JP6631953B2 - Ground drilling method - Google Patents

Description

  The present invention relates to a method of drilling a ground, and more particularly to a method of drilling a saturated unconsolidated sandy ground without disturbing the ground.

  2. Description of the Related Art Conventionally, for the purpose of embankment and the like, tests for examining properties such as water permeability of the ground have been performed. Such tests are performed in situ, for example, by excavating and forming a hole from the ground to the target ground, and by changing the water level in the hole, the permeability of the target ground exposed at the bottom of the formed hole (The tube method (Non-Patent Document 1) of the single-hole type water permeability test method). As a method of forming a hole used in the test, for example, there is a method of drilling a ground in which a casing pipe is inserted into the ground, and a formation inside the casing pipe is removed to form a hole.

However, for example, when the target ground is below the level of groundwater and the ground is saturated and the sandy ground includes an unconsolidated sandy soil layer, excavation of the upper layer of the target ground may result in excavation. , The lower target ground may be disturbed from the original state of the original position.
That is, there is a case where the bonding state of the soil particles greatly changes and the size and shape of the gap between the soil particles greatly change. When a test is performed using the target ground that has been disturbed in this way, there is a problem that even a small change in the disturbance greatly affects the test results.

Geotechnical Society Geotechnical Survey Standards and Standards Committee (2013): Geotechnical Survey Methods and Explanations-Two volumes, 1-Geotechnical Society, p. 521

  The present invention has been made in view of the above problems, and has an object to provide a ground drilling method capable of suppressing disturbance of a target ground when excavating a hole from the ground to the target ground. I do.

  In one aspect of the ground drilling method according to the present invention, there are provided (a) a step of inserting a casing pipe so that a tip thereof is located at a depth of a target ground from the ground, and (b) selecting a formation inside a casing pipe. (C) discharging the non-collecting layer from the inside of the casing tube, and removing the target ground inside the casing tube. Exposing to form a hole from the ground to the target ground.

  Therefore, according to the ground drilling method of the present invention, when excavating a hole from the ground to the target ground, disturbance of the target ground can be suppressed.

It is process sectional drawing which illustrates typically the ground drilling method which concerns on embodiment of this invention (the 1). It is process sectional drawing which illustrates typically the ground drilling method which concerns on embodiment of this invention (the 2). It is process sectional drawing which illustrates typically the ground drilling method which concerns on embodiment of this invention (the 3). It is process sectional drawing which illustrates typically the ground drilling method which concerns on embodiment of this invention (the 4). It is process sectional drawing which illustrates typically the ground drilling method which concerns on embodiment of this invention (the 5). It is process sectional drawing which illustrates typically the ground drilling method which concerns on embodiment of this invention (the 6).

Hereinafter, embodiments of the present invention will be described. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimension, the ratio of the thickness of each device and each member, and the like are different from actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description.
In addition, it is needless to say that dimensional relationships and ratios are different between drawings. Further, the directions of “left and right” and “up and down” in the following description are simply definitions for convenience of description, and do not limit the technical idea of the present invention. Therefore, 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.

<How to drill the ground>
A ground drilling method according to an embodiment of the present invention will be exemplarily described with reference to FIGS. The target ground to be exposed is the sandy soil layer G, and the cohesive soil layer F exists between the sandy soil layer G and the ground, forming an upper layer of the sandy soil layer G. In the method for drilling the ground according to the embodiment of the present invention, the clay soil layer F is mainly excavated and drilled as a hole extending from the ground to the sandy soil layer G without disturbing the upper surface of the sandy soil layer G. Used to make holes. Further, as shown by a water level line drawn to the left above the cohesive soil layer F in FIG. 1, the sandy soil layer G exists below the groundwater level and is saturated.
Although FIGS. 1 to 6 illustrate an example in which the upper surface of the sandy soil layer G as the target ground is exposed, the present invention can of course drill holes other than the boundary of the ground layer. . Further, FIGS. 5 to 6 show an example in which all the formation remaining in the inside of the casing pipe 12 is removed. However, the present invention is not limited to the fact that the drilling can be performed so as to remove only a part of the remaining formation. Of course.

