JP2022089863A - Method for confirming bearing ground in construction of foundation pile and auger for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To directly measure soil bearing capacity of a bearing ground in a state in which an auger having a spiral blade around a rod shaft is penetrated into the ground when a foundation pile is constructed using the auger.

SOLUTION: A hydraulic jack 19 is internally provided on the tip of an auger 1, a loading plate 15 for measuring soil bearing capacity is supported on the tip of a piston, in a state in which the auger 1 is restricted so as not to move in a vertical direction when the tip of the auger 1 reaches a support layer, the hydraulic jack 19 is extended and a load is applied to the loading plate 15 for measuring the soil bearing capacity, a jack pressure and a jack extension amount are measured, and thereby a soil bearing capacity measuring test according to a flat plate loading test is performed.

SELECTED DRAWING: Figure 8

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention is a method for confirming the bearing capacity of the supporting ground in a state where the auger is penetrated into the ground when constructing a foundation pile using an auger provided with spiral blades around the rod axis. Regarding the auger.

There are various construction methods for constructing foundation piles for civil engineering structures, and one of them is to use an auger with spiral blades around the rod axis and use this auger around the axis. After excavating the ground in a columnar shape by penetrating into the ground while rotating, a pile is inserted into the excavation hole to construct a foundation pile.

In the construction of the foundation pile, it is important for construction management to confirm whether the tip has reached the support layer at the time of excavating the auger. As a method of confirming the supporting ground, the supporting ground has traditionally been supported by measuring the integrated current value of the auger drive device, focusing on the fact that the N value is higher and the excavation resistance is larger than the other layers. Judgment of reaching the layer was being done.

Specifically, in the following Patent Document 1, the current data detecting means for detecting the current value at the time of excavation of the auger driving motor for driving the auger of the excavator for drilling the ground and the vertical movement distance of the auger are detected. Depth detection means, a signal conversion device that converts the detection signal from each of the detection means into a digital signal for personal computer input, and current data integrated based on the signal input from this signal conversion device, and the depth is input in advance as the vertical axis. A pile support layer detection device is proposed, which comprises a personal computer having a CRT that displays the N value data on the same screen together with the obtained N value data.

Further, in Patent Document 2 below, the reference value acquisition depth setting unit for setting the reference value acquisition depth at a depth shallower than the assumed depth of the support layer and the torque of the excavation drill during excavation of the pile hole correspond to the torque. The reference value is set based on the chart display unit configured to display the integrated value of the current value on the monitor as a chart associated with the excavation depth of the excavation drill and the integrated value corresponding to the reference value acquisition depth. The excavation drill reaches the support layer based on the reference value acquisition unit to be acquired, the reference value acquired by the reference value acquisition unit, and the integrated value corresponding to a depth deeper than the reference value acquisition depth. A support layer arrival determination device including a determination unit configured to determine whether or not the determination has been made and a notification unit configured to notify the determination result of the determination unit has been proposed.

Japanese Unexamined Patent Publication No. 5-2800031 Japanese Unexamined Patent Publication No. 2018-35635

FIG. 13 shows an example of a graph in which the relationship between the integrated current value, the current, and the N value is measured along the depth during actual auger excavation.

The correlation between the integrated current value and the N value is not always in an absolute proportional relationship, and even if the N value is the same, the integrated current value often differs depending on the ground. On the other hand, it is also a fact that there is a certain degree of correlation between the integrated current value and the ground N value, and the supporting ground is exclusively confirmed by measuring the integrated current value of the auger device.

However, since the method of measuring the integrated current value at the time of auger excavation is only an indirect method, a method of directly confirming the supporting ground without impairing the construction efficiency of auger excavation has been desired.

Therefore, the main problem of the present invention is to improve the bearing capacity of the supporting ground while keeping the auger penetrated into the ground when constructing a foundation pile using an auger equipped with spiral blades around the rod axis. It is an object of the present invention to provide a method for confirming a supporting ground by direct measurement and an auger for that purpose.

