JP6604575B2 - Test hole creation method and test method using the test hole - Google Patents

Description

  The present invention relates to a method for creating a test hole and a test method using the test hole, and more particularly to a method for creating a test hole in a saturated unconsolidated sandy ground and a test method using the test hole.

  Conventionally, tests for examining properties such as water permeability of the ground have been conducted for the purpose of embankment and the like. When such tests are performed in-situ, first, in order to grasp the position of the target ground more accurately, a boring survey is performed in which a sampler or the like is inserted into the ground to collect a sample of the formation. After determining the target ground, this time, a test hole is separately drilled around the position where the sampler is inserted, and water is poured or pumped into the test hole. The characteristics of the target ground, such as water permeability characteristics and piping characteristics, are investigated by causing a water level difference during the period (Non-patent Document 1).

  However, if the hole for collecting the sample specimen and the test hole are created separately in this way, the ground around the test hole may be disturbed from the original state of the original position due to the drilling in the preceding boring survey. That is, there are cases where the bonding state of the soil particles varies greatly and the size and shape of the gaps between the soil particles change greatly. For this reason, the sampling hole and the test hole are set apart from each other by a certain distance, but the ground properties may be different from each other because they are separated by a certain distance.

  Even when the sampling hole and the test hole serve as one hole, the surrounding ground is generally disturbed by excavation. Such ground disturbance occurs particularly when, for example, the ground to be tested is below the level of groundwater, the ground is saturated, and sandy ground including unconsolidated sandy soil layers. Cheap. And the ground that needs to be tested is often a turbulent formation. When a water permeability test or the like is performed on the target ground in a disturbed state, the reliability of the test results is greatly reduced, and therefore a countermeasure for suppressing the ground disturbance as much as possible has been demanded.

Geotechnical Society Geotechnical Survey Standards and Standards Committee Edition (2013): Geotechnical Survey Method and Explanation-2-Volume 1-, Geotechnical Society, p. 521

  The present invention has been made paying attention to the above-described problem, and when creating a test hole for pouring water into the target ground or pumping water from the target ground, disturbance of the state around the test hole can be suppressed as much as possible. It is an object of the present invention to provide a test hole creation method and a test method using the test hole.

  An aspect of the method for creating a test hole according to the present invention includes: (a) a step of inserting a cylindrical casing tube having a perforated portion on the peripheral surface from the ground toward the target ground; and (b) an inner side of the casing tube. A step of selectively collecting the stratum inside the casing tube so that the stratum remains on the surface, and investigating the collected stratum, and (c) a state in which the stratum below the tip of the casing tube is suppressed by the remaining stratum Forming a hole from the ground to the target ground as a test hole, and (d) investigating the properties of the target ground by circulating a fluid between the casing tube and the target ground through the perforated portion. The gist is to use test holes.

  Further, an aspect of the test method according to the present invention includes (a) a step of inserting a cylindrical casing tube having a perforated portion on the peripheral surface from the ground toward the target ground, and (b) a formation on the inner side of the casing tube. A step of selectively collecting the formation inside the casing tube so as to remain, and investigating the collected formation, and (c) the ground in a state where the formation below the tip of the casing tube is suppressed by the remaining formation. A step of forming a hole from the target ground to the target ground as a test hole, and (d) a step of testing to examine the properties of the target ground by circulating a fluid between the casing tube and the target ground through the hole portion, It is made to include.

  Therefore, according to the present invention, there are provided a test hole creation method and a test method using the test hole, which can suppress disturbance of the state around the test hole as much as possible.

Fig.1 (a) is a front view which illustrates typically the drilling apparatus which has a perforated part which concerns on embodiment of this invention, FIG.1 (b) is the AA line in Fig.1 (a). It is sectional drawing seen from the direction, and FIG.1 (c) is sectional drawing seen from the BB line direction in FIG.1 (b). FIG. 2 is an enlarged view of a portion C in FIG. It is process sectional drawing which illustrates typically the preparation method of the test hole which concerns on embodiment of this invention (the 1). It is process sectional drawing which illustrates typically the creation method of the test hole which concerns on embodiment of this invention (the 2). It is process sectional drawing which illustrates typically the production method of the test hole which concerns on embodiment of this invention (the 3). It is process sectional drawing which illustrates typically the production method of the test hole which concerns on embodiment of this invention (the 4). It is process sectional drawing which illustrates typically the production method of the test hole which concerns on embodiment of this invention (the 5). It is process sectional drawing which illustrates typically the production method of the test hole which concerns on embodiment of this invention (the 6). It is process sectional drawing which illustrates typically the production method of the test hole which concerns on embodiment of this invention (the 7). It is process sectional drawing which illustrates typically the preparation method of the test hole which concerns on embodiment of this invention (the 8). It is process sectional drawing which illustrates typically the production method of the test hole which concerns on embodiment of this invention (the 9).

Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and it should be noted that the relationship between the thickness and the planar dimensions, the ratio of the thickness of each device and each member, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description.
Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings. Also, the directions of “left and right” and “up and down” in the following description are merely definitions for convenience of description, and do not limit the technical idea of the present invention. Thus, for example, if the paper is rotated 90 degrees, “left and right” and “up and down” are read interchangeably, and if the paper is rotated 180 degrees, “left” becomes “right” and “right” becomes “left”. Of course.

<Drilling device having a perforated portion>
First, a drilling apparatus having a perforated portion used in a test hole creation method and a test method according to an embodiment of the present invention will be described. As shown in FIG. 1A, a drilling device (11, 21) having a perforated portion includes a substantially cylindrical casing tube 11 forming a main body and a longitudinal center on the outer peripheral surface of the casing tube 11. And a net-like member 21 provided in the region.
The casing tube 11 can be manufactured using a tubular member made of a material such as a steel tube or a reinforced plastic composite tube as a base material. Further, the length of the casing tube 11 can be set as appropriate in consideration of the depth of the target ground and the like, but in the case illustrated in FIG. 1, the length is about 1.0 m to about 1.5 m.

  The front end of the casing tube 11 on the lower side in FIG. 1, which is located on the front side in the direction of insertion into the ground, is sharpened from the center side toward the end surface so as to reduce resistance during insertion into the ground. Yes. Further, as shown in FIG. 1 (b), the tube wall extends from a position spaced apart from the tip of the casing tube 11 toward the center by a certain distance to a region having a certain width toward the rear end on the upper side in FIG. A recess having a thickness less than other portions is formed to form a step.

In the region of the thinned tube wall, a plurality of holes penetrating the tube wall are provided along the longitudinal direction and the circumferential direction of the casing tube 11, and the perforated portion of the casing tube 11 is formed by the whole of the plurality of holes. 11a is formed. Moreover, the area | region between the front-end | tip of the casing pipe | tube 11 and the perforated part 11a has comprised the non-hole part 11b in which the hole which penetrates a pipe wall is not provided.
The width _Whole measured along the height direction of the perforated part 11a can be set as appropriate in consideration of the thickness of the target ground and the thickness of the water injection or pumping range targeted in a planned water permeability test or the like. is there. In the case of the perforated portion 11a of the casing tube 11 shown in FIG. 1, the width W _hole is about 30 cm.

Here, for example, when excavating a ground in which the ground to be excavated is a sandy soil layer and a viscous soil layer is disposed on the upper side of the sandy soil layer, the width W _solid of the non-hole portion 11b is 40 cm. It can be set to about ˜60 cm, more preferably about 50 cm. If the width W _solid of the non-perforated portion 11b is less than 40 cm, a sufficient separation distance between the perforated portion 11a and the stratum remaining below the perforated portion 11a cannot be secured inside the casing tube 11, and The ground disturbance near the hole 11a may increase.

Further, when the width W _solid of the non-hole portion 11b is increased, when the casing tube 11 is press-fitted into the ground, the ground of the casing tube 11 is increased due to an increase in frictional force between the outer and inner walls of the non-hole portion 11b and the ground. The resistance force when press-fitting into is increased. If it exceeds 50 cm, the resistance force during press-fitting into the ground becomes too large, so that it is necessary to apply a load to the ground by applying an impact or rotating the casing tube 11 from the upper side during insertion. Therefore, the possibility of inducing disturbance of the ground around the test hole is increased.