(Step 1)
First, a rough depth position of the underground sandy soil layer G is investigated in advance by performing boring or the like in the vicinity. At that time, be aware that if a boring survey is performed in advance at a location extremely close to the point where the ground test is to be performed, the ground on which the test is to be performed may be disturbed and the test results may be affected.
Next, as shown in FIG. 1, the casing tube 12 is inserted into the ground so that the lower end of the casing tube 12 reaches the upper surface of the sandy soil layer G. The casing tube 12 illustrated in FIG. 1 is substantially cylindrical, has a sharpened tip, and has a cutting edge shape, and has reduced resistance when inserted into the ground.

  The insertion is basically performed by a press-fitting operation that pushes in slowly, with consideration given to suppressing disturbance of the ground around the casing tube 12. For insertion, for example, vibration from a vibration penetrating mechanism or the like may be applied from the upper side, but it is preferable that the insertion be limitedly used in order to suppress the influence of the vibration work on the surrounding ground. In the case of a method in which a rotating machine or the like is provided on the upper part of the casing pipe 12 and the casing pipe 12 is inserted while rotating, the vibration during excavation transmitted to the sandy soil layer G can be reduced, and the disturbance of the ground can be further suppressed. Is desirable.

When the front end (lower end) of the casing tube 12 is aligned with the upper surface of the sandy soil layer G, it is preferable that the rear end (upper end) is located at a position with a protrusion height Δh of about 5 cm or more and about 50 cm or less from the ground. If the protrusion height Δh is less than about 5 cm, there is a possibility that inconveniences may occur in terms of entry of foreign matter into the holes, safety of the operator, and the like.
In addition, the longer the projecting height Δh of the casing tube 12 is, the larger the amount of water that can be stretched inward can be increased, which is effective as a lid for the sandy soil layer G described later. However, when the protrusion height Δh exceeds about 50 cm, handling of the casing tube 11 becomes complicated, and workability deteriorates.

(Step 2)
Next, as shown in FIG. 2, the sampler 40 is inserted inside the inserted casing tube 12 such that the lower end of the sampler 40 reaches a position separated by a certain distance ΔD from the upper surface of the sandy soil layer G. I do. As for the insertion, as in the case of inserting the casing tube 12, a method of inserting by rotation is desirable.
When the upper layer of the sandy soil layer G is the cohesive soil layer F, the distance ΔD is preferably about 30 cm or more and about 50 cm or less. When it is less than about 30 cm, the force as a lid for suppressing the sandy soil layer G is weakened. If it exceeds about 50 cm, the amount of the non-collecting layer Fa remaining inside the casing tube 12 in step 3 to be described later becomes too large, and the burden of the operation of discharging later becomes large.

(Step 3)
Next, as shown in FIG. 3, the sampler 40 is collected from the inside of the casing tube 12 to collect the formation. On the other hand, part of the viscous soil layer F remaining between the lower end of the sampler 40 and the lower end of the casing tube 12 at the time of insertion becomes a non-collecting layer Fa.
That is, the sampling by the sampler 40 does not collect the entire clay soil layer F inside the casing pipe 12, but selectively collects the non-collecting layer Fa having a thickness corresponding to the distance ΔD. The non-collecting layer Fa forms a “cover” that suppresses the sandy soil layer G on the sandy soil layer G, and the weight between the non-collecting layer Fa and the inner peripheral surface of the casing pipe 12 and the non-collecting layer Fa. Using the frictional force, the turbulence of the sandy soil layer G is suppressed.

(Step 4)
Next, as shown in FIG. 4, water is injected into the inside of the casing tube 12 by the water injection device 10. By spreading the water Wa on the non-collecting layer Fa by water injection, the weight of the stretched water Wa is added to the “cover” on the sandy soil layer G, and the disturbance of the sandy soil layer G is further suppressed. In addition, by performing this water injection treatment as soon as possible after extracting the sampler 40, it is possible to suppress the rise of the hole bottom due to unloading on the sandy soil layer G.
Note that FIG. 4 shows the water injection device 10 having a faucet that opens to the casing tube 12 on the ground side, but this is a schematic example. In fact, it goes without saying that water can be pumped 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 and injected.