In order to solve the above problem, as the present invention according to claim 1, an auger provided with spiral blades around the rod axis is used, and the auger is rotated around the axis and penetrated into the ground to excavate the ground. It is a method for confirming the bearing capacity of the supporting ground at the tip of the auger.
A hydraulic jack is internally installed at the tip of the auger, and the loading plate for measuring the bearing capacity is supported at the tip of the piston, and when the tip of the auger reaches the support layer, the auger is restrained so as not to move in the vertical direction. In the state of
A foundation pile characterized in that a ground bearing capacity measurement test similar to a flat plate loading test is performed by extending the hydraulic jack to apply a load to the loading plate for measuring the bearing capacity and measuring the jack pressure and the amount of expansion of the jack. A method for confirming the supporting ground at the time of construction is provided.

In the invention according to claim 1, a hydraulic jack is internally provided at the tip of the auger, and the loading plate for measuring the bearing capacity is supported at the tip of the piston. Then, when the tip of the auger reaches the support layer, the auger is restrained so as not to move in the vertical direction. Then, the hydraulic jack is extended to apply a load to the loading plate for measuring the bearing capacity, and the jack pressure and the amount of expansion of the jack are measured to perform the bearing capacity measurement test according to the flat plate loading test. Therefore, it is possible to directly measure the bearing capacity of the supporting ground while the auger is intruded into the ground.

The present invention according to claim 2 is characterized in that a spiral blade is provided around an axis, a hydraulic jack is internally provided at the tip thereof, and the loading plate for measuring the bearing capacity is supported at the tip of the piston. An auger is provided for the method of confirming the supporting ground at the time of the above-mentioned foundation pile construction.

The invention according to claim 2 describes the structure of an auger for a method of confirming a supporting ground at the time of foundation pile construction.

As described in detail above, according to the present invention, when constructing a foundation pile using an auger equipped with spiral blades around a rod axis, the ground of the supporting ground is maintained with the auger penetrated into the ground. It is possible to confirm the supporting ground by directly measuring the bearing capacity.

Reference It is a side view of the auger 1 used in the ground bearing capacity measurement test method which concerns on the 1st form example. FIG. 1 is a view taken along the line II-II of FIG. FIG. 3 is a view taken along the line III-III of FIG. It is a procedure diagram (No. 1) of the bearing capacity measurement test. It is a procedure diagram (No. 2) of the bearing capacity measurement test. It is a procedure diagram (No. 3) of the bearing capacity measurement test. It is a figure which shows the modification of the projection method of the loading plate 15 for ground bearing capacity measurement. It is a figure which shows the ground bearing capacity measurement test method which concerns on the example of this invention form. Reference It is a side view of the auger 1 used in the ground bearing capacity measurement test method according to the second embodiment. It is a side view which shows the sampler 4 for penetration test and the weight 5 for striking. It is a vertical sectional view of the weight for striking 5. It is a procedure diagram (A)-(D) of the bearing capacity measurement test. It is a graph which shows an example of the measurement result of the integrated current value, the current, and the N value at the time of auger excavation.

Hereinafter, using an auger equipped with spiral blades around the rod axis, the bearing capacity of the supporting ground at the tip of the auger is confirmed when the auger is rotated around the axis and penetrates into the ground to excavate the ground. The method for this (first to third embodiment examples) will be described in detail with reference to the drawings.

[ Reference 1st form example]
The ground bearing capacity measurement test method of the supporting ground according to the reference first embodiment will be described in detail with reference to FIGS. 1 to 7.

Reference In the test method according to the first embodiment, a loading plate 15 for measuring the bearing capacity is stored at the tip of the auger 1 so as to be protruding in the direction of the auger axis, and when the tip of the auger 1 reaches the support layer. The ground bearing capacity measurement test is performed according to the flat plate loading test by measuring the sinking amount of the auger 1 by applying the weight of the auger 1 with the loading plate 15 for measuring the bearing capacity protruding. ..

Further, it will be described in detail in detail.

As shown in FIG. 1, the auger 1 is composed of an auger head 2 at the tip and an auger shaft 3 having spiral blades provided on the peripheral surface. In the auger head 2, a pair of left and right spiral blades 11A and 11B are fixedly fixed on the outer surface (around the axis) of the head shaft 10, and a plurality of excavation bits 12 and 12 are provided on the lower end edges of the spiral blades 11A and 11B. The structure is provided with ... To be shipped.

