JP7237218B2 - Confirmation method of supporting ground during foundation pile construction - Google Patents

Description

The present invention relates to a method for confirming the bearing capacity of the supporting ground with the auger penetrating into the ground when constructing a foundation pile using an auger having spiral blades around the rod axis. .

There are various construction methods for constructing the foundation piles of civil engineering structures. After excavating the ground in a columnar shape by penetrating into the ground while rotating, piles are inserted into the ground into the excavated holes to construct foundation piles.

In the construction of the above foundation piles, it is important for construction management to confirm whether or not the tip of the auger has reached the bearing layer during excavation of the auger. Conventionally, as a method of confirming the supporting ground, the supporting ground has a high N value compared to other layers, and focusing on the fact that the excavation resistance increases, the supporting ground is measured by measuring the integrated current value of the auger drive device. Determining the reach of the layer was done.

Specifically, in Patent Document 1 below, a current data detecting means for detecting a current value during excavation of an auger driving motor for driving an auger of an excavator for drilling a ground, and a vertical movement distance of the auger are detected. Depth detection means, a signal conversion device for converting detection signals from each of the detection means into digital signals for input to a personal computer, and based on the signal input from the signal conversion device, the current data is integrated and the depth is input in advance as the vertical axis. There has been proposed a pile bearing layer detection apparatus characterized by comprising a personal computer having a CRT for displaying on the same screen together with the obtained N-value data.

In addition, in Patent Document 2 below, at a depth shallower than the assumed depth of the support layer, a reference value acquisition depth setting unit for setting the reference value acquisition depth and a pile hole corresponding to the torque of the excavation drill during excavation a chart display unit configured to display on a monitor the integral value of the current value as a chart associated with the excavation depth of the drill; and a reference value based on the integral value corresponding to the reference value acquisition depth. The excavating drill reaches the support layer based on the reference value acquisition unit that acquires the reference value acquired by the reference value acquisition unit and the integrated value corresponding to the depth deeper than the reference value acquisition depth. A support layer reach determination device has been proposed that includes a determination unit that is configured to determine whether or not a support layer has been reached, and a notification unit that is configured to notify the determination result of the determination unit.

JP-A-5-280031 JP 2018-35635 A

FIG. 13 shows an example of a graph showing the relationship between the integral current value, the current, and the N value 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 true that there is a certain degree of correlation between the integrated current value and the ground N value, and confirmation of the supporting ground is exclusively performed by measuring the integrated current value of the auger device.

However, since the method of measuring the integrated current value during auger excavation is only an indirect method, there has been a demand for a method of directly confirming the supporting ground without hindering the construction efficiency of auger excavation.

Therefore, the main object of the present invention is to construct a foundation pile using an auger equipped with spiral blades around the rod axis, and to increase the bearing capacity of the supporting ground while the auger is penetrating into the ground. To provide a method for confirming the bearing ground by direct measurement.

In order to solve the above problems, as the present invention according to claim 1, an auger having spiral blades around a rod axis is used, and the auger is rotated around the axis to penetrate the ground and excavate the ground. At the time, a method for confirming the bearing capacity of the supporting ground at the tip of the auger,
A hydraulic jack is installed at the tip of the auger, and the loading plate for soil bearing force measurement is supported at the tip of the piston. In a state where the auger is constrained so as not to move vertically by using a device that
A foundation pile characterized by performing a soil bearing force measurement test according to a flat plate load test by extending the hydraulic jack and applying a load to the load plate for measuring the soil bearing force and measuring the jack pressure and the amount of jack extension. A method for confirming the supporting ground during 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 bearing force measurement is supported at the tip of the piston. When the tip of the auger reaches the support layer, the auger is restrained from moving vertically by using a device that holds the auger to prevent it from moving. Then, the hydraulic jack is extended to apply a load to the load bearing plate for bearing force measurement, and the jack pressure and the amount of extension of the jack are measured to perform a bearing force measurement test according to the flat plate load test. Therefore, it is possible to directly measure the bearing capacity of the supporting ground while the auger is in the ground.