  As shown in FIG. 1 (c), the plurality of holes of the perforated portion 11a are provided at almost equal intervals over the entire peripheral surface of the tube wall of the casing tube 11, and during the water injection or pumping work following the drilling. The water poured into the inside of the casing pipe 11 is horizontally fed to the target ground through the perforated part 11a of the casing pipe 11, or the ground water of the target ground is supplied through the perforated part 11a of the casing pipe 11 to the casing pipe. 11 can be used to pull horizontally inside. However, the arrangement pattern of the plurality of holes is not limited to the one shown in FIG. 1 (c), and is appropriately changed depending on the contents of the planned test, the presence / absence of the rotating operation of the casing tube 11 at the time of insertion, and the like. May be.

The net-like member 21 is preferably made of a metal such as iron or stainless steel as a material from the viewpoint of durability, but is not limited thereto, and may be another material such as reinforced plastic. As shown in FIG. 1B, the mesh member 21 is fixedly fitted into a recess on the outer peripheral surface of the casing tube 11.
The depth of the recess is set to substantially correspond to the thickness of the mesh member 21, and the position of the outer surface of the mesh member 21 attached to the recess is substantially aligned with the position of the outer peripheral surface of the casing tube 11. In FIG. 1B and FIG. 1C, the depth of the recess corresponding to the thickness of the mesh member 21 is exaggerated deeper than the actual depth.

Since the mesh member 21 is attached in a state of being wound around the outer peripheral surface of the casing tube 11 so as to cover almost all of the recessed region, it is included in the perforated portion 11a of the casing tube 11 as shown in FIG. All of the plurality of holes overlap the mesh of the upper mesh member 21.
The shape of the hole of the perforated part 11a is arbitrary, such as circular, elliptical or rectangular, but the sum of the opening areas of the holes included in the perforated part 11a is set in consideration of the strength of the casing tube 11. The

The size of one hole of the perforated part 11a is arbitrary. Further, the mesh opening of the mesh member 21 is set to a size that can prevent fine particles of earth and sand from entering the casing tube 11 from the outside of the casing tube 11. Specifically, from experience, the mesh opening of the mesh member 21 is preferably about 150 μm. In addition, it is desirable that the effective aperture ratio obtained by multiplying the aperture ratio of the perforated portion 11a and the aperture ratio of the mesh member 21 is large in the execution of the test. For example, it is conceivable to devise the selection of members and the shape and dimensions of the perforated portion by securing an effective aperture ratio of about 10%.
Thus, by setting the hole diameter of the perforated part 11a and the mesh openings of the mesh member 21, it is possible to effectively prevent fine particles of earth and sand from entering the inside of the casing pipe 11 from the outside of the casing pipe 11. .

<Test hole creation method and test method>
Next, a test hole creation method and a test method using the hole drilling device (11, 21) having the perforated portion shown in FIG. 1 will be exemplarily described with reference to FIGS. The target ground to be drilled and tested is a sandy soil layer G, and a viscous soil layer F exists between the sandy soil layer G and the ground, and forms an upper layer of the sandy soil layer G. Set.
Therefore, the test hole creating method according to the embodiment of the present invention excavates the viscous soil layer F and the sandy soil layer G, and water is poured into the sandy soil layer G without disturbing the ground around the test hole. It is used to create a hole for pumping water from the sandy soil layer G. Moreover, as shown by the water level line drawn on the left side of the upper part of the viscous soil layer F in FIG. 3, the sandy soil layer G exists below the groundwater level and is saturated.

(Step 1)
First, the rough depth position of the upper surface of the sandy soil layer G in the ground and the thickness of the sandy soil layer G are investigated in advance by performing boring in the vicinity. At that time, it should be noted that if a boring survey is conducted in advance at a position extremely close to the point where the ground test is to be performed, the ground to be tested may be disturbed and the test result may be affected. Next, the casing pipe 11 is inserted into the ground up to the vicinity of the sandy soil layer G.
The insertion is performed while considering so as to suppress the disturbance of the ground around the casing tube 11 by a press-fitting operation that pushes in slowly. During the press-fitting, when the casing tube 11 comes into contact with the hard part of the sandy soil layer G, for example, vibration by a vibration penetration mechanism or the like may be applied from the upper side. In order to suppress, it is preferable to use it limitedly.