On the other hand, the auger shaft 3 is a shaft-shaped shaft member in which spiral blades 13, 13 ... Are fixed on an outer surface (around the shaft), and is connected to the upper end of the auger head 2 by screwing. There is. Inside the auger shaft 3, an excavation liquid supply path 14 is provided in the center, and is discharged from the tip of the auger head 2 during excavation. This kind of auger 1 is mainly applied to relatively soft strata such as silt layer, clay layer and sand layer.

In the auger 1 according to the present invention, a loading plate 15 for measuring the bearing capacity is provided at the tip in a stored state so as to be able to project in the direction of the auger axis.

Specifically, a support rod 16 having a screw formed on the outer surface is integrally provided on the back surface side of the load bearing plate 15 for measuring the bearing capacity. On the other hand, a female screw hole 10a into which the support rod 16 can be screwed is formed on the side of the head shaft 10 with an opening facing the tip. As shown in FIG. 2, recessed flow paths 10b are formed in the cross direction of the female screw holes 10a, and the recessed flow paths 10b communicate with the excavation liquid supply path 14 to allow the excavation liquid to flow. It can be discharged from the tip of the auger.

As shown in FIG. 3, the loading plate 15 for measuring the bearing capacity is a member in which ribs 18 are formed in a cross shape on the lower surface side of the steel plate 17 and excavation liquid discharge holes 15a are formed at four locations. The support rod 16 is stored and held in a state of being screwed into a female screw hole 10a provided on the tip surface of the auger.

<Procedure for bearing capacity measurement test>
(1) Step 1
As shown in FIG. 4, the auger 1 is made to penetrate into the ground while rotating forward around the axis, and a drilling hole is formed in a columnar shape.

When the tip of the auger reaches the support layer H, excavation is temporarily stopped and the measurement test of the bearing capacity is started.

(2) Step 2
As shown in FIG. 5, in a state where the loading plate 15 for measuring the bearing capacity is in contact with the ground, the auger 1 is moved upward by rotating the auger 1 in the reverse direction around the axis, and is used for measuring the bearing capacity. The loading plate 15 is in a protruding state. The lower surface of the loading plate 15 for measuring the bearing capacity has a cross-shaped rib 18, which is held by biting into the ground so as not to rotate together.

(3) Step 3
As shown in FIG. 6, the ground bearing capacity measurement test according to the flat plate loading test is performed by applying the own weight (weight is known) of the auger 1 and measuring the subsidence amount (L) of the auger 1. The measurement of the subsidence amount L can be measured on the ground.

The flat plate loading test is a method of ground characteristic test specified in JGS1521 (Japanese Geotechnical Society standard), and a load is applied to a circular loading plate installed on the target ground, and the load and sinking amount of the loading plate are adjusted. From the relationship, it is a test to obtain the deformation characteristics and bearing capacity characteristics of the ground such as the ground reaction force coefficient and the ultimate bearing capacity. Although the loading plate and load loading method used are different from the ground bearing capacity test in the present invention, the test method according to the present invention can be obtained by examining in advance the correlation between the test method in the present invention and the test method by the flat plate loading test. It is possible to convert the result of the above into a flat plate loading test.

<Examples of other forms>
(1) In the above embodiment, a support rod 16 having a screw formed on the outer surface is integrally provided on the back surface side of the load bearing plate 15 for measuring the bearing capacity, and the support rod 16 is provided on the tip surface of the auger. As shown in FIG. 7, a hydraulic jack 19 is internally installed at the tip of the auger 1 and a loading plate 15 for measuring the bearing capacity is supported at the tip of the piston 20. When the tip of the auger 1 reaches the support layer, the piston 20 of the hydraulic jack 19 may be extended so that the loading plate 15 for measuring the bearing capacity of the ground is projected from the stored state.

[Example of the embodiment of the present invention ]
Next, the ground bearing capacity measurement test method of the supporting ground according to the embodiment of the present invention will be described in detail with reference to FIG.

The homeland proof stress measurement test method is a test method performed using the auger 1 shown in FIG. 7.

When the tip of the auger reaches the support layer, the auger 1 is restrained so as not to move in the vertical direction. For example, on the ground side, a device that grips and fixes the auger 1 so as not to move is used to restrain the vertical movement.