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

It is a side view of the auger 1 used for the soil-bearing-force measurement test method based on the reference 1st form example. FIG. 2 is a view taken along line II-II of FIG. 1; FIG. 2 is a view taken along line III-III in FIG. 1; It is a procedure chart (part 1) of a bearing capacity measurement test. It is a procedure chart (part 2) of a bearing capacity measurement test. It is a procedure diagram (part 3) of a bearing capacity measurement test. It is a figure which shows the modification of the projecting method of the loading plate 15 for bearing-force measurement. It is a figure which shows the soil-bearing-force measurement test method based on the example of this invention . It is a side view of the auger 1 used for the soil-bearing-force measurement test method based on the reference 2nd example of a form. It is a side view which shows the sampler 4 for penetration tests, and the weight 5 for an impact. 4 is a longitudinal sectional view of the impact weight 5. FIG. 4 is a procedure diagram (A) to (D) of a soil bearing force measurement test. 7 is a graph showing an example of measurement results of integrated current value, current, and N value during auger excavation.

Below, using an auger with helical blades around the rod axis, when excavating the ground by penetrating the ground while rotating this auger around the axis, confirm the bearing capacity of the supporting ground at the tip of the auger. A method (first to third embodiments) for this purpose will be described in detail with reference to the drawings.

[ Reference first form example]
Based on FIGS. 1 to 7, the method for measuring and testing the load-bearing force of the supporting ground according to the first reference embodiment will be described in detail.

In the test method according to the reference first embodiment, the loading plate 15 for bearing force measurement is stored at the tip of the auger 1 so as to protrude in the axial direction of the auger, and when the tip of the auger 1 reaches the support layer A soil bearing force measurement test is carried out according to the flat plate load test by measuring the amount of settlement of the auger 1 by applying the weight of the auger 1 with the loading plate 15 for bearing force measurement protruding. .

Furthermore, it will be specifically described in detail.

The auger 1, as shown in FIG. 1, is composed of an auger head 2 at the tip and an auger shaft 3 having helical blades on its peripheral surface. The auger head 2 has a pair of left and right spiral blades 11A and 11B fixed to the outer surface (around the shaft) of a head shaft 10, and a plurality of excavation bits 12 and 12 at the lower edges of the spiral blades 11A and 11B. . . are provided, and as the head shaft 10 rotates, the excavation bits 12, 12 . . . to haul.

On the other hand, the auger shaft 3 is a shaft-shaped shaft member having spiral blades 13, 13 . . . there is The auger shaft 3 has a drilling fluid supply passage 14 at its center, and the drilling fluid is discharged from the tip of the auger head 2 during excavation. This type of auger 1 is mainly applied to relatively soft strata such as silt layers, clay layers and sand layers.

In the auger 1 according to the present invention, a loading plate 15 for bearing force measurement is provided at the tip so as to protrude in the axial direction of the auger in a housed state.

Specifically, a support rod 16 having a screw formed on the outer surface is integrally provided on the back side of the loading plate 15 for bearing force measurement. On the other hand, on the side of the head shaft 10, a female threaded hole 10a is formed with an opening facing the tip thereof and into which the support rod 16 can be screwed. In addition, as shown in FIG. 2, recessed passages 10b are formed in the cross direction of the female screw holes 10a, respectively. Discharge is possible from the tip of the auger.

As shown in FIG. 3, the load bearing plate 15 for measuring soil bearing capacity is a member having cross-shaped ribs 18 formed on the underside of a steel plate 17 and drilling fluid discharge holes 15a formed at four locations. The support rod 16 is housed and held in a state of being screwed into a female screw hole 10a provided on the tip surface of the auger.

<Procedure for soil bearing strength measurement test>
(1) Step 1
As shown in FIG. 4, the auger 1 is penetrated into the ground while rotating forward about its axis to form a cylindrical excavation hole.

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

(2) Step 2
As shown in FIG. 5, the auger 1 is rotated in the opposite direction around its axis while the loading plate 15 for bearing force measurement is in contact with the ground, thereby moving the auger 1 upward. The loading plate 15 is projected. A cross-shaped rib 18 is provided on the lower surface of the load bearing plate 15 for measuring soil bearing force, and is held by digging into the ground so as not to co-rotate.

