approximately equal to the outer diameter of the sample sampling depth (D); At the same time, install the frozen outer tube (2) in the frozen outer tube (2).
The inner cryotube (3) is inserted and installed inside the tube, and on its outer periphery there is an insulated tube (3) that reaches the upper limit position (D_1) of the sampling depth D.
(d) supplying refrigerant through the frozen inner pipe (3) to freeze the outer peripheral ground of the frozen outer pipe (2) to a required thickness; (e) positioning the frozen outer pipe (2); The double core tube (11) is inserted through the through hole (15b) at a desired position in the bottom plate (15), the frozen soil (a) is cut to remove the core to the non-frozen part, and core sampling is performed. (11) A freezing sampling method for a soil sample containing gravel, comprising the steps of: [2] Freezing outer tube (2) according to claim 1
is soil containing gravel, where the part shallower than the upper limit position D_1 of the sampling depth (D) is an insulating tube (2a), and the deeper part is a thermally conductive tube (2b). Sample freezing sampling method. [3] Freezing outer tube (2) according to claim 1
is equipped with an insulating lid (8) at its lower end, and a thermocouple (10) for checking the frozen thickness of the ground. Sampling method. [4] The step of core sampling using the double core tube (7) described in claim 1 is performed by freezing a soil sample containing gravel while supplying circulating mud water at an appropriate temperature to the double core tube (7). Sampling method.