When the auger 1 is fixed so as not to move in the vertical direction, the hydraulic jack 19 is extended to apply a load to the load bearing plate 15 for measuring the bearing capacity, and the jack pressure and the amount of extension of the jack are measured to load the flat plate. Perform a ground bearing capacity measurement test according to the test. The jack pressure can be measured by measuring the hydraulic pressure, and the jack extension amount can be measured by the stroke sensor provided on the hydraulic jack.

[ Reference second form example]
Next, the ground bearing capacity measurement test method of the supporting ground according to the reference second embodiment will be described in detail with reference to FIGS. 9 to 12.

Reference: In the test method according to the second embodiment, a penetration test sampler 4 is provided by providing through holes 21 in the spiral blades 3, 11A, and 11B of the auger 1 and continuously along the axial core direction of the auger 1. An insertion passage 22 for insertion is formed, and when the tip of the auger 1 reaches the support layer, the penetration test sampler 4 is inserted from the insertion passage 22 and hits the penetration test sampler 4. The impact weight 5 is inserted, and the impact weight 5 is pulled up to a predetermined height position and freely dropped to give an impact to the penetration test sampler 4, and the penetration test sampler 4 is used. By determining the number of hits N'required to drive to a predetermined depth, a ground bearing capacity measurement test according to a standard penetration test is performed.

The standard penetration test is a test specified in JIS A1219, and is a test method for obtaining an N value, which is an index of the hardness and tightness of the ground at the in-situ position, and for collecting a sample. Here, the N value is for a standard penetration test attached to the tip of the boring rod by free-falling a drive hammer with a mass of 63.5 ± 0.5 kg from a height of 76 ± 1 cm to hit the knocking block attached to the head of the boring rod. It is the number of hits required to hit the sampler 30 cm into the ground.

Further, it will be described in detail in detail.

As shown in FIG. 9, in the auger 1, a through hole 21 is provided in the spiral blades 13, 11A, 11B, and a penetration test sampler 4 continuous along the axial core direction of the auger 1 is inserted. The insertion passage 22 for the purpose is formed. The diameter of the insertion passage 22 (through hole 21) is about 100 mm + α.

On the other hand, the details of the test apparatus including the penetration test sampler 4 and the striking weight 5 are shown in FIG.

In the penetration test sampler 4 and the striking weight 5, the penetration test sampler 4 is arranged so as to fit the guide rod 6 on the lower side of the guide rod 6, and the guide rod is provided. The striking weight 5 is arranged on the upper side of the material 6 so as to fit the guide rod 6 outward, and the sampler 4, the striking weight 5, and the guide rod 6 are independently suspended. The striking weight 5 is pulled up along the guide rod 6 and freely dropped on the upper end of the penetration test sampler 4 to give a striking structure.

The penetration test sampler 4 is a circular tubular member having an upper lid 23 having an opening on the lower side and a through hole 23a through which the guide rod 6 penetrates on the upper surface. The diameter is about 50 mmφ. The suspension wire 24 is connected to the upper surface of the upper lid 23 at a position eccentric from the center (the position where the pipe member 28 of the impact-oriented 5 described later is arranged).

As shown in FIG. 11 in detail, the striking weight 5 has a double pipe structure consisting of an outer pipe 25 and an inner pipe 26, the upper end thereof is closed by the upper lid 27A, and the lower end is the lower lid. It is blocked by 27B. A pipe material 28 having a relatively small diameter is arranged between the outer pipe 25 and the inner pipe 26 in order to form a through hole 29 penetrating in the vertical direction. The through hole 29 is for passing the hanging wire 24 of the penetration test sampler 4.

The diameter φ1 of the outer tube 25 is approximately 100 mm, and the diameter φ2 of the inner tube 26 is approximately 30 to 35 mm. The space between the outer pipe 25 and the inner pipe 26 is filled with molten lead 30 in order to gain weight. Since it is desirable that the length l of the striking weight 5 is always engaged with the spiral blade 13 of the auger 1 at at least two points, the length l is twice the vertical spacing of the spiral blade 13 + α. It is desirable to do. The striking weight 5 is suspended by a suspension wire 31.