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

The plate load test is a method of ground characteristics test stipulated in JGS1521 (Geotechnical Society standard), a load is applied to a circular loading plate installed on the target ground, and the load and settlement amount Therefore, it is a test to determine the deformation characteristics and bearing capacity characteristics of the ground, such as the ground reaction force coefficient and the ultimate bearing capacity. The soil bearing strength test in the present invention differs from the loading plate and load loading method used, but by investigating the correlation between the test method in the present invention and the test method by the flat plate loading test in advance, the test method according to the present invention It is possible to convert the results of the above into the plate load test.

<Other form examples>
(1) In the above embodiment, the support rod 16 having a screw formed on the outer surface is integrally provided on the back side of the loading plate 15 for measuring earth bearing force, and the support rod 16 is provided on the tip surface of the auger to form a female screw hole 10a. However, as shown in FIG. 7, a hydraulic jack 19 is installed at the tip of the auger 1, and the bearing plate 15 for bearing force measurement 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 to project the load plate 15 for bearing force measurement from the stored state.

[Example of embodiment of the present invention]
Next, based on FIG. 8, a detailed description will be given of a test method for measuring and testing the load-bearing force of the supporting ground according to the embodiment of the present invention.

The soil strength measurement test method is a test method using the auger 1 shown in FIG.

When the tip of the auger reaches the support layer, the auger 1 is restrained so as not to move vertically. For example, on the ground side, a device that holds the auger 1 to prevent it from moving is used to restrain 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 bearing force measurement, and the jack pressure and the amount of extension of the jack are measured to obtain a flat plate load. Carry out soil bearing capacity measurement test according to the test. The jack pressure can be measured by measuring the hydraulic pressure, and the extension amount of the jack can be measured by a stroke sensor provided on the hydraulic jack.

[ Reference second form example]
Next, based on FIGS. 9 to 12, a detailed description will be given of a test method for measuring the bearing capacity of the supporting ground according to the second reference embodiment.

In the test method according to the reference second embodiment, through holes 21 are provided in the spiral blades 3, 11A, and 11B of the auger 1, and a penetration test sampler 4 continuous along the axial direction of the auger 1 is installed. 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 the penetration test sampler 4 is hit. Insert the impact weight 5 in order to give the penetration test sampler 4 a impact by pulling up the impact weight 5 to a predetermined height position and allowing it to fall freely, and the penetration test sampler 4 By obtaining the number of impacts N' required for driving to a predetermined depth, a soil bearing strength measurement test is conducted according to the standard penetration test.

The standard penetration test is a test specified in JIS A1219, and is a test method for obtaining the N value, which is an index of the hardness and firmness of the ground in the original position, and for collecting samples. Here, the N value is the standard penetration test attached to the tip of the boring rod by allowing a drive hammer with a mass of 63.5 ± 0.5 kg to freely fall from a height of 76 ± 1 cm to hit the knocking block attached to the boring rod head. It is the number of blows required to drive the sampler into the ground 30 cm.

Furthermore, it will be specifically described in detail.

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

On the other hand, FIG. 10 shows the details of the test apparatus including the penetration test sampler 4 and impact weight 5 .

In the penetration test sampler 4 and the impact weight 5, the penetration test sampler 4 is arranged so that the guide bar 6 is fitted on the lower side of the guide bar 6, and the guide bar The hitting weight 5 is arranged on the upper side of the material 6 so as to fit the guide bar 6, and the sampler 4, the hitting weight 5 and the guide bar 6 are independently suspended. The impact weight 5 is pulled up along the guide bar 6 and allowed to fall freely onto the upper end of the penetration test sampler 4 to give impact.

The penetration test sampler 4 is a cylindrical member having an upper cover 23 which is open on the lower side and has a through hole 23a through which the guide bar 6 passes through the upper surface. The diameter is approximately 50 mmφ. A suspension wire 24 is connected to a position on the top surface of the upper lid 23 that is eccentric from the center (a position at which a pipe member 28 for striking 5, which will be described later) is arranged.