(Step 5)
Next, as shown in FIG. 5, the non-collecting layer Fa remaining in the lower part of the casing tube 12 is agitated while being crushed by a stirring rod 19 to be muddy, thereby enhancing fluidity. In FIG. 5, the boundary between the fluidized non-collecting layer Fa and the water Wa is illustrated by a flat horizontal line. However, in reality, the soil particles float in the water and the boundary position flows. I have.
Next, a water pump 27 and a nozzle 29 attached to the water pump 27 via a tube 26 are prepared. The nozzle 29 can be composed of, for example, a PVC pipe such as VP13, and in that case, the stirring rod 19 and the nozzle 29 can also be used. Thereafter, a water pump 27 is installed on the ground, and the tip on the pumping side of the nozzle 29 is inserted into the water Wa stretched inside the casing tube 12 so as to be positioned inside the fluidized non-collecting layer Fa. I do.

  Then, the pump 27 is driven to pump up and discharge the muddy water inside the casing tube 12, and in parallel with the pumping, water is injected by the water injection device 10 to keep the water level in the hole high. FIG. 5 illustrates a state in which the water Wa is stretched so that the water level in the hole is higher than the groundwater level. By raising the water level in the hole, the load on the sandy soil layer G can be maintained at a high level without lowering the weight of the lid as much as possible even when muddy water is pumped up, and the rise of the hole bottom can be prevented. .

  The nozzle 29 is spaced apart from the upper surface of the sandy soil layer G such that the tip has a clearance of, for example, about 1 cm or more and about 2 cm or less from the upper surface of the sandy soil layer G. By providing such a small clearance and separating the sandy soil layer G, it is possible to prevent the sandy soil layer G from being disturbed by collecting muddy water. Also, the pumping amount of the pumping pump 27 is controlled so that the sandy soil layer G is not disturbed by the pumping force. The separation distance between the tip of the nozzle 29 and the upper surface of the sandy soil layer should be appropriately adjusted according to the capacity of the water pump 27.

By the pumping of the muddy water and the continuous water injection, the amount of the muddy water present inside the casing tube 11 gradually decreases. As shown in FIG. 6, the muddy water is discharged until the soil particles contained in the non-collecting layer Fa are sufficiently discharged to the outside of the casing tube 12 and the water in the hole is cleaned. The degree of cleanliness can be set, for example, by measuring the degree of transparency of the pumped water and confirming 50 degrees (50 cm) or more.
If the drilled hole is not sufficiently cleaned and a certain degree of turbidity remains, and the drilled hole is used for a test later, fine particles of the turbid soil particles settle at the bottom of the hole. It is more likely that the test of the soil layer G will be hindered. In addition, in the case of a test in which water injection and pumping are performed simultaneously in these holes, the possibility of the clogging of tubes and pumps with fine particles at the time of pumping increases, so that the burden of preparation and maintenance of these devices increases.

According to the method for drilling the ground according to the embodiment of the present invention, the sampler 40 does not collect the entire clay soil layer F inside the casing pipe 12 but selectively collects the non-collected layer Fa so as to remain. Then, the lower stratum is suppressed by using the self-weight and the peripheral friction of the remaining non-collected layer Fa. Therefore, it is possible to suppress the occurrence of a state in which the bottom of the hole rises after the sample sample is collected and the surrounding ground is disturbed.
Immediately after collecting the sample, water is injected into the inside of the casing tube 12 to keep the water level in the hole high and to give a sufficient weight to the sandy soil layer G. Disturbance of G can be prevented.

  Further, when discharging the non-collecting layer Fa remaining inside the casing tube 12, the flowability of the non-collecting layer Fa is increased by adding water and stirring the inside, and then the position of the nozzle 29 and the pumping amount are increased. Performed by controlled pumping. Therefore, the connection state between the non-collecting layer Fa and the sandy soil layer G below the non-collecting layer Fa can be loosened and gently separated, without disturbing the ground around the test hole.