As shown in FIG. 10, the guide rod 6 is arranged in a state of being inserted into the through hole 23a of the penetration test sampler 4 and inserted into the inner pipe 26 of the striking weight 6. The striking weight 6 is pulled up and freely dropped onto the upper end of the penetration test sampler 4 to give a striking effect, and also functions as a guide for penetrating the penetration test sampler 4 into the ground. It is a thing. The guide rod 6 is suspended by the suspension wire 32.

<Procedure for measuring test of bearing capacity>
(1) Step 1
First, the auger 1 is made to penetrate into the ground while rotating forward around the axis, and a drilling hole is formed in a columnar shape. When the tip of the auger reaches the support layer H, excavation is temporarily stopped and the measurement test of the bearing capacity is started.

(2) Step 2
If the auger 1 is restrained so as not to move in the vertical direction, the penetration test sampler 4 is inserted into the insertion passage 22 formed in the spiral blades 3, 11A, 11B from the ground as shown in FIG. At the same time, a striking weight 5 is inserted to impact the penetration test sampler 4, and as shown in FIG. 12A, the solicitation test sampler 4 and the guide rod 6 are supported by the support layer H. To abut.

(3) Step 3
Next, as shown in FIGS. 12B and 12C, the penetration test sampler is pulled up to a predetermined height position by using the striking weight 5 as a guide and the guide rod 6 as a guide, and then freely dropped. Repeat the work of giving a blow to 4. Then, the number of hits N'required to drive the penetration test sampler 4 to a predetermined depth L is obtained.

If the test conditions are matched to the standard penetration test, the pull-up height of the striking weight 5 is 76 ± 1 cm, and the penetration depth of the penetration test sampler 4 is 30 cm, but the standard penetration test is performed. Since the mass of the drive hammer in the above is 63.5 ± 0.5 kg, which is likely to be different from the mass of the striking weight 5 of the present invention, it is not always necessary to meet the standard penetration test. By investigating the correlation between the test method in the present invention and the test method by the standard penetration test in advance, the result of the test method according to the present invention (number of hits N') can be converted into the N value of the standard penetration test. It is possible.

The penetration depth L of the penetration test sampler 4 is measured by marking the suspension wire 31 on the ground with the striking weight 5 mounted on the penetration test sampler 4 at the marking position. It is possible by measuring the amount of movement.

(4) Step 4
When the penetration test sampler 4 is driven to a predetermined depth L, the penetration test sampler 4, the striking weight 5, and the guide rod 6 are suspended as shown in FIG. 12 (D). The hanging wires 24, 31, and 32 are pulled up to the ground side to collect the penetration test sampler 4, the striking weight 5, and the guide rod 6. Sediment (sample) is collected inside the sampler 4 for penetration test.

1 ... auger, 2 ... auger head, 3 ... auger shaft, 4 ... penetration test sampler, 5 ... striking weight, 6 ... guide rod, 10 ... head shaft, 11A / 11B ... spiral blade, 12 ... excavation Bit, 13 ... spiral blade, 14 ... excavation liquid supply path, 15 ... loading plate for measuring the bearing capacity, 16 ... support rod, 17 ... steel plate, 18 ... rib, 19 ... hydraulic jack, 20 ... piston, 21 ... through Hole, 22 ... Insertion passage, H ... Support layer

Claims (2)

Using an auger equipped with spiral blades around the rod axis, to check the bearing capacity of the supporting ground at the tip of the auger when excavating the ground by penetrating the auger into the ground while rotating it around the axis. It ’s a method,
A hydraulic jack is internally installed at the tip of the auger, and the loading plate for measuring the bearing capacity is supported at the tip of the piston, and when the tip of the auger reaches the support layer, the auger is restrained so as not to move in the vertical direction. In the state of
A foundation pile characterized in that a ground bearing capacity measurement test similar to a flat plate loading test is performed by extending the hydraulic jack to apply a load to the loading plate for measuring the bearing capacity and measuring the jack pressure and the amount of expansion of the jack. How to check the supporting ground at the time of construction. The supporting ground at the time of foundation pile construction according to claim 1 , wherein a spiral blade is provided around the shaft, a hydraulic jack is internally installed at the tip, and the loading plate for measuring the bearing capacity is supported at the tip of the piston. Auger for confirmation method.

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