As shown in detail in FIG. 11, the striking weight 5 has a double tube structure consisting of an outer tube 25 and an inner tube 26, the upper end of which is closed by an upper lid 27A, and the lower end of which is closed by a lower lid. 27B. Between the outer tube 25 and the inner tube 26, a relatively small-diameter tube member 28 is arranged to form a through hole 29 penetrating vertically. The through hole 29 is for passing the suspension 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 tube 25 and the inner tube 26 is filled with molten lead 30 to gain weight. Since it is desirable that the striking weight 5 engages with the spiral blade 13 of the auger 1 at least at two points at all times, the length l of the striking weight 5 is equal to twice the vertical interval of the spiral blade 13 + α. It is desirable to The impact weight 5 is suspended by a suspension wire 31 .

As shown in FIG. 10, the guide bar 6 is a rod-shaped member inserted through the through hole 23a of the penetration test sampler 4 and through the inner tube 26 of the impact weight 6. It is a member that raises the impact weight 6 and gives an impact by free-falling to the upper end of the penetration test sampler 4, and functions as a guide when penetrating the penetration test sampler 4 into the ground. It is. This guide bar 6 is suspended by a suspension wire 32 .

<Procedure for measurement test of bearing capacity>
(1) Step 1
First, the auger 1 is penetrated into the ground while being forwardly rotated around its axis to form a cylindrical excavation hole. When the tip of the auger reaches the support layer H, the excavation is temporarily stopped, and the soil bearing capacity measurement test is started.

(2) Step 2
When the auger 1 is restrained so as not to move in the vertical direction, as shown in FIG. At the same time, a striking weight 5 is inserted to strike the penetration test sampler 4, and as shown in FIG. abut on.

(3) Step 3
Next, as shown in FIGS. 12(B) and 12(C), the impact weight 5 is lifted up to a predetermined height while using the guide bar 6 as a guide, and allowed to fall freely, thereby obtaining the penetration test sampler. 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 lifting height of the impact weight 5 is 76 ± 1 cm, and the penetration depth of the penetration test sampler 4 is 30 cm. The mass of the drive hammer is 63.5±0.5 kg, which is likely to be different from the mass of the striking weight 5 of the present invention, so it is not necessary to match 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, it is possible to convert the result of the test method according to the present invention (the number of hits N') to the N value of the standard penetration test. It is possible.

In addition, the penetration depth L of the penetration test sampler 4 is measured by marking the suspension wire 31 on the ground while the impact weight 5 is placed on the penetration test sampler 4. It is possible by measuring the amount of movement.

(4) Step 4
After driving the penetration test sampler 4 to a predetermined depth L, as shown in FIG. The suspension wires 24, 31, and 32 are pulled up to the ground side, and the penetration test sampler 4, the impact weight 5, and the guide bar 6 are recovered. Soil (sample) is collected inside the penetration test sampler 4 .

DESCRIPTION OF SYMBOLS 1... Auger, 2... Auger head, 3... Auger shaft, 4... Sampler for penetration test, 5... Impact weight, 6... Guide bar, 10... Head shaft, 11A/11B... Spiral blade, 12... Excavation Bit 13 Spiral blade 14 Drilling fluid supply path 15 Loading plate for soil bearing force measurement 16 Support rod 17 Steel plate 18 Rib 19 Hydraulic jack 20 Piston 21 Pass hole, 22... insertion path, H... supporting layer

Claims (1)

Using an auger with helical blades around the rod axis, this auger is rotated around the axis and penetrates into the ground to excavate the ground. a method,
A hydraulic jack is installed at the tip of the auger, and the loading plate for soil bearing force measurement is supported at the tip of the piston. In a state where the auger is constrained so as not to move vertically by using a device that
A foundation pile characterized by performing a soil bearing force measurement test according to a flat plate load test by extending the hydraulic jack and applying a load to the load plate for measuring the soil bearing force and measuring the jack pressure and the amount of jack extension. How to check the supporting ground during construction.

Images