  In addition, the casing tube 11 may be rotated and inserted. However, if the mesh member 21 is made of a material such as metal, the formation around the casing tube 11 is in rotational contact with the mesh member 21 to increase frictional heat. However, the formation may be heated greatly. In that case, the mesh of the mesh member 21 is likely to be clogged by the heated soil particles. In particular, when the ground to be inserted is a viscous soil layer, clogging is very likely to occur. Therefore, the rotational insertion is preferably performed while controlling the number of rotations of the casing tube 11 so as to suppress clogging. FIG. 3 illustrates a state in which the tip of the casing tube 11 has reached the inside of the sandy soil layer G after the casing tube 11 is inserted in this manner.

(Step 2)
Next, as shown in FIG. 4, the sampler 40 is inserted inside the inserted casing tube 11. Since the casing tube 11 exists between the sampler 40 and the sandy soil layer G inside the casing tube 11, even if the sampler 40 is quickly inserted by using, for example, rotation, the ground is formed outside the casing tube 11. It does not induce turbulence.

The sampler 40 is inserted so that the tip end is spaced from the lower end of the perforated portion 11a by a constant distance ΔD1 and reaches the position spaced above the tip end of the casing tube 11 by a constant distance ΔD2. . That is, the sampling of the formation by the sampler 40 does not collect the entire formation inside the casing tube 11, but remains inside the casing tube 11 so that the formation remains with a thickness corresponding to a certain distance ΔD2. Collect selectively.
This distance ΔD2 is empirically set within a range of about 30 cm to about 50 cm. Then, the formation position of the formation by the sampler 40 is separated from the lower end of the perforated part 11a by a certain distance ΔD1. Thereby, the disturbance of the ground around the perforated part 11a induced by the cutting of the formation by the sampler 40 can be suppressed.

  And the upper surface of the formation which remained inside the casing pipe | tube 11 makes the hole bottom located between the perforated part 11a and the front-end | tip of the casing pipe | tube 11, as shown in FIG. Further, the remaining formation forms a “lid” that suppresses the formation below the tip of the casing tube 11. Then, by using the remaining weight of the formation and the frictional force between the remaining formation and the inner peripheral surface of the casing tube 11, the bottom of the inner hole of the casing tube 11 is prevented from rising, and the disturbance of the surrounding ground is suppressed. can do.

(Step 3)
Next, as shown in FIG. 5, the sampler 40 is collected on the ground from the inside of the casing tube 11 to collect the formation. On the ground, the collected formation is analyzed as a sample. As a result of the analysis, when the collected stratum includes the sand of the sandy soil layer G, it is understood that the casing tube 11 has reached the sandy soil layer G, and the thickness of the collected sandy soil layer G is It compares with the width | variety of the net-like member 21 as aim of the existence range of the perforated part 11a.
And how much the presence range of the perforated portion 11a of the casing pipe 11 in the soil overlaps with the thickness of the planned water injection or pumping range of the sandy soil layer G, that is, at the current position of the casing pipe 11 as it is. Determine if testing is possible immediately. If water injection or pumping is possible, the process proceeds to step 5 shown in FIG.

(Step 4)
On the other hand, when water injection or pumping is impossible, as shown in FIG. 6, the casing tube 11 is inserted further deeply so that the perforated part 11a reaches a position sufficiently overlapping the planned water injection or water pumping range, Further, the sampler 40 is inserted into the casing tube 11 and collected to collect the formation.
In FIG. 6, the thickness of the sandy soil layer G is illustrated as being sufficiently thicker than the width of the net-like member 21, but the present invention is not limited to this. It may be configured to be the same level. The casing tube 11 is disposed so that the upper end of the mesh member 21 is aligned with the upper surface of the sandy soil layer G. However, the casing tube 11 may be disposed so that the mesh member 21 is at a deeper position.
It is confirmed by the sampled sample whether the perforated part 11a of the casing tube 11 is inserted at the position of the ground to be tested. If it is determined that water injection or pumping is impossible, for example, the thickness of the sandy soil layer G is smaller than the width of the mesh member 21, steps 2 to 4 are repeated.