  In this respect, a slimy stratum having a relatively strong binding force with the soil particles constituting the sandy soil stratum G, such as the cohesive soil stratum F, is collected near the boundary between the strata, and both strata are collected. In the case of separation, the upper region of the sandy soil layer G may be greatly lifted in conjunction with the lifting. This becomes more remarkable when the sandy soil layer G is in a saturated unconsolidated state, and the bonding state of the internal soil particles greatly fluctuates from the in-situ state. obtain. Therefore, the ground drilling method according to the embodiment of the present invention is particularly effective when applied to excavating the cohesive soil layer F on the sandy soil layer G.

In addition, since the water level in the hole is maintained high even during the discharging operation of the non-collected layer Fa, it is possible to apply a sufficient weight to the upper surface of the sandy soil layer G inside the casing pipe 12, and Ground disturbance is more effectively suppressed.
As described above, when the test hole is formed by using the ground drilling method according to the embodiment of the present invention, the disturbance of the sandy soil layer G is entirely reduced from the start to the end of the drilling operation. Therefore, it can be drilled as a suitable hole for various in-situ tests scheduled after excavation.

<Other embodiments>
Although the invention has been described with reference to the embodiments disclosed above, it should not be understood that the description and drawings forming part of this disclosure limit the invention. From this disclosure, it is to be considered that various alternative embodiments, embodiments, and operation technologies become clear to the present invention.
For example, the method for drilling the ground according to the present invention, which is used for forming test holes, is not limited to excavation of the sandy soil layer G and the cohesive soil layer. The present invention can be applied to other layers such as a sandy soil layer G.

The liquid to be injected to fluidize the non-collecting layer Fa is not necessarily limited to the water Wa, but may be an aqueous solution containing a solute such as various chemicals. However, water Wa, such as tap water or river water, which is not an aqueous solution containing such a particular solute, is more effective than other liquids in terms of convenience of procurement and cost.
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 claims that are appropriate from the above description. Things.

INDUSTRIAL APPLICABILITY The present invention can be widely used for excavation of a hole used for a test for determining the hydraulic conductivity of the ground. For example, the method is suitable for examining the water permeability of a sandy soil layer by the tube method (Non-Patent Document 1) of the single-hole water permeability test method.
Further, the present invention can be widely used, for example, for excavation of a hole used for a test for scrutinizing the necessity of piping countermeasures for the foundation ground of a river embankment and for performing a prioritization test. 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 pumping hole is formed out of two holes that are spaced apart from each other. It is suitable for use in cases.

10 Water injection device 12 Casing pipe 19 Stirrer rod 26 Tube 27 Pumping pump 29, 29a Nozzle 29a1 Opening 40 Sampler G Sandy soil layer F Cohesive soil layer Fa Non-collecting layer Wa Water ΔD Between the tip of the casing pipe and the tip of the sampler Distance Δh Projection height of casing tube

Claims (4)

Inserting the casing tube from the ground so that the tip is located at the depth of the target ground;
Selectively harvesting the formation inside the casing tube, leaving a non-collected layer with a certain thickness inside the casing tube;
Discharging the non-collecting layer from the inside of the casing pipe, exposing the target ground inside the casing pipe, and forming a hole from the ground to the target ground,
A method for drilling a ground, comprising:   The drilling of the ground according to claim 1, wherein the process of discharging the non-collecting layer includes injecting a liquid into the inside of the casing tube and fluidizing the non-collecting layer with the liquid. Method.   Performing the process of discharging the fluidized non-collecting layer and the process of injecting the liquid in parallel so that the height of the liquid is equal to or higher than the groundwater level, and maintaining the height of the liquid. 3. The method for drilling a ground according to claim 2, wherein: The method according to claim 3, wherein the process of discharging the non-collected layer is continuously performed until the liquid becomes transparent.

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