  Further, the casing tube 11 preferably has a rear end at a position with a protrusion height Δh of about 5 cm or more and about 50 cm or less from the ground when the depth of the perforated portion 11a is adjusted. If the protrusion height Δh is less than about 5 cm, there is a possibility that a problem may occur in terms of contamination of foreign matter in the hole, operator safety, and the like. Further, when the protrusion height Δh exceeds about 50 cm, the handling of the casing tube 11 becomes complicated, and the length and shape of the piping of the test apparatus to be described later may have to be increased, so that workability is improved. Getting worse.

(Step 5)
Next, as shown in FIG. 7, water is poured into the casing tube 11 by the water pouring device 10, and the wire brush 19 is inserted into the casing tube 11 and reciprocated in the vertical direction to move the inside of the casing tube 11. The perforated part 11a, the non-perforated part 11b and the mesh member 21 on the peripheral surface are cleaned. At this time, earth and sand adhering to the perforated part 11a, the non-perforated part 11b, the net-like member 21 and the like are mixed into the pore water, and the pore water becomes muddy. In addition, in FIG. 7, although the water injection apparatus 10 which has the faucet opened to the casing pipe | tube 11 on the ground side is shown, this is a typical illustration. In practice, water can be injected by pumping water from a water source separated from the casing tube 12 by a pump or the like via a hose or the like connected to the water source.

(Step 6)
Next, as shown in FIG. 8, a pumping pump 27 and a nozzle 29 attached to the pumping pump 27 via a tube 26 are prepared. The nozzle 29 can be composed of a PVC pipe such as VP13, for example. Thereafter, the pump 27 is installed on the ground, and the tip of the nozzle 29 on the pumping side is inserted so as to be positioned inside the water Wa stretched inside the casing tube 11.
Then, the pump 27 is driven to pump up and discharge the turbid water Gt inside the casing tube 11 while stirring, and water is injected by the water injection device 10 in parallel with the pumping to replace the in-hole water. Thereby, the earth and sand adhering to the net | network of the perforated part 11a, the non-porous part 11b, and the net-like member 21 are removed also including a fine grain part.

(Step 7)
The amount of muddy water Gt existing inside the casing pipe 11 is gradually reduced by pumping up the muddy water Gt and continuing water injection. The muddy water Gt is discharged until the water in the hole is cleaned as shown in FIG. The degree of cleanliness can be set, for example, by measuring the transparency of the pumped water and confirming 50 degrees (50 cm) or more. FIG. 9 illustrates a state in which the pore water is cleaned and the formation having a certain thickness left inside the casing tube 11 is left without being fluidized.

(Step 8)
Next, as shown in FIG. 10, water injection and pumping are stopped, the nozzle 29 in the water Wa is lifted from the hole, and the recovery state of the water level in the hole is observed. At this time, it is possible to confirm the clogging state of the perforated portion 11a of the casing tube 11 and the mesh of the mesh member 21 and predict the water permeability of the sandy soil layer G.
In addition, by recording the water level (generally called "equilibrium water level") after the groundwater level naturally recovers to a certain level, it can be used as reference data in later scheduled tests. However, in the case of continuing the work of Step 9, the water level in the hole fluctuates by inserting a water injection or pumping test machine. Therefore, after inserting the water injection or pumping test machine and inflating the packer, the equilibrium water level is adjusted. You may want to confirm.

(Step 9)
Next, water is poured or pumped into the hole, and preparation for a test for examining the water permeability of the sandy soil layer G is performed. First, water injection or pumping test machines (36, 37, 38, 39) used for the test are prepared as shown in FIG. The water injection or pumping tester (36, 37, 38, 39) includes, for example, a pump 37 capable of pumping and suction, a water injection pipe or water pumping pipe 36 having one end connected to the pump 37, and this water injection pipe or water pumping pipe. A double packer (38, 39) provided concentrically with the water injection pipe or pumping pipe 36 is provided at the other end of 36.

  In the region sandwiched between the double packers (38, 39) at the other end of the water injection pipe or the water pumping pipe 36, a plurality of holes forming the water injection part or the water pumping part 36a are provided. Water is sent out from the water injection part or pumping part 36 a to the outside of the water injection pipe or pumping pipe 36. In the case of pumping, when sucked by the pump 37, water is sucked into the water injection pipe or the water pumping pipe 36 via the water injection part or the water pumping part 36a. As a specific water injection or pumping procedure, the other end of the water injection pipe or pumping pipe 36 on the side of the water injection part or the water pumping part 36a is overlapped with the water injection part or water pumping part 36a in the existence range of the perforated part 11a of the casing pipe 11. And insert into the hole together with the double packer (38, 39).

  For example, as shown in FIG. 11, the upper packer 38 forming the double packer (38, 39) is located above the perforated part 11a, and the lower packer 39 is located below the perforated part 11a. Inflated and crimped to the inner peripheral surface of the casing tube 11. And the position of the water injection part or the pumping part 36a inside the casing pipe | tube 11 is fixed so that it may overlap with the perforated part 11a. Then, the space between the upper packer 38 and the lower packer 39 is sealed.

Thereafter, the pump 37 is driven to pump or suck water into the water injection pipe or pumping pipe 36, and the water is sent out to the sealed space between the double packers (38, 39) via the water injection part or the water pumping part 36a. Or suck up from the enclosed space. The water sent out to the sealed space is sent so as to flow almost horizontally inside the sandy soil layer G outside the casing pipe 11 through the hole of the perforated part 11a of the casing pipe 11. Alternatively, the water inside the sandy soil layer G outside the casing tube 11 is drawn into the sealed space through the hole of the perforated portion 11a of the casing tube 11 by sucking water from the sealed space.
In addition, in FIG. 11, the mode in the case of pouring water into the sandy soil layer G is illustrated, but it is clear if the direction of water indicated by the arrow in FIG. 11 is replaced with the opposite direction. The groundwater can also be pumped from the sandy soil layer G. Hereinafter, if a predetermined test process is performed, the water permeability of the sandy soil layer G can be examined.

According to the method for creating a test hole according to the embodiment of the present invention, the confirmation work of the target ground by collecting the sample sample of the target ground and the subsequent water injection or pumping work to the target ground are continuously performed in one hole. Do it. That is, since it is only necessary to excavate one hole that serves as both a hole for collecting a sample and a test hole, the ground disturbance around the test hole due to drilling can be greatly suppressed.
Further, when drilling, the entire inner layer of the casing tube 11 is not sampled, but the sample is selectively sampled so that a part of the geological layer remains, and the lower side is obtained by using the weight of the remaining geological layer and the peripheral surface friction. Suppress the formation of Therefore, it is possible to suppress the occurrence of a state in which the hole bottom is raised after the sample is collected and the surrounding ground is disturbed.

In particular, when the surrounding ground is disturbed, rearrangement of the soil particles occurs, changing the void structure between the soil particles. If the void structure between the soil particles changes, the water permeability of the ground changes, so the water permeability at the original position of the ground, which is the purpose of the test, cannot be grasped correctly. According to the test hole creating method according to the embodiment of the present invention, it is advantageous in that occurrence of such trouble can be effectively prevented.
As described above, according to the method for creating a test hole according to the embodiment of the present invention, the ground disturbance around the test hole is totally reduced from the start of drilling operation to the start of water injection or pumping. Therefore, it is possible to create a test hole suitable for various in-situ tests scheduled after excavation.

  Further, according to the test method according to the embodiment of the present invention, water was circulated as a fluid between the casing tube 11 and the sandy soil layer G through the perforated portion 11a, and used for collecting a sample sample. Since the hole can be continuously used as the water injection hole or the pumping hole as it is, the labor of drilling can be saved greatly. Therefore, it is possible to quickly prepare for the test while reducing the overall work load. Moreover, since the ground disturbance around the test hole is suppressed before the test, the reliability of the test results of various in-situ tests including water injection or pumping operation can be improved. The fluid to be circulated may be an aqueous solution in which various chemicals other than water are dissolved, or a gas such as a gas.

<Other embodiments>
Although the present invention has been described by the embodiments disclosed above, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, it should be understood that various alternative embodiments, embodiments and operational techniques will become apparent to the present invention. For example, the method for creating the test hole according to the present invention is not limited to excavation of the sandy soil layer G and the viscous soil layer F, and the target ground may be another layer such as a gravel layer or a silt layer. Applicable.
In addition, for example, the net-like member 21 is displayed as a one-layer structure in FIG. 1B and FIG. 1C for convenience of explanation, but is not limited to this, and a two-layer double mesh structure, A multi-layer structure of three or more layers may be used. By adopting a structure of two or more layers, the strength is improved, and the resistance to resistance when the casing tube 11 is inserted can be increased.

Moreover, in description of the preparation method of the test hole shown in FIGS. The state of passing through and reaching the inside has been described as the initial state. However, the depth of the sandy soil layer G is deeper than the length of the single casing tube 11, and the tip cannot reach the sandy soil layer G simply by inserting the single casing tube 11. Can happen.
In that case, for example, first, a single casing tube 11 is inserted to collect a sample sample, and then the casing tube 11 is further deepened and inserted. Then, another casing tube having a structure connectable to the rear end of the casing tube 11 on the ground side is prepared, and the two casing tubes are connected through the connecting structure to have a perforated portion (11, 21) Stretch the entire length.

As an example of such a connection structure, a female screw is provided on the inner peripheral surface of the rear end of the preceding casing tube 11 and a male screw corresponding to this female screw is provided at the tip of the subsequent casing tube 11. it can. In addition to the fastening structure using screws, other connection structures such as a fitting structure and a pin connection may be used.
Then, the sampler 40 is fed into the inside of the expanded casing tube 11, and a sample sample is collected and drilled. Such casing digging may be repeated sequentially until the tips of the casing tube 11 and the sampler 40 reach the positions shown in FIG.
As described above, the present invention includes various embodiments and the like not described above, and the technical scope of the present invention is determined only by the invention specifying matters according to the appropriate claims from the above description. Is.

  INDUSTRIAL APPLICABILITY The present invention can be widely used for excavation of a hole used for a test for determining the permeability coefficient of the ground. For example, it is suitable when investigating the water permeability of a sandy soil layer by the packer method (Non-patent Document 1) of the single hole type water permeability test methods.

  Further, the present invention can be widely used for excavation of a hole used in a test for scrutinizing the necessity of piping countermeasures on the foundation ground of a river dike and prioritizing, for example. For example, when performing a test for examining the water permeability of a sandy soil layer as disclosed in Japanese Patent Application No. 2015-104668, a water injection hole is formed among two holes that are drilled apart from each other. It is suitable for the case.

DESCRIPTION OF SYMBOLS 10 Water injection apparatus 11 Casing pipe 11a Perforated part 11b Non-hole part 19 Wire brush 21 Net-like member 26 Tube 27 Pumping pump 29 Nozzle 36 Injection pipe or pumping pipe 36a Injection pipe or pumping part 37 Pump 38 Packer 39 Packer 40 Sampler F Cohesive soil Layer G Sandy soil layer Gt Turbid water Wa Water W _hole Perforated part width W _Solid non-perforated part width ΔD1 Distance between the lower end of the perforated part and the tip of the sampler ΔD2 Between the front end of the casing tube and the front end of the sampler Distance Δh Projection height of casing tube

Claims (4)

Inserting a cylindrical casing tube having a perforated portion on the peripheral surface from the ground toward the target ground; and
Selectively collecting a stratum inside the casing tube so that a stratum remains inside the casing tube, and examining the collected stratum;
Forming a hole from the ground to the target ground as a test hole in a state in which the formation below the tip of the casing tube is suppressed by the remaining formation;
Including
A test hole creating method, wherein the test hole is used for a test for examining a property of the target ground by flowing a fluid between the casing tube and the target ground through the perforated portion.   The test according to claim 1, wherein the test includes a process of feeding water into the target ground through the perforated part or a process of drawing ground water in the target ground through the perforated part. How to create a hole. Inserting a cylindrical casing tube having a perforated portion on the peripheral surface from the ground toward the target ground; and
Selectively collecting a stratum inside the casing tube so that a stratum remains inside the casing tube, and examining the collected stratum;
Forming a hole from the ground to the target ground as a test hole in a state in which the formation below the tip of the casing tube is suppressed by the remaining formation;
Testing to examine the properties of the target ground by circulating fluid between the casing tube and the target ground through the perforated portion;
A test method comprising: The test according to claim 3, wherein the test includes a process of feeding water to the target ground through the perforated part or a process of drawing groundwater in the target ground through the perforated part. Method.

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